2013
Transportation & Automotive

The most efficient engines in the world are two-stroke diesels. They are used in locomotives and ships where fuel cost is the most important thing. However their peak efficiency (about 50%) is at one power level, which is usually the maximum power. Locomotives solve this problem by having multiple engines and running as many as needed. That way they can have the peak efficiency at any load. Four-stroke diesels are used in trucks and buses. They are not as efficient (about 40%) but have a wide useful power range. Gasoline car engines are less efficient (peak at about 35%) but engineers have improved hybrid car efficiency. Generally hybrids run the engine at its most efficient power level. The Prius ...

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