Investigation of in-cylinder heat transfer in a low heat rejection diesel engine

In this study, it is investigated heat transfer characteristics of combustion chamber of a direct-injection diesel engine. The piston bowls were coated with a material with low heat transfer coefficient. The tests were performed at constant speed and four different engine loads. Piston bowls were coated with Yttria stabilized zirconia by plasma spray method. Woschni, Hohenberg and Eichelberg models, adopted frequently in the literature, were based on for the heat transfer calculation. As main heat transfer parameters, heat transfer coefficient, heat flux, cumulative gross heat release and cumulative heat transfer were handled. From the study, it was concluded that cumulative gross heat release and heat flux in combustion chamber increased in a significant rate with enhanced loads and piston coating application. In compression period, it was determined that Hohenberg's model usually gave higher heat transfer rate values; whereas, Woschni's model gave lower heat transfer rate values. With Woschni model, the heat transfer parameters were lower at low load, while they achieved to maximum values at high load. At highest load, cumulative heat release rate values were founded further close to each other for all used models in both engines.