Probably everyone wondered about the efficiency (Coefficient of Efficiency) of the engine internal combustion. After all, the higher this indicator, the more efficient it works. power unit. The most efficient for this moment time is considered an electric type, 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 is painstaking work to increase efficiency, in which each "step" is given by trial and error. However, let's start with a definition.
is the value of the ratio of two quantities, the power that is supplied to crankshaft 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 combustion fuel mixture(air and gasoline) to mechanical. 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, 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 improved, an injector 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 is lost from 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 simply, the language and not to climb into the wilds technical terms then - if we compare two efficiencies - the most efficient of them, of course, is diesel, and here's why:
1) Gas engine converts only 25% of energy into mechanical energy, but diesel about 40%.
2) If equipped diesel type turbocharging, it is possible to 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, you don’t need to spin the crankshaft furiously - it does all diesel variant efficiency champion.
About Diesel Fuel Efficiency
FROM more high value coefficient useful action– followed by fuel efficiency. So, for example, a 1.6-liter engine can consume only 3-5 liters in the city, unlike petrol 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 moments are achieved due to the greater value, there is a direct relationship between efficiency and compression, see a 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 is clearly with electric options - it remains only to find efficient batteries that are not afraid of frost and hold a charge for a long time.
« Physics - Grade 10 "
What is a thermodynamic system and what parameters characterize its state.
State the first and second laws of thermodynamics.
It was the creation of the theory of heat engines that led to the formulation of the second law of thermodynamics.
The reserves of internal energy in the earth's crust and oceans can be considered practically unlimited. But to solve practical problems, having energy reserves is still not enough. It is also necessary to be able to use energy to set in motion machines in factories and plants, vehicles, tractors and other machines, to rotate the rotors of generators. electric current etc. Mankind needs engines - devices capable of doing work. Most of the engines on Earth are heat engines.
Heat engines are devices that convert the internal energy of fuel into mechanical work.
The principle of operation of heat engines.
In order for the engine to do work, a pressure difference is needed on both sides of the engine piston or turbine blades. In all heat engines, this pressure difference is achieved by increasing the temperature working body(gas) hundreds or thousands of degrees above the temperature environment. This increase in temperature occurs during the combustion of fuel.
One of the main parts of the engine is a gas-filled vessel with a movable piston. The working fluid in all heat engines is a gas that does work during expansion. Let's denote the initial temperature of the working fluid (gas) through T 1 . This temperature in steam turbines or machines acquires steam in a steam boiler. in internal combustion engines and gas turbines temperature rise occurs when fuel is burned inside the engine itself. The temperature T 1 is called heater temperature.
The role of the refrigerator
As work is done, the gas loses energy and inevitably cools to a certain temperature T 2 , which is usually somewhat higher than the ambient temperature. They call her refrigerator temperature. The refrigerator is the atmosphere or special devices for cooling and condensing exhaust steam - capacitors. In the latter case, the temperature of the refrigerator may be slightly lower than the ambient temperature.
Thus, in the engine working body when expanding, it cannot give all its internal energy to do work. Part of the heat is inevitably transferred to the cooler (atmosphere) along with exhaust steam or exhaust gases from internal combustion engines and gas turbines.
This part of the internal energy of the fuel is lost. A heat engine performs work due to the internal energy of the working fluid. Moreover, in this process, heat is transferred from hotter bodies (heater) to colder ones (refrigerator). circuit diagram heat engine shown in Figure 13.13.
The working fluid of the engine receives from the heater during the combustion of fuel the amount of heat Q 1, does work A "and transfers the amount of heat to the refrigerator Q2< Q 1 .
In order for the engine to work continuously, it is necessary to return the working fluid to its initial state, at which the temperature of the working fluid is equal to T 1 . It follows from this that the operation of the engine occurs according to periodically repeating closed processes, or, as they say, according to a cycle.
Cycle is a series of processes, as a result of which the system returns to its initial state.
Coefficient of performance (COP) of a heat engine.
The impossibility of complete conversion of the internal energy of the gas into the work of heat engines is due to the irreversibility of processes in nature. If heat could spontaneously return from the refrigerator to the heater, then the internal energy could be completely converted into useful work with any heat engine. The second law of thermodynamics can be formulated as follows:
Second law of thermodynamics:
impossible to create perpetual motion machine of the second kind, which would completely convert heat into mechanical work.
According to the law of conservation of energy, the work done by the engine is:
A" \u003d Q 1 - | Q 2 |, (13.15)
where Q 1 - the amount of heat received from the heater, and Q2 - the amount of heat given to the refrigerator.
The coefficient of performance (COP) of a heat engine is the ratio of work A "performed by the engine to the amount of heat received from the heater:
Since in all engines some amount of heat is transferred to the refrigerator, then η< 1.
The maximum value of the efficiency of heat engines.
The laws of thermodynamics allow us to calculate the maximum possible efficiency a heat engine operating with a heater having a temperature of T 1 and a refrigerator with a temperature of T 2 , and also to determine ways to increase it.
For the first time, the maximum possible thermal efficiency the engine was calculated by the French engineer and scientist Sadi Carnot (1796-1832) in his work “Reflections on the driving force of fire and on machines capable of developing this force” (1824).
Carnot came up with an ideal heat engine with an ideal gas as the working fluid. An ideal Carnot heat engine operates in a cycle consisting of two isotherms and two adiabats, and these processes are considered reversible (Fig. 13.14). First, a vessel with a gas is brought into contact with a heater, the gas expands isothermally, making positive work, at a temperature T 1 , while he receives the amount of heat Q 1 .
Then the vessel is thermally insulated, the gas continues to expand already adiabatically, while its temperature decreases to the temperature of the refrigerator T 2 . After that, the gas is brought into contact with the refrigerator, under isothermal compression, it gives off the amount of heat Q 2 to the refrigerator, compressing to a volume V 4< V 1 . Затем сосуд снова теплоизолируют, газ сжимается адиабатно до объёма V 1 и возвращается в первоначальное состояние. Для КПД этой машины было получено следующее выражение:
As follows from formula (13.17), machine efficiency Carnot is directly proportional to the difference absolute temperatures heater and refrigerator.
The main meaning of this formula is that it indicates the way to increase the efficiency, for this it is necessary to increase the temperature of the heater or lower the temperature of the refrigerator.
Any real heat engine operating with a heater having a temperature T 1 and a refrigerator with a temperature T 2 cannot have an efficiency exceeding the efficiency of an ideal heat engine: 
The processes that make up the cycle of a real heat engine are not reversible.
Formula (13.17) gives a theoretical limit for the maximum value of the efficiency of heat engines. It shows that a heat engine is more efficient, the greater the temperature difference between the heater and the refrigerator.
Only at the temperature of the refrigerator, equal to absolute zero, η = 1. In addition, it has been proved that the efficiency calculated by formula (13.17) does not depend on the working substance.
But the temperature of the refrigerator, the role of which is usually played by the atmosphere, practically cannot be lower than the ambient temperature. You can increase the temperature of the heater. However, any material (solid body) has limited heat resistance or heat resistance. When heated, it gradually loses its elastic properties, and when sufficiently high temperature melts.
Now the main efforts of engineers are aimed at increasing the efficiency of engines by reducing the friction of their parts, fuel losses due to incomplete combustion, etc.
For a steam turbine, the initial and final steam temperatures are approximately as follows: T 1 - 800 K and T 2 - 300 K. At these temperatures, the maximum efficiency is 62% (note that efficiency is usually measured as a percentage). The actual value of the efficiency due to various kinds of energy losses is approximately 40%. Diesel engines have the maximum efficiency - about 44%.
Environmental protection.
It is hard to imagine modern world without heat engines. They provide us with a comfortable life. Heat engines drive vehicles. About 80% of electricity, despite the presence of nuclear power plants, is generated using heat engines.
However, during the operation of heat engines, inevitable environmental pollution occurs. This is a contradiction: on the one hand, every year humanity needs more and more energy, the main part of which is obtained by burning fuel, on the other hand, combustion processes are inevitably accompanied by environmental pollution.
When fuel is burned, the oxygen content in the atmosphere decreases. In addition, the combustion products themselves form chemical compounds harmful to living organisms. Pollution occurs not only on the ground, but also in the air, since any aircraft flight is accompanied by emissions of harmful impurities into the atmosphere.
One of the consequences of the operation of the engines is the formation of carbon dioxide, which absorbs infrared radiation from the Earth's surface, which leads to an increase in the temperature of the atmosphere. This is the so-called greenhouse effect. Measurements show that the temperature of the atmosphere rises by 0.05 °C per year. Such a continuous increase in temperature can cause the ice to melt, which in turn will lead to a change in the water level in the oceans, i.e., to the flooding of the continents.
Let's note one more negative point when using heat engines. So, sometimes water from rivers and lakes is used to cool engines. The heated water is then returned back. The increase in temperature in water bodies disrupts the natural balance, this phenomenon is called thermal pollution.
For environmental protection, various cleaning filters preventing release into the atmosphere harmful substances engine designs are being improved. There is a continuous improvement of fuel, which gives less harmful substances during combustion, as well as the technology of its combustion. Alternative energy sources using wind, solar radiation, and core energy are being actively developed. Electric vehicles and vehicles powered by solar energy are already being produced.
In reality, the work done with the help of any device is always more useful work, since part of the work is done against the friction forces that act inside the mechanism and when moving its individual parts. So, applying movable block, commit extra work, lifting the block itself and the rope and, overcoming the friction forces in the block.
We introduce the following notation: we denote useful work by $A_p$, full work- $A_(full)$. In doing so, we have:
Definition
Coefficient of performance (COP) called the ratio of useful work to full. We denote the efficiency by the letter $\eta $, then:
\[\eta =\frac(A_p)(A_(poln))\ \left(2\right).\]
Most often, the efficiency is expressed as a percentage, then its definition is the formula:
\[\eta =\frac(A_p)(A_(poln))\cdot 100\%\ \left(2\right).\]
When creating mechanisms, they try to increase their efficiency, but mechanisms with an efficiency equal to one (and even more than one) do not exist.
And so, the efficiency factor is a physical quantity that shows the share that useful work is from all the work done. With the help of efficiency, the efficiency of a device (mechanism, system) that converts or transmits energy that performs work is evaluated.
To increase the efficiency of mechanisms, you can try to reduce the friction in their axes, their mass. If friction can be neglected, the mass of the mechanism is significantly less than the mass, for example, of the load that the mechanism lifts, then the efficiency is slightly less than unity. Then the work done is approximately equal to the useful work:
The golden rule of mechanics
It must be remembered that a gain in work cannot be achieved using a simple mechanism.
Let us express each of the works in formula (3) as the product of the corresponding force by the path traveled under the influence of this force, then we transform formula (3) into the form:
Expression (4) shows that using a simple mechanism, we gain in strength as much as we lose on the way. This law called the "golden rule" of mechanics. This rule was formulated in ancient Greece by Heron of Alexandria.
This rule does not take into account the work to overcome friction forces, therefore it is approximate.
Efficiency in power transmission
The efficiency factor can be defined as the ratio of useful work to the energy expended on its implementation ($Q$):
\[\eta =\frac(A_p)(Q)\cdot 100\%\ \left(5\right).\]
To calculate the efficiency of a heat engine, the following formula is used:
\[\eta =\frac(Q_n-Q_(ch))(Q_n)\left(6\right),\]
where $Q_n$ is the amount of heat received from the heater; $Q_(ch)$ - the amount of heat transferred to the refrigerator.
The efficiency of an ideal heat engine that operates according to the Carnot cycle is:
\[\eta =\frac(T_n-T_(ch))(T_n)\left(7\right),\]
where $T_n$ - heater temperature; $T_(ch)$ - refrigerator temperature.
Examples of tasks for efficiency
Example 1
Exercise. The crane engine has a power of $N$. For a time interval equal to $\Delta t$, he lifted a load of mass $m$ to a height $h$. What is the efficiency of the crane?\textit()
Solution. Useful work in the problem under consideration is equal to the work of lifting the body to a height $h$ of a load of mass $m$, this is the work of overcoming the force of gravity. It is equal to:
The total work that is done when lifting a load can be found using the definition of power:
Let's use the definition of the efficiency factor to find it:
\[\eta =\frac(A_p)(A_(poln))\cdot 100\%\left(1.3\right).\]
We transform formula (1.3) using expressions (1.1) and (1.2):
\[\eta =\frac(mgh)(N\Delta t)\cdot 100\%.\]
Answer.$\eta =\frac(mgh)(N\Delta t)\cdot 100\%$
Example 2
Exercise. An ideal gas performs a Carnot cycle, while cycle efficiency equals $\eta$. What is the work in the gas compression cycle at constant temperature? The work done by the gas during expansion is $A_0$
Solution. The efficiency of the cycle is defined as:
\[\eta =\frac(A_p)(Q)\left(2.1\right).\]
Consider the Carnot cycle, determine in which processes heat is supplied (it will be $Q$).
Since the Carnot cycle consists of two isotherms and two adiabats, we can immediately say that there is no heat transfer in adiabatic processes (processes 2-3 and 4-1). In isothermal process 1-2 heat is supplied (Fig.1 $Q_1$), in isothermal process 3-4 heat is removed ($Q_2$). It turns out that in expression (2.1) $Q=Q_1$. We know that the amount of heat (the first law of thermodynamics) supplied to the system during an isothermal process goes completely to perform work by the gas, which means:
The gas performs useful work, which is equal to:
The amount of heat that is removed in the isothermal process 3-4 is equal to the work of compression (the work is negative) (since T=const, then $Q_2=-A_(34)$). As a result, we have:
We transform the formula (2.1) taking into account the results (2.2) - (2.4):
\[\eta =\frac(A_(12)+A_(34))(A_(12))\to A_(12)\eta =A_(12)+A_(34)\to A_(34)=( \eta -1)A_(12)\left(2.4\right).\]
Since by condition $A_(12)=A_0,\ $finally we get:
Answer.$A_(34)=\left(\eta -1\right)A_0$
Example. The average traction force of the engine is 882 N. It consumes 7 kg of gasoline per 100 km. Determine the efficiency of its engine. Find a useful job first. It is equal to the product of the force F by the distance S, overcome by the body under its influence Ап=F∙S. Determine the amount of heat that will be released when burning 7 kg of gasoline, this will be the work expended Az = Q = q∙m, where q is specific fuel, for gasoline it is equal to 42∙10^6 J/kg, and m is the mass of this fuel. Engine efficiency will be equal to efficiency=(F∙S)/(q∙m)∙100%= (882∙100000)/(42∙10^6∙7)∙100%=30%.
IN general case to find the efficiency of any heat engine (internal combustion engine, steam engine, etc.), where the work is done by the gas, has a coefficient useful actions equal to the difference in the heat given off by the heater Q1 and received by the refrigerator Q2, find the difference in the heat of the heater and the refrigerator, and divide by the heat of the heater Efficiency = (Q1-Q2)/Q1. Here the efficiency is in submultiples from 0 to 1, to translate the result, multiply it by 100.
To obtain the efficiency of an ideal heat engine (Carnot engine), find the ratio of the temperature difference between the heater T1 and cooler T2 to the temperature of the heater COP=(T1-T2)/T1. This is the maximum possible efficiency for a specific type of heat engine with given temperatures of the heater and refrigerator.
Define a common . This kind of information can be obtained by referring to the population census data. To determine the total birth, death, marriage and divorce rates, you need to find the product of the total population and the estimated period. Write the resulting number in the denominator.
Put on the numerator an indicator corresponding to the desired relative. For example, if you are faced with determining the total fertility rate, then in place of the numerator there should be a number reflecting the total number of births for the period you are interested in. If your goal is the death rate or marriage rate, then put the number of deaths in the place of the numerator. billing period or the number of people married, respectively.
Multiply the resulting number by 1000. This will be the overall coefficient you are looking for. If you are faced with the task of finding the total growth rate, then subtract the death rate from the birth rate.
Related videos
Sources:
- General Vital Rates
The word "work" refers primarily to activities that give a person a livelihood. In other words, he receives a financial reward for it. Nevertheless, people are ready in their free time either free of charge or for a purely symbolic fee to also participate in socially useful work aimed at helping those in need, landscaping yards and streets, planting trees and shrubs, etc. The number of such volunteers would certainly be even greater, but they often do not know where their services may be needed.
Many people want to take part in the improvement of their native city. They should contact the relevant structures of the local municipality, for example, those responsible for cleaning the territories, landscaping. There will be work for sure. In addition, you can, for example, on your own initiative, break a flower bed under the windows of the house, plant flowers.
There are people who love animals very much and want to help stray dogs and cats. If you are in this category, contact your local animal rights organizations or animal shelter owners. Well, if you live in major city where there are zoos, ask the administration if animal care assistants are needed
Moisture coefficient
The humidity coefficient is a special indicator developed by meteorologists to assess the degree of climate humidity in a particular region. At the same time, it was taken into account that the climate is a long-term characteristic weather conditions in this locality. Therefore, it was also decided to consider the humidification coefficient in a long time frame: as a rule, this coefficient is calculated on the basis of data collected during the year.Thus, the humidity coefficient shows how much precipitation falls during this period in the region under consideration. This, in turn, is one of the main factors determining the predominant type of vegetation in the area.
Moisture coefficient calculation
The formula for calculating the moisture coefficient is as follows: K = R / E. In the indicated formula, the symbol K denotes the moisture coefficient itself, and the symbol R denotes the amount of precipitation that fell in a given area during the year, expressed in millimeters. Finally, the symbol E denotes the amount of precipitation that evaporated from the surface of the earth, over the same period of time.The indicated amount of precipitation, which is also expressed in millimeters, depends on , the temperature in a given region at a particular time period and other factors. Therefore, despite the apparent simplicity of the above formula, the calculation of the moisture coefficient requires a large number of preliminary measurements using accurate instruments and can only be carried out by a fairly large team of meteorologists.
In turn, the value of the moisture coefficient in a particular area, which takes into account all these indicators, as a rule, makes it possible to determine with a high degree of certainty which type of vegetation is predominant in this region. So, if the moisture coefficient exceeds 1, this indicates a high level of humidity in the area, which entails the predominance of vegetation types such as taiga, tundra or forest tundra.
A sufficient level of humidity corresponds to a moisture coefficient equal to 1, and, as a rule, is characterized by a predominance of mixed or. Moisture coefficient ranging from 0.6 to 1 is typical for forest-steppe massifs, from 0.3 to 0.6 - for steppes, from 0.1 to 0.3 - for semi-desert territories, and from 0 to 0.1 - for deserts .
Sources:
- Humidification, humidification coefficients
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, ideal gas), then we can 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.
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Isobaric-isochoric |
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Isochoric-adiabatic |
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Isobaric-adiabatic |
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Isobaric-isochoric-isothermal |
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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 the efficiency of heat 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.).
