EFFECTS OF WALL TEMPERATURE ON THERMOPHYSICAL CHARACTERISTICS OF SPRAY-WALL IMPINGEMENT

Abstract

For small- and medium-bore diesel engines, the phenomenon of spray-wall impingement is unavoidable, which affects the evaporation of the fuel, thermal efficiency, and emissions. Wall temperature is an important parameter in this process because it has an important influence on fuel evaporation. In this paper, the thermophysical characteristics of spray-wall impingement at different wall temperatures were studied. The results showed that with increase of the initial wall temperature, the impingement spray radius increased, but its rate of increase decreased, while the impingement spray height first increased and then decreased. During this process, the surface heat flux first increased and then decreased with the increase of initial wall temperature, which was due to the change of heat transfer regime on the wall. The transient heat transfer process at different initial wall temperatures was characterized by the Biot and Fourier numbers and the dimensionless surface heat fluxes were highly similar. A dimensionless correlation was developed to quantify the transient heat transfer process, which showed that the ratio of the internal thermal resistance of heat conduction in the wall to the wall surface convective heat transfer resistance changes almost linearly during the process of spray-wall impingement.