The objective of this study was to reduce pollutant emissions during cold start conditions in a spark-ignited direct injection engine, by exploring the potential of oxygenated fuels. With their high oxygen content and lack of direct C-C bonds, they effectively reduce particle number (PN) and NOx emissions under normal conditions.
Methanol was chosen due to its wide availability. As methanol is toxic to humans and associated with cold-start issues, a second promising synthetic fuel was selected to be benchmarked against gasoline, comprising 65 vol% of dimethyl carbonate and 35 vol% of methyl formate (C65F5).
Currently, there is a lack of detailed investigations on the cold start performance for both oxygenated fuels utilizing today’s injector capabilities.
Spray measurements were caried out in a constant volume chamber to assess the spray of C65F35. Reduced fuel temperature increased spray-penetration length and compromised fast vaporization. Therefore, the injection strategy becomes crucial to avoid spray-liner interaction and improve mixture formation. This was evaluated in a single-cylinder research engine, with the engine’s coolant water temperature maintained at -5°C.
Compared to gasoline’s optimal single injection at 7 bar indicated mean effective pressure, C65F35 achieved a ten-fold reduction in PN emissions. Simultaneously, fuel-losses were reduced by ~10% as blow-by was effectively avoided. For both oxygenated fuels, a single late compression stroke injection was found to be effective while maintaining reasonable combustion stability. Delayed injection timing during the compression stroke resulted in lower NOx emissions, but increased emissions of CO, CH4, and CH2O due to reduced homogenization time.