Optimal operating conditions for wet ethanol in a HCCI engine using exhaust gas heat recovery

Abstract

This study explores optimal operating conditions for power generation from wet ethanol in a HCCI engine using exhaust gas heat recovery. Wet ethanol is a difficult fuel to ignite as it requires high compressed gas temperatures to achieve ignition causing the requirement for substantial intake charge heating. A heat exchanger is retrofitted to a HCCI engine in this study to recover excess heat from the exhaust gases to provide the energy input for intake charge heating. This study builds on prior experimental research by focusing on optimal operating conditions for wet ethanol in HCCI with exhaust gas heat recovery. Operating points include intake pressures of 1.8 and 2.0bar absolute, equivalence ratios of 0.50 and 0.55, combustion timings from just before TDC to misfire, and fuel mixtures from 70% to 100% ethanol (with water being the balance).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 timing. With a 2bar absolute intake pressure, an equivalence ratio of 0.55, and a combustion timing near 8 CAD ATDC, 70% ethanol produced a power output of nearly 7.25bar gross IMEP with low ringing and low nitrogen oxide emissions. This operating point was sustained by using heat transfer from hot exhaust gases into the intake charge, and thus no external heat addition was required – a substantial improvement over prior studies.