Efficiency of an Internal Combustion Engine

WR is the reversible work performed AH is the enthalpy change of the reaction 

The efficiency of an ICE is normally around 20% and, in general, the efficiencies of ICEs do not surpass 50% for the most efficient engines, for example, the steam turbines thus, in general a fuel cell is more efficient than a heat engine [128], 

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The thermal efficiency of a typical gasoline engine is approximately 25 to 30% and for a diesel ermine is 35 to 40%. The thermal efficiency of an internal combustion engine is defined as... 

When oil is used for lubrication of an internal combustion engine its primary function is to reduce the friction of moving parts under a wide range of operating temperatures and loads. At the same time it has to perform efficient heat transfer, deal effectively with accumulating carbon and dust particles, gum deposits, water and corrosive gases, and accomplish all of this without... 

Properly designed fuel cells may be as much as 70 percent efficient, about twice as efficient as an internal combustion engine. In addition, fuel-cell generators are free of the noise, vibration, heat transfer, thermal pollution, and other problems normally associated with conventional power plants. Nevertheless, fuel cells are not yet in widespread use. A major problem lies in the lack of cheap electrocatalysts able to function efficiently for long periods of time without contamination. The most successful application of fnel cells to date has been in space vehicles (Figure 19.12). 

Diesel generators are the energy source for many RAPS systems. Such units consist of an internal combustion engine (fuelled by diesel oil) and an alternator that produces a.c. power. Generators that deliver d.c. power have also been used, but they are no longer common as they are not as efficient as their a.c. counterparts. Petrol generators can also be employed for RAPS duty, but they have greater maintenance requirements and are more expensive to operate. 

Flow cells are ideal for stors e systems in remote locations. Vanadium redox systems, for instance, deliver up to 500 kW for up to ten hours. Zinc-bromine systems have been produced for 50-kWh and 500-kWh systems to reinforce weak distribution networks or prevent power fluctuations. Hydrogen fuel cells can potentially do almost anything a battery can do provide backup power, perform power leveling, run handheld devices, and supply primary or auxiliary power to cars, trucks, buses, and boats. In many cases they are more efficient than petrochemical fuels. A hydrogen fuel cell in a vehicle that uses an electric motor, for example, can be 40 to 60 percent efficient, compared with the 35 percent peak efficiency of the internal combustion engine. 

As an example, if the hot temperature is 1273 K (1000 °C) and the cold temperature 373 K (100 °C) then the efficiency is approximately 70%. In practice the operation of a real engine does not follow the Carnot cycle and the efficiency is considerably lower. For a medium sized motor car with an internal combustion engine the fuel efficiency is about 12%, much of the wasted 88% demanding water cooling. There are continuous improvements made in petrol and diesel engine technologies and in the fuels and projections suggest that thermal efficiencies a little over 50% will eventually be achieved. 

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