G071021 An Investigation on Potential of Combustion Improvement by Direct Injection in a Natural Gas Engine

Abstract

The aim of this study is to investigate the potential of direct injection (DI) for improvement of thermal efficiency of a compressed natural gas (CNG) engine. The thermal efficiency, burning velocity, combustion stability and exhaust emissions of the DI were compared to those of conventional PFI under various engine loads and equivalence ratio conditions. The thermal efficiency of the CNG engine was improved by DI particularly at low engine loads and lean mixture conditions as a result of improved burning velocity. However, at high load condition, the thermal efficiency of DI was lower than that of conventional PFI due to insignificant improvement in burning velocity and insufficient mixing time. The DI showed higher unburned emissions than PFI regardless of engine operating conditions due to insufficient mixing time and corresponding deterioration in mixing quality.