Review:CalculateAdiabatic Flame TemperatureAs the equivalence ratio change,flametemperature willalso change9=Target reaction:methane-air flame:When [ = 1]: CH4 + 2(O, +3.76N,) -> CO, + 2H,O + 7.52NAH.XmF=2243KT,a = T。 + Cp,c02Mco2 +Cp,H20 ×2× M20 + Cp.N2 ×7.52 × Mn2=1.5When[Φ=1.5]:1.5CH,+2(O,+3.76N2)->CO,+2H,O+7.52N,+0.5CH4AH.XmFTf,ad = To +Cp,C02Mc02+Cp,H20×2×MH20+Cp,N2×7.52×MN2+Cp,CH4×0.5×McH4=2070K11FireScienceDrXinyan Huang
Fire Science 11 Dr Xinyan Huang Review: Calculate Adiabatic Flame Temperature As the equivalence ratio change, flame temperature will also change Target reaction: methane-air flame: When [φ = 1.5]: 1.5CH4 + 2(O2 +3.76N2 ) -> CO2 + 2H2O + 7.52N2 + 0.5CH4 𝑇𝑓,𝑎𝑑 = 𝑇𝑜 + ∆𝐻𝑐 × 𝑚𝐹 𝐶𝑃,𝐶𝑂2𝑀𝐶𝑂2 + 𝐶𝑃,𝐻2𝑂 × 2 × 𝑀𝐻2𝑂 + 𝐶𝑃,𝑁2 × 7.52 × 𝑀𝑁2 + 𝐶𝑃,𝐶𝐻4 × 0.5 × 𝑀𝐶𝐻4 = 2070 𝐾 When [φ = 1]: CH4 + 2(O2 +3.76N2 ) -> CO2 + 2H2O + 7.52N2 𝑇𝑓,𝑎𝑑 = 𝑇𝑜 + ∆𝐻𝑐 × 𝑚𝐹 𝐶𝑃,𝐶𝑂2𝑀𝐶𝑂2 + 𝐶𝑃,𝐻2𝑂 × 2 × 𝑀𝐻2𝑂 + 𝐶𝑃,𝑁2 × 7.52 × 𝑀𝑁2 = 2243 K φ = 1 φ = 1.5
Ignition:FlammabilityLimitTherefore,wecandefinetwoflammability limits(1)Lowerflammabilitylimit (LFL)or X,:f.mabelowwhichthefuelistooleantoburn(2)Upper flammabilitylimit (UFL) or Xu:abovewhichthefuelistoorichtoburnFuelUFL (%)LFL (%)Tf,min2.5100AcetyleneFuelFuel1.37.9Benzeneleanrich1.88.4n-Butane[1d12.574CarbonmonoxideFlammableregion2.736Ethylene6.71.05n-HeptaneXXuXcH4,stoicXp (%)754.0Hydrogen上5.0Methane15.0LowerflammabilitylimitUpperflammabilitylimit2.19.5PropaneorFuelrich limitorFuelleanlimit1240Trichlorethylene12Fire Science12DrXinyan Huang
Fire Science 12 Dr Xinyan Huang Ignition: Flammability Limit 12 𝜙 𝑇𝑓,𝑎𝑑 𝑇𝑓,𝑚𝑎𝑥 𝑇𝑓,𝑚𝑖𝑛 X𝐿 X𝐶𝐻4,𝑠𝑡𝑜𝑖𝑐 X𝑈 1 Flammable region Fuel lean Fuel rich X𝐹 (%) Lower flammability limit or Fuel lean limit Upper flammability limit or Fuel rich limit Therefore, we can define two flammability limits (1) Lower flammability limit (LFL) or X𝐿 : below which the fuel is too lean to burn (2) Upper flammability limit (UFL) or X𝑈 : above which the fuel is too rich to burn
Flammability Limit:Temperatureeffect.Increasethe initialtemperature can extendtherangeofflammabilitylimitmpHcDroplet-gas>Tmin~1350KT, =To+2cppmp +CpmexUFLboundaryFurtherincreasingthemixturetemperature(>400C),auto-ignition willoccur.FuelAutoignitionGaseousflammabledropletsFuelLFL (%)UFL (%)AIT(C)mixtures2.5Acetylene1003051.37.9560Benzene1.88.4405n-ButaneLFL/I7412.5609Carbonmonoxide2.736Ethylene4906.71.05215n-Heptane754.0400HydrogenTLAIT5.015.0540Methane2.19.5Temperature450Propane1240420Trichlorethylene1313FireScienceDrXinyanHuang
Fire Science 13 Dr Xinyan Huang Flammability Limit: Temperature effect 13 𝑇𝑓 = 𝑻𝟎 + 𝑚𝐹∆𝐻𝑐 σ 𝑐𝑝,𝑝𝑚𝑝 + 𝑐𝑝𝑚𝑒𝑥 > 𝑇𝑚𝑖𝑛 ≈ 1350K • Increase the initial temperature can extend the range of flammability limit • Further increasing the mixture temperature (>400 ℃), auto-ignition will occur
Flammability Limit:PropaneGasTHEBOOMBOXSSE#https://www.youtube.com/watch?v=Ww-pxYcYgBw14FireScienceDrXinyanHuang
Fire Science 14 Dr Xinyan Huang https://www.youtube.com/watch?v=Ww-pxYcYgBw Flammability Limit: Propane Gas
DepartmentofTHEHONGKONGBuilding Environmentand Energy EngineeringPOLYTECHNICUNIVERSITY建筑璟境及能源工程學系香港理工大學Outline1.Flammability of Gas andIgnition2.lgnitionProcessesPilotedvs.Autoignition。SolidfuelLiquidfuel3.Self-heatingignition1515Fire ScienceDrXinyanHuang
Fire Science 15 15 Dr Xinyan Huang Outline 1. Flammability of Gas and Ignition 2. Ignition Processes • Piloted vs. Auto ignition • Solid fuel • Liquid fuel 3. Self-heating ignition