Investigations on energy efficiency enhancement under knock threshold limit conditions for a turbocharged direct-injection spark-ignition engine fueled with wet ethanol

Abstract

Wet ethanol is a promising biofuel whose properties fit with turbocharged direct-injection spark-ignition (DISI) engines for countries with yearly production capacity. Even though it has a higher life-cycle efficiency than regular ethanol, which reduces significantly the energy required on ethanol production, wet ethanol’s potential is wasted by the continuous dehydration process. In order to highlight such potential as a fuel for engines, this study investigates the early injection of different blends of wet ethanol (E100W0, E95W5, E90W10, and E80W20, respectively) via an in-house engine simulator to improve engine operating conditions — enhancing engine and ethanol’s life-cycle efficiencies. This study searched for the highest sustainable values of engine energy and exergy efficiencies based on the threshold value of the knock index number. The combustion phasing model used correlations obtained from a machine learning algorithm fed with experimental data for a DISI engine. This investigation provided 120 different cases under different compression ratios (r), engine speeds, relative air-fuel ratios, and wet ethanol blends. Results showed that E80W20 can operate with a turbocharger at r = 18. The highest efficiencies (43% and 40%, respectively) were found for E90W10 and E80W20 — values 30% higher than regular Brazilian FFV. Lastly, cases involving the best conditions for torque, lean air-fuel conditions at high compression ratios and water content, and downspeeding are presented as interesting alternatives to either stationary engines or hybrid vehicles, therefore highlighting the potential of wet ethanol for DI engines.