| With increasingly stringent regulations placed on exhaust emissions of small utility engines, more opportunities for reduction in emissions are being explored. This thesis presents the results of a study in which the influence of spark plug electrode shape on exhaust emissions of three small utility engines is analyzed. The spark plugs studied were Champion models of standard electrode shape and spark plugs with a crown-shaped electrode, believed by the manufacturer (Pyrotek) to give improved combustion.; The experimental results indicate that the Pyrotek spark plug causes an appreciable reduction in hydrocarbon emissions with a moderate increase in emissions of oxides of nitrogen. The Pyrotek plug was more sensitive to changes in the angular position of the ground electrode, spark gap, engine speed, and to minor changes (i.e. notches) to the electrode's geometry. The reduction in hydrocarbon emissions is attributed to a faster burning rate and frame front propagation. The Pyrotek plug is also thought to favor the formation of more spherical flame fronts than the baseline spark plug and to influence the bulk charge motion in the vicinity of the spark gap. |
