Are diesel engines more efficient? If so why?

Are diesel engines more efficient? If so why?
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answer:From Wikipedia : “Diesel engines often achieve greater fuel efficiency than petrol (gasoline) engines. Diesel engines have energy efficiency of 45% and petrol engines of 30%.[3] That is one of the reasons why diesels have better fuel efficiency that equivalent petrol cars. A common margin is 40% more miles per gallon for an efficient turbodiesel….The higher compression ratio is helpful in raising efficiency, but diesel fuel also contains approximately 10–20% more energy per unit volume than gasoline.” And this from http://autorepair.about.com: “A gasoline engine compresses at a ratio of 8:1 to 12:1, while a diesel engine compresses at a ratio of 14:1 to as high as 25:1. The higher compression ratio of the diesel engine leads to better efficiency.”
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