Effects of biofuel blends on RCCI combustion in a light-duty, multi-cylinder diesel engine

Reactivity Controlled Compression Ignition (RCCI) is an engine combustion strategy that utilizes in-cylinder fuel blending to produce low NO_x and PM emissions while maintaining high thermal efficiency. Previous RCCI research has been investigated in single-cylinder heavy-duty engines [1, 2, 3, 4, 5, 6]. The current study investigates RCCI operation in a light-duty multi-cylinder engine over a wide number of operating points representing vehicle operation over the US EPA FTP test. Similarly, previous RCCI engine experiments have used petroleum based fuels such as ultra-low sulfur diesel fuel (ULSD) and gasoline, with some work done using high percentages of biofuels, namely E85 [7]. The current study was conducted to examine RCCI performance with moderate biofuel blends, such as E20 and B20, as compared to conventional gasoline and ULSD. The engine experiments consisted of in-cylinder fuel blending using port fuel-injection (PFI) of gasoline or E20 and early-cycle, direct-injection (DI) of ultra-low sulfur diesel (ULSD) or B20 fuel. At the selected load points, the results from RCCI combustion using biofuels and petroleum fuels are compared. Preliminary results show that with E20, the peak load was able to be raised from 8 to 10 bar BMEP, due to ethanol's lower propensity for autoignition. Ethanol's low reactivity enabled an increased reactivity gradient and reduced the pressure rise rate (PRR) compared to gasoline. This increase in peak load also allowed for a 5% relative increase in brake thermal efficiency (BTE). Replacing ULSD with B20 was shown to increase combustion efficiency at low loads. The unique fuel properties of these biofuel blends increases the benefits of the use of RCCI combustion compared to conventional diesel combustion (CDC).