Evaluation of a novel miniaturised microwave resonating igniter: The Flat Panel Igniter

This study evaluates the ignition performance of a new miniaturised igniter that operates based on microwave resonance phenomenon. This igniter, named Flat Panel Igniter (FPI), consists of a flat ceramic panel with a metal strip inlay on the top surface acting as a resonance cavity. The FPI and a standard spark plug is used to ignite air-propane mixtures at various equivalence ratio inside a constant volume chamber. The results show that FPI requires much less ignition energy than spark plug at any given equivalence ratio. Furthermore, at the same energy, ignition with FPI results in a faster ignition delay and a shorter burnt duration. FPI ignition also allows for better lean limit as the ignition energy increases. Observation at non-reactive condition shows that the plasma from FPI is a lot larger than that of the spark plug, most likely due to the enhancement by MW energy. Via optical spectroscopy, FPI spectrum is also shown to be much more intense than the spark plug, with a higher level of OH* radicals and slightly higher temperature. Schlieren images of the combustion shows a more spherical appearance of the resulting flame, suggesting that the design of the FPI will induce less heat loss to the early flame kernel and hence facilitate faster flame growth. The igniters were also tested under the influence of cross flow by injecting an air stream across the plasma location. Due to its geometry the FPI plasma has a longer stretch distance compared to the spark discharge from spark plug and interestingly, the FPI does not suffer from blow-off even at high flow speed where spark plug suffers from very early blow-off and restrikes. Overall, the FPI has been shown to be a promising igniter that outperforms the traditional spark plug to enable further advancement in engine design. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.