Xiangang Wang

Laminar Burning Velocities and Markstein Lengths of 2,5-Dimethylfuran-Air Premixed Flames at Elevated Temperatures

Laminar burning velocities and Markstein lengths of 2,5-dimethylfuran (DMF)-air premixed mixtures at different initial temperatures and equivalence ratios were obtained using a constant volume combustion chamber and high-speed schlieren imaging system. The results indicate that both unstretched flame propagation speed and laminar burning velocity peak near the equivalence ratio of 1.2, and increase with increasing initial temperature. The peak unstretched flame propagation speed moves to the rich mixture side as the initial temperature increases, whereas the peak laminar burning velocity is unaffected by the variation of initial temperature. The Markstein length decreases with increasing equivalence ratio and increases with the increasing initial temperature. Based on the experimental data, a formula to calculate the laminar burning velocities of 2,5-DMF-air mixtures is provided.

Effect of Injection Pressure on Flame and Soot Characteristics of the Biodiesel Fuel Spray

The authors studied the effect of injection pressure on nonevaporating spray and spray flame characteristics of biodiesel fuel injected by a common rail injection system in a constant volume combustion vessel. Two biodiesels, biodiesel from palm oil (BDFp) and biodiesel from cooked oil (BDFc) were investigated, including JIS#2 Diesel. Mie scattering technique was employed to investigate nonevaporating spray characteristics. High-speed direct photography and two-color pyrometry were applied for spray flame characteristics. Injection pressures of 100, 200, and 300 MPa and ambient environment typical of diesel engine were used. Nonevaporating spray result showed that biodiesel fuels give longer spray tip penetrations and narrower spray angles especially for BDFp. Integrated flame luminosity of BDFp and BDFc show lower values compared to that of diesel at injection pressure of 100 MPa, and integrated flame luminosity of BDFp and BDFc is even lower than that of diesel at injection pressures of 200 and 300 MPa. Flame luminosity area follows a similar trend as that of integrated flame luminosity. Two-color pyrometry measurements show that the integrated KL factor of BDFp and BDFc yields smaller values than that of diesel at injection pressure of 100 MPa, and BDFp and BDFc present even lower values of integrated KL factors than diesel at injection pressure of 200 MPa. At an injection pressure of 300 MPa, the soot formation is extremely low for BDFp and BDFc. This indicates that the effect of soot reduction by using BDFp and BDFc is increased at high injection pressures. Flame luminosity and KL factor show the same trend at each injection pressure. Flame temperatures of BDFp and BDFc are lower than that of diesel at injection pressures of 100 and 200 MPa. BDFp and BDFc give higher flame temperature than diesel at injection pressure of 300 MPa. A simplified estimate for fuel jet air entrainment was made to interpret trends between different fuels and injection pressures. Analysis indicates that oxygen from fuel molecule plays a significant role on soot formation propensity at injection pressures of 200 and 300 MPa, and poor spray atomization and low mixing rate prohibit the effect of fuel molecule oxygen on soot reduction at injection pressure of 100 MPa. Combination of nonevaporating spray and spray combustion measurements provides a unique opportunity to understand the difference of spray flame characteristics between biodiesels and diesel fuel.

Effect of Injection Pressure on Ignition, Flame Development and Soot Formation Processes of Biodiesel Fuel Spray

The effect of injection pressure ranging from 100 to 300MPa on the ignition, flame development and soot formation characteristics of biodiesel fuel spray using a common rail injection system for direct injection (D.I.) diesel engine was investigated. Experiments were carried out in a constant volume vessel under conditions similar to the real engine condition using a single hole nozzle. Biodiesel fuels from two sources namely; palm oil (BDFp) and cooked oil (BDFc) with the commercial JIS#2diesel fuel were utilized in this research. The OH chemiluminescence technique was used to determine the ignition and the lift-off length of the combusting flame. The natural luminosity technique was applied to study the flame development and the two color pyrometry was applied for the soot formation processes. Ignition delay decreased as the injection pressure progressed from 100 to 300MPa. This was as a result of the enhanced mixing achieved at higher injection pressures. The BDFp’s higher cetane number facilitated shortest ignition delay when compared to the other fuels under all injection pressures. For all the fuels, the lift-off length increased as the injection pressure increased. The percentage of the stoichiometric air entrained upstream of the lift-off length by the BDFp was the lowest. The integrated, average natural luminosities and flame areas of the BDFp and BDFc were smaller at increasing pressures as compared to that of the diesel fuel flames. At the 100MPa injection pressure, the two color pyrometry measurements indicated that there was no significant difference in the integrated and averaged KL factors for all the fuels. At 200 and 300MPa injection pressures, the BDFp and the BDFc presented much lower integrated and averaged KL factors than diesel. The averaged flame temperatures of the BDFp and the BDFc were found to be lower than that of diesel except at the 300MPa injection pressure. The oxygen contents in the BDFp and the BDFc fuels played a significant role on the soot formation process.