Probably, it is worth talking more about the exhaust systems of DVS in general to learn how to divide "flies from the kitlet" in this not easy to understand the area. Not easy from the point of view of physical processes occurring in the muffler after the engine has already completed another worker, and, it would seem, did his job.
Then we will discuss the model two-stroke engines, but all the reasoning is true for four-strokes, and for engines "non-model" cubatures.
Let me remind you that far from each exhaust tract of DVS, even built according to the resonant diagram, can give an increase in power or engine torque, as well as reduce its noise level. By and large, these are two mutually exclusive requirements, and the task of the exhaust system designer is usually reduced to the search for a compromise between the noise of DVS, and its power in one or another operation mode.
This is due to several factors. Consider the "ideal" engine, in which the internal loss of energy for friction of sliding nodes is zero. We will not take into account losses in rolling bearings and loss, inevitable when internal flows gas-dynamic processes (suction and purge). As a result, all the energy released during combustion fuel mixeswill be spent on:
1) the useful work of the model drivers (propeller, wheel, etc. It is not possible to consider the efficiency of these nodes, it is a separate topic).
2) losses arising from another cyclical phase of the process the work of the DVS - Exhaust.
It is the loss of exhaust worth considering in more detail. I emphasize that it is not about the work stroke tact (we agreed that the engine "inside itself is ideal), but about the" ejecting "losses of the combustion of the fuel mixture from the engine into the atmosphere. They are determined mainly, the dynamic resistance of the exhaust path itself is the whole thing that joins the motor of the motor. From the entrance to the outlet holes of the "silencer". I hope you do not need to convince anyone that the smaller the resistance of the channels, according to which the gases from the engine are "departed", the less you will have to spend the efforts on it, and the faster the process of "gas separation" will pass.
Obviously, it is the phase of the exhaust of the internal combustion system that is the main in the process of noise formation (forget about the noise arising during suction and the burning of fuel in the cylinder, as well as about mechanical noise from the operation of the mechanism - the perfect MEX mechanical noise can simply be). It is logical to assume that in this approximation, the total efficiency of the DVS will be determined by the relationship between the useful work, and the loss of exhaust. Accordingly, the reduction in the exhaust loss will increase the efficiency of the engine.
Where is the energy lost when the exhaust is spent? Naturally, it is converted into acoustic fluctuations in the environment (atmosphere), i.e. In noise (of course, there is also a heating of the surrounding space, but we still default about it). The place of occurrence of this noise is a cut of an exhaust window of the engine, where there is a jump-like expansion of exhaust gases, which initiates acoustic waves. The physics of this process is very simple: at the time of opening the exhaust window in a small volume of the cylinder there is a large portion of compressed gaseous residues of fuel combustion products, which when entering the surrounding space is quickly and sharply expanded, and a gas-dynamic blow occurs, provoking subsequent floating acoustic oscillations in the air (Remember the cotton arising from the scolding of a bottle of champagne). To reduce this cotton, it is enough to increase the expiration time of compressed gases from the cylinder (bottle), limiting the cross section of the exhaust window (smoothly opening the plug). But this method of reducing noise is not acceptable for a real engine, which, as we know, power directly depends on the revolutions, therefore - from the speed of all flowing processes.
You can reduce the noise of the exhaust in another way: do not limit the cross-sectional area of \u200b\u200bthe exhaust window and the expiration time of exhaust gases, but limit the speed of their expansion in the atmosphere. And this method was found.
Back in the 30s of the last century, sports motorcycles and cars began to equip the peculiar conical exhaust pipes with a small opening angle. These silencers were called "MegaFones". They slightly reduced the level of exhaust noise of the engine, and in some cases, it was also insignificant, to increase the engine power due to improving the cleaning of the cylinder from the remnants of the spent gases due to the inertia of the gas pillar moving inside the conical exhaust pipe.
Calculations and practical experiments have shown that the optimal angle of the megaphone is close to 12-15 degrees. In principle, if you make a megaphone with such an angle of revealed very long, it will effectively extinguish the engine noise, almost without reducing its capacity, but in practice such structures are not implemented due to obvious design deficiencies and restrictions.
Another way to reduce the noise of DVS is to minimize pulsations of exhaust gases at the output of the exhaust system. For this, the exhaust is made not directly into the atmosphere, and in an intermediate receiver of sufficient volume (ideally, at least 20 times higher than the working volume of the cylinder), with subsequent release of gases through a relatively small hole, the area of \u200b\u200bwhich can be several times less than the exhaust area window. Such systems smooth the pulsating nature of the movement of the gas mixture at the outlet of the engine, turning it into close to the uniform-progressive at the outlet of the muffler.
Let me remind you that the speech at the moment goes about the devastating systems that do not increasing gas-dynamic resistance to exhaust gases. Therefore, I will not concern all sorts of tricks of the type of metal grids inside the devastating chamber, perforated partitions and pipes, which, of course, allow you to reduce the noise of the engine, but to the detriment of its power.
The next step in the development of silencers was systems consisting of various combinations of the methods described above. I will say right away, for the most part they are far from ideal, because In one degree or another, the gas-dynamic resistance of the exhaust path increases, which uniquely leads to a decrease in the power of the engine transmitted to the propulsion.
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The use of resonant exhaust pipes on motor models of all classes allows you to dramatically increase the sports results of the competition. However, the geometric parameters of pipes are determined, as a rule, by the method of trial and error, since so far there is no clear understanding and clear interpretation of the processes occurring in these gas-dynamic devices. And in the few sources of information on this occasion, conflicting conclusions that have an arbitrary interpretation are given.
For a detailed study of processes in the pipes of a customized exhaust, a special installation was created. It consists of a stand for running engines, an adapter Motor - a pipe with fittings for the selection of static and dynamic pressure, two piezoelectric sensors, two-beam oscilloscope C1-99, a camera, a resonant exhaust pipe from the R-15 engine with a "telescope" and a homemade tube with black Surfaces and additional thermal insulation.
Pressures in the pipes in the exhaust area was determined as follows: the motor was displayed on resonant revisions (26000 rpm), data from the Piezoelectric sensors attached to the octuers of the Piezoelectric sensors were displayed on the oscilloscope, the frequency of the sweep of which is synchronized with the engine rotation frequency, and the oscillogram was recorded on the film.
After the film is manifested in a contrasting developer, the image was transferred to the traction on the scale of the oscilloscope screen. The results for the pipe from the engine R-15 are shown in Figure 1 and for a homemade tube with black and additional thermal insulation - in Figure 2.
On schedules:
P dyn - dynamic pressure, p st - static pressure. OSO - Opening of the exhaust window, NMT - Lower dead point, the link is the closure of the exhaust window.
Analysis of curves allows you to identify the distribution of pressure at the input of the resonant tube in the function of the crankshaft rotation phase. Increasing the dynamic pressure from the moment the exhaust window is discovered with the diameter of the output nozzle 5 mm occurs for R-15 approximately 80 °. And its minimum is within 50 ° - 60 ° from the bottom of the dead point at maximum purge. Increased pressure in the reflected wave (from a minimum) at the time of closing the exhaust window is about 20% of the maximum value of R. delay in the action of reflected exhaust wave - from 80 to 90 °. For static pressure, it is characterized by an increase in 22 ° C "Plateau" on the chart up to 62 ° from the opening of the exhaust window, with a minimum of 3 ° from the bottom of the dead point. Obviously, in the case of using a similar exhaust pipe, purge fluctuations occur at 3 ° ... 20 ° after the bottom of the dead point, and by no means 30 ° after the opening of the exhaust window was previously thought.
These studies of the homemade pipe differ from the data R-15. Increased dynamic pressure up to 65 ° from the opening of the exhaust window is accompanied by a minimum located 66 ° after the bottom of the dead point. At the same time, the increase in pressure of the reflected wave from the minimum is about 23%. Loading in the action of exhaust gases is less, which is probably due to increasing temperature in the heat insulated system, and is about 54 °. Purge oscillations are marked at 10 ° after the bottom of the dead point.
Comparing graphics, it can be noted that static pressure in the heat insulated pipe at the time of closing the exhaust window is less than in R-15. However, dynamic pressure has a maximum of a reflected wave of 54 ° after the closure of the exhaust window, and in R-15, this maximum shifted by 90 "! The differences are associated with the difference in the diameters of the exhaust pipes: on R-15, as already mentioned, the diameter is 5 mm, and on the heat insulated - 6.5 mm. In addition, due to the more advanced geometry of the pipe R-15, the coefficient of restoration of static pressure is more.
The efficiency coefficient of the resonant exhaust pipe largely depends on the geometric parameters of the pipe itself, the cross-section of the exhaust pipe of the engine, temperature regime, and gas distribution phases.
The use of control traverses and selecting the temperature regime of the resonant exhaust pipe will allow to shift the maximum pressure of the reflected exhaust gas wave by the time the exhaust window is closed and thus sharply increase its efficiency.
480 rub. | 150 UAH. | $ 7.5 ", Mouseoff, Fgcolor," #FFFFCC ", BGColor," # 393939 ");" Onmouseout \u003d "Return nd ();"\u003e Dissertation period - 480 rub., Delivery 10 minutes , around the clock, seven days a week and holidays
Grigoriev Nikita Igorevich. Gas Dynamics and heat exchange in the exhaust pipeline of piston engine: the dissertation ... Candidate of Technical Sciences: 01.04.14 / Grigoriev Nikita Igorevich; [Place of protection: Federal State Autonomous educational institution Higher Professional Education "Ural Federal University named after the first president of Russia B. N. Yeltsin" http://lib.urfu.ru/mod/data/view.php?d\u003d51&rid\u003d238321 ].- Ekaterinburg, 2015.- 154 with .
Introduction
Chapter 1. State of the issue and setting the objectives of the study 13
1.1 Types of exhaust systems 13
1.2 Experimental studies of the effectiveness of exhaust systems. 17.
1.3 Settlement studies of the effectiveness of graduation systems 27
1.4 Characteristics of heat exchange processes in the exhaust system of piston internal combustion engine 31
1.5 Conclusions and setting Tasks 37
Chapter 2. Research methodology and description of experimental installation 39
2.1 Choosing a methodology for the study of gas dynamics and heat exchange characteristics of the process of output of the piston engine 39
2.2 Constructive execution of the experimental installation for the study of the process of release in the Piston DVS 46
2.3 Measurement of the angle of rotation and frequency of the distribution shaft 50
2.4 Definition of instant flow 51
2.5 Measurement of instantaneous local heat transfer coefficients 65
2.6 Measurement of overpressure flow in the graduation path 69
2.7 Data Collection System 69
2.8 Conclusions to chapter 2 s
Chapter 3. Gas Dynamics I. consumables Release process 72
3.1 Gas Dynamics and Consumables Release Process in Piston Engine internal combustion Without superimposed 72.
3.1.1 with a pipeline with a circular cross section 72
3.1.2 For pipeline with square cross section 76
3.1.3 with triangular pipeline cross section 80
3.2 Gas dynamics and expenditure characteristics of the release process piston Engine Internal combustion with supervision 84
3.3 Conclusion to Chapter 3 92
Chapter 4. Instant heat transfer in the exhaust channel of the piston engine of internal combustion 94
4.1 Instant local heat transfer process of an internal combustion of an internal combustion engine without supercharow 94
4.1.1 with pipeline with round cross section 94
4.1.2 For pipeline with square cross section 96
4.1.3 with a pipeline with a triangular cross section 98
4.2 Instant heat transfer process of the outlet of the piston engine of internal combustion with reducing 101
4.3 Conclusions to Chapter 4 107
Chapter 5. Stabilization of the flow in the exhaust channel of the piston engine of internal combustion 108
5.1 Changing the flux pulsations in the exhaust channel of the piston engine using a constant and periodic ejection 108
5.1.1 Suppression of flux pulsations in the outlet using a constant ejection 108
5.1.2 Changing the pulsations of flow in the exhaust channel by periodic ejection 112 5.2 Constructive and technological design of the exhaust tract with ejection 117
Conclusion 120.
Bibliography
Estimated studies of the effectiveness of graduation systems
The exhaust system of piston engine is to remove the exhaust gas engine cylinders and supplying them to the turbocharger turbine (in supervising engines) in order to convert the energy left after the workflow mechanical work on the TK tree. The exhaust channels are performed by a shared pipeline, cast from gray or heat-resistant cast iron, or aluminum in the case of cooling, or from separate cast iron nozzles. To protect the service personnel from burns, the exhaust pipe can be cooled with water or coated with heat-insulating material. The heat-insulated pipelines are more preferable for engines with gas turbine superimposses. Since in this case, the loss of exhaust gas energy is reduced. Since when heated and cooled the length of the exhaust pipeline changes, then special compensators are installed before the turbine. On the large engines The compensators also combine individual sections of exhaust pipelines, which according to technological reasons make composite.
Information about the parameters of the gas before the turbochargeor turbine in the dynamics during each DVS working cycle appeared in the 60s. Some results of studies of the dependence of the instantaneous temperature of the exhaust gases from the load for the four-stroke engine on a small area of \u200b\u200bthe crankshaft rotation dated with the same period of time are also known. However, neither in this nor in other sources there are such important characteristics As the local heat transfer intensity and gas flow rate in the exhaust channel. Diesels with a superior can be three types of gas supply organization from the cylinder head to the turbine: a system of permanent gas pressure in front of the turbine, a pulse system and a supercharge system with a pulse converter.
In the system of constant pressure, the gases from all cylinders go into a large exhaust manifold of a large volume, which serves as a receiver and largely smoothes pressure pulsations (Figure 1). During the release of gas from the cylinder in the exhaust pipe, a high amplitude pressure wave is formed. The disadvantage of such a system is a strong decrease in gas performance while flowing from the cylinder through the collector to the turbine.
With such an organization of the release of gases from the cylinder and the supply of them to the nozzle apparatus of the turbine decreases the loss of energy associated with their sudden expansion during the expiration of the cylinder into the pipeline and the two-time conversion of energy: the kinetic energy arising from the cylinder of gases into the potential energy of their pressure in the pipeline, and the last Again in the kinetic energy in the nozzle apparatus in the turbine, as it occurs in the graduation system with constant pressure pressure at the entrance to the turbine. As a result of this, during the pulsed system, the disposable operation of gases in the turbine increases and their pressure decreases during the release, which reduces the cost of power to carry out gas exchange in the cylinder of the piston engine.
It should be noted that with a pulsed superior, the conditions for the conversion of energy in the turbine are significantly deteriorated due to nonstationarity of the flow, which leads to a decrease in its efficiency. In addition, the definition of the calculated parameters of the turbine is hampered due to variables of pressure and temperature of the gas before the turbine and behind it, and the separation supply of gas to its nozzle apparatus. In addition, the design of both the engine itself and the turbocharger turbine is complicated due to the introduction of separate collectors. As a result, a number of firms with mass production Engines with gas turbine superior applies a constant pressure boost system before turbine.
The supervision of the impulse converter is intermediate and combines the benefits of pressure pulsations in the exhaust manifold (reducing the poverty operation and improving the cylinder purge) with a winner from reducing pressure ripples before the turbine, which increases the efficiency of the latter.
Figure 3 - Superior system with pulse converter: 1 - nozzle; 2 - nozzles; 3 - camera; 4 - Diffuser; 5 - pipeline
In this case, the exhaust gases on pipes 1 (Figure 3) are summarized through nozzles 2, into one pipeline, which combines the releases from cylinders, the phases of which are not superimposed by one to another. At a certain point in time, the pressure pulse in one of the pipelines reaches a maximum. In this case, the maximum gas expiration rate from the nozzle connected to this pipeline becomes the maximum, which results in the effect of ejection to the resolution in another pipeline and thereby facilitates the purge of cylinders attached to it. The process of expiration of the nozzles is repeated with a high frequency, therefore, in chamber 3, which performs the role of a mixer and a damper, a more or less uniform stream is formed, the kinetic energy of which in the diffuser 4 (speed reduction) is transformed into a potential due to increase in pressure. From the pipeline 5 gases enter the turbine at almost constant pressure. A more complex structural diagram of the pulse converter consisting of special nozzles at the ends of the exhaust pipes, combined by a common diffuser, is shown in Figure 4.
The flow in the exhaust pipeline is characterized by pronounced nonstationarity caused by the frequency of the process itself, and the nonstationarity of gas parameters at the borders of the exhaust pipeline-cylinder and the turbine. Channel rotation, profile breakdown and periodic change of it geometrical characteristics At the input portion of the valve slit, it is the cause of the separation of the boundary layer and the formation of extensive stagnant zones, the dimensions of which are changed over time. In stagnation zones, a refundable flow with large-scale pulsating vortices, which interact with the main flow in the pipeline and largely determine the flow characteristics of the channels. The nonstationarity of the stream is manifested in the exhaust channel and under stationary boundary conditions (with a fixed valve) as a result of ripples of congestion zones. The dimensions of non-stationary vortices and the frequency of their ripples can significantly determine only by experimental methods.
The complexity of experimental study of the structure of non-stationary vortex flows forces designers and researchers to use when choosing the optimal geometry of the exhaust channel by comparing the integral consumables and energy characteristics of the flow, usually obtained under stationary conditions on physical models, that is, with static purge. However, the substantiation of the reliability of such studies is not given.
The paper presents the experimental results of studying the stream structure in the exhaust channel of the engine and carried out comparative analysis structures and integral characteristics of streams under stationary and nonstationary conditions.
The test results of a large number of output variants indicate the insufficient effectiveness of the usual approach to profiling based on the perpetrators of the stationary flow in the knees of pipes and short pipes. There are often cases of inconsistency of the projected and real dependences of the expenditure characteristics from the geometry of the channel.
Measurement of the angle of rotation and frequency of rotation of the camshaft
It should be noted that the maximum differences between the values \u200b\u200bof the TPs defined in the center of the channel and near its wall (the variation on the radius of the channel) are observed in control sections close to the input to the channel under study and reach 10.0% of the IPI. Thus, if the forced ripples of the gas flow for 1x to 150 mm would be much less with a period than IPI \u003d 115 ms, the current should be characterized as a course with a high degree of non-stationary. This suggests that the transitional flow regime in the channels of the energy installation has not yet been completed, and the next indignation has already affected. And on the contrary, if the pulsations of the flow would be much more with a period than TR, the current should be considered a quasistationary (with a low degree of nonstationary). In this case, before the occurrence of the perturbation, the transitional hydrodynamic mode has time to complete, and the course to be aligned. And finally, if the flow rate of flow was close to the value of TR, the current should be characterized as moderately non-stationary with an increasing degree of nonstationary.
As an example of the possible use of the characteristic times proposed to assess the characteristic times, the flow of gas in the exhaust channels of piston engineers is considered. First, refer to Figure 17, at which the dependences of the WX flow rate from the angle of rotation of the crankshaft F (Figure 17, a) and on the time T (Figure 17, b). These dependences were obtained on the physical model of the same-cylinder DVS dimension 8.2 / 7.1. It can be seen from the figure that the representation of the dependence WX \u003d F (F) is a little-informative, since it does not exactly reflect physical essence processes occurring in the graduation channel. However, it is precisely in this form that these graphics are taken to submit in the field of engine field. In our opinion, it is more correct to use temporal dependences WX \u003d / (T) to analyze.
We analyze the dependence WX \u003d / (T) for n \u003d 1500 min "1 (Figure 18). As can be seen, at this crankshaft speed, the duration of the entire release process is 27.1 ms. Transitional hydrodynamic process In the outlet begins after opening the exhaust valve. In this case, it is possible to select the most dynamic area of \u200b\u200bthe lifting (the time interval, during which a sharp increase in the flow rate occurs), the duration of which is 6.3 ms. After that, the growth of the flow rate is replaced by its decline. As shown earlier (Figure 15), for this configuration hydraulic system Relaxation time is 115-120 ms, i.e. significantly larger than the duration of the lifting section. Thus, it should be assumed that the beginning of the release (the lifting section) occurs with a high degree of nonstationary. 540 Ф, hail of PKV 7 a)
The gas was supplied from the total network on the pipeline, on which the pressure gauge 1 was installed to control the pressure on the network and the valve 2, to control the flow. The gas flowed into the tank receiver 3 with a volume of 0.04 m3, it contained an alignment grille 4 to quench pressure pulsations. From the tank-receiver 3, the gas pipeline was supplied to the cylinder-blowing chamber 5, in which Honeycomb 6 was installed. Honaycomb was a thin grille, and was intended to clean residual pressure ripples. The cylinder-blowing chamber 5 was attached to the cylinder block 8, while the inner cavity of the cylinder-cell chamber was combined with the inner cavity of the head of the cylinder block.
After opening the exhaust valve 7, the gas from the simulation chamber went through the exhaust channel 9 to the measuring channel 10.
Figure 20 shows in more detail the configuration of the exhaust path of the experimental installation, indicating the locations of the pressure sensors and the thermoemometer probes.
Due to the limited number of information on the dynamics of the release process, a classic direct outlet channel with a round cross section was chosen: the head of the cylinder block 2 was attached to the studs of an experimental exhaust pipe 4, the pipe length was 400 mm, and a diameter of 30 mm. In the pipe, three holes were drilled at distances L \\, lg and b, respectively, 20,140 and 340 mm for the installation of pressure sensors 5 and thermo-chaser sensors 6 (Figure 20).
Figure 20 - configuration of the exhaust channel of the experimental installation and location of the sensor: 1 - cylinder - blowing chamber; 2 - the head of the cylinder block; 3 - exhaust valve; 4 - an experimental graduation tube; 5 - pressure sensors; 6 - thermoemometer sensors for measuring the flow rate; L is the length of the outlet pipe; C_3- Diases to the locations of the thermo-chaser sensors from the exhaust window
The installation measurement system made it possible to determine: the current corner of the rotation and the rotational speed of the crankshaft, the instantaneous flow rate, the instantaneous heat transfer coefficient, excess flow pressure. Methods for defining these parameters are described below. 2.3 Measurement of the corner of rotation and frequency of rotation of the distribution
To determine the speed of rotation and the current angle of rotation of the camshaft, as well as the moment of finding the piston in the upper and lower dead points, a tachometric sensor was applied, the installation scheme, which is shown in Figure 21, since the parameters listed above must be unambiguously determined in the study of dynamic processes in ICC . four
The tachometric sensor consisted of a toothed disk 7, which had only two teeth located opposite each other. The disk 1 was installed with an electric motor 4 so that one of the discs of the disk corresponded to the position of the piston in the upper dead point, and the other, respectively, the bottom dead point and was attached to the shaft using the coupling 3. The motor shaft and the piston engine shaft were connected by the belt transmission.
When passing one of the teeth near the inductive sensor 4, fixed on the tripod 5, the output of the inductive sensor is formed a voltage pulse. Using these pulses, you can determine the current position of the camshaft and, accordingly, determine the position of the piston. In order for the signals corresponding to NMT and NMT, the teeth were performed from each other from each other, the configuration is different from each other, due to which the signals at the outlet of the inductive sensor had different amplitudes. The signal obtained at the outlet from the inductive sensor is shown in Figure 22: the voltage pulse of a smaller amplitude corresponds to the position of the piston in the NTC, and the pulse of a higher amplitude, respectively, position in NMT.
Gas dynamics and consumables process of the output of the piston internal combustion engine with a superposition
In classical literature on the theory of workflow and engineering, the turbocharger is mainly considered as the most effective method of engine forcing, due to an increase in the amount of air entering the engine cylinders.
It should be noted that in literary sources, the influence of the turbocharger on the gas-dynamic and thermophysical characteristics of the gas flow of the exhaust pipeline is extremely rare. Mainly in the literature, the turbine turbine turbine is considered with simplifications, as an element of a gas exchange system, which has hydraulic resistance to the flow of gases at the outlet of the cylinders. However, it is obvious that the turbocharger turbine plays an important role in the formation of the flow of exhaust gases and has a significant impact on the hydrodynamic and thermophysical characteristics of the flow. This section discusses the results of the study of the effect of the turbocharger turbine on the hydrodynamic and thermophysical characteristics of the gas flow in the exhaust pipeline of the piston engine.
Studies were carried out on an experimental setup, which was previously described, in the second chapter, the main change is the installation of a TKR-6 turbocharger with a radial-axial turbine (Figures 47 and 48).
Due to the influence of the pressure of the exhaust gases in the exhaust pipeline to the workflow of the turbine, the patterns of changes in this indicator are widely studied. Compressed
The turbine turbine installation in the exhaust pipeline has a strong effect on the pressure and flow rate in the exhaust pipeline, which is clearly seen from the plugness of the pressure and the flow rate in the exhaust pipe with the turbocharger from the corner of the crankshaft (Figures 49 and 50). Comparing these dependencies with similar dependencies for the exhaust pipeline without a turbocharger under similar conditions, it can be seen that the installation of a turbocharger turbine into the exhaust pipe leads to the emergence of a large number of ripples throughout the entire output of the output caused by the action of the blade elements (nozzle apparatus and impeller) of the turbine. Figure 48 - General type of installation with turbocharger
Another characteristic feature of these dependencies is a significant increase in the amplitude of pressure fluctuations and a significant reduction in the amplitude of the speed fluctuations in comparison with the execution of the exhaust system without a turbocharger. For example, at with the rotation frequency of the crankshaft of 1500 minutes, the maximum gas pressure in the pipeline with a turbocharger is 2 times higher, and the speed is 4.5 times lower than in the pipeline without a turbocharger. Increased pressure and Reducing the speed in the graduation pipeline is caused by the resistance created by the turbine. It is worth noting that the maximum pressure value in the turbocharger pipeline is shifted relative to the maximum pressure value in the pipeline without a turbocharger by up to 50 degrees of the rotation of the crankshaft. SO
The dependences of the local (1x \u003d 140 mm) excess pressure of the PC and the flow rate of the WX in the exhaust pipeline of the circular cross-section of the piston engine with a turbocharger from the angle of rotation of the crankshaft p at an overpressure of the release of the P t \u003d 100 kPa for different crankshaft speeds:
It was found that in the exhaust pipeline with a turbocharger, the maximum flow rate values \u200b\u200bare lower than in the pipeline without it. It is worth noting that at the same time the moment of achieving the maximum flow rate value towards an increase in the corner of the crankshaft turn is characteristic of all installation modes. In the case of turbocharger, the rate of speed is most pronounced at low speeds of rotation of the crankshaft, which is also characteristic and in the case without a turbocharger.
Similar features are characteristic and for dependence Px \u003d / (P).
It should be noted that after closing the exhaust valve, the gas speed in the pipeline in all modes is not reduced to zero. Installing the turbocharger turbine in the exhaust pipeline leads to the smoothing of the flow rate pulsations on all modes of operation (especially with the initial overpressure of 100 kPa), both during the output tact and after its end.
It is worth noting that in the pipeline with a turbocharger, the intensity of the attenuation of the fluctuations of the flow pressure after the exhaust valve is closed higher than without a turbocharger
It should be assumed that the changes described above the changes in the gas-dynamic characteristics of the flow when the turbocharger is installed in the exhaust pipeline, the flow of flow in the outlet canal, which inevitably should lead to changes in the thermophysical characteristics of the release process.
In general, the dependence of the pressure change in the pipeline in DVS with the superior is consistent with the previously obtained.
Figure 53 shows the graphs of the dependence of the mass flow G through the exhaust pipeline from the speed of rotation of the crankshaft P at different values \u200b\u200bof the excessive pressure of the P and the configurations of the exhaust system (with a turbocharger and without it). These graphics were obtained using the technique described in.
From the graphs shown in Figure 53 it can be seen that for all initial excess pressure values mass flow G Gas in the exhaust pipeline is about the same as if there is a TC and without it.
In some modes of operation of the installation, the difference of the expenditure characteristics slightly exceeds a systematic error, which is about 8-10% to determine the mass flow rate. 0.0145 g. kg / s
For pipeline with square cross section
The exhaust system with ejection functions as follows. The exhaust gases into the exhaust system come from the engine cylinder into the channel in the cylinder head 7, from where they pass to the exhaust manifold 2. In the exhaust manifold 2, an ejection tube 4 is installed in which air is supplied via an electropneumoclap 5. Such an execution allows you to create a discharge area immediately behind the channel cylinder head.
In order for the ejection tube does not create significant hydraulic resistance in the exhaust manifold, its diameter should not exceed 1/10 diameter of this collector. It is also necessary in order to create a critical mode in the exhaust manifold, and the ejector locking appears. The position of the ejection tube axis relative to the exhaust collector axis (eccentricity) is selected depending on the specific configuration of the exhaust system and the engine operation mode. In this case, the effectiveness criterion is the degree of purification of the cylinder from the exhaust gases.
Search experiments showed that the discharge (static pressure) created in the exhaust manifold 2 using the ejection tube 4 should be at least 5 kPa. Otherwise, insufficient leveling of the pulsating flow will occur. This can cause the formation of feed currents in the channel, which will lead to a decrease in the efficiency of the cylinder purge, and, accordingly, reduce the power of the engine. The electronic motor control unit 6 must organize the operation of the electropneumoclap 5, depending on the rotational speed of the engine crankshaft. To enhance the effect of ejection at the output end of the ejection tube 4, a subsonic nozzle may be installed.
It turned out that the maximum values \u200b\u200bof the flow rate in the outlet canal with constant ejection is significantly higher than without it (up to 35%). In addition, after closing the exhaust valve in the exhaust channel with a constant ejection, the speed of the output flow drops slower compared to the traditional channel, which indicates the continuing cleaning of the channel from the exhaust gases.
Figure 63 shows the dependences of the local volume flow VX through the outlet channels of different execution from the rotational speed crankshaft P. They indicate that in the entire range of the rotation frequency of the crankshaft, with a constant ejection, the volume flow rate through the exhaust system increases, which should lead to better cleaning of cylinders from exhaust gases and increase engine power.
Thus, the study showed that the use of a constant ejection in the exhaust system in the exhaust system improves the cylinder gas purification compared to traditional systems by stabilizing the flow in the exhaust system.
The main fundamental difference of this method on the method of quenching flow pulsations in the exhaust channel of the piston engine using the effect of constant ejection is that the air through the ejection tube is supplied to the exhaust channel only during the release tact. This may be feasible by setting the electronic motor control unit, or the use of a special control unit, the diagram of which is shown in Figure 66.
This scheme developed by the author (Figure 64) is applied if it is impossible to ensure the control of the ejection process using the engine control unit. The principle of operation of such a scheme consists in the following, special magnets should be installed on the engine flywheel, special magnets must be installed, the position of which would correspond to the moments of opening and closing the engine outlet valves. Magnets must be installed in different poles relative to the Hall bipolar sensor, which in turn should be in the immediate vicinity of magnets. Passing next to the sensor Magnet, set by respectively the point of opening of the exhaust valves, causes a small electrical pulse, which is enhanced by the signal amplification unit 5, and is fed to the electropneumoclap, the conclusions of which are connected to the outputs 2 and 4 of the control unit, after which it opens and air supply begins . It happens when the second magnet runs next to the sensor 7, after which the electropneumoclap closes.
We turn to experimental data that were obtained in the range of rotation frequencies of the crankshaft P from 600 to 3000 minutes. 1 with different permanent overpressure pins on the release (from 0.5 to 200 kPa). In experiments, compressed air with a temperature of 22-24 with The ejection tube received from the factory highway. Deflection (static pressure) for the ejection tube in the exhaust system was 5 kPa.
Figure 65 shows the graphs of the local pressure dependences Px (y \u003d 140 mm) and the WX flow rate in the exhaust pipeline of the round transverse section of the piston engine with a periodic ejection from the angle of rotation of the crankshaft r under the excess pressure of the № \u003d 100 kPa for various rotation frequencies of the crankshaft .
From these graphs, it can be seen that throughout the entire tact of release there is a oscillation of absolute pressure in the graduation path, the maximum values \u200b\u200bof pressure oscillations reach 15 kPa, and the minimum reaches the discharge of 9 kPa. Then, as in the classic graduation path of the circular cross section, these indicators are respectively 13.5 kPa and 5 kPa. It is worth noting that the maximum pressure value is observed at the speed of the crankshaft of 1500 min. "1, on the other modes of operation of the pressure oscillation engine do not reach such values. Recall. That in the initial pipe of the round cross section, the monotonous increase in the amplitude of pressure fluctuations was observed depending on the increase The rotation frequency of the crankshaft.
From the charts of the local gas flow rate of the gas flow from the corner of the crankshaft rotation, it can be seen that local speeds during the release tact in the channel using the effect of periodic ejection is higher than in the classic channel of the circular cross section on all modes of the engine. This indicates the best cleaning of the graduation channel.
Figure 66, graphs of comparing the dependences of the volumetric flow rate of the gas from the rotational speed of the crankshaft in the round cross section of without ejection and the round cross section with a periodic ejection at various overpressure at the inlet input canal are considered.
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Federal Agency for Education
GOU VPO "Ural State Technical University - UPI named after the first president of Russia B.N. Yeltsin "
For manuscript rights
Thesis
for the degree of candidate of technical sciences
Gas dynamics and local heat transfer in the intake system of piston engine
Carpenters Leonid Valerevich
Scientific adviser:
doctor Physico-Mathematical Audience,
professor Zhilkin B.P.
Ekaterinburg 2009.
piston Engine Gas Dynamics Intake System
The thesis consists of administration, five chapters, conclusion, a list of references, including 112 names. It is set out on 159 pages of computer dialing in the MS Word program and is equipped with text 87 drawings and 1 table.
Keywords: gas dynamics, piston engine, inlet system, transverse profiling, consumables, local heat transfer, instantaneous local heat transfer coefficient.
The object of the study was the non-stationary air flow in the inlet system of the piston engine of internal combustion.
The goal of the work is to establish the patterns of changes in the gas-dynamic and thermal characteristics of the inlet process in the piston internal combustion engine from geometric and regime factors.
It is shown that by placing the profiled inserts, it is possible to compare with a traditional channel of the constant round, to acquire a number of advantages: an increase in the volume flow of air entering the cylinder; The increase in the steepness of the dependence V on the number of rotation of the crankshaft N in the operating range of the rotation frequency at the "triangular" insert or linearization of the expenditure characteristic in the entire range of rotation numbers of the shaft, as well as suppressing high-frequency air flow pulsations in the inlet channel.
Significant differences in the patterns of changing the heat transfer coefficients from the velocity W under the stationary and pulsating flow of air in the intake system of KBS. The approximation of the experimental data was obtained equations for calculating the local heat transfer coefficient in the inlet tract of the FEA, both for stationary flow and for a dynamic pulsating flow.
Introduction
1. State of the problem and setting the objectives of the study
2. Description of the experimental installation and measurement methods
2.2 Measurement of the rotational speed and corner of the crankshaft rotation
2.3 Measurement of the instantaneous consumption of suction air
2.4 System for measuring instantaneous heat transfer coefficients
2.5 Data Collection System
3. Gas dynamics and consumables input process in the internal combustion engine at various intake system configurations
3.1 Gas dynamics of the intake process without taking into account the effect of the filter element
3.2 Influence of the filter element on the gas dynamics of the intake process in various intake system configurations
3.3 Consumables and spectral analysis of the inlet process with various intake system configurations with different filter elements
4. The heat transfer in the intake channel of the piston engine of internal combustion
4.1 Calibration of the measuring system to determine the local heat transfer coefficient
4.2 Local heat transfer coefficient in the inlet channel of the internal combustion engine at inpatient mode
4.3 Instant local heat transfer coefficient in the inlet channel of the internal combustion engine
4.4 Influence of the configuration of the inlet system of the internal combustion engine on the instantaneous local heat transfer coefficient
5. Questions practical application Results of work
5.1 Constructive and technological design
5.2 Energy and resource saving
Conclusion
Bibliography
List of basic designations and abbreviations
All symbols are explained when they are first used in the text. The following is only a list of only the most consumable designations:
d -Diameter of pipes, mm;
d e is an equivalent (hydraulic) diameter, mm;
F - surface area, m 2;
i - current strength, and;
G - mass flow of air, kg / s;
L - Length, m;
l is a characteristic linear size, m;
n is the rotational speed of the crankshaft, min -1;
p - atmospheric pressure, PA;
R - resistance, Ohm;
T - absolute temperature, to;
t - the temperature on the Celsius scale, O C;
U - voltage, in;
V - air flow rate, m 3 / s;
w - air flow rate, m / s;
An excess air coefficient;
g - angle, hail;
The angle of rotation of the crankshaft, hail., P.K.V.;
Thermal conductivity coefficient, W / (M K);
Coefficient kinematic viscosity, m 2 / s;
Density, kg / m 3;
Time, s;
Resistance coefficient;
Basic cuts:
p.K.V. - rotation of the crankshaft;
DVS - internal combustion engine;
NMT - upper dead point;
NMT - Lower Dead Point
ADC - analog-to-digital converter;
BPF - Fast Fourier transformation.
Numbers:
Re \u003d WD / - Rangeld's number;
Nu \u003d D / - number of nusselt.
Introduction
The main task in the development and improvement of the piston internal combustion engines is to improve the filling of the cylinder with a fresh charge (or in other words, an increase in the filling coefficient of the engine). Currently, the development of the DVS has reached such a level that the improvement of any technical and economic indicator at least on the tenth share of the percentage with minimal material and temporary costs is a real achievement for researchers or engineers. Therefore, to achieve the goal, the researchers offer and use a variety of methods among the most common can be distinguished by the following: dynamic (inertial) reducing, turbocharging or air blowers, inlet channel of variable length, adjustment of the mechanism and phases of gas distribution, optimization of the intake system configuration. The use of these methods allows to improve the filling of the cylinder with a fresh charge, which in turn increases the engine power and its technical and economic indicators.
However, the use of most of the methods under consideration require significant material investments and a significant modernization of the design of the inlet system and the engine as a whole. Therefore, one of the most common, but not the simplest, to date, the methods of increasing the filling factor is to optimize the configuration of the engine inlet path. In this case, the study and improvement of the inlet channel of the engine is most often carried out by the method of mathematical modeling or static purges of the intake system. However, these methods cannot give correct results at the modern level of engine development, since, as is known, the real process in the gas-air paths of the engines is a three-dimensional gas inkjet expiration through the valve slot into a partially filled space of the variable volume cylinder. An analysis of the literature showed that the information on the intake process in real dynamic mode is practically absent.
Thus, reliable and correct gas-dynamic and heat exchange data for the intake process can be obtained exclusively in studies on dynamic MODELS OF DVS or real engines. Only such experienced data can provide the necessary information to improve the engine at the present level.
The aim of the work is to establish the patterns of changing the gas-dynamic and thermal characteristics of the process of filling the cylinder with a fresh charge of piston internal combustion engine from geometric and regime factors.
The scientific novelty of the main provisions of the work is that the author for the first time:
The amplitude-frequency characteristics of the pulsation effects arising in the stream in the intake manifold (pipe) of the piston engine;
A method for increasing air flow (on average by 24%) entering the cylinder using profiled inserts in the intake manifold, which will lead to an increase in engine power;
The patterns of changes in the instantaneous local heat transfer coefficient in the piston engine inlet tube are established;
It is shown that the use of profiled inserts reduces the heating of fresh charge at the intake by an average of 30%, which will improve the filling of the cylinder;
Generalized in the form of empirical equations The obtained experimental data on the local heat transfer of the pulsating flow of air in the intake manifold.
The accuracy of the results is based on the reliability of experimental data obtained by the combination of independent research methodologies and confirmed by the reproducibility of experimental results, their good agreement at the level of test experiments with these authors, as well as the use of a complex of modern research methods, selection of measuring equipment, its systematic testing and targeting.
Practical significance. The experimental data obtained create the basis for the development of engineering methods for calculating and designing ink-ink systems, and also expand theoretical representations about gas dynamics and local air heat transfer during the intake in piston engine. The individual results of the work were made to the implementation of the Ural Diesel Motor Plant LLC in the design and modernization of 6DM-21L and 8DM-21l engines.
Methods for determining the flow rate of the pulsating air flow in the inlet pipe of the engine and the intensity of instantaneous heat transfer in it;
Experimental data on gas dynamics and an instantaneous local heat transfer coefficient in the inlet channel of the input channel in the intake process;
The results of the generalization of the data on the local coefficient of air heat transfer in the inlet channel of the DVS in the form of empirical equations;
Approbation of work. The main results of studies set forth in the thesis reported and were presented at the "Reporting Conferences of Young Scientists", Yekaterinburg, UGTU-UPI (2006 - 2008); scientific seminars Department "Theoretical heat engineering" and "Turbines and engines", Yekaterinburg, UGTU-UPI (2006 - 2008); Scientific and Technical Conference "Improving the efficiency of power plants of wheeled and tracked machines", Chelyabinsk: Chelyabinsk Higher Military Automobile Communist Party School (Military Institute) (2008); Scientific and Technical Conference "Development of Engineering in Russia", St. Petersburg (2009); on the Scientific and Technical Council under Ural Diesel Motor Plant LLC, Yekaterinburg (2009); On the Scientific and Technical Council for OJSC NII Autotractor Technology, Chelyabinsk (2009).
The dissertation work was performed at the departments "Theoretical heat engineering and" turbines and engines ".
1. Review of the current state of the study of piston inlet inlet systems
To date, there are a large number of literature, in which the constructive performance of various systems of piston engines of internal combustion, in particular, individual elements of the inlet systems of the ink systems are considered. However, there is practically no substantiation of the proposed design solutions by analyzing gas dynamics and heat transfer of the inlet process. And only in individual monographs provide experimental or statistical data on the results of operation, confirming the feasibility of one or another constructive performance. In this regard, it can be argued that until recently, insufficient attention was paid to the study and optimization of piston engines inlet systems.
In recent decades, in connection with the tightening of economic and environmental requirements for internal combustion engines, researchers and engineers are beginning to pay more and more attention to improving intake systems of both gasoline and diesel engines, believing that their performance is largely dependent on the perfection of processes occurring In gas-air paths.
1.1 Basic elements of piston inlet inlet systems
The intake system of the piston engine, in general, consists of a air filter, an intake manifold (or inlet tube), cylinder heads that contain intake and outlet channels, as well as the valve mechanism. As an example, in Figure 1.1, a diagram of the intake system of the YMZ-238 diesel engine is shown.
Fig. 1.1. Scheme of the intake system of the YMZ-238 diesel engine: 1 - intake manifold (tube); 2 - rubber gasket; 3.5 - connecting nozzles; 4 - Estimated gasket; 6 - hose; 7 - Air filter
The choice of optimal structural parameters and the aerodynamic characteristics of the intake system predetermine the efficient workflow and high level of output indicators of internal combustion engines.
Briefly consider each composite element of the intake system and its main functions.
The cylinder head is one of the most complex and important elements in the internal combustion engine. From the correct selection of the shape and size of the main elements (first of all, the perfection of filling and mixing processes is largely depends on the size of intake and exhaust valves).
The cylinder heads are mainly made with two or four valves on the cylinder. The advantages of the two-flame design are the simplicity of manufacturing technology and the design scheme, in smaller structural mass and value, the number of moving parts in the drive mechanism, maintenance and repair costs.
The advantages of four-flaped structures consists in better use of the area limited by the cylinder circuit, for the passing areas of the valve gorlovin, in a more efficient gas exchange process, in a smaller thermal tension of the head due to a more uniform thermal state, in the possibility of central placement of the nozzle or candles, which increases the uniformity of the thermal state details piston group.
There are other designs of cylinder heads, for example, with three inlet valves and one or two graduation per cylinder. However, such schemes are applied relatively rare, mainly in highly affiliated (racing) engines.
The influence of the number of valves on gas dynamics and heat transfer in the inlet path is generally practically not studied.
The most important elements of the cylinder head from the point of view of their influence on gas dynamics and heat exchange input process in the engine are the types of inlet channels.
One of the ways to optimize the filling process is profiling inlet channels in the cylinder head. There is a wide variety of shapes of profiling in order to ensure the directional movement of fresh charge in the engine cylinder and improving the mixing process, they are described in the most detailed.
Depending on the type of mixing process, the intake channels are performed by one-functional (disgustable), providing only filling with cylinders with air, or two-function (tangential, screw or other type) used for inlet and twisting air charge in the cylinder and combustion chamber.
Let us turn to the question of the features of the design of intake collectors of gasoline and diesel engines. An analysis of the literature shows that the intake collector (or ink tube) is given little attention, and it is often considered only as a pipeline for supplying air or fuel-air mixture into the engine.
Air filter It is an integral part of the piston engine inlet system. It should be noted that in the literature, more attention is paid to the design, materials and resistance of the filter elements, and at the same time the effect of the filtering element on gas-dynamic and heat exchanged indicators, as well as the expenditure characteristics of piston internal combustion system, is practically not considered.
1.2 Gas dynamics of flow in inlet channels and methods for studying the inlet process in piston engine
For a more accurate understanding of the physical essence of the results obtained by other authors, they are outlined simultaneously with the theoretical and experimental methods used, since the method and result are in a single organic communication.
Methods for the study of inlet systems of the KHOs can be divided into two large groups. The first group includes theoretical analysis of the processes in the inlet system, including their numerical simulation. To the second group, we will draw all the ways to experimentally study the inlet process.
The choice of research methods, estimates and adjusting intake systems is determined by the goals set, as well as existing material, experimental and calculated possibilities.
To date, there are no analytic methods that allow it to be fairly accurate to estimate the level of intensity of gas in the combustion chamber, as well as solve private problems associated with a description of the movement in the intake path and the gas expiration from the valve gap in the real unsaluable process. This is due to the difficulties of describing the three-dimensional flow of gases on curvilinear channels with sudden obstacles, a complex spatial stream structure, with a jet gas outlet through the valve slot and a partially filled space of a variable volume cylinder, the interaction of flows between themselves, with the walls of the cylinder and the movable bottom of the piston. Analytical determination of the optimal field of velocity in the inlet tube, in the ring valve slot and the distribution of flows in the cylinder is complicated by the lack of accurate methods for evaluating aerodynamic losses arising from a fresh charge in the inlet system and when gas in the cylinder and flow around its internal surfaces. It is known that in the channel there are unstable zones of the transition of the flow from laminar to the turbulent flow mode, the region of the separation of the boundary layer. The flow structure is characterized by variables by time and the place of Reynolds, the level of non-stationarity, intensity and the scale of turbulence.
Many multidirectional work is devoted to numerical modeling of the movement of the air charge on the inlet. They produce modeling of the vortex intake-flux of the inlet of the inlet of the inlet of the inlet valve, the calculation of the three-dimensional flow in the inlet channels of the cylinder head, modeling the stream in the inlet window and the engine cylinder, an analysis of the effect of direct-flow and swirling streams on the mixing process and calculated studies of the effect of the charge twisting in the diesel cylinder The magnitude of emissions of nitrogen oxides and indicator cycle indicators. However, only in some of the works, numerical simulation is confirmed by experimental data. And solely on theoretical studies it is difficult to judge the accuracy and degree of applicability of the data. It should also be emphasized that almost all numerical methods are mainly aimed at studying the processes in the already existing design of the inlet of the inlet system of the intensity of the DVS to eliminate its deficiencies, and not to develop new, effective design solutions.
In parallel, the classical analytical methods for calculating the workflow in the engine and separate gas exchange processes in it are applied. However, in the calculations of the flow of gas in the inlet and exhaust valves and channels, the equations of one-dimensional stationary flow are mainly used, taking the current quasi-stationary. Therefore, the calculation methods under consideration are exclusively estimated (approximate) and therefore require experimental refinement in laboratory or on a real engine during bench tests. Methods for calculating the gas exchange and the main gas-dynamic indicators of the inlet process in a more difficult formulation are developing in the works. However, they also give only general information about the processes discussed, do not form a sufficiently complete representation of gas-dynamic and heat exchange rates, since they are based on statistical data obtained in mathematical modeling and / or static purges of the inlet tract of the ink and on the methods of numerical simulation.
The most accurate and reliable data on the inlet process in the piston engine can be obtained in the study on real-operating engines.
To the first studies of the charge in the engine cylinder on the shaft test mode, the classic experiments of Ricardo and the Cash can be attributed. Riccardo installed an impeller in the combustion chamber and recorded its rotational speed when the engine shaft is checked. The anemometer fixed the average gas speed value for one cycle. Ricardo introduced the concept of "vortex ratio", corresponding to the ratio of the frequency of the impeller, measured the rotation of the vortex, and the crankshaft. The CASS installed the plate in the open combustion chamber and recorded the effect on the air flow. There are other ways to use plates associated with tensidate or inductive sensors. However, the installation of plates deform the rotating stream, which is the disadvantage of such methods.
Modern research of gas dynamics directly on engines requires special Tools measurements that are capable of working under adverse conditions (noise, vibration, rotating elements, high temperature and pressure when combustion of fuel and in exhaust channels). In this case, the processes in the DVS are high-speed and periodic, so the measuring equipment and sensors must have very high speed. All this greatly complicates the study of the inlet process.
It should be noted that at present, methods of natural research on engines are widely used, both to study the flow of air in the inlet system and the engine cylinder, and for the analysis of the effect of vortex formation on the inlet for the toxicity of exhaust gases.
However, natural studies, where at the same time a large number of diverse factors acts, do not allow to penetrate the details of the mechanism of a separate phenomenon, do not allow to use high-precision, complex equipment. All this is the prerogative of laboratory studies using complex methods.
The results of the study of gas dynamics of the intake process, obtained in the study on engines are quite detailed in the monograph.
Of these, the greatest interest is the oscillogram of changes in the air flow rate in the input section of the inlet channel of the engine of C10.5 / 12 (D 37) of the Vladimir Tractor Plant, which is presented in Figure 1.2.
Fig. 1.2. Flow parameters in the input section of the channel: 1 - 30 s -1, 2 - 25 s -1, 3 - 20 s -1
Measurement of the air flow rate in this study was carried out using a thermoemometer operating in DC mode.
And here it is appropriate to pay attention to the very method of thermoemometry, which, thanks to a number of advantages, received such widespread gas-dynamics of various processes in research. Currently, there are various schemes of thermoanemometers depending on the tasks and the field of research. The most detailed theory of thermoenemometry is considered in. It should also be noted a wide variety of thermoemometer sensor designs, which indicates the widespread use of this method in all areas of industry, including engineering.
Consider the question of the applicability of the thermoenemometry method for studying the inlet process in piston engine. Thus, the small dimensions of the sensitive element of the thermoemometer sensor do not make significant changes in the nature of the flow of air flow; High sensitivity of the anemometers allows you to register fluctuations with small amplitudes and high frequencies; The simplicity of hardware scheme makes it possible to easily record the electrical signal from the output of the thermoemometer, followed by its processing on a personal computer. In thermomemometry, it is used in the sizing modes of one-, two- or three-component sensors. A thread or films of refractory metals with a thickness of 0.5-20 μm and a length of 1-12 mm are usually used as a sensitive element of the thermoemometer sensor, which is fixed on chromium or chromium-leather legs. The latter pass through a porcelain two-, three-way or four-grate tube, which is put on the metal case sealing from the breakthrough, the metal case, oked into the block head for the study of the intra-cylinder space or in pipelines to determine the average and ripple components of the gas velocity.
And now back to the oscillogram shown in Figure 1.2. The chart draws attention to the fact that it presents a change in the air flow rate from the angle of rotation of the crankshaft (P.K.V.) only for the intake tact (? 200 degrees. P.K.V.), whereas the rest Information on other clocks as it were "cropped". This oscillogram is obtained for the rotation frequency of the crankshaft from 600 to 1800 min -1, while in modern engines Range of operating speeds is much wider: 600-3000 min -1. Attention is drawn to the fact that the flow rate in the tract before opening the valve is not zero. In turn, after closing the intake valve, the speed is not reset, probably because in the path there is a high-frequency reciprocating flow, which in some engines is used to create a dynamic (or inertigice).
Therefore, it is important for understanding the process as a whole, data on the change in air flow rate in the inlet tract for the entire workflow of the engine (720 degrees, PKV) and in the entire operating range of the crankshaft rotation frequency. These data is necessary for improving the inlet process, searching for ways to increase the magnitude of a fresh charge entered into the engine cylinders and creating dynamic supercharow systems.
Let us briefly consider the features of dynamic supercharged in the piston DVS, which is carried out different ways. Not only the gas distribution phases, but also the design of intake and graduation paths affect the intake process. The movement of the piston when the intake tact leads to an open intake valve to the formation of the backpressure wave. At an open intake pipeline, this pressure wave occurs with a mass of fixed ambient air, reflected from it and moves back to the inlet pipe. The fluctuate airfold of the air column in the inlet pipeline can be used to increase the filling of cylinders with fresh charge and, thereby obtaining a large amount of torque.
With a different form of dynamic superchard - inertial superior, each inlet channel of the cylinder has its own separate resonator tube, the corresponding length acoustics connected to the collecting chamber. In such resonator tubes, the compression wave coming from cylinders can spread independently of each other. When agreeing the length and diameter of the individual resonator tubes with the phases of the gas distribution phase of the compression wave, reflected in the end of the resonator tube, returns through the open inlet valve The cylinder, thereby, provides its best filling.
The resonant reducing is based on the fact that in the air flow in the inlet pipeline at a certain rotational speed of the crankshaft there are resonant oscillations caused by the reciprocating movement of the piston. This, with the correct layout of the intake system, leads to a further increase in pressure and an additional adhesive effect.
At the same time, the mentioned dynamic boost methods operate in a narrow range of modes, require a very complex and permanent setting, since the acoustic characteristics of the engine are changed.
Also, gas dynamics data for the entire workflow of the engine can be useful to optimize the filling process and searches for increasing air flow through the engine and, accordingly, its power. At the same time, the intensity and scale of the turbulence of the air flow, which are generated in the inlet canal, as well as the number of vortices formed during the inlet process.
The rapid flow of charge and large-scale turbulence in the air flow provide good mixing of air and fuel and, thus, complete combustion with a low concentration of harmful substances in the exhaust gases.
One of the way to create the vortices in the intake process is the use of a flap that shares the intake path into two channels, one of which can overlap it, controlling the movement of the charge of the mixture. There are a large number of design versions to give the tangential component of the flow movement in order to organize directional vortices in the inlet pipeline and engine cylinder
. The purpose of all these solutions is to create and manage vertical vortices in the engine cylinder.
There are other ways to control the filling fresh charge. The design of a spiral intake canal is used in the engine with a different step of turns, flat venues on the inner wall and sharp edges at the channel output. Another device for regulating the vortex formation in the Cylinder of the engine is a spiral spring installed in the inlet channel and rigidly fixed by one end before the valve.
Thus, it is possible to note the trend of researchers to create large whirlwinds of different distribution directions on the inlet. In this case, the air flow must mainly contain large-scale turbulence. This leads to an improvement in the mixture and subsequent combustion of fuel, both in gasoline and in diesel engines. And as a result, the specific consumption of fuel and emissions of harmful substances with spent gases are reduced.
At the same time, in the literature there are no information about attempts to control the vortex formation using transverse profiling - a change in the shape of the transverse section of the channel, and it is known to strongly affect the nature of the flow.
After the foregoing, it can be concluded that at this stage in the literature there is a significant lack of reliable and complete information on the gas dynamics of the inlet process, namely: change the speed of the air flow from the corner of the crankshaft for the entire workflow of the engine in the operating range of the crankshaft rotation frequency shaft; The effect of the filter on the gas dynamics of the intake process; the scale of the turbulence occurs during the intake; The influence of hydrodynamic nonstationarity on the consumables in the inlet tract of DVS, etc.
The urgent task is to search for the methods of increasing air flow through the engine cylinders with minimal engine refinement.
As already noted above, the most complete and reliable input data can be obtained from studies on real engines. However, this direction of research is very complex and expensive, and for a number of issues is almost impossible, therefore, the combined methods of studying processes in ICC have been developed by experimenters. Consider widespread from them.
The development of a set of parameters and methods of calculating and experimental studies is due to the large number of comprehensive analytical descriptions of the design of the inlet system of piston engine, the dynamics of the process and movement of the charge in inlet channels and the cylinder.
Acceptable results can be obtained when a joint study of the intake process on a personal computer using numerical modeling methods and experimentally through static purges. According to this technique, many different studies have been made. In such work, either the possibilities of numerical modeling of swirling flows in the inlet system of the ink system are shown, followed by the results of the results using the purge in static mode on the inspector installation, or the calculated mathematical model Based on experimental data obtained in static modes or during the operation of individual modifications of engines. We emphasize that the basis of almost all such studies is taken experimental data obtained by the help of static blowing of the inlet system of the ink system.
Consider a classic way to study the intake process using a porch anemometer. With fixed valve lips, it produces a purge of the test channel with various second air consumption. For purge, real cylinder heads are used, cast from metal, or their models (collapsible wooden, gypsum, from epoxy resins, etc.) assembled with valves that guide bush lines and saddles. However, as described comparative tests, this method provides information on the effect of the form of the path, but the impeller does not respond to the action of the entire flow of air in cross section, which can lead to a significant error when estimating the intensity of the charge in the cylinder, which is confirmed mathematically and experimentally.
Another widespiliated method of studying the filling process is a method using a hidden lattice. This method differs from the previous one by the fact that the absorbed rotating air flow is sent to the fairing on the blade of the hidden grid. In this case, the rotating stream is stolen, and a jet moment is formed on the blades, which is recorded by the capacitive sensor in the magnitude of the Torcion spin angle. The hidden stream, having passed through the grille, flows through an open section at the end of the sleeve into the atmosphere. This method allows you to comprehensively evaluate the intake channel for energy indicators and by the magnitude of aerodynamic losses.
Even despite the fact that the methods of research on static models give only the most general idea of \u200b\u200bthe gas-dynamic and heat exchange characteristics of the inlet process, they still remain relevant due to their simplicity. Researchers are increasingly using these methods only for preliminary assessment of the prospects of intake systems or conversion already existing ones. However, for a complete, detailed understanding of the physics of phenomena during the inlet process of these methods is clearly not enough.
One of the most accurate and efficient ways to study the inlet process in the engine are experiments on special, dynamic installations. Under the assumption that gas-dynamic and heat exchange features and characteristics of the charge in the inlet system are functions of only geometric parameters and regime factors for the study, it is very useful to use a dynamic model - experimental installation, which most often represents a single-dimensional engine model on various high-speed modesacting by testing the crankshaft from an extraneous energy source and equipped with sensors different types . In this case, you can estimate the total effectiveness from certain solutions or their effectiveness is element. IN general Such an experiment is reduced to determine the flow characteristics in various elements of the intake system (instantaneous values \u200b\u200bof temperature, pressure and speed) varying at the corner of the rotation of the crankshaft.
Thus, the most optimal way to study the inlet process, which gives full and reliable data is the creation of a single-cylindrous dynamic model of piston engine, driven to rotation from an extraneous energy source. In this case, this method allows to investigate both gas-dynamic and heat exchangers of the filling process in the piston internal combustion engine. The use of thermoenemometric methods will make it possible to obtain reliable data without a significant effect on the processes occurring in the intake system of the experimental engine model.
1.3 Characteristics of heat exchange processes in the inlet system of piston engine
The study of heat exchange in piston internal combustion engine began in fact from the creation of the first working machines - J. Lenoara, N. Otto and R. Diesel. And of course at the initial stage, special attention was paid to the study of heat exchange in the engine cylinder. The first classic works in this direction can be attributed.
However, only work carried out by V.I. Grinevik, became a solid foundation, which turned out to be possible to build the theory of heat exchange for piston engines. The monograph in question is primarily devoted to the thermal calculation of intra-cylinder processes in the OI. At the same time, it can also find information about the heat exchanged indicators in the inlet process of interest to us, namely, there are statistical data on the magnitude of the heating of fresh charge, as well as empirical formulas to calculate the parameters at the beginning and end of the intake tact.
Further, researchers began to solve more private tasks. In particular, V. Nusselt received and published a formula for heat transfer coefficient in a piston engine cylinder. N.R. The brilling in his monograph clarified the formula of Nusselt and quite clearly proved that in each case (engine type, method of mixing formation, speed-rate, booming level) Local heat transfer coefficients should be clarified by the results of direct experiments.
Another direction in the study of piston engines is the study of heat exchange in the flow of exhaust gases, in particular, obtaining data on heat transfer during a turbulent gas flow in the exhaust pipe. A large number of literature is devoted to solving these tasks. This direction is quite well studied both in static purge conditions and under hydrodynamic nonstationarity. This is primarily due to the fact that, by improving the exhaust system, it is possible to significantly increase the technical and economic indicators of the piston internal combustion engine. In the course of the development of this area, many theoretical works were conducted, including analytical solutions and mathematical modeling, as well as many experimental studies. As a result of such a comprehensive study of the release process, a large number of indicators characterizing the process of release were proposed for which the quality of the design of the exhaust system can be assessed.
The study of heat exchange of the intake process is still given insufficient attention. This can be explained by the fact that studies in the field of heat exchange optimization in the cylinder and the exhaust tract were initially more effective in terms of improving the competitiveness of piston engine. However, currently the development of the engine industry has reached such a level that an increase in the engine indicator at least a few tenths percent is considered to be a serious achievement for researchers and engineers. Therefore, taking into account the fact that the directions of improving these systems are mainly exhausted, currently more and more specialists are looking for new opportunities for improving the workflows of piston engines. And one of such directions is the study of heat exchange during the inlet in the inlet.
In the literature on heat exchange in the intake process, work can be distinguished on the study of the influence of the intensity of the vortex flow of charge on the inlet on the thermal state of the engine parts (cylinder head, intake and exhaust valve, cylinder surfaces). These works are of great theoretical character; Based on solving the nonlinear Navier-Stokes equations and Fourier-Ostrogradsky, as well as mathematical modeling using these equations. Taking into account a large number of assumptions, the results can be taken as a basis for experimental studies and / or be estimated in engineering calculations. Also, these works contain experimental studies to determine local non-stationary heat fluxes in a diesel combustion chamber in a wide range of intensity inlet air intensity.
The above-mentioned heat exchange work in the inlet process most often do not affect the influence of gas dynamics on the local intensity of heat transfer, which determines the size of the heating of fresh charge and temperature voltages in the intake manifold (pipe). But, as is well known, the magnitude of the heating of fresh charge has a significant effect on the mass consumption of fresh charge through the engine cylinders and, accordingly, its power. Also, a decrease in the dynamic intensity of heat transfer in the inlet path of the piston engine can reduce its temperature tension and thus will increase the resource of this element. Therefore, the study and solving these tasks is an urgent task for the development of the engine building.
It should be indicated that currently for engineering calculations use static purging data, which is not correct, since non-stationarity (flow pulsation) strongly affect heat transfer in the channels. Experimental and theoretical studies indicate a significant difference in heat transfer coefficient in nonstationary conditions from a stationary case. It can reach a 3-4-fold value. The main reason for this difference is the specific restructuring of the turbulent stream structure, as shown in.
It is established that as a result of the effect on the flow of dynamic nonstationarity (stream acceleration), it takes place in the kinematic structure, leading to a decrease in the intensity of heat exchange processes. Also, the work was found that the acceleration of the flow leads to a 2-3-to-alarm increase in the tanning tangent stresses and the subsequently as much as the decrease in local heat transfer coefficients.
Thus, for calculating the size of the heating of fresh charge and determining the temperature stresses in the intake manifold (pipe), data on the instantaneous local heat transfer is needed in this channel, since the results of static purges can lead to serious errors (more than 50%) when determining the heat transfer coefficient in the intake tract that is unacceptable even for engineering calculations.
1.4 Conclusions and setting the objectives of the study
Based on the above, the following conclusions can be drawn. Technological characteristics The internal combustion engine is largely determined by the aerodynamic quality of the intake path as a whole and individual elements: the intake manifold (intake pipe), the channel in the cylinder head, its neck and valve plates, combustion chambers in the bottom of the piston.
However, it is currently the focus on the optimization of the channel design in the cylinder head and complex and expensive cylinder filling systems with a fresh charge, while it can be assumed that only by profiling intake manifold can be affected by gas-dynamic, heat exchange and engine consumables.
Currently, there are a wide variety of means and measurement methods for a dynamic study of the inlet input process, and the main methodological complexity consists in their proper choice and use.
Based on the above analysis of literature data, the following dissertation tasks may be formulated.
1. To establish the effect of the intake manifold configuration and the presence of the filtering element on the gas dynamics and the consumables of the piston engine of the internal combustion, as well as reveal the hydrodynamic factors of the heat exchange of the pulsating stream with the walls of the inlet channel channel.
2. Develop a method for increasing air flow through an inlet system of piston engine.
3. Find the main patterns of changes in the instantaneous local heat transfer in the inlet path of the piston engine in the conditions of hydrodynamic nonstationarity in the classic cylindrical channel, and also find out the effect of the intake system configuration (profiled inserts and air filters) On this process.
4. To summarize the experimental data on an instantaneous local heat transfer coefficient in the piston inlet inlet manifold.
To solve the tasks to develop the necessary techniques and create an experimental setup in the form of a tool model of piston engine, equipped with a control and measuring system with automatic collection and data processing.
2. Description of the experimental installation and measurement methods
2.1 Experimental installation for the study of the inlet inlet
The characteristic features of the studied intake processes are their dynamism and frequency due to a wide range of rotational speed of the engine and the harmonicity of this periodicals associated with the uneven piston movement and changes in the intake path configuration in the valve zone zone. The last two factors are interconnected with the action of the gas distribution mechanism. Reproduce such conditions with sufficient accuracy can only with the help of a field model.
Since gas-dynamic characteristics are functions of geometric parameters and regime factors, the dynamic model must match the engine of a certain dimension and operate in characteristic high-speed modes of the crankshaft test, but already from an extraneous energy source. Based on this data, it is possible to develop and evaluate the total effectiveness from certain solutions aimed at improving the intake path as a whole, as well as separately by different factors (constructive or regime).
For the study of gas dynamics and heat transfer process in the piston engine of internal combustion, an experimental installation was designed and manufactured. It was developed on the basis of the engine model 11113 VAZ - Oka. When creating the installation, the prototype details were used, namely: connecting rod, piston finger, piston (with refinement), gas distribution mechanism (with refinement), crankshaft pulley. Figure 2.1 shows a longitudinal section of the experimental installation, and in Figure 2.2 is its transverse section.
Fig. 2.1. Lady cut of the experimental installation:
1 - elastic coupling; 2 - rubber fingers; 3 - rod cervical; 4 - native cervix; 5 - cheek; 6 - nut M16; 7 - counterweight; 8 - Nut M18; 9 - indigenous bearings; 10 - supports; 11 - Bearings connecting rod; 12 - rod; 13 - piston finger; 14 - piston; 15 - cylinder sleeve; 16 - cylinder; 17 - base of the cylinder; 18 - cylinder supports; 19 - Fluoroplast Ring; 20 - reference plate; 21 - hexagon; 22 - gasket; 23 - inlet valve; 24 - graduation valve; 25 - distribution shaft; 26 - camshaft pulley; 27 - crankshaft pulley; 28 - toothed belt; 29 - Roller; 30 - tensioner stand; 31 - tensioner bolt; 32 - Maslenka; 35 - Asynchronous Engine
Fig. 2.2. Transverse section of experimental installation:
3 - rod cervical; 4 - native cervix; 5 - cheek; 7 - counterweight; 10 - supports; 11 - Bearings connecting rod; 12 - rod; 13 - piston finger; 14 - piston; 15 - cylinder sleeve; 16 - cylinder; 17 - base of the cylinder; 18 - cylinder supports; 19 - Fluoroplast Ring; 20 - reference plate; 21 - hexagon; 22 - gasket; 23 - inlet valve; 25 - distribution shaft; 26 - camshaft pulley; 28 - toothed belt; 29 - Roller; 30 - tensioner stand; 31 - tensioner bolt; 32 - Maslenka; 33 - Insert profiled; 34 - measuring channel; 35 - Asynchronous Engine
As can be seen from these images, the installation is a natural model of the single-cylinder internal combustion engine of dimension 7.1 / 8.2. A torque from an asynchronous engine is transmitted through an elastic coupling 1 with six rubber fingers 2 on the crankshaft of the original design. The clutch used is capable of significantly compensate for the inconseability of the compound of the shafts of the asynchronous motor and the crankshaft of the installation, as well as to reduce dynamic loads, especially when starting and stopping the device. The crankshaft in turn consists of a connecting rod cervix 3 and two indigenous necks 4, which are connected to each other with cheeks 5. The rod cervix is \u200b\u200bpressed with tension in the cheek and fixed using nuts 6. To reduce vibrations to cheeks are fastened with anti-test bolts 7 . The axial movement of the crankshaft hinders the nut 8. The crankshaft rotates in the closed rolling bearings 9 fixed in the supports 10. Two closed rolling bearing 11 are installed onto a connecting rod neck, on which the connecting rod 12 is mounted. The use of two bearings in this case is associated with the landing size of the connecting rod . To the connecting rod with a piston finger 13, the piston 14 is mounted on the cast-iron sleeve 15, pressed in the steel cylinder 16. The cylinder is mounted on the base 17, which is placed on the cylinder supports 18. One wide fluoroplastic ring 19 is installed on the piston, instead of three standard Steel. The use of pig-iron sleeve and fluoroplastic ring provides a sharp decline in friction in pairs of piston - sleeves and piston rings - sleeve. Therefore, the experimental installation is capable of working a short time (up to 7 minutes) without a lubrication system and cooling system on the operating frequencies of the crankshaft rotation.
All major fixed elements of the experimental installation are fixed on the base plate 20, which, with two hexagons, 21 is attached to the laboratory table. To reduce the vibration between the hexagon and the support plate there is a rubber gasket 22.
The mechanism of timing experimental installation is borrowed from the VAZ 11113 car: a block head is used assembly with some modifications. The system consists of an intake valve 23 and exhaust valve 24, which are controlled using a camshaft 25 with pulley 26. The camshaft pulley is connected to the crankshaft pulley 27 using toothed belt 28. At the crankshaft of the installation shaft there are two pulleys for simplifying the camshaft drive belt tension system. The belt tension is controlled by roller 29, which is installed on the rack 30, and the tensioner bolt 31. Masliners 32 were installed for lubrication of the camshaft bearings, oil, of which gravity comes to the sliding bearings of the camshaft.
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