Enhancing flame flashback resistance against Combustion Induced Vortex Breakdown and Boundary Layer Flashback in swirl burners

Abstract

Swirl combustors have proven to be effective flame stabilisers over a wide range of operation conditions thanks to the formation of well-known swirl coherent structures. However, their employment for lean premixed combustion modes while introducing alternative fuels such as high hydrogenated blends results in many combustion instabilities. Under these conditions, flame flashback is considered one of the major instability problems that have the potential of causing considerable damage to combustion systems hardware in addition to the significant increase in pollutant levels. Combustion Induced Vortex Breakdown is considered a very particular mode of flashback instability in swirling flows as this type of flashback occurs even when the fresh mixture velocity is higher than the flame speed, a consequence of the interaction between swirl structures and swirl burner geometries. Improvements in burner geometries and manipulation of swirling flows can increase resistance against this type of flashback. However, increasing resistance against Combustion Induced Vortex Breakdown can lead to augmentation in the propensity of another flashback mechanism, Boundary Layer Flashback. Thus, this paper presents an experimental approach of a combination of techniques that increase Combustion Induced Vortex Breakdown resistance, i.e. by repositioning a central injector and using central air injection, while simultaneously avoiding Boundary Layer Flashback, i.e. by changing the wall boundary layer characteristics using microsurfaces on the nozzle wall. Results show that using these techniques together has promising potentials regarding wider stable operation for swirl combustors, enabling them to burn a broader variety of fuel blends safely, while informing developers of the improvements obtained with the combined techniques.

Experimental Investigation of the Confinement Effect on Flashback in Multi Combustion Modes Tangential Swirl Burner

“…However, in spite of many studies in this field but the subject remains very difficult to research because of the interaction between heat and chemical reactions with different types of burner as well as the nature of use and different quality of fuel . Micro surfaces of burner nozzle wall with use a properly central air injection are also play an important role in the reduction of boundary layer flashback and combustion induced vortex breakdown [26] .…”

Experimental Study of the Effect of Swirl Number and Bluff Body Size on the Stability Map of Premixed LPG Flames in a Tangential Swirl Burner

“…Some parameters can affect this equilibrium degree, such as fuel type, mixing degree, burner configuration, swirl number, etc. [15]. The swirl number is considered an important factor on which to focus.…”

“…This can be due to the CRZs that form, which act as a flame holder and then can lead to the movement of the flame within the premixing zone [22]. On the other hand, as a result of the interaction between swirl burner geometries and swirl structures, this type of flashback (CIVB) can happen even when the velocity of the incoming mixture exceeds the speed of the flame [15]. The flashback of the flame in the swirl burner without the use of a bluff-body was verified byFritz et al [23].…”

“…Tong et al [30]examined the impact of a bluff-body position on flame stability. They reported that the size and strength of the CRZ were influenced when the bluff-body position was changed; the flame was more stable when it was placed 10 mm above the outlet of the annular channel.Hatem et al [15]experimentally investigated the influence of the central fuel injector position, the possibility of axially injecting air, and the use of microsurfaces as a lining for the inner nozzle wall on the swirl burner operation map. They found that there was an improvement and increase in the flame stability map when these three techniques were used together.…”

Combustion Characteristics of Methane-Air Mixtures in Millimeter-Scale Systems With a Cavity Structure: An Experimental and Numerical Study

“…One reason that flame stabilization is required in combustion systems is to prevent the flame front from moving upstream from the combustion zone toward the source of fuel, i.e., a flashback (Jeong et al, 2017). During a flashback event, the heat of combustion moves upstream and may damage numerous structures within the fuel and air mixing region of the combustor (Hatem et al, 2018;Zangeneh and Alipoor, 2021). Flashback may occur due to auto-ignition of a fuel-air mixture caused by a residence time of the fuel-air mixture in a region upstream of the combustion zone that exceeds the auto-ignition delay time of that fuel-air mixture at the temperature and pressure of that region.…”