Comparative Study on Gasoline HCCI and DICI Combustion in High Load Range with High Compression Ratio for Passenger Cars Application 2017-01-2257

This study compared the combustion and emission characteristics of Homogeneous Charge Compression Ignition (HCCI) and Direct Injection Compression Ignition (DICI) modes in a boosted and high compression ratio (17) engine fueled with gasoline and gasoline/diesel blend (80% gasoline by volume, denoted as G80). The injection strategy was adjusted to achieve the highest thermal efficiency at different intake pressures. The results showed that Low Temperature Heat Release (LTHR) was not observed in gasoline HCCI. However, 20% additional diesel could lower down the octane number and improve the autoignition reactivity of G80, which contributed to a weak LTHR, accounting for approximately 5% of total released heat.

The combustion efficiency in gasoline DICI was higher than those in gasoline HCCI and G80 HCCI, while the exhaust loss and heat transfer loss in DICI mode were higher than those in HCCI mode. Increasing intake pressure improves the Indicated Thermal Efficiency (ITE) in both HCCI and DICI mode, and when the intake pressure was 2.1 bar, gasoline DICI achieved the highest ITE of 49.3%, while the ITE of G80 HCCI was the lowest of 47.7%. When the intake pressure was increased, earlier CA50 and longer combustion duration were observed in HCCI mode, while only slight change in CA50 for DICI mode was observed and the combustion duration became shorter. CO and HC emissions in gasoline DICI were dramatically lower than those in gasoline HCCI and G80 HCCI. However, gasoline DICI resulted in NOx and soot emissions, while gasoline HCCI achieved near-zero NOx and soot emissions.