Effects of Some Engine Variables and Control Systems on Composition and Reactivity of Exhaust Hydrocarbons 660404

The effects of air-fuel ratio, spark timing, an engine modification system, and the Air Injection Reactor System on the composition and reactivity of the exhaust hydrocarbons are reported. The reactivity index and composition changes are compared to those indicated by the nondispersive infrared analyzer.
Either retarding the spark timing or leaning the air-fuel ratio reduced the hydrocarbon concentration measured by the infrared analyzer. In contrast, the reactivity index increased as the spark timing was retarded and the decrease in the reactivity index due to leaning the air-fuel ratio was only 1/2 the decrease in the concentration measured by the infrared analyzer.
For equal reductions in the concentration measured by the infrared analyzer, the reactivity index with the engine modification system was 37% higher than that with the Air Injection Reactor System. Conversely, in order to produce an exhaust with the same level of reactivity, the engine modification system has to reduce the concentration measured by the infrared analyzer about 70 ppm n-hexane more than the Air Injection Reactor System.
The use of the reactivity index points out significant differences in smog-forming potential resulting from both changes in engine design variables and exhaust control systems; these differences are not revealed by measurements made using the infrared analyzer.


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