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This paper presents an experimental investigation conducted to determine the parameters that control the behavior of autoignition in a small-bore, single-cylinder, optically-accessible diesel engine. Depending on operating conditions, three types of autoignition are observed: a single ignition, a two-stage process where a low temperature heat release (LTHR) or cool flame precedes the main premixed combustion, and a two-stage process where the LTHR or cool flame is separated from the main heat release by an apparent negative temperature coefficient (NTC) region. Experiments were conducted using commercial grade low-sulfur diesel fuel with a common-rail injection system. An intensified CCD camera was used for ultraviolet imaging and spectroscopy of chemiluminescent autoignition reactions under various operating conditions including fuel injection pressures, engine temperatures and equivalence ratios.

Biodiesel is a desirable alternative fuel for the diesel engine due to its low engine-out soot emission tendency. When blended with petroleum-based diesel fuels, soot emissions generally decrease in proportion to the volume fraction of biodiesel in the mixture. This paper presents an experimental investigation of biodiesel impact on in-cylinder soot temperature and concentrations in a single-cylinder, small-bore, optical access, compression ignition engine. While in-cylinder soot measurements have been widely performed with two-color thermometry implemented on digital cameras, their finite dynamic range limits the observation of soot due to its dramatically different radiation intensities. To expand the dynamic range of two-color measurements, this investigation utilizes three cameras. A high-speed CMOS color camera with a wide-band Bayer filter is used to obtain simultaneous measurements of soot temperature and KL factor for high intensity soot clouds within one cycle.