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Efficiency of engine

8 Answers
Which engine has the maximum efficiency ?
B

The maximum efficiency of an engine is strictly defined by the laws of thermodynamics. In particular, this is defined by the Carnot efficiency which states that the efficiency is

eta <= 1 - T_c / T_h,

where T_c is the temperature of the cooling side, typically surrounding and T_h is the temperature of the hot side, that is, combustion temperature. As we can see, the hotter the combustion temperature the more efficient the engine will run. Simultaneously we must ensure proper cooling to keep T_c as cool as possible.

In any case, for practical cases, the most efficient engine that we can mass produce is the Diesel engine. This engine manages to maximize its efficiency by compressing the gas to very high pressures, coupled with a turbo this ensures that once the fuel ignites due to the high pressure and heat, the combustion temperature will similarly be very high. In addition, the added pressure results in more exchange of gas expansion by the combustion since the gas molecules are more tightly packed.

The most efficient type of Diesel engines, known as direct injection type, are known to have efficiencies of about 40%.

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N

The Carnot cycle has the greatest theoretical efficiency due to the concept of perpetual motion. A liquid or gas can flow through the cycle freely without any energy input, again in theory, however due to friction, and other forces that act against the liquid (such as a work output or turbine) the Carnot cycle is renamed the Diesel cycle. This is more efficient than the Otto cycle because the Diesel cycle requires pressure to ignite the fuel rather than a spark from a spark plug.

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P

The Carnot engine represents an engine with maximum efficiency, however, an engine like this has never been created and never will. An internal Combustion engine, such as the engines in your car, 62% of the energy from the gasoline being burned is lost to the environment in the form of heat, sound, CO2, etc.

As Angels55 said, the electric motor is much more efficient

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S

In my opinion the most efficient engine would be a steam engine.(or heat engine) where it is very well insulated to avoid heat loss and also have an intake exhaust heat exchanger to recycle as much heat back to the air intake as possible. This is what is being done now on heating units for homes where the exhaust is so cool that it can be ducted with PVC piping.

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A

For heat engines, the one describe by Carnot is theoretically the most efficient. However, an engine based on the Carnot cycle does not exist. Diesel designed his engine to follow the Carnot cycle, and that engine is one of the more efficient practical ones.

In general, electric motors, as in electric cars, are more efficient.

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H

In a woking engine some of the energy are lost inform of heat contrary to non working engine where there is no energy loss therefore a working engine has less efficiency than non working engine.

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H

reversible Heat engines is the one which has the maximum efficiency

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S

Efficiency of an Engine is a ratio of output power to input power.

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