Measuring Ignition Temperature and the Rate of Energy Generation From Canola Methyl Ester and Soy Methyl Ester in Oxygen-Nitrogen Mixtures on Platinum-Rhodium

Abstract

A heated plug flow reactor was used to study the reactions of nonflammable mixtures of canola methyl ester-oxygen and soybean methyl ester-oxygen diluted with nitrogen over a coiled 90%:10% platinum:rhodium wire catalyst. The temperature the catalyst needed to reach to initiate surface reactions (ignition temperature) and the subsequent rate of energy generation were determined. The absolute volume fraction of fuel was varied from 0.238% to 0.445% and the relative fuel-oxygen equivalence ratio, φ, was varied between 0.4 and 1.0. The 127 micrometer diameter Pt-Rh wire was coiled and suspended crosswise in the quartz tube of the reactor. Evaporated biodiesel was delivered by heated nitrogen into the apparatus and blended with oxygen in a mixing nozzle. The wire catalyst was electrically heated and acted as a resistance thermometer to measure its average temperature. Ignition temperatures increased with increasing equivalence ratio and volumetric fuel vapor percentage, thus indicating initial fuel coverage of the catalyst surface. Temperatures as low as 912 K at φ = 0.4 for 0.268% Soy Methyl Ester (SME) and as high as 991 K at φ = 1.0 for 0.445% Canola Methyl Ester (CME) were recorded. The rate of energy generated due to surface reactions for both biodiesels decreased with increasing equivalence ratio and generated less energy as fuel percentages decreased. The lowest and highest rates of energy generation were both obtained from experiments with CME with 6.9 W/cm2 at φ = 1 for 0.268% fuel and 25.3 W/cm2 at φ = 0.4 for 0.445% fuel. The extremes of the rate of heat generated from SME reactions were 5.1 W/cm2 and 28.6 W/cm2, both at φ = 0.4, with 0.238% and 0.417% fuel, respectively. Another outcome of this work was achieving steady evaporation of microliter/hour heavy fuel vapor flow rates. This was aided by thermogravimetric analysis (TGA) to determine thin-film vaporization temperatures. CME and SME had the lowest evaporation temperatures of 188 K and 186 K, respectively.