Graduate Thesis Or Dissertation
 

The effect of air injection at the exhaust ports of a gasoline engine on the oxides of nitrogen emissions

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  • The importance of automobile exhaust as a source of atmospheric pollutants has been recognized for several years. With the control of stationary sources in geographic areas such as Los Angeles County, the automobile has become the major uncontrolled source of air pollution. The three major pollutants emitted by automobiles are unburned hydrocarbons, carbon monoxide, and oxides of nitrogen. Seventy percent of the emissions are from the exhaust. Maximum emission standards of 275 ppm hydrocarbons as n-hexane and 1.5 mole percent carbon monoxide in automotive exhaust have been enacted in California. Control measures for the oxides of nitrogen may possibly be effective for 1970 model vehicles. Exhaust control devices for hydrocarbon and carbon monoxide emissions submitted to the California Motor Vehicle Pollution Control Board for approval have included catalytic converters, direct-flame afterburners, engine modification systems, and secondary air injection at the exhaust port systems. Three of the automobile manufactures may use the fourth system which involves introduction of secondary air into the engine exhaust ports to promote flameless oxidation of hydrocarbons and carbon monoxide to carbon dioxide and water. Since this control system introduces air to the high temperature exhaust gases at the exhaust port, the question arises whether oxides of nitrogen might be formed. This would be detrimental from the outlook that oxides of nitrogen must be controlled. The purpose of this work was to determine the effects on the emissions of oxides of nitrogen from a gasoline engine by the installation and operation of an exhaust port secondary air injection system. The engine under test, given to Oregon State University by the Ford Motor Company, was installed in a vehicle and operated on a chassis dynamometer. Measurements of oxides of nitrogen emissions with and without the air injection system in operation were made both during steady state and transient conditions. For transient measurements, the vehicle was operated on the California seven-mode test cycle. Oxides of nitrogen samples were taken by a progressive grab sampling technique and analyzed with an absorption spectrophotom eter built at Oregon State University. Further measurements included unburned hydrocarbon, carbon monoxide, and carbon dioxide analyses with commercial non-dispersive infrared analyzers and total carbon measurement with a commercial hydrogen flame ionization analyzer. These analyses were made for the purpose of determining air dilution factors and correlating data with other work being done in the field. The results of the investigation are summarized as follows: 1) The addition of secondary air at the exhaust ports in creased the oxides of nitrogen emissions during acceleration for both rich and lean mixture operation. As high as 40 percent in crease occurred during operation with the rich carburetor. Appreciable increase also occurred during high speed steady state cruise conditions with the rich carburetor. Weighted average concentrations of NO[subscript x] for operation on the California cycle were not determined. 2) The grab sampling and spectrophotometric analysis methods for the oxides of nitrogen worked well during the testing. However, the time required to take a grab sample, three seconds, was too long to obtain instantaneous analysis. Sampling probes should be located closer to the engine to avoid mixing of exhaust from separate modes in the exhaust pipe prior to analysis. 3) Temperatures in the exhaust manifold were not markedly changed by the injection of secondary air into the exhaust ports. However, temperatures were 50 to 100° F higher at the end of the tailpipe due to increased exhaust mass flow rate. 4) The vehicle with the air system installed met California standards for operation with the rich carburetor, but emitted a higher concentration of unburned hydrocarbons than the standard during operation with the lean carburetor.
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