Investigation On Combustion Characteristics Of Methane And Blended Methane/Dimethyl Ether In Micro-channels

Continuous breakthroughs in micro-power systems based on hydrocarbon fuel combustion have been achieved due to the rapid development of Micro Electronic Mechanical Systems.Since these combustion-based systems have the advantages of high energy density,long working time and small size,they have great potential in the field of portable electronics.The working performance of micro-combustor which is the core component of micro power system can directly determine the power output of the whole system.Compared to conventional scale combustion,the heat loss from the external wall is significantly improved because of the large area-to-volume ratio as the size of the combustor is scaled down.In the meanwhile,the residence time of mixture in micro-channel is also shortened.These two problems can restrict the development of micro-power generators remarkably.Therefore,a deep understanding of the fundamental flame characteristics will help to enhance flame stability and is of great importance.In the present paper,the flame characteristics under micro-scale condition are investigated using experiment and numerical simulation,and a simple and effective blended combustion scheme is proposed.It is for sure that the research results found in this study can provide some references for the follow-up investigation in micro-combustion.The main objective and novelty in this paper are summarized as follows:(1)A micro-scale experimental platform is built for visualization study,and a transparent micro-planar quartz combustor is manufactured.Seven flame propagation modes,including flame repetitive extinction ignition,weak flame,planar flame,U-shaped flame,cellular flame,inclined flame as well as oscillating flame,are observed with varying inlet velocity for methane-air premixed combustion in micro-channel.(2)A three-dimensional computational model for premixed methane-air combustion in micro-channel is constructed with the detailed chemical reaction mechanism.To demonstrate the accuracy of computational model,the numerical results are compared with the experimental data.The flame fundamental characteristics are obtained,andthe effects of inlet velocity as well as equivalence ratio on flame structure and blowout limit are investigated.Moreover,the correction between flame structure and blowout limit is concluded.(3)In order to systematically understand the effects of other factors on flame characteristics and combustion process,the geometry parameter and material of combustor are further analyzed,and the optimum geometry for enhancing flame stability is obtained.Furthermore,the effect of wall thermal conductivity on some special flame structures is investigated and the flame stability as a function of thermal conductivity is concluded.(4)In view of the narrow flammable range and poor flame stability for pure methane-air combustion,a novel blended fuel combustion scheme is proposed and its effect on combustion process is analyzed using experiment approach.To further reveal the enhancement mechanism of blended combustion on flame stability,the effect of blended ration on the existence range of various flame structures,flame transition point,the frequency of unsteady flame as well as the flame structure and location of steady flame are investigated.