Improvement of combustion in a direct injection diesel engine by micro-hole nozzle

In an attempt to promote the atomization of fuel spray and the mixing of fuel and air in diesel engines, a micro-hole nozzle which has orifices with a diameter smaller than 0.10 mm was developed. In this study, the combustion tests were carried out using a single cylinder diesel engine equipped with a micro-hole nozzle and a common rail type high-pressure fuel injection system. A comparison with the results of a conventional nozzle experiment showed that the peak of initial premixed combustion'increased, but the peak of diffusion combustion decreased. As a result, when nozzle orifice diameter become small from ø 0.15 mm to ø 0.10 mm, the combustion was accompanied by smokeless with the same levels of NOx emission and fuel economy. And results of a comparison the toroidal type chamber with the shallow dish type chamber revealed that the optimization of combustion chamber is necessary for the increase of the injection stage with increasing of the number of nozzle orifice. If an orifice diameter becomes ø 0.06 mm, the diffusion combustion can not be observed and the combustion is formed of only premixed combustion. The combustion in the case of ø 0.06 mm was accompanied with the drastic deterioration of fuel economy, smoke and HC with all over load. But the micro-hole nozzle has a potential for the formation of the lean and homogeneous premixed mixture until the fuel-air mixture ignites.