RCCI With High Reactivity S8-ULSD Blend and Low Reactivity N-Butanol

Abstract

Abstract A fuel blend consisting of 10% S8 by mass (a Fischer-Tropsch synthetic kerosene), and 90% ULSD (Ultra Low Sulfur Diesel) was investigated for their combustion characteristics and impact on emissions during RCCI (Reactivity Controlled Compression Ignition) combustion in a single cylinder experimental engine utilizing a 65% by mass n-butanol port fuel injection (PFI). RCCI is a dual fuel combustion strategy achieved with the introduction of a PFI fuel of the low-reactive n-butanol, and a direct injection (DI) of a high-reactivity blend (FT-BLEND) into an experimental diesel engine. The combustion analysis and emissions testing were conducted at 1500 RPM at an engine load of 5 bar IMEP (Indicated Mean Effective Pressure), and CA50 of 9° ATDC (After Top Dead Center); CDC (Conventional Diesel Combustion) and RCCI with 65Bu-35ULSD were utilized as the baseline for AHRR (Apparent Heat Release Rate), ringing and emissions comparisons. It was found during a preliminary investigation with a Constant Volume Combustion Chamber (CVCC) that the introduction of 10% by mass S8 into a mixture with 90% ULSD by mass only increased Derived Cetane Number (DCN) by 0.8, yet it was found to have a significant effect on the combustion characteristics of the fuel blend. This led to the change in injection timing necessary for maintaining 65Bu-35F-T BLEND RCCI at a CA50 of 5° ATDC (After Top Dead Center) to be shifted 3° closer to TDC, thus affecting the Ringing Intensity (RI), Pressure Rise Rate, and heat release of the blend all to decrease. CDC was conducted with a primary injection of 14° BTDC at a rail pressure of 800 bar, all RCCI testing was conducted with 65% PFI of n-butanol by mass and 35% DI, to prevent knock, with a rail pressure of 600 bar and a pilot injection of 60° BTDC for 0.35 ms. 65Bu-35ULSD RCCI was conducted with a primary injection at 6° BTDC with neat ULSD#2, the fuel 65Bu-35F-T BLEND in RCCI had a primary injection at 3° BTDC to maintain CA50 at 9° ATDC. 65Bu-35ULSD RCCI experienced a NOx and soot emissions decrease of 40.8% and 91.44% respectively in comparison to CDC. The fuel 65Bu-35F-T BLEND in RCCI exhibited an additional decrease of NOx and soot of 32.9 and 5.3%, in comparison to 65Bu-35ULSD RCCI for an overall decrease in emissions of 73.7% and 96.71% respectively. Ringing Intensity followed a similar trend with reductions in RI for 65Bu-35ULSD RCCI decreasing only by 6.2% whereas 65Bu-35F-T BLEND had a decrease in RI of 76.6%. Although emissions for both RCCI fuels experienced a decrease in NOx and soot in comparison to CDC, UHC and CO did increase as a result of RCCI. CO emissions for 65Bu-35ULSD RCCI and 65Bu-35F-T BLEND where increased from CDC by a factor of 5 and 4 respectively with UHC emissions rising from CDC by a factor of 3.4. The fuel 65Bu-35F-T BLEND had a higher combustion efficiency than 65Bu-35ULSD in RCCI at 91.2% due to lower CO emissions of the blend.