Influence of the Methanol Proportion on the Combustion Characteristics of Methanol-Biodiesel -F-T Diesel Blended Fuel

The F-T diesel made from coal by Fischer-Tropsch synthesis (F-T) can be used as a clean alternative fuel of diesel engine. To alleviate the drawback of high cost and low viscosity of F-T diesel, the Methanol-Biodiesel -F-T diesel multiple fuel (MBFT) was prepared by adding low-cost methanol and high-viscosity biodiesel as modifiers. Considering the immiscibility between alcohols and hydrocarbons, this paper carried out a series of stability tests and found that n-decanol was the optimum co-solvent of MBFT. The MBFTs blended by biodiesel with the volume fraction of 10% (10% vol.) and methanol with varying proportions of 0%, 5%, 10% and 15% vol. were denoted as M0, M5, M10 and M15, respectively. The increasing methanol proportion caused the increase of the oxygen content in the blended fuels and the reduction of heat value, surface tension and cetane number. The influence of methanol proportion on combustion characteristics of turbo-charging engine was studied. The study indicates that with the increase of the proportion of methanol, the ignition delay period of MBFT is prolonged 17.3∼37.1% while the normal combustion period and post combustion period is shortened 7.5∼16.0% and 28.3%∼49.0%, respectively; the peak value of heat release rate is increased 8.3%∼32.7% and the peak value phase is delayed 20.8%∼51.6%, the peak value of pressure rise rate also presents this trend. The combustion pressure oscillation amplitude increases 10.8%∼60.0% with the increase of methanol ratio, and the peak value phase of pressure oscillation is delayed 23.5%∼134.6%.