Influence of the in-cylinder gas density and fuel injection pressure on the combustion characteristics in a large-bore diesel engine

Engine research is going toward higher specific power and downsizing. This topic is of increasing interest in compression-ignition engines, due to high output demand and more restrictive legislation. This study focuses on the influence of in-cylinder gas density and fuel injection pressure on the combustion and performance in a large-bore medium speed research engine. From a baseline setup close to a commercial engine, the specific power density was augmented by higher in-cylinder pressure ranging from 200 to 300 bar. This corresponds to gas density between 65 and 90 kg/m³ at top dead center. In addition, fuel injection pressure was varied between 1500 and 2400 bar. Based on the literature, this is the first study to report engine operation with 300 bar cylinder pressure. The results show that ignition delay is significantly reduced by increasing the injection pressure, while gas density has only a moderate effect. In addition, specific nitrogen oxides increase strongly with higher injection pressure but only moderately with higher gas density. Running with high gas density permits to improve the engine fuel economy. The test outcomes also show that the combustion duration can be decreased by increasing the in-cylinder density.