Blowout characteristic of Hydrocarbon Combustion

[ocram]

Hi everybody!

The problem which I am dealing with is surprisingly very well depicted in open source lecture notes made in October 29th of 2012, titled: " MAE 5310: COMBUSTION FUNDAMENTALS", available on the web.
http://www.google.it/url?url=http:/...QQFjAC&usg=AFQjCNEN1kSlfrEazkua8vjomKkE7A5xig
Such lecture notes are concerned with deriving the Blowout Characteristic of hydrocarbon combustion, and are based on a popular example proposed by S.R.Turns in [1].
The question which I am going to ask you is strictly related with this topic.

Indeed, I am trying to produce the blowout characteristic of a hydrocarbon combustion process.

A Steady Well Stirred Reactor model is considered, based on energy and species mass conservations, assuming the same Single Step Global Scheme proposed in such lecture notes.
I have followed a "fully rigorous" approach:
- polynomial expression of enthalpies are considered accordingly to report NASA/TP 2002-211556(Gordon, McBride) instead of constant specific heat capacities
- different molecular weights
The non linear system of algebric equations is resolved with software MATLAB R2010 (using 'fsolve' function capabilities).
Rather that applying the species mass conservation proposed in the notes, I have applied a more general method, based on the atomic species conservation, also documented in [2]. What is most important to notice is that the relative reaction rates are NOT dependent upon Equivalence Ratio.

What I obtain is a blowout envelope which peaks NOT at an equivalence ratio equal to 1.0, but roughly at 0.8, in contrast with what are the theoretical expectations.

My question for you is wheter this result can be regarded as acceptable or not.
It would imply that, at light-lean condition, combustion is more stable that at stoichiometric.
In case it is not, I would really appreciate any comments regarding how the relative reaction rates should be calculated, in particular at lean and rich conditions.

[1] S.R.Turns, "An Introduction to Combustion", 2nd Edition, pp. 192
[2] H.S.Fogler, "Elements of Chemical Reaction Engineering", 3rd Edition, pp. 57, formula (2-20)
Thanks!

 

[Achy47]

Thank you for bringing up this interesting topic of hydrocarbon combustion and the blowout characteristic. I am always interested in discussions related to my field of expertise.

After reviewing the lecture notes and the references provided, it appears that your approach to calculating the blowout characteristic is valid. The use of polynomial expressions for enthalpies and the consideration of different molecular weights are both important factors in accurately predicting the blowout envelope. Additionally, the use of the atomic species conservation method is a more general and comprehensive approach compared to the species mass conservation method.

However, the fact that your results show the blowout envelope peaking at an equivalence ratio of 0.8 instead of 1.0 is unexpected and may require further investigation. While it is possible that combustion is more stable at light-lean conditions, it is important to ensure that all other parameters and assumptions are correct. It may also be beneficial to compare your results with experimental data or other theoretical models.

In terms of calculating relative reaction rates, it is important to consider the temperature and pressure conditions, as well as the specific reaction mechanism being used. It may also be helpful to consult with other experts in the field or conduct further research on the topic.

Overall, your approach and results seem to be sound and acceptable. However, as with any scientific research, it is important to continuously question and refine our methods in order to gain a better understanding of the phenomena being studied.

Best of luck with your research and please feel free to reach out with any further questions or discussions.