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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 Volvo 9.6L diesel engine was converted to run on 100 percent compressed natural gas in order to demonstrate “significantly reduced exhaust emissions.” A descendent of the natural gas 9.6L engine developed on this project is being used in bus applications in Göteborg, Sweden. At the time this paper was written, Volvo had manufactured two out of 20 gas buses for the city of Goteborg. A lean-burn, stratified-charge combustion system was originally chosen for this project which included a precombustion chamber (prechamber) located in the cylinder head. The prechamber was used to replace the original diesel fuel injector and was fitted with its own fuel supply and spark plug. A near stoichiometric air/fuel mixture was produced in the prechamber and ignited by the spark plug. As combustion progressed in the prechamber, a violent jet was produced that ignited a lean mixture in the main combustion chamber.

Homogeneous Charge Compression Ignition (HCCI) combustion is limited in maximum load due to high peak pressures and excessive combustion rate. If the rate of combustion can be decreased the load range can be extended. From previous studies it has been shown that by using a deep square bowl in piston geometry the load range can be extended due to decreased heat release rates, pressure rise rates and longer combustion duration compared to a disc shaped combustion chamber. The explanation for the slower combustion was found in the turbulent flow field in the early stages of the intake stroke causing temperature stratifications throughout the charge. With larger temperature differences the combustion will be longer compared to a perfectly mixed charge with less temperature variations. The methods used for finding this explanation were high-speed cycle-resolved chemiluminescence imaging and fuel tracer planar laser induced fluorescence (PLIF), together with large eddy simulations (LES).