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The need for Power Micro Electro Mechanical Systems (Power MEMS) is growing as microfabrication techniques and microelectronics advance. Conventional chemical batteries have insufficient energy density to use Power MEMS. Hydrogen and hydrocarbon fuel combustion provides a more attractive alternative to traditional batteries. The micro burner has a small combustion chamber, surface area to volume ratio increases, which causes heat losses and instability. Therefore, fuel burns inefficiently, and the flame is unstable because of the short residence time of the premixed fuel/air. Flame instability, short residence time, and poor combustion efficiency are the main issues affecting micro combustion. Therefore, enhancing the fuel's residence time and flame stabilization in micro combustions is essential. To achieve better combustion, the current review articles mainly discuss micro combustion techniques, which have progressed in recent and last decades. Introducing a porous medium could enhance micro combustor performance. Catalytic combustion and integration of porous medium into MTES and MTPVS are recommended. Catalytic combustion aims to accelerate the reaction rate, prolong the time fuels spend in the combustion chamber, and maintain a constant flame. It was suggested that hydrogen be added to the combined gas. It would be ideal if the combined gas's equivalence ratio φ is between 0.9 and 1.1 for better performance. Its recommended bluff body blockage ratio ζ set between 0.4 and 0.5 enhances combustion stability and fuel residence time. This article overviews the micro combustion characteristics, micro combustion techniques, and their mechanism. At the end of this article, we also discussed the best strategies to overcome the issues of micro combustion for designing a new efficient micro combustor in the future. • Techniques used to improve flame stability in micro combustion are explained. • Techniques used to increase fuel residence time in micro combustion are explained. • Future perspectives to improve the performance of micro combustors are outlined. [ABSTRACT FROM AUTHOR]

Experimental and numerical study of premixed methane-oxygen combustion characteristics in a catalytic micro-combustor with different hydrogen addition ratios has been presented in this paper. The objective is to examine the effects of platinum catalysts and hydrogen additions on methane and oxygen combustion. The simulation of a three-dimensional micro rectangular model was carried out with a gas phase reaction mechanism combined with a surface reaction mechanism, and the model was validated with experimental results with a maximum deviation of just 1.56 percent. In the experimental phase, the effects of flammability limit, equivalence ratio, and inlet velocity were studied, while in the numerical phase, the effect of hydrogenation on combustion characteristics was investigated. Experimental results show that adding 10 % hydrogen to a premixed methane-oxygen mixture significantly increases its flammability limit. The maximum external wall temperature along the centerline was observed at an equivalent ratio of 1. Additionally, an increase in the inlet velocity leads to a corresponding increase in the external wall centerline temperature. Catalytic reaction wall temperatures show a gradual decline, with the highest temperatures located at the inlet. An observed trend revealed a decrease in the external wall centerline temperature as the hydrogen addition increased from 0 % to 40 % due to the reduced total heating value of the blended fuel. Due to its higher reactivity and ability to promote complete combustion, hydrogen also plays an important role in CH 4 and O 2 conversion. In addition, CO and CO 2 emissions decreased with increased hydrogen percentage in fuel mixtures. Furthermore, hydrogen addition can reduce external wall heat losses as well. After adding 0–40 % hydrogen to a premixture of (CH 4 –O 2) fuel, the total heat loss of the external wall was reduced from 19.48 W to 17.11 W. • The catalytic combustion of premixed CH 4 –O 2 in micro-combustor was studied experimentally and numerically. • The flammability limit was improved significantly by adding 10 % hydrogen to a premixed fuel. • An analysis of the effects of equivalence ratio and inlet velocity on combustion was conducted. • Hydrogen addition played an important role in the complete conversion of CH 4 and O 2. • The addition of hydrogen can also reduce heat losses through the external wall. [ABSTRACT FROM AUTHOR]

Ammonia is considered one of the most promising fuels, and mixing ammonia with hydrogen as fuel can achieve zero carbon emissions for engines. In this study, an experimental platform for an ammonia/hydrogen rotary engine was constructed, and successful ignition combustion was performed, demonstrating the possibility of the ammonia/hydrogen rotary engine. A 3-dimensional computational model of the ammonia/hydrogen rotary engine coupled with chemical reaction mechanisms was established, and the dependability of the model was confirmed using experimental data. Using numerical simulations, the impact of hydrogen injection position and time on the distribution of the fuel-air mixture, the propagation of flames, and the emissions of NO X in the cylinder under direct hydrogen injection have been studied. The research shows that the injection position and timing of hydrogen can affect airflow movement by changing the impingement angle and cylinder swirl intensity to alter hydrogen distribution in the cylinder under the guidance of the cylinder wall. Furthermore, with a delay in hydrogen injection timing, the turbulence kinetic energy in the cylinder gradually increases and is consistently more significant than that under premixed conditions, with turbulence kinetic energy in Case B-190 approximately 60% higher than that under premixed conditions. When more hydrogen is around the spark plug, the initial flame kernel is formed faster, resulting in a notable acceleration of the fuel-air mixture's combustion rate within the cylinder. In contrast to alternative hydrogen injection strategies, the injection strategy that employs nozzle A and an injection timing of 230°CA (BTDC) can achieve the highest cylinder pressure and lower NO X emissions. • A CFD computational model of ammonia/hydrogen rotor engine was established and validated. • Hydrogen has a greater impact on the flame development compared to ammonia. • Direct injection of hydrogen enhances the turbulent kinetic energy within the cylinder. • Optimizing the direct injection method of hydrogen can effectively reduce the emission of NOx. [ABSTRACT FROM AUTHOR]