Search Results

A wide variety of exhaust emissions are reported for three diesel engines typically used in heavy-duty intercity truck and intracity bus operation. Particulate, odor, sulfate, sulfur dioxide, and selected non-reactive hydrocarbons were measured in addition to the regulated pollutants from Detroit Diesel 6V-7l and 8V-7lTA engines and a turbocharged Cummins 855 cu in research engine. The 855-TC engine was run in standard and a variable injection timing configuration, while the 6V-7l city bus engine was run with two types of injector designs. Emission rates are summarized in terms of grams per unit of fuel consumed and per unit of power output. The data allows direct comparison between engines and engine configurations, as well as a function of engine speed and load condition.

Exhaust emissions from in-use diesel trucks and buses can be reduced by application of retrofits consisting of new parts and adjustments. The results of fleet test demonstrations of two retrofit kits, one for 2-stroke diesel-powered buses and the other for 4-stroke diesel trucks, are described. Except for the catalytic muffler, the components and adjustments composing the General Motors environmental improvement proposal kit for General Motors city buses were found helpful in reducing exhaust odor, smoke, and certain gaseous emissions. The turbocharger kit and adjustments marketed by Cummins Engine for its NHC 250, an in-use naturally aspirated truck engine, was likewise found to reduce visible smoke satisfactorily. The fleet test data are from three city buses operated for two years and three intercity truck tractors operated for eight months.

A fleet of 64 heavy-duty 1970-71 model trucks and buses powered by a variety of diesel engines were tested periodically to determine exhaust smoke behavior. Smoke tests were made when the vehicle was new or nearly new and at four month intervals thereafter, or until 160,934 km (100,000 miles) odometer reading was reached. Gaseous emissions of hydrocarbon (HC), carbon monoxide (CO), and nitric oxide (NO) were measured at one point early in the project. Both smoke and gaseous emission tests were performed with chassis versions of the engine dynamometer Federal Test Procedures (FTP). Results in terms of “a” (acceleration), “b” (lugging), and “c” (peak) smoke factors versus mileage are reported for the 13 engine-vehicle-application groupings.

The use of diesel exhaust-emissions measurements to predict the observed odor from diesel engine exhaust has been studied, using a group of 31 trucks and buses powered by a variety of diesel engines. Regression analysis of gaseous emissions at a variety of conditions has resulted in equations for use in predicting odor. Acrolein, carbon dioxide, total hydrocarbons, selected light hydrocarbons, nitric oxide, carbon monoxide, and aliphatic aldehydes have been related to perceived odor. Some of these exhaust products are odorous and some are nonodorous yet indicative of the completeness of combustion. The empirical method, however, is somewhat less reliable than the observed odor based on a trained panel rating supra-threshold levels in terms of the PHS Quality-Intensity Odor Rating kit. In general, the greater variety of measurements and the fewer type of engines will increase odor prediction accuracy.

Exhaust emissions from heavy duty gasoline-powered vehicles have been studied in detail, under NAPCA support, at South west Research Institute. The principal exhaust emissions studied were carbon monoxide, hydrocarbons, and oxides of nitrogen. A broad variety of vehicles was tested with three variable speed experimental procedures using chassis dynamometers to simulate actual road operations. Approximately 150 trucks and buses of all weight classes were investigated to determine the ability of each vehicle to perform with the respective experimental cycle, each vehicle’s contribution of contaminants on a mass basis per mile driven, and the applicability of these cyclic test procedures for federal testing.

A program of research on diesel smoke and odor was sponsored by the U.S. Public Health Service by contract with Southwest Research Institute. A test facility was developed in which full-scale trucks and buses were operated on a chassis dynamometer through operating modes that yielded maximum exhaust smoke and odor. A system of exhaust dilution was employed to provide realistic odor concentrations to a panel of judges who rated the intensity and quality of the exhaust in terms of a set of chemical standards. Smoke levels were measured with a PHS-designed full-flow optical smokemeter. After an initial baseline evaluation of groups of buses and trucks with standard engines, various control techniques were evaluated to determine their effectiveness in reducing smoke and/or odor. Chemical analyses of the exhaust were made for the purpose of correlating the smoke and odor reductions with changes in exhaust composition.