Compression ratio influence on the performance of an advanced single-cylinder Diesel engine operating in conventional and low T combustion mode

The present paper describes a detailed experimental analysis on the effect of the compression ratio on the performance of a single-cylinder research diesel engine operating with both conventional combustion and Low Temperature Combustion mode for low NOx emissions. The single-cylinder engine was developed with the same combustion system architecture of the four-cylinder FIAT 1.9 liter Multi-Jet. Starting from an engine configuration with a compression ratio of 16.5, the compression ratio was reduced to 14.5. For both the geometric configurations, engine performance was evaluated in terms of thermodynamic parameters, emissions and fuel consumption in some operating test points representative of the engine behavior running on the NEDC cycle. The results of compression ratio reduction evidenced a strong improvement in NOx-particulate trade-off coupled with penalties in unburned compounds emissions (HCs+CO) and fuel consumption, highlighting advantages and limits of low compression ratio engines employing low temperature combustion concept.