Ignition, Combustion and Emissions in a DI Diesel Engine Equipped with a Micro-Hole Nozzle 960321
In an attempt to achieve lean combustion in Diesel engines which has a potential for simultaneous reduction in no and soot, the authors developed a micro-hole nozzle which has orifices with a diameter as small as 0.06 mm. Combustion tests were carried out using a rapid compression-expansion machine which has a DI Diesel type combustion chamber equipped with the micro-hole nozzle. A comparison with the result of a conventional nozzle experiment revealed that the ignition delay was shortened by 30 %, and in spite of that, both peaks of initial premixed combustion and diffusion combustion increased significantly. The combustion in the case of the micro-hole nozzle experiment was accompanied with a decrease in soot emission, whereas an increase in NO emission. The trends in the heat release pattern and exhaust emissions described above could possibly be attributed to the fact that locally stoichiometric mixtures which are responsible for NO formation still remain in the combusting region in the flame even if the mean equivalence ratio in the flame is lean.