Abstract:With the increasing global concerns about the impacts of byproducts from the combustion of fossil fuels, researchers have made significant progress in seeking alternative fuels that have cleaner combustion characteristics. Such fuels are most suitable for addressing the increasing demands on combustion-based micro power generation systems due to their prominently higher energy density as compared to other energy resources such as batteries. This cultivates a great opportunity to develop portable power devices,… Show more
“…The design and manufacture of micro burners, which have dimensions at the millimeter or submillimeter level, pose unique challenges when compared to conventional combustors, which make it not trivial to obtain a stable flame, as documented in Hossain and Nakamura [10], Ju and Maruta [1], Nakamura et al [2], Resende et al [11], and Lee et al [12]. These challenges extend to combustion in microscale environments, where the effects of viscosity are amplified in small channels, the physical residence time of mixed gases is shortened, and the ratio of area to volume of the combustion chamber increases sharply [13,14].…”
Section: Challenges Within Microcombustionmentioning
This work presents a state-of-the-art review of micro-combustion flame dynamics and micro propulsion systems. In the initial section, we focus in on the different challenges of micro-combustion, investigating the typical length and time scales involved in micro-combustion and some critical phenomena such as flammability limits and the quenching diameter.We present an extensive collection of studies on the principal types of micro-flame dynamics, including flashback, blow-off, steady versus non-steady flames, mild combustion, stable flames, flames with repetitive extinction, and ignition and pulsatory flame burst. In the final part of this review, we focus on micropropulsion systems, their performance metrics, conventional manufacturing methods, and the advancements in Micro-Electro-Mechanical Systems manufacturing.
“…The design and manufacture of micro burners, which have dimensions at the millimeter or submillimeter level, pose unique challenges when compared to conventional combustors, which make it not trivial to obtain a stable flame, as documented in Hossain and Nakamura [10], Ju and Maruta [1], Nakamura et al [2], Resende et al [11], and Lee et al [12]. These challenges extend to combustion in microscale environments, where the effects of viscosity are amplified in small channels, the physical residence time of mixed gases is shortened, and the ratio of area to volume of the combustion chamber increases sharply [13,14].…”
Section: Challenges Within Microcombustionmentioning
This work presents a state-of-the-art review of micro-combustion flame dynamics and micro propulsion systems. In the initial section, we focus in on the different challenges of micro-combustion, investigating the typical length and time scales involved in micro-combustion and some critical phenomena such as flammability limits and the quenching diameter.We present an extensive collection of studies on the principal types of micro-flame dynamics, including flashback, blow-off, steady versus non-steady flames, mild combustion, stable flames, flames with repetitive extinction, and ignition and pulsatory flame burst. In the final part of this review, we focus on micropropulsion systems, their performance metrics, conventional manufacturing methods, and the advancements in Micro-Electro-Mechanical Systems manufacturing.
“…This type of system needs external power supply and, given the typical battery limitations, efforts have been made to develop alternatives based on microcombustion in order to take advantage of the high-density energy of the hydrocarbon and hydrogen fuels. Nevertheless, early experimental studies involving microcombustion presented some difficulties to obtain a stable flame caused mainly by two phenomena: the low residence time inside of the microcombustor to complete combustion and the higher heat losses from the combustion chamber walls [2,3].…”
This work reports a numerical investigation of microcombustion in an undulate microchannel, using premixed hydrogen and air to understand the effect of the burner design on the flame in order to obtain stability of the flame. The simulations were performed for a fixed equivalence ratio and a hyperbolic temperature profile imposed at the microchannel walls in order to mimic the heat external losses occurred in experimental setups. Due to the complexity of the flow dynamics combined with the combustion behavior, the present study focuses on understanding the effect of the fuel inlet rate on the flame characteristics, keeping other parameters constant. The results presented stable flame structure regardless of the inlet velocity for this type of design, meaning that a significant reduction in the heat flux losses through the walls occurred, allowing the design of new simpler systems. The increase in inlet velocity increased the flame extension, with the flame being stretched along the microchannel. For higher velocities, flame separation was observed, with two detected different combustion zones, and the temperature profiles along the burner centerline presented a non-monotonic decrease due to the dynamics of the vortices observed in the convex regions of the undulated geometry walls. The geometry effects on the flame structure, flow field, thermal evolution and species distribution for different inlet velocities are reported and discussed.
“…In our recent study [28], combustion characteristics were analyzed for syngas laminar micro diffusion flames. Resende et al [29] summarized the numerical studies on micro diffusion combustion flame. The review concluded that the numerical simulations are capable of predicting the micro diffusion flame behavior both quantitatively and qualitatively.…”
Characteristics of microjet hydrogen diffusion flames stabilized near extinction are investigated numerically. Two-dimensional simulations are carried out using a detailed reaction mechanism. The effect of burner wall material, thickness, and thermal radiation on flame characteristics such as flame height and maximum flame temperature are studied. Results show that the flame stabilizes at lower fuel jet velocities for quartz burner than steel or aluminum. Higher flame temperatures are observed for low conductive burners, whereas the flame length increases with an increase in thermal conductivity of the burner. Even though thermal radiation has a minor effect on flame characteristics like flame temperature and flame height, it significantly influences the flame structure for low conductive burner materials. The burner tip and its vicinity are substantially heated for low conductive burners. The effect of burner wall thickness on flame height is significant, whereas it has a more negligible effect on maximum flame temperature. Variation in wall thickness also affects the distribution of H and HO2 radicals in the flame region. Although the variation in wall thickness has the least effect on the overall flame shape and temperature distribution, the structure near the burner port differs.
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