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Experiments and modeling of a spray impinged onto a cavity wall of a simulated piston were performed under simulated diesel engine conditions (pressure and density) at an ambient temperature. The diesel fuel was delivered from a Bosch-type injection pump to a single-hole nozzle, the hole being drilled in the same direction as the original five-hole nozzle. The fuel was injected into a high-pressure bomb in which an engine combustion chamber, composed of a piston, a cylinder head and a cylinder liner, was installed. Distributions of the spray impinged on the simulated combustion chamber were observed from various directions while changing some of the experimental parameters, such as combustion chamber shape, nozzle projection and top-clearance. High-speed photography was used in the constant volume bomb to examine the effect of these parameters on the spray distributions.

The homogeneous charge, compression-ignition (HCCI) combustion process has the potential to significantly reduce NOx and particulate emissions, while achieving high thermal efficiency and the capability of operating with a wide variety of fuels. This makes the HCCI engine an attractive technology that can ostensibly provide diesel-like fuel efficiency and very low emissions, which may allow emissions compliance to occur without relying on lean aftertreatment systems.

A program to explore the effects of natural and additive-derived cetane on various aspects of diesel performance and combustion has been carried out. Procedures have been developed to measure diesel engine fuel consumption and power to a high degree of precision. These methods have been used to measure fuel consumption and power in three heavy-duty direct-injection diesel engines. The fuel matrix consisted of three commercial fuels of cetane number (CN) of 40-42, the same fuels raised to CN 48-50 with a cetane improver additive, and three commercial fuels of base CN 47-50. The engines came from three different U.S. manufacturers and were of three different model years and emissions configurations. Both fuel economy and power were found to be significantly higher for the cetane-improved fuels than for the naturally high cetane fuels. These performance advantages derive mainly from the higher volumetric heat content inherent to the cetane-improved fuels.

Distributions of non-evaporating diesel sprays impinging on a simulated combustion chamber wall were observed from various directions while changing some of the experimental parameters, such as nozzle projection and top-clearance. High-speed photography was used in this study to examine the effects of these parameters on the spray distributions. Moreover, the spray distributions were predicted by using a spray model based on a multi-package model. The calculated distributions were displayed three-dimensionally using a volume rendering application developed by the authors. The predicted spray distributions were compared with the experimental results observed from various directions in order to evaluate the spray model.

The combustion processes in the prechamber and the main chamber of a small indirect injection (I.D.I.) diesel engine were observed simultaneously by high-speed photography. These observations made it possible to characterize the behavior of flames in both chambers, that is, ignition of fuel, developing and rotating flames in the prechamber, and a flame jet spouting into the main chamber. The effect of engine variables, such as fuel injection timing, cross-sectional area of a throat, fuel injector location, and a recess in a piston top, on the combustion process as well as the engine performance were considered. A flame jet spouting into the main chamber separated into two directions and induced two vortexes. Brown sooty flames appeared along the prechamber wall and inside the flame jet which struck on the piston top. The higher-velocity flame jet and the two Intense vortexes induced by the flame jet realized superior fuel consumption and lower smoke emission.

A high-speed photographic study is presented illustrating the influence of engine variables such as an introduced air swirl, the number of nozzle holes and the piston cavity diameter, on the combustion process in a small direct-injection (D.I.) diesel engine. The engine was modified for optical access from the under and lateral sides of the combustion chamber. This modification enabled a three-dimensional analysis of the flame motion in the engine. The swirling velocity of a flame in a combustion chamber was highest in the piston cavity, and outside the piston cavity it became lower at the piston top and at the cylinder head in that order. The swirl ratio of the flame inside the cavity radius attenuated gradually with piston descent and approached the swirl ratio outside the cavity radius, which remained approximately constant during the expansion stroke. Engine performance was improved by retarding the attenuation of the swirl motion inside the cavity radius.