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The primary objective of this study was to evaluate the impact of three different biodiesel feedstocks on emissions compared to a baseline CARB ULSD with two heavy-duty trucks equipped with and without aftertreatment technologies. The biodiesels included a soybean oil methyl ester (SME), a waste cooking oil methyl ester (WCO), and a methyl ester obtained from animal fat (AFME), blended at a 50% level by volume with the CARB diesel. The vehicles were equipped with a 2010 Cummins ISX-15 engine with a selective catalytic reduction (SCR), diesel oxidation catalyst (DOC) and a diesel particulate filter (DPF) and with a 2002 Cummins ISX-450 engine. Both vehicles were tested over the Urban Dynamometer Driving Schedule (UDDS) on a heavy-duty chassis dynamometer. For this study, nitrogen oxides (NOx), carbon monoxide (CO), carbon dioxide (CO2), total hydrocarbons (THC), methane (CH4), non-methane hydrocarbons (NMHC), and particulate matter (PM) were measured.

Urban air quality in California can have a large impact on the state's economy, natural and managed ecosystems, and human health and mortality. The use of alternative, low-carbon fuels is considered to be an effective measure to meet strict emissions regulations of particulate matter (PM) and oxides of nitrogen (NOx). Natural gas may be a potential alternative to conventional liquid fuels for use in automotive internal combustion engines, and can be used in fulfilling these requirements. The primary objective of this study is to evaluate the impact of varying natural gas composition on the exhaust emissions from a transit bus equipped with a 2003 Cummins C Gas Plus, lean-burn, spark-ignited natural gas engine and an oxidation catalyst while operating on the Central Business District (CBD) cycle on a chassis dynamometer.