Investigations of fuel injection strategy for cold starting direct-injection diesel engines

The introduction of high-pressure common-rail fuel injection systems for diesel engines has given much greater electronic control over the patterns of fuel injection. Fuel delivery per cycle can be split into several small injections. The effect of the number, proportionate size and timing of these on work output per cycle and cycle-by-cycle variability under cold-start conditions has been investigated experimentally. High work output and low variability are consistent with short repeatable start times. Fuel per cycle has been delivered in one, two, or three injections. The injection timing and quantity of each part were varied. Cold tests were carried out at an engine soak temperature of -10 degrees C and engine speed was motored up to 300 r/min before enabling fuelling. The average gross indicated mean effective pressure (IMEP) of the first five fuelled engine cycles was recorded as the prime measure of quality. Splitting the injection into two parts maximizes the IMEP produced on firing cycles; a three-part split confers no additional advantage. The timing and separation of the injections strongly influence the probability that non-firing cycles occur and in turn this strongly influences average IMEP values.