Particulate matter indices using fuel smoke point for vehicle emissions with gasoline, ethanol blends, and butanol blends

Abstract

Recent studies have led to significant improvements in the prediction of particulate matter (PM) emissions from gasoline vehicles based on differences in fuel composition. This is an issue that has taken on increased importance recently given the introduction of gasoline direct injection (GDI) technology to improve fuel economy and the challenges it has meeting new stringent PM emissions standards. One productive effort in this area is the PM Index (PMI) developed by Aikawa and collaborators. This approach relates the effects of fuel composition on its PM forming potential. The present work explores the use of experimental smoke point measurements and various fuel volatility metrics to better characterize these effects. Smoke point (SP) values as scaled by the Oxygen Extended Sooting Index (OESI) incorporate all fuel molecular structural effects known to have an impact on soot formation, including branching, degree of saturation, carbon chain length, and oxygenate functional group effects. A strong correlation is found for vehicle-level particle number (PN) and PM emissions with SP, OESI and PMI. Fuel volatility effects are considered, including characteristics derived from molecular weight, distillation, vapor pressure, and heat of vaporization. For hydrocarbon blends, no volatility factor significantly improved the correlation as compared to PMI, SP, or OESI alone. However, inclusion of a heat of vaporization term with OESI better matched the emissions trend for ethanol–gasoline blends. Sooting tendencies for n-butanol- and isobutanol-gasoline blends exhibited trends similar to those with ethanol.