Spectroscopic Investigation of Chemiluminescence in Gasoline Homogeneous Charge Compression Ignition Engine

Abstract

A spectroscopic diagnostic system has been designed to study the effects of different engine parameters on the chemiluminescence characteristic of HCCI combustion. Light emitted during the combustion process was collected by an optical fiber installed in the spark plug hole. An imaging spectrograph separated the light into the component wavelength and a high speed CCD camera captured the resulting light spectrum. The engine parameters studied in this work were intake temperature, fuel delivery method, fueling rate, air-fuel ratio, and intake charge preheating. Two different fuels were used in this experiment: pure isooctane and a primary reference fuel blend with an octane number of 87 (PRF 87). At each data point, a set of time-resolved chemiluminescence spectra were obtained, along with the cylinder pressure and exhaust emissions data. Based on the results, it was determined that different engine parameters affect the start of ignition timing in HCCI combustion without altering the reaction pathways of the fuel. The thermal history of the air-fuel mixture greatly affects the ignition timing. However, once the ignition starts, the fuel follows the same reaction pathways and produces the same intermediate species regardless of the thermal history of the mixture. The chemiluminescence spectra of HCCI combustion appear as several distinct peaks corresponding to emissions from CHO, CH2O, CH, and OH superimposed on top of a CO-O continuum. A strong correlation was found between the chemiluminescence light intensity and the rate of heat release. At the lower fueling rate conditions, the light intensity was too weak for further analysis.