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NUMERICAL ANALYSIS OF HOT JET INJECTION AND PREMIXED FLAME PROPAGATION IN A CHANNEL Dhruv Baronia Graduate Research Assistant Department of Mechanical Engineering Purdue School of Engineering and Technology, IUPUI Graphics: Rolls Royce Source: ABB Source: NASA

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Purdue School of Engineering and Technology, Indianapolis, IN Design of Experiment (DOE) Numerical Simulations Using Star-CD Outline Single Channel Test Rig Conclusions and Recommendation Motivation

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Purdue School of Engineering and Technology, Indianapolis, IN Motivation High cost of experiments Guide future experiments on Single Channel Rig for efficient data collection Optimize wave rotor performance

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Purdue School of Engineering and Technology, Indianapolis, IN IUPUI Single-Channel Internal Combustion Wave Rotor Premixed Chamber Supersonic Injection Nozzle Pyrex Window

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Purdue School of Engineering and Technology, Indianapolis, IN Previous Experimental Results

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Purdue School of Engineering and Technology, Indianapolis, IN Numerical Simulation in Single Channel Test Rig With Star-CD Star-CD is a commercial Computational Fluid Dynamics (CFD) code It is a finite-volume solver and is selected because of relatively advanced modeling of transient and propagating combustion phenomena It is a pressure-based solver hence it is not expected to capture shock waves sharply Used extensively in IC engine and gas turbine combustion simulations

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Purdue School of Engineering and Technology, Indianapolis, IN Combustion Modeling Hundreds of elementary reactions Simplified models to predict overall temperature, pressure and enthalpy changes Reaction rates determined by both mixing and kinetics

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Purdue School of Engineering and Technology, Indianapolis, IN Numerical Combustion Modeling Computation Cell flame front averaged thermodynamic, species and turbulence values turbulent flame thickness ~ 0.3mm burned unburned minimum cell size 0.5mm

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Purdue School of Engineering and Technology, Indianapolis, IN Single Channel Test Rig Simulation: Geometry And Grid For Numerical A 2D geometry is created to preserve the volume ratio to maintain realism of mass, energy and pressure history

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Purdue School of Engineering and Technology, Indianapolis, IN Body fitted grid with refinement near the boundary and in the shear layer Single Channel Test Rig Simulation: Geometry And Grid For Numerical

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Purdue School of Engineering and Technology, Indianapolis, IN Initial Conditions Thermodynamic Properties and Mass Fraction Test CellPrechamber Equivalence Ratio (prior to burn) Propane Oxygen Carbon Dioxide Water Vapor Nitrogen Pressure (abs, Pa)1.0E058.4E05 Temperature (K) Turbulence Kinetic Energy (m 2 /s 2 )0.0 Eddy Dissipation (m 2 /s 3 )0.0

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Purdue School of Engineering and Technology, Indianapolis, IN Combustion Models One-step combustion reaction with combined (kinetic & turbulent) time scale model Four-step combustion reaction [Glassman] based on pure kinetics Four-step combustion reaction [Glassman] with hybrid reaction modeling

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Purdue School of Engineering and Technology, Indianapolis, IN One-Step Reaction With Combined Time Scale Reaction time scale is a sum of turbulence time and kinetic time Activation energy, pre-exponent factor, etc. are calculated by Westbrook and validated for laminar flames Model will not predict ignition delay time

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Purdue School of Engineering and Technology, Indianapolis, IN Baroclinic Effect Initial configuration Vorticity generation Deformation

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Purdue School of Engineering and Technology, Indianapolis, IN Results for One-Step Reaction With Combined Time Acceleration and stretching of the flame front on interaction with shock wave Some amount of fuel/air mixture is left unburned at the left end of the channel

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Purdue School of Engineering and Technology, Indianapolis, IN Comparison With Non-reacting Case Pressure wave moving ahead Stretching of the flame front due to baroclinic effect No Combustion Combustion

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Purdue School of Engineering and Technology, Indianapolis, IN Baroclinic Effect on Reacting and Non- Reacting Cases Combustion No combustion exp(grad ρ) exp(grad p) Density gradient Pressure gradient combustion front shock wave

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Purdue School of Engineering and Technology, Indianapolis, IN Combustion Effects higher mass injection in no combustion case

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Purdue School of Engineering and Technology, Indianapolis, IN Four-Step Reaction Initiation Propagation Oxidation

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Purdue School of Engineering and Technology, Indianapolis, IN Four Step Reaction 1234 x E a /R (K) a b c Note: negative exponent

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Purdue School of Engineering and Technology, Indianapolis, IN Validation of Four-Step Reaction Geometry: 5X5X5 cells with symmetry boundary on all sides Initial Conditions: p=1 atm, T=1200 K, φ=1.34

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Purdue School of Engineering and Technology, Indianapolis, IN Results

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Observations Ignition delay time of 6.2 ms which is in good agreement with experimental data Dissociation of propane is endothermic Oxidation of hydrogen takes place at all temperatures All propane is dissociated in ethylene

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Purdue School of Engineering and Technology, Indianapolis, IN Results Geometry, BCs and ICs (expect for φ=1.34 in test cell) are similar to the previous one step reaction Reflected shock wave initiates autoignition resulting in further compression waves to complete the combustion

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Purdue School of Engineering and Technology, Indianapolis, IN Key Issues One-step global reaction is too coarse assumption Four-step reaction (pure kinetics) is able to simulate low temperature chemistry before ignition, which is purely based on kinetics Four-step reaction (kinetics + turbulence mixing) includes the influence of turbulence and can model the turbulent flame propagation after auto-ignition These inferences call for a hybrid reaction model that can switch between pure kinetics and combined time (kinetics + turbulence mixing)

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Purdue School of Engineering and Technology, Indianapolis, IN Hybrid Reaction Model For (T < T ign ) Use reaction rates (for all four reactions) based on kinetics For (T > T ign ) Reaction time scale is a sum of kinetic time scale and turbulent mixing time scale Where f (0.0 < f < 1.0) is a delay constant that simulates the influence of turbulence on combustion after ignition [Kong] The choice of T ign is arbitrary and some experimentation will be required

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Purdue School of Engineering and Technology, Indianapolis, IN Hybrid Reaction Model: Initial Conditions Hybrid model I : T ign =1200 K Hybrid model II : T ign =1500 K Initial conditions inside the prechamber is calculated using mole balance and water gas shift reaction Thermodynamic Properties and Mass FractionsTest CellPrechamber Equivalence Ratio (prior to burn) Propane Oxygen Carbon Dioxide Water Vapor Nitrogen Ethylene0.01.0E-18 Hydrogen Carbon Monoxide Pressure (abs, Pa)1.0E+058.4E+05 Initial Turbulence Kinetic Energy (m 2 /s 2 )0.0

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Purdue School of Engineering and Technology, Indianapolis, IN Propane Mass Fraction Contours T ign = 1200 KT ign = 1500 K Stretching of flame front

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Purdue School of Engineering and Technology, Indianapolis, IN Temperature Contours T ign = 1200 K T ign = 1500 K

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Purdue School of Engineering and Technology, Indianapolis, IN Ethylene Mass Fraction Contours No oxygen in this region

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Purdue School of Engineering and Technology, Indianapolis, IN Propane Consumption Plots

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Purdue School of Engineering and Technology, Indianapolis, IN Hybrid Reaction Model: Results With the 1500K threshold temperature ignition occurs as soon as the hot gas jet mixes with cold gas whereas with 1200K threshold temperature it happens upon second compression by the reflected shock wave Hybrid model II shows the stretching of the flame front due to baroclinic effect In hybrid model II, the peak pressure inside the test channel is about 2 atmospheres higher and average pressure is about 1.5 atmospheres higher

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Purdue School of Engineering and Technology, Indianapolis, IN Key Issues Two model options predicted different combustion behavior Effects of equivalence ratio and initial turbulence are not evaluated

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Purdue School of Engineering and Technology, Indianapolis, IN Design of Experiment (DOE) DOE is a statistical method to do the numerical experiments DOE provides information about the interactions of parameters and shows how parameters affect the combustion model Box Behnken Model: Individual and Combined effect of design parameters

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Purdue School of Engineering and Technology, Indianapolis, IN DOE :Design and model parameters Design ParameterLow ValueMid ValueHigh Value Equivalence Ratio Initial Turbulence Kinetic Energy (m 2 /s 2 ) Threshold Temperature (T ign, K)

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Purdue School of Engineering and Technology, Indianapolis, IN Propane Consumption Plots Different Ignition delay

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Purdue School of Engineering and Technology, Indianapolis, IN DOE : Results

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Purdue School of Engineering and Technology, Indianapolis, IN DOE: Results t = 0.5ms t = 1.0ms t = 2.0ms

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Purdue School of Engineering and Technology, Indianapolis, IN Conclusion and Recommendations Combustion regimes inside the channel is studied numerically using available combustion models Hybrid model is proposed which was able to predict autoignition and subsequent turbulent flame propagation Hybrid model was found to be more sensitive to model parameter T ign

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Purdue School of Engineering and Technology, Indianapolis, IN Conclusion and Recommendations Hybrid model needs further development to be predictive of combustion effects Suggested model parameter: entropy

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Purdue School of Engineering and Technology, Indianapolis, IN Publications Akbari P., Baronia D., Nalim M. R., 2006, Single-Tube Simulation of a Semi-Intermittent Pressure-Gain Combustor, appears in ASME Turbo-Expo 2006, GT- 2006_91061

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Purdue School of Engineering and Technology, Indianapolis, IN Acknowledgement Department of Mechanical Engineering, IUPUI Computer Network Center CD-Adapco Colleagues and friends

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Purdue School of Engineering and Technology, Indianapolis, IN Thank you … Questions?

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