Efficiency formula (coefficient of efficiency)

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Author temass

Date
Jul 18, 2017
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Among the many useful characteristics, engine efficiency is of no small importance. The duration and efficiency of the power unit depends on this indicator.

Efficiency of an internal combustion engine - what is it?
Power losses - where and why
Comparison of efficiency of heat engines - gasoline and diesel
Asynchronous motor and stirling
Maximum efficiency value of an ideal engine
How to increase efficiency?

More about losses

Looking ahead, we can confidently say that the efficiency of a gasoline engine ranges from 20 to 25%. And there are many reasons for this. If we take the incoming fuel and convert it into percentages, then we seem to get “100% of the energy” that is transferred to the engine, and then there are losses:

1) Fuel efficiency . Not all the fuel is burned, a small part of it goes with the exhaust gases, at this level we already lose up to 25% efficiency. Of course, now fuel systems are improving, an injector has appeared, but it is far from ideal.

2) The second is thermal losses and . The engine warms itself and many other elements, such as radiators, its body, and the liquid that circulates in it. Also, some of the heat leaves with exhaust gases. All this results in up to 35% loss of efficiency.

3) The third is mechanical losses . ON all kinds of pistons, connecting rods, rings - all places where there is friction. This can also include losses from the load of the generator, for example, the more electricity the generator generates, the more it slows down the rotation of the crankshaft. Of course, lubricants have also made progress, but again, no one has yet been able to completely overcome friction - losses are still 20%.

Thus, the bottom line is that the efficiency is about 20%! Of course, among the gasoline options, there are standout options in which this figure is increased to 25%, but there are not many of them.

That is, if your car consumes fuel 10 liters per 100 km, then only 2 liters of them will go directly to work, and the rest are losses!

Of course, you can increase the power, for example, by boring the head, watch a short video.

If you remember the formula, it turns out:

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Designations

Lowercase η

In optics, the refractive index of an optical medium (although the letter n
is used more often).
In thermodynamics, the efficiency of a Carnot heat engine.
In particle physics there are η-mesons.
In statistics, η²
is the “partial regression coefficient.”
In lambda calculus - η-conversion
In fluid dynamics, dynamic viscosity, also denoted by the letter μ.

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Let's say we are relaxing at the dacha, and we need to fetch water from the well. We lower the bucket into it, scoop up the water and begin to lift it. Have you forgotten what our goal is? That's right: get some water. But look: we are lifting not only the water, but also the bucket itself, as well as the heavy chain on which it hangs. This is symbolized by a two-color arrow: the weight of the load we lift is the sum of the weight of the water and the weight of the bucket and chain.

Engine thermal efficiency. Not so scary physics.

Typically, if someone hears the slogan “engine thermal efficiency,” they immediately change the topic. You can talk about engines about their power, about their fuel consumption or - earning the respect of your interlocutors as an expert - about performance systems such as Diesel, Otto, Wankel and Atkinson. But thermal efficiency sounds like physics homework, that is, it causes disgust and negative reactions. Meanwhile, all this merges into one...

Engine efficiency - denoted by the Latin symbol η (eta) - is a parameter that characterizes a given engine and means how much supplied heat is converted into useful work. In the case of an internal combustion engine, this is the conversion of thermal energy resulting from the combustion of fuel into mechanical energy released by the engine as a result of the rotation of the crankshaft.

The values of this efficiency vary for different types of engines and, for example, for spark-ignition engines it is about 0.30–0.36, and for diesel engines it is about 0.40–0.45. This means nothing more than that when filling a tank with 50 liters of fuel, only 15-18 liters of gasoline and 20-22.5 liters of diesel fuel are used to drive the vehicle components. The rest is irretrievably lost.

How can you increase efficiency

Modern science is constantly looking for ways to increase the efficiency of engines and individual mechanisms, introducing new technical solutions and technological innovations.

The higher the efficiency, the more economical the engine will be, the more energy resources will be saved.

Heat engine

From formula (2) it follows that there are two ways : a) increasing the heater temperature; b) lowering the temperature of the refrigerator. Both paths are unpromising.

The heater cannot be heated indefinitely, since any material has a heat resistance limit. The refrigerator is almost always the environment, and introducing an additional heat exchanger (for example, a cylinder with liquid nitrogen) into the system is impractical: this will sharply increase the weight, dimensions and cost of the engine.

It has been established that the efficiency is not affected by the characteristics of the working fluid. What remains?

But there remain many practically feasible methods, such as reducing friction in mechanical components, minimizing heat loss by achieving the most complete combustion of fuel, creating streamlined shapes to reduce head-on comparison (air or water), etc.

an efficiency of 30-40% is currently considered a good indicator , scientists and practitioners have something to work on.

Power losses - where and why

fuel efficiency - the fuel does not burn completely, a small part of it simply flies out into the exhaust pipe. At this stage, 25% is lost;
thermal - the engine heats not only itself, but also its other elements. To obtain heat, energy is required, this is loss. Another 35% is spent on them;
mechanical - friction occurs during the movement of mechanisms. Of course, lubricants weaken its effect, but it has not yet been possible to completely defeat it. That's another 20%.

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At the output we find that the engine efficiency is only 20-25%. In fact, if a car consumes 10 liters of gasoline per 100 km, then only 2 liters will be spent on work, the rest is losses.

Which engine has the highest efficiency?

Now I want to talk about gasoline and diesel options, and find out which of them is the most efficient.

To put it in simple language and without getting into the weeds of technical terms, if you compare the two efficiencies of gasoline and diesel units, the more efficient of them is, of course, diesel and here’s why:

1) A gasoline engine converts only 25% of energy into mechanical energy, but a diesel engine converts about 40%.

2) If you equip a diesel type with turbocharging, you can achieve an efficiency of 50-53%, and this is very significant.

So why is it so effective? It's simple - despite the similar type of work (both are internal combustion units), diesel does its job much more efficiently. It has greater compression, and the fuel ignites using a different principle. It heats up less, which means there is a saving on cooling, it has fewer valves (saving on friction), and it also does not have the usual ignition coils and spark plugs, which means it does not require additional energy costs from the generator. It operates at lower speeds, there is no need to frantically spin the crankshaft - all this makes the diesel version a champion in terms of efficiency.

What is efficiency? Let's understand what efficiency is

Blue LEDs are needed to produce white light in combination with red and green. These two colors were learned to be produced in sufficiently bright LEDs much earlier; blue ones have long remained too dim and expensive for mass use. Another example of effective but very expensive devices is solar cells based on gallium arsenide (a semiconductor with the formula GaAs). Their efficiency reaches almost 30%, which is one and a half to two times higher than the batteries used on Earth based on the much more common silicon. High efficiency only pays off in space, where delivering one kilogram of cargo can cost almost as much as a kilogram of gold. Then the savings on battery weight will be justified.

The efficiency of power lines can be increased by replacing copper with better-conducting silver, but silver cables are too expensive and therefore are used only in isolated cases. But the idea of building superconducting power lines from expensive rare-earth ceramics that require cooling with liquid nitrogen has been approached in practice several times in recent years. In particular, such a cable has already been laid and connected in the German city of Essen. It is designed for 40 megawatts of electrical power at a voltage of ten kilovolts. In addition to the fact that heating losses are reduced to zero (however, in return it is necessary to power cryogenic installations), such a cable is much more compact than usual and due to this you can save on the purchase of expensive land in the city center or refuse to lay additional tunnels.

Not according to general rules

Many people remember from school courses that efficiency cannot exceed 100% and that the greater the temperature difference between the refrigerator and the heater, the higher it is. However, this is true only for the so-called heat engines: steam engine, internal combustion engine, jet and rocket engines, gas and steam turbines.

Electric motors and all electrical devices do not obey this rule, since they are not heat engines. For them, the only thing that is true is that the efficiency cannot exceed one hundred percent, and particular restrictions in each case are determined differently.

In the case of a solar battery, losses are determined both by quantum effects during the absorption of photons, and by losses due to the reflection of light from the surface of the battery and to absorption in the focusing mirrors. The calculations showed that in principle a solar battery cannot go beyond 90%, but in practice values of about 60-70% are achievable, and even those with a very complex structure of photocells.

Fuel cells have excellent efficiency. These devices receive certain substances that react chemically with each other and produce an electric current. This process, again, is not a cycle of a heat engine, so the efficiency is quite high, about 60%, while a diesel or gasoline engine usually does not go beyond 50%.

It was the fuel cells that were installed on the Apollo spacecraft that flew to the Moon, and they can run, for example, on hydrogen and oxygen. Their only drawback is that the hydrogen must be quite pure and, moreover, it must be stored somewhere and somehow transferred from the plant to consumers. Technologies that make it possible to replace ordinary methane with hydrogen have not yet been brought to mass use. Only experimental cars and a few submarines run on hydrogen and fuel cells.

Comparison of efficiency of heat engines - gasoline and diesel

If we compare the useful power, we immediately note that the gasoline one is not as efficient. Its value is only 25-30%, while for diesel it is -40%.

Despite the similarity of the units, they have different types of mixture formation.

In a gasoline engine, the pistons operate at higher temperatures, which requires good cooling. Therefore, thermal energy that could be transformed into mechanical energy is wasted, thereby reducing efficiency.
In a diesel engine, the working mixture ignites during compression, so the pressure in the cylinders is much higher.
In addition, the motor is much smaller and more environmentally friendly. At low speeds and large displacement, efficiency levels can increase to 50%.

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Is efficiency above 100% possible?

It's no secret that electric motors whose efficiency exceeds 100% cannot exist in nature, since this contradicts the basic law of conservation of energy. The fact is that energy cannot come from nowhere and disappear in the same way. Any engine needs an energy source: gasoline, electricity. However, gasoline does not last forever, just like electricity, because their reserves have to be replenished. But if there was an energy source that did not need replenishment, then it would be quite possible to create a motor with an efficiency of over 100%. Russian inventor Vladimir Chernyshov showed a description of a motor that is based on a permanent magnet, and its efficiency, as the inventor himself assures, is more than 100%.

Formula for working in physics

For mechanical work, the formula is simple: A = F x S. If deciphered, it is equal to the applied force along the path along which this force acted. For example, we lift a load weighing 15 kg to a height of 2 meters. The mechanical work to overcome the force of gravity will be equal to F x S = mxgx S. That is, 15 x 9.8 x 2 = 294 J. If we are talking about the amount of heat, then A in this case is equal to the change in the amount of heat. For example, water was heated on the stove. Its internal energy has changed, it has increased by an amount equal to the product of the mass of water and the specific heat capacity by the number of degrees by which it has heated up.

Solving Examples

Problem 1. A train at a speed of 54 km/h develops a power of 720 kW. It is necessary to calculate the traction force of power units. Solution: To find the power, use the formula N=F x v. If you convert the speed to SI units, you get 15 m/s. Substituting the data into the equation, it is determined that F is equal to 48 kN.

Problem 2. The mass of the vehicle corresponds to 2200 kg. A car, going uphill at a slope of 0.018, covers a distance of 100 m. The speed reaches 32.4 km/h, and the friction coefficient corresponds to 0.04. It is necessary to determine the average power of the car when driving. Solution: the average speed is calculated - v/2. To determine the traction force of the motor, a drawing is made that displays the forces acting on the machine:

severity - mg;
ground reaction - N;
friction - Ftr;
thrust - F.

The first quantity is calculated according to Newton's second law: mg+N+Ftr+F=ma. For acceleration, the equation a=v2/2S is used. If you substitute the last values and use cos, you get the average power. Since the acceleration is considered constant and equal to 9.8 m/s2, therefore v= 9 m/s. Substituting the data into the first formula, you get: N= 9.5 kBt.

When solving complex problems in physics, it is recommended to check the compliance of the units of measurement provided in the conditions with international standards. If they differ, it is necessary to translate the data taking into account the SI.

Physics Pressure formula - examples and calculation conditions

PhysicsAbsolutely elastic and inelastic impact of two bodies - formulas and examples of calculations

Asynchronous motor and stirling

Today, asynchronous machines are presented on the market, most of which are electric. An asynchronous mechanism converts electrical energy into mechanical energy.

Their main advantages:

ease of manufacture and relatively low cost;
high reliability;
operating costs are low.

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The efficiency formula is calculated as follows: η = P2 / P1 = (P1 - (Pob - Ps - Pmx - Pd)) / P1, where Rob = Pob1 + Rob2 - the total losses in the windings of an asynchronous motor. For most modern mechanisms of this type, the coefficient reaches 80 - 90%.

Another internal combustion engine that can be powered by any heat source is the Stirling engine.

It should be noted that such mechanisms are used on spacecraft and modern submarines.

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It operates at any temperature, does not require additional systems to start, and their efficiency is 50-70 higher than that of conventional engines.

Electric motor efficiency and power

Efficiency and power are what you should first pay attention to when choosing an AIR asynchronous electric motor. The essence of the operation of any electric engine is that electrical energy, with accompanying losses, is converted into mechanical energy. The lower the losses during this process, the higher its efficiency and the more efficient the electric motor. But, despite the importance of efficiency, do not forget about the power of the motor. After all, even with extremely high efficiency and the power it produces, it may not be enough to solve the problems you need. Therefore, when purchasing, it is very important to know not only what the efficiency of the electric motor is, but also what useful power it can produce on its shaft. Both of these values must be specified by the manufacturer. Sometimes it happens that you don’t have access to the motor’s passport (for example, if you buy it secondhand, which is highly not recommended) and you have to independently calculate such important parameters. First, it’s worth defining what the coefficient of performance, or simply efficiency, is. And so, this is the ratio of useful work to energy expended.

Determination of electric motor efficiency

It turns out that in order to determine this parameter it is necessary to compare the energy it produces with the energy it needs to function. The efficiency is calculated using the expression:

η=P2/P1 where η is efficiency

P2 – useful mechanical power of the electric motor, W P1 – electrical power consumed by the motor, W;

Efficiency is a value ranging from 0 to 1; the closer its value is to unity, the better. Accordingly, if the efficiency has a value of 0.95, this shows that 95 percent of electrical energy will be converted into mechanical energy and only 5 percent will be losses. It is worth noting that efficiency is not a constant value, it can vary depending on the load, and it reaches its maximum at loads around 80 percent of the rated power, that is, that stated by the motor manufacturer. Modern asynchronous electric motors have a nominal efficiency (declared by the manufacturer) of 0.75 - 0.95. Losses during engine operation are mainly caused by heating of the motor (part of the consumed energy is released in the form of thermal energy), reactive currents, bearing friction and other negative factors. Motor power refers to the mechanical power that it produces on its shaft. In general, power is a parameter that shows how much work a mechanism does in a certain unit of time.

The efficiency of an electric motor is a very important parameter that determines, first of all, the efficiency of using the energy resources of an enterprise . As you know, the efficiency of an electric motor decreases significantly after its repair; we wrote about this in this article. As the efficiency decreases, electricity losses will correspondingly increase. Recently, energy-efficient electric motors from different manufacturers have been gaining popularity; in Russia, motors produced by Vladimir Electric Motor Plant OJSC are popular. Any asynchronous electric motors are presented in the product catalog. You can find additional useful information in the catalog of articles.

CHAPTER 3. ACTUAL CYCLES, POWER, EFFICIENCY OF INTERNAL COMBUSTION ENGINES

Home / Publications / Literature / Bookshelf / A. Agatov. Outboard motors

Four-stroke engine.
We constructed theoretical indicator diagrams without taking into account the losses that always occur during engine operation. So, for example, during suction, the carburetor, suction valve and suction pipe exert hydraulic resistance to the movement of gases, and the greater the gas speed in the suction system, the greater the resistance. For this reason, the actual suction pressure is always lower than atmospheric pressure and depends on the length and flow area of the pipe, the smoothness of the transitions, the precision of the manufacture of valves and valve seats, the resistance in the carburetor and the streamlined shape of the parts encountered along the flow path. This is taken into account by the dotted curve a1;b1;
in the diagram fig. 11, i.e. the charge enters the cylinder of reduced density. The heating of the mixture from hot parts also contributes to a decrease in its density.

Thus, the weight amount of charge in the cylinder is reduced, which is taken into account by the filling factor

ηv. The filling factor shows how much, by weight, of fresh charge filled the cylinder compared to what could have been contained if the temperature and pressure of the charge had been equal to atmospheric conditions.

For modern high-speed light engines, the filling coefficient at full throttle opening is in the range of 0.8-0.9, i.e. the engine cylinder is filled only to 80-90% of its full volume under normal conditions (1).

ηv is affected to a certain extent by excess fuel, which lowers the suction temperature and. combustion, and with them the temperature of the cylinder, piston and head.

A mixture containing more fuel than required for a normal mixture is called rich. However, working with a rich mixture is uneconomical, since part of the fuel does not burn completely due to lack of air and goes out with exhaust gases in the form of soot, and partly carbon monoxide CO.

The type of fuel also affects. Each type of fuel has its own latent heat of vaporization, which determines the temperature and amount of the mixture sucked in. For example, the use of alcohol as fuel increases ηv by 5-10% compared to gasoline.

Since the amount of released thermal energy, and therefore the engine power, is directly dependent on the weight charge of the cylinder, the driver’s task is to use all factors that contribute to an increase in ηv.

Let's consider the influence of valve timing on cylinder filling.

In high-speed engines, when the cycles follow each other very quickly, the intake mixture moves through the pipeline at a speed of approximately 100 m/sec. With the closing of the intake valve, due to the inertia of the moving gases, by the beginning of the intake of the next cycle, a certain pressure (compression) of the mixture is formed in front of the valve, exceeding atmospheric pressure. At this moment, the intake valve begins to open again and the pressurized mixture rushes into the cylinder with force; This way you can get better filling of the cylinder. Therefore, most often, depending on the speed of the engine, the intake start is advanced from 8 to 40°, and in racing cars it is brought up to 75° and higher. This intake advance is usually established experimentally. The intake valve is also closed not at BDC, as in the theoretical cycle, but later, at approximately 45-70°, giving more time to fill the cylinder. In this way, the filling period is extended from 220 to 290° along the crankshaft rotation instead of 180° of the theoretical cycle, which increases the filling coefficient ηv.

The next factor influencing the filling of the cylinder is the residual gases from the previous cycle. In four-stroke engines, burnt gases are partially retained in the so-called harmful space, i.e. in the compression chamber Vc.

Since the compression stroke follows directly after the suction stroke, the compression of the mixture actually begins not at BDC, but with a delay equal to the end of the exhaust, which results in some loss of part of the stroke. In addition, during the compression stroke we have additional heat loss both for heating the cylinder wall and head, and the piston bottom, which is reflected by a decrease in compression pressure (dashed curve ac1; in the diagram in Fig. 11).

Compressing the mixture is necessary in order to speed up the process of its combustion and obtain greater pressure on the piston both during the flash and during the working stroke. Increasing operating pressure increases engine power. The higher the compression ratio in the engine, the greater its power, the lower the specific fuel consumption, i.e. consumption per 1 liter. With. h., the higher the thermal efficiency of the engine. However, increasing the compression ratio is only possible up to a certain limit, depending mainly on the auto-ignition temperature of the working mixture and on the occurrence of detonation (2) in the engine. Both self-ignition and detonation are undesirable: they disrupt the normal operation of the engine. In modern high-speed engines, the compression ratio usually reaches 5-8, and the compression end pressure is about 7.5-11 kg/cm². In this case, the temperature reaches 270-350°.

The combustion of the mixture does not actually occur instantly, but requires from 1/300 to 1/600 of a second, so the mixture is ignited with some advance c1.

During expansion, due to the large temperature difference between the wall and the gases, some of the heat is lost into the walls and the pressure decreases. All pressure transitions from the compression stroke to the expansion stroke occur smoothly, without sharp peaks and depend entirely on the amount of ignition timing (Fig. 11, dotted curve c1c2z1e1).

The amount of pressure reduction during the expansion stroke depends on the intensity of cooling of the cylinder walls, its diameter and the number of revolutions; The higher the speed and the larger the cylinder diameter, the higher the expansion pressure line on the indicator diagram. Not reaching approximately 50-70° to BDC during expansion, in order to better clean the cylinder, the exhaust is advanced: the exhaust valve opens, exhaust gases flow out of the cylinder at a critical speed (the speed of sound) and the pressure drops sharply, which is shown in the diagram by line e1a1.

The release of exhaust gases always occurs at an increased pressure of the order of 1.1-1.2 cm², and the temperature of the gases at the end of the release reaches approximately 500-600°. Closing the exhaust valve to better clean the cylinder from burnt gases is also done not at TDC, as in the theoretical cycle, but much later. For high-speed engines, the release delay is increased to 30-40°, and for racing engines to 55° and higher. It is useful to note here that near TDC, the intake valve and exhaust valve are open for some time at the same time, since the intake valve opens before TDC, and the exhaust valve closes after TDC. This overlap often reaches 60° in engines, reaching 100-120° in racing engines.

Similar diagrams can be obtained directly from a running engine using a device called an indicator.

This is where these charts got their name
indicator
.

Indicator diagrams characterize the operation of the piston during one engine cycle, where the ordinate axis shows the pressure in the cylinder in kilograms per square centimeter, and the abscissa axis shows the volumes in cubic centimeters on a certain scale. By measuring the area of the diagram using some method and multiplying it by the scale taken to depict it, we obtain the engine operation in one cycle.

Most often, the area of the diagram is reduced to an equal-sized rectangle, the base of which is equal to the stroke of the piston on the scale we choose, and the height is equal to the average pressure during the stroke of the piston (line cl). This pressure is called the average indicator pressure

and is of great importance when calculating the indicated engine power and when comparing different engines with each other.

Two-stroke engine. The actual indicator diagram of a two-stroke engine, like the indicator diagram of a four-stroke engine, also differs greatly from the theoretical one due to the advance of ignition of the mixture in the cylinder, hydraulic losses in windows and pipelines, heat leakage into the cylinder walls and purge losses during expansion and compression (see Fig. 15).

At the end of the compression stroke, to obtain the working stroke of the piston, as already mentioned, it is necessary to ignite the mixture. Fuel combustion does not occur instantly, but requires, albeit a very short (about 1/zoo fraction of a second), time, during which the piston will have time to advance approximately 8-9% of its working stroke. This leads to a strong decrease in both the maximum and average pressure along the piston, i.e., to a loss of engine power and incomplete combustion of the mixture.

In order to better use the heat contained in the fuel, it is necessary to give more time for its combustion, and for this the mixture is ignited much earlier than the piston reaches TDC, or, as they say, with some advance, the greater the faster the engine (line c2c3).

It is also undesirable to do very early ignition, as the engine becomes rough (hard running). Shocks appear, the torque on the shaft becomes uneven, and sometimes this even causes the crankshaft to turn back and stop the engine.

Ignition is carried out in such a way as to obtain maximum pressure 10-20° after TDC. To achieve this, ignition timing in high-speed engines is usually set within 30-45° before TDC. The operating diagram is more advanced and the power is greater than when the mixture is ignited at TDC.

In practice, ignition advance is carried out either by hand, by turning a special lever, or using an automatic regulator installed on the magneto and increasing! ignition advance with increasing engine speed. Such regulators are installed on our latest domestic designs of outboard motors LMM-6 and LMR-6.

One of the significant losses that distorts the theoretical diagram is the loss on the stroke of the piston due to the presence of purge and exhaust ports.

Since in two-stroke engines the cleaning of the cylinders from burnt gases and filling them with a fresh mixture occurs through the corresponding windows, then from the beginning of the opening of the latter until the moment of closing, the pressure in the cylinder is established close to atmospheric and the compression process does not begin immediately after BDC, but only from the moment the windows are closed ; the same thing and the working stroke ends not at BDC, as we considered in the ideal cycle, but earlier, from the moment they begin to open. Thus, over the height of the windows, there is a loss of working stroke. The height of these windows takes about 10-15% of the piston stroke.

The duration of opening of each row of windows is obviously determined by its height: the higher the window, the longer the path traversed by the piston along the window, and therefore the longer the period of time the window remains open. The time, or period, of a particular process, expressed in degrees of rotation of the crankshaft, is called the process phase

, or
valve timing
. Valve timing is usually represented by pie charts. This kind of diagram for the LMR-6 motor is shown in Fig. 16.

From Fig. 16a it can be seen that when the piston moves upward, the purge windows close first, while the exhaust windows are still open and the release of gases continues, as a result of which part of the sucked mixture flies out. This reduces the filling factor ?v and reduces engine power. The increase in engine filling is greatly influenced by the suction process. A significantly better filling of the crankcase with the mixture is obtained with spool distribution, when suction can begin immediately after closing the purge windows, and the mixture is pressurized immediately after the piston passes TDC, as shown in the diagram (Fig. 16.6), and occurs throughout the rest of the piston stroke, until new opening of purge windows.

In Fig. 17 shows a number of designs for spool valve intake control. The disc spool is a disc with a through window for air intake. With its polished side, it is constantly pressed by means of a weak spring against the end of one of the side walls of the crankcase, on which the suction window is cut. When the spool rotates, its window runs into the crankcase window, periodically communicating the latter with the atmosphere.

Rice. 16. Circular diagrams of gas distribution with piston and spool inlet of the mixture: a - piston distribution; b - spool distribution

Sometimes spools are made in the form of a hollow drum with a window on a cylindrical surface. Cylindrical spools for free rotation are made with some clearance. During compression, the mixture will partially flow through the gap into the crankcase; cylindrical spools are used only on high-speed engines, where the influence of the clearance is negligible.

Hydraulic losses and pressure drop throughout the power stroke remain approximately the same as for a four-stroke engine.

The sum of all the listed losses in the indicator diagram of a two-stroke engine is approximately 8-10% of the theoretical cycle diagram, and therefore, to determine the operation of the cycle, you can use the latter, reducing it by the specified percentage.

You can determine the area of the diagram either using a special device (planimeter), or by drawing it on graph paper and counting the number of millimeters contained inside the diagram. The area is multiplied by the scale of the diagram to obtain the actual work done by the cylinder in one cycle.

The duration of individual phases according to the angle of rotation of the crankshaft in modern two-stroke outboard engines varies within the following range: for suction ports 100–115°, for vent ports 86–115°, for exhaust ports 110–135°.

Making a summary of all the phenomena in the cylinder of a two-stroke engine for a full cycle, we get the following picture: 1st stroke - piston stroke to TDC:

above the piston compression of the mixture / below the piston suction of the mixture.

Rice. 17. Designs of spools for inlet of the working mixture into the crankcase: a - disk spool; b - cylindrical spool of a two-cylinder engine; c - cylindrical spool driven from a gear connected to the crankshaft; g - cylindrical spool of a four-cylinder engine

2nd stroke - piston stroke to BDC:

above the piston combustion and expansion / below the piston compression of the mixture

The cleanliness of the charge in two-stroke engines depends on the quality of the purge. The amount of exhaust gases after purging varies within very wide limits: from 3% for two-stroke engines with direct-flow purging in the presence of excess air or mixture during purging and reaches 40-50% with chamber purging.

Engine power and efficiency. From mechanics it is known that power is work done per unit of time. Work for one full cycle is expressed by the product of the average indicator pressure pi and the working volume of the cylinder.

Knowing the engine speed per minute and the average indicator pressure, it is easy to calculate its power using the formulas:

The resulting power is called
engine indicated power
. It gives an idea of the gas work transferred to the piston.

From the above formulas it is clear that the indicator power increases:

1) with increasing engine displacement Vs;

2) with increasing engine crankshaft speed n;

3) with an increase in the average indicator pressure pi;

4) with increasing number of cylinders i.

The indicator power cannot be fully used for useful work due to existing losses in the engine itself, or the so-called “mechanical losses”, which are taken into account by the mechanical efficiency factor. The power we can actually have on the crankshaft is called "effective power".

Thus, the mechanical efficiency is understood as the ratio of the effective engine power, i.e., the power actually received on the engine shaft Ne to the indicator power, i.e., the power transmitted by the gases to the engine piston Ni:

Since at different speeds ηm is not the same, it is customary to attribute to the engine only ηm obtained at the maximum achievable power Nemaks

Mechanical losses in the engine can be divided into three main types:

1. For friction losses of all moving parts of the engine: piston, piston rings, bearings. The magnitude of this type of loss is the largest and mainly depends on: a) the condition of the surfaces of the rubbing parts, b) the pressure between them and c) the nature and quality of the lubricant and is equal to approximately 55-65% of the total amount of mechanical losses.

2. Losses when actuating auxiliary mechanisms (magneto, pumps) usually fall from 6 to 18% of the total losses.

3. Losses when filling the cylinder with fresh mixture and cleaning it from exhaust gases, the so-called “hydraulic” or “pumping losses”, account for everything else. The latter losses are made up of resistance in the suction pipe, in the carburetor and in the intake windows. This includes the friction of gases on the rough surface of the channels.

Typically, mechanical losses, based on practical data, are taken equal to 10-25% of the indicated power, i.e., only 90-75% of the power transmitted by the gases to the engine pistons can be supplied to the propeller.

Effective power, like indicator power, can be expressed by the corresponding formulas:

the Pef value included in the effective power formula is called
the average effective pressure
(by analogy with the average indicator pressure). It actually cannot be measured on the engine and is conditional. It is obtained by calculating from the power formula if the engine displacement, speed and power developed by the engine on the propeller shaft are known. When the engine is built, the effective power, and therefore the average effective pressure, is determined by testing the motor or its engine on a brake machine, where the torque developed by the engine is usually measured, and the effective power is determined from the torque using the formula where Mk is expressed in kgm, and the effective the pressure is already obtained from the previously given power formulas in kilograms per square centimeter. Mean effective pressure is an important quantity and is often used when comparing different engines with each other.

For two-stroke engines of conventional outboard motors, the average effective pressure at maximum power ranges from 4 to 6 kg/cm² and for sports and racing engines - from 7 to 12 kg/cm².

As the speed increases, mechanical losses increase greatly, requiring the expenditure of useful energy, and the charge of the cylinder decreases. Losses do not increase in direct proportion to the engine speed, but with some excess and, finally, reach the value of the increase in power; this corresponds to maximum power, after which, with a further increase in the speed, the engine power begins to decrease.

Rice. 18. Typical graph of the external characteristics of the engine: Ni and Ne - power; Mk - torque; Ce - specific fuel consumption per 1 liter. With. h.; ηm - mechanical efficiency of the engine

Diagrams showing the change in effective power depending on the number of revolutions at full throttle are called
engine characteristics .
Often the same graph shows fuel consumption curves, changes in pt versus speed, changes in torque Mk, mechanical efficiency ηm, specific fuel consumption Ce and other data characterizing the engine. Such a diagram is shown in Fig. 18.

If the effective engine power is divided by the total engine displacement, expressed in liters, then we get the so-called liter power, i.e. power per liter of engine displacement.

Liter power characterizes the complete use of the volume of all engine cylinders.

For racing engines currently, liter power reaches 60-70 hp. s, and in some cases it can be much more.

Two-stroke engines, being inferior in efficiency to four-stroke engines, have, in turn, such advantages as the absence of valves and a distribution mechanism, increased liter power, ease of design and maintenance, lower specific weight and low cost of the engine to manufacture. The simpler the engine, the fewer reasons for its malfunction, the more reliable it is. Here it is necessary to note another important advantage of two-stroke engines: greater uniformity of torque, since in four-stroke engines, due to the inertia of the flywheel, three strokes are carried out, and in a two-stroke engine only one. Therefore, to establish torque uniformity, significantly lighter flywheels are required, which further reduces the overall weight of the two-stroke engine by about 10-20% or even more.

(1) Normal atmospheric conditions are defined as an atmospheric pressure of 1 kg/cm² and a temperature of +15°.

(2) For detonation, see Chapter 6.

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Maximum efficiency value of an ideal engine

How to find the efficiency of an engine whose value would be ideal and equal to 100%. Is this possible? The answer to this question was given back in 1824 by engineer S. Carnot. In his developments, he came up with an ideal machine, where the formula for the efficiency of a heat engine looks like this: η = (T1 - T2)/ T1.

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As a result, it was found that a 100% coefficient can be achieved only if the cooler temperature is equal to absolute zero, and this is impossible, since it cannot be lower than the air temperature.

Interpretation of the concept

The electric motor and other mechanisms perform certain work, which is called useful. The device, while functioning, partially wastes energy. To determine the operating efficiency, the formula ɳ = A1/A2×100% is used, where:

A1 - useful work performed by a machine or motor;
A2 - general work cycle;
η - designation of efficiency.

The indicator is measured as a percentage. To find the coefficient in mathematics, the following formula is used: η = A/Q, where A is energy or useful work, and Q is the energy expended. To express the value as a percentage, efficiency is multiplied by 100%. The action has no meaningful meaning, since 100% = 1. For a current source, the efficiency is less than one.

In high school, students solve problems in which they need to find the efficiency of heat engines. The concept is interpreted as follows: the ratio of the work performed by the power unit to the energy received from the heater. The calculation is made using the following formula: η= (Q1-Q2)/Q1, where:

Q1 is the heat received from the heating element;
Q2 is the heat transferred to the refrigeration unit.

The maximum value of the indicator is typical for a cyclic machine. It operates at the specified temperatures of the heating element (T1) and refrigerator (T2). The measurement is carried out according to the formula: η= (T1-T2)/T1. To find out the efficiency of a boiler that operates on organic fuel, the lower calorific value is used.

The advantage of a heat pump as a heating device is the ability to receive more energy than it can spend on operation. The transformation index is calculated by dividing the heat of condensation by the work required to complete the process.

Power and torque

When the displacement figures are the same, the power of a naturally aspirated petrol engine is higher, but is only achieved at higher speeds. The unit needs to be “twisted” more strongly, while losses increase, and fuel consumption increases accordingly. In addition, it is worth mentioning torque, under the influence of which the force that is transmitted from the engine to the wheels increases and contributes to the movement of the car. Gasoline engines reach their maximum torque level only at high speeds.

An atmospheric diesel engine with the same parameters reaches peak torque only at low speeds. This contributes to less fuel consumption required to perform work, resulting in higher efficiency and more economical fuel consumption.

Compared to gasoline, diesel fuel generates more heat, since the combustion temperature of diesel fuel is much higher, which contributes to higher detonation resistance. It turns out that a diesel engine has much more useful work done on a specific amount of fuel.

The most common malfunctions of the diesel engine fuel system

Among the most common breakdowns in the diesel power system, the most common are the following:

Difficulty starting the engine.
Reduced power indicators.
Increased fuel consumption.
The appearance of smoke of various shades coming out of the exhaust pipe.
Increased work rigidity.
Inability to accelerate (in case of failures in acceleration, it is recommended to increase the accelerator pedal travel).
Unstability of idle speed (floating).
The engine stalls frequently.

Difficult start

To make it easier to start diesel engines in winter, manufacturers produce a special fuel called “Arctic”. However, the cause of difficult switching on is not always frozen diesel fuel. If it is impossible to start the diesel engine when cold, you need to check:

quality of operation of high pressure pump discharge parts;
degree of wear of injectors;
adjusting the fuel advance angle;
pre-start glow plugs;
pressure regulator;
leakage of fuel lines.

Power reduction

The power of a diesel engine decreases when malfunctions occur, fuel filters, or spray nozzle openings are clogged. When the filter elements fail, the amount of diesel fuel sent to the fuel pump is sharply reduced, which negatively affects the power performance of the engine.

Increased diesel fuel consumption

An incorrectly set injection timing is the main reason for high fuel consumption. The amount of fuel consumed is also affected by improper operation of the fuel injection pump. It is necessary to adjust the pressure level of the mixture at the time of injection. Reduced compression in the working cylinders can also cause increased diesel fuel consumption.

Exhaust black

If dark smoke appears from the exhaust system, it is recommended to check the quality of mixture formation. Violations can be caused by delayed injection of fuel, which does not have time to burn completely and settles on the cylinder walls in the form of soot. Layers of carbon also often form on valves that do not close tightly.

The appearance of white smoke in the form of steam does not cause alarm, because it quickly evaporates after the engine warms up. This can be observed especially often in diesel vehicles operating in areas of northern latitude.

Floating crankshaft speed in idle mode

For this defect you need:

replace the sealing elements located under the nozzles;
tighten the fuel wire connecting the filter to the injection pump;
check the condition of the pump support plate;
replace the crankshaft speed controller;
check the operation of the ventilation system to eliminate gas pressure.

The engine stalls

If the motor often stops working while driving, you will need to check the following points:

correct lead angle;
quality of connections at the pump connection points;
degree of filter contamination;
displacement and distortion of high-pressure pump elements.

This is interesting

Science has proven that the efficiency of any mechanism is always less than one. This is due to the second law of thermodynamics.

For comparison, the efficiencies of various devices:

hydroelectric power stations 93-95%;
NPP – no more than 35%;
thermal power plants – 25-40%;
gasoline engine - about 20%;
diesel engine - about 40%;
electric kettle – more than 95%;
electric vehicle – 88-95%.

Science and engineering do not stand still. Ways are constantly being invented to reduce heat loss, reduce friction between parts of the unit, and increase the energy efficiency of equipment.

Summary

In the production of modern internal combustion engines, manufacturing plants invest heavily in the pursuit of increasing the efficiency of their products by at least a few percent. To this end, engineers are improving and complicating motor designs and using new materials to manufacture individual elements.

Sometimes it happens that the financial costs of developers are inappropriate, in comparison with the obtained result of 2 - 3%. Therefore, it may be more profitable to subject standard engines to various boosts, fine-tuning, and modifications using tuning improvements in small repair shops. As a result, the power and other traction characteristics of power units increase.

Coefficient of performance (COP) is a widely used characteristic of the efficiency of some system or device. In our case, this system is the internal combustion engine. It would seem, what kind of efficiency can we talk about in the world of modern engines? Isn’t it equal to 100 percent? But it turns out that just as there is no ideal black or white in our world, there is no car in which all the energy received from burning fuel is completely converted into mechanical energy, and the latter, in turn, into useful energy that presses the driver of the car into his seat.

What does the efficiency depend on?

This value depends on how much total perfect work can turn into useful work. First of all, it depends on the design of the mechanism or machine itself. Engineers all over the world are struggling to increase the efficiency of machines. For example, for electric vehicles the coefficient is very high - more than 90%.

But an internal combustion engine, due to its design, cannot have η close to 100 percent. After all, fuel energy does not act directly on the rotating wheels. Energy is dissipated at each transmission link. Too many transmission links, and some of the exhaust gases still exit into the exhaust pipe.

About diesel fuel efficiency

FROM a higher efficiency value, fuel efficiency follows. So, for example, a 1.6-liter engine can consume only 3–5 liters in the city, in contrast to the gasoline type, where the consumption is 7–12 liters. A diesel engine has much more torque, the engine itself is often more compact and lighter, and, recently, also more environmentally friendly. All these positive aspects are achieved thanks to a higher compression ratio; there is a direct relationship between efficiency and compression, see the small plate.

However, despite all the advantages, it also has many disadvantages.

As it becomes clear, the efficiency of an internal combustion engine is far from ideal, so the future clearly belongs to electric options - all that remains is to find efficient batteries that are not afraid of frost and hold a charge for a long time.

Read more: Replacing the window lifter mechanism of a VAZ 2107

I’ll finish here, read our AUTOBLOG.

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Surely, many car enthusiasts have wondered how the power of an internal combustion engine corresponds to its utility. It is assumed that the higher the efficiency of a power system, the more efficient it is. Speaking in absolute terms, today the highest coefficient is for electric motors; in some models it reaches about 95 percent. As for internal combustion engines, for most of them, regardless of the type of fuel, this figure is very far from ideal figures.

Internal combustion engine efficiency

Of course, modern engines are much more efficient than those that were developed and released ten years ago, this is due to objective reasons for the development of technology. At the beginning of the 2000s, a one and a half liter engine produced an average of about seventy horsepower, and this was normal. Today, the number of heads in a herd of the same volume can reach more than 150. Every little step in terms of increasing the engine power factor is given to manufacturers through painstaking work and trial, error and success.

Safety

This is rarely mentioned when talking about gasoline or diesel. The pros and cons are worth considering in more detail, since the topic is important. So, diesel fuel is, so to speak, a slightly volatile substance. And this fuel will not ignite from a spark. Many people joke that you can even extinguish matches with it (of course, this statement is not worth checking). And the fact that this fuel requires incredibly high temperatures to ignite makes it safer.

Unlike gasoline! It is a highly flammable substance and also volatile. By the way, it is not the fuel that ignites, but only its vapor. If fuel is poured into the tank, and it, in turn, is tightly closed, then 80% of it has been protected from fire. In general, it is not the safest fuel. Everyone knows cases when serious accidents occurred, cars overturned, crashed, and the survivors tried to get out of there as quickly as possible. Why? And because in such cases the tank is usually damaged, the parts overheat. It is possible that a spark will occur and the car will simply explode. In this regard, diesel is safer. The pros and cons in this case are clearly laid out.

Thermal Cycle Analysis

The thermal cycle includes four thermodynamic basic processes. First, the state of the working fluid is transformed, and then it returns to its original state: compression, heat generation, expansion and heat removal.

Each of these processes is carried out according to the following scheme, which determines the conditions for the implementation of the cycle:

Isothermal - work is performed at a constant temperature.
Isobaric - the operating cycle is implemented at constant pressure.
Isometric - the thermal process occurs at a constant volume
Adiabatic - the cycle is carried out at constant entropy.

In order for the process to be as close to reversible as possible, there are two ways to move the piston: isothermal - this means that heat gradually enters or leaves the reservoir at a temperature infinitely different from the temperature of the gas in the piston, and adiabatic, in which no heat exchange occurs at all, the gas acts like a spring.

Thus, when heat is added and the gas expands, the temperature of the gas must remain the same as that of the heat source, with the gas expanding isothermally. Likewise, it will later be compressed in the cycle isothermally, releasing heat.

To find out efficiency, you need to follow the engine through its entire cycle, find out how long it runs, how much heat is taken from the fuel, and how much energy is lost in preparation for the next cycle.

The thermal cycle characteristics associated with a heat engine are typically described using two state diagrams : a PV diagram showing the pressure-volume relationship and a TS diagram showing the temperature-entropy pair.

For a constant mass of gas, the operation of a heat engine is a repeating cycle, and its PV diagram will look like a closed figure.

Friction

An engine has many moving parts that create friction. Some of these frictional forces remain constant (as long as the applied load is constant); Some of these friction losses increase with engine speed, such as piston forces and connecting bearing forces (due to increased inertial forces from the swinging piston). Some frictional forces are reduced at higher speed, such as the frictional force on the cam lobes, used to actuate the intake and exhaust valves (the inertia of the valves at high speed tends to pull the cam follower away from the cam lobe). In addition to friction forces, a running engine has pumping losses

, which represent the work required to move air in and out of the cylinders. These pumping losses are minimal at low speed, but increase approximately as the square of the speed until, at rated power, the engine uses about 20% of the total power produced to overcome friction and pumping losses.

Types of power systems

The carburetor option involves mixing air and gasoline in the inlet pipe of the carburetor. Recently, the production of such engine options has been significantly reduced due to the insignificant efficiency of such engines and their inconsistency with modern environmental standards.

In injection engine versions, fuel is supplied using one injector (nozzle) into the central pipeline.

In the case of distributor injection, fuel enters the engine through several injectors. In this case, the maximum power increases, which significantly increases the efficiency of the diesel engine.

At the same time, gasoline consumption and toxicity of processed gases are reduced due to a fixed fuel dosage by electronic control systems of the automobile engine.

When discussing the efficiency of a modern diesel engine, you need to know about the injection system of the gasoline mixture into the storage chamber. If fuel is supplied in portions, this guarantees that the engine runs on lean mixtures, which helps reduce fuel consumption and reduce the emission of harmful gases into the atmosphere.

Next, I present to your attention the WOT efficiency calculator

so that you can have an idea of which category you belong to:

W.G.R.

WN8

WN6

EFF

xTE

Let's start in order:

WGR is the official rating from Wargaming, a four-digit rating.

Probably the most difficult in terms of pumping up statistics. Here the greatest influence on the efficiency result is exerted by:

Average damage per battle

Average damage due to radio exposure

Average damage due to holding on gusle (it doesn't matter if you deal damage or allies)

————————

wn8 - WN8 rating is more advanced player statistics (reference statistics), in its original form it is four-digit.

The greatest influence on the result is exerted by:

Total player damage dealt

Total number of destroyed

It should be noted here that these statistics are highly dependent on the machine you are playing on, since reference statistics use reference readings for calculations. Roughly speaking, the standard damage of the ISU-152 will be 700. So, if you are playing on this tank destroyer, then you must knock out this same 700 damage from a shot, targeting the enemy’s weak spots or punching into the side and stern. In other words, the closer your damage is to the standard, the higher your statistics. (Note: the number 700 was taken out of thin air...)

————————

wn6 - four-digit efficiency, taken from behind the scenes and developed by American players. Here you will have to work hard to increase this efficiency. The wn6 formula is very large and complex, but we agreed that I will not burden you with formulas, so I will convey the main points. The main thing to remember here is:

base defense points do not greatly affect efficiency;

The first exposure of the enemy also has virtually no effect on efficiency;

Capturing a base is not taken into account at all;

Destroying low-level tanks has less impact on the rating, so choose a tank a couple of levels higher than you and bite;

It turns out that WN6 completely depends on your contribution to the battle

And special attention is paid to the total damage dealt to the player and the total number of tanks destroyed (this takes into account the strength of the enemy you destroyed)

To increase this rating, I would advise you to deal more damage and “take out” more enemy equipment. But not all tanks in the game can do this. For example, self-propelled guns, tank destroyers (top-end and pre-top, as well as French drum tanks). They have the highest damage per minute. The minimum damage per battle for you should be numbers above 1500-2000.

————————

EFF is the good old Efficiency Rating, also known as ER.

For those who are new to the tank, here the greatest influence on the result is exerted by:

Average damage per battle;

Average number of frags (killed opponents) per battle;

Average number of base defense points per battle;

Those. in other words, to increase this efficiency you need to destroy, kill, and also have time to defend your own base! Go for it

————————

xTE is a rating that evaluates your ability to play on a specific tank compared to all other players on that particular tank.

Here, just like in RE, the main thing will be:

Average damage per battle;

Average number of frags per battle;

WOT efficiency

Causes of brake pedal failure

A sharp drop in the level of brake fluid in the vehicle reservoir. In addition, the quality of the brake fluid used has a fairly large influence on the functioning of the brake pedal. Counterfeit brake fluid initiates swelling of brake hoses, delamination of their inner surface and, as a result, swelling of the cuffs of the master brake cylinder (hereinafter referred to as the brake master cylinder).
Failures and malfunction of the GTZ. This is one of the most technically difficult problems, since in this case the entire assembly has to be changed.
Consequences of incorrect replacement of brake components (brake pads, brake discs, etc.). Abnormal behavior of the brake pedal can be observed during the period of running-in of new elements, however, a violation of the “stiffness”, jerking and “beating” of the brake pedal is a direct indication for urgent diagnostics.
Corrosion of the brake pedal or rods connected to it.
Damage to the integrity of the accelerator pedal sensor.
Incorrect adjustment of the gap between the pedal rod and the turbocharger. This is checked by gently pressing it with your hand. The absence of a change in the smoothness of the pedal indicates a discrepancy between the gap size and the established operational requirements.
Failure of the vacuum pump or leakage of the hoses (cracks), which causes air to enter the brake system circuit.