Wet ethanol in HCCI engines with exhaust heat recovery to improve the energy balance of ethanol fuels
This study explores the use of wet ethanol as a fuel for HCCI engines while using exhaust heat recovery to provide the high input energy required for igniting wet ethanol. Experiments were conducted on a 4-cylinder Volkswagen engine modified for HCCI operation and retrofitted with an exhaust gas heat exchanger connected to one cylinder. Tested fuel blends ranged from 100% ethanol to 80% ethanol by volume, with the balance being water. These blends are directly formed in the process of ethanol production from biomass. Comprehensive data was collected for operating conditions ranging from intake pressures of 1.4–2.0 bar and equivalence ratios from 0.25 to 0.55. The heat exchanger was used to preheat the intake air allowing HCCI combustion without electrical air heating. The results suggest that the best operating conditions for the HCCI engine and heat exchanger system in terms of high power output, low ringing, and low nitrogen oxide emissions occur with high intake pressures, high equivalence ratios, and highly delayed combustion timings.
Removing the final 20% of water from ethanol is a major energy sink. The results of this study show that HCCI engines can use ethanol fuels with up to 20% water while maintaining favorable operating conditions. This can remove the need for the most energy-intensive portion of the water removal process.