efficiency of the internal combustion engine. How much is approximately equal, as well as power in percent

Among the many characteristics of various mechanisms in the car, the decisive factor is Efficiency of an internal combustion engine. In order to find out the essence of this concept, you need to know exactly what a classic internal combustion engine is.

The efficiency of an internal combustion engine - what is it?

First of all, the motor converts thermal energy arising from the combustion of fuel into a certain amount of mechanical work. Unlike steam engines, these engines are lighter and more compact. They are much more economical and consume strictly defined liquid and gaseous fuels. Thus, the efficiency of modern engines is calculated based on their technical characteristics and other indicators.

efficiency (coefficient useful action) is the ratio of the power actually transmitted to the motor shaft to the power received by the piston due to the action of gases. If we compare the efficiency of engines of different power, we can establish that this value for each of them has its own characteristics.

Both engines, despite the similarity of design, have different kinds mixture formation. Therefore, the pistons of a carburetor engine operate at higher temperatures that require high-quality cooling. Because of this, thermal energy, which could turn into mechanical energy, is dissipated to no avail, lowering general meaning efficiency.

However, in order to increase the efficiency gasoline engine certain measures are being taken. For example, two intake and exhaust valves can be installed per cylinder, instead of one intake and one exhaust valve. In addition, some engines have a separate ignition coil for each spark plug. Throttle control in many cases is carried out with the help of an electric drive, and not with an ordinary cable.

Diesel engine efficiency – noticeable efficiency

Diesel is one of the varieties of internal combustion engines, in which the ignition of the working mixture is carried out as a result of compression. Therefore, the air pressure in the cylinder is much higher than that of a gasoline engine. Comparing the efficiency of a diesel engine with the efficiency of other designs, one can note its highest efficiency.

In the presence of low speeds and a large displacement, the efficiency index can exceed 50%.

Attention should be paid to the relatively low consumption of diesel fuel and the low content of harmful substances in the exhaust gases. Thus, the value of the efficiency of an internal combustion engine depends entirely on its type and design. In many vehicles, low efficiency is offset by various improvements to improve overall performance. specifications.

Today we will tell you what efficiency (efficiency factor) is, how to calculate it, and where this concept is applied.

Man and machine

What unites washing machine and a cannery? The desire of a person to relieve himself of the need to do everything on his own. Before the invention of the steam engine, people had only their muscles at their disposal. They did everything themselves: they plowed, sowed, cooked, caught fish, wove flax. To ensure survival during the long winter, each member of the peasant family worked daylight hours from the age of two until his death. The youngest children looked after the animals and were helping (bring, tell, call, take) the adults. The girl was first put behind a spinning wheel at the age of five! Even deep old people cut spoons, and the most elderly and infirm grandmothers sat at looms and spinning wheels, if their eyesight allowed. They had no time to think about what stars are and why they shine. People got tired: every day they had to go and work, regardless of the state of health, pain and morale. Naturally, a person wanted to find assistants who would at least slightly relieve his overworked shoulders.

funny and strange

The most advanced technology in those days was the horse and the mill wheel. But they did only two or three times more work than a human. But the first inventors began to come up with devices that looked very strange. In "History" eternal love» Leonardo da Vinci attached small boats to his feet to walk on water. This led to several funny incidents when the scientist plunged into the lake with his clothes on. Although this episode is just an invention of the screenwriter, such inventions certainly looked like that - comical and funny.

19th century: iron and coal

But in the middle of the 19th century everything changed. Scientists have realized the pressure force of expanding steam. The most important goods of that time were iron for the production of boilers and coal for heating water in them. Scientists of that time had to understand what efficiency is in steam and gas physics, and how to increase it.

The formula for the coefficient in the general case is:

Work and warmth

Efficiency (abbreviated efficiency) is a dimensionless quantity. It is defined as a percentage and is calculated as the ratio of energy expended to useful work. The latter term is often used by mothers of negligent teenagers when they force them to do something around the house. But in fact, this is the real result of the effort expended. That is, if the efficiency of the machine is 20%, then it only converts one-fifth of the energy received into action. Now, when buying a car, the reader should not have a question about what engine efficiency is.

If the coefficient is calculated as a percentage, then the formula is:

η - efficiency, A - useful work, Q - expended energy.

Loss and reality

Surely all these arguments cause bewilderment. Why not invent a car that can use more fuel energy? Alas, the real world is not like that. At school, children solve problems in which there is no friction, all systems are closed, and the radiation is strictly monochromatic. Real engineers at manufacturing plants are forced to take into account the presence of all these factors. Consider, for example, what this coefficient is and what it consists of.

The formula in this case looks like this:

η \u003d (Q 1 -Q 2) / Q 1

In this case, Q 1 is the amount of heat that the engine received from heating, and Q 2 is the amount of heat that it gave to the environment (in the general case, this is called a refrigerator).

The fuel heats up and expands, the force pushes the piston, which drives the rotary element. But the fuel is contained in some vessel. When heated, it transfers heat to the walls of the vessel. This leads to energy losses. In order for the piston to descend, the gas must be cooled. To do this, part of it is released into the environment. And it would be good if the gas gave all the heat to useful work. But, alas, it cools very slowly, so hot steam comes out. Part of the energy is spent on heating the air. The piston moves in a hollow metal cylinder. Its edges fit snugly against the walls; when moving, friction forces come into play. The piston heats the hollow cylinder, which also leads to a loss of energy. The translational movement of the rod up and down is transmitted to a torque through a series of joints that rub against each other and heat up, that is, part of the primary energy is also spent on this.

Of course, in factory machines, all surfaces are polished to the atomic level, all metals are strong and have the lowest thermal conductivity, and piston oil has the best properties. But in any engine, the energy of gasoline goes to heat parts, air and friction.

Saucepan and cauldron

Now we propose to understand what the efficiency of the boiler is, and what it consists of. Any housewife knows: if you leave water to boil in a saucepan under a closed lid, then either water will drip onto the stove, or the lid will “dance”. Any modern boiler is arranged in much the same way:

heat heats a closed container full of water;
water becomes superheated steam;
when expanding, the gas-water mixture rotates turbines or moves pistons.

Just like in an engine, energy is lost to heat the boiler, pipes and friction of all joints, so no mechanism can have an efficiency equal to 100%.

The formula for machines that operate on the Carnot cycle looks like the general formula for a heat engine, only instead of the amount of heat - temperature.

η=(T 1 -T 2)/T 1 .

Space station

And if you put the mechanism in space? Free solar energy is available 24 hours a day, cooling of any gas is possible literally to 0 degrees Kelvin almost instantly. Maybe in space the efficiency of production would be higher? The answer is ambiguous: yes and no. All these factors could indeed significantly improve the transfer of energy to useful work. But delivering even a thousand tons to the desired height is still incredibly expensive. Even if such a factory works for five hundred years, it will not pay off the cost of raising the equipment, which is why science fiction writers are so actively exploiting the idea of a space elevator - this would greatly simplify the task and make it commercially profitable to transfer factories into space.

Probably, everyone wondered about the efficiency (Coefficient of Efficiency) of an internal combustion engine. After all, the higher this indicator, the more efficient the power unit works. At the moment, the electric type is considered the most efficient, its efficiency can reach up to 90 - 95%, but for internal combustion engines, whether it be diesel or gasoline, to put it mildly, it is far from ideal ...

To be honest, then modern options motors are much more efficient than their counterparts, which were released 10 years ago, and there are a lot of reasons for this. Think for yourself before the 1.6-liter option, it gave out only 60 - 70 hp. And now this value can reach 130 - 150 hp. This painstaking work over the increase in efficiency, in which each "step" is given by trial and error. However, let's start with a definition.

- this is the value of the ratio of two quantities, the power that is supplied to the crankshaft of the engine to the power received by the piston, due to the pressure of the gases that were formed by igniting the fuel.

In simple terms, this is the conversion of thermal or thermal energy that appears during the combustion of the fuel mixture (air and gasoline) into mechanical energy. It should be noted that this has already happened, for example, in steam power plants - also the fuel, under the influence of temperature, pushed the pistons of the units. However, the installations there were many times larger, and the fuel itself was solid (usually coal or firewood), which made it difficult to transport and operate it, it was constantly necessary to “feed” it into the furnace with shovels. Internal combustion engines are much more compact and lighter than steam engines, and fuel is much easier to store and transport.

More about losses

Looking ahead, we can confidently say that the efficiency of a gasoline engine is in the range of 20 to 25%. And there are many reasons for this. If we take the incoming fuel and recalculate it as a percentage, then we kind of get “100% of the energy” that is transferred to the engine, and then the losses went:

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

2) The second is heat losses.And . The engine warms up itself and many other elements, such as radiators, its body, the liquid that circulates in it. Also, part of the heat goes away with the exhaust gases. For all this, 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 includes losses from the load of the generator, for example, the more electricity the generator produces, the more it slows down the rotation of the crankshaft. Of course, lubricants have also stepped forward, but again, no one has yet completely defeated friction - another 20% loss

Thus, in the dry residue, the efficiency is about 20%! Of course, there are stand-out options from gasoline options, in which this figure is increased to 25%, but there are not so many of them.

That is, if your car consumes 10 liters of fuel 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, we are watching a short video.

If you remember the formula, you get:

Which engine has the highest efficiency?

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

To put it in simple terms, and not to go into the jungle of technical terms, then - if we compare two efficiencies - the most efficient of them, of course, is 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 the diesel type with a turbocharger, then 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), a diesel engine does its job much more efficiently. It has greater compression, and the fuel ignites from a different principle. It heats up less, which means it saves on cooling, it has fewer valves (savings on friction), and it also doesn’t have the usual ignition coils and spark plugs, which means it doesn’t require additional energy costs from the generator. It works at lower speeds, there is no need to crank the crankshaft wildly - all this makes the diesel version a champion in efficiency.

About Diesel Fuel Efficiency

From a higher value of the efficiency factor, fuel efficiency also 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 a lot, the engine itself is often more compact and lighter, and also more environmentally friendly lately. All these positive aspects are achieved thanks to greater value, there is a direct relationship between efficiency and compression, look at a small plate.

Coefficient of performance (COP) - a term that can be applied, perhaps, to every system and device. Even a person has an efficiency, though, probably, there is no objective formula for finding it yet. In this article, we will explain in detail what efficiency is and how it can be calculated for various systems.

efficiency definition

Efficiency is an indicator that characterizes the efficiency of a particular system in relation to the return or conversion of energy. Efficiency is a measureless value and is represented either as a numerical value in the range from 0 to 1, or as a percentage.

General formula

Efficiency is indicated by the symbol Ƞ.

The general mathematical formula for finding the efficiency is written as follows:

Ƞ=A/Q, where A is the useful energy/work done by the system, and Q is the energy consumed by this system to organize the process of obtaining a useful output.

The efficiency factor, unfortunately, is always less than one or equal to it, since, according to the law of conservation of energy, we cannot get more work than the energy spent. In addition, the efficiency, in fact, is extremely rarely equal to one, since useful work is always accompanied by losses, for example, for heating the mechanism.

Heat engine efficiency

A heat engine is a device that converts thermal energy into mechanical energy. In a heat engine, work is determined by the difference between the amount of heat received from the heater and the amount of heat given to the cooler, and therefore the efficiency is determined by the formula:

Ƞ=Qн-Qх/Qн, where Qн is the amount of heat received from the heater, and Qх is the amount of heat given to the cooler.

It is believed that the highest efficiency is provided by engines operating on the Carnot cycle. In this case, the efficiency is determined by the formula:

Ƞ=T1-T2/T1, where T1 is the temperature of the hot source, T2 is the temperature of the cold source.

Electric motor efficiency

An electric motor is a device that converts electrical energy into mechanical energy, so the efficiency in this case is the efficiency ratio of the device in relation to the conversion of electrical energy into mechanical energy. The formula for finding the efficiency of an electric motor looks like this:

Ƞ=P2/P1, where P1 is the supplied electrical power, P2 is the useful mechanical power generated by the engine.

Electrical power is found as the product of system current and voltage (P=UI), and mechanical power is found as the ratio of work to unit time (P=A/t)

transformer efficiency

A transformer is a device that converts alternating current of one voltage into alternating current of another voltage while maintaining frequency. In addition, transformers can also convert AC to DC.

The efficiency of the transformer is found by the formula:

Ƞ=1/1+(P0+PL*n2)/(P2*n), where P0 - no-load losses, PL - load losses, P2 - active power delivered to the load, n - relative degree of loading.

Efficiency or not efficiency?

It is worth noting that in addition to efficiency, there are a number of indicators that characterize the efficiency of energy processes, and sometimes we can find descriptions of the type - efficiency of the order of 130%, however, in this case, you need to understand that the term is not used quite correctly, and, most likely, the author or the manufacturer understands a slightly different characteristic by this abbreviation.

For example, heat pumps are distinguished by the fact that they can give off more heat than they consume. Thus, the refrigerating machine can remove more heat from the cooled object than is spent in energy equivalent for the organization of the removal. The efficiency indicator of a refrigerating machine is called the coefficient of performance, denoted by the letter Ɛ and is determined by the formula: Ɛ=Qx/A, where Qx is the heat removed from the cold end, A is the work expended on the removal process. However, sometimes the coefficient of performance is also called the efficiency of the refrigeration machine.

It is also interesting that the efficiency of boilers running on fossil fuels is usually calculated on the basis of the lower calorific value, while it can turn out to be more than one. However, it is still traditionally referred to as efficiency. It is possible to determine the efficiency of the boiler by the gross calorific value, and then it will always be less than one, but in this case it will be inconvenient to compare the performance of the boilers with the data of other installations.

The coefficient of performance (COP) is a value that expresses in percentage terms the efficiency of a particular mechanism (engine, system) regarding the conversion of the received energy into useful work.

Read in this article

Why diesel efficiency is higher

The efficiency index for different engines can vary greatly and depends on a number of factors. have a relatively low efficiency due to the large number of mechanical and thermal losses that occur during the operation of a power unit of this type.

The second factor is the friction that occurs during the interaction of mating parts. Most of the useful energy consumption is the driving of the engine pistons, as well as the rotation of the parts inside the motor, which are structurally fixed on the bearings. About 60% of the combustion energy of gasoline is spent only to ensure the operation of these units.

Additional losses are caused by the operation of other mechanisms, systems and attachments. It also takes into account the percentage of losses due to resistance at the time of the next charge of fuel and air, and then the release of exhaust gases from the internal combustion engine cylinder.

If we compare a diesel plant and a gasoline engine, a diesel engine has a noticeably higher efficiency compared to a gasoline unit. Gasoline power units have an efficiency of about 25-30% of the total amount of energy received.

In other words, out of 10 liters of gasoline spent on the engine, only 3 liters are spent on useful work. The rest of the energy from the combustion of fuel went to waste.

With the same displacement indicator, the power of an atmospheric gasoline engine is higher, but is achieved at higher speeds. The engine needs to be “turned”, losses increase, fuel consumption increases. It is also necessary to mention the torque, which literally means the force that is transmitted from the motor to the wheels and drives the car. Gasoline ICEs reach their maximum torque at higher RPMs.

A similar naturally aspirated diesel achieves peak torque at low rpm, while using less diesel to do useful work, which means higher efficiency and fuel economy.

Diesel fuel generates more heat compared to gasoline, the combustion temperature of diesel fuel is higher, and the knock resistance index is higher. It turns out that a diesel internal combustion engine has more useful work done on a certain amount of fuel.

Energy value of diesel fuel and gasoline

Diesel fuel is made up of heavier hydrocarbons than gasoline. The lower efficiency of a gasoline plant compared to a diesel engine also lies in the energy component of gasoline and the features of its combustion. Complete combustion of an equal amount of diesel fuel and gasoline will give more heat in the first case. Heat in a diesel engine is more fully converted into useful mechanical energy. It turns out that when burning the same amount of fuel per unit of time, it is the diesel engine that will do more work.

It is also worth considering the features of injection and the creation of appropriate conditions for the full combustion of the mixture. In a diesel engine, fuel is supplied separately from air, it is not injected into the intake manifold, but directly into the cylinder at the very end of the compression stroke. The result is a higher temperature and the most complete combustion of a portion of the working fuel-air mixture.

Results

Designers are constantly striving to improve the efficiency of both diesel and gasoline engines. An increase in the number of intake and exhaust valves per cylinder, active use, electronic control of fuel injection, throttle valve and other solutions can significantly increase efficiency. To a greater extent this applies to the diesel engine.

Thanks to these features, a modern diesel engine is able to completely burn a portion of diesel fuel saturated with hydrocarbons in the cylinder and produce a large amount of torque at low revs. Low RPMs mean less friction loss and the resulting drag. For this reason, a diesel engine is today one of the most productive and economical types of internal combustion engines, the efficiency of which often exceeds 50%.