Comparative Field Evaluation of Biodiesel Impact on Hot Stabilized Emissions from School Buses

This study investigated the impact of biodiesel (B20: 20% biodiesel, 80% conventional diesel), cruise speed, and average acceleration rates on emissions of oxides of nitrogen (NOx), hydrocarbons (HC), carbon monoxide (CO), and carbon dioxide (CO2) from diesel school buses. Two drive cycles were developed on the basis of the rural and urban drive cycle data collected with Global Positioning System technology. Five buses were selected according to the current model year mix in Texas and were driven following the developed drive cycles for three different fuels (TxLED, B20 market blend, and B20 all soy). The emission data were collected by using a portable emission measurement system. The data were aggregated to represent the current Texas school bus fleet mix and rural versus urban miles driven. The results of statistical analysis showed that use of B20 had no significant effect on the level of NOx and CO2 emissions by the school buses. However, it was found that the biodiesel resulted in a significant decrease of HC and an increase in CO emissions. Similarly, the effects of cruise speed and acceleration rates on pollution showed differences depending on the pollutant in question. Some recommendations for emission control plans can be drawn from the analysis.