Chemkin Applications: Distributor Training Course

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Sample Problem Auto-ignition Study
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Example Auto-ignition in Closed Homogeneous
System
HANDS ON

• What is the ignition time?
• How close is the final temperature to the
  adiabatic flame temperature?
• Tadiab for this system 2734 K
• How do the results change if you change the heat
  loss to a positive value (e.g. 10 cal/s)?
• How does NOx depend on time?

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Example Auto-ignition in a Closed Homogeneous
System
HANDS ON

• Auto-ignition occurs due to kinetics, without a
  spark or external heat source
• Affected by initial pressure, temperature and
  composition
• Important for
• HCCI, CAI Engine design
• Flammability or explosion limits
• Example
• Methane/Air mixture stoichiometric conditions
• Closed system, constant pressure
• Adiabatic (no heat loss)
• 1 atm
• Initial T 1500 K
• How long will the mixture take to ignite?

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Example Auto-ignition in Closed Homogeneous
System
HANDS ON

• A well accepted description of methane combustion
  kinetics is the GRI-Mech
• Kinetic rates
• Thermo data
• Validated over wide range of conditions
• The 0-D Closed Homogeneous Reactor Model
  describes a closed, transient system
• Constant pressure option allows volume expansion

http//euler.me.berkeley.edu/gri-mech/version30
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Example Auto-ignition in Closed Homogeneous
System
HANDS ON

• Create New project
• Select a Working Directory
• Use the System grimech30.cks chemistry set
• Set up the Closed Homogeneous Reactor
• Stoichiometric Methane/Air 3.76 N2 1.0 O2 0.5
  CH4
• Closed system, constant pressure
• Adiabatic (no heat loss)
• Pressure 1 atm
• Initial T 1500 K
• Time 5 msec
• Create Input and Run
• Plot the Temperature vs. time
• View the output file and search for ignition
• Plot reactant and product mole fractions vs. time
• H2, O2, CH4, CO, CO2, H2O
• Plot NOx vs. time

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Example Auto-ignition in Closed Homogeneous
System
HANDS ON
Adiabatic Flame Temperature
Reactants Products
T (K)
NOx
Ignition
1 ppm