Effects of passive slot and rib configurations on the flow and combustion characteristics of an advanced vortex combustor for a gas turbine

Passive Suppression of the Gradual Opening Effect in a Wave Rotor Combustor via Flow-Field Reconstruction Induced by an Unpartitioned Inlet Duct

The wave rotor combustor (WRC) represents a promising technology for pressure-gain combustion. However, its combustion stability remains constrained by inadequate fuel–air mixing, resulting from interface distortion and vortex formation induced by the gradual opening of the channels. This study numerically investigates the flow-field characteristics in inlet ducts with three different lengths (25, 50, and 75 mm), comparing partitioned and unpartitioned designs. Results demonstrated that the unpartitioned design significantly improves mixture distribution, reducing the axial length of the fuel distribution by 24.5%–38.2% and enhancing mixture uniformity by 28.5%–40.4%, while concurrently reducing the overall system pressure loss. These advantages are most pronounced at inlet duct lengths of 50 and 75 mm. Notably, within the unpartitioned inlet duct, the Euler number decreases dramatically from 11.71 to 0.06 as the inlet duct length increases from 25 to 75 mm, signaling a fundamental transition from pressure gradient–dominated to inertia-dominated flow. This flow shift effectively suppresses the interface distortion caused by gradual opening, promoting a more uniform mixture and shortening the flame propagation path. Consequently, our findings propose a passive, geometry-only strategy to enhance WRC performance and extend its operational envelope without requiring additional actuators or control hardware. This work provides a valuable foundation for advancing the engineering application of WRCs.

Investigation of the effects of swirler blade angle and micro-mixing hole diameter on performance and NOx emissions in hydrogen-fueled recirculation combustor

Abstract This study presents a three-dimensional numerical simulation investigation into two distinct swirl configurations (axial and radial) of hydrogen fuel recirculation combustor under a lean equivalence ratio of 0.3, focusing on the effects of swirler blade angle and micro-mixing hole diameter on combustion performance and pollutant emissions. The results demonstrate that: swirler blade angle significantly influences combustion efficiency, total pressure recovery coefficient, and NOx formation. For axial swirlers, the combustion efficiency peaks at 99.92 % when the blade angle is 30°, while the total pressure recovery coefficient decreases from 98.61 % to 97.26 %. The Emission Index (EI) exhibits an approximately linear increase with increasing blade angles. For radial swirlers, combustion efficiency rises from 99.56 % to 99.90 % as the blade angle increases from 30° to 60°, while the total pressure recovery coefficient drops from 98.68 % to 97.55 %. Temperature distribution factors (OTDF/RTDF) decrease continuously, and EI shows nonlinear growth. Micro-mixing hole diameter has a minimal impact on the total pressure recovery coefficient and temperature distribution metrics but significantly affects combustion efficiency. For axial swirlers, combustion efficiency reaches its maximum at 0.8 mm hole diameter, with negligible changes in total pressure recovery (<1 %) and temperature distribution coefficients. The EI index exhibits nonlinear growth. For radial swirlers, combustion efficiency peaks at 99.90 % when the micro-mixing hole diameter is 0.8 mm, with near-constant total pressure recovery and insignificant variations in OTDF/RTDF. The EI index shows nearly linear growth under these conditions.

A Numerical Investigation of the Effects of Piston Bowl Geometry and Spray Angle on Combustion, Performance and Emission of a Diesel Engine

A piston bowl's design and spray angle improve air–fuel mixing, resulting in more complete combustion and higher efficiency. Ansys Forte 2023 R1 a CFD software was used to analyze the effects of five combustion chamber geometries of cylinder, modified re‐entrant, re‐entrant, double‐stepped, and stepped on engine performance, combustion, and emission characteristics at spray angles of 1000°, 1050°, 1100°, 1150°, and 1200°, respectively. This study looks into the effects of piston bowl shape and spray angle on engine performance and emission characteristics. The numerical investigation is carried out with a load of 0.44 MPa and a start of injection at 7° bTDC. The double stepped piston bowl with spray angles of 110°–115° has the maximum thermal efficiency and the lowest ISFC, while reducing VOC, UHC, soot, and CO emissions. The combustion and performance parameters for piston bowl geometries are optimized at spray angles of 110° and 115°. At these spray angles, improved fuel–air interaction leads to higher peak cylinder pressure, peak cylinder temperature, thermal efficiency, and ISFC consumption while producing reduced emissions. The results show that spray angle optimization is crucial, with 110°–115° emerging as the optimal spray angle range for piston bowl selection and combustion optimization. Among the bowl geometries, the double stepped demonstrate the most balanced performance‐emission trade‐off at spray angles of 110° and 115° compared to stepped, modified re‐entrant, re‐entrant, and cylindrical shapes.

A DIMENSIONLESS DESIGN FRAMEWORK AND MECHANISTIC STUDY OF A PERFORATED-WALL TRANSVERSE-JET MIXER FOR RAPID COOLING OF HIGH-TEMPERATURE GAS STREAMS

In conventional aero-engine testing, the combustor and afterburner are usually evaluated separately, which increases cost and energy consumption because two high-temperature sources are required. This study proposes a flange-type mixer for integrated testing, in which ambient air is transversely injected to cool the combustor exhaust through jet-induced mixing. RANS simulations were conducted for 16 flange configurations at a jet-to-mainstream temperature ratio of 0.14 and a mass flow ratio of 1.0, and the numerical approach was assessed against experimental measurements. The results show that mixing is strongly affected by the number of holes and the momentum ratio, and is further influenced by the inlet-pipe-to-hole feeding characteristics of the flange. Recirculation occurs only when the momentum ratio is 3009 and the number of holes is 36 or less, but it does not result in distinctly better mixing. Meanwhile, azimuthal asymmetry and hole-to-hole maldistribution may, in some cases, enhance downstream mixing by producing alternating strong and weak jets and locally increasing penetration. To unify jet-trajectory behavior across configurations, a nondimensional analysis was conducted, and a modified Holdeman-type trajectory correlation was developed for the present confined circumferential injection. In addition, a feeding-imbalance index was proposed. When combined with the penetration metric, it improved the correlation with mixing performance. These findings provide guidance for the design of compact mixers for high-enthalpy integrated test systems.

Flow and Combustion Characteristics of a Novel Triple-Swirler Combustor Under Multiple Operating Conditions

A Realizable k−ε turbulence model and a finite-rate/eddy-dissipation combustion model, together with experimental validation, were used to investigate the flow and combustion characteristics of a novel triple-swirler combustor under multiple operating conditions. The results show that, compared with the conventional baseline configuration, the ring-cooled radial structure induces a third-stage swirl through inclined cooling holes. This swirl regulates the recirculation structure formed by the first two axial swirlers, transforms the core reaction zone from a single large-scale recirculation vortex into multiple vortical structures, forms a low-temperature cooling coverage outside the main reaction zone, and weakens the near-wall entrainment and high-speed sweeping induced by the kidney-shaped vortex pair downstream of the primary holes. The peak temperature of the outer liner is reduced by 14.72%, and the wall-temperature uniformity is improved by 36.02%. The outlet temperature distribution factor (OTDF) decreases by 14.81% and 15.79% under high and medium operating conditions, respectively, indicating an improved outlet temperature field. This study provides engineering guidance for the design of high-performance combustors.

Impact of flow distribution on the combustion and emission performances in a high temperature rise combustor based on RQL