Correlation between Piston Surface Temperature and Piston Material and their Influence on Spray-Wall-Interaction and Spray Combustion

Abstract

Empirical models instead of physical knowledge mostly describe the heat transfer between combusting diesel sprays and piston walls in IC engines. Many influences on the wall heat transfer interfere with each other. This makes it difficult to investigate single parameters, which would be necessary for physical descriptions. Optical spray chambers offer test conditions suitable for such investigations. Thus, pervious work describes the heat transfer of impinging diesel sprays on flat walls under diesel relevant conditions or the influence of the impingement on the combustion of diesel fuel. Parameters like ambient conditions, wall distance and injection pressure were studied. Due to increasing power densities of IC engines, the wall material is a new parameter that has to be addressed. The increasing thermal and mechanical loads onto the piston demand changes in the used material or the surface after treatment. Accordingly, the resulting surface temperatures and heat fluxes are interdependent with the combustion. In this work, we show the temporal evolution of surface temperatures of different wall materials under impinging diesel flames in a constant pressure combustion chamber. The aluminum configuration reaches higher surface temperatures, than the steel configuration. The flames are planar characterized by their soot temperature (KL-method) and their OH* radical appearance. Due to higher surface temperatures a higher amount of rich fuel burns close to the wall in the aluminum configuration. In contrast the steel configuration shows a high ratio of premixed combustion in the wall jet vortex with less soot formation. The findings offer a detailed view on approved engine research, where aluminum The results of the current work count for the moment and place of flame wall interaction and do not average over an engine cycle. The local and temporal temperature peaks on the wall surface can influence the emission and soot formation as well lead to crack initialization and mechanic fatigue operating close the critical material temperatures.