A New Design of a Pinwheel-Shaped High-G Combustor

Abstract

High-g combustor (HGC) is a significant branch of the ultracompact combustor, an innovative gas turbine combustor with the ability to shorten the combustor length and improve engine efficiency. To improve the feasibility of the HGC concept, a new HGC was designed to substitute the conventional combustor of a KJ66 small turbine engine. The KJ66 was modified to fit an instrumentation system and test bench to conduct relative experiments. Based on the experiment results, design iterations were conducted relying on simulation methods. The design iteration was comprised of six primary configurations, of which the first four configurations focused on establishing an appropriate high-centrifugal environment to accelerate primary combustion, while the last two modifications focused on improving overall combustion performance. In configuration 4, a pinwheel-shaped swirl inlet was designed to successfully create the high-g environment and balance the flow distribution while bringing insignificant total pressure loss. One modification of configuration 4 was a grid inlet design that divided the inlet channel into several subchannels to constrain the inlet flow and establish an ideal high-g environment. The other modification was a divergent mainstream channel to encourage the dilution process and improve the exit temperature profile. The final design could save at least 1/3 of combustor length while maintaining the same level of performance as the original combustor. Further, the engine was predicted to save at least 12% of the total engine weight and improve at least 14% of the engine thrust-to-weight ratio.

Gear-Shaped High-g Combustion Chamber for Micro Turbojet Engine Applications

“…After determining the computational region, an initial estimation of the mesh characteristics was performed according to the designed HGC scheme while the maximum laminar flame thickness was in the range 0.6–1.4 mm, which was derived from the following equation δ L = 2 false( λ / ρ C P S L false) false( T 2 / T 1 ) 0.7 where δ L is the estimated laminar flame thickness, λ is the thermal conductivity, C P is the specific heat capacity, and S L is the laminar flame speed, and T 1 , and T 2 are the temperatures of the unburned and post-burned mixtures, respectively.…”

“…After determining the computational region, an initial estimation of the mesh characteristics was performed according to the designed HGC scheme while the maximum laminar flame thickness was in the range 0.6–1.4 mm, which was derived from the following equation. 30 where δ L is the estimated laminar flame thickness, λ is the thermal conductivity, C P is the specific heat capacity, and S L is the laminar flame speed, and T 1 , and T 2 are the temperatures of the unburned and post-burned mixtures, respectively. Based on the estimation results, the initial wall mesh size and growth rate must be determined to ensure that the boundary layer mesh is created at the wall with sufficient mesh resolution; at least 10 layers of boundary mesh are required.…”

“…The remainder of the computational setup was based on previous works by Bohan, 28 Liu, 30 Cottle, 33 and others, who all performed experimental investigations for comparison with simulation results; these were used to validate the CFD computational setup for the turbulent combustion of the HGC. The realizable k –ε model was selected for the turbulence model.…”

“…After determining the computational region, an initial estimation of the mesh characteristics was performed according to the designed HGC scheme while the maximum laminar flame thickness was in the range 0.6−1.4 mm, which was derived from the following equation. 30…”

“…The combustion efficiency, dynamic pressure characteristics, and emissions were found to be affected by the inlet injection velocity, and the main combustion chamber volume and flame structure of the stabilizer had different degrees of influence on the combustion and stabilization characteristics. In addition, Bohan and Polanka and Liu et al − investigated methods for adapting the HGC to a micro turbojet engine and found that the new HGC design could reduce the axial length of the engine.…”