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Conventional diesel fuel (1) has been on the market for decades and used successfully to run diesel engines of all sizes in many applications.* In order to reduce emissions and to foster energy source diversity, new fuels such as alternative and renewable, as well as new formulations, have entered the market. These include biodiesel, gas-to-liquid, and alternative formulations by states such as California. Performance variations in fuel economy, emissions, and compatibility for these fuels have been evaluated and debated. In some cases, contradictory views have surfaced. “Renewable” and “clean” designations have been interchanged. Adding to the confusion, results from one fuel in one type of engine, such as an older heavy-duty engine, is at times compared to that of another type, such as a modern light-duty engine.

Effects of methyl ester biodiesel fuel blends on NOx emissions are studied experimentally and analytically. A precisely controlled single cylinder diesel engine experiment was conducted to determine the impact of a 20% blend of soy methyl ester biodiesel (B20) on NOx emissions. The data were then used to calibrate KIVA chemical kinetics models which were used to determine how the biodiesel blend affects NOx production during the combustion process. In addition, the impact on the engine control system of the lower specific energy content of biodiesel was determined. Both factors, combustion and controls, must be taken into account when determining the net NOx effect of biodiesel compared to conventional diesel fuel. Because the magnitude and even direction of NOx effect changes with engine load, the NOx effect associated with burning biodiesel blends over a duty cycle depends on the duty cycle average power and fuel cetane number.

A prototype 2007 ISL Cummins diesel engine equipped with a diesel oxidation catalyst (DOC), diesel particle filter (DPF), variable geometry turbocharger (VGT), and cooled exhaust gas recirculation (EGR) was tested at Southwest Research Institute (SwRI) under a high-load accelerated durability cycle for 1000 hours with B20 soy-based biodiesel blends and ultra-low sulfur diesel (ULSD) fuel to determine the impact of B20 on engine durability, performance, emissions, and fuel consumption. At the completion of the 1000-hour test, a thorough engine teardown evaluation of the overhead, power transfer, cylinder, cooling, lube, air handling, gaskets, aftertreatment, and fuel system parts was performed. The engine operated successfully with no biodiesel-related failures. Results indicate that engine performance was essentially the same when tested at 125 and 1000 hours of accumulated durability operation.