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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.

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.

The application of planar laser-induced Rayleigh scattering for quantitative 2-D measurements of vapor-phase fuel concentration in the main combustion zone of a direct-injection Diesel engine has been explored, developed and demonstrated. All studies were conducted in an optically accessible direct-injection Diesel engine of the “heavy-duty” size class at 1200 rpm and motored TDC conditions which were typical of the production version of this engine. First, this study verifies that beyond 27 mm from the injector all the fuel is vapor phase. This was done by investigating the Diesel jet under high magnification using 2-D elastic scatter imaging and subsequently evaluating the signal intensities from the droplets and other interfering particles (Mie scattering) and the vapor (Rayleigh scattering).

A combination of optical imaging diagnostics has been applied to the fuel jet of a direct-injection diesel engine to study the ignition and early soot formation processes. Measurements were made in an optically accessible direct-injection diesel engine of the “heavy-duty” size class at a representative medium speed (1200 rpm) operating condition. Two fuels were used, a 42.5 cetane number mixture of the diesel reference fuels and a new low-sooting fuel (needed to reduce optical attenuation at later crank angles) that closely matches both the cetane number and boiling point of the reference fuel mixture. The combustion and soot formation processes are found to be almost identical for both fuels. Ignition and early combustion were studied by imaging the natural chemiluminescence using a calibrated intensified video camera. The early soot development was investigated via luminosity imaging and simultaneous planar imaging of laser-induced incandescence (LII) and elastic scattering.

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.

Experiments have been conducted in a firing single-cylinder spark-ignition engine employing a Ford Zetec cylinder head that has been modified to operate with either standard port-fuel-injection, air-forced port-fuel-injection or direct-injection. The engine utilizes a fused silica cylinder and therefore provides extensive optical access to the combustion chamber. Tests were conducted using a constant speed simulated cold start procedure, which is composed of an initial start-up transient and a quasi-steady-state idle period. In this procedure, the engine is briefly motored at 889 rpm and then combustion commences shortly after the start of fuel injection. Measurements which were performed include in-cylinder pressure as well as intake valve, exhaust valve, piston, cylinder, head, and intake air temperature throughout each cycle of the test period. The engine-out total hydrocarbon emissions were also measured.