Loss Quantification and Reduced Order Modeling of Rotating Detonation Combustor Performance

Abstract

Detonation combustion is a highly energy-dense mechanism by which chemical energy is converted into usable work. Numerous attempts have been made to utilize detonation combustion, yet the proposed higher performance has yet to be realized. This research focuses explicitly on the Rotating Detonation Combustors (RDC) application, which allows for a continuously propagating detonation wave, potentially producing a device-level pressure gain. Like many other applications, these devices incur different losses, which are not fully captured by an idealized analysis. Therefore, one goal of this research is to capture and quantify the loss mechanisms that affect the performance of detonation waves and RDC devices. Care must be taken not to assume that decreases in the performance of one is indicative of a loss in the other, though they are often influenced by one another.

This research characterized the loss mechanisms inherent to detonation combustion using reduced order models of different processes within the detonation wave. Showing that detonation performance is particularly susceptible to parasitic pre-detonation deflagrative burning. Across many detonation performance metrics, parasitic combustion accounts for 40-80% of the total losses, where the highest impact of parasitic combustion is seen in the pressure ratio across the detonation wave.

The same methodology was used to study loss mechanisms specific to the RDC. These results showed how the performance of the RDC is directly impacted by the losses incurred through the RDC inlet; however, the inlet performance is also influenced by the detonation, where one must make an appropriate trade-off between detonation and device performance. Through a state-based RDC cycle model, the combination of parasitic combustion and inlet pressure loss can significantly reduce RDC performance. Without losses, the specific impulse gained by the RDC device over a constant pressure analog was between 0% to +58%; however, including moderate inlet pressure losses, this dropped to -13% to +50%, showing a specific impulse degradation versus an ideal deflagrative device.

Using the lessons learned, a non-ideal reduced order cycle model was developed to integrate the different losses across detonations and RDC devices. This model was also developed to improve evaluation times for future use cases. Across a wide range of test conditions and parametric model evaluation, the new cycle model provided an accurate prediction of the operation of the RDC device using performance metrics such as thrust and inlet blockage. However, the model requires some improvements to better capture conditions of low inlet mass flux, where the predicted performance and operating conditions differ from the experimental measurements by up to 200%. For moderate mass flow rates around 300 g/s, the model offers 2-6x improvements in predictive capability relative to current state-of-the-art models while also providing a 10-10000x improvement in model evaluation time.

Finally, this research provided a broader discussion on the performance of RDCs, specifically the pressure gain, and whether this metric is achievable within RDCs. The cycle model results did not predict any pressure gain and did not show a correlation between the detonation performance and the pressure gain metric; therefore, the author offered other metrics, such as thrust gain, or applications, such as rocket-style RDC motors, in which RDCs may show improvements.