<div class="htmlview paragraph">A study has been made of an automotive direct-injection diesel engine in order to identify the effects of the combustion chamber geometry on combustion, with special emphasis focused on a re-entrant combustion chamber.</div> <div class="htmlview paragraph">Conventional combustion chambers and a re-entrant one were compared in terms of the combustion process, engine performance and NOx and smoke emissions. Heat transfer calculations and heat release analyses show that the re-entrant chamber tends to reduce ignition lag due to the higher temperatures of the wall on which injected fuel impinges.</div> <div class="htmlview paragraph">Analyses of turbulent flow characteristics in each chamber indicate that the re-entrant chamber enhances combustion because of the higher in-cylinder velocity accompanied by increased turbulence. Further, analyses of in-cylinder gas samples show lower soot levels in the re-entrant chamber. As a result, a good compromise can be achieved between fuel economy and exhaust emissions by retarding the fuel injection timing.</div>