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Modes of Engine Combustion

Modes of Engine Combustion

The movies above show three unique types of engine combustion. The movies were acquired at the ERC using a highly modified engine that allows optical access through the piston and a high-speed CMOS camera. The view is up towards the head of the combustion chamber. All of the movies are synchronized to start at the same time, and are shown at an equivalent frame rate of 14,000 frames per second. The high temperature, chemically active products give off light, and this is detected by the camera.

Spark ignition combustion is typically found in automotive, motorcycle, outboard marine and utility engines. A fuel-air mixture is inducted into the engine, and the mixture is ignited by a spark plug. A flame propagates out from the spark plug, consuming the reactant mixture.

Diesel combustion is found in over-the-road trucks, heavy machinery and a small fraction of automobiles in North America. Air is inducted into the engine and compressed to a high pressure and temperature. At the desired time, the fuel injector is actuated. For this engine, there are eight small holes through which the fuel is injected. The high temperature air mixes with the fuel and it ignites. Much of the light observed is from radiation from soot particles.

Homogeneous-charge compression-ignition combustion (HCCI) is a hybrid combustion strategy that is being actively researched. Like a spark-ignition engine, a mixture of fuel and air is inducted into the chamber; but instead of igniting the mixture with a spark plug, the high temperature that results from compression of the mixture to a high pressure causes the mixture to spontaneously react. The time for ignition is slightly different at the different locations in the chamber. One benefit of this type of combustion is how quickly it consumes the fuel - note that the HCCI process is over before the spark-ignition combustion even gets established.