A single-shot optical engine driven by a rapid compression and expansion machine(RCEM) was built to simulate the combustion process. It could be raised its speed up to 4500 rpm during combustion period in the first operating cycle. Tests were performed in order to investigate the effects of engine speed, ignition position and swirl on early combustion and overall performance with premixed LPG-air charge. The combustion visualization was employed for this purpose simultaneously with the cylinder pressure measurements. The variation of volumetric efficiency with swirl was eliminated during the tests by maintaining uniform charging while heat transfer effects were minimized by limiting the experiment to early stage of combustion. Therefore, the investigation was concentrated on examining the combined engine speed and swirl strength effects on early combustion performance.
For central ignition, swirl showed consistently favorable effects on combustion-related performances displayed in terms of maximum cylinder pressure, flame growth rate and flame front wrinkling. However, at half radius ignition the desirable swirl effect persisted at low engine speeds but faded away as the speed increased. This reversing of trends can be partially explained by difference in the above mentioned performances.
