Fuel Distributions in a Firing Direct-Injection Spark-Ignition Engine Using Laser-Induced Fluorescence Imaging

Two- and three-dimensional images of fuel distributions in a continuously firing direct-injection stratified-charge engine have been recorded under moderate-load conditions using planar laser-induced fluorescence (LIF) from commercial gasoline. Cyclic variations in the fuel concentration at the spark gap (deduced from individual-cycle two-dimensional images) appear sufficient to account for the observed incidence of misfires and partial burns. Tomographic three-dimensional LIF images of the average fuel distribution at the time of spark indicate that ignitable mixture is present only in a thin shell around the periphery of the fuel cloud. Differences in power output and combustion stability during engine warm-up observed with two injectors of the same type are reflected in systematic differences in the fuel concentration near the spark gap as inferred from LIF data.