ChemkinPro

Chemical Kinetics

• University of Cincinnati has a 20 Chemkin network licenses Installation Procedure:

• Step 1: Download 32 or 64 bit Chemkinpro from – http://www.ase.uc.edu/~chemkin/ – Install both Chemkin (20) and ChemkinPro (1)

• Step 2: Copy the license file, chemkin.lic • Step 3: Connect to university Network through VPN

– Students can install on their personal laptops but for license file connect to university network

– The license is a Network license, so step 3 is always needed when running ChemkinPro

• The link in step 1 contains installation procedure, if difficulties arise contact network administrator Rob Ogden

email: Rob.Ogden@uc.edu or bhayaruh@ucmail.uc.edu

ChemkinPro Installation

Overview of Chemical Kinetics

• You need basic combustion concepts required to run the Chemkin software • Reaction occurs when two or more molecules collide • The probability of two molecules colliding is higher than three or more

molecules at an instant (bimolecular collision rates higher) • Assume during collision only one bond is broken • Inelastic collisions

- Involves conversion of KE to Internal energy/chemical energy - Endothermic, exothermic

O2

activation energy

H C H

H H

CH4 CH3 OH

H2O

O2

CO2

Overview of Chemical Kinetics

• Presence of fuel and oxidizer in a control volume not necessarily mean there will be a reaction

• Needs Activation Energy to start the reaction process • Typical example: spark plug • Once the activation energy is given to a system with fuel and oxidizer a chain of

reaction occur which leads to conversion of reactants to products.

Control volume with CH4 + O2

O2

activation energy

O2

Overview of Chemical Kinetics

• When activation energy is given the first reaction the starts is called chain initiation • In case of methane it is CH4+O2-> CH3+HO2 • Once the reaction is started by chain initiation, the subsequent reactions are started

called chain propagation • Finally when there are reactions which leads to final conversion products. In this

case CO2 and H2O • The reactions further don’t proceed as an when they reach their minimum state of

energy level represented by Gibbs Free Energy • As can be observed from the chain reaction diagram, the longer the path required to

convert from CH4 to CO2, the more time it takes. Its represented by Rate constant or rate of reaction

- Based on the time given for the reaction to occur, if there is ample time

given for the reactions to occur, the reactants leads to the products where they are at lowest energy state. A complete combustion is achieved -> reaching equilibrium state or Chemical Equilibrium – NASA CEA code

- Chemical Equilibrium calculations will give a reasonable estimate of products and temperatures. As one can guess the temperatures will be higher

- From Chain Reactions, a Mechanism of conversion from reactants to products, TIME factor is involved. Rate of Reaction-> time it takes for the process to occur TIME -> How Much time

Overview of Chemical Kinetics

- In practical systems like gas turbine combustion or IC engines: Does the system has enough time for all these reactions to occur: Quantitative ??

- If not sufficient time is given, non-equilibrium states are achieved - Pollutant levels is a non-equilibrium - Equilibrium = steady state = unsteady state

- Tchem vs Tflow, Tmixing, Tdiffusion… - Fast kinetics, Tchem << Tother - Chemically frozen, Tchem >> Tother

- Time Dependent Processes - Global Reactions (Fast Rate Chemistry) energy release rate vs

Elementary Reactions ignition, explosion, emissions

Reactants IN At velocity V1

Products OUT at velocity V2

Time spent by the mixture in the control volume Tresidence time, Tchem Damköhlar number

Overview of Chemical Kinetics

Overview of Chemical Kinetics

Fuel/air mixture IN At velocity V1

Fuel/air mixture OUT at velocity V2

Time spent by the mixture in the control volume Tresidence time, Tchem, Tmixing Damköhlar number

- If there is no flow in and out during reaction-closed reactors (0D models) - Constant volume or constant pressure reactors

- If there is flow in and out of the reactor during chemical reactions, open reactors (0D models) Well Stirred Reactor

- If flow properties changes along the length of the reactor (1D models), it is plug flow reactor

- Chamber/Reactor-where chemical reactions occur

How To Use ChemkinPro Software

• Four Problems will be discussed – Problem 1: Adiabatic Flame Temperature : Chemical

Equilibrium Calculations – Problem 2: Steady-state Gas-phase Combustion : PSR – Problem 3: Plug Flow Reactor – Problem 4: Gas Turbine Network : PSRs+ PFRs

ChemkinPro Tutorials

Start Menu Things to Observe

Contains 0D and 1D models, A series of these models are used for to simulate a gas turbine combustor

A project is created for each Network model

ChemkinPro Tutorials

Reactor models typically used in IC Engines: Closed volume Well stirred reactor (WSR or PSR) typically used in Gas Turbine combustion modeling: open volume means flow in and out Flow Reactors to simulate the flow

Models to simulate the Flame, to study flame extinction, lean blowout limits, flammability limits

Mathematical Model to simulate combustion related engineering problems

ChemkinPro Tutorials

Example 1 Adiabatic Flame Temperature

Chemical Equilibrium Calculations (For Hydrogen and Air)

Parameters:

Initial Temperature 300,400,500,600 K Pressure 1 atm

Equivalence Ratio 1 H2 1 Fuel N2 0.79 O2 .21 Air

Examples can be found here

Example 1

Chemical equilibrium calculations Similar to NASA SP273 or CEA code

Select Models and select chemical equilibrium icon, drag and drop in the diagram view

Example 1

Recollect: For chemical Equilibrium calculations, Thermodynamic data, species involved in the reaction mechanism are needed Select Preprocessing

Example 1

In the preprocessing stage, we mention what is required to define a chemical reaction Thermodynamic data File Reaction Mechanism File (Reaction Mechanisms Kinetics) Transport Properties File

For chemical kinetics, example 2 Reaction Rate: Activation Energy: Arrhenius Equation parameters Thermodynamic data Mixing = flame zone, recirculation, flame speed

Example 1

For Equilibrium calculations reactions rates are irrelevant. Just mention the species that are expected

Run the pre-processor to update the boundary conditions

Example 1

Give the concentration of species in moles or normalized mole fractions

Select the problem type, constant pressure enthalpy

Example 1

If equivalence ratio is given then make sure that complete combustion products are included(H2O, N2)

If an effect of a parameter has to be studied, give that parameter and the range you want to study in continuations Here we are studying the effect of initial temperature on equilibrium temperature

Example 1

Click on Run Calculations to carry out the calculations

Example 1

Before you Run Calculations, you can change solver settings. These settings are mainly to control how the ODE’s are solved. Typically you can leave the default settings. At advanced level calculations solver settings need to be changed for solution convergence, mainly depends on the stiffness of the problem

Once the calculations are carried out, the software gives an output of several parameters We can plot the information using analyze results In this example we wish to see the effect of initial temperature on equilibrium temperature

Example 1

Homework 1: Can we compare Equilibrium Calculations between Chemkin and NASA CEA code. If So, Compare the Equilibrium Temperature between both the software for H2+Air and CH4+Air. For 5 equivalence ratios. Make sure that the number of species selected are same

Example 1

In equilibrium calculations we have not given any Rate parameters like how fast the reaction takes to complete. Only initial state is required. Now We will take an example where chemical kinetics are linked with fluid and thermodynamic systems Not in Chemical Equilibrium The process of conversion from reactants to products as a function of time Species concentrations as a function of time Well Stirred Reactor (we assume perfectly mixed mixture and the spatial

variations are fully ignored, 0D reactor) Plug Flow Reactor Partially Stirred Reactor etc are used to model the flow

ChemkinPro Tutorials

Example 2 Steady-state Gas-phase Combustion

Perfectly Stirred Reactor (PSR) (For Hydrogen and Air)

Parameters: Residence Time 0.03 ms-0.2ms

Pressure 1 atm Equivalence Ratio 1 H2 0.8 N2 0.2 Fuel N2 0.79 O2 .21 Air

In this example, we demonstrate the effect of residence time on the final temperature attained by products

Watch out: closed and open reactors

Well stirred reactor (PSR) is an open 0D Reactor

Example 2

3 Columns Observe the difference between example 1 and this example The three column contains Arrhenius constants for elementary reactions: information on rate of reactions-> Time

Example 2

Need to mention mole and mass fraction as inputs

Example 2

Residence time in the reactor. Also defined by volume flow rate or mass flow rate or velocity

Example 2

In the continuations this time, we give residence time as a parameter of interest. Give typical residence times in gas turbines

Example 2

Homework 2: Compare the temperature with Equilibrium and how much residence time it required to reach to the equilibrium temperature for CH4+Air for 5 equivalence ratios. USE GRI Mech 3.0

Example 2

Open File Editor window. Look for <filename>.out

If there are input boundary conditions are missing or if the solver cannot converge to the solution, software gives out an error

Debugging Errors

Example 3 Plug Flow Reactor (Diffuser)

Parameters: Initial Temperature 1500 K

Pressure 1 atm Equivalence Ratio 1

Length 5 cm, Diameter varying from 2-5 cm Axial Velocity 25 cm/2

Species mixture: AR 0.8, CO 0.006, CO2 0.065, H2O .09,N2 .002895, NH3 .002, NO

.001, O2 0.007,OH .00005

Example 3

• Why do we need a Plug Flow Reactor? What does it used for? • Used to simulate flow in nozzles, diffusors where there is an area change • Change in geometrical conditions effects the flow properties like T, P,

species composition • The reactor also takes into consideration heat losses

Example 3

Thermodynamic data can be seen in graphical form with this option

Example 3

Mention here the variation of cross sectional area

Simulate with Heat Flux

Use the example problem in Chemkin software for plug flow reactor. Homework 3. Simulate a diffuser with inlet with diameter A cm to exit with diameter B cm. The length of the diffuser to be C cm. Simulate with Heat Flux D and initial Temperature E Choose A,B,C,D,E which are realistic

Why does the temperature Increase ?

Example 3

Example 2 : PSR

Example 3 : PFR

Network Modeling

Each Individual component is mathematically modeled based on fundamentals The exit conditions of one component are the input conditions for the next

component To study the overall performance of the combined system, all the individual

components have to be integrated into one system Then one can study the system performance and can carry a systematic

parametric analysis during its flight path Further for much detailed study, each individual component contains further

subcomponents which are modeled

inlet combustor nozzle

RCS Aerodynamics Flow control

exhaust

Typical Gas Turbine Combustor

Most mixtures will NOT burn so far away from stoichiometric Often called Flammability Limit Gas turbine can NOT operate at (or even near) stoichiometric levels as temperatures are way too hot for turbine

Fixed Tt4 implies roughly f < 0.5

What do we do? Burn (keep combustion going) fuel rich with some of ingested air Then mix very hot gases with remaining air to lower temperature for turbine

Typical Gas Turbine Combustor

44

APPLICATION TO COMBUSTION SYSTEM MODELING

Conceptual model of a gas-turbine combustor using 2 WSRs and 1 PFR

Air

Com

pres

sor

Turb

ine

φ ~ 1.0 T~2500 K

φ~0.3

Primary Zone

Simulating Gas Turbine Combustor

Example 4

Example 4 Gas Turbine Network Model

PSRs+ PFRs Parameters:

Initial Temperature 650 K, Pressure 10 atm Primary Air: 50 g/s, Premixed Air: 500 g/s, Cooling Air 100g/s

Equivalence Ratio 0.6 Mixing Zone: Residence time 0.5 ms, Temp 800K Flame Zone: Residence time 1.5 ms, Temp 1600K

Recirculation Zone: Residence time 1.5 ms, Temp 1600K Split recirculation zone gases 0.15: 0.85

split of gases from flame zone to post flame zone 0.15:0.85 Post flame zone length 5 cm, diameter 10 cm

Create clusters when there is recirculation or downstream conditions effect the upstream conditions, to isolate with remaining flow

Example 4

Change the temperature in the flame zone and check the effect on the species concentration and temperature in the reactors. Which Temperature should be higher flame zone temperature or recirculation zone temperature

One can study how the flow conditions effect the NOX and CO formation and in which zones of the combustor NOX formation is high Based on these initial analysis one can redesign the combustor Chemkin is integrated with CFD softwares like CFX and Fluent in Ansys to obtain reactor network model

Example 4

Typical Gas Turbine Combustor Simulation in Chemkin

Homework 4: Carry out a literature survey on the RQL and LPP combustor. Get typical engine conditions. Create a Reactor Network model for RQL combustor and LPP combustor and predict the NOx Levels in the combustor.

MID TERM PROJECT WORK

Simulate Real Gas Turbine Combustor and Obtain Temperature and NOX distribution in the combustor and obtain EI of emissions

Mid Term Project : A network of ideal reactors

Example 2 : PSR

Example 3 : PFR

Example 4 : Simple Gas turbine Combustor Network

model

Inlet/ inlets

PSR

PSR

PSR

PSR

PSR

PSR

PSR

PSR

PSR

PSR

mixer PFR mixer

Inlet Inlet

PFR

Inlet

outlet

PROJECT WORK

Engine Annular Combustor Dimension (unit = cm)

Proposed E3 annular combustion chamber design it has 24 fuel injectors

Engine Conditions

Comparison of combustor operating conditions

Combustor Air Flow Distribution

remaining % air for Turbine cooling • Use 10 PSRs for primary zone, each PSR occupies equal volume in the

primary zone • Calculate primary zone equivalence ratios at different engine power conditions • scale up or down the equivalence ratio based on the distribution shown in this

chart if the primary zone is not operated at equivalence=1.0

Mid Term Project

• Estimate the emission index of CO, NO, CO2 at 5 engine power conditions at two different flight conditions

• A written report should be submitted (~ 10 pages) • You need to certify that you have conducted this

project “ independently” when you submit the project report.

• Due Date

Where to Find Reaction Mechanisms and Thermodynamic data Reaction Design Website has links to several research groups webpages where a constant update of reaction mechanisms are available http://www.reactiondesign.com/support/chemical-mechanisms-data/ GRI Mech for methane http://combustion.berkeley.edu/Combustion_Laboratory/gri-mech/ Constant update of reaction mechanisms for Jet A http://web.eng.ucsd.edu/mae/groups/combustion/mechanism.html For IC engines http://www.erc.wisc.edu/chemicalreaction.php Reduced order mechanisms http://lcg.princeton.edu/research/chemical-kinetic-mechanisms.aspx

ChemkinPro : Further Information

57

(CH4+2O2<--> CO2+2H20) GRI Mech. for consists of 325 reactions that involve 53 species Reactions occur through multiple paths Each path, an elementary reaction is controlled by rate of reaction, k(T) How can we be sure that such an elementary reaction occurs and how to get parameters like k These are measured laser absorption techniques for species detection or predicted through simulations

Chemical Kinetics: Final Note

H2 combustion 7 species 20 reactions CH4 combustion 30 species 200 reactions C3H8 combustion 100 species 400 reactions Real Fuels are complex mixtures of several components Gasoline contains components ranging from 6<C<10 Jet A contains components ranging from 9<C<13 Diesel contains components ranging from 13<C<22 C12H26+ Jet A fuel combustion ??? Species ??? reactions

Chemical Kinetics: Final Note