The increasing use of spark ignition engines throughout the world has confronted the engine designer with new problems such as air pollution, world-wide temperature extremes, as well as legislative, economic, and human considerations. To meet these situations and improve the competitive position of the spark ignition engine requires considerable research and development effort. This paper reports on work conducted by Champion Spark Plug Company in attempting to evaluate the potential contribution that ignition system and spark plug designs can make towards improving spark ignition engine operation. Almost all the work reported here covers investigations in current large displacement United States passenger car engines. The three main characteristics of the overall ignition systems that are investigated are (1) the available output voltage characteristics of the ignition systems; (2) the effect of the ignition system spark discharge characteristics on engine performance; and (3) the effect of several spark plug design features on engine performance. This investigation shows that the inter-relationship of the ignition system spark discharge characteristics and the spark plug design requires that the overall evaluation must consider the dependence of both items. It also suggests that significant improvements can result in other United States and European engines, through the careful evaluation of ignition system and spark plug designs. The results of this work indicate that a fast rise time, short arc duration system results in reduced spark plug gap growth and better resistance to spark plug fouling. However, the arc duration must not be shorter than a minimum value, or a loss in engine performance may result. High output systems are desirable as they provide a higher voltage reserve to provide longer spark plug life, but the higher voltages that occur with the larger spark plug gaps can stress other ignition system components. The spark plug designs which incorporate a projection of the spark plug gap result in better performance in the engines tested, and possibly even reduce exhaust emissions. Certainly other features which engine manufacturers must consider, which are not discussed in detail here, are costs, durability, and maintenance of the new systems. At least one other important related problem is that of interference.
Use of the mathematical model of the ignition system to analyze the spark discharge, including the destruction of spark plug electrodes
