Experiment Study of Ignition Characteristics in An Axial-flow-injector Burner for Stirling Engine

To investigate the ignition characteristics of an axial-flow injection burner for a Stirling engine, a combustion chamber was designed. Diesel was used as fuel and oxygen as oxidant. The experiments of ignition characteristics were carried out with an electric plug igniter. The ignition characteristics under different combustion chamber pressure, pre-oxygen supply time, oxygen supply flow and ignition position were studied. The experimental results show that, with the increase of the pressure, the ignition time of the burner increases gradually, and the ignition success rate decreases gradually. The oxygen flow rate is related to ignition time in a certain range, while the pre-oxygen supply time has little effect. With the ignition position moving downward, the ignition time decreases gradually.

SIMULATION OF BIOGAS COMBUSTION IN INJECTION BURNER WITH HEAT DIVIDER

The purpose of this work is to develop a design of a biogas combustion equipped with a thermal divider and study the process of burning biogas of different composition. To study the biogas combustion process in the burner of the developed design, the Ansys Fluent modeling software package is used. An injection burner for biogas combustion with a cone-shaped thermal divider and primary air regulator has been developed. Studies of the process of burning biogas of different composition in burners of 5 designs were carried out: without a divider, with a divider with a length of L = 6 mm, with a divider L = 12 mm, with a divider L = 18 mm and a divider L = 24 mm. As a result of modeling, it is found that the placement of a divider with a length of 6 mm and 12 mm does not affect the temperature of the gas-air mixture in the burner body. Increasing the length of the divider to 18 mm allows to increase the temperature of the flow of the gas-air mixture passing along the divider. A further increase in the length of the divider to 24 mm leads to a slight increase in the temperature of the gas-air mixture. The dependences of the flame temperature on the length of the divider during the combustion of biogas with a methane content of 60% and 70% are obtained. When a divider with a length of 6 mm and 12 mm is placed in the burner body, the flame temperature decreases, with an increase in the length of the divider to 18 mm, the flame temperature increases, and with an increase in the length of the divider to 24 mm, the flame temperature remains practically unchanged. Consequently, the placement of a divider with a length of 18 ... 24 mm in the burner body ensures preliminary heating of the gas-air mixture and allows increasing the efficiency of the biogas combustion process.

RESEARCH OF THE DISTRIBUTION OF A GAS-AIR MIXTURE IN THE BODY OF INJECTION BURNER WITH THERMAL DIVIDER

The article is devoted to the development of the design of a low-pressure injection burner equipped with a thermal divider and the study of the process of distribution of methane concentration and velocity of gas-air mixture velocity in the burner body. The Solid Works Flow Simulation software complex is used to study the process of formation of the gas-air medium in the burner body. The design of a low pressure injection burner with a conical-shaped heat spreader has been developed. Placing the divider in the burner body provides preheating of the gas-air mixture and allows to increase the speed of flame propagation. Computer simulation of the process of gas-air mixture formation in the burner body for 3 burner constructions is performed: without a divider, with a divider length of 11 mm and a divider length of 25,5 mm. As a result of modeling, it is found that the placement of the divider with a length of L = 11 mm does not affect the distribution of methane and the velocity of the gas-air mixture in the burner body and at the exit of the firing holes. Increasing the length of the divider to 25,5 mm leads to an increase in the speed of the gas-air mixture and an increase in the concentration of methane in the firing holes. Therefore, the placement of the burner housing to the heat spreader with a length of 11 mm is the best solution to improve the efficiency and stability of the combustion process.

Numerical Study of Flame Shapes and Structures in a Two-Stage Two-Injection Aeronautical Burner With Variable Fuel Staging Using Eulerian Large Eddy Simulations

The aim of the present work is to evaluate the ability of large eddy simulation (LES) to predict flame shape and structures in a two-stage two-injection burner representative of new generation staged aeronautical engine: the Banc à Injection Multiple pour les Écoulements Réactifs (BIMER) burner. This combustor is a unique design because of an additional parameter, the staging factor, which controls the fuel mass flow rate splitting between the two swirl stages. Experiments conducted on the BIMER combustor at atmospheric pressure and for a constant power output have revealed that the shape of the flame changes with the staging factor; this shape also depends on the staging factor evolution history (SFEH). Targeting a single operating point and three staging situations, the objectives are to prove the ability of our simulation strategy to predict the proper shapes by reproducing these stabilization processes and to participate in their explanation, using numerical post-treatments. After validation through comparisons with experiments, our study focuses on these three configurations, two of them only differing by their SFEH. Remarkably, correct flame shapes are obtained numerically for the same operating point, fuel staging factors and SFEH. Qualitative and quantitative comparisons show very satisfactory agreement. In a second step, the three flame shapes are analyzed in depth. The key role played by the central and corner recirculation zones in the flames' existence and stabilization processes is emphasized. An original composition space analysis highlights the combustion regimes observed in these three cases, confirming the distinct stabilization scenarios proposed here for the three operating points.

Multi-Swirl Lean Direct Injection Burner for Enhanced Combustion Stability and Low Pollutant Emissions

Control of emissions is a big challenge plaguing the gas turbine industry for years. This necessitates new combustor designs addressing the problem. This paper discusses the characterization of a novel burner* employing Lean Direct Injection (LDI) technology for reduced pollutant emissions and improved combustion. The burner is an array of multiple swirlers arranged closely, facilitating distributed mixing of fuel and air at each swirler throughout the length of the burner. This results in a uniform and rapid mixing, thus eliminating hot spots and enabling efficient combustion. The burner thus developed is capable of operating at very lean conditions of fuel, leading to overall temperatures being low. The burner is characterized in terms of lean blow out equivalence ratio, pressure drop, average exit temperature of the burnt mixture, pattern factor and emissions — CO, CO2, unburned hydrocarbon (UHC), NOx and soot. Results show very low NOx emissions. Enhanced combustion also results in reduction in overall emissions. It overcomes the drawback of flame flashback encountered in lean premixed pre-vaporized concept. LDI is also less susceptible to combustion instability. Pressure drop across the burner is observed to be very less compared to the conventional gas turbine combustors. Thus, this concept of multi-swirl LDI burner can be a potential contender to be employed in the combustors of gas turbine engines.

Large Eddy Simulation of a Multiple-Injection Dry Low NOx Combustor for Hydrogen-Rich Syngas Fuel at High Pressure

The successful development of coal-based integrated gasification combined cycle (IGCC) technology requires gas turbines capable of achieving the dry low-nitrogen oxides (NOx) combustion of hydrogen-rich syngas for low emissions and high plant efficiency. Therefore we have been developing a multiple-injection burner for hydrogen-rich syngas fuel in order to achieve high efficiency and low environmental load. This burner consists of a perforated plate with multiple air holes and fuel nozzles. The multiple air holes and the fuel nozzles are arranged coaxially. The burner is based on the concept of premixed combustion configured by mixing fuel and air in the each air hole rapidly and dispersing fuel with multiple fuel-air jet. This rapid mixing can reduce NOx emissions by getting homogeneous lean premixed combustion, and preventing flashback despite the high flame speed for hydrogen-rich syngas fuels. The unsteady phenomena that occur in the combustion field should be understood in detail in order to confirm this burner concept. However, their measurement under high pressure is difficult. Meanwhile computational fluid dynamics (CFD) is able to investigate the detailed distributions of various emissions and temperature even though under combustion fields of high pressure and high temperature. The purpose of this paper is to validate this concept of the multiple-injection burner by using CFD. The burner can change the combustion form between premixed and non-premixed combustion by controlling the mixing, so the combustion field coexisting with premixed combustion and non-premixed combustion is complicated. Therefore, we have developed a hybrid turbulent combustion (HTC) model applicable to both non-premixed and premixed flames. The HTC model is hybridized with the flamelet progress variable (FPV) model and a flame propagation model. The FPV model is based on the laminar flamelet concept. The flame propagation model considers the flame stretch effect, diffusion enhancement effect, and increasing rate of flame surface area. The turbulent flow model adopts large eddy simulation (LES) with a dynamic sub-grid scale (SGS) based on the local inter-scale equilibrium assumption (LISEA4). Both the turbulent combustion model and turbulent flow model were programmed into a simulation tool based on the OpenFOAM library. We validated the concept of this burner for hydrogen-rich syngas fuel by using the simulation tool. The simulation results showed the rapid mixing of fuel and air in the air holes, and by using HTC model we confirmed that premixed combustion is the combustion configuration of this multiple-injection burner. In addition, the multiple-injection burner has high flame stability. There is no zone of high temperature in the air hole and high temperature is maintained near the burner. The multiple-injection burner can thus maintain flame stability without any flashback.