Tutorials Manual

Chemkin 4.1.1
Chapter 2: Combustion in Gas-phase Processes
There are various ways of defining the ignition time, experimentally as well as
computationally, for combustion applications. For example, it is often defined as the
time at which either the maximum or onset of certain species concentrations is
reached, the time at which a specified rate of increase of temperature occurs, the time
at which luminous radiant output from the system is first observed, etc. The reported
experimental data can vary greatly, depending on which definition was used in the
experiments 5, 7 . Thus, it is often useful to select which ignition-delay time definition
should be used in numerical computations. CHEMKIN 4.1 allows the user such
flexibility. For example, in CHEMKIN'S homogeneous, perfectly-stirred reactor, the
ignition time can be defined to be the time during which the maximum amount of heat
is released during a combustion process (as indicated by the inflection point in the
temperature profile), as well as the time of the maximum of a certain species
concentration chosen by the user. CHEMKIN 4.1 further allows the user to input his/her
specific definition of the ignition time via the Ignition Criterion User Routine.
2.3.3.2 Project Setup
The project file is called closed_homogeneous__ignition_delay.ckprj. The data
files used for this sample are located in the
samples41\closed_homogeneous\transient\ignition_delay directory. This sample
uses the mechanism and thermodynamic data from the University of California, San
Diego 6, 8 . This reactor diagram contains only one closed homogeneous reactor.
Open the project file. On the Reactor Physical Properties tab of the C1_Closed
Homogeneous panel, the problem type is selected as a constant-pressure simulation
where the energy equation will be solved (the default). The initial temperature
(1000 K) is then input, along with the pressure (1 atm). A volume is not specified as it
is not important for the results of this simulation, so the default value of 1 cm 3 will be
used for the initial volume. Since this is an isobaric closed homogeneous system, the
results in terms of species fraction and temperature will be the same, regardless of
the volume value. If surface chemistry were included, the volume-to-surface ratio
would be important, but in this case only gas-phase chemistry is present. On the
Reactant Species sub-tab, the starting gas mixture is given as 0.02 C 3 H 8 , 0.05 O 2 ,
and 0.93 Ar. These rather dilute conditions are representative of shock-tube
experimental conditions.
7. Combustion Theory, Second Edition, F.A. Williams, Addison-Wesley Publishing Company,
The Advanced Book Program, Redwood City, CA, 1985
8. http://maemail.ucsd.edu/combustion/cermech/
© 2007 Reaction Design 28 RD0411-C20-000-001