Simulation, Design and Development of a High Frequency Corona Discharge Ignition System

Depleting oil reserves and increasing concern over global warming caused by green house gases like carbon dioxide is driving efforts all over the world to improve fuel efficiencies of internal combustion engines. A method of achieving this in spark ignition engines is to use lean air-fuel mixtures. But for burning lean air-fuel mixtures the energy released by conventional spark ignition systems which produce a maximum voltage only of around 20000 V may not be sufficient. A corona discharge spark ignition is a method which can produce voltages as high as 100 kV which can ignite very lean air-fuel mixtures. The objective of this work is to numerically simulate the corona discharge in a point plane configuration and to investigate the applicability of corona discharge to automobile ignition systems. The domain for the simulation is chosen so as to match the engine cylinder and dimensions. The governing equations, namely the Poisson's equation and charge transport equation are solved using the finite difference method and the effect of pressure on corona discharge is studied. A circuit is designed and fabricated to provide high frequency voltages of the order of 30 kV and testing of the circuit is done in ambient conditions. The corona discharged produced was captured using Schlieren imaging method and the intensity of the spark was calculated by processing the captured image. The variation of spark intensity at different distances from the spark plug was compared with the electric field obtained from the simulation and was found to be in agreement.