The effect of oil layers on the hydrocarbon emissions generated during closed vessel combustion

Abstract

The exhaust gas from a high pressure reactor generated during spark ignited closed vessel combustion in the presence and absence of oil has been analyzed by gas chromography. Five fuels (methane, ethane, propane, n-butane, and hydrogen) and three oils (a synthetic motor oil, a petroleum based motor oil, and a diffusion pump fluid) were tested during these experiments at a variety of fuel-air equivalence ratios (=0.7–1.6). Experiments carried out under lean (=0.9) conditions have demonstrated that the total exhaust hydrocarbon concentration increases by 30, 120, and 400 ppmC for ethane, propane, and n-butane respectively when 0.14 gm of a synthetic motor oil is placed onto a 60 cm2 surface area of the reactor. This exhaust hydrocarbon concentration consists primarily (>95%) of initial fuel in all cases and is directly proportional to both the amount of oil in the reactor and the solubility of the specific fuel in the oil. These results show that absorption of the fuel occurs in the oil prior to ignition. This dissolved fuel is then desorbed into the cooled burned gas after combustion is complete, significantly increasing the exhaust hydrocarbon concentration. In contrast to the above results for lean mixtures, when rich (=1.1–1.5) propane-air mixtures were ignited in the presence of oil, a very large increase in the total hydrocarbon concentrations (30,000 ppmC) was observed in the exhaust. Only 1% of these emissions were unburned fuel, and 20% more total carbon was observed in the exhaust than was present in the initial fuel mixture. This carbon imbalance coupled with other experimental evidence has demonstrated that the oil layer is being extensively degraded to light hydrocarbons under fuel rich conditions during passage of a single flame. This oil degradation is very sensitive to the equivalence ratio and to the type of fuel used.