Effects of equivalence ratio on the near-stoichiometric combustion and emission characteristics of a compression ignition (CI) engine

Abstract

In the present study, the combustion and emission characteristics under near-stoichiometric conditions were investigated for a compression ignition engine. In order to control the equivalence ratio, the exhaust gas recirculation (EGR) rate was changed while the amount of fuel was held constant. Furthermore, two different injection pressures (50 and 100 MPa) were used to study the effects of injection pressure on combustion and emissions. The experimental apparatus consisted of a test engine based on a single-cylinder applied common-rail direct-injection system with a displacement volume of 373.3 cm(3), a compression ratio of 17.8, a re-entrant type piston-bowl, and exhaust emission measurements. The results showed that the indicated mean effective pressure (IMEP) gradually decreased as the equivalence ratio increased for cases of near TDC injection. The operating range of the injection timing was extended at higher injection pressures. Furthermore, extremely low NOx emission was achieved under near-stoichiometric combustion conditions, even at a high injection pressure of 100 MPa. While soot emission significantly increased in the near-stoichiometric combustion regime, it was subsequently reduced at a high injection pressure.