Gas Flow Measurements in Engine Cylinders

Interest in the measurement of gas flow in both spark ignition and compression ignition engine cylinders has increased since it has become evident that both swirl and turbulence can have an important influence on combustion and hence exhaust emissions. Among the methods available for indicating such flows, the hot wire anemometer would seem on balance to be the most suitable. Since the hot wire probe is sensitive to both mass flow rate and temperature of the gas, a circuit was devised which compensated automatically for variations in the latter. Measurements of gas velocity and turbulence were obtained during the induction and compression strokes of a motored 4-stroke engine in which the level of swirl could be varied by means of masked inlet valves. The validity of steady flow methods of assessing the swirl level associated with a given cylinder head geometry is discussed.