Numerical Study On Fire Characteristics Of Hydrogen/Methane Fires Based On OpenFOAM

In the development and construction of sustainable,reliable and cost-effective energy,hydrogen stands out from many renewable clean energies because of its superior characteristics.In 2020 China’s National Development and Reform Commission,the Ministry of Justice issued by "Opinions of speed up the rules of green production and consumption policy system" clearly reported that the standards and support policies of new energy such as hydrogen will be formulated.Blending hydrogen into the existing natural gas pipeline network has been proposed as a means of increasing the output of renewable energy systems.The National Renewable Energy Laboratory of the US proposes to mix hydrogen within 20%(volume fraction)into the existing natural gas pipeline network to store and transport hydrogen,which will neither increase the risk of using end-user equipment nor harm existing pipelines.I participated in the National Key Research and Development Program of the National Intergovernmental Science and Technology Innovation Special Project(Ministry of Science and Technology)"Safety Explosion Research Project in Hydrogen Energy Utilization(No.2016YFE0113400)",and conducted research on the safety of hydrogen energy mixed with methane.According to the literature survey,previous studies mainly focused on flame length,temperature,flame stability and pollutant emissions of enriched-hydrogen methane.However,the investigations on how the hydrogen volume fraction affects the characteristic parameters of hydrogen-methane fires need to be paid more attention to.And the study of numerical model on simulating multi-fuels need to be developed and improved.Therefore,in order to explore the effect of blending small quantity of hydrogen on fire behavior of hydrogen/methane fires,hydrogen/methane buoyant fires and under-expanded hydrogen/methane jet fires with hydrogen volume fraction ranging from 0% and 20% were experimentally and numerically studied in this paper.An experimental facility was built to explore the effect of hydrogen volume fraction on hydrogen/methane buoyant fires.All experiments were carried out at 0℃ and 101325 Pa.In the experiment,the flow rates of hydrogen and methane were controlled by flow controllers.Digital camera was used to record the flame shape and flame height.Moreover,the centerline temperature and radiation were measure by Ktype thermocouple and radiation heat flux meter.The combustion characters of hydrogen/methane buoyant fires with different hydrogen volume fraction were studied by changing the flow rate of hydrogen and methane in the experiment.The numerical study was conducted based on Open FOAM.The modified eddy dissipation concept combustion model for multi-fuels in the large eddy simulation(LES)framework was employed for combustion,and especially the infinitely fast rate based on “global” concept was improved.Combined with the weighted sum of gray gas model for emission/absorption coefficient,the finite volume discrete ordinates model was used to compute the radiative heat transfer.The details of the research are as follows:The numerical model and empirical models were verified.Several pure methane fire,hydrogen/propane fires,under-expanded jet fire and hydrogen/methane fires were simulated in this paper.The numerical model has been validated and the limitation of the model has also been proposed.The research further validated empirical models such as Heskestad model,Mc Caffrey temperature model,Schefer model and Studer radiation model.The effect of hydrogen volume fraction(0%-20%)on hydrogen/methane buoyant fire was revealed in this paper.The combustion characteristics of hydrogen/methane buoyant fires with different hydrogen volume fraction,such as flame height,centerline temperature,flame radiation and smoke particle volume fraction,were discussed.The detailed analysis on the dependency of the parameters on hydrogen volume fraction was conducted.The effect of burner size on hydrogen/methane buoyant fire was studied.In this paper,hydrogen/methane buoyant fires of three different burners with diameter 10 cm,20cm and 30 cm were simulated respectively.And the combustion characteristics of hydrogen/methane buoyant fires,such as flame height,centerline temperature,surface emission power and soot volume fraction were discussed.The detailed analysis on the dependency of the parameters on burner size was conducted.The effect of hydrogen volume fraction(0%-20%)on under-expanded hydrogen/methane jet fires was revealed.In this paper,five groups of under-expanded hydrogen/methane jet fires with different hydrogen volume fractions were numerically studied.The detailed analysis on the dependency of the parameters such as flame height,centerline temperature,radiant fraction and soot volume fraction on hydrogen volume fraction was conducted.