Effects of isobutanol fraction in diesel-biodiesel blends on combustion, injection, performance and emission parameters

High carbon alcohols such as isobutanol have gained much research interest recently in diesel engines due to their higher mixing stability, lower water retention, higher energy density and higher cetane number compared to low carbon alcohols like ethanol and methanol. Therefore, the effects of increasing isobutanol fractions in diesel-biodiesel blends on combustion, injection, performance and emission parameters were investigated on a common rail diesel engine with two stage injection strategy at different engine speeds and loads. Six test fuels were; pure diesel, binary mixtures of biodiesel and isobutanol with diesel (B20 and I15), ternary blends of isobutanol-diesel-biodiesel (I15B20, I25B20 and I35B20) prepared on mass basis. Results showed that increasing isobutanol fraction in the blends retarded start of combustion (SOC) and decreased cylinder gas pressure and maximum rate of heat release. Ignition delay increased and combustion duration decreased with increasing isobutanol proportion in test fuels. Maximum pressure rise rate of ternary blends slightly increased with increasing load and speed and observed slightly above the knocking limit at 160 Nm and 2100 rpm, having 21.58 % higher value than that of diesel. Increasing isobutanol fraction in ternary blends increased brake specific fuel consumption (BSFC), while providing comparable thermal efficiencies with diesel at medium and high loads, where 4.72 % higher value obtained with I15B20 compared to pure diesel at 160 Nm. Generally, higher iso-butanol ratios decreased THC and CO emissions and suppressed cyclic variations at high load. All blends increased NOx emissions compared to diesel, whereas test fuels with high isobutanol content suppressed NOx emissions at low load. Increasing isobutanol ratio in the blends prevented further increase in NOx emissions, while B20 fuel evidently increased NOx emissions at 160 Nm. At high load and 1800 rpm, I35B20 fuel gave optimum results with 3.53 % and 12.66 % lower THC and CO emissions, 2.37 % and 7.27 % higher BTE and NOx, respectively, compared to pure diesel.