Exhaust emissions from engines of the Detroit Diesel Corporation in transit buses: A decade of trends

In the U.S.A., exhaust emissions from city buses fueled by diesel are not c haracterized well because current emission standards require engine tests r ather than tests of whole vehicles. Two transportable chassis dynamometer l aboratories developed and operated by West Virginia University (WVU) have b een used extensively to gather realistic emission data from heavy-duty vehi cles, including buses, tested in simulated driving conditions. A subset of these data has been utilized for a comprehensive introspection into the tre nds of regulated emissions from transit buses over the last 7 years, which has been prompted by continuously tightening restrictions on one hand, alon g with remarkable technological progress, on the other hand. Two widely use d models of diesel engines manufactured by the Detroit Diesel Corporation ( DDC) have been selected as a case-study for such an overview, based on full -scale, on-site testing of actual city buses, driven in accordance with the SAE J1376 standard of a Commercial Business District(CBD) cycle. The resul ts provide solid, quantitative evidence that most regulated emissions from engines produced by DDC have declined over the years, especially with the t ransition from the 6V-92TA to the Series 50 models. This improvement is rem arkable mainly for the emissions of particulate matter (PM), that are lower by over 70%, on average, for the Series 50 engines, though the emissions o f nitrogen oxides (NOx) exhibit a reversed trend, showing a degradation of about 6%, on average, with the transition from 6V-92TA to the Series 50 eng ines. The expected trend of decreasing emission levels with the model year of the engine is clear and consistent for particulate matter (PM), hydrocar bons (HC), carbon monoxide (CO), and nitrogen oxides (NOx), starting with t he 1990 models, although it is not conclusive for carbon dioxide (CO2) emis sions.