Two-stroke diesel engine
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A two stroke diesel engine is a diesel engine that works in two strokes. A diesel engine is an internal combustion engine which operates using the Diesel cycle. Invented in 1892 by German engineer Rudolf Diesel, it was based on the hot bulb engine design and patented on February 23, 1893. During the period of 1900 to 1930, four-stroke diesel engines enjoyed a relative dominance in practical diesel applications. Charles F. Kettering and colleagues, working at the various incarnations of Electro-Motive and at the General Motors Research Corporation during the 1930s, advanced the art and science of two-stroke diesel technology to yield engines with much higher power-to-weight ratios than the two-stroke diesels of old. This work was instrumental in bringing about the dieselisation of railroads in the 1940s and 1950s.
All diesel engines use compression ignition, a process by which fuel is injected after the air is compressed in the combustion chamber causing the fuel to self ignite. By contrast, gasoline engines utilize the Otto cycle, in which fuel and air are mixed before entering the combustion chamber and then ignited by a spark plug.
Two-stroke internal combustion engines are more simple mechanically than four-stroke engines, but more complex in thermodynamic and aerodynamic processes. In a two-stroke engine, the four "cycles" of internal combustion engine theory (intake, compression, ignition, exhaust) occur in one revolution, while in a four-stroke engine it occurs in two complete revolutions. In a two-stroke engine, more than one function occurs at any given time during the engine's operation.
- Intake begins when the piston is near the bottom dead center. Air is admitted to the cylinder through ports in the cylinder wall (there are no intake valves). All two-stroke Diesel engines require artificial aspiration to operate, and will either use a mechanically-driven blower or a hybrid turbo-supercharger to charge the cylinder with air. In the early phase of intake, the air charge is also used to force out any remaining combustion gases from the preceding power stroke, a process referred to as scavenging.
- As the piston rises, the intake charge of air is compressed. Near top dead center, fuel is injected, resulting in combustion due to the extremely high pressure and heat created by compression, which drives the piston downward. As the piston moves downward in the cylinder it will reach a point where the exhaust port is opened to expel the high-pressure combustion gasses. However, most current two-stroke diesel engines use top-mounted poppet valves and uniflow scavenging. Continued downward movement of the piston will expose the air intake ports in the cylinder wall, and the cycle will start again.
In most GM and EMD engines, very few parameters are variable and all the remaining ones are fixed. The scavenging ports are open from about 45 degrees before bottom dead center to about 45 degrees after bottom dead center (this parameter is necessarily symmetrical about bottom dead center) and the fuel is injected at 4 degrees before top dead center. The remaining parameters have to do with exhaust valve timing, and these are set to effect maximum exhaust scavenging and maximum intake charge air, and these two parameters are not necessarily symmetrical about top dead center. A single camshaft operates the valves and the Unit injector, using three lobes: two for exhaust valves (either two valves on the smallest engines or four valves on the largest; and the third for the Unit injector.
- Burmeister & Wain, double-acting diesels for marine propulsion from 1930 onwards, also made by shipbuilders under licence.
- Detroit Diesel, uniflow engines for on- and off-road trucks, on-road buses and stationary applications
- Electro-Motive Diesel, uniflow diesel engines for marine, railway and stationary applications
- Fairbanks-Morse, opposed-piston diesel engines for marine and stationary applications.
- Gray Marine, uniflow diesel engines for marine applications
- MAN Diesel & Turbo, crosshead diesel engines for marine propulsion
- Mitsubishi Heavy Industries, crosshead diesel engines for marine propulsion
- Rootes Group, the Commer TS3 engine for trucks
- Wärtsilä, crosshead diesel engines for marine propulsion
- Sloan, Alfred P. (1964), McDonald, John, ed., My Years with General Motors, Garden City, NY, USA: Doubleday, LCCN 64011306, OCLC 802024. Republished in 1990 with a new introduction by Peter Drucker (ISBN 978-0385042352).