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In the twenty-first century, exhaust emission control will remain a major technical challenge especially as additional pressures for fuel and energy conservation mount. To address these needs, a wide variety of engine and powertrain options must be considered. For many reasons, the piston engine will remain the predominant engine choice in the twenty-first century, especially for conventional and/or parallel hybrid drive trains. Emissions constraints favor the conventional port fuel-injected gasoline engine with 3-way exhaust catalyst, while energy conservation favors direct-injection gasoline and diesel engines. As a result of recent technological progress from a competitive European market, diesels, and most recently, direct-injection (DI) diesels now offer driveability and performance characteristics competitive with those of gasoline engines. In addition, DI diesels offer the highest fuel efficiency.

An experiment was performed using an optically accessible direct injection (DI) diesel engine to investigate the effects of exhaust gas recirculation (EGR) on diesel combustion. EGR was simulated using nitrogen and carbon dioxide as intake air diluents. Timing was adjusted to maintain constant start of combustion for all cases. Both diluents were found to be effective in reducing emissions of oxides of nitrogen. Soot emission was not changed by the addition of nitrogen; however, carbon dioxide substantially reduced soot emission while simultaneously reducing NOx emissions. NOx is reduced by intake air dilution is a change in flame temperature.

In this work, laser-induced incandescence (LII) and light scattering measurements are explored as means for the quantitative measurement of soot characteristics in a D.I. Diesel engine. Simultaneous, planar LII and light scattering signals from soot in an ethylene diffusion flame were imaged and calibrated against well-established data from laminar diffusion flame studies. The resulting calibration was transferred to results from an optically-accessible D.I. Diesel engine. Application of light scattering theory to the engine data produced planar images of the soot volume fraction, particle size and number density.

An experimental study has been conducted to characterize NO and soot evolution in an optically-accessible D.I. diesel engine with a square combustion chamber. Two-dimensional laser-induced fluorescence was used to characterize NO evolution. Soot evolution was characterized by two-dimensional laser-induced incandescence (LII) and Mie scattering techniques as well as direct photography of the flame luminosity. The engine operating parameters were set to provide optimum conditions for NO imaging. Attenuation of the UV beam proved to be the major obstacle in obtaining NO images. Therefore, oxygen was added to the intake air charge in order to reduce the optical density of the combustion medium. The NO images showed that the NO formation started almost immediately after ignition and ceased no later than 40 degrees ATDC. No soot images could be obtained by the laser-induced incandescence or Mie scattering methods before 20 degrees ATDC since the soot concentration was very low.

Simultaneous laser-induced incandescence and light scattering measurements were used to obtain images of the evolving soot field within an optically-accessible DI diesel engine. Optimum signal collection parameters were established based on preliminary measurements in an ethylene diffusion flame. The effects of intake air temperature on soot formation during diesel combustion were investigated. Although increased soot production was evident for the higher intake air temperature cases, local particle diameters and number densities of the soot were unaffected for each of the cases tested.