Strategies to Reduce HC-Emissions During the Cold Starting of a Port Fuel Injected Gasoline Engine

In view of tight emission standards, injection strategies to reduce raw HC-emissions during the cold starting of port fuel injected engines are evaluated in this study. The relevance of spray targeting and atomization is outlined in the first part of this paper. The foundation and performance of different injector concepts with respect to spray characteristics are discussed. Laboratory experiments demonstrate that concepts relying on auxiliary energy, such as air-assistance, fuel heating and injection at elevated system pressures, are capable of producing spray droplet sizes in the SMD-range of 25μm. For future injection strategies aimed at the compliance of SULEV emission levels, this target value is considered to be essential.

In the second part of this paper, emission tests of selected injector concepts are carried out using a V6-3.2I ULEV engine operated both in a vehicle and on a test bench. In this context, the relevance of an optimized start calibration as well as defining engine operating boundary conditions is discussed. Improving the fuel flow inside current injector designs already yields a 20-30% reduction of raw HC-emissions during cold starting. Significant reductions in the range of 40-50% are achieved by means of heated-tip injectors and fuel injection at elevated system pressures. Additionally, an FTP75 test series for selected concepts is presented.