Study of Exhaust Emissions from Idling Heavy Duty Diesel Trucks and Commercially Available Idle Reducing Devices 2003-01-0288

Heavy duty diesel truck idling contributes significantly to energy consumption in the United States. President Bush's May 2001 National Energy Policy tasks the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Transportation (DOT) to reduce truck idling. Consequently, the EPA initiated a study that would quantify long duration idling emissions and fuel consumption rates.

The idling study was conducted over a two year period at the U.S. Army's Aberdeen Test Center (ATC). A short introductory study with five tests was done in June 2001 and a larger study with 37 tests in May 2002. In the larger study, EPA worked with Oak Ridge National Laboratory (ORNL) and Rowan University with funding from the New Jersey Department of Transportation (NJDOT).

In total, ATC performed 42 tests on nine class-8 trucks (model years ranging from 1980's to 2001). Two of those trucks were equipped with 8.2 kW (11 hp) diesel auxiliary power units (APU's), and one was equipped with a diesel direct fired heater (DFH). The APU powers electrical accessories, heating, and air conditioning, whereas a DFH heats the cab in lieu of truck idling. All tests were run in a climate controlled chamber, where the trucks idled at high and low RPMs in the following environments: 32°C (90°F) with air conditioning on, -32°C (0°F) with the heater on, and 18°C (65°F) with no accessories on. ATC test technicians adjusted the air conditioning or heater to maintain a target cab temperature of 21°C (70°F). Each idling test was run for approximately three hours.

EPA's ROVER (Realtime On-road Vehicle Emissions Reporter) and ORNL laboratory emissions instruments were simultaneously used for measuring fuel consumption rates, HC (hydrocarbons), NOx (nitrogen oxides), CO (carbon monoxide), CO₂ (carbon dioxide), O₂ (oxygen), and PM (particulate matter) (ORNL only) during the May 2002 test runs. Only the ROVER was used during June 2001. The test data showed that, based on the data obtained from this study: (a) on average, a typical 1980s-2001 model year idling truck emits 144 g/hr of NOx and 8224 g/hr CO₂ and consumes about 3.1 L/hr (0.82 gal/hr) of diesel fuel; (b) there is good test repeatability when measuring idling emissions; and (c) use of an APU can reduce idling fuel consumption by 50% to 80% and reduce NOx by 89% to 94% whereas use of a DFH can reduce fuel consumption by 94% to 96% and reduce NOx by 99%.