The use of a phase change material within a cylinder wall in order to detect knock in a gas SI engine

Abstract

The present paper studies the possibility to develop a new method of knock detection in a gas SI engine. This method is based on the increase in'the wall heat flux when knock occurs. It also must be simple enough to be used by industry. In order to achieve this goal, a metallic Phase Change Material is put within the wall cylinder. The melting of the PCM means that knock has occurred and is persistent. The melting of such a phase change material would be easy to detect using industrial measurement tools. In this paper, numerical simulations of unsteady heat transfer across the cylinder wall are presented. Unsteady heat transfer from the hot gas to the wall chamber is simulated by a self-developed program. This program allows fixing instantaneous local heat flux values deduced from the literature in case of both normal and knocking combustion. Heat transfer across the cylinder wall is solved by the finite volume technique. Grid is validated by comparison with analytical results. Melting is treated by the Voller and Prakash model and Sodium is chosen as PCM. Among all the results, we can notice that an increase in the knock intensity changes the shape of the isothermal curves around and inside the PCM. This leads to an increase in the melting velocity with a higher rate than the increase in the heat flux.