Just the Basics: Diesel Engine

How Diesel Engines Work. Like a gasoline engine, a diesel is an … engines, but Diesel saw that. as a plus. According to his …

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Just the Basics: Diesel Engine
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U.S. Department of Energy • Office of Energy Efficiency and Renewable Energy freedomCAR & vehicle technologies program Today’s direct-injection diesel engines are more rugged, powerful, durable, and reliable than gasoline engines, and use fuel much more efficiently, as well. Diesel Engines Yesterday, Today, and Tomorrow Diesels are workhorse engines. That’s why you find them powering heavy- duty trucks, buses, tractors, and trains, not to mention large ships, bulldozers, cranes, and other construction equipment. In the past, diesels fit the stereotype of muscle-bound behe- moths. They were dirty and sluggish, smelly and loud. That image doesn’t apply to today’s diesel engines, however, and tomorrow’s diesels will show even greater improvements. They will be even more fuel efficient, more flexible in the fuels they can use, and also much cleaner in emissions. How Diesel Engines Work Like a gasoline engine, a diesel is an internal combustion engine that converts chemical energy in fuel to mechanical energy that moves pistons up and down inside enclosed spaces called cylinders. The pistons are connected to the engine’s crankshaft, which changes their linear motion into the rotary motion needed to propel the vehicle’s wheels. With both gasoline and diesel engines, energy is released in a series of small explosions (combustion) as fuel reacts chemically with oxygen from the air. Diesels differ from gasoline engines primarily in the way the explosions occur. Gasoline engines start the explosions with sparks from spark plugs, whereas in diesel engines, fuel ignites on its own. Air heats up when it’s compressed. This fact led German engineer Rudolf Diesel to theorize that fuel could be made to ignite spontaneously if the air inside an engine’s cylinders became hot enough through compression. Achieving high temperatures meant producing much greater air compression than occurs in gasoline engines, but Diesel saw that as a plus. According to his calculations, high compression should lead to high engine efficiency. Part of the reason is that compressing air concen- trates fuel-burning oxygen. A fuel that has high energy content per gallon, like diesel fuel, should be able to react with most of the concentrated oxygen to deliver more punch per explosion, if it was injected into an engine’s cylin- ders at exactly the right time. Diesel’s calculations were correct. As a result, although

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