Numerical simulations of aeronautical engine ignitions under realistic high altitude conditions

Overview & Synopsis

The relight capability is a critical aspect of the aeronautical engine design and safety standards require the ignition of the engine under high altitude conditions (low pressure: P = 0.3 bar and low temperature: T = 233 K). Therefore the influence of low pressure and low temperature conditions on the ignition processes must be better understood. For this purpose, the effect of these conditions on the chemical phenomena has been first evaluated with purely gaseous configurations. The results have shown the detrimental effect of sub-atmospheric conditions via a slowing down of the chemical reactivity and thus a reduction of the power released. In addition, direct numerical simulations performed using a multi-component ARC chemistry enable to compare the kernel developments depending on the pressure and temperature conditions and indicate that low pressure kernels are less robust to extinction phenomena. On the other hand, the influences of high altitude conditions on the two-phase flow have also been evaluated. Firstly, at the fuel injection, the available experimental measurements have shown that low pressure reduces the atomization phenomenon resulting in a spray with larger and fewer droplets. Two-phase ignition simulations have thus been performed taking into account the different droplet distribution due to the high altitude conditions. A complete modification of the combustion regime has then been observed compared to the gaseous case. Finally, this work enables to develop new numerical methods which have been used to simulate the ignition under realistic high altitude conditions in the MERCATO configuration. This computation highlighted the critical role of the two-phase phenomena in the formation and development of the kernel. Furthermore, the detrimental effect of low pressure and low temperature on the ignition has been recovered once again.