Experimental Study On Premixed Catalytic Combustion Characteristics Of Hydrogen And Alkanes In Micro Tubes

The development of micro fabrication, micro electronics and information technology has promoted the development of portable devices. Microscale combustion systems are becoming more and more widely used in the fields of energy, photovoltaic, control, etc. Combustion stability and combustion efficiency are the key performance of micro-scale combustion system, and how to improve combustion stability and efficiency is the difficult and hot issue in micro energy power system which is based on combustion. This paper focused on the two scientific problems, catalytic combustion experiments of hydrogen, methane and n-heptane were carried out in micro tubes.The effects of different mixing ratios, equivalence ratios, catalyst layouts and diameters on the combustion characteristics(stable combustion limits, flame shapes, wall temperature distributions, conversion rates and heat dissipations) of fuels were analyzed.Catalytic combustion of hydrogen/methane/air was conducted in a double tube. The experimental results showed that when R increased, the lower limit of stable inlet flow rate v decreased, while it decreased firstly and then increased with the increase of 0. The flame could be stable in R=0.9,Φ=1.6 condition as v varied from 0.25 to 19m/s. Simultaneously, the highest wall temperature and maximum length of heat recirculation zone were achieved. The front of the flame became inclined cone-shaped and its root moved downstream with the increase of R. Heat loss of the tube wall increased with the increase of R and v, but its rate decreased with the increase of v. Radiative heat loss accounting for the proportion of the total heat loss increased firstly and then decreased with the increase of 0, it reached 63.93% when 0=1.6.n-Heptane catalytic combustion experiments were conducted in micro converging-diverging combustors using continuous (type A) and two-sectional (type B) types. Type B significantly expanded the upper limit of stable combustion, maintaining stable combustion at Re=1500 under fuel-rich conditions at Φ=1.6. But type A was more advantageous at low Re values, and the lower Re limit was reduced to 12. Types A and B displayed a single peak and a bimodal distribution of wall temperature, respectively. The bimodal distribution in type B not only slowed down the variation in wall temperature with Re but also proved homogenous combustion being motivated without catalyst in the throat. As a result of the different combustion processes, type A showed different variation trends of products compared with type B. Moreover, the conversion rates of the two types reached their maximum values of 84.4% and 88.3% at Re=160.n-Heptane combustion experiments were performed in packed-bed micro tubes with different inner diameters. Pt/Ce0.8Zr0.2O2 was adopted as catalyst. Tubes of d=3,4,5mm achieved the widest stable combustion ranges under the rich-fuel conditions of Φ=2.0,1.6,1.2, respectively. As Re was small, the highest wall temperatures of the d=4mm and 5mm were similar; But as Re became large, the high temperature region in d=5mm was longer. Tubes with different diameters achieved the maximum values of conversion rates under the condition of Re=160, and with the increase of d, the conversion rate became higher. With the increase of Re, the ratio of heat loss to the generated heat gradually decreased.