Effect of Injection Strategy on Cold Start Performance in an Optical Light-Duty DI Diesel Engine

The present study investigates cold start at very low temperatures, down to −29 deg C. The experiments were conducted in an optical light duty diesel engine using a Swedish class 1 environmental diesel fuel. In-cylinder imaging of the natural luminescence using a high speed video camera was performed to get a better understanding of the combustion at very low temperature conditions. Combustion in cold starting conditions was found to be asymmetrically distributed in the combustion chamber. Combustion was initiated close to the glow plug first and then transported in the swirl direction to the adjacent jets. A full factorial study was performed on low temperature sensitivity for cold start. The effects of cooling down the engine by parts on stability and noise were studied. Furthermore, different injection strategies were investigated in order to overcome the limited fuel evaporation process at very low temperatures. A strategy with 3 pilot injections and increasing fuel quantity for each injection gave a more homogeneous combustion. The natural luminescence was symmetrically distributed in the piston bowl and all the jets contributed to the combustion. Significant improvements in combustion stability, load level and potential for load increase were observed as well.