Numerical Investigations of Combustion Dynamics and Thermo-Mechanical Stress in the Ignition Assistance System for Small Aircraft Engines

The utilization of ignition assistance devices offers an effective solution to overcome the challenges associated with ignition control in the development of propulsion systems for unmanned aerial vehicles (UAVs) that rely on sustainable aviation fuels. These devices actively control the combustion process to ensure successful ignition at different altitudes. The objective is achieved by introducing a controlled thermal energy deposit into the combustion chamber, mitigating potential ignition failures. This research presents a comprehensive analysis of the ignition characteristics and subsequent flame structure based on varying electric-circuit energy inputs, employing three-dimensional simulations. The ignition delay patterns are further examined from a fuel chemistry perspective, specifically focusing on the negative temperature coefficient (NTC). Additionally, this study introduces a strategic analysis of the thermo-mechanical stress experienced by the ignition assistance device when subjected to the impact of the spray-jet flame. To accomplish this, a coupled simulation approach combining computational fluid dynamics (CFD) and finite element analysis (FEA) is employed to analyze the transient wall stress. The parametric inputs obtained from the CFD simulations facilitate the FEA analysis, revealing critical mechanical-thermal stress accumulation on the heating element of the ignition assistance device.