In order to improve engine-out emissions and performance of Diesel combustion systems, continued insight into the complex combustion and fuel spray processes must be gained. An optically accessible Diesel engine and modern diagnostic imaging methods can contribute to the understanding of the fuel spray, combustion, and soot formation phenomena that occur during the four-stroke engine cycle. This work will discuss non-intrusive methods of data acquisition used to gather in-cylinder information using an International VT275-based, optical DI Diesel engine with an electro-mechanical engine control system implemented for consistency of engine boundary conditions. Infrared, visible, and intensified OH imaging techniques are used to characterize fuel spray, combustion, and soot formation processes over a range of different operating conditions, including conventional and low-temperature combustion schemes. Probability maps of the in-cylinder occurrence of fuel, combustion, and soot volumes under low temperature combustion conditions are presented to analyze the effects that changes in engine load have on the process of combustion. The influence of the injector nozzle geometry on fuel spray characteristics and how these characteristics affect combustion is discussed. Comparisons between the combustion and soot production processes of oxygenated, bio-derived fuels and pump Diesel fuel are evaluated. General trends of in-cylinder soot formation are shown to compare well with engine-out filter smoke number emissions data across a range of loads, nozzle geometries, and fueling conditions.
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