The concept of direct-injection spark-ignited engines is attractive for many reasons, but the literature has shown that implementation of the concept is difficult. Specifically, the performance and emission of these types of engines have been shown to be extremely sensitive to engine operating conditions. A thorough understanding of the interaction between the fuel spray and in-cylinder gas flow is required for successful implementation of this engine concept. To this end, the primary objective of this dissertation was to investigate the in-cylinder interaction in a motored direct-injection spark-ignited engine.
The methodology of this investigation involved two steps. First, the performance of a candidate fuel injector was characterized outside of an engine. Next, the injector was characterized inside an engine and the results were compared to those obtained out-of-cylinder. Three representative loads, injection pressures, and injection timings were examined.
The injector used in this investigation was a single fluid, single hole fuel injector, actuated by an electronically controlled solenoid. In-cylinder experiments were performed using a single cylinder Ricardo Hydra optical engine fitted with a four-valve pent-roof cylinder head.
The principal measurement diagnostics employed for experiments were solid-state imaging and diffraction based particle sizing, both of which were developed for the purposes of this investigation.
The results of the low load in-cylinder experiments indicated that the interaction between the spray and the in-cylinder gas was minimal. The results of the in-cylinder experiments closely resembled those of the out-of-cylinder experiments.
In the case of the medium and high load operating conditions, the interaction between the in-cylinder gas and spray was found to be much more significant. This was particularly true for the high load case. In-cylinder spray shapes were dramatically altered by the in-cylinder gas flow when the start of injection was set to occur during the intake stroke. Effects due to high in-cylinder gas pressures were observed when the start of injection was set to occur during the compression stroke. Penetration of the spray was reduced and features due to the internal geometry of the injector became visible.