Hi all!  This is my first post, and looking forward to interacting with everyone for my little side project.  I am not a chemist or chem engineer.  To my partial dismay, I am an electrical engineer that happens to be a car performance nut who loves to learn new topics.  I did take 2 semesters of organic chemistry and a semester of thermo, however it didnt do much for me because I didnt care at the time.  Now I do. .  

Anyway, I am currently writing a spreadsheet tool for learning about how engines are effected by geometery, rpm, fuel mixtures, compression ratio, etc.  One of the things that has gotten me started on this is the lack of learning guides that show how all of this interacts.  There are desktop dynos which cost lots of money which show this in a way, but its only meant for end to end information.  I wanted to create a free tool that anyone can use.  This partly came about when I finally had to the chance to pickup John B Heywood's "Fundamentals of Internal Combustion Engines."  Holy crap this book rocks.  While I have alot of the information I need from this book, a few things are still lacking.  These things that are lacking both in data and some understanding on my part.

This brings me to my question. 'Finding Specific Heat Ratios...'  Becaue the compression cycle is a isentropic (or that is what i assumed... no heat loss), I used the equations that would net me this:
    p2 / p1 = (v1 / v2) ^ (gamma)
    T2 / T1 = (p2 / p1) ^ [(gamma - 1)/gamma]
with gamma being the specific heat ratio - cp/cv.

Since I know my start data of pressure and temperature, I was using them to calculate the next crank angle (or volume position)... and using this progression until I get to the end of the compression cycle.  

Now it is my understanding that specific heat (or heat capacity) is temperature dependent.  Isnt that a little recursive since my equations require me to calculate pressure first and then temperature?  Or is it allowable to substitue and come up with:
   T2/T1 = ([v1 / v2]^[gamma])^[(gamma - 1)/gamma)]

This would allow me to calculate temperature first to factor into the specific heat?  I dunno.  This is where I get horribly confused as this is new to me.


I appreciate your help and patience with me.  Thanks!
Frank

   p2 / p1 = (v1 / v2) ^ (gamma)
    T2 / T1 = (p2 / p1) ^ [(gamma - 1)/gamma]

i am not sure if the perfect gas assumption is valid for the conditions inside an internal combustion engine.

the equations you got from http://www.grc.nasa.gov/WWW/K-12/airplane/compexp.html are all based on the perfect gas assumption, ie. PV = nRT. This assumption is only valid at conditions below 5bar. Any chance your internal combustion engine operates below 5bar?

I would recommend you to get hold on thermodynamic table of the fuel-air mixture. You may use perfect gas assumption to interpolate between the tabulated values, but not actually directly using perfect gas calculations.

Hello Frank,

I tried to open your excel sheet at: http://www.squirrelpf.com/site/files/tech/dd.xl
but only viewed your website page.  Any suggestions on how to view your excel sheet?

Eugene

Opps!  Thanks Borek!

Frank

Thanks!  I still have a lot planned for it and there is still alot of work left... aka dealing with the Mass Fraction Burned once I get past the specific heat!  I will also probably then incorporate the negative work output (aka work used for compression, etc) to get an somewhat more accurate model.


Frank

Hi Frank,

After many hours of searching, I have not been able to find any reasonable information.  Is there any chance that some information may exist in the reference book that you have?  

I hope that you can find a little more information on your end.

Sincerely,

Eugene

It might help some!  I am going to sit down one of these days and go thru my book some more and this document and re do some posting here.  Its been a crazy quick summer with car, racing, house, house, work, work, work.  


Frank