Influence of the Nozzle Spray Angle on Pollutant Formation and Combustion Efficiency for a PCCI Diesel Engine 2009-01-1445
In Common-Rail DI Diesel Engines, a low combustion temperature process is considered as one of the most important possibilities to achieve very small emissions and optimum performance. To reduce NOx and Soot strongly, it is necessary to achieve a homogenization of the mixture in order to avoid the higher local temperatures which are responsible for the NOx formation . Through the homogenization it is also possible to obtain a stoichiometric air-fuel ratio in order to significantly reduce the Soot emissions. One way to achieve this homogeneous condition is to start injection very early together with the use of higher EGR rates. The direct effect of these conditions cause a longer ignition delay (this is the time between start of the injection and auto-ignition during physical and chemical sub processes such as fuel atomization, evaporation, fuel air mixing and chemical pre-reactions take place) so that the mixture formation has more time to achieve a homogeneous state. This situation is unfortunaly applicable for only low- and part-load conditions. For high load conditions it is very difficult to obtain a homogeneous mixture because the start of the injection should be very late, i.e. close to the Top Dead Center and the consequence is that not enough time is available to form homogeneous mixture. A solution for this problem is the development of a closed loop control through an injection strategy. Additionally an optimum injection spray angle and bow low piston geometry should be found, which make it possible to achieve the lowest emissions under all load conditions .
In the present work, the influence of the spray angle was investigated in a Common-Rail DI Diesel engine. The engine was operated at conventional part-load conditions at 2000 rpm, three different EGR rates, and an injected fuel mass of 15 mg/cycle. All the fuel was injected in one injection event (one main injection).
For the single injection event, a variation of start of injection was carried out. The Nozzle type were conical and flow optimized geometries (ks nozzle) with hole diameters of 0.141 mm, length of hole of 1mm. Three spray angle were investigated 100°, 120° and 148° respectively.