Performance Evaluation - Combustion, Emissions and Vibrations-of n-Butanol Binary Mixture with ULSD in an Indirect Injection Engine

This paper investigates the performance of an indirect injection (IDI) diesel engine fueled with Bu25, 75% ultra-low sulfur diesel (ULSD#2) blended with 25% n-butanol by mass. N-butanol, derivable from biomass feedstock, was used given its availability as an alternative fuel that can supplement the existing limited fossil fuel supply. Combustion and emissions were investigated at 2000 rpm across loads of 4.3-7.2 bar indicated mean effective pressure (IMEP). Cylinder pressure was collected using Kistler piezoelectric transducers in the precombustion (PC) and main combustion (MC) chambers. Ignition delays ranged from 0.74 - 1.02 ms for both operated fuels. Even though n-butanol has a lower cetane number, the high swirl in the separate combustion chamber would help advance its premixed combustion. The heat release rate of Bu25 became initially 3 J/crank-angle-degree (CAD) higher than that of ULSD#2 as load increased to 7.2 bar IMEP. Cylinder pressure was 2.25 bar higher within the main chamber for Bu25 compared to the peak values of the ULSD#2 reference. The mechanical efficiency increased with load from 45% to 70% while indicated thermal efficiency reached 44% for 7.2 IMEP load for both fuels. Using an AVL SESAM Fourier Transformed Infrared (FTIR) system and an AVL smoke meter, emissions for the Bu25 fuel blend were measured and showed a decrease of 40% in soot and 2.5% in nitrogen oxides (NO_x) at 7.2 bar IMEP. Noise and vibrations measurements were additionally collected using a tri-axial Brüel & Kjær (B&K) accelerometer placed on the valve cover and a B&K multi-field microphone and these were processed in B&K PULSE 19 software. Comparable engine radial vibrations were observed at 7.2 bar IMEP load for both fuels while constant percentage bandwidth (CPB) analysis showcased similar sound levels with a maximum increase of 4 dB at 40 Hz for Bu25. Engine noise and vibrations were not significantly increased at 7.2 bar IMEP during Bu25 operation. The study suggests that n-butanol can be used at 25% as a renewable binary mixture with ULSD#2 while sustaining IDI engine performance.