Search Results

In response to a growing need for a practical and technically valid method for measuring exhaust sound pressure levels (SPL) of on-highway motorcycles, the SAE Motorcycle Technical Steering Committee has developed Surface Vehicle Recommended Practice J28251, “Measurement of Exhaust Sound Pressure Levels of Stationary On-Highway Motorcycles,” which includes a new stationary sound test procedure and recommendations for limit values. Key goals of the development process included: minimal equipment requirements, ease of implementation by non-technical personnel, and consistency with the federal EPA requirements; in particular, vehicles compliant with the EPA requirements should not fail when assessed using J2825. Development of the recommended practice involved a comprehensive field study of 25 motorcycles and 76 different exhaust systems, ranging from relatively quiet OEM systems to unbaffled, aftermarket exhaust systems.

The constant volume sampling (CVS) technique, which has been part of the Federal Test Procedure (FTP) for the exhaust emissions testing of light-duty vehicles since the 1972 model year, involves the collection of a sample of exhaust gas after it has been diluted to a constant volume. The FTP specifies a formula for calculating a dilution factor (DF) that is used to correct the emission measurement for the pollutant concentration in the dilution air. Once the DF has been determined, emission measurements made using the CVS technique can be converted to a “raw,” undiluted concentration. This enables a single sampling system to be used to determine either mass emissions or tailpipe concentrations, both of which are required in certain vehicle inspection and maintenance (I/M) programs. Review of the DF calculation procedure specified in the FTP indicates that it is a simplification of a more rigorous calculation needed to most accurately determine the true DF.

This paper discusses some trends and influencing factors in passenger car fuel economy. Fuel economy and fuel consumption were calculated by a carbon balance method from HC, CO, and CO2 emissions measured by the 1972 Federal Test Procedure. The information presented was derived from nearly 4000 tests of passenger cars ranging from 1957 production models to 1975 prototypes. Data are presented for various model year and vehicle weight categories. Trends in fuel economy are discussed on an overall sales-weighted basis and for each individual weight class. Some of the factors that influence fuel economy are quantified through the use of a regression analysis. Particular emphasis is placed on the differences in fuel economy between those vehicles that were subject to federal emission regulations and those vehicles that were not. Three ways to characterize vehicle specific fuel consumption are presented and discussed.

The use of fuel economy data from the Federal Test Procedure (FTP) has provided a substantial amount of data on the fuel economy of passenger cars in urban driving conditions. Since the FTP does not represent the type of driving done in rural areas, especially on highways, a driving cycle to assess highway fuel economy was a desirable supplement to the FTP. The new Environmental Protection Agency (EPA) “highway” cycle was constructed from actual speed-versus-time traces generated by an instrumented test car driven over a variety of nonurban roads and highways. This cycle reflects the correct proportion of operation on each of the four major types of nonurban roads and preserves the non-steady-state characteristics of real-world driving. The average speed of the cycle is 48.2 mph and the cycle length is 10.2 miles, close to the average nonurban trip length.

Recent tests conducted by the Alaska Department of Environmental Conservation and low ambient temperature tests previously conducted by a variety of other organizations indicate that less progress is being achieved in the control of emissions during cold weather than under temperatures similar to those used during EPA certification testing. Although CO emission standards dropped from 15 grams per mile to 7 grams per mile between 1975 and 1981, far less of a change occurred in CO emissions from new vehicles at 20°F. Cold start CO emissions at 20°F are about 60 grams per mile for late model cars at low mileages. The available test data on these cars seem to indicate that results achieved using the standard emission test procedure are poorly correlated with emissions at lower temperatures. However, the low temperature CO emissions of cars certified at 3.4 grams per mile CO are nearly 502 lower than vehicles certified to a standard of 15 grams per mile.

The California Bureau of Automotive Repair (BAR) and Sierra Research, Inc. (Sierra) have evaluated a large number of alternative emissions test procedures and developed new procedures that could substantially increase the ability to identify defective vehicles under vehicle inspection and maintenance (I/M) programs. The primary focus of the study was to determine whether an economical “loaded mode” (dynamometer-based) test procedure could be developed that would accurately identify vehicles with emissions in excess of the applicable standards using the Federal Test Procedure (FTP). The results of the BAR/Sierra study show that, using a new “Acceleration Simulation Mode” (ASM) test, 90% of all excess oxides of nitrogen (NOx) emissions can be identified without the use of transient testing or mass emission measurement.

A comprehensive vehicle emission testing program has determined that the California vehicle inspection and maintenance (I/M) program (called “Smog Check”) is reducing emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen from vehicles subject to the program by 12%, 10%, and 4%, respectively. Although substantial, the emission reductions of HC and CO are falling short of the 25% reduction goal set by the Environmental Protection Agency. Reasons for the shortfall include limitations in the ability of idle emission standards to detect defective vehicles; poor quality of visual and functional inspections; and ineffective repair of many failed vehicles. The overriding problem with the program can be summarized as the failure of participating mechanics to identify and correct emissions defects, especially in 1980 and later model vehicles. There are two types of mechanic performance problems which need to be addressed.