# Flame Evolution Characteristics for Hydrogen/LPG Co-Combustion in a Counter-Burmer
## 1 Introduction  
In the context of the ongoing energy shortage and global warming, it is imperative to significantly reduce emissions resulting from processes of industrial combustion that utilize fossil fuels. The steel and iron industry accounts for 20% of industrial energy consumption and is responsible for around 7-9% of CO emissions [1,2]. While the electrification of industrial processes will be essential, most operations already utilize natural gas to attain necessary high temperatures. Consequently, the most straightforward alternative within these established processes is to substitute fossil fuels with alternative fuels, thereby diminishing emissions and environmental effects, rather than overhauling the entire process [3,4]. Practically, the steel industry employs numerous burners in heat treatment furnaces to achieve the requisite temperature, contingent upon the furnace load. To diminish natural gas usage and the pollutants resulting from its burning, it is essential to investigate alternate fuels. Green hydrogen emerges as a viable option, as demonstrated in recent studies [4,5]. In this context, it is imperative for burner manufacturers and end-users in the steel sector to meticulously examine the effects of hydrogen combustion on their burners [6,7]. Numerous uncertainties and unresolved inquiries persist regarding the logistics of large-scale hydrogen production, storage, and transportation [8,9]. [PERSON] et al. [10] conducted a comprehensive examination of current advancements in the principal facets of hydrogen-enhanced combustion. The inquiry encompassed various topics, including the minimum energy necessary for the ignition of hydrogen and hydrocarbon mixtures and the combustion characteristics of hydrocarbon/hydrogen fuel mixture. The results indicated that substantial reductions in energy requirements corresponded with an increased proportion of hydrogen, and three separate behaviors emerged with a rise in the hydrogen fraction. Moreover, the incorporation of hydrogen influenced the instability behavior of the flame front by a synergy of body force, hydrodynamic effects, and thermal-diffusion effects [11,12]. A coaxial nozzle burner (CNB) was utilized to investigate the properties of hydrothermal hydrogen combustion by developing a computational fluid mechanics model and comparing it with experimental data [13]. Hydrothermal combustion is a fast exothermic oxidation event that transpires in water at critical thresholds, applicable in the treatment of highly concentrated organic substances. The model simulated the flow field, flame stabilization process, and effects of different operating parameters on combustion in the coaxial nozzle burner. The findings revealed that, downstream of the injector, a V-shaped area where reactants flowed in reverse due to recirculation enhanced turbulence and heat transmission, serving as the principal site of combustion. The combustion zone advanced toward the nozzle outlet as the flame's length and diameter diminished due to gravity acting in the same direction as the jet. The kinetic rate and peak temperature could be improved by increasing the feed temperature and concentration. The feed flow rate mostly altered the axial temperature gradient near the nozzle outlet by adjusting the reactant's residence time [14,15]. This article will examine the utilization of H\({}_{2}\)/LPG mixes as the final phase in the logistical chain. Fresh studies indicate that hydrogen's existence in fossil fuel burners alters NO emission, flame stability, and heat release due to its physical properties, including elevated laminar flame speed, increased flame adiabatic temperature, and broader flammability limits, among others [16,17,18]. In this context, MILD (Moderate or Intense Low-oxygen Dilution) combustion technology in the iron industry is flameless, which has garnered attention in recent decades [19]. Burning H/NG blends with elevated hydrogen concentration has benefits, including reduced emissions and consistent, uniform heat release [20,21,22].