Electric field distribution in spark plugs insulators - Modeling and computer simulation

Automotive spark plugs are essential ignition circuit components being of importance for combustion engine reliability and performance. The majority of spark plugs have ribbed ceramic insulator to ensure high resistance along the surface from the terminal to the metal shell to minimize leakage current and to provide flashover protection. The leakage current intensity depends on electric field distribution, physical insulator properties and such factors as humidity, insulator contamination or defects in insulation material. Furthermore, leakage current not infrequently interferes with discharge process causing misfire effect being harmful to exhaust manifold components, mainly to catalytic converters. This paper presents simulation results of electric field distribution in ceramic insulator, in silicone rubber boot and in space surrounding a spark plug. Assuming that a spark plug can be considered as an object having cylindrical symmetry the electric field distribution was calculated for a two-dimensional case in accordance with Laplace's and Poisson's equations. In this paper, the finite difference method (FDM) for the solution of the Laplace's equation was applied. The FDM algorithm based on the Liebmann's method was developed in the MATLAB environment. Presented simulation results can be helpful to automotive spark plugs and high-tension cables manufacturers interested in improvement of insulating properties.