Numerical Study of Wall-Impinging Ignition at Different Wall Distances for Cold Start of Heavy-Duty Diesel Engine

The effect of the cold wall with different wall distances on ignition at low temperatures is complex and systematic analyses are still needed. Therefore, this work numerically reveals the effect mechanism of wall distance on the spray and ignition characteristics for the diesel engines. In which a four-component surrogate fuel was used, and the simulation well represents the experiments. The results show that the cold wall has little influence on the ignition when the wall distance is larger than a critical distance, and the critical distance is determined by the proportion of vapor phase in the impinged fuel and the chemical reaction degree at the time of impingement. As the wall distance reduces, the mass of impinged liquid fuel and the fuel film increases, resulting in less and earlier disappearance of appropriate air-fuel mixture; the fuel evolution process is more inclined to the route of low temperature and low concentration, causing the delay of chemical reactions. The misfire occurs when the time required for chemical reactions exceeds the time of fuel dissipation. Moreover, varying wall distance changes the timing of the local fuel cooling, which leads to diverse effects. The results of the 0-D simulation show that during the transition from low-temperature reaction to high-temperature reaction, earlier the fuel cooling leads to a more substantial inhibition effect. The fuel cooling after the start of the high-temperature reactions has little impact on the chemical reaction