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Some results of a systematic study of the effects of fuel and chamber gas properties on the transient evaporating spray mixing process are presented. The study uses an existing two-dimensional stochastic thick spray model. The results show that the combustion process in typical heavy duty, quiescent, DI diesel engines can be mixing limited rather than vaporization limited. In addition, the results show that the mixing process of a transient evaporating spray is characterized by the combined effects of fuel evaporation and its turbulent mixing with the surrounding air. In general, increasing the evaporation rate alone does not necessarily increase the fuel-air mixing rate. Furthermore, two dimensionless parameters have been used to quantify the relative effects of fuel and chamber gas properties on the transient spray evaporation process. Finally, through detailed comparisons between spray and gas jet results, the transient evaporating spray mixing process is better understood.

A transient spray mixing model forming the basis of heterogeneous combustion in direct injection diesel engines is described. Experimental results of transient fuel sprays in a high pressure, high temperature chamber form the basis of spray growth equations. Use of similarity of concentration profile across the spray in conjunction with spray geometry and mass conservation yields a complete description of spatial and temporal fuel-air distribution. Fuel preparation and air entrainment rates are calculated from the history of fuel-air distribution. Progressive evolution of combustion zones is determined by the fuel-air mixing process. Energy conservation and chemical kinetics calculations in each zone yield cylinder pressure and local nitric oxide concentration. The role of fuel-air mixing in diesel combustion is discussed. The model results are compared with experimental data.

Lucas Industries Noise Centre has introduced a combustion noise meter which is designed to predict the contribution of the combustion process to overall diesel engine noise. The performance of the meter is evaluated using Cummins B series engines in naturally-aspirated and turbocharged form. Combustion noise levels predicted by the meter are compared to levels determined using traditional techniques. The effects of several engine operating parameters on combustion noise are investigated under both steady state and accelerating conditions. The meter reliably predicts changes in combustion noise levels, and is a useful tool for performance development engineers. Combustion noise is shown to be related to the maximum rate of pressure rise at the onset of combustion, but combustion noise is not reliably related to maximum cylinder pressures.

Recent engine design trends towards increasing power, reducing weight, advancing of injection timing and increasing of injection rate and pressure could result in increased incidence of liner pitting. Liner pitting due to coolant cavitation is a complex function of many engine design parameters and operating conditions as described in reference [1]*. Traditionally, liner cavitation problems were not detected early in the development cycle. Traditional liner vibration and coolant pressure measurements in conjunction with a numerous amount of expensive engine endurance tests were then needed to resolve cavitation problems. A method newly developed by the author and described in reference [2] for cavitation intensity measurements was successfully utilized to map out engine operating condition and develop limit curves. This method could also be applied in a non intrusive fashion.

The Cummins V504 and V555 engines were developed for construction, industrial, agricultural, marine and medium duty automotive market requirements of lightweight, compact diesel engines in the 185-240 hp range. The engine design and development objectives were to obtain high reliability and durability combined with good overall efficiency in a compact package size. These objectives were achieved by careful attention to design details, combustion system development and extensive laboratory and field evaluation.

Measurements have been made to determine the effect of piston crown surface properties on combustion. Back-to-back engine tests were conducted to compare surface modified pistons to a production piston. Each modified piston was found to prolong combustion duration. Porous coatings and a non porous, roughened piston were observed to increase fuel consumption. Increase in fuel consumption was determined to be the result of increased heat release duration. The data show surface roughness alone affects the duration of heat release. The shift in magnitude of the centroid of heat release was similar to the shift observed in insulated engine experiments.

Water was inducted with the intake air and injected emulsified with the fuel, in a conventional single cylinder D.I. diesel engine. The major effects of inducted water were an increase in ignition delay, and reduction in the oxides of nitrogen and smoke at a constant fuel/air ratio. When the water was emulsified with the fuel, the ignition delay increased so much that no benefits were obtained except for a reduction in smoke. The results are compared to a similar study on an engine with the “M” combustion system. The major differences between the results obtained with the two combustion systems are attributed to the differences in the ignition delay caused by the water addition.