Effects of injection timing and fuel pulse width on mixture preparation and hydrocarbon emissions of the first cranking cycle under different initial piston positions

A fuel-injection strategy has been developed to reduce the hydrocarbon emissions and improve the performance of the first cranking cycle. The strategy is to deliver fuel injection individually according to the initial piston position in each cylinder. It allows cylinders at different initial phases to obtain appropriate and similar air–fuel mixtures. The objective of this study is to investigate the effects of the injection timing and fuel pulse width on the mixture preparation and the hydrocarbon emissions when the piston is cranked to start from different initial positions. Experiments were conducted on cylinder No.1 of a four-cylinder port fuel injection engine in both the ambient mode and hot mode. For each initial position of the piston, different injection timings and fuel pulse widths were tested. The effects of the injection timing and fuel pulse width on the mixture and hydrocarbon emissions were evaluated by measuring the hydrocarbon concentrations of the in-cylinder mixture and exhaust gas after each injection. The experimental results show that, the effects of the injection timing and fuel pulse width depend largely on the initial position of the piston. For example, when the piston is cranked to start from the mid-intake, fuel injection can barely form an ignitable mixture under different injection timings and fuel pulse widths. In addition, the temperature of the coolant can also influence the effects of the injection timing and fuel pulse width. To formulate the independent injection strategy for each cylinder for the first cranking cycle, the initial phase of the piston and the coolant temperature must be taken into consideration.