Quantitatively Accurate Methods of Estimating Combustion Efficiency in Rotating Detonation Engines

Combustion efficiency has a significant impact on the overall performance of rotating detonation engines (RDEs). In this work, candidate methods for estimating combustion efficiency are proposed and evaluated using a numerical model that generates compositions representing potential RDE exhaust gases. Across a range of conditions, accuracy is evaluated against a formal combustion efficiency definition from thermodynamic cycle analysis based on the ideal heat release rate within the engine. Focusing on hydrocarbon–air mixtures, the current work features the SAE International Aerospace Recommended Practice 1533 (SAE ARP1533) as a benchmark and ethylene as the example fuel. SAE ARP1533 captures all trends, but errors for near-stoichiometric and rich conditions reach nearly 10 and 15 percentage points (pp), respectively. Modifications to this approach are developed and assessed, and multiple measurement options are considered. Options based on measurements of only two product-species mole fractions (e.g., [Formula: see text] and [Formula: see text]) perform similarly to the SAE approach, and adding a third product-species mole fraction (e.g., [Formula: see text]) measurement yields maximum errors of less than 5 pp. Exhibiting the generality of the approach, an extension to [Formula: see text]–air combustion yields a single-measurement (i.e., [Formula: see text]) method producing a maximum error of approximately 5 pp.