Measurements of spatial flame propagation and flow velocities in a spark ignition engine

Abstract

Knowledge of flame propagation and flow characteristics enables a more detailed description of in-cylinder processes as well as assessing the influences of engine operating conditions and design parameters, particularly in regard to fuel economy and emission control. Spatial flame propagation in a single-cylinder spark-ignition engine is studied by a measuring technique that uses optical fibers coupled with photomultipliers. The propagation process is monitored through a large number of optical fibers arranged in a matrix in the combustion chamber wall. The spatial flame front shape, the flame volume, and the flame front velocity as a function of time are derived from these measurements. A dual beam laser-doppler-velocimeter (LDV), operating in forward scatter mode, is used to measure flow velocities of fluid motion in a motored and fired engine. Measurements are performed at several points within the combustion chamber. Signal processing is done by a counter. By averaging measurements over several engine cycles, mean flow velocity and RMS values are obtained. It was found that increasing the air-fuel ratio decreases the flame propagation rate and the burning velocity, whereas mean flow velocities of fluid motion are hardly affected. Swirl flow, generated by a shrouded inlet valve, leads to higher mean flow velocities, higher flame front velocities, and higher burning velocities, and the flame front is deformed.