Week 7 - Auto ignition using Cantera

Aim:

1. To calculate the auto-ignition delay for Methane using Cantera for varying pressure between 1-5 atm at constant tempertaure=1250K

2.To calculate the auto-ignition delay for Methane using Cantera for varying temperatures between 950-1450 Kelvin at a constant pressure=5 atm

3. To print the rate of change of molar concentrations of the given elements "H2O, O2, OH" with respect to the time, (simulation time = 10 secs)

Experimental definition of auto-ignition delay is the time at which the system temperature becomes equal to 400 K + initial temperature.

Theory:

The Cantera reactor is the simplest reactor which doesn't have any spatial gradients in the composition and thermodynamic properties of the reactants. There are other types of reactors depending on the reactor state. These define the Navier-Stokes equation on the basis of their interaction with the surrounding. (Source:https://cantera.org/science/reactors.html)

1. Standard reactor

2. Constant pressure reactor

3. Ideal gas reactor

4. Ideal gas constant pressure reactor

5. Wall interactions

6. Well-stirred reactor

7. Plug flow reactor

For this assignment, a Cantera simple reactor is called.

case 1:

https://drive.google.com/file/d/1v08UU-NaRqax3qK0vBIGI-2aM41Bn_HJ/view?usp=sharing

case 2:

https://drive.google.com/file/d/1bJwx0iuQGKUti1ZrJZgymKLK-w58tbMh/view?usp=sharing

case 3:

https://drive.google.com/file/d/1K6QC5V79Qfec0jbp7Npxqy9APQa1jO3s/view?usp=sharing

AT 500 K of initial temperature

At 1000K of initial temperature

It can be clearly observed that the auto-ignition delay decreases with an increase in initial pressure, this is because physically as the pressure increases the kinetic energy of fuel molecules increasing the temperature of the system to reach autoignition fairly quickly. For this range of pressure for methane, the variation isn't that much, can be concluded to be a fairly constant ignition delay from a human perspective. The same is true when the initial temperature of the system is raised. As pressure and temperature are related to each other and define the state of the system, increasing either of them will reduce the auto-ignition delay.

It is observed that the autoignition temperature of CH4 is around 2980K at 5 bar when the initial temperature is 1000K the concentration of product (H2O) increases rapidly in a short span of time, and the intermediate elements on the reactant size tend to deplete as they are getting converted to product. However, at 500K this process is slow and increase rather non-linearly instead of a sharp rise.