A two stroke diesel 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.
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, most gasoline engines utilizes the Otto cycle, in which fuel and air are mixed before entering the combustion chamber and then ignited by a spark plug.
[edit] Two strokes
- Intake begins when the piston is near bottom dead centre. Air is admitted to the cylinder through ports in the cylinder wall (there are no intake valves). Since the piston is moving downward at this time, aspiration due to atmospheric pressure isn't possible. Therefore a positive displacement blower or hybrid turbo-supercharger (a turbocharger that is mechanically driven from the crankshaft at low engine speeds) is employed 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 previous power stroke, a process referred to as scavenging. As the piston passes through bottom dead center, the exhaust valves will be closed and, owing to the pressure generated by the blower or turbocharger, the cylinder will be filled with air. Once the piston starts upward, the air intake ports in the cylinder walls will be covered, sealing the cylinder. At this point, compression will commence. Note that exhaust and intake actually occur in one stroke, the period during which the piston is near the bottom of the cylinder.
- As the piston rises, compression takes place and near top dead center, fuel injection will occur, resulting in combustion, driving the piston downward. As the piston moves downward in the cylinder it will reach a point where the exhaust valves will be opened to expel the combustion gases. Continued movement of the piston will expose the air intake ports in the cylinder wall, and the cycle will start anew. Note that the cylinder will fire on each revolution, as opposed to the four-stroke engine, in which the cylinder fires on every other revolution.
[edit] Roots blower
The Roots blower is commonly used on the two stroke diesel engine, which requires some form of forced induction. In this application, the blower does not provide significant compression and these engines are considered naturally aspirated; turbochargers are generally used when significant "boost" is needed. The Rootes Co. two-stroke diesel engine, used in Commer and Karrier vehicles, had a Roots-type blower but the two names are not connected.
[edit] Brands
Front of an old Commer bus
- Commer was a British manufacturer of commercial vehicles which existed from 1905 until 1979. Many Commer vans and lorries are notable for being fitted with the Rootes TS3 engine, a two-stroke diesel three-cylinder horizontally-opposed piston engine, which came to be known as the "Commer Knocker" due to the unique noise it produced. Newer Commer vehicles had Perkins and Cummins diesel engines, and less commonly Mercedes diesel engines. [1]
- In 1954, Rootes Group introduced a supercharged diesel engine, based on a Sulzer Brothers concept. This was the TS3 2-stroke 3-cylinder engine, with 2 opposed inward facing pistons per cylinder, which drove the crankshaft through rockers. The 3.25 litre engine developed 90 hp (67 kW), equivalent to contemporary 4-stroke diesel engines of more than twice the capacity. The engine was used in Commer trucks as well as an industrial engine. Production ceased in 1968 after the Chrysler takeover.
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