Exploiting new combustion regime using multiple premixed compression ignition (MPCI) fueled with gasoline/diesel/PODE (GDP)

- Gasoline/diesel/PODEn (GDP) has medium CN, high volatility and high oxygen content.
- MPCI could be achieved with GDP two-stage direct injection in diesel engine.
- GDP MPCI break the trade-off between thermal efficiency and combustion noise.
- GDP MPCI achieves high-efficiency and ultra-low PM and NOx.

GDP is a blend fuel containing gasoline, diesel, and polyoxymethylene dimethyl ethers (PODE). Previous study has shown that by combining premixed ratio and high fuel oxygen content, GDP partially premixed combustion ignition (PPCI) broke the trade-off between NOx and soot with moderate exhaust gas recirculation (EGR) while maintaining high engine efficiency. In this work, multiple premixed compression ignition (MPCI) mode was adopted to break the trade-off between fuel economy and combustion noise, which is the major challenge of the single injection GDP PPCI combustion. In this work, the MPCI adopted a double injection strategy with the second injection timing fixed at 6 crank angle degree (CAD) before top dead center (BTDC). The effects of first injection timing and split injection ratio on emissions and combustion were investigated. The results showed that GDP MPCI mode exhibited two-stage combustion. With the advance of first injection timing and the decrease of first injection quantity, the amount and rate of the first-stage heat release decreased, and those of the second-stage heat release increased. Compared with single injection PPCI, MPCI reduced the maximum HC and CO emissions by 59% and 44%, respectively. Soot emissions of MPCI mode were below 0.01 g/kW.h, while NOx emissions were controlled under 0.4 g/kW.h. The results indicated that MPCI mode could improve engine efficiency and reduce combustion noise simultaneously (low MPRR), and the optimal engine performance and emissions were achieved with 26-31 CAD BTDC first injection timing and 30-40% first injection ratio.