An Experimental Study of Gas Velocity, Flame Propagation and Pressure in a Spark Ignition Engine

A laser Doppler velocimeter, flame ionisation gauge and piezoelectric transducer have been used to measure two components of velocity, arrival of the flame front and pressure in the cylinder of a four-stroke spark ignition engine. The engine was operated with a sequence of five firing and ten non-firing cycles with the former having an equivalence ratio of 0.9 and giving rise to a misfire, a subsequent high-charge cycle, and three normal-charge cycles. The resulting fast- and slow-burn cycles were identified readily in terms of maximum pressure and flame-arrival times. The two-dimensional velocity vectors suggest that the flame fronts were initially spherical and subsequently distorted by the expansion of burned gas with increase in velocity fluctuations. The magnitude of the maximum velocity fluctuations was quantified by sampling according to the maximum velocity for each cycle, corresponding to the arrival of the flame front, and shown to be larger in the direction of propagation and in front of the flame.