Reduction of PAH and Soot Precursors in Benzene Flames by Addition of Ethanol

The Potential of Oxygenates to Increase the Risk of Exposure to Polycyclic Aromatic Hydrocarbons through Groundwater Contamination

The Clean Air Act (42 U.S. Code § 7401) is one of the United States of America’s most influential environmental laws. Under the Clean Air Act Amendments of 1990, oxygen-containing organic compounds must be added to some fossil fuels with the goal of combating CO2 and particulate emissions. However, one major implication is the effect of co-solvency on the leaching potentials of polycyclic aromatic hydrocarbons (PAHs) into groundwater. Our research investigated this effect on three groups of recalcitrant PAHs that are present in diesel fuel. Our results reveal that ethanol addition enhances the leaching potentials of these otherwise hydrophobic contaminants, with 10% ethanol (E10) resulting in elution of all the PAHs studied. While 5% ethanol addition to diesel fuel resulted in the elution of an average of 2.5% of all the trimethylnaphthalenes and 6.0% of the C2 alkylphenanthrenes present in diesel fuel, 10% ethanol addition led to the elution of more than 80% of each of the studied trimethylnaphthalene peaks and more than 70% of each of the studied C2 alkylphenanthrene peaks present in diesel fuel. In view of the known mutagenic and carcinogenic risks associated with exposure to PAHs through groundwater contamination, our study highlights the need for energy scientists to carefully consider the environmental and health implications of ethanol-blended innovations holistically. It is not enough to save the atmosphere but ruin the hydrosphere and most importantly, human health.

Global ab initio exploration of potential energy surfaces for radical generation in the initial stage of benzene oxidation

The potential energy surfaces (PESs) of benzene oxidation by molecular oxygen were explored using the anharmonic downward distortion following (ADDF) and artificial force induced reaction (AFIR) methods of the global reaction route mapping (GRRM) strategy. The reaction mechanism of benzene activation by initial molecular oxygen depends on the combustion temperature. At high temperature, the benzene molecule could be oxidized by abstracting hydrogen atoms and form the radical fragments, C₆H₅ and OOH. However, before reaching its auto-ignition point, the formation of a singlet bridging peroxide molecule C₆H₆O₂ from the triplet reactants via electronic non-adiabatic transition will play a critical role in the increase of the combustion temperature by the generation of initial free radicals. Bridging peroxide C₆H₆O₂ could isomerize to other stable isomers by a consecutive series of oxygen and hydrogen atom transfers. Importantly, these C₆H₆O₂ isomers are vital sources of free radical generation in the initial stage of benzene oxidation. Free radicals, such as OOH, O, and OH, could be generated during the further oxidation of these oxygenated hydrocarbon species C₆H₆O₂ due to the presence of active groups or sp³-C-H bonds.

Black carbon emissions in gasoline exhaust and a reduction alternative with a gasoline particulate filter

Black carbon (BC) mass and solid particle number emissions were obtained from two pairs of gasoline direct injection (GDI) vehicles and port fuel injection (PFI) vehicles over the U.S. Federal Test Procedure 75 (FTP-75) and US06 Supplemental Federal Test Procedure (US06) drive cycles on gasoline and 10% by volume blended ethanol (E10). BC solid particles were emitted mostly during cold-start from all GDI and PFI vehicles. The reduction in ambient temperature had significant impacts on BC mass and solid particle number emissions, but larger impacts were observed on the PFI vehicles than the GDI vehicles. Over the FTP-75 phase 1 (cold-start) drive cycle, the BC mass emissions from the two GDI vehicles at 0 °F (-18 °C) varied from 57 to 143 mg/mi, which was higher than the emissions at 72 °F (22 °C; 12-29 mg/mi) by a factor of 5. For the two PFI vehicles, the BC mass emissions over the FTP-75 phase 1 drive cycle at 0 °F varied from 111 to 162 mg/mi, higher by a factor of 44-72 when compared to the BC emissions of 2-4 mg/mi at 72 °F. The use of a gasoline particulate filter (GPF) reduced BC emissions from the selected GDI vehicle by 73-88% at various ambient temperatures over the FTP-75 phase 1 drive cycle. The ambient temperature had less of an impact on particle emissions for a warmed-up engine. Over the US06 drive cycle, the GPF reduced BC mass emissions from the GDI vehicle by 59-80% at various temperatures. E10 had limited impact on BC emissions from the selected GDI and PFI vehicles during hot-starts. E10 was found to reduce BC emissions from the GDI vehicle by 15% at standard temperature and by 75% at 19 °F (-7 °C).

Effect of ethanol addition on soot precursors emissions during benzene oxidation in a jet-stirred reactor

A constant volume reactor model (PSR) was used to investigate the effect of ethanol addition on the formation of some pollutants during benzene oxidation in a jet-stirred reactor. The blended fuels were formed by incrementally adding 4% wt of oxygen (ethanol) to the neat benzene fuel and by keeping the inert mole fraction (nitrogen) and the equivalence ratio constants. The main objective of this work was to obtain fundamental understanding of the mechanisms through which the oxygenate compound affects soot precursor amounts. The modeling results showed that C2H2, C5H5, and C3H3 mole fractions decreased upon increasing the ethanol percentage in the fuel mixture.