Experimental study of entrainment phenomenon in a trapped vortex combustor

Trapped vortex combustor （TVC） is an advanced low-pollution gas turbine combustor, with the adoption of staged combustion technique. To achieve low-pollutant emission and better combustion performance, the proportion of the air flow in each combustion zone should be precisely determined in the design of the combustor. Due to the presence of entrainment phenomenon, the total air flow in the cavity zone is difficult to estimate. To overcome the measurement difficulty, this study adopts the indirect measurement approach in the experimental research of entrainment phenomenon in the cavity. In accordance with the measurement principle, a TVC model fueled by methane is designed. Under two experimental conditions, i.e. with and without direct air intake in the cavity, the influence of the mainstream air flow velocity, the air intake velocity in the cavity, the height of inlet channel, the structure of holder and the structural proportion of the cavity on entrainment in the cavity is studied, respectively, through experiment at atmospheric temperature and pressure. The results suggest that the air flow velocity of mainstream, the air intake velocity of the cavity and the structure of the holder exert significant influence on the air entrainment, while the influence of structural proportion of the cavity is comparatively insignificant. The square root of momentum ratio of cavity air to mainstream air could be used to analyze the correlation of the entrainment data.

Flow Field Measurements in the Cavity of a Trapped Vortex Combustor Using PIV

The experimental research on cavity flow field plays an important part in the structural design and optimization study of trapped vortex combustor (TVC). Many of the previous flow field experiments were conducted in the cold condition instead of during combustion. This paper adopting PIV system and Lambda-2 vortex criterion in-vestigates the influence of various factors, such as equivalent ratio in the cavity, air intake parameter in the cavity, mainstream air intake parameter and mainstream holder structure, on cavity flow field for a TVC using methane as the fuel. The experimental research showed that cold-condition flow field differed from the combustion flow field, in terms of either vortex core position or vortex structure. Mainstream air intake velocity and cavity air intake velocity affected the flow field structure. U-type and V-type mainstream holders had significant influence on cavity flow field.

Design and Performance of an Improved Trapped Vortex Combustor

A trapped vortex combustor （TVC） has been a very promising novel concept for it offers improvements in lean blow out, altitude relight, operating range, as well as a potential to decrease NOx emissions compared to conventional combustors. The present paper discusses the improved designs of the new combustor over the prior ones of our research group, including that：a） the over-all dimensions, both axial and radial, are reduced to those of an actual aero-engine combustor; b） the air flow distribution is optimized, and especially 15% of the air is fed into the liner as cooling air; c） a straight-wall diffuser with divergence angle 9°is added. A series of experiments （cavity-fueled only, under atmospheric pressure） has been conducted to investigate the performance of the improved TVC. Experimental results show that at the inlet temperature of 523 K, the inlet pressure of 0.1 MPa, stable operation of the TVC test rig is observed for the Mach number 0.15-0.34, indicating good flame stability; the combustion efficiency obtained in this paper falls into the range of 60%-96%; as the total excess air ratio increases, the combustion efficiency decreases, while the increase of the inlet temperature is beneficial to high combustion efficiency; besides, the optimal Mach numbers for high combustion efficiency under different inlet conditions are confirmed. The outlet temperature profiles feature a bottom in the midheight of the exit. This paper demonstrates the feasibility for the TVC to be applied to a realistic aero-engine preliminarily and provides reference for TVC design.

Effect of structure parameters of the flow guide vane on cold flow characteristics in trapped vortex combustor

The cold flow characteristics are investigated to show the effect of the structural parameters of the flow guide vane on the trapped vortex combustor（TVC）. The results show that the structural parameters have significant effects on the TVC. As a/ H increases, the total pressure loss, the wall shear stress at the bottom of the cavity and the turbulent intensity in the main combustion zone increase. b/ B does not have a significant effect on the cavity flow structure and the total pressure loss, and the wall shear stress at the bottom of the cavity increases as b/ B increases. There is no significant increase of the turbulent intensity with the increase of b/ B. The increase of c/ L has little effect on the total pressure loss, and it is not conducive to a stable combustion. As c/ L increases, the wall shear stress at the bottom of the cavity decreases. When a/ H= 0.4, b/ B= 0.4, c/ L= 0.1, a desirable dual-vortex structure is formed with an acceptable pressure loss to achieve a stable combustion. Moreover, to ascertain that the flame is stable for different values of Vm a with the optimal structural parameters, the effect of Vm a on the flow field is discussed. Results suggest that the dual-vortex structure has no relationship with the increase of Vm a. Furthermore, an unsteady simulation is conducted to show the generation and the development of the dual-vortex.

Combustion of Hydrogen in an Experimental Trapped Vortex Combustor

Combustion performances of pure hydrogen in an experimental trapped vortex combustor have been tested underdifferent operating conditions. Pressure fluctuations, NOx emissions, OH distributions, and LBO (Lean Blow Out)were measured in the tests. Results indicate that the TVC test rig has successfully realized a double vortex constructionin the cavity zone in a wide range of flow conditions. Hydrogen combustion in the test rig has achievedan excellent LBO performance and relatively low NOx emissions. Through comparison of dynamic pressure data,OH fluctuation images, and NOx emissions, the optimal operating condition has been found out to be Φp=0.4,fuel split=0.4, and primary air/fuel premixed.

Investigations on Emission Characteristics of a Liquid-Fueled Trapped Vortex Combustor

The combustion and emission formation process of liquid fuel in the trapped vortex combustor(TVC)are very complicated.A trapped vortex combustor with replaceable bluff-bodies was designed to investigate these processes.The bluff-body widths varied from 0.021 m to 0.036 m.Experimental tests were carried out.Liquid RP-3 aviation kerosene was used in the tests.Emissions were measured under atmospheric pressure.The combustion process was analyzed theoretically in the viewpoints of relative evaporation time,mixing time and reaction time.Numerical simulations were also conducted to help analyze the formation and depletion processes of pollutants in TVC.The results reveal that atomization was a critical factor for formation and depletion processes of pollutants.By controlling mixing speed of burned and unburned gases and thus fuel-air uniformity,turbulence intensity could also affect emission levels.In addition,residence time also affected the emissions by affecting combustion completeness and the time for NOx formation.All these factors were combined in a complicated way to affect combustion process and pollutant emissions.

Syngas Fuel Combustion in Re-circulating Vortex Combustor

This paper presents results on the combustion of syngas fuel in re-circulating vortex combustor. The combustion stability is achieved through the use of cavities in which recirculation zones of hot products generated by the direct injection of fuel and air are created and acting as a continuous source of ignition for the incoming main fuel-air stream. CFD （computational fluid dynamics） analysis was performed in this study to test the combustion performance and emissions from the vortex trapped combustor using synthetic gas or syngas fuel produced from the gasification process. The flame temperature, the flow field and species concentrations inside the vortex trapped combustor were obtained. Several syngas fuels with different fuel compositions （H2, CO, CH4, CO2, N2 and H20） and lower heating values were tested in this study. The changes on the flame temperature and species concentrations inside the combustor, the emissions of NOx, CO, CO2 at the exit of the combustor, the combustor efficiency and the total pressure drop for syngas fuels are presented in this paper. The effect of H2/CO ratio and the mass fraction of each constituent of syngas fuels and hydrogen-methane fuel mixtures on the combustion and emissions performances were investigated.

Experimental Study on Emission Performance of an LPP/TVC

A key issue in the commercial aircraft engine design is environmental acceptability, and designers are continually challenged to reduce emissions. In this paper, an experimental investigation is performed to evaluate the emission performance of a liquid-fueled trapped vortex combustor （TVC） under lean premixed prevaporized （LPP） mode. When operating as an LPP system, a TVC is fueled both in the cavities and in the main stream. The correlations between the emission performance and the total ex- cess air ratio, the positions （4 positions） of the fuel injectors in the main stream, and the inlet temperature are obtained. Experimental results show that both the volume concentrations of unburnt hydrocarbon （UHC） and NOv （NO, NOxusually grouped together as NOx） increase with the increase of total excess air ratio from 1.5 to 3.0; the emission performance relies heavily on the position of the main stream injector, and the best perfomlance is achieved at Position 4 in the experiments, the increase of the inlet temperature impacts on the emission performance positively： the smallest volume concentrations of UHC and NO,. obtained in the experiment are 94×10^-6 and 2.3× 10 ^-6 respectively. This paper validates the feasibility of low emissions for an LPP/TVC and provides a reference for further optimization of TVCs.