<Li> 2016: Electro - Motive Diesel introduces locomotives powered by its new 1010J four - stroke Diesel engine to comply with USEPA Tier 4 emissions requirements . Over 80 years of emphasis on two - stroke Diesel power by EMD and its ancestral companies comes to an end . </Li> <P> The diesel internal combustion engine differs from the gasoline powered Otto cycle by using highly compressed hot air to ignite the fuel rather than using a spark plug (compression ignition rather than spark ignition). </P> <P> In the true diesel engine, only air is initially introduced into the combustion chamber . The air is then compressed with a compression ratio typically between 15: 1 and 23: 1 . This high compression causes the temperature of the air to rise . At about the top of the compression stroke, fuel is injected directly into the compressed air in the combustion chamber . This may be into a (typically toroidal) void in the top of the piston or a pre-chamber depending upon the design of the engine . The fuel injector ensures that the fuel is broken down into small droplets, and that the fuel is distributed evenly . The heat of the compressed air vaporizes fuel from the surface of the droplets . The vapour is then ignited by the heat from the compressed air in the combustion chamber, the droplets continue to vaporise from their surfaces and burn, getting smaller, until all the fuel in the droplets has been burnt . Combustion occurs at a substantially constant pressure during the initial part of the power stroke . The start of vaporisation causes a delay before ignition and the characteristic diesel knocking sound as the vapour reaches ignition temperature and causes an abrupt increase in pressure above the piston (not shown on the P-V indicator diagram). When combustion is complete the combustion gases expand as the piston descends further; the high pressure in the cylinder drives the piston downward, supplying power to the crankshaft . </P> <P> As well as the high level of compression allowing combustion to take place without a separate ignition system, a high compression ratio greatly increases the engine's efficiency . Increasing the compression ratio in a spark - ignition engine where fuel and air are mixed before entry to the cylinder is limited by the need to prevent damaging pre-ignition . Since only air is compressed in a diesel engine, and fuel is not introduced into the cylinder until shortly before top dead centre (TDC), premature detonation is not a problem and compression ratios are much higher . </P>

How much compression does a diesel engine have