A Thermodynamic Analysis of the Pressure Gain of Continuously Rotating Detonation Combustor for Gas Turbine

Abstract

Considering the potential applications of continuously rotating detonation (CRD) combustors in gas turbines, this paper performed a numerical investigation into the pressure gain performance of CRD combustors, using methane-air as a reactive mixture and under the operating conditions of a micro gas turbine. To analyze the formation process of CRD waves, the variation characteristics of several typical thermodynamic parameters involving thermal efficiency, pressure ratio, and available energy loss were discussed in terms of time and space scales. Numerical results showed that the pressure gain characteristics of the CRD combustors was associated with the corresponding change in Gibbs free energy. Compared to approximate constant pressure-based combustors, usually used in the gas turbines studied, CRD combustors with lower Gibbs free energy loss could offer a significant advantage in terms of pressure ratio. It was found that detonation waves played an important role in increasing pressure ratios but that oblique shock waves caused the loss of extra Gibbs free energy. Due to the changing oblique shock wave height, the effects of CRD combustor axial length on pressure ratios and Gibbs free energy loss were more significant than the effects on detonation wave propagating characteristics and combustion thermal efficiency. When the axial length was changed from 200 mm to 100 mm, the pressure ratio increased by approximately 15.8%.

Effects of Diverging Nozzle Downstream on Flow Field Parameters of Rotating Detonation Combustor

“…2019, 9, In this study, considering the characteristics of detonation combustion and the waves, the model validation was conducted to compare the complex waves captured to the results of Innovative Scientific Solutions Inc. (ISSI), and then compare the propagation speed of detonation wave quantitatively to the CJ speed value of the NASA program. This kind of validation method has been used in many literatures [10,11,36,46]. Figure 3 compares the results of ISSI [47] with the results in this study.…”

“…Obviously, in the tail region of RDC, the detonation wave degenerates into the oblique shock wave after an unstable stage, thereby reducing the ability of pressure gain, which causes the total pressure to decrease. The detailed mechanism causing pressure loss can be found in our previous studies [10,11,36]. It can be seen from the curves that the total pressure of RDC with θ = 15 • , 30 • , 45 • is all lower than that of θ = 0 • from the initial stage, and their decline degree gradually increases with the axial distance and reaches the maximum at the outlet.…”

“…(1) Inlet of RDC: mass flow inlet boundary. According to the performance parameters of a micro gas turbine, the injection total pressure and total temperature are set at constant values of 1.209 MPa and 665 K. The mixture is injected by shrink nozzles and the mass flow is determined by a user defined function (UDF) [10,11,36] of FLUENT. Considering the relationship of injection pressure between the inlet pressure and critical pressure, the specific settings are: (a) In the case of p w ≥ p in , g = 0; p cr is the injection critical pressure determined by the equation:…”

“…Here we simplify the intake nozzles along the inlet of the RDC to the inlet surface [10,11] (as is shown in Figure 1). According to our previous analysis on a micro gas turbine with an RDC [36], the inner diameter, outer diameter, and axial length of the RDC were 234.8 mm, 274.8 mm, and 200 mm, respectively. In order to investigate the effects of diverging nozzle on wave formation and RDC performance, the outer wall expanded outwards with an angle of θ(0 • , 15 • , 30 • , 45 • ).…”

Numerical Assessment of the Convective Heat Transfer in Rotating Detonation Combustors Using a Reduced-Order Model

“…The thermal optimization of these combustors is constrained by the availability of precise and time-effective thermal solvers that can evaluate the thermal performance in a timely manner. Currently, RDCs are numerically examined with computationally-expensive Euler [8,9] or unsteady Reynolds-averaged Navier-Stokes solvers [10], where the injection process is either modeled as premixed mixture or as non-premixed flow. The detonation process can be modeled in several ways: using one-step reaction kinetics [11] with a limited number of species; or with two-step chemical reaction models [12]; or with an induction parameter which allows for larger grid size and time steps [13][14][15][16]; or with detailed reaction kinetics [17] which lead to expensive computations.…”