Thermal Efficiency of Oxyhydrogen Gas Burner

One of the main methods used to generate thermal energy is the combustion process. Burners are used in both industrial and residential applications of the open combustion process. The use of fuels that reduce polluting gas emissions and costs in industrial and residential processes is currently a topic of significant interest. Hydrogen is considered an attractive fuel for application in combustion systems due to its high energy density, wide flammability range, and only produces water vapor as waste. Compared to research conducted regarding hydrocarbon combustion, studies on hydrogen burners have been limited. This paper presents the design and evaluation of an oxyhydrogen gas burner for the atmospheric combustion process. The gas is generated in situ with an alkaline electrolyzer with a production rate of up to 3 sL min−1. The thermal efficiency of a gas burner is defined as the percentage of the input thermal energy transferred to the desired load with respect to a given time interval. The experimental results show a thermal efficiency of 30% for a minimum flow rate of 1.5 sL min−1 and 76% for a flow rate of 3.5 sL min−1. These results relate to a 10 mm height between the burner surface and heated container.

Convection Type Electric Stove with Air Ionization

Increasing the efficiency of electric stoves currently remains an unsolved problem. The present study proposes a new design scheme for the electric convection stove with an air ionization device (Electric Stove PE-UIEV). This will reduce energy costs and speed up the cooking process. The stove in question is based on the method of electrothermal convection of heat-exchange surfaces of the frying deck. The proposed design reduces the formation of carcinogenic substances and improves the taste of fried and stewed dishes. The improved device increases the heat transfer coefficient from the burner surface to the cooker by 3 times since it creates better conditions for electrothermal convection. Treating air with electricity gives it adhesive properties: the air sticks to grounded surfaces of boilers. Ionized air intensively performs the function of heat carrier. Ionization reduces carcinogenic substances by 2–4 times and disinfects of ready-made dishes. The practical significance of the technical solution lies in the fact that the proposed design reduces the load on the ventilation and air conditioning system. In addition, the stove can be used for cooking in restricted (closed) spaces, and it improves the taste quality indicators. Unlike other stoves, this one reduces hot air circulation and, thus, its losses.

Impact of Geometric Parameters of Fuel-Air Distribution System on the Temperature Variation and Emission of a Sideway Faced Porous Radiant Burner (SFPRB)

The present work describes the state-of-the-art technology for a Sideway Faced Porous Radiant Burner (SFPRB) of 10–15 kW capacity, operated by liquefied petroleum gas (LPG) applicable for industrial furnace and incinerator. The newly developed SFPRB is a two layer burner, consisting of a reaction zone and a preheat zone. The combustion zone is of reticulated SiC ceramic matrix of porosity 90%, diameter 120 mm and thickness 20 mm and the preheat zone is of Al2O3 ceramic having 463 through holes (diameter 1.5 mm), with 15 mm thickness and 120 mm diameter. The work presents the effect of geometrical parameters (length of mixing pipe and diameter of orifice) on the radial temperature distribution of burner surface. Experimentation has been done in 15 kW input power to study the behavior of air-fuel mixture entering the burner. Ultimately, it is focused for uniform temperature distribution on the burner surface with a suitable arrangement. The work also presents a detailed account of the temperature distribution along the two main burner axes and the emission measurements (CO and NOx) for the suitable SFPRB. Investigation was done for an input power range of 10–15 kW with an equivalence ratio of 0.5.

Prediction of Confined Flame Flashback Limits Using Boundary Layer Separation Theory

Premixed combustion is a common technology applied in modern gas turbine combustors to minimize nitrogen oxide emissions. However, early mixing of fuel and oxidizer opens up the possibility of flame flashback into the premixing section upstream of the combustion chamber. Especially, for highly reactive fuels, boundary layer flashback (BLF) is a serious challenge. For high preheating and burner surface temperatures, boundary layer flashback limits for burner stabilized flames converge to those of so-called confined flames, where the flame is stabilized inside the burner duct. Hence, the prediction of confined flashback limits is a highly technically relevant task. In this study, a predictive model for flashback limits of confined flames is developed for premixed hydrogen–air mixtures. As shown in earlier studies, confined flashback is initiated by boundary layer separation upstream of the flame tip. Hence, the flashback limit can be predicted identifying the minimum pressure rise upstream of a confined flame causing boundary layer separation. For this purpose, the criterion of Stratford is chosen which was originally developed for boundary layer separation in mere aerodynamic phenomena. It is shown in this paper that it can also be applied to near-wall combustion processes if the pressure rise upstream of the flame tip is modeled correctly. In order to determine the pressure rise, an expression for the turbulent burning velocity is derived including the effects of flame stretch and turbulence. A comparison of the predicted flashback limits and experimental data shows high prediction accuracy and wide applicability of the developed model.

Prediction of Confined Flame Flashback Limits Using Boundary Layer Separation Theory

Premixed combustion is a common technology applied in modern gas turbine combustors to minimize nitrogen oxide emissions. However, early mixing of fuel and oxidizer opens up the possibility of flame flashback into the premixing section upstream of the combustion chamber. Especially for highly reactive fuels boundary layer flashback is a serious challenge. For high preheating and burner surface temperatures, boundary layer flashback limits for burner stabilized flames converge to those of so-called confined flames, where the flame is stabilized inside the burner duct. Hence, the prediction of confined flashback limits is a highly technically relevant task. In this study, a predictive model for flashback limits of confined flames is developed for premixed hydrogen-air mixtures. As shown in earlier studies, confined flashback is initiated by boundary layer separation upstream of the flame tip. Hence, the flashback limit can be predicted identifying the minimum pressure rise upstream of a confined flame causing boundary layer separation. For this purpose, the criterion of Stratford is chosen which was originally developed for boundary layer separation in mere aerodynamic phenomena. It is shown in this paper that it can also be applied to near wall combustion processes if the pressure rise upstream of the flame tip is modeled correctly. In order to determine the pressure rise, an expression for the turbulent burning velocity is derived including the effects of flame stretch and turbulence. A comparison of the predicted flashback limits and experimental data shows high prediction accuracy and wide applicability of the developed model.

A comparison of experimental results of soot production in laminar premixed flames

Soot emission has been the focus of numerous studies due to the numerous applications in industry, as well as the harmful effects caused to the environment. Thus, the purpose of this work is to analyze the soot formation in a flat flame burner using premixed compressed natural gas and air, where these quasi-adiabatic flames have one-dimensional characteristics. The measurements were performed applying the light extinction technique. The air/fuel equivalence ratiowas varied to assess the soot volume fractions for different flame configurations. Soot production along the flamewas also analyzed by measurements at different heights in relation to the burner surface. Results indicate that soot volume fraction increases with the equivalence ratio. The higher regions of the flamewere analyzed in order to map the soot distribution on these flames. The results are incorporated into the experimental database for measurement techniques calibration and for computational models validation of soot formation in methane premixed laminar flames, where the equivalence ratio ranging from 1.5 up to 8.

Numerical Study of the Heat Radiation from the Porous Cylindrical Burner with Radiative Heat Exchange

The problem of premixed gas combustion in porous cylindrical burner is investigated numerically. Two-temperature diffusional-thermal model taking into account radiative heat transfer described in the framework of Eddington model is applied. It was found that radiative heat transfer affects the characteristics of filtration combustion, such as temperature distribution and the flame radius, substantially. It is demonstrated that the overall heat flux from outer burner surface is significantly caused by heat radiation from the inner regions of the porous media. Account of the thermal radiation from the burner interior leads to the shift of the spectral power distribution maximum towards the short wave region in comparison with spectral density calculated on the base of burner outlet surface temperature.

Analytical and Experimental Study of Combustion and Heat Transfer in Submerged Flame Metal Fiber Burners/Heaters

A theoretical model has been developed to predict the thermal performance of inert, direct-fired, woven-metal fiber-matrix porous radiant burner. The local chemical heat release was modeled by a detailed mechanism, and convection heat transfer between the gas and the solid phases in the burner was described by an empirical heat transfer coefficient. The solid matrix was modeled as a gray medium, and the discrete ordinates method was used to solve the radiative transfer equation to calculate the local radiation source/sink in the energy equation for the solid phase. The fully coupled nature of the calculations without external specification of flame location represents a key advance over past efforts towards modeling of porous radiant burners, because for a given mass flow rate the actual heat loss from the flame determines its position and is not a free parameter. The calculated results for the burner surface temperature, the gas exhaust temperature and the radiation efficiency for a single layer Fecralloy burner were compared with experimental data from this laboratory and reasonable agreement was obtained for a range of operating conditions.

Characterization of Particulate From Fires Burning Silicone Fluids

The optical properties of particulate emitted from fires burning two distinct polydimethylsiloxane fluids (D4 and M2 or MM, where D=CH32SiO and M=CH33SiO2) were obtained using a transmission cell-reciprocal nephelometer in conjunction with gravimetric sampling. The specific absorption coefficient of particulate ash from fires burning D4 and MM is significantly lower than that of particulate soot from an acetylene (hydrocarbon) flame. Scattering is the dominant part of extinction in fires burning the silicone fluids. This is very different from extinction by soot particles in hydrocarbon fires, where absorption is approximately five times greater than scattering. Temperatures and particulate volume fractions along the axis of a silicone fire D4 were measured using multi-wavelength absorption/emission spectroscopy. The structure of the D4 flames is markedly different from hydrocarbon flames. The temperatures and particulate volume fractions very close to the burner surface are much higher than in comparably sized hydrocarbon flames.