Numerical Studies on Minimum Ignition Energies of Lean Primary Reference Fuels at Elevated Pressure

The minimum ignition energy (MIE) is a crucial parameter that signifies the minimum external energy required for a successful-induced ignition. Focusing on primary reference fuel (PRF), a popular gasoline surrogate, we employed numerical simulations to investigate the flame initiation and early flame propagation process at elevated pressures. This study aims to explore the flame initiation and evolution after external energy and the dependence of MIE on pressure and mixture composition. It uses numerical simulations involving detailed treatment of chemistry and molecular transport for the solution of the conservation equations during ignition and the early stages of flame propagation. Due to the low temperature chemistry (LTC) at elevated pressure, four distinct flame types can be observed after ignition energy deposition: ignition failure, cool flame ignition and extinction, two-stage ignition, and hot flame ignition. In contrast to 1 bar conditions, where the hot flame might quench due to curvature, the hot flame is always self-sustained at elevated pressure for the conditions investigated in this work. The MIE for a self-sustained flame, M⁢𝐼⁢𝐸𝑝𝑟𝑜𝑝 at low pressure increases with pressure, but experiences a sudden drop at some specific pressure, when the cool flame can evolve into a hot flame. The fact that the LTC of n-heptane is much more stronger than iso-octane affects the M⁢𝐼⁢𝐸𝑝𝑟𝑜𝑝 of PRF mixtures. Our results corporate the significance of LTC for induced ignition and early flame propagation processes of PRFs at elevated pressure, bearing implications in practical combustion engines and safety considerations.