Experimental and Numerical Investigations of the Early Flame Development Produced by a Corona Igniter

In order to reduce engine emissions and fuel consumption, extensive research efforts are being devoted to develop innovative ignition devices, able to extend the stable engine operating range towards increasing lean conditions. Among these, radio frequency corona ignition systems, which produce a strong electric field at a frequency of about 1 MHz, can create discharges characterized by simultaneous thermal and kinetic effects. These devices can considerably increase the early flame growth speed, initiating the combustion process in a wide region, as opposed to the local ignition generated by traditional sparks. To explore the corona ignition behavior, experimental campaigns were carried out to investigate different operating conditions, in a constant volume calorimeter designed to measure the deposited thermal energy. The present work compares the combustion development generated by a traditional spark and the corona igniter through computational fluid dynamics simulations. First, simulations are carried out to reproduce the experimental results in the calorimeter, comparing the measured and predicted pressure traces in an inert environment. The validated approach is then applied in a second step to the engine simulations to predict the combustion behavior, using a RANS turbulence model. Computational results are able to reproduce the faster burn rate generated by the corona system in the initial stage of the combustion.