Heat loss is one of the main causes of energy losses in modern direct injection diesel engines. This heat loss of the engine occurs during combustion, mainly due to the heat transfer between the impinging spray flame and the piston cavity wall. It is of more critical in small size engines. In order to decrease heat transfer, we need to examine the phenomenon of heat transfer through the combustion chamber walls more fully. To achieve this, we investigated the effects of flame impingement on transient heat flux to the wall. By using a constant volume vessel with a fixed impingement wall, the surface heat flux of the wall at the locations of spray flame impingement was measured with three thin film thermocouple heat flux sensors. The combined effect of impingement distance and injection pressure on the heat transfer was investigated parametrically. The results showed that an increase of injection pressure with longer impinging distance led to an increase in the heat transfer coefficient, which had a dominant effect on local heat flux compared with local temperature distribution. Moreover, we confirmed that the relation between Nusselt number and Reynolds number is a useful measure for describing the heat transfer phenomena in diesel combustion.

<div class="section abstract"><div class="htmlview paragraph">Substantial amount of fuel energy input is lost by heat transfer through combustion chamber walls in the internal combustion engines. Thus, these heat losses account for reduced thermal efficiency, in that spray-wall impingement plays a crucial role in Direct Injection diesel engines. The objective of this study is to investigate the mechanism of the heat transfer from the spray/flame to the impinging wall under small diesel engine-like condition and how the spray characteristics are affected with regards to effect of injection pressure, nozzle hole diameter and impingement distance. The experiment results showed that injection pressure was predominant factor on spray-wall heat transfer.</div></div>

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