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Approximately 245 passenger cars were involved in a Cooperative Test Program (CTP) conducted by EPA and industry. The purpose of this program was to examine ways of improving the effectiveness of I/M tests, specifically for the 1981 and later vehicles with closed loop fuel metering. Detroit area vehicles failing the Michigan Auto Exhaust Testing (AET) program were recruited and investigated to determine the cause of the failures. Complete FTP emission tests were run as received, and at each step of the repair sequences. A variety of I/M preconditioning methods were evaluated to understand false failures. GM's portion of the CTP was sixty vehicles, half 1981-1982, and half 1983 and later model years. During the time period of the CTP, the AET failure rates were 14.5% for the 1981-1982 model years and 6.6% for the 1983 and later model years. Although all sixty vehicles had failed the Michigan AET, thirty-three (55%) passed “as-received” when tested in the 6M laboratory.

EPA and GM test programs have quantified the in-use emission performance of the GM closed-loop emission control systems. In-use exhaust emission levels, adjusted to the 50,000 mile point, show averages under the standards for the 1986 model year cars. In-use evaporative emission levels are under the standard, on average, for the 1985 and 1986 model year cars. Fuel injection systems have inherent evaporative emission performance advantages over carburetor systems. Average exhaust emission levels for the national fleet will continue to decrease as the closed-loop fleet replaces the older models. Predictions of future inventories are lower if the GM data reflecting the 1981+ emission improvements are used instead of the estimates currently in the MOBILE3 model.

Analysis of today's closed loop systems shows in-use emission levels - measured using the Federal Test Procedure - greatly reduced from those of vehicles produced in the mid ‘70s. The tailpipe concentration measurements (idle tests) used in I/M programs do not correlate well with in-use emissions from today's vehicles. I/M tests are not very effective in identifying emission failures and are costly compared to other control strategies. Additionally, I/M programs which do not include adequate vehicle preconditioning increase the number of false failures and cause unnecessary expense. A majority of today's closed loop vehicles have on-board diagnostic systems to identify failures. Interrogating these on-board diagnostic systems, together with parameter inspections, offers a more effective alternative to current I/M programs.

Major technical advances have been introduced in the area of engine controls over the last several years. General Motors has applied many of these product advances including a digital microcomputer to coordinate the major control functions of the engine’s operation: fuel, spark advance, idle speed, EGR, and transmission. Motivation for these advances is based upon maximizing fuel economy and driveability for the customer while achieving effective emission control performance. This paper will provide a description of the systems that have been introduced nationwide in 1981 and 1982 and highlight some of the production activities that were undertaken to ensure quality and reliability.

Six vehicles that have achieved the Federal research objective emission levels at low mileage are described. Two vehicles have completed 50,000 miles of durability below the .41/3.4/.41 g/mi levels. Two vehicles failed these emission levels by 10,000 miles. There is a loss in fuel economy of about 7% and the driveability ranged from non-commercial to borderline commercial. The ongoing program objectives are to reduce the sensitivity of these systems to emission deterioration and driveability defects and to reduce the fuel economy losses.

Previous investigations have shown that fuel economy gains are possible in vehicles with increased compression ratio engines that meet 1978 Federal emission standards using oxidizing converter-EGR emission control systems. There has been no incentive to raise compression ratios, however, since the vehicle gains are offset by energy losses in the refinery due to refining the higher octane unleaded fuel required by high compression ratio engines. This paper discusses the application of an electronic closed loop knock control system to a higher compression ratio engine to allow operation on 91 Research Octane Number fuel. Two cars with different compression ratios are compared with both oxidizing converter - EGR and 3-way oxidizing-reducing converter-EGR closed loop carburetor emission control systems.

NOx emissions can be controlled through engine operation with lean homogeneous air/fuel mixtures. This emission control approach precludes the need for exhaust gas recirculation (EGR) and secondary air injection systems. The Lean Mixture concept results in similar emissions, fuel economy, and driveability when compared to EGR systems tailored to similar emission levels with similar aftertreatment systems. The Lean Mixture approach does offer the potential for less engine emission control hardware. The minimum NOx level achieved experimentally at the lean driveability limit was about 1.2 g/mi but with significantly higher HC emissions. Lean Mixture systems are sensitive to variations in engine air/fuel ratio which produce a significant effect on their emissions and fuel economy.

This paper describes the results of a study to evaluate the relationship of compression ratio on fuel energy conservation with the constraint of the 1977 Federal emission standards (1.5 HC, 15.0 CO and 2.0 NOx). The influence of the energy losses in the refinery process to produce higher octane fuels was considered as well as the effect of compression ratio on engine efficiency. Two different emission control systems were evaluated; a catalytic converter-EGR system and a manifold reactor-EGR system. These systems were evaluated on six vehicles; three intermediate size with 350 CID engines at compression ratios of 7.4, 8.3 and 9.2:1 and three sub-compact size with 151 CID engines at the same three compression ratios. Based upon total energy conservation, there does not appear to be an incentive for increasing unleaded or leaded fuel octane levels to allow for the use of higher compression ratios with converter-EGR or reactor-EGR control systems at the 1977 Federal emission standards.

In addition to designing and developing hardware to control the exhaust gas recirculation (EGR) rate, it is equally important to tailor the other engine variables. Optimization of air-fuel ratio (A/F) and spark timing is required to achieve the best combination of oxides of nitrogen (NOx), hydrocarbon (HC), and carbon monoxide (CO) control, while minimizing the losses in fuel economy and drivability. This paper describes an engine dynamometer and vehicle study which defines the relationship between the above para meters. In general, increasing the spark advance with increasing EGR rates will minimize the losses in fuel economy and vehicle drivability while achieving significant reductions in NOx emissions. This approach is limited by a deterioration in HC emission control. The loss in HC control can be minimized by spark retard, but with a loss in fuel economy.

General Motors Engineering Staff built and tested three small, lightweight urban cars with the numerical identity 512. These special purpose, two passenger cars are designed to provide short range personal transportation with some package carrying capability. Their top speed is limited at 30-45 mph. Separate roads or restricted driving areas would be required for these cars since they could not safely mix with full-sized cars and trucks. These small cars would help relieve urban traffic and parking problems. Their low power and energy requirements result in low vehicle emissions. The 512 car series utilizes one basic body configuration as a test bed for different powerplants. Three have been tested to date: a conventional gasoline engine, a battery-electric, and a hybrid gasoline-electric. The gasoline powertrain consists of a 19.6 cu in., 2-cyl engine coupled with an automatic variable-ratio vee-belt transmission.