Standard: API 4101


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The effects of mandatory vehicle inspection and maintenance were investigated to assess the most cost-effective procedures for periodically diagnosing and restoring to specification those engine components having significant effects on vehicle exhaust emissions. Two classes of inspection procedures were evaluated:

• Direct measurement of engine parameter adjustments (malfunctions) using conventional or more sophisticated garage-type equipment

• Inference of engine parameter maladjustments or malfunctions from the measurement of engine exhaust emission levels (signatures) under varying loading conditions.

The former inspection procedure would most likely be performed in a franchised or certified, privately owned garage. The effectiveness of combinations of direct parameter measurements which resulted in short (approximately 3 minutes) and long (approximately 30 minutes) inspections were evaluated. Because direct parameter measurements using existing diagnostic equipment are time consuming, remote sensing instruments felt to be technically feasible were hypothesized and evaluated for use in direct diagnosis in state inspection lanes.

The emission signature inspection procedure requires more sophisticated equipment and instrumentation. Emission signatures for hydrocarbons, carbon monoxide and carbon dioxide would be measured under several engine loads. The use of emission signature inspection results in a higher vehicle inspection throughput but at the expense of a greater investment in capital equipment.

The general framework of the study focuses on those system elements which affect the ranking.of the alternative inspection and maintenance procedures in an economic effectiveness sense. The tasks include:

• Systems definition

• Statistical characterization of vehicle maintenance states in an urban region

• Development of procedures for inspecting and maintaining those malfunctioning engine parameters which significantly influence emissions

• Development of a computerized system model for evaluating the candidate procedures within a systematic application framework.

A summary of these tasks is presented in the following sections of this volume.

Conclusions derived from this study are:

• The six most effective engine parameters to maintain are the three idle adjustments (air-to-fuel ratio, rpm and basic timing), elements of the ignition system when causing misfire, as well as the positive crankcase ventilation valve and air cleaner of the induction system. The air injection system should be inspected and maintained on cars equipped with this type of air pollution control equipment.

• Inspection and maintenance of the idle adjustments was found to be a very cost effective procedure for controlling carbon monoxide emissions. Typical average emission reductions over a four year period are between 2 to 3 percent for hydrocarbons and 10 to 15 percent for carbon monoxide. Oxides of nitrogen emissions are increased by 4 to 7 percent.

• Control of both hydrocarbon and carbon monoxide emissions requires inspection and maintenance of the ignition and induction systems in addition to the idle parameters. Optimum inspection/maintenance procedures yield a typical average emission reduction over a four year period of 15-22 percent for hydrocarbons and 20-33 percent for carbon monoxide. Oxides of nitrogen emissions are increased from 3 to 5 percent by this treatment.

• The most cost effective inspection frequency is once yearly.

• State inspection lanes are usually more cost effective than franchised garages.

• Nondispersive, infrared emission measurement instruments are preferred for state-lane applications.

The above conclusions were based on currently available data, some of which were either of limited reliability or based upon small test populations. In addition, the effectiveness of maintenance was inferred from a limited set of representative power trains ( i.e ., 1966-1970 vehicles). Considerable emission reductions may be possible when the precontrolled vehicle population is included in the inspection/maintenance program.

Additional experiments are recommended to determine the effect on inspection/maintenance procedures of:

•  Precontrolled  and NOx controlled vehicles in an urban population

• The reliability with which commercial repair agencies can diagnose and repair vehicle exhaust control and related systems

• Differing urban regional air quality requirements, vehicle population composition, and general vehicle maintenance states.

Organization: American Petroleum Institute
Document Number: api 4101
Publish Date: 1971-08-09
Page Count: 55
Available Languages: EN
DOD Adopted: NO
ANSI Approved: NO
Most Recent Revision: YES
Current Version: NO
Status: Inactive