- #1

imadagron89

- 7

- 0

PV=nRT

What I know:

Auto Ignition Temp of 93 Octane = 280C or 553.15K

Auto Ignition Temp of Ethanol = 365C or 638.15K

My work:

First I want to find how many moles can fit inside of a single cylinder of a 2.5 liter engine 4 cylinder engine. 2.5L/4 = .625L.

Assuming when the pressure is in the downward position the atmospheres = 1

Temperature for this example when the cylinder is downward = 311.15K

So plugging information into the equation we get

1*.625L = n* .082(L atm K−1 mol−1) * 311.15K = 0.0244960669114967 mole

Now when the cylinder is completely in the up position the volume decreases from .625L to 0.05 L. I want to figure out what make pressure we can have given the moles we just calculated for since it won't change.

P(atm) *.05L=0.0244960669114967 * .082(L atm K−1 mol−1) * 553.15K = 22.2219 atm

22.2219 atm = 326.57 psi.

Since the volume decreased 12.5 times, we can assume the pressure inside the cylinder if starting at 1 atm would increase to 12.5 atm or 183.75psi.

326.57 psi - 183.75psi = 142.82 psi. So what I get is that basically this fuel will never achieve the ability to detonate until ~143 psi which is not the case. Usually 22psi is the limit you can go before you start entering dangerous territory. What am I doing wrong? I know this is calculated for a perfect world but its not anywhere near what I know is the right answer. What am I doing wrong?