Effects of DME pilot quantity on the performance of a DME PCCI-DI engine

The combination of premixed charge compression ignition and conventional direct-injection compression ignition combustion is studied in a DME engine. This combustion mode is referred to as PCCI-DI combustion. The pilot quantity is found to be one of main variables affecting the PCCI-DI combustion. So, the main objectives of this paper are to examine the effect of different DME pilot quantities on combustion and emission characteristics in a single-cylinder direct-injection DME engine and to determine whether PCCI-DI is a viable in-cylinder NOx emissions reduction technology. In order to evaluate the characteristics of PCCI-DI combustion, the conventional direct-injection compression-ignition engine performance is supplied to make a comparison with their results. Furthermore, special emphasis is put upon the combined combustion process analysis. Results show that DME engine can operate at a wide range of speeds and loads at PCCI-DI mode. In comparison to the conventional DME CI combustion, the brake thermal efficiency slightly increases for DME PCCI-DI operation. PCCI-DI is capable to decrease NOx effectively for all loads. NOx emission shows an obviously descending tendency with an increase in DME pilot quantity at low loads, while it shows a mildly elevating tendency with an increase in DME pilot quantity at high loads. HC and CO emissions increase for DME PCCI-DI operation under various DME pilot quantities.