Search

• Blending DME greatly enhances the stability limit of methane combustion in micro-scale combustion. • The intrinsic factors for the transition from inclined flame to U-shaped and double-peak U-shaped flames are investigated. • The reasonable blending ratio and combustion conditions of DME in microscale combustion are clarified. • The kinetic mechanism of blending dimethyl ether in the enhanced combustion is elucidated. This paper presented a novel blended combustion solution for mixing methane/dimethyl ether/air in a micro combustion chamber. Simulations were used to compare the pure methane combustion with the blended combustion, focusing on the OH species distribution, y -axis velocity, and strain rate to reveal the flame dynamics differences in different combustion conditions. The results showed that the blowout limit was enhanced from 0.53 m/s to 1.18 m/s at a blending ratio of 50 %. The blending of DME was also beneficial in weakening the flame asymmetry, delaying the generation of inclined flames in the original combustion, and replacing the inclined flames by a double-peaked U-shaped flame and an inverted U-shaped flame at an equivalence ratio of 0.9. Overall, this study not only provides a reliable fuel mixture for enhancing the combustion process under microscale conditions, but also reveals the flame transition characteristics. [Display omitted] [ABSTRACT FROM AUTHOR]

• The impact of Pt catalyst and heat recirculation on combustion performance is evaluated. • The homogenous chemistry can be substantially extended in the presence of a catalyst. • Outer wall temperature and uniformity are enhanced with proposed strategies. • Radiation energy and efficiency exhibit a different trend with the inlet flow rate. In this work, the joint effect of applying Pt catalyst and heat-recirculating structure on the flame stability and thermal performance has been numerically investigated in methane-air-fueled micro-combustors by a detailed three-dimensional computational model. Numerical results indicate that such strategies contribute to improving outer wall temperature by 14.4% and extending the blowout limit by a factor of 0.6 compared to those in the straight non-catalytic combustor. Such enhancements are due to the intensified heat transfer, thus highlighting the contributions of heterogeneous combustion chemistry and heat-recirculating effect. Homogeneous chemistry in the presence of a Pt catalyst is shown to be self-sustained over wide-ranging conditions. Meanwhile, the effectiveness of heat recirculation structure on combustion performance is more significant as compared to that of the catalytic combustion effect, as evidenced by a 4% and 17.6% improvement in the wall mean temperature and blowout limit respectively. Further analysis of the heat recirculation catalytic combustors is conducted to obtain the optimal geometry. There exists a critical flow rate corresponding to the maximum outer wall temperature and radiation energy. In general, this work demonstrates the viability of applying a Pt catalyst and heat-recirculating structure to extend the flame stability limit and energy conversion performance in micro-power systems. [ABSTRACT FROM AUTHOR]

The present study experimentally explores the combustion instability characteristics of premixed methane/air flames in a planar micro-combustor by utilizing the high-speed camera and the noise data acquisition system. It aims to identify the sound pressure fluctuation of unstable flames and shed light on the relationship between flame structure and thermoacoustic instability under micro-scale conditions. Four types of flame structures, i.e., flame with repetitive extinction and ignition (FREI), weak flame, steady flame, and oscillating flame, are experimentally observed by varying operating parameters. Among them, the weak flame at low flow velocities and the oscillating flame at high flow velocities form thermoacoustic oscillation. For weak flames, the collision with the wall and the local deformation of the flame result in high-frequency harmonics. Varying the inlet velocity from 0.14 m/s to 0.15 m/s leads to the pressure fluctuation of the weak flame being reduced by 10 Pa, and the dominant frequency being changed from 125 Hz to 167 Hz. As for oscillating flame, the variation of the inlet velocity plays a decisive role in the sound pressure fluctuation. At the equivalence ratio of 0.7, an increase of 0.01 m/s in the inlet velocity reduces the pressure fluctuation by 4 Pa. • Different flame regimes are observed by varying the operating parameters. • The acoustic and dynamic characteristics of unsteady flame are examined. • The spectral analysis of unstable flames is conducted. • The main factors of dynamics flame formation are identified. [ABSTRACT FROM AUTHOR]