Influence of the wall temperature and combustion chamber geometry on the performance and emissions of a mini HCCI engine fueled with diethyl ether

Nowadays for small-scale power generation there are electrochemical batteries and mini engines. Many efforts have been done for improving the power density of the batteries but unfortunately the value of 1 MJ/kg seems to be asymptotic. If the energy source is an organic fuel which has an energy density of around 29 MJ/kg with a minimum overall efficiency of only 3.5%, this device would surpass the batteries. This paper is the fifth of a series of publications aimed to study the HCCI combustion process in the milli domain at high engine speed in order to design and develop VIMPA, Vibrating Microengine for Low Power Generation and Microsystems Actuation. Previous studies ranged from general characterization of the HCCI combustion process by using metal and optical engines, to more specific topics for instance the influence of the boundary layer and quenching distance on the quality of the combustion. The result of all these studies was that the heat losses are a formidable problem when the combustion takes place in the milli domain. The aim of this paper is to study the influence of the wall temperature and combustion chamber geometry in order to understand if it is possible to reduce the heat losses and improve the combustion process hence higher energy density. The results have shown that improvements can be achieved by an appropriate choice of the materials and minimization of the area to volume ratio but with attention to the quenching phenomenon.