The evolution of the diesel combustion system toward the near zero emission goal.

In the present paper, a new concept of combustion at low flame temperature, based on the use of highly diluted charge, is presented and its advantages and drawbacks on diesel engine application are critically discussed. In particular, the focus is on the mechanism of soot suppression at a low flame temperature achieved by an adequate use of cooled exhaust gas recirculation (EGR) and injection setting without changing the engine architecture. It was found that the flame temperature limit, corresponding to soot and NOx free conditions, can be achieved at a low load by accurate control of the EGR and injection parameters. Tests have demonstrated that near zero emission limits can be reached in a diesel engine at low load without strong fuel economy penalties. The use of a low temperature super-diluted combustion mode is limited to low load range, indicating that further major research activity is needed to reach reliable practical applications.