We assessed the emissions response of a fleet of seven light-duty gasoline vehicles for gasoline fuel aromatic content while operating over the LA92 driving cycle. The test fleet consisted of model year 2012 vehicles equipped with spark-ignition (SI) and either port fuel injection (PFI) or direct injection (DI) technology. Three gasoline fuels were blended to meet a range of total aromatics targets (15%, 25%, and 35% by volume) while holding other fuel properties relatively constant within specified ranges, and a fourth fuel was formulated to meet a 35% by volume total aromatics target but with a higher octane number. Our results showed statistically significant increases in carbon monoxide, nonmethane hydrocarbon, particulate matter (PM) mass, particle number, and black carbon emissions with increasing aromatics content for all seven vehicles tested. Only one vehicle showed a statistically significant increase in total hydrocarbon emissions. The monoaromatic hydrocarbon species that were evaluated showed increases with increasing aromatic content in the fuel. Changes in fuel composition had no statistically significant effect on the emissions of nitrogen oxides (NOx), formaldehyde, or acetaldehyde. A good correlation was also found between the PM index and PM mass and number emissions for all vehicle/fuel combinations with the total aromatics group being a significant contributor to the total PM index followed by naphthalenes and indenes.

This study investigated the impacts of varying natural gas composition on the exhaust emissions from different technology transit buses. For this study, two CNG (compressed natural gas) buses equipped with lean burn combustion and OCs (oxidation catalysts), and one stoichiometric CNG bus equipped with a TWC (three-way catalyst) and EGR (exhaust gas recirculation) were tested on a chassis dynamometer over the CBD (Central Business District) cycle on six different gas blends each. The gases represented a range of compositions from gases with high levels of methane and correspondingly lower energy contents/WN (Wobbe number) to gases with higher levels of heavier hydrocarbons and correspondingly higher energy contents/WN. For the lean burn buses, gases with low methane contents exhibited higher NO x (nitrogen oxides) (19%e53%) and NMHC (non-methane hydrocarbon) (39%e102%) emissions, but lower emissions of THC (total hydrocarbon) (9%e24%), CH 4 (methane) (23%e33%), and formaldehyde emissions (14%e45%). The stoichiometric engine bus with a TWC showed significantly reduced NO x and THC emissions compared to the lean burn buses, but did show higher levels of CO (carbon monoxide) and NH 3 (ammonia). PM (particulate matter) mass emissions did not show any fuel effects, while PN (particle number) emissions exhibited some reductions for the higher WN gases.

The impact of biodiesel and second generation biofuels on nitrogen oxides (NO(x)) emissions from heavy-duty engines was investigated using a California Air Resources Board (CARB) certified diesel fuel. Two heavy-duty engines, a 2006 engine with no exhaust aftertreatment, and a 2007 engine with a diesel particle filter (DPF), were tested on an engine dynamometer over four different test cycles. Emissions from soy- and animal-based biodiesels, a hydrotreated renewable diesel, and a gas to liquid (GTL) fuel were evaluated at blend levels from 5 to 100%. NO(x) emissions consistently increased with increasing biodiesel blend level, while increasing renewable diesel and GTL blends showed NO(x) emissions reductions with blend level. NO(x) increases ranged from 1.5% to 6.9% for B20, 6.4% to 18.2% for B50, and 14.1% to 47.1% for B100. The soy-biodiesel showed higher NO(x) emissions increases compared to the animal-biodiesel. NO(x) emissions neutrality with the CARB diesel was achieved by blending GTL or renewable diesel fuels with various levels of biodiesel or by using di-tert-butyl peroxide (DTBP). It appears that the impact of biodiesel on NO(x) emissions might be a more important consideration when blended with CARB diesel or similar fuels, and that some form of NO(x) mitigation might be needed for biodiesel blends with such fuels.

No abstract

h i g h l i g h t s Natural gas composition impacts the emissions from lean-burn engines. Lower THC, CH 4 , and NO x emissions for stoichiometric vs. lean-burn engines. NH 3 emissions produced important increases for the stoichiometric engines. Lubricant oil combustion was the main source for particle number formation. Higher carbonyl emissions for lean-burn vs. stoichiometric engines.