THE EFFECTS OF ENGINE OPERATING AND DESIGN VARIABLES ON EXHAUST EMISSIONS 620404
To determine the influence of engine variables on the composition of exhaust gas, engine dynamometer tests were conducted on single and multi-cylinder reciprocating engines. The following engine variables were investigated: air-fuel ratio, power output, engine speed, spark timing, exhaust back pressure, valve overlap, combustion chamber deposits, and intake manifold pressure.
Hydrocarbon concentrations were found to be considerably affected by changes in air-fuel ratio, spark timing, intake manifold pressure, and combustion chamber deposits. Somewhat less change in hydrocarbon concentration was obtained by varying valve overlap and engine speed. Changes in engine power output and exhaust back pressure had little effect on hydrocarbon concentrations.
Carbon monoxide concentrations were principally affected by changes in the air-fuel ratio. No other variables affected carbon monoxide concentration except where air-fuel ratio was indirectly influenced.
The influence of changes in the variables on hydrocarbon and carbon monoxide emissions in pounds per hour was also determined.
Vehicles were tested on the road and chassis dynamometer to investigate the effect of air-fuel ratio, spark timing, and valve overlap on hydrocarbon and carbon monoxide concentrations. Carburetion leaning, spark timing retardation and reduction of valve overlap produced concentration reductions in line with those predicted from engine dynamometer studies.