A Conjugate Heat Transfer Numerical Framework Applied to Energy-Assisted Ignition of Jet Fuel in a Rapid Compression Machine

Airborne compression ignition engines operating with aviation fuels are a promising option for reducing fuel consumption and increasing the range of hybrid-electric aircraft. However, the consistent ignition of Jet fuels at high-altitude conditions can be challenging. A potential solution to this problem is to ignite the fuel sprays by means of a glow-plug-based ignition assistant (IA) device. The interaction between the IA and the spray, and the subsequent combustion event result in thermal cycles that can significantly affect the IA’s durability. Therefore, designing an efficient and durable IA requires detailed understanding of the influence that the IA temperature and insertion depth have on the complex physics of fuel-air mixture ignition and flame propagation. The objective of this study is to design a conjugate heat transfer (CHT) modeling framework that can numerically replicate F-24 Jet fuel spray ignition using a glow-plug-based IA device in a rapid compression machine (RCM). A new phenomenological energy source model has been introduced to simulate the heat generation inside the heating element of the IA. The thermodynamic state prior to the spray injection is accurately modeled by simulating the RCM compression process. The ignition and combustion events were simulated using two different approaches, i.e., via a multi-component surrogate fuel and single-species surrogate fuel reaction mechanisms. Comparisons against experimental data of time evolution of the IA’s temperature showed that the CHT framework accurately predicts the IA’s transient heating process prior to spray injection. This approach avoids the need for ad-hoc, case-by-case calibration of the IA preheating duration in numerical simulations. Also, comparisons against available experimental data for reacting sprays showed that the multi-component surrogate fuel approach not only correctly predicts the volumetric and spray ignition modes but also captures the IA temperature for which the transition between the two combustion modes occurs.