Efficiency. Formula, definition. Why is diesel efficiency higher?

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

Man and mechanism

What do a washing machine and a cannery have in common? A person’s desire 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, weaved flax. To ensure survival during the long winter, each member of a peasant family worked during daylight hours from the age of two until death. The smallest children looked after the animals and assisted the adults (bring them, tell them, call them, take them away). The girl was put to spinning for the first time at the age of five! Even very old people cut spoons, and the oldest and most frail 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 were tired: every day they had to go and work, regardless of their health, pain and morale. Naturally, the man wanted to find assistants who would at least slightly relieve his strained shoulders.

Funny and weird

The most advanced technologies in those days were the horse and the mill wheel. But they only did two to three times more work than a human. But the first inventors began to come up with devices that looked very strange. In the film “The Story of Eternal Love,” Leonardo da Vinci attached small boats to his feet to walk on water. This led to several funny incidents when the scientist plopped into the lake with his clothes on. Although this episode is just an invention of the screenwriter, such inventions probably looked like this - comical and amusing.

19th century: iron and coal

But in the middle of the 19th century everything changed. Scientists realized the force of pressure from 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 needed to understand what efficiency is in the physics of steam and gas, and how to increase it.

The formula for the coefficient in the general case is:

Work and heat

The efficiency factor (abbreviated as efficiency) is a dimensionless quantity. It is determined as a percentage and is calculated as the ratio of energy expended to useful work. The last term is often used by mothers of careless 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 a machine is 20%, then it converts only one-fifth of the received energy 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 - energy expended.

Loss and reality

Surely all this reasoning is puzzling. 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. Let's consider, for example, what this coefficient is and what it consists of.

The formula in this case looks like this:

η=(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 released into the environment (in general, this is called a refrigerator).

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

Of course, in factory cars, all surfaces are polished to the atomic level, all metals are strong and have the lowest thermal conductivity, and the oil for lubricating the pistons has the best properties. But in any engine, the energy of gasoline is used to heat parts, air and friction.

Pan and cauldron

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

• the 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 connections, so no mechanism can have an efficiency of 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 it is temperature.

η=(T 1 -T 2)/T 1.

Space station

What if you place the mechanism in space? Free energy from the Sun is available 24 hours a day; cooling of any gas is possible literally to 0° Kelvin almost instantly. Maybe production efficiency would be higher in space? The answer is ambiguous: both 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 required height is still incredibly expensive. Even if such a factory operates for five hundred years, it will not recoup the costs of lifting 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 viable to move factories into space.

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

To be honest, modern engine options are much more efficient than their counterparts that were released 10 years ago, and there are many reasons for this. Think for yourself before, the 1.6 liter version produced only 60 - 70 hp. And now this value can reach 130 - 150 hp. This is painstaking work to increase 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 engine crankshaft 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 a fuel mixture (air and gasoline) into mechanical energy. It should be noted that this has already happened, for example, with 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 was constantly necessary to “feed” it into the furnace with shovels. Internal combustion engines are much more compact and lighter than “steam” ones, and the fuel is much easier to store and transport.

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 also far from ideal.

2) The second is thermal lossesAnd . 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:

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 efficiency factors, 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.

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. Diesel is much more efficient; the engine itself is often more compact and lighter, and also, recently, more environmentally friendly. All these positive aspects are achieved thanks to the larger value, there is a direct relationship between efficiency and compression, see the small plate.

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

Efficiency of an internal combustion engine - what is it?

First of all, the motor converts the thermal energy generated by 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 of performance) is the ratio of the actual power transmitted to the engine 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 in design, have different types of mixture formation. Therefore, the pistons of a carburetor engine operate at higher temperatures, requiring high-quality cooling. Because of this, thermal energy, which could be converted into mechanical energy, is dissipated without any benefit, lowering the overall efficiency value.

However, in order to increase the efficiency of a gasoline engine, certain measures are taken. For example, one cylinder may have two intake and one exhaust valves, rather than having one intake and one exhaust valve. In addition, some engines have a separate ignition coil installed for each spark plug. The throttle valve is controlled in many cases using an electric drive rather than an ordinary cable.

Diesel engine efficiency – noticeable efficiency

Diesel is one of the types of internal combustion engines in which the working mixture is ignited 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, we can note its highest efficiency.

At low speeds and a large displacement, the efficiency indicator can exceed 50%.

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

Efficiency (Efficiency) - characteristic of the efficiency of a system (device, machine) in relation to the conversion or transmission of energy. Determined by the ratio of usefully used energy to the total amount of energy received by the system; usually denoted η (“this”). η = Wpol/Wcym. Efficiency is a dimensionless quantity and is often measured as a percentage. Mathematically, the definition of efficiency can be written as:

X 100%,

Where A- useful work, and Q- energy expended.

Due to the law of conservation of energy, efficiency is always less than or equal to unity, that is, it is impossible to obtain more useful work than the energy expended.

Heat engine efficiency- the ratio of the complete useful work of the engine to the energy received from the heater. The efficiency of a heat engine can be calculated using the following formula

where is the amount of heat received from the heater, is the amount of heat given to the refrigerator. Highest efficiency among cyclic machines operating at given hot source temperatures T 1 and cold T 2, have heat engines operating on the Carnot cycle; this marginal efficiency is equal to

Not all indicators characterizing the efficiency of energy processes correspond to the above description. Even if they are traditionally or erroneously called "", they may have other properties, in particular exceeding 100%.

Boiler efficiency

Main article: Boiler heat balance

The efficiency of fossil fuel boilers is traditionally calculated based on the lower calorific value; it is assumed that the moisture of the combustion products leaves the boiler in the form of superheated steam. In condensing boilers, this moisture is condensed, and the heat of condensation is usefully used. When calculating efficiency based on the lower calorific value, it may end up being greater than one. In this case, it would be more correct to calculate it by the higher calorific value, which takes into account the heat of steam condensation; however, the performance of such a boiler is difficult to compare with data on other installations.

Heat pumps and chillers

The advantage of heat pumps as heating equipment is the ability to sometimes receive more heat than the energy consumed for their operation; similarly, a refrigeration machine can remove more heat from the cooled end than is expended in organizing the process.

The efficiency of such heat engines is characterized by coefficient of performance(for refrigeration machines) or transformation ratio(for heat pumps)

where is the heat taken from the cold end (in refrigeration machines) or transferred to the hot end (in heat pumps); - the work (or electricity) spent on this process. The reverse Carnot cycle has the best performance indicators for such machines: it has a coefficient of performance

where , are the temperatures of the hot and cold ends, . This value, obviously, can be arbitrarily large; Although it is difficult to approach practically, the coefficient of performance can still exceed unity. This does not contradict the first law of thermodynamics, since, in addition to the energy taken into account A(e.g. electric), to heat Q There is also energy taken from the cold source.

Literature

• Peryshkin A.V. Physics. 8th grade. - Bustard, 2005. - 191 p. - 50,000 copies. - ISBN 5-7107-9459-7.

Notes

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• Turbo Pascal
• Efficiency

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Efficiency is a characteristic of the operating efficiency of a device or machine. Efficiency is defined as the ratio of the useful energy at the output of the system to the total amount of energy supplied to the system. Efficiency is a dimensionless value and is often determined as a percentage.

Formula 1 - efficiency

Where- A useful work

—Q total work that was spent

Any system that does any work must receive energy from outside, with the help of which the work will be done. Take, for example, a voltage transformer. A mains voltage of 220 volts is supplied to the input, and 12 volts is removed from the output to power, for example, an incandescent lamp. So the transformer converts the energy at the input to the required value at which the lamp will operate.

But not all the energy taken from the network will reach the lamp, since there are losses in the transformer. For example, the loss of magnetic energy in the core of a transformer. Or losses in the active resistance of the windings. Where electrical energy will be converted into heat without reaching the consumer. This thermal energy is useless in this system.

Since power losses cannot be avoided in any system, the efficiency is always below unity.

Efficiency can be considered for the entire system, consisting of many individual parts. So, if you determine the efficiency for each part separately, then the total efficiency will be equal to the product of the efficiency coefficients of all its elements.

In conclusion, we can say that efficiency determines the level of perfection of any device in the sense of transmitting or converting energy. It also indicates how much energy supplied to the system is spent on useful work.