Turbine Durability Impacts of High Fuel-Air Ratio Combustors: Part 1 — Potential for Intra-Turbine Oxidation of Partially Reacted Fuel

Demand for greater engine efficiency and thrust-to-weight ratio has driven the production of aircraft engines with higher core temperatures and pressures. Such engines operate at higher fuel–air ratios, resulting in the potential for significant heat release through the turbine if energetic species emitted from the combustor are further oxidized. This paper outlines the magnitude and potential for turbine heat release for current and future engines. The analysis indicates that in the future, high fuel-air ratio designs may have to consider changes to cooling strategies to accommodate turbine heat release. A characteristic time methodology is developed to evaluate the chemical and fluid mechanical conditions that lead to combustion within the turbine. The local concentration of energetic emissions partly determines the potential for energy release. An energy release parameter, here defined as a maximum increase in total temperature (ΔT_t), is used to specify an upper limit on the magnitude of impact. The likelihood of such impacts relies on the convective, mixing, and chemical processes that determine the fate and transport of energetic species through the turbine. Appropriately defined Damko¨hler numbers (Da)—the comparative ratio of a characteristic flow time (τ_flow) to a characteristic chemical time (τ_chem)—are employed to capture the macroscopic physical features controlling the flow-chemistry interactions that lead to heat release in the turbine.