Experimental Study of the Scavenging and Combustion Processes in a Two-Stroke Cycle Research Engine

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.