Four-stroke Engine Four-stroke Engine
The forerunner of the four-stroke engine was the internal combustion engine without compression. The new invention in 1876 was the compression of the mixture in the 'compression cycle'. By compressing the air, a better combustion developed, because of shorter distances (carbon- seeks for oxygen atom). For the first stationary experimental engine, running on illuminating gas and with 6.1 litres capacity and 3 HP with 180 1/min, this was still a rather theoretical concept.
Contrary to the two-stroke engine, the four strokes, intake stroke, compression stroke, combustion stroke, and exhaust stroke, take place one after the other during one lift of the piston, half a crankshaft, in the same combustion chamber. The engine management influences the incoming and outgoing gases.
The speed of the crankshaft is not homogeneous during the course of the different strokes. In Particular, there are differences comparing the compression and the combustion stroke. During the former, the piston is obstructed, during the latter it is accelerated. This is also true for the starter, during the compression stroke, especially with diesel engines, it becomes substantially slower.
The majority of four-wheeled vehicles is surely equipped with four (or more)-cylinder engines featuring the four-cycle principle. The cylinder filling is improved and kept relatively free of exhaust gases by controlling the in- and outgoing gas flows.
Using the exhaust gas recirculation, the exhaust gases might be redirected to the fresh air flow.