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1 for the rights of manuscript Mashkis Makhmud A. Mathematical model of gas dynamics and heat exchange processes in intake and exhaust systems of the DVS specialty "Thermal motors" dissertation author's abstract on competition of a scientific degree of Candidate of Technical Sciences St. Petersburg 2005
2 General characteristics of work The relevance of the thesis in the current conditions of the accelerated pace of engine development, as well as the dominant trends in the intensification of the workflow, subject to increasing its economy, more close attention is paid to the reduction in the creation of the creation, finishing and modifying the available types of engines. The main factor that significantly reduces both temporary and material costs, in this task is the use of modern computing machines. However, their use can be effective only if the adequacy of the created mathematical models of real processes determining the functioning of the internal combustion system. Especially acute at this stage of the development of the modern engine building is the problem of the heat-staring of the details of the cylinda group (CPG) and the cylinder heads, inextricably associated with an increase in aggregate power. The processes of the instant local convective heat exchange between the working fluid and walls of gas-air channels (GVK) are still not sufficiently studied and are one of the narrow places in the theory of DVS. In this regard, the creation of reliable, experimentally substantiated calculation methods for the study of local convective heat exchange in GVK, which makes it possible to obtain reliable estimates of the temperature and heat-stressed state of DVS parts, is an urgent problem. Its solution will allow to carry out a reasonable choice of design and technological solutions, increase the scientific technical level of design, will provide an opportunity to reduce the engine creating cycle and obtain an economic effect by reducing the cost and costs for experimental engines. The purpose and objectives of the study The main objective of the dissertation work is to solve the complex of theoretical, experimental and methodological tasks, 1
3 related to the creation of new refinery mathematical models and methods for calculating local convective heat exchange in the GVK of the engine. In accordance with the purpose of the work, the following basic tasks were solved, a large extent determined and a methodological sequence of performance of work: 1. Conduct the theoretical analysis of the non-stationary flow flow in GVK and assessing the possibilities of using the theory of the boundary layer in determining the parameters of the local convective heat exchange in engines; 2. Development of an algorithm and numerical implementation on the computer for the problem of the imperious flow of the working fluid in the elements of the intake-release system of the multi-cylinder engine in nonstationary formulation to determine the speeds, temperature and pressure used as boundary conditions for the further solution of the gas-dynamics problem and heat exchange in the cavities of the engine GVK. 3. Creating a new methodology for calculating fields of instantaneous velocities by the working bodies of the GVK in three-dimensional formulation; 4. Development of a mathematical model of local convective heat exchange in GVK using the foundations of the theory of the boundary layer. 5. Check the adequacy of mathematical models of local heat exchange in GVK by comparing experimental and calculated data. The implementation of this complex task allows you to achieve the main objective of the work - the creation of an engineering method for calculating the local parameters of convective heat exchange in GVK gasoline engine. The relevance of the problem is determined by the fact that the solution of the tasks will allow to carry out a reasonable selection of design and technological solutions at the engine design stage, increase the scientific technical level of design, will reduce the engine creating cycle and to obtain an economic effect by reducing the cost and costs for experimental finiteness of the product. 2.
4 The scientific novelty of the dissertation work is that: 1. For the first time, a mathematical model was used, rationally combining one-dimensional representation of gas-dynamic processes in the intake and exhaust system of the engine with a three-dimensional representation of gas flow in GVK to calculate the parameters of local heat exchange. 2. The methodological basis for the design and finishing of the gasoline engine is developed by upgrading and clarifying methods for calculating local thermal loads and the thermal state of the elements of the cylinder head. 3. New calculated and experimental data on the spatial gas flows in the inlet and exhaust channels of the engine and the three-dimensional temperature distribution in the body of the head of the gasoline engine cylinders are obtained. The accuracy of the results is ensured by the application of approved methods of computational analysis and experimental studies, common systems equations reflecting the fundamental laws of conservation of energy, mass, pulse with appropriate initial and boundary conditions, modern numerical methods for the implementation of mathematical models, the use of guests and other regulatory acts corresponding to the graduation of the elements of the measuring complex in the experimental study, as well as satisfactory agreement of the results of modeling and experiment. The practical value of the results obtained is that the algorithm and a program for calculating the closed operating cycle of a gasoline engine with a one-dimensional representation of gas-dynamic processes in the intake and exhaust engine systems, as well as an algorithm and a program for calculating the parameters of heat exchange in GVK of the head of the gasoline engine cylinder head in three-dimensional production, recommended for implementation. The results of theoretical research, confirmed 3
5 experiments, allow you to significantly reduce the cost of designing and finishing the engines. Approbation of the results of work. The main provisions of the dissertation work was reported at scientific seminars of the Department of DVS SPbGPU in G.G., at the XXXI and XXXIII weeks of Science SPbGPU (2002 and 2004). Publications on the dissertation materials published 6 printed works. Structure and scope of work The dissertation work consists of introduction, fifth chapters, conclusion and literature of literature from 129 names. It contains 189 pages, including: 124 pages of the main text, 41 drawings, 14 tables, 6 photographs. The content of the work in the introduction is justified the relevance of the topic of the thesis, the purpose and objectives of the research are determined, the scientific novelty and the practical significance of the work are formulated. The overall characteristic of the work is given. The first chapter contains the analysis of basic work on theoretical and experimental studies of the process of gas dynamics and heat exchange in ICC. Tasks are subject to research. An overview was carried out by constructive forms of graduation and intake channels in the head of the cylinder block and the analysis of methods and results of experimental and calculating and theoretical studies of both stationary and nonstationary gas flows in the gas-air paths of engines internal combustion. Currently, the current approaches to the calculation and modeling of thermo- and gas-dynamic processes, as well as heat transfer intensity in GVK, are considered. It was concluded that most of them have a limited application area and do not give a complete picture of the distribution of heat exchange parameters on the surfaces of the GVK. First of all, this is due to the fact that the solution of the problem of the movement of the working fluid in GVK is produced in a simplified one-dimensional or two-dimensional 4
6 formulation, which is not applicable to the case of a complex form. In addition, it was noted that for calculating convective heat transfer, in most cases, empirical or semi-empirical formulas are used, which also does not allow to obtain the necessary accuracy of the solution. The most fully these questions were previously considered in the works of Bavyin V.V., Isakova Yu.N., Grishina Yu.A., Kruglov M.G., Kostina A.K., Kavtaradze R.Z., Ovsyannikova M.K. , Petrichenko R.M., Petrichenko M.R., Rosenlands GB, Strakhovsky M.V., Thairov, N.D., Shabanova A.Yu., Zaitseva A.B., Mundstukova D.A., Unru P.P., Shehovtsova A.F., Imaging, Haywood J., Benson RS, Garg Rd, Woollatt D., Chapman M., Novak Jm, Stein Ra, Daneshyar H., Horlock JH, WinterBone DE, Kastner LJ , Williams TJ, White BJ, Ferguson CR et al. Analysis of existing problems and methods of research of gas dynamics and heat exchange in GVK made it possible to formulate the main objective of the study as the creation of a methodology for determining the gas flow parameters in GVK in a three-dimensional formulation with the subsequent calculation of the local heat exchange in the Cylinder Cylinder Cylinder heads and the use of this technique to solve practical Problems of reducing the thermal tension of cylinder heads and valves. In connection with the following tasks set out in the work: - create a new methodology for one-dimensional-three-dimensional modeling of heat exchange in the engine output and intake systems, taking into account the complex three-dimensional gas flow in them in order to obtain the source information to specify the boundary conditions of heat exchange when calculating the tasks of heat change of piston cylinder heads DVS; - develop a methodology for setting the boundary conditions at the inlet and outlet of the gas-air channel on the basis of solving a one-dimensional nonstationary model of the working cycle of the multi-cylinder engine; - to check the accuracy of the methodology using test calculations and comparing the results obtained with the experimental data and calculations according to techniques previously known in the engine engineering; five
7 - conduct an inspection and finalization of the technique by performing a calculating experimental study of the thermal state of the engine cylinder heads and carry out the comparison of experimental and calculated data on the temperature distribution in the part. The second chapter is devoted to the development of a mathematical model of a closed working cycle of multi-cylinder internal combustion engine. To implement the one-dimensional calculation scheme of the working process of the multi-cylinder engine, a known characteristic method is selected, which guarantees the high speed of convergence and stability of the calculation process. The gas-air system of the engine is described as an aerodynamically interconnected set of individual elements of cylinders, sections of intake and outlet channels and pipes, collectors, silencers, neutralizers and pipes. The processes of aerodynamics in the intake-release systems are described using the equations of one-dimensional gas dynamics of the imperious compressible gas: the equation of continuity: ρ u ρ u + ρ + u + ρ t x x f df dx \u003d 0; F 2 \u003d π 4 D; (1) Motion equation: U T U + U x 1 P 4 F + + ρ x D 2 U 2 U u \u003d 0; f τ \u003d w; (2) 2 0.5ρU Energy conservation equation: P P + U A T x 2 ρ \u200b\u200bx + 4 F d U 2 (k 1) ρ q U \u003d 0 2 u u; 2 kp a \u003d ρ, (3) where A- the speed of the sound; ρ-density of gas; U-velocity flow along the x axis; t- time; P-pressure; F-coefficient of linear losses; D-diameter with pipeline; k \u003d P ratio of specific heat capacity. C V 6.
8 As boundary conditions are set (based on the basic equations: Inclipatibility, energy conservation and density ratio and sound rate in the non-satropical nature of the flow) Conditions on valve creams in cylinders, as well as conditions on the inlet and output from the engine. The mathematical model of the closed engine working cycle includes the calculated relationships describing the processes in the engine cylinders and parts of the intake and outcomes. The thermodynamic process in the cylinder is described using the technique developed in SPbGPU. The program provides the ability to define instantaneous gas flow parameters in cylinders and in inlet and output systems for different engine designs. The general aspects of the application of one-dimensional mathematical models by the method of characteristics (closed working body) are considered and some results of the calculation of the change in gas flow parameters in cylinders and in inlet and outcomes of single and multi-cylinder engines are considered. The results obtained allow you to estimate the degree of perfection of the organization of the engine intake systems, the optimality of the gas distribution phases, the possibility of gas-dynamic configuration of the workflow, the uniformity of individual cylinders, etc. Pressures, temperatures and speed of gas flows at the inlet and output to gas-air cylinder head channels defined using this technique are used in subsequent calculations of heat exchange processes in these cavities as boundary conditions. The third chapter is devoted to the description of the new numerical method, which makes it possible to realize the calculation of the boundary conditions of the thermal state by gas-air channels. The main stages of the calculation are: one-dimensional analysis of the non-stationary gas exchange process in the sections of the intake system and production by the method of characteristics (second chapter), three-dimensional calculation of the filter flow in the inlet and 7
9 graduate channels by finite elements of the MKE, the calculation of local coefficients of the working fluid heat transfer coefficients. The results of the first stage of the program of the closed cycle are used as boundary conditions at the subsequent stages. To describe gas-dynamic processes in the channel, a simplified quasistationary scheme of the slice gas (system of the Euler equations) was selected with a variable form of the region due to the need to take into account the valve movement: R v \u003d 0 RR 1 (V) V \u003d P, the complex geometric configuration of the channels, presence in The volume of the valve, the fragment of the guide sleeve makes it necessary 8 ρ. (4) As boundary conditions, instantaneous, averaged gas-averaged gas velocities at the input and output section were set. These speeds, as well as temperatures and pressure in the channels, were set as a result of calculating the workflow of the multi-cylinder engine. To calculate the gas dynamics problem, the ICE finite element method was chosen, providing high modeling accuracy in combination with acceptable costs for the implementation of the calculation. The calculated ICE algorithm To solve this problem is based on the minimization of the variational functional, obtained by converting the Euler equations using the Bubnov method, Gallerykin: (LLLLLLMM) K Uu φ x + Vu φ y + wu φ z + p ψ x φ) lllllmmk (UV Φ x + vv φ y + wv φ z + p ψ y) φ) lllllmmk (uw φ x + vw φ y + ww φ z + p ψ z) φ) lllllm (u φ x + v φ y + w φ z ) ψ dxdydz \u003d 0. dxdydz \u003d 0, dxdydz \u003d 0, dxdydz \u003d 0, (5)
10 Using the current model of the calculated area. Examples of the calculated models of the intake and exhaust channel of the VAZ-2108 engine are shown in Fig. 1. -B--and Fig.1. The inlet and (b) models (a) of the VAZ engine of the VAZ for calculating the heat exchange in GVK are chosen a bulk two-zone model, the main permissions of which is the separation of the volume on the region of the non-voiceic kernel and the boundary layer. To simplify, the solution of gas dynamics problems is carried out in a quasi-stationary formulation, that is, without taking into account the compressibility of the working fluid. The analysis of the calculation error showed the possibility of such an assumption with the exception of a short-term section of the time immediately after opening the valve gap not exceeding 5 7% of the total gas exchange cycle time. The heat exchange process in GVK with open and closed valves has a different physical nature (forced and free convection, respectively), therefore, they are described in two different techniques. At closed valves, the method is used proposed by MSTU, in which two heat loading processes are taken into account on this section of the working cycle at the expense of the free convection itself and due to the forced convection due to the residual vibrations of the column 9
11 gas in the channel under the influence of pressure variability in the collectors of the multi-cylinder engine. With the valves open, the heat exchange process is subject to the laws of forced convection initiated by organized movement Work body on gas exchange tact. The calculation of heat exchange in this case implies a two-stage solution of the problem Analysis of the local instantaneous structure of the gas flow in the channel and the calculation of the heat exchange intensity through the borderline layer formed on the channel walls. The calculation of the processes of convective heat exchange in GVK was built according to the heat exchange model when the flat wall is streamlined, taking into account either a laminar or turbulent structure of the boundary layer. The criterion dependences of heat exchange were refined based on the results of comparing the calculation and experimental data. The final form of these dependencies is shown below: for a turbulent boundary layer: 0.8 x RE 0 Nu \u003d Pr (6) x for a laminar boundary layer: Nu Nu XX αxx \u003d λ (m, PR) \u003d φ Re Tx Kτ, (7) where: α x local heat transfer coefficient; Nu x, Re x Local values \u200b\u200bof Nusselt and Reynolds numbers, respectively; PR number of Prandtl at the moment; m flow gradient characteristics; F (M, PR) function depending on the indicator of the gradient of the flow M and the number 0.15 of the PRANDTL of the PR working fluid; K τ \u003d RE D - correction factor. According to the instantaneous values \u200b\u200bof heat fluxes in the calculated points of the heat-visible surface, averaging was carried out per cycle based on the valve closing period. 10
12 The fourth chapter is devoted to the description of the experimental study of the temperature state of the head of the gasoline engine cylinders. An experimental study was carried out in order to verify and clarify the theoretical technique. The task of the experiment included to obtain the distribution of stationary temperatures in the body of the cylinder head and comparing the results of calculations with the data obtained. Experimental work was carried out at the Department of DVS SPbGPU on the test stand with car Engine VAZ Cylinder Head Preparations are made by the author at the Department of DVS SPbGPU according to the method used in the research laboratory of Zvezda OJSC (St. Petersburg). To measure the stationary temperature distribution in the head, 6 chromel-Copel thermocouples installed along the surfaces of the GVK are used. The measurements were carried out both by speed and loading characteristics at different constant frequencies of rotation of the crankshaft. As a result of the experiment, the thermocouple was obtained during the operation of the engine through speed and load characteristics. Thus, studies have shown, what are the real temperatures in the details of the block head cylinder DVS. More attention is paid to the chapter processing experimental results and evaluation of errors. The fifth chapter provides data from the estimated research, which was carried out in order to verify the mathematical model of heat transfer in GVK by comparing the calculated data with the results of the experiment. In fig. 2 presents the results of modeling the speed field in the intake and exhaust channels of the VAZ-2108 engine using the end element method. The data obtained fully confirm the impossibility of solving this task in any other formulation, except for three-dimensional, 11
13 Since the valve rod has a significant impact on the results in the responsible zone of the cylinder head. In fig. 3-4 shows examples of the results of the calculation of the intensities of the heat exchange in the inlet and exhaust channels. Studies have shown, in particular, the substantial uneven nature of heat transfer as over the channel forming and in the azimuthal coordinate, which is obviously explained by the substantial uneven structure of the gas-entertainment in the channel. The final fields of heat transfer coefficients were used to further calculate the temperature state of the cylinder head. The boundary conditions of heat exchange along the surfaces of the combustion chamber and cooling cavities were set using techniques developed in SPbGPU. The calculation of temperature fields in the cylinder head was carried out for the steady engine operating modes with a crankshaft rotation frequency of 2500 to 5600 rpm along external high-speed and load characteristics. As the Cylinder Cylinder Cylinder Cylinder Circuit Scheme, the head section belonging to the first cylinder is selected. When modeling the thermal state, the finite element method is used in three-dimensional production. Full picture Thermal fields for the calculated model are shown in Fig. 5. The results of the settlement study are represented as a change in temperature in the body of the cylinder head at the installation places of the thermocouple. Comparison of the calculation data and the experiment showed their satisfactory convergence, the calculation error did not exceed 3 4%. 12
14 outlet channel, φ \u003d 190 inlet channel, φ \u003d 380 φ \u003d 190 φ \u003d 380 Fig.2. The fields of speeds of the working fluid in the graduation and intake channels of the VAZ-2108 engine (n \u003d 5600) α (W / m 2 K) α (W / m 2 K), 0 0.2 0.4 0.6 0.8 1 , 0 S -B- 0 0,0 0.2 0.4 0.6 0.8 1.0 S -A- Pic. 3. Curves Changes in the intensities of heat exchange by external surfaces - Graduation channel -B - intake channel. 13
15 α (W / m 2 K) at the beginning of the intake channel in the middle of the intake channel at the end of the intake channel section-1 α (W / m 2 K) at the beginning of the final channel in the middle of the exhaust channel at the end of the exhaust channel cross section angle turning angle of rotation - Battail channel - outlet channel Fig. 4. Curves change in the intensities of heat exchange depending on the corner of the rotation of the crankshaft. -but- -B- Fig. 5. General form of the finite element model of the cylinder head (A) and the calculated temperature fields (n \u003d 5600 rpm) (b). fourteen
16 Conclusions for work. According to the results of the work carried out, the following main conclusions can be drawn: 1. A new one-dimensional-three-dimensional model of calculating complex spatial processes of the working fluid flow and heat exchange in the channels of the cylinder head of an arbitrary piston engine, characterized greater compared to previously proposed methods and complete versatility Results. 2. New data was obtained about the features of gas dynamics and heat exchange in gas-air channels, confirming the complex spatial uneven nature of the processes, practically excluding the possibility of modeling in one-dimensional and two-dimensional variants of the task. 3. The need to set the boundary conditions for calculating the task of gas-dynamics of intake and outlet channels is confirmed based on the solution of the problem of non-stationary gas flow in pipelines and multi-cylinder channels. It is proved the possibility of considering these processes in one-dimensional formulation. The method of calculating these processes based on the characteristics method is proposed and implemented. 4. The conducted experimental study made it possible to clarify the developed settlement techniques and confirmed their accuracy and accuracy. The comparison of the calculated and measured temperatures in the details showed the maximum error of the results not exceeding 4%. 5. The proposed settlement and experimental technique can be recommended for the introduction of the engine industry in the enterprises in the design of new and adjustment of already existing piston four-stroke. fifteen
17 On the topic of the thesis, the following works were published: 1. Shabanov A.Yu., Mashkir M.A. Development of a model of one-dimensional gas dynamics in intake and exhaust systems of internal combustion engines // dep. in vinity: N1777-B2003 from, 14 s. 2. Shabanov A.Yu., Zaitsev A.B., Mashkir M.A. The finite-element method of calculating the boundary conditions of thermal loading of the head of the cylinder block of the piston engine // dep. in vinity: N1827-B2004 from, 17 s. 3. Shabanov A.Yu., Makhmud Mashkir A. Calculated and experimental study of the temperature state of the engine cylinder head // Engineering: Scientific and technical collection, tagged with a 100th anniversary of the Honored Worker of Science and Technology Russian Federation Professor N.Kh. Dyachenko // P. ed. L. E. Magidovich. St. Petersburg: Publishing House of Polytechnic Un-Ta, from Shabanov A.Yu., Zaitsev A.B., Mashkir M.A. A new method for calculating the boundary conditions of thermal loading of the head of the cylinder block of the piston engine // Engineering, N5 2004, 12 s. 5. Shabanov A.Yu., Makhmud Mashkir A. The use of the method of finite elements in determining the boundary conditions of the thermal state of the cylinder head // XXXIII Science Week of SPbGPU: Materials of the Inter-University Scientific Conference. SPb.: Publishing House of Polytechnic University, 2004, with Mashkir Mahmud A., Shabanov A.Yu. The use of the method of characteristics to the study of gas parameters in gas-air channels of DVS. XXXI SPBGPU Science Week. Part II. Materials of the Interuniversity Scientific Conference. SPB: Publishing House of SPbGPU, 2003, with
18 The work was carried out at the State Educational Institution of Higher Professional Education "St. Petersburg State Polytechnic University", at the Department of Internal Combustion Engines. Scientific leader - Candidate of Technical Sciences, Associate Professor Shabanov Aleksandr Yuryevich Official opponents - Doctor of Technical Sciences, Professor Erofeev Valentin Leonidovich Candidate of Technical Sciences, Associate Professor Kuznetsov Dmitry Borisovich Leading organization - GUP "Tsnidi" Protection will be held in 2005 at the meeting of the dissertation council The state educational institution of higher professional education "St. Petersburg State Polytechnic University" at the address :, St. Petersburg, ul. Polytechnic 29, Main Building, Aud .. The dissertation can be found in the Fundamental Library of GOU "SPBGPU". Abstract of the Dissertation Council Scientific Secretary of the Dissertation Council, Doctor of Technical Sciences, Associate Professor Khrustalev B.S.
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UDC 621.436
Effect of aerodynamic resistance of intake and exhaust systems of automotive engines on gas exchange processes
L.V. Carpenters, bp Zhilkin, Yu.M. Brodov, N.I. Grigoriev
The paper presents the results of an experimental study of the influence of the aerodynamic resistance of intake and exhaust systems piston engines on gas exchange processes. The experiments were carried out on the on-line models of single-cylinder engine. Installations and methods for conducting experiments are described. The dependences of the change in the instantaneous speed and pressure of the flow in the gas-air paths of the engine from the corner of the crankshaft rotation are presented. The data was obtained at various coefficients of resistance of intake and exhaust systems and different frequencies of rotation of the crankshaft. Based on the data obtained, conclusions were made of the dynamic features of gas exchange processes in the engine at different conditions. It is shown that the use of the noise muffler smoothes the flow ripple and changes the flow characteristics.
Keywords: piston engine, gas exchange processes, process dynamics, speed pulsation and flow pressure, noise muffler.
Introduction
A number of requirements are made to intake and outcomes of piston engines of internal combustion, among which the main decrease in aerodynamic noise and minimal aerodynamic resistance are the main. Both of these indicators are determined in the interconnection of the design of the filter element, inlet silencers and the release, catalytic neutralizers, the presence of a superior (compressor and / or turbocharger), as well as the configuration of intake and exhaust pipelines and the nature of the flow in them. At the same time, there are practically no data on the influence of additional elements of intake and exhaust systems (filters, silencers, turbocharger) on gas dynamics in them.
This article presents the results of a study of the effect of the aerodynamic resistance of intake and exhaust systems on gas exchange processes in relation to the piston engine of dimension 8.2 / 7.1.
Experimental plants
and data collection system
Studies of the effect of aerodynamic resistance of gas-air systems on gas exchange processes in piston engineers were carried out on the simulation model of the dimension 4.2 / 7.1, driven by rotation asynchronous engineThe frequency of rotation of the crankshaft of which was adjusted in the range n \u003d 600-3000 min1 with an accuracy of ± 0.1%. An experimental installation is described in more detail.
In fig. 1 and 2 show configurations and geometrical dimensions intake and exhaust tract of the experimental installation, as well as the installation location for measurement of instantaneous
values mid speed and air flow pressure.
For measurements of instant pressure values \u200b\u200bin the stream (static) in the PC channel, the pressure sensor £ -10 was used by Wika, the speed of which is less than 1 ms. The maximum relative average mean-square pressure measurement error was ± 0.25%.
To determine the instantaneous medium in the section of the air flow channel, the thermoenemometers of the constant temperature of the original design, the sensitive element of which was the nichrome thread with a diameter of 5 μm and a length of 5 mm. The maximum relative average mean-of-mean error of measuring the speed WX was ± 2.9%.
The measurement of the rotational frequency of the crankshaft was carried out using a tachometric meter consisting of a toothed disk fixed on crankshaft Vale, and inductive sensor. The sensor formed a voltage pulse at a frequency proportional to the rotation speed of the shaft. According to these pulses, the frequency of rotation was recorded, the position of the crankshaft (angle f) was determined and the moment of passing the piston of VMT and NMT.
Signals from all sensors entered an analog-to-digital converter and transmitted to a personal computer for further processing.
Before carrying out experiments, a static and dynamic targeting of the measuring system was carried out in general, which showed the speed necessary to study the dynamics of gas-dynamic processes in the inlet and exhaust systems of piston engines. The total average mean-of-mean error of experiments on the effect of the aerodynamic resistance of gas-air systems of DVS. Gas exchange processes were ± 3.4%.
Fig. 1. Configuration and geometric sizes of the intake path of the experimental installation: 1 - cylinder head; 2-bubbling pipe; 3 - measuring tube; 4 - thermoanemometer sensors for measuring air flow rate; 5 - Pressure Sensors
Fig. 2. Configuration and geometric dimensions of the exhaust path of the experimental installation: 1 - cylinder head; 2 - working plot - graduation pipe; 3 - pressure sensors; 4 - thermoemometer sensors
The effect of additional elements on the gas dynamics of intake and release processes was studied with different system resistance coefficients. Resistance was created using various intake filters and release. So, as one of them, a standard air automobile filter was used with a resistance coefficient of 7.5. A tissue filter with a resistance coefficient 32 was chosen as another filter element. The resistance coefficient was determined experimentally through static purge in laboratory conditions. Studies were also conducted without filters.
Effect of aerodynamic resistance on the inlet process
In fig. 3 and 4 show the dependences of the air flow rate and PC pressure in the inlet can
le from the angle of rotation of the crankshaft f at different of its rotation frequencies and when using various intake filters.
It has been established that in both cases (with a silencer and without) pulsation of pressure and air flow rates are most expressed at high speed of rotation of the crankshaft. At the same time in the intake canal with the silencer of noise maximum speed Air flow, as it should be expected, less than in the channel without it. Most
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Fig. 3. The dependence of the air velocity WX in the intake channel from the angle of rotation of the crankshaft shaft at different frequencies of the rotation of the crankshaft and different filtering elements: a - n \u003d 1500 min-1; B - 3000 min-1. 1 - without a filter; 2 - standard air filter; 3 - fabric filter
Fig. 4. The dependence of the PC pressure in the inlet channel from the angle of rotation of the crankshaft f at different frequencies of rotation of the crankshaft and different filtering elements: a - n \u003d 1500 min-1; B - 3000 min-1. 1 - without a filter; 2 - standard air filter; 3 - fabric filter
it was brightly manifested with high frequencies of rotation of the crankshaft.
After closing the intake valve, the pressure and speed of the air flow in the channel under all conditions do not become equal to zero, and some of their fluctuations are observed (see Fig. 3 and 4), which is also characteristic of the release process (see below). At the same time, the installation of the inlet noise muffler leads to a decrease in pressure pulsations and air flow rates under all conditions both during the intake process and after the intake valve is closed.
Effect of aerodynamic
resistance to the release process
In fig. 5 and 6 shows the dependences of the air flow rate of the WX and the pressure PC in the outlet from the angle of rotation of the crankshaft form at different rotational frequencies and when using various release filters.
The studies were carried out for various frequencies of rotation of the crankshaft (from 600 to 3000 min1) at different overpressure on the release of PI (from 0.5 to 2.0 bar) without a silent noise and if it is presented.
It has been established that in both cases (with the silencer and without) pulsation of the air flow rate, the most brightly manifested at low frequencies of the crankshaft rotation. In this case, the values \u200b\u200bof the maximum air flow rate remain in the exhaust channel with the noise silencer
merilly the same as without it. After closing the exhaust valve, the air flow rate in the channel under all conditions does not become zero, and some speed fluctuations are observed (see Fig. 5), which is characteristic of the inlet process (see above). At the same time, the installation of the noise muffler on the release leads to a significant increase in the pulsations of the air flow rate under all conditions (especially at ry \u003d 2.0 bar) both during the release process and after the exhaust valve is closed.
It should be noted the opposite effect of aerodynamic resistance on the characteristics of the inlet process in the engine, where air filter Pulsation effects in the intake process and after closing the inlet valve were present, but they were clearly faster than without it. In this case, the presence of a filter in the inlet system led to a decrease in the maximum air flow rate and weakening the dynamics of the process, which is consistent well with previously obtained results in the work.
An increase in aerodynamic resistance exhaust system It leads to some increase in the maximum pressure in the process of release, as well as the displacement of peaks for NMT. In this case, it can be noted that the installation of the silencer of the noise of the output leads to a decrease in the pulsations of the pressure of the air flow under all conditions both during the production process and after the exhaust valve is closed.
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Fig. 5. The dependence of the air velocity WX in the outlet from the angle of rotation of the crankshaft shaft at different frequencies of the rotation of the crankshaft and different filtering elements: a - n \u003d 1500 min-1; B - 3000 min-1. 1 - without a filter; 2 - standard air filter; 3 - fabric filter
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Fig. 6. The dependence of the pressure PC in the outlet from the angle of rotation of the crankshaft f at different frequencies of rotation of the crankshaft and different filtering elements: a - n \u003d 1500 min-1; B - 3000 min-1. 1 - without a filter; 2 - standard air filter; 3 - fabric filter
Based on the processing of dependency changes in the flow rate for separate tact, a relative change in the volume flow of air q was calculated through the exhaust channel when the muffler is placed. It has been established that with low overpressure on the release (0.1 MPa), the consumption q in the exhaust system with a silencer is less than in the system without it. At the same time, if at the frequency of rotation of the crankshaft 600 min-1, this difference was approximately 1.5% (which lies within the error), then with n \u003d 3000 min4 this difference reached 23%. It is shown that for high overpressure of 0.2 MPa, the opposite tendency was observed. The volume flow of air through the exhaust channel with the silencer was greater than in the system without it. At the same time, at low frequencies of rotation of the crankshaft, this exceeded was 20%, and with n \u003d 3000 min1 - 5%. According to the authors, such an effect can be explained by some smoothing of the pulsations of the air flow rate in the exhaust system in the presence of a silent noise.
Conclusion
The conducted study showed that the inlet engine of internal combustion is significantly influenced by the aerodynamic resistance of the intake path:
The increase in the resistance of the filter element smoothes the dynamics of the filling process, but at the same time reduces air flow rate, which corresponds to the filling coefficient;
The effect of the filter is enhanced with the increasing rotation frequency of the crankshaft;
The threshold value of the filter resistance coefficient (approximately 50-55), after which its value does not affect the flow rate.
It has been shown that the aerodynamic resistance of the exhaust system also significantly affects the gas-dynamic and consumables of the release process:
Increasing the hydraulic resistance of the exhaust system in the piston DVS leads to an increase in the pulsations of the air flow rate in the exhaust channel;
With low overpressure on the release in the system with a silent noise, there is a decrease in volumetric flow through the exhaust channel, while at high ry - on the contrary, it increases compared to the exhaust system without a silencer.
Thus, the results obtained can be used in engineering practice in order to optimally choose the characteristics of the inlet and outbuilding silencers, which can provide
the influence on the filling of the cylinder of the fresh charge (filling coefficient) and the quality of the cleaning of the engine cylinder from the exhaust gases (the residual gas coefficient) on certain high-speed modes of the work of the piston engine.
Literature
1. Draganov, B.H. Construction of intake and exhaust channels of internal combustion engines / B.Kh. Draganov, MG Kruglov, V. S. Obukhov. - Kiev: Visit School. Head ed, 1987. -175 p.
2. Internal combustion engines. In 3 kN. Kn. 1: Theory of workflows: studies. / V.N. Lou-Kanin, K.A. Morozov, A.S. Khachyan et al.; Ed. V.N. Lukanina. - M.: Higher. Shk., 1995. - 368 p.
3. Champraozs, B.A. Internal combustion engines: theory, modeling and calculation of processes: studies. In the course "Theory of workflows and modeling of processes in internal combustion engines" / B.A. Chamolaoz, M.F. Faraplatov, V.V. Clementev; Ed. Castle Deat. Science of the Russian Federation B.A. Champrazov. - Chelyabinsk: SUURSU, 2010. -382 p.
4. Modern approaches to the creation of diesel engines for passenger cars and small-calm
zovikov /a. Blinov, P.A. Golubev, Yu.E. Dragan et al.; Ed. V. S. Peponova and A. M. Mineyev. - M.: NIC "Engineer", 2000. - 332 p.
5. Experimental study of gas-dynamic processes in the inlet system of piston engine / b.p. Zhokkin, L.V. Carpenters, S.A. Korzh, I.D. Larionov // Engineering. - 2009. -№ 1. - P. 24-27.
6. On the change in gas dynamics of the process of release in piston engine in the installation of the muffler / L.V. Carpenters, bp Zhokkin, A.V. Cross, D.L. Padalak // Bulletin of the Academy of Military Sciences. -2011. - № 2. - P. 267-270.
7. Pat. 81338 RU, MPK G01 P5 / 12. Thermal mechanical temperature of constant temperature / S.N. Pochov, L.V. Carpenters, bp Vilkin. - No. 2008135775/22; Stage. 09/03/2008; publ. 03/10/2009, Bul. № 7.
1This article discusses the assessment of the effect of the resonator on the filling of the engine. In the example of the example, a resonator was proposed - by volume equal to the engine cylinder. The geometry of the intake tract together with the resonator was imported into the FlowVision program. Mathematical modification was carried out taking into account all the properties of the moving gas. To estimate the flow rate through the inlet system, estimates of the flow rate in the system and the relative air pressure in the valve slit, computer simulation was carried out, which showed the effectiveness of the use of additional capacity. An assessment of the flow rate through the valve gap, the speed of flow, flow, pressure and flow density for the standard, upgraded and intake system with the Rexiver was evaluated. At the same time, the mass of the incoming air increases, the flow rate of the flow is reduced and the density of air entering the cylinder increases, which is favorably reflected on the output TV-televons.
inlet tract
resonator
filling a cylinder
math modeling
upgraded canal.
1. Jolobov L. A., Dydykin A. M. Mathematical modeling of the processes of gas exchange DVS: monograph. N.N.: NGSHA, 2007.
2. Dydyskin A. M., Zholobov L. A. Gasodynamic studies of the DVS methods of numerical modeling // Tractors and agricultural machines. 2008. № 4. P. 29-31.
3. Pritr D. M., Turkish V. A. Aeromechanics. M.: Oborongiz, 1960.
4. Khaylov M. A. Calculated pressure fluctuation equation in the suction pipe of the internal combustion engine // Tr. Cyam. 1984. No. 152. P.64.
5. Sonkin V. I. Study of air flow through the valve gap // Tr. US. 1974. Issue 149. P.21-38.
6. Samsky A. A., Popov Yu. P. Difference methods for solving the problems of gas dynamics. M.: Science, 1980. P.352.
7. Rudoy B. P. Applied nonstationary gas dynamics: Tutorial. Ufa: Ufa Aviation Institute, 1988. P.184.
8. Malivanov M.V., Khmelev R. N. On the development of mathematical and software for the calculation of gas-dynamic processes in the DVS: Materials of the IX International Scientific and Practical Conference. Vladimir, 2003. P. 213-216.
The magnitude of the torque of the engine is proportional to the mass of air, attributed to the frequency of rotation. Increasing the filling of the cylinder of gasoline engine, by upgrading the intake path, will lead to an increase in the pressure of the end of the intake, improved mixing formation, an increase in the technical and economic indicators of the engine operation and a decrease in the toxicity of exhaust gases.
The basic requirements for the inlet path are to ensure minimal resistance to the inlet and the uniform distribution of the combustible mixture through the engine cylinders.
Ensuring the minimum resistance to the inlet can be achieved by eliminating the roughness of the inner walls of pipelines, as well as sharp changes in the flow direction and eliminate sudden narrowings and extensions of the tract.
A significant effect on the filling of the cylinder provides various types of boost. The simplest type of superior is to use the dynamics of the incoming air. A large volume of the receiver partially creates resonant effects in a specific rotational speed range, which lead to improved filling. However, they have, as a result, dynamic disadvantages, for example, deviations in the composition of the mixture with a rapid change in the load. Almost the ideal torque flow ensures that the inlet tube is switching, in which, for example, depending on the engine load, the rotational speed and position of the throttle are possible variations:
The length of the pulsation pipe;
Switch between pulsation pipes of different lengths or diameter;
- selective shutdown of a separate pipe of one cylinder in the presence of a large amount of them;
- Switching the volume of the receiver.
In the resonant superior of the cylinder group with the same flagel interval attach short pipes to resonant receiver, which are connected through the resonant pipes with the atmosphere or with the collection receiver acting as a gölmgolts resonator. It is a spherical vessel with an open neck. The air in the neck is the oscillating mass, and the volume of air in the vessel plays the role of an elastic element. Of course, such separation is true only approximately, since some of the air in the cavity has inertial resistance. However, with a sufficiently large value of the area of \u200b\u200bthe opening to the area of \u200b\u200bthe cross section of the cavity, the accuracy of such an approximation is quite satisfactory. The main part of the kinetic oscillation energy is concentrated in the neck of the resonator, where the oscillatory velocity of air particles has the greatest value.
The intake resonator is established between the throttle and cylinder. It begins to act when the throttle is covered enough so that its hydraulic resistance becomes comparable to the resistance of the resonator channel. When the piston moves down, the combustible mixture enters the engine cylinder not only from under the throttle, but also from the tank. With a decrease in the vacuum, the resonator begins to suck the combustible mixture. This will follow the same part, and quite large, reverse ejection.
The article analyzes the flow movement in the intake channel of 4-stroke gasoline engine at the rated crankshaft rotation frequency on the example of the VAZ-2108 engine at the rotational speed of the crankshaft N \u003d 5600min-1.
This research task was solved by the mathematical way using the software package for modeling gas-hydraulic processes. Simulation was carried out using the FlowVision software package. For this purpose, geometry was obtained and imported (under the geometry is understood in the internal volumes of the engine - intake and exhaust pipes, an atrigance of the cylinder) using various standard file formats. This allows SAPR SOLIDWORKS to create a settlement area.
Under the calculation area it is understood as the volume in which the equations of the mathematical model and the border of the volume on which the boundary conditions are determined, then maintain the obtained geometry in the format supported by the FlowVision and use it when creating a new calculated option.
This task used ASCII, Binary format, in the STL extension, type stereolithographyFormat with an angular tolerance of 4.0 degrees and a deviation of 0.025 meters to improve the accuracy of the resulting modeling results.
After receiving the three-dimensional model of the settlement area, a mathematical model is set (a set of laws of changes in the physical parameters of gas for this problem).
In this case, a substantially subsonic gas flow is made at small Reynolds numbers, which is described by the system of turbulent flow of fully compressible gas using the standard K-E of the turbulence model. This mathematical model is described by a system consisting of seven equations: two Navier - Stokes equations, the equations of continuity, energy, the state of the ideal gas, mass transfer and the equation for the kinetic energy of turbulent ripples.
(2)
Energy equation (complete enthalpy)
The equation of the state of the ideal gas:
Turbulent components are associated with the remaining variables through the turbulent viscosity value, which is calculated in accordance with the standard K-ε model of turbulence.
Equations for k and ε
turbulent viscosity:
constants, parameters and sources:
(9)
(10)
Σk \u003d 1; σε \u003d 1.3; Cμ \u003d 0.09; Cε1 \u003d 1.44; Cε2 \u003d 1.92
The working substance in the inlet process is air, in this case, considered as the perfect gas. The initial values \u200b\u200bof the parameters are set for the entire settlement area: temperature, concentration, pressure and speed. For pressure and temperature, the initial parameters are equal to reference. The speed inside the calculated region in directions x, y, z is zero. Variable temperature and pressure in FlowVision are represented by relative values, the absolute values \u200b\u200bof which are calculated by the formula:
fa \u003d F + Fref, (11)
where Fa is the absolute value of the variable, F is the calculated relative value of the variable, Fref - the reference value.
Boundary conditions are specified for each of the calculated surfaces. Under the boundary conditions it is necessary to understand the combination of equations and laws characteristic of the surfaces of the calculated geometry. Boundary conditions are necessary to determine the interaction of the settlement area and the mathematical model. On the page for each surface indicates a specific type of boundary condition. The type of the boundary condition is installed on the input channel input windows - free entry. The remaining elements - the wall-bound, which does not let and not transmitting the calculated parameters of the current area. In addition to all of the above boundary conditions, it is necessary to take into account the boundary conditions on the moving elements included in the selected mathematical model.
Movable parts include inlet and exhaust valve, piston. At the boundaries of movable elements, we determine the type of boundary condition of the wall.
For each of the movable bodies, the law of movement is set. Changing the piston rate is determined by the formula. To determine the laws of the valve motion, the valve lift curves were removed in 0.50 with an accuracy of 0.001 mm. Then the speed and acceleration of the valve movement were calculated. The data obtained are converted to dynamic libraries (time - speed).
The next stage in the simulation process is the generation of the computational grid. FlowVision uses a locally adaptive computational net. Initially, an initial computational grid is created, and then the criteria for grinding grid are specified, according to which FlowVision breaks the cells of the initial grid to the desired degree. Adaptation is made in both the volume of the channels of the channels and the cylinder walls. In places with a possible maximum speed, adaptation with additional grinding of the computational grid are created. By volume, the grinding was carried out up to 2 levels in the combustion chamber and up to 5 levels in valve slots, along the walls of the cylinder, adaptation was made up to 1 level. This is necessary to increase the time integration step with an implicit method of calculation. This is due to the fact that the time step is defined as the ratio of the cell size to the maximum speed in it.
Before starting to calculate the created option, you must specify the parameters of numerical modeling. At the same time, the time to continue the calculation is equal to one full cycle of operation of the engine, 7200 PK., The number of iterations and the frequency of saving these calculation options. For subsequent processing, certain stages of calculation are preserved. Set the time and options for the calculation process. This task requires a time step setting - a method of choice: an implicit scheme with a maximum step 5E-004C, explicit number of CFL - 1. This means that the time step determines the program itself, depending on the convergence of the pressure equations itself.
The postprocessor is configured and the parameters of the visualization of the results are interested in. Simulation allows you to obtain the required layers of visualization after the completion of the main calculation, based on the calculation stages remained with a certain frequency. In addition, the postprocessor allows you to transmit the resulting numeric values \u200b\u200bof the parameters of the process under study in the form of an information file into external electronic table editors and to obtain the time dependence of such parameters as speed, consumption, pressure, etc.
Figure 1 shows the installation of the receiver on the inlet channel of the DVS. The volume of the receiver is equal to the volume of one engine cylinder. The receiver is set as close as possible to the inlet channel.
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Fig. 1. Upgraded with the receiver Settlement area in CadsolidWorks |
The own frequency of the Helmholtz resonator is:
(12)
where F is the frequency, Hz; C0 - sound speed in the air (340 m / s); S - hole cross section, m2; L is the length of the pipe, m; V is the volume of the resonator, M3.
For our example, we have the following values:
d \u003d 0.032 m, s \u003d 0.00080384 m2, v \u003d 0.000422267 m3, L \u003d 0.04 m.
After calculating F \u003d 374 Hz, which corresponds to the rotational speed of the crankshaft N \u003d 5600min-1.
After setting the calculated option and, after setting the parameters of numerical simulation, the following data were obtained: flow rate, speed, density, pressure, gas flow temperature in the inlet channel of the intensity of the Crankshaft rotation.
From the graph presented (Fig. 2), in terms of flow flow in the valve slit, it is clear that the upgraded channel with the receiver has the maximum consumables. Consumption value is higher than 200 g / s. The increase is observed for 60 G.P.K.V.
Since the opening of the inlet valve (348 G.K.V.) The flow rate (Fig. 3) begins to grow from 0 to 170m / s (at the modernized intake channel 210 m / s, with the -190m / s receivers) in the interval Up to 440-450 G.K.V. In the channel with the receiver, the speed value is higher than in a standard approximately 20 m / s starting from 430-440. P.K.V. The numeric value of the channel in the channel with the receiver is significantly more even than the upgraded inlet channel, during the opening of the inlet valve. Next, there is a significant reduction in the flow rate, up to the closure of the inlet valve.
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Fig. 2. Consumption of the gas flow in the valve slot for the channels of standard, upgraded and with the receiver at n \u003d 5600 min-1: 1 - standard, 2 - upgraded, 3 - upgraded with the receiver |
Fig. 3. The flow rate of the flow in the valve slot for the channels of standard, upgraded and with the receiver at n \u003d 5600 min-1: 1 - standard, 2 - upgraded, 3 - upgraded with the receiver |
Of the relative pressure graphs (Fig. 4) (atmospheric pressure, P \u003d 101000 PA is received for zero), it follows that the pressure value in the upgraded channel is higher than in the standard, by 20 kPa at 460-480 GP.K.V. (associated with a large flow rate value). Starting from 520 G.K.V. The pressure value is aligned, which cannot be said about the channel with the receiver. The pressure value is higher than in the standard one, by 25 kPa, starting from 420-440 GP.K.V. Up to the closure of the inlet valve.
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Fig. 4. Flow pressure in standard, upgraded and channel with a receiver at n \u003d 5600 min-1 (1 - standard channel, 2 - upgraded channel, 3 - upgraded channel with receiver) |
Fig. 5. Flow density in standard, upgraded and channel with a receiver at n \u003d 5600 min-1 (1 - standard channel, 2 - upgraded channel, 3 - upgraded channel with receiver) |
The flow density in the area of \u200b\u200bthe valve gap is shown in Fig. five.
In the upgraded channel with the receiver, the density value is below 0.2 kg / m3 starting from 440 G.K.V. Compared with a standard channel. This is associated with high pressure and gas flow rates.
From the analysis of graphs, you can draw the following conclusion: the channel of the improved form provides better filling of the cylinder with a fresh charge due to a decrease in the hydraulic resistance of the inlet channel. With the increase in the piston velocity at the time of opening the inlet valve, the channel form does not significantly affect the speed, density and pressure inside the intake channel, it is explained by the fact that during this period the inlet process indicators are mainly dependent on the speed of the piston and the valve slot area ( Only the shape of the intake channel changed in this calculation), but everything changes dramatically at the time of slowing down the movement of the piston. The charge in the standard channel is less inert and more stronger "stretch" along the length of the channel, which in the aggregate gives less filling of the cylinder at the time of reducing the speed of the piston movement. Up to the closure of the valve, the process flows under the denominator of the flow rate already obtained (the piston gives the initial flow rate of the cached volume, with a decrease in the velocity of the piston, the inertia component of the gas flow has a significant role on the filling. This is confirmed by higher speed indicators, pressure.
In the inlet canal with the receiver, due to additional charge and resonant phenomena, in the Cylinder of DVS there is a significantly large mass of the gas mixture, which provides higher technical indicators of the DVS operation. The growth increase in the end of the inlet will have a significant impact on the increase in the technical and economic and environmental performance of the DVS work.
Reviewers:
Gots Alexander Nikolaevich, Doctor of Technical University, Professor of the Department of Heat Engines and Energy Installations of the Vladimir State University of the Ministry of Education and Science, Vladimir.
Kulchitsky Aleksey Ramovich, D.N., Professor, Deputy Chief Designer LLC VMTZ, Vladimir.
Bibliographic reference
Jolobov L. A., Suvorov E. A., Vasilyev I. S. Effect of an additional capacity in the inlet system for filling of DVS // Modern problems of science and education. - 2013. - № 1;URL: http://science-education.ru/ru/Article/View?id\u003d8270 (date of handling: 25.11.2019). We bring to your attention the magazines publishing in the publishing house "Academy of Natural Science"
In parallel, the development of the devastating exhaust systems, the systems developed, conventionally referred to as "silencers", but designed not so much to reduce the noise level of the operating engine, how much to change its power characteristics (engine power, or its torque). At the same time, the task of stitching noise went to the second plan, such devices are not reduced, and cannot significantly reduce the exhaust noise of the engine, and often enhance it.
The work of such devices is based on resonant processes within the "silencers" themselves, possessing, like any hollow body with the properties of the gameholts resonator. Due to the internal resonances of the exhaust system, two parallel problems are solved at once: the cleaning of the cylinder is improved from the residues of the combustible mixture in the previous tact, and the filling of the cylinder is a fresh portion of the combustible mixture for the next compression tact.
The improvement in the cleaning of the cylinder is due to the fact that the gas pillar in the graduate manifold, who scored some speed during the output of gases in the previous tact, due to inertia, like a piston in the pump, continues to suck out the remains of the gases from the cylinder even after the cylinder pressure comes With pressure in the graduate manifold. At the same time, another, indirect effect occurs: due to this additional minor pumping, the pressure in the cylinder decreases, which favorably affects the next purge tact - in the cylinder it falls somewhat more than a freshly combustible mixture than could get if the cylinder pressure was equal to atmospheric .
In addition, the reverse wave of exhaust pressure, reflected from the confusion (rear cone of the exhaust system) or blend (gas-dynamic diaphragm) installed in the cavity of the silencer, returning back to the exhaust window of the cylinder at the time of its closure, additionally "rambling" fresh fuel mixture in the cylinder , even more increasing its filling.
Here you need to clearly understand that it is not about the reciprocal movement of gases in the exhaust system, but about the wave oscillatory process within the gas itself. Gas moves only in one direction - from the exhaust window of the cylinder in the direction of the outlet at the outlet of the exhaust system, first with sharp jesters, the frequency of which is equal to the vehicle turnover, then gradually the amplitude of these jolts is reduced, in the limit turning into a uniform laminar movement. And "There and here" the pressure waves are walking, the nature of which is very similar to acoustic waves in the air. And the speed of these vibrations of pressure is close to the speed of sound in the gas, taking into account its properties - primarily density and temperature. Of course, this speed is somewhat different from the known value of the speed of sound in the air, under normal conditions equal to about 330 m / s.
Strictly speaking, the processes flowing in the exhaust systems of DSV is not quite correctly called pure acoustic. Rather, they obey the laws used to describe the shock waves, albeit weak. And this is no longer standard gas and thermodynamics, which is clearly stacked in the framework of isothermal and adiabatic processes described by laws and the equations of Boylya, Mariotta, Klapaireron, and others like them.
I came across this idea a few cases, the witness of which I myself was. The essence of them is as follows: Resonance Dudges of high-speed and racing motors (Avia, Court, and Auto), working on the proceedable modes, in which the engines are sometimes unchecked up to 40,000-45.000 rpm, and even higher, they start "sailing" - they are literally In the eyes change the shape, "pinpoint", as if not made of aluminum, but from plasticine, and even tritely roast! And it happens on the resonant peak of the "twin". But it is known that the temperature of the exhaust gases at the exit of the exhaust window does not exceed 600-650 ° C, while the melting point of pure aluminum is slightly higher - about 660 ° C, and its alloys and more. At the same time (the main thing!), Not the exhaust megaphone tube, adjacent directly to the exhaust window, is more often melted and deformed, where it would seem the highest temperature, and the worst temperature conditions, but the region of the reverse cone confusion, to which the exhaust gas reaches With a much smaller temperature, which decreases due to its expansion inside the exhaust system (remember the basic laws of gas dynamics), and besides, this part of the muffler is usually blown by the incident air flow, i.e. Additionally cooled.
For a long time I could not understand and explain this phenomenon. Everything fell into place after I accidentally hit the book in which the processes of shock waves were described. There is such a special section of gas dynamics, the course of which is read only on special taps of some universities that are preparing explosive technicians. Something similar happens (and studied) in aviation, where half a century ago, at the dawn of supersonic flights, they also encountered some inexplicable facts of destruction of the aircraft glider's design at the time of the supersonic transition.
The gas-dynamic supervision includes methods for increasing the charge density at the inlet by use:
· The kinetic energy of air moving on the receiving device in which it is converted to the potential pressure of pressure when braking the stream - high-speed supervision;
· Wave processes in intake pipelines -.
In the thermodynamic cycle of the engine without boosting the beginning of the compression process occurs at pressure p. 0, (equal atmospheric). In the thermodynamic cycle of the piston engine with a gas-dynamic supervision, the beginning of the compression process occurs at pressure p K. , due to the increase in the pressure of the working fluid outside the cylinder from p. 0 BE p K.. This is due to the transformation of the kinetic energy and the energy of the wave processes outside the cylinder into the potential energy of pressure.
One of the energy sources to increase the pressure at the beginning of the compression may be the energy of the incident air flow, which takes place when the aircraft, car, etc. means. Accordingly, adding in these cases is called high-speed.
High-speed supervision Based on aerodynamic patterns of transformation of high-speed air flow in static pressure. Structurally, it is realized as a diffuser air intake nozzle, aimed at towing the air flow when the vehicle is moving. Theoretically increase the pressure Δ p K.=p K. - p. 0 Depends on speed c. H and density ρ 0 incident (moving) air flow
The high-speed supervision finds the use mainly on aircraft with piston engines and sports cars, where speed speeds are more than 200 km / h (56 m / s).
The following varieties of gas-dynamic supervision of engines are based on the use of inertial and wave processes in the engine inlet system.
Inertial or dynamic reducing takes place at relatively high speed of moving fresh charge in the pipeline c. Tr. In this case, equation (2.1) takes
where ξ t is a coefficient that takes into account the resistance to the movement of gas in length and local.
Real speed c. The gas flow of gas in intake pipelines, in order to avoid elevated aerodynamic losses and deterioration in the filling of cylinders with fresh charge, should not exceed 30 ... 50 m / s.
The frequency of processes in the cylinders of piston engines is the cause of oscillatory dynamic phenomena in gas-air paths. These phenomena can be used to substantially improve the main indicators of engines (liter power and economy.
Inertial processes are always accompanied by wave processes (fluctuations in pressure) arising from the periodic opening and closing of the inlet valves of the gas exchange system, as well as the return-transit movement of the pistons.
At the initial stage of inlet in the inlet nozzle before the valve, a vacuum is created, and the corresponding wave of pouring, reaching the opposite end of the individual inlet pipeline, reflects the compression wave. By selecting the length and passage section of the individual pipeline, you can get the arrival of this wave to the cylinder at the most favorable moment before closing the valve, which will significantly increase the filling factor, and therefore torque M E. Engine.
In fig. 2.1. A diagram of a tuned intake system is shown. Through the intake pipeline, bypassing the throttle, the air enters the receiving receiver, and the input pipelines of the configured length to each of the four cylinders.
In practice, this phenomenon is used in foreign engines (Fig. 2.2), as well as domestic engines for passenger cars with configured individual intake pipelines (for example, ZMZ engines), as well as on a 2h8.5 / 11 dysperse of a stationary electric generator having one configured pipeline on Two cylinders.
The greatest efficiency of gas-dynamic supervision takes place with long individual pipelines. Advance pressure depends on the coordination of the engine rotation frequency n., pipeline lengths L. Tr and corners
bending the closure of the intake valve (organ) φ A.. These parameters are related addiction
where is the local sound speed; k. \u003d 1.4 - the adiabatic indicator; R. \u003d 0.287 kJ / (kg ∙ hail.); T. - average gas temperature for the pressure period.
Wave and inertial processes can provide a noticeable increase in charge in a cylinder at large valve discoveries or in the form of increasing recharge in compression tact. The implementation of effective gas-dynamic supervision is possible only for a narrow range of engine rotation frequency. The combination of the phases of the gas distribution and the length of the intake pipeline must provide the greatest filling coefficient. Such selection of parameters are called setting the inlet system.It allows you to increase the engine power by 25 ... 30%. To preserve the efficiency of gas-dynamic supervision in a wider range of rotational speed of the crankshaft, various methods can be used, in particular:
· Applying a pipeline with a variable length l. Tr (for example, telescopic);
· Switching from a short pipeline for long;
· Automatic regulation of gas distribution phases, etc.
However, the use of gas-dynamic supervision for engine boost is associated with certain problems. First, it is not always possible to rationally comply with sufficiently extended intake pipelines. It is especially difficult to do for low-speed engines, because with a decrease in the speed of rotation, the length of the adjusted pipelines increases. Secondly, fixed pipelines geometry gives dynamic setting only in some, quite a certain range of speed mode.
To ensure the effect in a wide range, a smooth or step adjustment of the length of the configured path is used when moving from one speed mode to another. Step regulation using special valves or rotary dampers is considered more reliable and successfully used in automotive engines of many foreign firms. Most often use control with switching into two customized pipeline lengths (Fig. 2.3).
In the position of the closed flap, the corresponding mode up to 4000 min -1, air supply from the intake receivers of the system is carried out along a long path (see Fig. 2.3). As a result (compared to the base version of the engine without gas-dynamic supervision), the flow of torque curve is improved on an external speed characteristic (at some frequencies from 2500 to 3500 min -1, the torque increases on average by 10 ... 12%). With increasing rotation speed N\u003e 4000 min -1 Feed switches to a short path and this allows you to increase the power N E. on nominal mode by 10%.
There are also more complex all-life systems. For example, designs with pipelines covering a cylindrical receiver with a rotary drum having windows for messages with pipelines (Fig. 2.4). When the cylindrical receiver is rotated, the length of the pipeline is increased and vice versa, when turning clockwise, it decreases. However, the implementation of these methods significantly complicates the engine design and reduces its reliability.
In multi-cylinder engines with conventional pipelines, the efficiency of gas-dynamic supervision is reduced, which is due to the mutual influence of intake processes in various cylinders. In the car engines, intake systems "set up" usually on the maximum torque mode to increase its stock.
The effect of gas-dynamic superior can also be obtained by the corresponding "setting" of the exhaust system. This method finds use on two-stroke engines.
To determine the length L. Tr and inner diameter d. (or passage section) of the adjustable pipeline it is necessary to carry out calculations using numerical methods of gas dynamics describing the non-stationary flow, together with the calculation of the workflow in the cylinder. The criterion is the increase in power,
torque or reducing the specific fuel consumption. These calculations are very complex. Simpler definition methods L. three d. Based on the results of experimental studies.
As a result of the processing of a large number of experimental data to select internal diameter d. The adjustable pipeline is proposed as follows:
where (μ. F. Y) MAX is the most effective area of \u200b\u200bthe inlet valve slot. Length L. The trifle pipeline can be determined by the formula:
Note that the use of branched tuned systems such as a common pipe - receiver - individual pipes turned out to be very effective in combination with turbocharging.
