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A steady state mobile test was developed to measure the concentration of breathable particles that can enter the cabin of a school bus. The principles of experimental design were used to identify the experimental conditions for the test and to analyze the data. The design consisted of a series of steady-state tests using a 1992 International school bus. The testing was performed on a closed three mile track at the Army Test Center in Aberdeen, MD. The mass concentrations of particles smaller than 2.5 microns were measured at three locations inside the bus and at the air intake into the engine. The number concentration of particles was measured at the tailpipe. Three factors were varied at three levels in a Box-Benhken design. The steady state speed was set at 5, 30, and 55 mph. A load was applied to the engine with a mobile dynamometer to simulate a 0, 0.67% and 1.33% road grade.

The New Jersey Department of Transportation (NJDOT) is currently sponsoring a research study at Rowan University to develop strategies for reducing diesel emissions from mobile sources such as school buses and class 8 trucks. One such source of diesel emissions results from unnecessary idling of school buses, which is a typical practice that occurs in the mornings to warm up engines and in the afternoon while bus drivers wait to pick up children for their afternoon routes. To quantify emissions and fuel consumption during idling, three school buses equipped with an International T444E, an International DT466E, and a Cummins 5.9L B series engine were instrumented and tested in an environmental chamber. To simulate a wide variety of idling situations, tests were conducted at four different ambient temperatures (20°F, 40°F, 65°F and 85°F) and relative humidity ranging from 37 to 90%.

A significant fraction of diesel emissions can be attributed to heavy-duty diesel vehicles at idle conditions during which power is being used for systems such as cabin heating or cooling. Although, a variety of low emission, auxiliary power solutions already exist for HDDV trucks, they are not in wide spread use. Moreover, very little work has been done to date to quantify the total emissions and fuel consumption from truck idling. Accordingly, the U.S. Environmental Protection Agency, in collaboration with the New Jersey Department of Transportation, the U.S. Army Aberdeen Test Center, Oak Ridge National Laboratory and Rowan University has initiated a study to quantify the idling emissions and fuel consumption rates for HDDV trucks. Testing was performed in an environmental chamber on five different class 8 trucks with model years ranging from 1990's to 2001.