1998-02-23

Comparisons of Computed and Measured Results of Combustion in a Diesel Engine 980786

Results of computations of flows, sprays and combustion performed in an optically- accessible Diesel engine are presented. These computed results are compared with measured values of chamber pressure, liquid penetration, and soot distribution, deduced from flame luminosity photographs obtained in the engine at Sandia National Laboratories and reported in the literature. The computations were performed for two operating conditions representing low load and high load conditions as reported in the experimental work. The computed and measured peak pressures agree within 5% for both the low load and the high load conditions. The heat release rates derived from the computations are consistent with expectations for Diesel combustion with a premixed phase of heat release and then a diffusion phase. The computed soot distribution shows noticeable differences from the measured one. In general, the soot distribution indicates that the penetration of the computed combusting jet is less than that indicated in the measurements. The computed liquid penetration rate appears to agree adequately with that deduced from measurements though the maximum penetration does not. The effect of numerical resolution was also investigated. Noticeable differences are observed with different resolutions suggesting that the results may be used only as indicative of trends. However, with the higher resolution that was selected the computed and measured pressures agree adequately but there still are differences in the details of the flowfield. Hence, it appears that when global parameters associated with heat release agree adequately with measurements, the details of the flow field may still not be in agreement.

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