Electromagnetic design of a novel microwave internal combustion engine ignition source, the quarter wave coaxial cavity igniter

Abstract

New ignition sources are needed to operate the next generation of lean high-efficiency internal combustion engines. A significant environmental and economic benefit could be obtained from these lean engines. Towards this goal, the quarter wave coaxial cavity resonator (QWCCR), igniter was examined. A brief overview of the QWCCR's history is presented, followed by an electromagnetic analysis of the resonator. Microwave and radio-frequency gas breakdown at atmospheric and higher conditions are reviewed briefly. The presented analysis focuses on geometric and material parameter relations compared with performance characteristics, such as resonator quality factor and developed tip electric field which initiates a single-electrode high-pressure microwave gas breakdown. Conductor surface losses, dielectric losses, and radiation losses of the device are considered in the analysis, for which parameters of a prototype QWCCR were chosen for construction and evaluation of a resonator. Improved designs allowed successful integration of a QWCCR into a Briggs and Stratton engine. Given the capability of precise control, high power, and high energy delivery, and the opportunity for further optimization, the QWCCR has the potential to deliver more energy per ignition than a conventional spark plug and thus should be considered for application as a lean ignition source.