Experimental investigations of hydrogen pre-ignition phenomenon induced by two different lubricating oils in a rapid compression expansion machine

The growing interest in utilizing hydrogen (H₂) as a zero-carbon fuel has ignited extensive research on its potential application within internal combustion engines (ICEs). However, a major challenge regarding H₂ ICEs is the pre-ignition phenomenon. Various factors, including hot spots, oil droplets/deposits, and the ignition system, contribute to pre-ignition. This study focuses on pre-ignition caused by engine lubricating oil droplets/deposits. A Rapid Compression Expansion Machine (RCEM), equipped with optical access is employed to conduct a comparative analysis of the pre-ignition characteristics of two distinct engine lubricating oils called oil A and oil B. Oil A is an API (American Petroleum Institute) Group II lubricating oil with Ca (calcium) detergents, while oil B is of API Group V with a combination of Mg (magnesium) and Ca (calcium) components. The study identifies pre-ignition limits for both oils across various air-to-fuel ratios (λ = 2, 2.5, 3) and compression ratios (ɛ = 11-14.5). Comparative assessments are also performed through a chemical analysis (homogenous constant volume ignition delay time (IDT) simulations) as well as investigating the cylinder pressure and heat release rate (HRR) curves for the tested lubricating oils. This study represents the first exploration of the H₂ pre-ignition phenomenon in response to different engine lubricating oils within the context of an RCEM. The findings reveal that oil A is more susceptible to pre-ignition. In contrast, oil B exhibits pre-ignition at higher ɛ while maintaining constant λ. Simultaneously, oil B displays an accelerated flame propagation and more robust combustion due to the incidence of pre-ignition at higher ɛ. Hence, in the context of H₂ ICEs, the Group V oil sample (oil B) presents itself as a more advantageous choice compared to the Group II oil sample (oil A) for alleviating undesirable pre-ignition.