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A comparison of scanning mobility particle sizer (SMPS) and laser-induced incandescence (LII) measurements of diesel particulate matter (PM) was performed. The results reveal the significance of the aggregate nature of diesel PM on interpretation of size and volume fraction measurements obtained with an SMPS, and the accuracy of primary particle size measurements by LII. Volume fraction calculations based on the mobility diameter measured by the SMPS substantially over-predict the space-filling volume fraction of the PM. Correction algorithms for the SMPS measurements, to account for the fractal nature of the aggregate morphology, result in a substantial reduction in the reported volume. The behavior of the particulate volume fraction, mean and standard deviation of the mobility diameter, and primary particle size are studied as a function of the EGR for a range of steady-state engine speeds and loads for a turbocharged direct-injection diesel engine.

Diesel and gasoline engines face tightening particulate matter emissions regulations due to the environmental and health effects attributed to these emissions. There is increasing demand for measuring not only the concentration, but also the size distribution of the particulates. Laser-induced incandescence has emerged as a promising technique for measuring spatially and temporally resolved soot volume fraction and size. Laser-induced incandescence has orders of magnitude more sensitivity than the gravimetric technique, and thus offers the promise of real-time measurements and adds information on the increasingly desirable size and morphology information. Quantitative LII is shown to provide a sensitive, precise, and repeatable measure of the soot concentration over a wide measurement range.

A widely held belief in the combustion community is that the chemical and hydrodynamic structure of a stretched laminar premixed flame can be preserved in a turbulent flow field over a range of conditions collectively known as the flamelet regime, and the homogeneous charge spark-ignition engine combustion falls within the domain of this regime. The major assumption in the laminar flamelet concept as applied to the turbulent premixed flames is that the flame front behaves as a constant-property passive scalar surface, and an increase in the wrinkled flame surface area with increasing turbulence intensity is the dominant mechanism for the observed flame velocity enhancement. The two approaches that have been recently used for estimating a measure of the wrinkled flame surface area in spark-ignition engines and other premixed flames are the flame surface density concept and fractal geometry.

Diesel engines face tightening particulate matter emissions regulations due to the environmental and health effects attributed to these emissions. There is increasing demand for measuring not only the concentration, but also the size distribution of the particulates. Laser-induced incandescence has emerged as a promising technique for measuring spatially and temporally resolved particulate volume fraction and size. Laser-induced incandescence has orders of magnitude more sensitivity than the gravimetric technique, and thus offers the promise of real-time measurements and adds the increasingly desirable size and morphology information. The usefulness of LII as a diagnostic instrument for the precise measurement of particulate concentration and primary particle size has been demonstrated. Measurements have been performed in the exhaust of a single cylinder DI research diesel engine. Simultaneous gravimetric filter measurements were made for direct comparison with the LII technique.

Laser-induced incandescence has emerged as a promising technique for measuring spatially and temporally resolved particulate volume fraction and size. Laser-induced incandescence has orders of magnitude more sensitivity than the gravimetric technique, and thus offers the promise of real-time measurements and adds the increasingly desirable size and morphology information. Particulate matter emissions have been measured by laser-induced incandescence and the standard gravimetric procedure in a mini dilution tunnel connected to the exhaust of a single-cylinder diesel engine. The engine used in this study incorporates features of contemporary medium- to heavy-duty diesel engines and is tuned to meet the U.S. EPA 1994 emission standards. The engine experiments have been run using the AVL 8-mode steady-state simulation of the U.S. EPA heavy-duty transient test procedure.

A technique to determine flame surface density in a spark-ignition engine from planar laser-induced fluorescence (PLIF) images of the flame front is presented. To resolve the flame surface density in a three-dimensional fully turbulent flow field from two-dimensional images, the direction cosine (angle of intersection between the PLIF laser sheet and the normal to the flame front) must be known. To determine the direction cosine, images from orthogonal planes in the engine have been used to resolve the mean orientation angle along the line of intersection of the planes. The effect of engine speed and fuel-air equivalence ratio on the flame surface density are investigated. The flame surface density (∑) profiles and orientation angle are presented as a function of the progress variable. The direction cosines are almost identical in both orthogonal planes, indicating the isotropic nature of the flame front. As the engine speed is reduced, the direction cosine increases slightly.

Intermittent and highly transient dense diesel sprays were investigated using laser diffraction and laser sheet illumination techniques to decipher the internal spray structure. Through careful experimental design, the unperturbed structure of the dense core region of a transient full cone diesel spray was observed for the first time. Diffraction measurements showed that larger droplets exist at the spray periphery and the Sauter mean diameter decreases from the periphery to the spray centerline. The results from both laser diffraction and 2-D imaging are inconsistent with the existence of an intact liquid core extending to a few hundred nozzle diameters. The intermittent and highly transient nature of diesel sprays ensures rapid and complete atomization within no more than twenty nozzle diameters.