Experimental study of homogeneous charge compression ignition combustion in a light-duty diesel engine fueled with isopropanol-gasoline blends

Homogeneous charge compression ignition (HCCI) is a high-efficiency, ultra-low emission generating com-bustion technique that can potentially phase out conventional diesel combustion (CDC). Due to wide misfire and knocking limits, a limited load range impedes its commercial success. The present work addresses HCCI limitations using isopropanol-gasoline blends in a port fuel injected light-duty diesel engine. A cetane booster additive, 2-ethylhexyl nitrate (2-EHN), at 5vol.% was mixed with the test fuels to broaden the HCCI lower load limits. The tested fuels include biofuel isopropanol that replaced non-renewable gasoline in 20% increments to achieve higher loads during HCCI. The results show a substantial increment in HCCI operating load range (24%-86%) with test fuels over diesel HCCI (20%-38%). The characteristics of HCCI combustion in the modified test engine were benchmarked with CDC in the unmodified production engine. The significant benefits of HCCI over CDC were the concomitant reduction of indicated specific energy consumption (ISEC), oxides of nitrogen (NOx), and soot emissions, especially at higher loads. For instance, at 80% load, the ISEC, soot, and NOx were decreased by 5%, 99%, and 77%, respectively, for 60% isopropanol/35% gasoline/5% 2-EHN fueled HCCI than CDC. The exergy analysis was conducted to gain insight into irreversibility sources in thermodynamic processes during HCCI and CDC. The second law efficiency of HCCI improved with increased isopropanol content in the test fuels at a specific load. Overall, the present work shows that isopropanol- gasoline blends are viable alternatives to diesel to operate the HCCI engine that meets the desired emission and performance targets.

Automated summary

This study investigates the limitations of homogeneous charge compression ignition (HCCI) in a light-duty diesel engine using isopropanol-gasoline blends. By adding 2-ethylhexyl nitrate (2-EHN) as a cetane booster additive, the lower load limits of HCCI were broadened, and the HCCI with isopropanol-gasoline blends showed significant reductions in energy consumption, nitrogen oxides (NOx), and soot emissions compared to conventional diesel combustion (CDC), especially at higher loads. Exergy analysis demonstrated that the second law efficiency of HCCI improved with increased isopropanol content in the test fuels at a specific load. Overall, the results suggest that isopropanol-gasoline blends are viable alternatives to diesel for operating HCCI engines that meet emission and performance targets.