Lifting a flame from the flow generating nozzle to some distance apart has a wide variety of effects on the properties of the resulting combustion phenomenon. The reason of this influence is the generation of a non-reacting flow domain where mixing takes place prior to the combustion reaction. It is obvious that the quality of premixing that can be achieved strongly depends on the time that is given to flow and the intensity of the turbulence that is mixing fuel and air. The most important parameter that is characterizing this time is the size of the premixing zone quantified by the so called lift-off height (LOH). Additionally, when employing liquid fuel the lift-off of a flame provides time to achieve better pre-evaporation of the fuel. As a consequence, better mixing of fuel and air helps to avoid high temperature regions that may be a result from an inhomogeneous equivalence ratio distribution. From safety considerations a major advantage of this method compared to the application of a premixing duct is that the risk of hardware destruction by flame flash back can be eliminated. The current work extents the knowledge on lifted flames by the investigation of flames that are generated with an airblast atomizing nozzle that was designed to resemble systems close to application. Lifting of the flame is achieved applying a combination of swirling and non-swirling inflow ducts. A wide range of operating conditions as well as gaseous and liquid fuels are used to investigate their influence on the lift-off height. The lift-off height and location of the reaction zone was determined by means of chemiluminescence of OH* and it is shown, that the impact of pressure drop and preheating temperature on the LOH is different for gaseous and liquid fuels.
Lifted flames have been investigated in the past years for their benefits in terms of NOx emissions reduction for gas turbine applications. In a lifted flame, the flame front stabilized on a position that is significantly detached from the nozzle exit, improving the premixing process before the reaction zone. The distance between the flame front and the nozzle exit is called liftoff height and it represents the main parameter that characterize this type of flame. In the present work, a partially premixed lifted flame employing air-methane mixture is investigated through numerical simulation. Indeed, even if lifted jet flames have been widely studied in the literature, there are only a few examples of lifted partially premixed flames. Nevertheless, this kind of flames assumes an important role considering the current gas turbine applications, since their benefits in terms of stability and low pollutant emissions. This study has been performed with LES calculations using a commercial software suite and the numerical results are compared with experimental data coming from a dedicated campaign held at Karlsruher Institute für Technologie (KIT) on a novel low-swirl injector nozzle. Quenching effects due
The configuration of a jet in crossflow appears in many practical applications such as combustion and mixing processes in the chemical industry. This kind of flow is particularly complex due to the presence of various interacting vortex systems and it is widely studied in literature both experimentally and numerically. In addition to the physical interest, this flow configuration serves as a benchmark for numerical methods such as Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) because of its prototypic nature. The present work aims at generating benchmark data for a jet in crossflow configuration under highly turbulent conditions. In this context, the investigated operating conditions were chosen carefully to match the conditions existing in gas turbines and hence the experiments were carried out for two different Reynolds-numbers of the crossflow, Re∞ = 60000 and 40000. Keeping the flow rate of the jet flow constant, two different velocity ratios between jet and crossflow of r = 4.15 and 6.25 result. The measurements were performed in an appropriate air channel, which was built with the objective to obtain accurately controlled flow conditions at the measurement section. Two-dimensional laser induced fluorescence (2d-LIF) combined with particle imaging velocimetry (PIV) was used for the measurements of simultaneous scalar concentration and velocity fields and the experimental acquisition of Reynolds-fluxes and -stresses. The knowledge of Reynolds-fluxes and -stresses is of fundamental concern not only for the understanding of the mechanisms which are responsible for the formation of the vortex-structures in a jet in crossflow, but also for the development and validation of turbulence- and mixing-models.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.