Numerical simulations were used to study the effect of reduced nozzle hole size and nozzle tip hole configuration on the combustion characteristics of a high speed direct injection diesel engine. The KIVA code coupled with the Chemkin chemistry solver was used for the calculations. The calculations were performed over wide ranges of equivalence ratio, injection timing and injection pressure. Three nozzle hole layouts were considered; the baseline conventional nozzle, and multi- and group-hole configurations. In the multi-hole case, the number of holes was doubled and the hole size was reduced, while keeping the same hole area as for the baseline nozzle. The group-hole configuration used the same hole number and hole size as the multi-hole case, but pairs of holes were grouped with a close (0.2mm) spacing between the holes. The results of the mixture distributions showed that the group hole configuration provides similar penetration and lower inhomogeneity to those of the baseline large hole nozzle with the same nozzle flow area. Consequently, the fuel consumption and pollutant emissions, such as CO and soot, are improved by using the group-hole nozzle instead of the conventional hole nozzle over wide operating ranges. On the other hand, the multi-hole nozzle has advantages in its fuel consumption and CO emissions over the conventional hole layout at intermediate equivalence ratios (equivalence ratios from 0.46–0.84) and conventional injection timings (SOI: 15° BTDC).

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