A study of using E10 and E85 under direct dual fuel stratification (DDFS) strategy: Exploring the effects of the reactivity-stratification and diffusion-limited injection on emissions and performance in an E10/diesel DDFS engine

Abstract

One promising pathway to directly control combustion is Direct Dual Fuel Stratification (DDFS). DDFS has comparable thermal efficiency to RCCI, acceptable levels of emissions, and lower cyclic variation. The primary drawback of DDFS is soot production owing to the diffusion-limited nature of the near-TDC injection. In this paper, E10 (10% ethanol in gasoline by volume) and E85 were studied as alternative fuels to gasoline to tackle soot formation. In the first step, E10 and E85 were compared, and the best alternative to gasoline was chosen based on emissions and performance. E10 reduced soot by 40%, and E85 eradicated soot completely. However, E85 had 25 times higher NOX than gasoline. Next, diesel energy fraction and its start of injection (SOI2) were swept to explore the domain of the reactivity controlled regime. It was found that for SOI2s before −80° ATDC, the regime was premixed, and for SOI2s after −40° ATDC, the regime was diffusion-limited. Diesel energy fractions, more than 11%, yielded unintended combustion. Then, the energy fraction and injection timing of the near-TDC injection (SOI3) was swept and studied. The best domain for both injectors was discovered based on the EURO6 emission mandate. Spray angles of both injectors were swept from 50 to 80°, and 55° for diesel injector and 65° for the E10 injector showed the best results regarding emissions, performance, and fuel consumption. Finally, the effects of the injection pressure of SOI3 on emissions and performance were studied. The suitable domain for injection pressure was chosen based on EURO6.