Investigation of electrode wear during spark discharges using planar laser-induced fluorescence

Abstract Reducing greenhouse gas emissions and achieving carbon neutrality require enhancing spark-ignition engine efficiency and compatibility with renewable fuels. However, electrode wear of spark plugs presents a significant challenge in hydrogen-fueled spark-ignition internal combustion engines. Such excessive wear increases the total cost of ownership and may delay the introduction of such low-emission transportation alternatives. Hence, understanding the interaction between spark discharges and the electrodes to reveal the mechanisms of such wear is crucial. Unlike conventional, ex-situ long-term tests, laser-induced fluorescence (LIF) can assess the wear process during the spark discharges by detecting the target species from the electrodes with high temporal resolution. In this work, spatiotemporal characteristics of gas phase nickel atoms originated from nickel-based alloy spark plug electrodes are performed with two-dimensional planar LIF in elevated pressures. A higher intensity and an earlier peak of laser-induced nickel fluorescence signal are observed under higher pressure. The spatial distribution of nickel atoms within the electrodes gap is observed to be different at varied pressures. Lengthening the dwell time, i.e. charging of the coil between DC spark discharges, and thus increasing the energy of sparks can significantly increase the loss of material. Similarly, increasing the peak current of AC sparks results in a higher power of spark discharges and thus increasing the removal of material. Moreover, the low signal intensity in pure nitrogen indicates that the existence of oxygen enhances the evaporation process and accelerates the erosion of the electrodes. The unique experimental data of electrode wear provides valuable insights not only into the development of next-generation ignition systems for renewable fuels, but also other aspects involving the interactions between the gas discharges and the electrodes, such as spark nanoparticle generation.