In recent years, governmental agencies around the world have implemented legislation that targets growing the use of renewable fuels in the transportation sector. In the U.S., the Energy Independence and Security Act of 2007 mandates the use of 36 billion gallons of biofuels in the transportation fuel pool by 2022. In California, the low carbon fuel standard (LCFS) was implemented in 2011 to promote the reduction of greenhouse gas emissions by targeting a reduction in the carbon intensity of transportation fuels by 10% by 2020. In addition, the implementation of more stringent standards for heavy-duty vehicles is a key strategy for the improvement of air quality in the South Coast Air Quality Management District (AQMD). These facts, coupled with the continuously growing concern over global warming and environmental degradation, have accentuated the public and scientific awareness and led to a substantial effort to develop alternative fuel sources and improve engine technologies. The main goals of this study was to carry out chassis dynamometer testing of heavy-duty diesel trucks using different types of biodiesel fuel blends and a typical CARB ultra-low sulfur diesel while measuring: 1) regulated emissions; 2) unregulated emissions such as ammonia, carbonyl compounds, and volatile organic compounds (VOCs); 3) the physical properties of particulate matter (PM) emissions (e.g., PM mass, number, and size distributions); 4) the chemical properties of PM emissions (e.g., PAHs, WSOC, inorganic ions, organic compounds, and metals); and 5) the toxicological characteristics of PM emissions (e.g., redox activity, electrophilic properties, and proinflammatory properties). This study tested two heavy-duty diesel vehicles that were equipped with a 2002 model year Cummins ISX-450 engine without any emission control technology and a 2010 Cummins ISX-15 engine fitted with a diesel oxidation catalyst (DOC) followed by a diesel particle filter (DPF) and selective catalytic reduction (SCR), respectively. The emission results for both vehicle/fuel combinations are summarized as such: THC, NMHC, CO, and PM mass emissions for the uncontrolled Cummins ISX-450 engine showed reductions with the use of biodiesel blends compared to CARB ULSD. In most cases, the B50 blends resulted in statistically significant reductions for THC, NMHC, CO, and PM mass emissions relative to the reference fuel. These phenomena were as expected and can be explained by the higher oxygen content in the methyl ester moiety, which help reducerich combustion zones and promote more complete combustion and reduce the sooting tendency of biodiesel. For the heavily controlled Cummins ISX-15 engine, THC and NMHC emissions were practically below the detection limits, as these species were effectively fully oxidized in the DOC/DPF system. CO and PM mass emissions were also low for the DOC/DPF equipped engine, and did not show any strong fuel effects. CO2 emissions showed some moderate decreases with the biodiesel blends relative to CARB ULSD, which is an indication that the engine efficiency wasn’t influenced by the high biodiesel blend ratio. Overall, NOx emissions exhibited increases with biodiesel for both vehicles with the differences in NOx emissions relative to CARB ULSD being statistically significant for the newer Cummins ISX-15 engine.
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