The compression ratio is a calculated value demonstrating the change in volume before and after compression. And the compression is the value that is actually measured. In the process of compression, there is a change in not only volume and pressure, but also temperatures, therefore, in a working engine, the compression is usually slightly higher. It has an impact and possible leakage of valves, gaskets, rings, etc. Manual to the engine usually contains an indication of the minimum compression value at which it is allowed to ride.

Basic concept

It is important to know which degree of compression for the motor is optimal. This is a difficult question, because the engine developers with ignition from sparks are aimed at increasing this indicator. And if the engine runs on ignition from compression, then this parameter is correct to reduce. It is the compression ratio represents the characteristics of the engines. internal combustionwhich causes the greatest number of erroneous opinions.

The most common misconception is that much depends on the degree of compression. However, everything is simple - this indicator is a reflection of the ratio of the cylinder volume to a similar parameter of the combustion chamber, and if differently, it is equal to the part of the division of space over the piston to the volume of the combustion chamber. It turns out that the degree of compression in the geometrical plan is a reflection of whether the volume of the fuel-air mixture is reduced in the engine cylinders during the movement of the piston from the bottom to the top dead point. Of course, in life, everything is rarely similar to expressed in theory.

How does everything work?

The degree of engine compression at the dawn of motorism was low - 4-5, so that the detonation does not occur as a result of working on gasoline with a small octane number. For example, with a cylinder at 400 cubes, the volume of the combustion chamber will be 100 ml. It turns out that for such an engine, the degree of compression will be: E \u003d (400 + 100): 100 \u003d 5. If we reduce the volume of the fuel chamber to 40 cubic centimeters, then the degree of compression will occur: e \u003d (400 + 40): 40 \u003d 11 .

What will be the result? Increase thermal Efficiency engine Almost 30%. Provided that the motor of 2.4 liters with 6 cylinders with a compression ratio 5 reaches the power of 100 horsepower, then with the value of the compression ratio 11 it will become almost 130 liters. from. In this case, the fuel is consumed in the same volume. It turns out that in the calculation of one horsepower At an hour, we can talk about reducing fuel consumption by 22.7%.

This result is amazing, and the means to achieve it is incredibly simple. This is not mystic. The greater the degree of engine compression, the lower the gas temperature, which after testing goes to the exhaust.

Ases of heat engineering

Car engines are a kind of thermal aggregates obeying the laws of thermodynamics. The physicist Sadi Karno in the first half of the nineteenth century proposed the first foundations of the theory of thermal machines. In accordance with his theory, the efficiency of such a motor is higher than the greater difference between the gas temperature by the end of the combustion of the mixture of fuel with air and the temperature indicator on the release. This difference is most affected by the degree of expansion of working gases inside the cylinders. There is here important momentIn accordance with its theory, it is more important for thermal efficiency is not a compression ratio, but the degree of expansion. The stronger the expansion of hot gases on the working move occurs, the lower the temperature becomes completely, which is quite natural. In motors with conventional design, the compression ratio fully corresponds to the degree of expansion. That is why many do not share these terms. And the degree of compression and compression in the aggregate cause detonation. The stronger the compression of the fuel-air mixture in the motor cylinders occurs, the higher the temperature and pressure at the time of formation of the spark, the more high the likelihood of the appearance of shock waves in the detonation and combustion chamber. It is precisely it that reduces the degree of compression, but there is nothing to do with the extension of gases when working.

Five-way cycle

There is a five-way cycle, which is designed to breed the degree of compression and extension degree. For example, the compression ratio of the VAZ 2112 begins to work only at 75 degrees above the lower meter point, and there is a certain tact of the mixture. Now the clocks 5: injection, reverse displacement, compression, work move and release. The question arises, associated with the need to drive the mixture in both directions. For example, 20% of the mixture will be supplanted back, and 80% is compressed as it should be. Even under such conditions, the real degree of compression and compression is 10.6.

Practical value

If the design has real indicatorequal to 10.6, and expansion of working gases - 13, then it is quite normal. In this case, in fact, the thermal efficiency of the engine is 1.0518 times the one that is by the degree of compression. This is not enough, however, engine designers are trying to change the situation so as to achieve these 5% of fuel economy. W. passenger cars Engines operate on the basis of the 5-stroke cycle.

This solution seems brilliant, but there is also a disadvantage. The geometrical indicator of the extension of the working gases 13, and for the real degree of compression - 10.5. The process of displacing the mixture backs from a 1.5 liter engine for power and torque 1.2 liter. The outcome is to increase the thermal efficiency due to the loss of litter. "On Nizakh", the engine with the late closure of the inlet valves does not pull. The five-way cycle is appropriately used on vehicles with hybrid units, where the traction electric motor at the lowest revolutions takes the load on itself. Next, the operation is included in the work. And here it is not so important, what is the degree of compression from the motor, most importantly, the degree of gases expansion during work.

Output

Due to the supervision, the degree of compression is required to lower. In the process of supplying the fuel-air mixture, with an excess of pressure, it turns out that in the cylinders there is an increased real compression. Therefore, it is necessary to retreat. That is why there is a need to reduce the thermal efficiency and increase the fuel consumption, if the combustible fuel is not used.

I think many are asked by this question on the expanses of endless russian roads. What nevertheless gasoline is better pouring into his iron horse 92 or 95? Are there a critical difference between them, and what will happen if instead of 95 use 92 gasoline? After all, it is cheaper by about 5 - 10%, and, accordingly, from each tank there will be really savings! But is it worth it to act and is not dangerous for your power unit, we will analyze on the shelves, there will be a video version and voting at the end ...

At the very beginning I suggest thinking what these numbers are, 80, 92, 95, and in soviet times Also 93? Never thought? Here everything is simple, this is an octane number. And then what is it? We read on.

Octane number of gasoline

The octane number of gasoline is an indicator characterizing the detonation fuel resistance, that is, the magnitude of the fuel ability to resist self-ignition when compressed for internal combustion engines. That is, simple words, the higher the "octane level" of fuel, the less likely to self-ignition fuel in compression. With this study, the fuel levels are distinguished by this indicator. Studies are carried out on a single-cylinder installation with a variable level of fuel compression (they are called WWT-65 or WEAT-85).

Installations are operating at 600 rpm, air and a mixture of 52 degrees Celsius, and the ignition advance angle is about 13 degrees. After such tests, the eyes (octane number of research) are displayed. This study should show how gasoline will behave with minimal and average loads.

With the maximum load on the fuel, there is another experiment that displays (OPC - an octane number of motor). Tests are carried out on this, single-cylinder, installation, only turns of 900 rpm, air temperature and mixture 149 degrees Celsius. Ocarm has a lower value than the eyes. When experiment, output maximum loads, for example, when throttle acceleration or when moving uphill.

Now I think, at least it became clear what it is. And how it is determined.

Now let's go back to the selection - 92 or 95. Any kind be 92 or 95, and even 80. When processing it does not have this, ultimate, octane number. With a direct distillation of oil, it turns out only 42 - 58. That is, very low quality. "How so" do you ask? Can not be distilled immediately with a high indicator? It is possible, but it is very expensive. A liter of such fuel would cost several times more expensive on the market. The development of such fuel is called catalytic reforming. It is produced in this way of only 40 - 50% of the total mass and mainly in Western countries. In Russia, this method produces much less gasoline. The second production technology, which is less expensive - is called catalytic cracking or hydrocracking. Gasoline with this processing has an octane number of only 82-85. In order to bring it to the desired figure, you need to add special additives.

Additives in gasoline

1) Additives based on metal-containing compositions. For example, on Tetraethylswinse. Conditionally called eaten gasoline. Very effective, make fuel work, for the whole, as they say. But very harmful. As can be seen from the name Tetraeethylswin, there are metal - "lead". When combustion, gaseous lead compounds in the air, which is very harmful, settles in the lungs, developing complex diseases, such as "cancer". Therefore, such types are now prohibited worldwide. In the USSR, there was a brand AI - 93, he was just based on Tetraethylswinse. Conditionally, it is possible to name this fuel outdated and harmful.

2) more advanced and safe based on ferrocene, nickel, manganese, but most often used monomethylaniline (MMNA)His octane number reaches 278 points. These additives are directly mixed with gasoline, bringing the mixture to the desired consistency. But such additives are also not perfect, they form a raid on pistons, candles, litter catalysts and all sorts of sensors. Therefore, sooner or later, such fuel is brused by the engine, in the literal sense of the word.

3) the last and the most perfect is ethers and alcohols.. The most environmental and do not harm environment. But there are disadvantages of such fuel, it is a low octane number of alcohols and ether, the maximum value of 120 points. Therefore, such additives are required in fuel for quite a lot of about 10-20%. Another disadvantage is the aggressiveness of alcohol and essential additives, with a large content they faster corrosive rubber and plastic nozzles and sensors. Therefore, such additives are limited within 15% of the overall fuel level.

Degree of compression and modern car

Actually, why I began to tell from octane number and additives, but because you need to take into account fuel ignition or so-called detonation in modern units.

The fact is that manufacturers to increase power and reduce fuel consumption, slightly increase the compression ratio in the engine cylinders.

Here are some useful information:

• For the degree of compression to 10.5 and below, the octane number of gasoline AI is 92 (do not take into account the turbo motor options).
• From the mark of 10.5 to 12 - pour fuel not lower than Ai - 95!
• If the degree of compression is 12 and higher, it is recommended to pour out at least Ai - 98
• Of course, there are still very rare gasoline, such as AI - 102 and AI - 109, for them the degree of compression 14 and 16, respectively.

So what happens IN THEORY If we plug 92 gasoline into the motor, which is designed for 95? Yes, everything is simple, the fuel from the high degree of compression will be self-propaganda, "minibuses" will occur - that is, the detonation detonation effect will appear!

And what is dangerous detonation? Yes, everything is simple, the squeezing of the gasket between the head of the block and the block itself, the destruction of the rings (both compression and oiling), the squeezing of the pistons, etc.

But this is how I wrote above - All this in theory ! Especially in Russia! Why I say it. Many manufacturers understood - that high-quality gasoline (and now we are talking about 95 options), to find if it is possible - it is very difficult, even in the metropolitan regions (I am already silent about small cities). Often gasoline "Badejat" so that the octane number of 95 is unrealistic. I remember a couple of years ago, I read an article with an experiment - where in the capital they took samples from a lot of refills, and only at 20 - 25% of cases of gasoline approached the standards, the rest were far from the figure 95 and even 92. Just think! And how do you check the quality yourself? Right - in no way.

So if you pour such poor-quality fuel engine immediately? Right away? Not certainly in that way. Machines are now smart, and it is that your motor does not go "into the spread" was invented detonation sensor, it allows the motor to work with another octane number. It monitors the mechanical oscillations of the engine block, converts them to electrical impulses and constantly.

If the impulses "go beyond the normal state", the ECU decides to adjust the angle of ignition and quality fuel mixes. Thus, the modern motor, calculated for 95 gasoline, will calmly work even on 92.

But! Such work will be successful on low and medium turnover, on high revolutions (Almost a maximum), the detonation sensor works not so effectively, so "fry" in a low-intensive mixture is undesirable!

Let's summarize.

What will happen if pour 92 instead of 95?

In fact, the difference between 92 and 95 gasoline is minimal, total "3 numbers". If you choose to refuel in the company that you guarantee exactly the "hard indicators" that is, "92 is 92", and "95 is 95" and you will be sure of it. The difference will show for your motor rather on high speeds, and not largely (up to 2 - 3%) power loss, also this percentage will grow fuel consumption.

And what is the most interesting if you don't often spin your force aggregate up to 5000 - 7000 revolutions, and moving from 2000 to 4000, then 92 will not give you any negative moments. Yet electronics all adjusts itself.

Prejudice -, this is not. The extension of the valves was characteristic of the eaten types that metallic additives had. High-octane eaten gasolines could harm the engine configured to use AI-76 (and it has not had an electronic correction of the ignition angle and fuel injection). But now such a danger is simply no, because such fuel has long been prohibited.

But ideally! You need to fill in such a fuel that your manufacturer recommends. After all, if suddenly a new engine, will cover, and it turns out that the breakdown is associated with gasoline, then you fall on a very expensive repair, and at your own expense. Savings of 10% on gasoline you will "get out sideways."

I think many are asked by this issue on the expanses of endless Russian roads. How nevertheless gasoline is better pouring into his iron horse 92 or 95? Are there a critical difference between them, and what will happen if instead of 95 use 92 gasoline? After all, it is cheaper by about 5 - 10%, and, accordingly, from each tank there will be really savings! But is it worth it to act and is not dangerous for your power unit, we will examine on the shelves, there will be a video version and voting at the end.

At the very beginning, I suggest thinking what these numbers, 80, 92, 95, and in Soviet times 93 more? Never thought? Here everything is simple, this is an octane number. And then what is it? We read on.

Octane number of gasoline

The octane number of gasoline is an indicator characterizing the detonation fuel resistance, that is, the magnitude of the fuel ability to resist self-ignition when compressed for internal combustion engines. That is, simple words, the higher the "octane level" of fuel, the less likely to self-ignition fuel in compression. With this study, the fuel levels are distinguished by this indicator. Studies are carried out on a single-cylinder installation with a variable level of fuel compression (they are called WWT-65 or WEAT-85).

Installations are operating at 600 rpm, air and a mixture of 52 degrees Celsius, and the ignition advance angle is about 13 degrees. After such tests, the eyes (octane number of research) are displayed. This study should show how gasoline will behave with minimal and average loads.

With the maximum load on the fuel, there is another experiment that displays (OPC - an octane number of motor). Tests are carried out on this, single-cylinder, installation, only turns of 900 rpm, air temperature and mixture 149 degrees Celsius. Ocarm has a lower value than the eyes. In the experiment, the level of maximum loads, for example, with throttle acceleration or when moving uphill, is derived.

Now I think, at least it became clear what it is. And how it is determined.

Now let's go back to the selection - 92 or 95. Any kind be 92 or 95, and even 80. When processing it does not have this, ultimate, octane number. With a direct distillation of oil, it turns out only 42 - 58. That is, very low quality. "How so" do you ask? Can not be distilled immediately with a high indicator? It is possible, but it is very expensive. A liter of such fuel would cost several times more expensive on the market. The development of such fuel is called catalytic reforming. It is produced in this way of only 40 - 50% of the total mass and mainly in Western countries. In Russia, this method produces much less gasoline. The second production technology, which is less expensive - is called catalytic cracking or hydrocracking. Gasoline with this processing has an octane number of only 82-85. In order to bring it to the desired figure, you need to add special additives.

Additives in gasoline

1) Additives based on metal-containing compositions. For example, on Tetraethylswinse. Conditionally called eaten gasoline. Very effective, make fuel work, for the whole, as they say. But very harmful. As can be seen from the name Tetraeethylswin, there are metal - "lead". When combustion, gaseous lead compounds in the air, which is very harmful, settles in the lungs, developing complex diseases, such as "cancer". Therefore, such types are now prohibited worldwide. In the USSR, there was a brand AI - 93, he was just based on Tetraethylswinse. Conditionally, it is possible to name this fuel outdated and harmful.

2) more advanced and safe are based on ferrocene, nickel, manganese, but most often used monomethylaniline (MMNA), its octane number reaches 278 points. These additives are directly mixed with gasoline, bringing the mixture to the desired consistency. But such additives are also not perfect, they form a raid on pistons, candles, litter catalysts and all sorts of sensors. Therefore, sooner or later, such fuel is brused by the engine, in the literal sense of the word.

3) the latter and most perfect are ethers and alcohols. The most environmental and do not cause harm to the environment. But there are disadvantages of such fuel, it is a low octane number of alcohols and ether, the maximum value of 120 points. Therefore, such additives are required in fuel for quite a lot of about 10-20%. Another disadvantage is the aggressiveness of alcohol and essential additives, with a large content they faster corrosive rubber and plastic nozzles and sensors. Therefore, such additives are limited within 15% of the overall fuel level.

Degree of compression and modern car

Actually, why I began to tell from octane number and additives, but because you need to take into account fuel ignition or so-called detonation in modern units.

The fact is that manufacturers to increase power and reduce fuel consumption, slightly increase the compression ratio in the engine cylinders.

Here are some useful information:

For the degree of compression to 10.5 and below, the octane number of gasoline AI is 92 (do not take into account the turbo motor options).

From the mark of 10.5 to 12 - pour fuel not lower than Ai - 95!

Of course, there are still very rare gasoline, such as AI - 102 and AI - 109, for them the degree of compression 14 and 16, respectively.

So what happens, in theory, if we board 92 gasoline in the motor, which is designed for 95? Yes, everything is simple, the fuel from the high degree of compression will be self-propaganda, "minibuses" will occur - that is, the detonation detonation effect will appear!

And what is dangerous detonation? Yes, everything is simple, the squeezing of the gasket between the head of the block and the block itself, the destruction of the rings (both compression and oiling), the squeezing of the pistons, etc.

But this is how I wrote above - all this in theory! Especially in Russia! Why I say it. Many manufacturers understood - that high-quality gasoline (and now we are talking about 95 options), to find if it is possible - it is very difficult, even in the metropolitan regions (I am already silent about small cities). Often gasoline "Badejat" so that the octane number of 95 is unrealistic. I remember a couple of years ago, I read an article with an experiment - where in the capital they took samples from a lot of refills, and only at 20 - 25% of cases of gasoline approached the standards, the rest were far from the figure 95 and even 92. Just think! And how do you check the quality yourself? Right - in no way.

So if you pour such poor-quality fuel engine immediately? Right away? Not certainly in that way. Machines are now smart, and it is that your motor does not go "into the spread" was invented detonation sensor, it allows the motor to work with another octane number. It monitors the mechanical oscillations of the engine block, transforms them into electrical impulses and constantly sends them to the ECU.

If the impulses "go beyond the normal state", the ECU decides to adjust the ignition angle and the quality of the fuel mixture. Thus, the modern motor, calculated for 95 gasoline, will calmly work even on 92.

But! Such work will be successful on low and medium-sized circulation, at high speed (almost maximum), the detonation sensor is not so effective, so "fry" in a low-juice mixture is undesirable!

Let's summarize.

What will happen if pour 92 instead of 95?

In fact, the difference between 92 and 95 gasoline is minimal, total "3 numbers". If you choose to refuel in the company that you guarantee exactly the "hard indicators" that is, "92 is 92", and "95 is 95" and you will be sure of it. The difference will show for your motor rather on high speeds, and not largely (up to 2 - 3%) power loss, also this percentage will grow fuel consumption.

And what is the most interesting, if you do not often spin your power unit up to 5000 - 7000 revolutions, and moving from 2000 to 4000, then 92 does not take you any negative points. Yet electronics all adjusts itself.

Prejudice - what the valve can burn, this is not. The extension of the valves was characteristic of the eaten types that metallic additives had. High-octane eaten gasolines could harm the engine configured to use AI-76 (and it has not had an electronic correction of the ignition angle and fuel injection). But now such a danger is simply no, because such fuel has long been prohibited.

But ideally! You need to fill in such a fuel that your manufacturer recommends. After all, if suddenly a new engine, will cover, and it turns out that the breakdown is associated with gasoline, then you fall on a very expensive repair, and at your own expense. Savings of 10% on gasoline you will "get out sideways."

What the final result I want to withdraw - to each one, if your motor is not designed for the 92nd, then it is not worth pouring it! Yet it can be fraught! However, if the cock is the modern engine, the automatic, adjusts the ignition angles and you may not even feel the fuel replacing (that is, on the 92nd you can ride, without spinning your motor up to a maximum). But if the breakdown happens, and the warranty will find out what is flooded not that fuel, the repair will be at your expense! And this, for sure, does not cost 2 - 3 rubles saving from a liter.

Now a detailed video version, look.

In any adjustable engine, one of the parameters, which without any doubt should be changed and usually upwards, is the degree of compression. Since improving the compression ratio increases the efficient engine power, therefore it is desirable to have a compression ratio as high as possible within certain limits. The upper limit is always determined depending on the point in which detonation occurs.

Since detonation can very quickly destroy the engine, so it will be better if we will know exactly what a compression ratio is or it will be to be able to withstand a reasonable ratio. The compression ratio is determined by the following formula (V + C) / C \u003d CRwhere V. This is a working cylinder volume, and FROMthis is the volume of combustion chamber.

You can simply determine the working volume or capacity of one cylinder. To do this, you just need to divide the working volume (litter) of the engine to the number of cylinders, for example, if the filter of the four-cylinder engine is 1100 cu. cm, the container or working volume of one cylinder will be 1100/4 \u003d 275 cubic meters. See Find the volume of the combustion chamber is somewhat more complicated. To determine the volume, we must physically measure it and for this we need to have a pipette or burette, graduated in the cube. See the volume of the combustion chamber is the full volume that remains above the piston when it is in the NWT. It includes the volume of the cavity in the head plus a volume equal to the thickness of the gasket, plus the volume between the top of the piston and the top of the cylinder block in the VMT and plus the volume of the recess in the bottom of the piston when using the pistons with concave bottoms or minus the volume of the bulge on the bottom of the piston when used Pistons with convex bottoms. After it is done, you can add a volume equal to the thickness of the gasket. If the gasket has a circular hole, then this volume is easiest possible to determine using the following formula: VCC \u003d [(P d2 * L) / 4] / 1,000where V. \u003d volume p. = 3,142, D. \u003d Diam. holes in the laying in mm, L. \u003d gasket thickness in the clamping state in mm. If a hole in the laying is non-circular, as it takes place in many cases, then we can measure the required amount by using the bureau. To do this, the fascinated gasket is glued to the glass sheet using a sealant designed for cylinder head laying, then place the glass on the horizontal surface and fill the hole in the laying of the liquid using the burette. Try to do it so that the liquid is not pulled out of the hole or covered the entire surface of the gasket, because in this case the measurements will be incorrect. The liquid should be poured as long as its level does to the edge of the gasket. If all the holes are round, you can easily calculate the volume between the upper surface of the piston and the upper part of the unit. This can be done using the above formula, but at the same time D. will be equal to dia. cylinder holes in mm, and L. The distance from the top bottom of the piston to the top of the block is again in mm. At some stages it is necessary to determine how much it is necessary to remove the metal from the end surface of the cylinder head to get the desired degree of compression. To do this, you first need to calculate the required full volume of the combustion chamber. From the resulting value, you will deduct the volume equal to the thickness of the gasket, the volume in the block above the piston when it is in the NTC and, if the piston is used with a concave bottom, the volume of the excavation. The remaining value is now a volume that should have a cavity in the head to obtain the compression degree we need. To make it more clear, consider the following example. Suppose that we need to have a compression ratio of 10/1, and the engine litter is 1000 cm3 and it has four cylinders. CR \u003d (V \u003d C) / Cwhere V. - working volume of one cylinder, and FROM - Full volume of combustion chamber. As we know that V. (working cylinder volume) \u003d 1000 cm3 / 4 \u003d 250 cm3 and know the desired degree of compression, so we transform the equation to get the full volume of the combustion chamber FROM. As a result, you will receive the following equation: C \u003d V / (CR-1). Substitute the specified values C \u003d 250 / (10 - 1) \u003d 27.7 cm3 . Thus, the total volume of the combustion chamber is 27.7 cm3. From this value, you deduct all components of the combustion chamber that are not in the head. Suppose that the piston has a concave bottom, the volume of the cavity in the bottom is 6 cm3 and that the remaining volume above the piston when it is in VMT, to the end of the head is 1.5 cm3. In addition, the volume equal to the thickness of the gasket is 3.5 cm3. The sum of all these volumes that are not included in the cavity in the head is 11 cm3. To obtain the degree of compression, 10/1, we must have the amount of cavity in the head (27.7 - 11) \u003d 16.7 cm3. To determine how many metal should be removed from the end surface of the head, place it on the horizontal surface, or rather place the head in such a way that its face surface is horizontal. After you do this, fill in the chamber with the amount of fluid equal to the required final volume. In this example, this volume is 16.7 cm3. Then measure the distance from the end surface of the head to the surface of the fluid and it will determine the amount of metal that will need to be deleted. There is one small problem when measuring the distance from the head of the head to the fluid level. As soon as the tip of the depth gauge is approaching the surface of the fluid, it is raised by the tip by capillary action. This capillary action takes place when using paraffin as a liquid volume medium, when the depth gauge tip is from 0.008 to 0.012 inches from the surface of the liquid and therefore it is necessary to make admission to this phenomenon. Due to small inaccuracies that occur during grinding and shaped processing of the combustion chamber, we recommend that you check the volume of each camera in exactly as well as others. If all volumes are not the same, then it should be removed from the chambers heads that have fewer volumes so that their volumes become the same as the camera large. The main reason for the need to balancing cameras is that it provides more smooth operation of the engine, especially on small revolutions, and allows you to slightly reduce vibrations arising from the same starting pulses. The second reason is that if we use the maximum possible degree of compression and, when checking, we find the chamber with the largest volume to determine the amount of metal removed, the degree of compression from other cameras may be higher than this limit value. As a result, detonation will arise, which can quickly lead to the destruction of the engine. When removing metal from the chambers, it is best to remove the metal in the top of the chambers or from the walls near the candle. The accuracy of the chambers balancing is about 0.2 cm3. Attempts to get smaller values \u200b\u200bcannot be implemented in practice, since with such extreme values, measurement features using the measuring instruments used are limited due to their errors. In addition, an error equal to 0.2 cm3, even for small-littered engines, is a small percentage of the full volume of the chamber in the head.

Change the degree of compression

After we decided with the degree of compression before us is the question of how to properly achieve the degree of compression. First you need to calculate how much it is necessary to increase the combustion chamber. It's not hard. The formula for calculating the compression ratio has the following form: e \u003d (VP + VB) / VB Where e.- compression ratio VP. - Working volume VB. - The volume of the combustion chamber converting the equation can be obtained by a formula for calculating the combustion chamber at a certain point of compression. VB \u003d VP1 / E Where VP1 - The volume of one cylinder according to this formula calculates the volume of the existing combustion chamber and subtract the volume of the desired (calculated according to the same formula), the difference obtained and there is a value that interests it to which and it is necessary to increase the combustion chamber. There are a variety of ways to increase the combustion chamber but not all of them are faithful. The combustion chamber modern car It is designed in such a way that when the piston is reached, the air mixture is supplied to the center of the combustion chamber. This is perhaps the most effective development predictation. Independent refinement of the camera in the GBC is far from many. This is due to the fact that you can violate the designed form of the chamber, as well as the walls can "open up" when finalizing. Their thickness is not known. It is also not recommended to "squeeze the motor" with thick gaskets. This will violate the processes of displacement in the combustion chamber. The simplest and right way is to install new pistons in which the required volume of the chamber is specified. For a turbo engine, a spherical form is considered the most efficient. It is better to use specially designed and manufactured pistons for these purposes. A variant of independent finalization of stock pistons is possible. But here you need to consider that the thickness of the bottom of the piston should not be less than 6% of the diameter.

The degree of compression in the turbo engine

One of the most important and perhaps the most difficult task in the design of a turbo engine is to decide on the degree of compression. This parameter affects a large number of factors in overall characteristic car. Power, efficiency, rigging, detonation resistance (the parameter of which the operational reliability of the engine as a whole strongly depends), all these factors are largely determined by the degree of compression. It also affects fuel consumption and the composition of the exhaust gases. In theory, the degree of compression for the turbo-motor is not to calculate much work. First we will analyze the concept of "compression" or "geometric degree of compression". It is the ratio of the total volume of the cylinder (the operating volume plus the compression space remaining over the piston when the position in the upper dead point (NTT)), to the pure compression space. The formula has the following form: E \u003d (VP + VB) / VB Where E.- compression ratio VP. - Working volume VB. - The volume of the combustion chamber does not need to forget about the essential discrepancies between the geometric and actual degree of compression even on atmospheric motors. In turbo engines, the mixture is added to the same processes and pre-compressed compressor. For all, actually to increase the degree of compression, it is seen from the following formula: E EFF \u003d EGEOM * K√ (PL / PO) Where eff. - Effective compression E Geom. - geometric compression ratio E \u003d (VP + VB) / VB, PL - pushing pressure (absolute value), PO. - Environmental pressure, k.- adiabatic exhibitor (numerical value of 1.4) This simplified formula will be valid provided that the temperature at the end of the compression process for pressing engines and without boost reaches the same value. In other words, the higher the supervision pressure, the less possible geometric compression. So, according to our formula for the atmospheric engine with a compression ratio of 10: 1 at a pressure of 0.3 babe, the compression ratio should be reduced to 8.3: 1, at a pressure of 0.8 bar to 6.6: 1. But, thank God, this is theory. All modern turbocharge engines do not work with such a lot of low values. The correct degree of compression for work is determined by complex thermodynamic calculations and comprehensive tests. All this from the area high technologies and complex calculations, but many tuning motors are assembled on the basis of some experience, both own and brought for an example, from known car manufacturers. These rules will be fair in most cases.

The dependence of the octane number from the degree of compression

There are some important factors The compression degree affecting the calculation and they should be taken into account when designing. I will list the most important. Of course, this is the desired reducing, the octane number of fuel, the form of the combustion chamber, the effectiveness of the intermediate cooler, and, of course, the measures that you are able to reduce the temperature tension in the combustion chamber. The angle of ahead of the ignition (VN) can also partially compensate for the increased loads. But these are the topics for a separate conversation, and we will definitely affect them later in the following articles.

Nov 1 2014.

Engine compression ratio, compression and octane number

The concept of "compression ratio" refers to piston engineswho have a combustion chamber. Under this term understands the ratio of the volume of space over the piston at the moment when it is at the bottom of the dead point to the volume of the epipper space at the upper dead point.

In other words, this is a pronounced mathematical difference in pressure inside the combustion chamber at the time of filing combustible mixture in the cylinder, and at the time of its ignition.

Around this term a lot of misunderstandings and myths. To understand what truth and what a lie should figure out why different engines This parameter is different, and what advantages gives a low or high degree of compression.

Advantages of high compression

The internal combustion engine operates due to the ignition of the mixture of air and fuel vapor. With ignition, the mixture expands and pushes the piston that rotates the crankshaft. With a greater degree of compression, the intensity of pressure on the piston increases, and Zak one clock engine makes more useful work.

The lack of detonation in diesel engines is simply explained: in the combustion chamber, clean air is first compressed, and the fuel is injected later.

In this case, it is understood that the amount of gasoline in the fuel-air mixture remains unchanged, and due to more air it burns with a higher efficiency.

At the present stage of design passenger cars The use of low compression engines has almost stopped. Despite the fact that they are permissible to use low-fledged and inexpensive gasoline A-80, their popularity is zero.

The fact is that modern consumers seek to acquire cars with a large number of "horses under the hood", and with engines designed for low-fledged gasoline (for example, the engine of UAZ 469, (which, however, with a modified degree of compression and a number of modernization is installed in UAZ Hunter ), It is impossible to remove greater power by constructive reasons.

Is it possible to change the compression ratio?

It is possible to increase the degree of compression by reducing the volume of the combustion chamber, but when modernizing the existing engine, the engineers have to constantly search for a compromise between efficiency and safety. The fact is that the increase in the degree of compression leads to a decrease in the detonation threshold.

If you increase the degree of compression too much, you can encounter the fact that the means to prevent the occurrence of detonation will not work. In other words, sometimes develop (or put from another, more powerful car) new engine It is easier than to upgrade the old one.

For modern engines Characterized high degrees of compression. In the overwhelming majority of cases, gasoline is used with an octane number of not lower than 95 or even 98.

One of the options for changing the degree of compression, affordable private tuners - milling of the head of the cylinder block. After "shorting" the CCC, the volume of combustion chamber decreases.

The degree of compression in this case will increase. There is I. back side Such manipulation (by the way, it is officially called the forcing) the total volume of the combustible mixture burning in the cylinder for one cycle will decrease.

Compression ratio or compression?

The compression ratio is often confused with the concept of "compression". This is not the same thing. Compressions are called maximum pressure In the cylinder when the piston moves from the bottom of the dead point to the top.

Compression is measured in the atmospheres, and the compression ratio has the form of a mathematical relationship, for example, 10: 1 (ten to one).

Premature ignition and detonation

The mixture coming into the combustion chamber should not explode, but to burn, and evenly, and throughout the entire segment of time until the piston moves down.

At the same time, the energy is consumed as efficiently as possible, and the details piston group wears evenly and do not overheat. The difficulty lies in the fact that the combustion rate of the mixture is usually much faster speed Piston movements.

In this regard, there is a major problem that stands on the path of those who set forth the goal to increase the degree of compression. With an increase in pressure, the mixture spontaneously flashes.

This phenomenon is called premature ignition. Moreover, the ignition of the mixture occurs when the piston also completes the compression phase. In this case, the energy of the combusting fuel creates additional resistance and is waste to perform a useless action.

Second problem: allocating excessive amounts of energy. Simply put - an explosion. This phenomenon is called detonation in the engine theory and has extremely negative consequences.

Thus, an increase in the degree of compression can play with the owner of the engine as a joke. To avoid unpleasant consequences, it is worth familiar with such a concept as an octane number.

What is an octane number and what does it affect?

Gasoline that is used for the work of the DVSIt is characterized by resistance to detonation and self-ignition. To indicate the level of this resistance, the concept of "octane number" is introduced.

Detonation occurs only in the combustion chamber gasoline engine. Burning diesel fuel It requires a greater degree of compression, and it is ignited by "by itself" distinguished under the influence of pressure and in contact with the hot metal parts.

It would seem that all conditions for the occurrence are created, but thanks to some features diesel engine It is completely protected from this harmful phenomenon.

Important fact - The octane number of gasoline does not affect the amount of energy that highlights the fuel during combustion. In other words, think that pouring gasoline into the engine with a higher octane number, you increase its power, erroneously.

It's very simple: with a high significance of the compression degree, it is necessary to use fuel with a large octane number.

The effects of fuel use with inappropriate octane number

It is worth paying attention to that when the fuel used is inconsistent with the manufacturer's requirements, the following problems may occur:

- When using fuel with a large octane number, it is possible to exhaust exhaust valves. This happens because gasoline with a large octane number is lit with a smaller temperature and slower. Accordingly, when used, on the release phase, instead of spent gases through exhaust valve Cleans a burning mixture.

- When using fuel with a high octane number on Candle, it is possible to form a car. The reasons are all the same: the combustion rate may not coincide with the cycles of the piston stroke.

- When using a fuel with a low octane number, the engine control unit (or octane-corrector of the distributor) will not be able to install the ignition advance angle excluding detonation.

Alternative way to change the degree of compression

In the modern practice of engine development, an alternative method for dynamic change in the degree of compression is actively applied - installation of the turbocharger.

It helps to increase the pressure in the combustion chamber without changing its physical volume. The principle of the supercharger is that there is more air per unit of time in the combustion chamber under pressure.

As a result, the compression ratio is constantly changing, reacting to an increase and reduce the load on the engine. This process occurs under the control of electronics, which promptly changes the conditions for inflammation of the fuel-air mixture.

As a result of all the above negative factors associated with changing pressure in the combustion chamber, it is possible to avoid.

In the United Arab Emirates, races on diesel SUVs are extremely popular. Maximum performance turbines are used to increase compression and power

Tuning fans perceived the use of turbocharger as a more flexible and controlled method of increasing engine power.

It can be said that the acquisition of turbo whales (set of parts intended for the installation of turbocharging on concrete Engine), It is much more common compared to forcing. Blooders different types Successfully used and, if necessary, increase the efficiency of the diesel engine.