Combustion and emission characteristics of naphtha-alcohol blends in HCCI engines under low intake temperature and ultra-lean conditions

The homogeneous charge compression ignition (HCCI) engine could be used in extended-range hybrid power, which not only reduces total energy consumption and emissions of the extended range vehicle, but also avoids HCCI load expansion problem. However, intake heating remains a significant challenge to the commercialization of HCCI in extended-range hybrid power. In this study, coal-based naphtha, a promising fuel, was studied for the combustion and emission characteristics at different methanol blending ratios and equivalence ratios on a single-cylinder HCCI engine. As methanol blending ratio decreases, HC and CO emissions gradually decrease, while NO x emissions gradually increase. Indicated mean effective pressure ( IMEP ) and indicated thermal efficiency ( η i ) gradually increase with the increase of methanol blending ratio. An appropriate methanol blending ratio is beneficial for the improvement of engine performance. From the perspective of promoting HCCI commercialization, N65M25B10 is an optimum blend ratio in this study which is capable of stable operation under low intake temperature and ultra lean conditions. For N65M25B10, with the decrease of Φ, P max , HRR max , T max , and PRR max are gradually reduced, and their corresponding phases are slightly retarded. As Φ increases, HC and CO emissions gradually decrease, while NO x emissions have a slight increase trend, remaining at a very low level. When Φ increases from 0.29 to 0.36, IMEP increases from 0.35 to 0.41 MPa, and η i varied between 37.7% and 39.4%. Emissions are generally maintained at a very low level for all fuels.