Numerical Prediction of Mixture Formation Process of an Ethanol Spray in a Rapid Compression and Expansion Machine

Abstract

This study deals with the development of controlled-ignition technology for high performance compression ignition alcohol engines. Among the alcohol fuels, we focused on Ethanol as a promising candidate of alternative fuels replacing from petroleum. In our previous study, visualization tests of spray mixture formation process up to auto-ignition for Ethanol-Diethyl either blend fuels had been conducted by using a constant volume electrical heating combustion chamber. Quantitative evaluation of auto-ignition quality was summarized in a form of 3D map that indicates the effects of surrounding gas pressure, temperature and Oxygen concentration on ignition delay. However, maximum surrounding gas pressure in the experiments was 2.8MPa much less than that of real engine due to the structure of the combustion chamber. As the next step, we originally designed and manufactured a RCEM (Rapid Compression and Expansion Machine with variable compression ratio) in order to investigate the mixture formation process up to auto-ignition of an Ethanol spray under surrounding gas conditions similar to real engine operating conditions with the consideration of the interaction between fluid motion of surrounding gas and fuel injection. Prior to carrying out the experiments, we numerically predicted the auto-ignition quality of an Ethanol spray in the rapid compression and expansion machine. One of the commercial CFD codes; CONVERGE was used in the computational calculation with the considerations of turbulence, atomization, evaporation and detailed chemical reaction. Effect of fluid motion and surrounding gas pressure and temperature inside the combustion chamber of the RCEM on an Ethanol spray mixture formation is mainly discussed in this paper.