Numerical Investigation On The Combustion Characteristics Of Methane/Air In A Micro-combustor With A Hollow Hemispherical/Regular Triangular Pyramid Bluff Body

Micro-combustor is widely used with the rapid development of MEMS, which is a new type of portable power devices. Micro combustion power plant has the advantages of small volume, light quality, large energy density, which has broad prospects in application of national defense, military, astronautics and the disadvantage of less combustion space, large surface to volume ratio, big heat loss, instable combustion and inefficient. How to guarantee the high efficiency and stable combustion of the micro combustor have become the key problems. Energy intensity of hydrocarbon fuels is several times than that in lithium battery. This paper studies the effect of bluff body on the combustion characteristics of micro-combustor, which is based on the in-depth analysis of the advantages and disadvantages of the current stage of the micro-channel stable combustion technology.The combustion characteristics of flat micro combustor, micro-combustor with a hollow hemispherical bluff body and micro-combustor with a regular triangular pyramid bluff body are simulated and analyzed by FLUENT.The results reveal that the blow-off limits of micro-combustor with a regular triangular pyramid bluff body and with a hollow hemispherical bluff body expand 2.3 and 2.5 times than that without a bluff body. The blow-off limits of the micro-combustor with a regular triangular pyramid bluff body and with a hollow hemispherical bluff body are 22.6 m/s and 24.5 m/s when the equivalence ratio is 1.0. The effect of hollow hemispherical bluff body on the promotion of combustion characteristics is better than that of regular triangular pyramid bluff body. The exhaust gas temperature increases firstly and then decreases with the increasing of inlet velocity in the micro-combustors with a regular triangular pyramid bluff body and with a hollow hemispherical bluff body. The difference values of the exhaust gas temperature between the two micro-combustors increase with the increasing of inlet velocity. With the increasing of inlet velocity, the areas of recirculation zones behind the regular triangular pyramid bluff body and hollow hemispherical bluff body increases gradually. The recirculation zone prolongs the residence time of the mixture gas and contributes to the methane/oxygen reaction.With the use of hollow hemispherical bluff body, methane conversion sharply increases from 0.24% to 17.95% at 3 mm along the inlet-flow direction when equivalence ratio is 1.0 and inlet velocity is 1.0 m/s, where is the location of bluff-body, which is not affected by equivalence ratio and inlet velocity. Methane conversion rates of micro-combustors with a regular triangular pyramid bluff body and with a hollow hemispherical bluff body reach maximum values when equivalence ratio is 1.0, the maximum values are 81.56% and 97.84%, respectively. Methane conversion rate increases firstly and then decreases with the inlet velocity. The blockage ratio of bluff body has determined influence on the combustion characteristics of micro-combustor. Methane conversion rate increases firstly and then decreases with the increasing of blockage ratio, which reaches maximum value when the blockage ratio are 0.22 and 0.3 in the micro-combustor with a regular triangular pyramid bluff body and the micro-combustor with a hollow hemispherical bluff body. Little blockage ratio of bluff body decreases the effect of bluff body and larger blockage ratio will decreases the circulation area of mixture gas. Adding hydrogen can promote the combustion of micro-combustor with proper operating conditions in the micro-combustor with a regular triangular pyramid bluff body and the micro-combustor with a hollow hemispherical bluff body.