Improvement of Combustion in a Direct Injection Diesel Engine by the Use of a Combination-Hole Injection Nozzle

Abstract

Suppression of pre-mixed combustion and activation of diffusion combustion in DI diesel engines are known to be effective in reducing both NO_x and fuel consumption. To achieve this concept, the authors have proposed a new type of fuel injection nozzle named combination-hole nozzle. This nozzle has very small holes with a diameter of 0.13 mm below (sub holes) for reducing ignition delay and normal holes (main holes) for keeping reasonable injection duration. The experiments conducted with a single cylinder research engine revealed that the combination-hole nozzle reduced the ignition delay and the peak value of the rate of heat release during the premixed combustion by 10% and 40% respectively compared with the experimental results of conventional nozzles and that the trade-off curve between NO_x and fuel consumption sifted to the low level corner at half and full load conditions at a low engine speed. The reason for this improvement was investigated by the measurement of flame temperature distribution in the combustion chamber by means of the two colors method. The result revealed that the flame temperature in regions between sub and main hole's flames of the nozzle was lower than that of the flames of a conventional nozzle at a full load and a low speed condition.