The 2-stroke Diesel Cycle
THE DIESEL ENGINE
The diesel engine was invented by French born engineer Rudolph Diesel in the late nineteenth century. The diesel is a compression ignition type of internal combustion engine in which fuel is injected or sprayed into the cylinder after the air in it has been compressed to a temperature of approximately 550oC, thus causing the instant ignition of the fuel, at substantially constant pressure. Diesel fuel is also much less volatile than petrol thus reducing the incidence of fires.
Diesel engines are either 2-stroke or 4-stroke cycle. The 2-stroke type, such as the General Motors Detroit Diesel 71 and 110 series, relied on a scavenging action to clear the burnt gases from the cylinder. To achieve this they were fitted with a Roots blower that was gear driven from the engine to maintain the scavenging action. The Roots blower provides the capacity to move air into the cylinders to carry out the scavenging action but does not provide any level of air compression such as that provided by a supercharger or turbocharger. These small 2-stroke diesels provided excellent performance for their capacity but have lost favour in recent years due to the increased levels of exhaust emissions from this type of engine. Indeed Detroit Diesel, a great proponent of the small 2-stroke diesel, has now ceased its production and moved to the 4-stroke type. However, the 2-stroke diesel does continue in production with the larger EMD locomotive type prime movers such as the Model 645 and Model 710 where there is sufficient scope to provide the necessary environmental controls without degrading engine performance.
The 2-stroke Diesel Cycle
4-stroke diesels are naturally aspirated, however, to achieve additional power output they are generally either supercharged or turbocharged. The supercharger is normally gear or belt driven from the engine and through compression, increases the volume of air fed into the engine cylinders thus effectively improving the combustion and increasing the engine's performance. A turbocharger performs the same function as the supercharger but is driven by the effect of engine exhaust gases on a turbine that drives the air compressor. An intercooler or aftercooler may also be provided between the turbocharger and the engine to cool the compressed air and increase the density of the air for combustion going into the cylinders.
The 4-stroke Diesel Cycle