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Information from the literature and from on-going test programs (government and industry) was analyzed with regard to the effect of gasoline Reid vapor pressure (RVP) on total vehicle hydrocarbon (HC) emissions, including evaporative, refueling, and exhaust emissions. A reduction in the average RVP of summer gasolines from present commercial levels to 9 psi was estimated to decrease total vehicle hydrocarbon emissions by 9-25 percent. With such reductions, hydrocarbon emission inventories for three major cities (Detroit, New York, and Dallas) would be decreased by 3-7 percent and, consequently, local ambient ozone levels would be reduced as much as 9 ppb. Accordingly, in many areas of the country, RVP reduction could make an important contribution toward achievement of the National Ambient Air Quality Standard (NAAQS) of 120 ppb ozone.

Hydrogen-supplemented fuel was investigated as a means of extending lean operating limits of gasoline engines for control of NOx. Single-cylinder engine tests with small additions of hydrogen to the fuel resulted in very low NOx and CO emissions for hydrogen-isooctane mixtures leaner than 0.55 equivalence ratio. Significant thermal efficiency improvements resulted from the extension beyond isooctane lean limit operation. However, HC emissions increased markedly at these lean conditions. A passenger car was modified to operate at 0.55-0.65 equivalence ratio with supplemental hydrogen. Vehicle emissions, as established by the 1975 Federal Exhaust Emissions Test, demonstrated the same trends as the single-cylinder engine tests. The success of the hydrogen-supplemented fuel approach will ultimately hinge on the development of both a means of controlling hydrocarbon emissions and a suitable hydrogen source on board the vehicle.

The effects of charge dilution on the exhaust emission of nitric oxide (NO) from a single-cylinder engine were evaluated over a range of engine design and operating parameters. Nitric oxide emission decreased as much as 70% as charge dilution fraction (volume fraction of product gases in the combustion chamber prior to ignition) was increased from 0.065 to 0.164 due to increased valve overlap, external exhaust recirculation, and reduced compression ratio. With these three variables, NO emission was strongly dependent on charge dilution fraction, but was independent of the specific method used to change charge dilution. Other variables such as valve overlap position, spark timing, and exhaust pressure also affected charge dilution and NO emission, but the relationship between charge dilution fraction and NO emission for these variables was not consistent.

The tedious, time consuming task of hand reducing data from the California exhaust emission test has been alleviated through the use of digital data acquisition equipment and a digital computer. Analog signals from exhaust gas analyzers and an engine speed transducer are converted to digital measurements which are recorded on tape and submitted to a digital computer for data analysis and computation of results. In the data analysis, the computer identifies the required driving modes from engine speed changes, taking into account the sample delay time. “Reported” composite emissions determined by the automatic data reduction method agree within 5% with results determined by careful hand analysis of analog strip chart recordings. The results determined by the automatic data reduction system are more consistent and accurate because human errors prevalent in hand analysis have been eliminated, and because nonlinear analyzer response is accounted for.

Factors influencing the effectiveness of exhaust port air injection in oxidizing the hydrocarbons and carbon monoxide in engine exhaust gas have been investigated in order to establish guidelines for the engineering of vehicle emission control systems. Single-cylinder engine and vehicle studies have demonstrated that the temperature, composition, and residence time of the exhaust gas-air mixture are basic factors determining both the effectiveness of air injection and the type of oxidation process which occurs in the exhaust system. Both luminous and nonluminous oxidation have been observed. These basic factors are affected by such variables as: engine spark timing and air-fuel ratio, insulation and size of exhaust manifolds, injection air temperature and airflow rate, and the warmup characteristics of the air injection system. The warmup characteristics can be influenced particularly by spark timing and exhaust manifold design.

USING a high-speed motion picture camera, flame photographs were taken of the combustion process associated with the starting of hot gasoline engines. Compression ignition at isolated points followed by normal combustion caused peak cylinder pressures to occur prior to top dead-center under some low-speed engine conditions. In addition, an abnormal combustion phenomenon was observed in the last part of the charge to burn. The reaction rate was appreciably faster than normal for the engine speed and much slower than is usually observed in knocking combustion at normal engine speeds.