Detection of mixture stratification in controlled auto-ignition engine using spontaneous optical emission signal

Abstract

In this study an optical-fiber sensor was utilized to observe spontaneous emissions of controlled auto-ignition (CAI) engine under stratified mixture combustion. Mixture stratification, achieved with the use of late direct fuel injection, is an effective approach to improve combustion controllability of the engine operated in the CAI mode. However, observed effects of injection timing on combustion show high combustion sensitivity even for early fuel injection. This study pertains identification of the reasons for such a high sensitivity to injection timing. To identify possible mixture stratification and resulting gradual combustion, optical-fiber sensor was used to observe spontaneous combustion emissions. Optical measurements enabled identification of stratified combustion, which was manifested by double optical signal peaks. The observed peaks of different amplitudes resulted from stepwise combustion in local zones with different mixture composition and flame temperature. The performed measurements enabled better understanding non-linear combustion timing behavior with variable degree of mixture stratification.