Effects Of Inlet Parameters On Combustion Characteristics Of Premixed CH₄/Air In Micro Combustors

The study of micro scale combustion has important significance for improving the performance of micro power systems,and enriches scientific exploration of the combustion theory.Based on the analysis and learning of the domestic and overseas research work,the inlet premixed gas was preheated,and the combustion characteristics of premixed CH₄/Air were experimentally investigated.The influence of different inlet parameters on it were analyzed,and we obtained the influence rules of preheating that affected combustion process.The main work and achievement of this paper are as follows:（1）The visualized micro-combustion test platform that could preheat inlet premixed gas was established,and different channel heights were fabricated for the research.On account of different inlet parameters,the combustion process of premixed flame,the flammable limits and the temperature of external wall were experimental investigated.And the three-dimensional numerical calculation model for premixed CH₄/Air combustion under micro scale was built,it was also validated by experiment.（2）The influence of improving the inlet premixed gas temperature on the flammable limits and the external wall temperature distribution were analyzed through testing experiment.The results indicate that compared with the condition of normal temperature,the range of flame stabilization in the micro-combustor with channel height of 3.0 mm was apparently widened after preheating the inlet gas.This shows that preheating inlet temperature enhances the combustion stability.Besides,the smallest channel height under which the flame can exist in the combustor reduced from 2.5 mm to 2.0 mm after preheating.And in the micro-combustor with channel height of 2.0 mm,when the mass flow rate of methane is smaller,the rich and lean combustion limit range shrink more significantly than that with the greater.This indicates that the limit of the channel height is reduced after preheating.In addition,the higher inlet temperature leads to the higher external wall temperature in the micro-combustor with channel height of 3.0 mm,this contributes to improve the intensity of the combustion.And the difference between the inlet temperature and the maximum temperature is decreased gradually,further improving the reaction efficiency.（3）The effect of different inlet parameters on the combustion characteristics of premixed CH₄/Air was researched through numerical simulation.The results shows that with the inlet preheating temperature rising,the highest OH mass fraction moves toward the entrance and the intensity of combustion increases.Besides,increasing the equivalence ratio apparently improves the intensity of gas-phase reaction as it not exceeds 1.0 after preheating.But when it is greater than 1.0,the intensity begins to fall.Because as the concentration of fuel is increased,the oxidant concentration is relatively decreased and the chemical reaction is relatively slow.And the increased preheating temperature also has great impact on the gas-phase reaction intensity with different methane mass flow rates,it is more apparent that the intensity becomes stronger after preheating.（4）The influence of different inlet parameters on the thermal loss characteristics of the micro-combustor was investigated by the combination of numerical simulation and experiment.The results show that when the inlet temperature is increased,the average temperature of the external wall rise,which indicates that the wall heat loss increases.And with the equivalence ratio increased after preheating,the wall heat loss shows the trend that first increases and then decreases,however,it continues to grow with the methane mass flow rate increased after preheating at the same equivalence ratio.When the inlet preheating temperature is lower,the gas incomplete combustion heat loss has a slight increase;but when the temperature is higher,the conversion rate of methane is obviously increased,thus it begins to decrease.When the equivalence ratio is increased after preheating,the gas incomplete combustion heat loss increases a lot,and it increases gradually with the methane mass flow rate increased after preheating at the same equivalence ratio.In addition,the exhaust heat loss was also studied.It has a trend of gradually increasing as the inlet preheating temperature rise.The equivalence ratio has less influence on it,however,the methane mass flow rate shows greater influential on it.