The mitigation of noise originating in self-ignition in gasoline engines at low speed (“self-ignition noise” below) is an issue in realizing increased commercial appeal. Low-speed self-ignition noise occurs sporadically, producing significant torque fluctuation and engine vibration in each cycle. Synchronizing measurements with the occurrence of the noise and reproducing the phenomenon has therefore represented a challenge, and progress has not been made in its analysis. The research discussed in this paper verified that an elementary process simulation was able to model combustion conditions in which self-ignition noise occurs with sufficient accuracy. Using this simulation, the research studied phenomena occurring at the level of elementary processes when self-ignition occurs, changes in self-ignition characteristics with changes in conditions, and methods of ameliorating self-ignition. The conditions varied in the simulations were air-fuel mixture temperature, compression ratio, excess air ratio, EGR, residual gas and octane number. The results of these studies showed that reducing fuel density by increasing leanness is an effective means of controlling self-ignition when the engine is restarted. In addition, it was shown that it is possible to control self-ignition by reducing the temperature of the air-fuel mixture through reduction of the ratio of residual gas. Further, the simulation can be utilized to predict self-ignition characteristics produced by changes in factors such as the octane number of the fuel and the temperature of the external air in different regions, and to set appropriate specifications, on the desktop.
Article of Honda R&D Technical Review Vol.25 No.1 (93 - 102)