Assessment of the emissions from the use of California Air Resources Board qualified diesel fuels in comparison with Federal diesel fuels

Abstract

The California Air Resources Board (CARB) has regulated the properties of diesel fuel sold in California since 1988 to lower emissions of particulate matter (PM) and oxides of nitrogen (NO x ). Although many studies have shown that reduced levels of aromatics and higher cetane numbers can improve emissions, the actual impact of CARB fuels on inuse diesel emissions has not yet been extensively studied, especially as diesel engine and aftertreatment technology has evolved over the years. This study evaluates the differences between California and Federal diesel fuels with heavy-duty engine and chassis dynamometer tests. The engine dynamometer results showed that NO x emissions for the Federal fuels ranged from 4.7% to 9.5% higher than the CARB diesel. These NO x reductions are similar to the estimates being used in the latest regulations. The chassis dynamometer test results did not show as consistent trends for NO x as those seen for the engine dynamometer testing. For the chassis dynamometer testing, four out of ten vehicles showed consistent reductions in NO x , with emissions for the Federal fuels ranging from 3.3% to 9.9% higher than the CARB diesel, while the other six vehicles did not show consistent fuel impacts. On an absolute level, the NO x benefit for CARB diesel shows a decline with continuing advances in engine technology. The results showed that CARB diesel did not show strong benefits for PM. The results also showed that the introduction of aftertreatment systems for PM and NO x will, over time, largely eliminate any potential benefits that might be obtained through the use of CARB diesel, although NO x benefits will persist through to 2020.