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In the United States, most school buses are powered by diesel engines. Some have advocated replacing diesel school buses with natural gas school buses, but little research has been conducted to understand the emissions from school bus engines. This work provides a detailed characterization of exhaust emissions from school buses using a diesel engine meeting 1998 emission standards, a low emitting diesel engine with an advanced engine calibration and a catalyzed particulate filter, and a natural gas engine without catalyst. All three bus configurations were tested over the same cycle, test weight, and road load settings. Twenty-one of the 41 “toxic air contaminants” (TACs) listed by the California Air Resources Board (CARB) as being present in diesel exhaust were not found in the exhaust of any of the three bus configurations, even though special sampling provisions were utilized to detect low levels of TACs.

This paper describes the findings of a laboratory effort to demonstrate improved automotive exhaust emission control with a cold-start hydrocarbon collection system. The emission control strategy developed in this study incorporated a zeolite molecular sieve in the exhaust system to collect cold-start hydrocarbons for subsequent release to an active catalytic converter. A prototype emission control system was designed and tested on a gasoline-fueled vehicle. Continuous raw exhaust emission measurements upstream and downstream of the zeolite molecular sieve revealed collection, storage, and release of cold-start hydrocarbons. Federal Test Procedure (FTP) emission results show a 35 percent reduction in hydrocarbons emitted during the cold-transient segment (Bag 1) due to adsorption by the zeolite.

The use of methanol as a “clean fuel” appears to be a viable approach to reduce air pollution. However, concern has been expressed about potentially high formaldehyde emissions from stoichiometrically operated light-duty vehicles. This paper presents results from an emission test program conducted for the California Air Resources Board (CARB) and the South Coast Air Quality Management District (SCAQMD) to identify and evaluate advanced catalyst technology to reduce formaldehyde emissions without compromising regulated emission control. An earlier paper presented the results of evaluating eighteen different catalyst systems on a hybrid methanol-fueled test vehicle. (1)* This paper discusses the optimization of three of these catalyst systems on four current technology methanol-fueled vehicles. Emission measurements were conducted for formaldehyde, nonmethane organic gases (NMOG), methanol, carbon monoxide, and oxides of nitrogen emissions.

A 1991 Toyota Camry equipped with an electrically-heated catalyst (EHC) system was evaluated in duplicate over the Federal Test Procedure (FTP) with three different fuels. Evaluations were conducted with the EHC in place but without any external heating, and with the EHC operated with a post-crank heating strategy. The EHC system was placed immediately upstream of an original production catalyst, which was then moved to a location 40.6 cm from the exhaust manifold. The three test fuels were: 1) the Auto/Oil industry average gasoline, RF-A; 2) a fuel meeting California's Phase II gasoline specifications; and 3) a paraffinic test fuel. Non-methane organic gas (NMOG) emission rates with the EHC active were similiar with all three fuels, with absolute levels less than or equal to California's 50,000 mile Ultra-Low Emission Vehicle (ULEV) standard. Substantial differences, however were observed in the ozone forming potential of these fuels with the EHC active.

Two additive blends proposed for improving the flame luminosity in neat methanol fuel were investigated to determine the effect of these additives on the exhaust emissions in a dual-fueled Volkswagen Jetta. The two blends contained 4 percent toluene plus 2 percent indan in methanol and 5 percent cyclopentene plus 5 percent indan in methanol. Each blend was tested for regulated and unregulated emissions as well as a speciation of the exhaust hydrocarbons resulting from use of each fuel. The vehicle exhaust emissions from these two fuel blends were compared to the Coordinating Research Council Auto-Oil national average gasoline (RF-A), M100, and M85 blended from RF-A. Carter Maximum Incremental Reactivity Factors were applied to the speciated hydrocarbon emission results to determine the potential ozone formation for each fuel. Toxic emissions as defined in the 1990 Clean Air Act were also compared for each fuel.

This paper describes experiments to determine the effect on exhaust emissions of starting on compressed natural gas (CNG) and then switching to gasoline once the catalyst reaches operating temperature. Carbon monoxide, oxides of nitrogen, and detailed exhaust hydrocarbon speciation data were obtained for dedicated CNG, then unleaded gasoline, and finally CNG start -gasoline run using the Federal Test Procedure at 24°C and at -7°C. The result was a reduction in emissions from the gasoline baseline, especially at -7°C. It was estimated that CNG start - gasoline run resulted in a 71 percent reduction in potential ozone formation per mile.

This paper describes experiments conducted to determine the regulated emissions, ozone-forming potentials, specific reactivities, and reactivity adjustment factors for eight butane and propane alternative fuel blends run on a light-duty vehicle, emission certified to be a California transitional low emission vehicle (TLEV) and converted to operate on liquefied petroleum gas (LPG). Duplicate EPA FTP emission tests were conducted with each fuel. Hydrocarbon speciation was utilized to determine reactivity-adjusted non-methane organic gases (NMOG) emissions for one test on each fuel. Results showed that all eight fuels could allow the converted vehicle to pass California ultra-low emission vehicle (ULEV) NMOG and oxides of nitrogen (NOx) standards. Six of the eight fuels could allow the vehicle to pass ULEV carbon monoxide (CO) standards. BUTANE has been an important gasoline blending component for many years.

This paper describes experiments conducted to determine Federal Test Procedure (FTP) exhaust emissions, ozone-forming potentials, specific reactivities, and reactivity adjustment factors for several butane/propane alternative fuel blends run on a light-duty EHC-equipped gasoline vehicle converted to operate on liquefied petroleum gas (LPG). Duplicate emission tests were conducted on the light-duty vehicle at each test condition using appropriate EPA FTP test protocol. Hydrocarbon speciation was utilized to determine reactivity-adjusted non-methane organic gas (NMOG) emissions for one test on each fuel.

The design and development of an instrument for the measurement of total hydrocarbons in diesel exhaust are described, and its ability to measure steady-state and transient hydrocarbon emissions is indicated. The two-section system comprises a sampling train and flame-ionization detector and a chromatograph electrometer, recorder and backpressure regulator. A mixture of 40% H2 and 60% He was found to be the best fuel for low O2 response with the system. The method has been used for more than a year in evaluating hydrocarbon emissions from a wide variety of diesel engines under a number of typical operating conditions. The greatest advantage of the high-temperature system is its potential for expressing the total hydrocarbon content in diesel exhaust.

In an attempt to characterize emissions from small air-cooled utility engines, five gasoline-fueled models were operated over a variety of speeds and loads, and important exhaust constituents were measured. These emissions included hydrocarbons, CO, CO2, NO, O2, aldehydes, light hydrocarbons, particulates, and smoke. Emissions of SOx were estimated on the basis of the fuel consumed; evaporative losses of hydrocarbons were also estimated. The impact of small engine emissions was calculated on the basis of the test results and information on national engine populations and usage. From these data, it appears that the 50 million or more small engines currently being used account for only a small part of pollutants from all sources.

The research program on which this paper is based included both laboratory emission measurements and extrapolation of results to the national population of heavy-duty farm, construction, and industrial engines. Emission tests were made on four gasoline engines and eight diesel engines typical of those used in F, C, and I equipment. Gaseous and particulate emissions were measured during engine operation on well-accepted steady-state procedures, and diesel smoke was measured during both steady-state conditions and the Federal smoke test cycle. Emissions measured were hydrocarbons, CO, CO2, NO, NOx, O2, aliphatic aldehydes, light hydrocarbons, particulate, and smoke. Emission of sulfur oxides (SOx) was estimated on the basis of fuel consumed, and both evaporative and blowby hydrocarbons were also estimated where applicable (gasoline engines only). Data on emissions obtained from this study were compared with those available in the literature, where possible.

This paper summarizes an investigation of reductions in exhaust emission levels attainable using various techniques appropriate to gasoline engines used in vehicles over 14,000 lbs GVW. Of the eight gasoline engines investigated, two were evaluated parametrically resulting in an oxidation and reduction catalyst “best combination” configuration. Four of the engines were evaluated in an EGR plus oxidation catalyst configuration, and two involved only baseline tests. Test procedures used in evaluating the six “best combination” configurations include: three engine emission test procedures using an engine dynamometer, a determination of vehicle driveability, and two vehicle emission test procedures using a chassis dynamometer. Dramatic reductions in emissions were attained with the catalyst “best combination” configurations. Engine durability, however, was not investigated.

This is a summary compilation and analysis of exhaust-emission results and operating parameters from forty-five heavy-duty gasoline and diesel-powered vehicles tested over a 7.24-mile road course known as the San Antonio Road Route (SARR); and, for correlative purposes, on a chassis dynamometer.(2) Exhaust samples were collected and analyzed using the Constant Volume Sampler (CVS) technique similar to that used in emission testing of light-duty vehicles. On the road course, all equipment and instrumentation were located on the vehicle while electrical power was supplied by a trailer-mounted generator. In addition to exhaust emissions, operating parameters such as vehicle speed, engine speed, manifold vacuum, and transmission gear were simultaneously measured and recorded on magnetic tape. The forty-five vehicles tested represent various model years, GVW ratings, and engine types and sizes.

This paper describes the results of a public opinion survey on testing of diesel exhaust odors conducted during 1969 and 1970. Major goals of the research were to relate public opinion of the odors and the objectionability associated with them to odor intensity, and to obtain a dose-response curve as the primary result. The dose-response curve was needed to assess odor-control technology by providing a criterion for deciding whether or not the effect of a given control item would be noticed by the general public, reduce complaints, or be worth the cost and effort required for its implementation. The engine used as the live odor source for the subject research was a two-stroke cycle type similar to those used in many buses. This engine type was chosen because its exposure to the public in urban bus applications is very widespread, and because a large portion of the Environmental Protection Agency's odor research had been performed with similar engines.

Seven motorcycles, ranging in size from 100 to 1200 cm3, were tested for emissions characterization purposes. They were operated on the federal seven-mode test procedure (for 1971 and older light-duty vehicles), the federal LA-4 test procedure (for 1972 and later LDVs), and under a variety of steady-state conditions. Four of the machines tested had 4-stroke engines, and the other three had 2-stroke engines. Emissions which were measured included hydrocarbons, CO, CO2, NO, NOx, O2, aldehydes, light hydrocarbons, particulates, and smoke. Emissions of SOx were estimated on the basis of fuel consumed, and evaporative hydrocarbon losses were also estimated. Crankcase “blowby” emissions from one 4-stroke machine were measured. The impact of motorcycles on national pollutant totals was estimated, based on the test results and information from a variety of sources on national population and usage of motorcycles.

This paper describes a research program on exhaust emissions from snowmobile engines, including both emissions characterization and estimation of national emissions impact. Tests were conducted on three popular 2-stroke twins and on one rotary (Wankel) engine. Emissions that were measured included total hydrocarbons, (paraffinic) hydrocarbons by NDIR, CO, CO2, NO (by two methods), NOx, O2, aldehydes, light hydrocarbons, particulate, and smoke. Emissions of SOx were estimated on the basis of fuel consumed, and evaporative hydrocarbons were projected to be negligible for actual snowmobile operation. During emissions tests, intake air temperature was controlled to approximately -7°C (20°F), and room air at approximately 24°C (75°F) was used for engine cooling. Based on test results and the best snowmobile population and usage data available, impact of snowmobile emissions on a national scale was computed to be minimal.

To characterize exhaust emissions from water-cooled 2-stroke outboard motors (the predominant type), four new motors were tested on dynamometer stands. The engines ranged from 4-65 hp in size, and operating conditions were chosen along lines of simulated boat loading. All the measurements were taken at steady-state conditions. Emission concentrations were measured in raw exhaust gas and after the gases had been bubbled through water in a specially constructed tank. Constituents measured included hydrocarbons, CO, CO2, NO, NOx, O2, light hydrocarbons, and aldehydes. Emissions of sulfur oxides (SOx) were estimated on the basis of fuel consumed, and all the exhaust emissions data were used with available information on population and usage of motors to estimate exhaust emission factors and national exhaust emissions impact.

This paper describes the development of a CVS compatible sampling system for automotive sulfate emissions. The design resulted from a consensus of ideas from EPA and industry. The system can be used with either a positive displacement pump or critical flow venturi CVS. A mist generator was developed to quantitatively inject sulfuric acid into the tunnel. While sulfate losses were acceptable using the mist generator, with actual automotive exhaust sulfate losses were much higher. The reasons for these losses were investigated. Sulfate losses in the tubing between the car and sulfate tunnel were also investigated.

Five light-duty vehicles were used to investigate HC, CO, and NOx emissions and fuel economy sensitivity to changes in the length of soak period preceding the EPA Urban Dynamometer Driving Schedule (UDDS). Emission tests were conducted following soak periods 10 minutes to 36 hours in length. Each of the first 8 minutes of the driving cycle was studied separately to observe vehicle warm-up. Several engine and fuel system temperatures were monitored during soak and run periods and example trends are illustrated. The extent to which emission rates and fuel consumption are affected by soak period length is discussed.

To develop a methodology for characterizing particulate emissions from diesel engines, one 2-stroke cycle engine and one 4-stroke cycle engine were operated in both individual steady-state modes and according to a variation of the 13-mode diesel emissions measurement procedure. Both engines were operated on three fuels, each used with one of two available diesel fuel additives as well as by itself. The primary particulate sampling technique employed was a dilution tunnel, and secondary evaluation techniques included a diluter-sampler developed under contract to EPA by another organization, a light extinction smokemeter, and a filter-type sampling smokemeter. Gaseous emissions were also measured, providing a running check on engine condition. Particulate mass rates were calculated from gravimetric data; and analysis of particulate included determination of sulfur, carbon, hydrogen, nitrogen, phenols, nitrosamines, trace metals, and organic solubles.