Investigating the Effects of the Air-to-Fuel Ratio and Fuel Type on the Formation of Environmentally Persistent Free Radicals in Combustion Particles

DESIREE SARMIENTO, Brian Majestic, University of Denver

     Abstract Number: 76
     Working Group: Combustion

Abstract
Environmentally persistent free radicals (EPFRs) are a newly identified class of environmental risk substances that have adverse effects on the environment and human health. The main source of EPFRs is the incomplete combustion of hydrocarbon fuel, wherein the free radicals that are formed become stabilized on the surface or within the structures of soot particles. This stabilization allows these radicals to persist in the environment for several months to a few years, which gives EPFRs an opportunity to contaminate various environmental matrices or react with other species in the atmosphere. These reactions involving EPFRs can form reactive oxygen species (ROS) and secondary EPFRs, which have importance in both biological and environmental systems. Internal combustion engines operate on different types of fuels and at various air-to-fuel (A/F) ratios depending on the motor vehicle and engine load. The fuel type and A/F ratio can influence EPFR formation from the resulting combustion reaction. In this study, soot particles were produced from the combustion of hexanes at various A/F ratios, and the EPFRs formed in each soot sample were quantitatively determined by electron paramagnetic resonance (EPR) spectroscopy. From these reactions, lower EPFR formation was generally found in soot samples produced from higher A/F ratios, and a strong negative correlation (R² = 0.971) was observed between the average number of EPFRs and the A/F ratio. Further investigation involving the A/F ratio will be conducted on soot formed from the combustion of different types of fuel to examine the effects of various fuel additives on EPFR formation.