The city of Santa Monica, Calif., is in the midst of testing biodiesel, along with selective catalytic reduction (SCR) technology designed by Extengine Transport Systems LLC, to reduce NOx emissions.

This project, in coordination with the South Coast Air Quality Management District (AQMD), is designed to demonstrate the viability of biodiesel in tandem with SCR technology to attain emissions capable of meeting the 2010 federal standards for NOx. Tests are being conducted with two 2005 International 9200i test trucks, which have been equipped with a catalyst and a system that injects urea into the exhaust stream. The urea breaks down to ammonia, which reacts with NOx to produce elemental nitrogen and water vapor. SCR technology has been used selectively in the past to control NOx emissions from power plants, reciprocating engines and gas turbines.

"We did not see an increase of NOx in our heavy equipment when we went from unleaded diesel to a B20 blend," said Rick Sikes, fleet superintendent for the city of Santa Monica. "We did see [a NOx] increase with B100, but that was expected, and we believe that the catalytic converter will reduce this pollutant in the same way it has in smaller passenger cars."

The total proposed cost of the project is approximately $280,000, according to Sikes. Funding has been provided by the South Coast AQMD, Tellurian Biodiesel in San Francisco, the National Renewable Energy Laboratory and Extengine, among others. According to the California Environmental Protection Agency, the state's current NOx requirement for new urban bus engines is 0.2 grams per brake horsepower hour (g/bhp-hr). The California and national heavy-duty truck new engine standard for 2007 is the same, but flexibilities in the heavy-duty truck rule result in the option of certifying all engines to an average NOx standard of 1.2 g/bhp-hr between 2007 and 2009.