Search Results

Ionization probes built into the head gasket and uniformly distributed around the cylinder bore of a knocking, spark-ignition engine have been used to locate the autoigniting end-gas region. As normal combustion evolves after spark ignition, the ionization probes individually respond to the arrival of the propagating flame. Then, when autoignition occurs, the probes located in the end-gas region respond in rapid succession. By utilizing pressure transducer measurements to determine when autoignition occurs, the ionization probe response becomes a means to locate the end-gas region. Knowledge of the location of the last ionization probe to detect the normal flame can then be used to infer where, within the end-gas region, autoignition first occurred.

Experimental investigations of the scavenging, mixture preparation and combustion processes occurring in a blower-scavenged, direct-injected, two-stroke cycle research engine are presented. As the delivery ratio is increased, combustion performance deteriorates rapidly. We used a variety of diagnostic techniques to investigate the causes of this behavior, including pressure measurements, schlieren and Mie-scattering flow visualization, and ionization-probe determination of flame-arrival times. By comparison with premixed-charge operation of the engine, we conclude that the improved scavenging that accompanies increased delivery ratio results in cooler gas temperatures that inhibit fuel vaporization, leading to a highly nonhomogeneous fuel-air mixture at the time of combustion.