NUMERICAL AND EXPERIMENTAL EVALUATION OF DI-DIESELSOOT AND NITROGEN OXIDE EMISSIONS IN RESPECT OFDIFFERENT INJECTION STRATEGIES

摘要

In direct injection diesel engines the fuel atomisation process strongly affectscombustion and exhaust emissions. The demands on modern injection systems concerning aminimisation of emissions and fuel consumption are significant driving forces for the optimisationof the fuel injection process and the mixture formation in the cylinder. Besides experimentalparametric studies CFD-Simulations are an excellent tool to understand physical processesmore thoroughly. In addition to a further increase of the maximum injection pressurefuture injection systems will have to offer a high flexibility of rate shaping as well as high reproducibility.The Institute of Technical Combustion (ITV) at the University of Hannover has developed anew piezoelectrically controlled common rail injection system for research purposes. Its fundamentaldifference to conventional common rail injectors is that the piezo-element is directlyconnected with the needle enabling a highly dynamic and extremely accurate movement andpositioning of the needle during the injection. The system is used to investigate the requirementsand the potential of different injection rates and their influence on the fuel atomisationprocess. Therefore optical investigations were accomplished on a rapid compression machineto get precise information about the spray. These investigations were followed by experimentalexaminations on a single cylinder research engine, which allows a verification by an emissionand cylinder pressure analysis. In order to support the experiments simulations with the3D-CFD-Code KIVA-3V were used to estimate the influences of different injection nozzlesand strategies on soot and nitrogen oxide emissions.The objective of this paper is to give fundamental methods to minimize toxic exhaust componentslike nitrogen oxides and soot. Thus the influence of different injection nozzles and injectionrates on the emissions were investigated with a piezoelectrically controlled researchinjector. Additionally the CFD-Simulation could emphasize the experimental results and givedetailed information about the physical sub-processes. It is shown that there are very reasonableagreements between the 3D-Simulation and the experimental examinations.