Coefficient useful action(EFFICIENCY) 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.
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Why diesel efficiency is higher
Efficiency index for various engines can be very different and depends on a number of factors. have a relatively low efficiency due to a large number 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 diesel plant and a gasoline engine diesel engine has a significantly higher efficiency compared to 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 engine operation, only 3 liters were used to perform useful work. The rest of the energy from the combustion of fuel went to waste.
With the same indicator of the working volume, the atmospheric power gasoline engine higher, but achieved at more high revs. 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 internal combustion engines reach maximum torque at higher rpm.
A similar naturally aspirated diesel engine peaks at low rpm while using less diesel to do useful work, which means more high 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. Less efficiency petrol plant compared with diesel also lies in the energy component of gasoline and the features of its combustion. Complete combustion an equal amount of diesel fuel and gasoline will give more heat in the first case. Heat in diesel ICE 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 intake manifold, but directly into the cylinder at the very end of the compression stroke. The result is more heat 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 engine. An increase in the number of intake and exhaust valves per cylinder, active application, electronic control fuel injection, throttle valve and other solutions can significantly increase the 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 rpm means less frictional losses and the resistance resulting from friction. For this reason, the diesel engine is today one of the most productive and economical ICE types, the efficiency of which often exceeds the mark of 50%.
Read also
Why it's better to warm up the engine before driving: lubrication, fuel, wear of cold parts. How to warm up a diesel engine in winter.
Efficiency factor (COP) is a measure of the efficiency of a system in terms of energy conversion or transfer, which is determined by the ratio of the energy usefully used to the total energy received by the system.
efficiency- the value is dimensionless, it is usually expressed as a percentage: 
Efficiency factor (COP) heat engine is determined by the formula: , where A = Q1Q2. thermal efficiency engine is always less than 1.
Carnot cycle- This is a reversible circular gas process, which consists of two consecutive isothermal and two adiabatic processes performed with a working fluid. 
The circular cycle, which includes two isotherms and two adiabats, corresponds to the maximum efficiency.
The French engineer Sadi Carnot in 1824 derived the formula for the maximum Ideal efficiency heat engine, where working body- This ideal gas, whose cycle consisted of two isotherms and two adiabats, i.e., the Carnot cycle. The Carnot cycle is the real working cycle of a heat engine that performs work due to the heat supplied to the working fluid in an isothermal process.
The formula for the efficiency of the Carnot cycle, i.e., the maximum efficiency of a heat engine, is: 
, where T1 - absolute temperature heater, T2 - the absolute temperature of the refrigerator.
Heat engines- These are structures in which thermal energy is converted into mechanical energy.
Heat engines are diverse both in design and purpose. These include steam engines, steam turbines, engines internal combustion, jet engines.
However, despite the diversity, in principle, the operation of various heat engines is common features. The main components of each heat engine:
- heater;
- working body;
- fridge.
The heater releases thermal energy, while heating the working fluid, which is located in the working chamber of the engine. The working fluid can be steam or gas.
Having accepted the amount of heat, the gas expands, because. its pressure is greater than the external pressure, and moves the piston, producing positive work. At the same time, its pressure drops, and its volume increases.
If we compress the gas, passing through the same states, but in the opposite direction, then we will perform the same absolute value, but negative work. As a result, all the work for the cycle will be equal to zero.
In order for the work of a heat engine to be different from zero, the work of compressing the gas must be less work extensions.
In order for the work of compression to become less than the work of expansion, it is necessary that the compression process take place at a lower temperature, for this the working fluid must be cooled, therefore, a refrigerator is included in the design of the heat engine. The working fluid gives off the amount of heat to the refrigerator when in contact with it.
Perhaps the main constructive element any car is its "heart", namely the engine. On how smoothly and efficiently this unit will work, speed, comfort, traction characteristics cars. An important indicator effective work engine of any unit and car is its efficiency.
This generally accepted abbreviation stands for simply - efficiency. But not every driver knows what is the efficiency of a car engine? Perhaps he does not need it, but he needs to know everything!
What is efficiency
Now a little about what constitutes efficiency, and what it depends on. According to the classical definition, this is the ratio of the work done and the energy expended for this. Defined in percentage. The higher the efficiency percentage, the more efficient the engine is. True, even modern cars can't brag enough high rates efficiency.
Today it is considered normal if the level of useful work of the car engine is in the range of 20 - 60%. For comparison, use electric motors makes it possible to obtain an efficiency of 95%. Loss of efficiency arises from various internal and external factors that affect the engine when it is in operation.
In particular, these include the loss of energy through the "washing out" of heat, inefficiently prepared air mixture, which later becomes the cause of its incomplete combustion, energy costs to overcome friction, heat loss in the process of removing burnt gases. In total, such losses can reach up to 60 - 80% of the initially received energy.
Of course, this approach leads to misuse of fuel, low power, rapid wear of parts of a particular type, the need to perform more frequent preventive inspections and repairs. Here important point is the need to use quality parts. After all, during the operation of the engine, all its parts are constantly in high voltage. And the slightest flaw in one of its parts can cause the failure of the entire unit.
Features of engine efficiency in a car
It must also be understood that the efficiency of engines running on gasoline is much lower than the same engines that run on diesel fuel. Distinctive feature these types of fuel is the use of additional incendiary elements (in the case of gasoline), or the supply of finished fuel mixture in a pre-prepared chamber with compressed air, where such fuel spontaneously ignites.
Separately, it is important to dwell on the quality of the fuel itself. After all, incomplete combustion of fuel can cause a loss of up to 25% of the energy released. Therefore, many companies carefully approach the choice of fuel suppliers. After all, the fourth part of the loss is quite an impressive figure. Moreover, unburned fuel tends not only to enter the atmosphere and pollute it (and you can get a hefty fine for this), but also settles on the internal walls of the engine and its parts, thereby leading to clogging and premature wear.
Using quality fuel, you have the opportunity, without carrying out any internal modernization of the car, or replacing its individual parts, in fact, out of the blue, it will significantly increase the efficiency of the engine.
Improving engine efficiency
Considering the increased demand of society for efficient, economical and comfortable cars, today scientists and experts from different countries participate in improvement programs automotive engines in order to bring their efficiency to the level of 80% and above.
To do this, various design improvements are used (for example, turbocharging), the metal components of the engine base are replaced with lighter alloys that can keep heat and reduce friction to a minimum at the minimum cost required for this.
All this becomes the basis for the production of more compact, lightweight engines capable of processing most of the energy initially received into useful work. Thus, all this allows you to really save in the process of further operation and maintenance of the machine.
At the same time, it is given great attention improvement and cleaning of existing elements (fuel, cooling systems, lubrication, fuel supply and exhaust gases), because, as we have already noted earlier, in this way you can increase the efficiency even without changing individual parts. Easy enough to pour correct fuel, reduce the level of heat transfer during engine operation, or exhaust exhaust.
Another point of efficient use of the vehicle is the optimal level of vehicle loading. withstanding average speed, correct passes without trying to show your excessive skill, you will be able to significantly reduce fuel consumption. You can also achieve optimal power and vehicle speed under certain conditions.
In the theoretical model of a heat engine, three bodies are considered: heater, working body And fridge.
Heater - a thermal reservoir (large body), the temperature of which is constant.
In each cycle of engine operation, the working fluid receives a certain amount of heat from the heater, expands and performs mechanical work. The transfer of part of the energy received from the heater to the refrigerator is necessary to return the working fluid to its original state.
Since the model assumes that the temperature of the heater and refrigerator does not change during the operation of the heat engine, then at the end of the cycle: heating-expansion-cooling-compression of the working fluid, it is considered that the machine returns to its original state.
For each cycle, based on the first law of thermodynamics, we can write that the amount of heat Q load received from the heater, amount of heat | Q cool |, given to the refrigerator, and the work done by the working body A are related to each other by:
A = Q load – | Q cold|.
In real technical devices, which are called heat engines, the working fluid is heated by the heat released during the combustion of fuel. Yes, in steam turbine power plant heater is a furnace with hot coal. In an internal combustion engine (ICE), combustion products can be considered a heater, and excess air can be considered a working fluid. As a refrigerator, they use the air of the atmosphere or water from natural sources.
Efficiency of a heat engine (machine)
Heat engine efficiency (efficiency) is the ratio of the work done by the engine to the amount of heat received from the heater:
The efficiency of any heat engine is less than one and is expressed as a percentage. The impossibility of converting the entire amount of heat received from the heater into mechanical work is the price to pay for the need to organize a cyclic process and follows from the second law of thermodynamics.
In real heat engines, the efficiency is determined by the experimental mechanical power N engine and the amount of fuel burned per unit time. So, if in time t mass fuel burned m and specific heat of combustion q, That
For Vehicle the reference characteristic is often the volume V fuel burned on the way s at mechanical engine power N and at speed. In this case, taking into account the density r of the fuel, we can write a formula for calculating the efficiency:
Second law of thermodynamics
There are several formulations second law of thermodynamics. One of them says that a heat engine is impossible, which would do work only due to a heat source, i.e. without refrigerator. The world ocean could serve for it as a practically inexhaustible source of internal energy (Wilhelm Friedrich Ostwald, 1901).
Other formulations of the second law of thermodynamics are equivalent to this one.
Clausius' formulation(1850): a process is impossible in which heat would spontaneously transfer from less heated bodies to more heated bodies.
Thomson's formulation(1851): a circular process is impossible, the only result of which would be the production of work by reducing the internal energy of the thermal reservoir.
Clausius' formulation(1865): all spontaneous processes in a closed non-equilibrium system occur in such a direction in which the entropy of the system increases; in a state of thermal equilibrium, it is maximum and constant.
Boltzmann's formulation(1877): a closed system of many particles spontaneously passes from a more ordered state to a less ordered one. The spontaneous exit of the system from the equilibrium position is impossible. Boltzmann introduced a quantitative measure of disorder in a system consisting of many bodies - entropy.
Efficiency of a heat engine with an ideal gas as a working fluid
If the model of the working fluid in the heat engine is given (for example, an ideal gas), then it is possible to calculate the change thermodynamic parameters working fluid during expansion and contraction. This allows you to calculate the efficiency of a heat engine based on the laws of thermodynamics.
The figure shows the cycles for which the efficiency can be calculated if the working fluid is an ideal gas and the parameters are set at the points of transition of one thermodynamic process to another.
|
|
Isobaric-isochoric |
|
Isochoric-adiabatic |
|
Isobaric-adiabatic |
|
Isobaric-isochoric-isothermal |
|
|
Isobaric-isochoric-linear |
Carnot cycle. Efficiency of an ideal heat engine
The highest efficiency at given heater temperatures T heating and refrigerator T cold has a heat engine where the working fluid expands and contracts along Carnot cycle(Fig. 2), the graph of which consists of two isotherms (2–3 and 4–1) and two adiabats (3–4 and 1–2).
Carnot's theorem proves that the efficiency of such an engine does not depend on the working fluid used, so it can be calculated using the thermodynamic relations for an ideal gas:
Environmental consequences of heat engines
The intensive use of heat engines in transport and energy (thermal and nuclear power plants) significantly affects the Earth's biosphere. Although there are scientific disputes about the mechanisms of the influence of human activity on the Earth's climate, many scientists point out the factors due to which such an influence can occur:
- Greenhouse effect– increase in the concentration of carbon dioxide (combustion product in the heaters of thermal machines) in the atmosphere. Carbon dioxide transmits visible and ultraviolet radiation from the Sun, but absorbs infrared radiation from the Earth. This leads to an increase in the temperature of the lower layers of the atmosphere, an increase in hurricane winds and global ice melting.
- Direct influence of poisonous exhaust gases on wildlife (carcinogens, smog, acid rain from by-products combustion).
- Destruction of the ozone layer during aircraft flights and rocket launches. The ozone of the upper atmosphere protects all life on Earth from excess ultraviolet radiation from the Sun.
The way out of the emerging ecological crisis lies in increasing thermal efficiency engines (the efficiency of modern heat engines rarely exceeds 30%); use serviceable engines and neutralizers of harmful exhaust gases; use alternative sources energy ( solar panels and heaters) and alternative means of transport (bicycles, etc.).
Efficiency (efficiency) - a characteristic of the efficiency of a system (device, machine) in relation to the conversion or transfer of energy. It is determined by the ratio of useful energy used 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- wasted energy.
By virtue of the law of conservation of energy, the efficiency is always less than unity or equal to it, that is, it is impossible to obtain more useful work than the energy expended.
Heat engine efficiency- the ratio of the perfect 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 - the amount of heat received from the heater, - the amount of heat given to the refrigerator. The highest efficiency among cyclic machines operating at given hot spring temperatures T 1 and cold T 2, have heat engines operating on the Carnot cycle; this limiting 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 "efficiency", they may have other properties, in particular, exceed 100%.
boiler efficiency
Main article: Boiler thermal balance
The efficiency of fossil fuel boilers is traditionally calculated from the net 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, the heat of condensation is usefully used. When calculating the efficiency according to the lower calorific value, it can eventually turn out to be more than one. IN this case it would be more correct to consider it according to the higher calorific value, taking into account the heat of steam condensation; however, the performance of such a boiler is difficult to compare with data from other installations.
Heat pumps and chillers
The advantage of heat pumps as a heating technique is the ability to sometimes receive more heat than the energy spent on their work; 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 chillers) 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. best performance productivity for such machines has a reverse Carnot cycle: in it the coefficient of performance
,where , are the temperatures of the hot and cold ends, . This value, obviously, can be arbitrarily large; although practically it is difficult to approach it, 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), into heat Q there is also energy taken from a 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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Synonyms:See what "Efficiency" is in other dictionaries:
efficiency- The ratio of output power to consumed active power. [OST 45.55 99] coefficient of useful action efficiency A value that characterizes the perfection of the processes of transformation, transformation or transfer of energy, which is the ratio of useful ... ... Technical Translator's Handbook
Or the coefficient of return (Efficiency) is a characteristic of the quality of work of any machine or apparatus in terms of its efficiency. By K.P.D. is meant the ratio of the amount of work received from the machine or energy from the device to that amount ... ... Marine Dictionary
- (efficiency), an indicator of the efficiency of the mechanism, defined as the ratio of the work performed by the mechanism to the work expended on its functioning. efficiency usually expressed as a percentage. An ideal mechanism would have to have efficiency = ... ... Scientific and technical encyclopedic dictionary
Modern Encyclopedia
- (efficiency) characteristic of the efficiency of the system (device, machine) in relation to energy conversion; is determined by the ratio of useful energy used (turned into work in a cyclic process) to the total amount of energy, ... ... Big Encyclopedic Dictionary
- (efficiency), a characteristic of the efficiency of a system (device, machine) in relation to the conversion or transfer of energy; is determined by the ratio of t) useful energy used (Wpol) to the total amount of energy (Wtotal) received by the system; h=Wpol… … Physical Encyclopedia
- (efficiency) the ratio of useful energy W p, for example. in the form of work, to the total amount of energy W received by the system (machine or engine), W p / W. Due to the inevitable energy losses due to friction and other non-equilibrium processes for real systems ... ... Physical Encyclopedia
The ratio of useful work expended or energy received to all work expended or energy consumed, respectively. For example, the efficiency of the electric motor is the ratio of mechan. the power they give off to the electric power supplied to it. power; TO.… … Technical railway dictionary
Exist., number of synonyms: 8 efficiency (4) return (27) fruitfulness (10) ... Synonym dictionary
Efficiency- - a value that characterizes the perfection of any system in relation to any process of transformation or energy transfer occurring in it, defined as the ratio of useful work to the work expended on putting into action. ... ... Encyclopedia of terms, definitions and explanations of building materials
Efficiency- (efficiency), a numerical characteristic of the energy efficiency of any device or machine (including a heat engine). Efficiency is determined by the ratio of useful energy used (i.e., converted into work) to the total amount of energy, ... ... Illustrated Encyclopedic Dictionary
