Effect of Hydrogen Addition on Ignition Energy in an Ammonia–Air Mixture Fueled Spark-Ignition Engine

The study presents the results of an assessment of the effect of hydrogen enrichment of an ammonia–air mixture on the minimum ignition energy (MIE) in a spark-ignition (SI) engine. The hydrogen energetic fraction was 9%. Experiments were conducted using a research SI engine operating at a compression ratio of 10. The influence of MIE on the averaged pressure traces was analyzed, and combustion stability was evaluated. Optimization of the ignition energy enabled the determination of MIE under the given engine operating conditions. It was found that an MIE of approximately 13 mJ ensured a proper ignition process; at this ignition energy level, no significant further increases in the maximum pressure ( p max ) were observed, and the coefficient of variation of indicated mean effective pressure (IMEP) decreased to an acceptable value of 0.59%. The assessment of combustion stability confirmed a very significant effect of ignition energy on pressure dispersion, not only in terms of its maximum value but also the crank angle corresponding to p max . With increasing ignition energy, the number of misfire cycles decreased, and upon reaching the MIE, no misfire cycles were recorded within a set of 150 consecutive engine cycles. For the engine fueled solely with ammonia, the MIE was approximately 31 mJ; thus, a 9% hydrogen addition reduces the ignition energy requirement by about 100%.