Influence of direct-injection ratio on combustion and emissions of a stoichiometric spark-ignition dual-injection gasoline engine at different throttle percentages and injection timings of direct-injection

Dual-injection in a spark-ignition engine has attracted extensive attention due to the advantage in controlling mixture formation and particulate emissions. The influence of direct-injection ratio (R-DI) on combustion and emissions of a stoichiometric spark-ignition dual-injection gasoline engine at different throttle percentages (TP) and injection timings of direct-injection (DIIT) was investigated experimentally. Experimental results show that at a constant R-DI (R-DI > 0), the MCP (maximum cylinder pressure)(TP=15%, DIIT=280 degrees CA BTDC) > MCPTP= 15%, DIIT=50 degrees CA BTDC >> MCPTP=7%, DIIT=280 degrees CABTDC > MCPTP= 7%, DIIT=50 degrees CA BTDC. The R-DI has a significant effect on low and medium loads and DIIT = 50 degrees CA BTDC. The maximum cylinder pressure, maximum heat release rate and maximum cylinder temperature fall significantly with increasing R-DI, and their corresponding crank angles are delayed obviously with increasing R-DI. The R-DI has an obvious influence on combustion starting point, combustion center and combustion duration at low load and late DIIT. At R-DI = 100%, the COVimep (coefficient of variation in indicated mean effective pressure) of TP = 7% and DIIT = 50 degrees CA BTDC reaches the highest value of 13%. Except TP = 7% and DIIT = 50 degrees CA BTDC, the COVimep of other case conditions can be controlled below 5%. At R-DI = 50%, BSNOX(brake-specific nitrogen oxides) TP=15%, DIIT=280 degrees CA BTDC emissions are approximately 23.3%, 128.4% and 214.1% higher than BSNOX TP=7%, DIIT=280 degrees CA BTDC, BSNOX TP=15%, DIIT=50 degrees CA BTDC and BSNOX TP=15%, DIIT=280 degrees CA BTDC emissions, respectively. At R-DI = 50%, the soot(TP= 15%, DIIT=50 degrees CA BTDC) emission is approximately 49.9% higher than soot(TP= 7%, DIIT=50 degrees CA BTDC) emission, soot(TP= 7%, DIIT=50 degrees CA BTDC) emission is approximately 28.6 times higher than soot(TP= 15%, DIIT=280 degrees CA BTDC) emission, and sootTP= 15%, DIIT=280 degrees CA BTDC emission is approximately 11.1% higher than soot(TP= 7%, DIIT=280 degrees CA BTDC) emission. Through comprehensive compromise of combustion and emission performance, the best R-DI is 40%-60%.

Automated summary

Dual-injection in a spark-ignition engine is important for controlling mixture formation and particulate emissions. The effects of direct-injection ratio (R-DI) on combustion and emissions were investigated in a stoichiometric spark-ignition dual-injection gasoline engine. The results showed that R-DI had a significant influence on combustion and emission performance, with the best R-DI found to be 40%-60%.