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!