Seems that you're enjoying the challenge of figuring this out too. I'm really happy to have someone so capable helping to figure this out with me. Thank you Chet. I'm still not up to speed yet and getting somewhat lost in some of the calculations. I'll post up some specific questions in the...
Thoughts... It's new territory for me. I'm having to look up a lot of the things you're mentioning to properly understand them, so I'm not quite eye to eye with you yet. Still a day or two worth of posts behind on the learning curve.
However, I have used equations for Adiabatic Compression...
Looks like a good book to have, although at over $100 used it's a little too spendy for my purposes.
If there's a way to do it without referencing the book, that would be my preference.
You're ahead of me, which is fine. Once it's here, I can soak up the information at whatever rate.
I'm not sure that the final temperature is what I expected. Seems high, but if that's what it is, then that's what it is.
I'm guessing that for adiabatic compression, we'll need to average the...
Whatever's easier. As long as the results accurately indicate a trend. I pretty much don't care how precise the product is, as long as it's repeatable per individual air/fuel ratios.
The ultimate reason behind my trying to figure this out is, engines make more horsepower with richer than...
Based on this percent of total mass composition of air breakdown, in/at engineeringtoolbox.com
% of Total Mass, Air
Oxygen .... 23.20%
Nitrogen ... 75.47%
Carbon Dioxide .. 0.046 %
Hydrogen ... ~ 0%
Argon ... 1.28 %
Neon .... 0.0012%
Helium ..... 0.00007%
Krypton .... 0.0003%
Xenon ...
I really appreciate your help with this Chestermiller
Imperial is easier for me to relate to. However, SI seems easier to calculate with.
Let's work in SI.
It seems that using the mass ratio to calculate nitrogen content is slightly more accurate than using the molar ratio. If there's not...
Since we're doing everything by weight, wouldn't you calculate the nitrogen weight from the oxygen weight and identify the number of moles N2 by it's weight per mole?
(12.5 * 32g/mol) = 400 g
400g / (79/21) = 1504 g
1504 / 28g/mol = 54 moles of N2
Simply basing it on the mole negates the...
Apparently the air composition of 79/21 is based on volume. By mass it's 23.2% O2 and 76.8% N2 and other inert gasses.
Adjusting for that brings the ratios quite a bit closer to what I expected to see.
15.09:1 for Octane
8.98:1 for Ethanol
6.46:1 for Methanol
The total mass now also balances between pre and post combustion
Post combustion
H2O ... 0.357452336 lb ... 8.03%
CO2 ... 0.7761953474 ... 17.44%
N2 ... 3.317310438 ... 74.53%
Total .. 4.4509581214 ... 100.00%
Still trying to wrap my mind around the concept of Moles.
0.2518309847 lb?
12.5
0.8818166987 lb.
53.7137754143
3.317310438
4.1991271367
16.6743863633 : 1 ?
Had a thought. I think the numbers are off because the actual ratio is slightly lower than the 14.7 rounded figure I used to calculate fuel mass from air mass. One end based on rounded figure, the other end from the actual precise stoichiometric calculation. I'll math it out tomorrow and...
I only barely grasp what I've been able to deduce in a week of trying to figure this out on my own through google searches and YouTube lectures. I'll take that as a compliment. Thank you Chestermiller.
I believe I understand roughly how to write a balanced chemical reaction equation, however...
Hi guys, 42 year old engine hobbyist here, not a student. I've had great luck figuring out my questions in this portion of the forum in the past and look forward to your input. Keep in mind that I'm not formally educated, so if it's possible to dumb something down a bit I'd appreciate it...
BINGO! Thank you.
So in the spreadsheet it looks like =0.61121*2.71828^((18.678-(T/234.5))*(T/(257.14+T))) Where T is the cell in the spreadsheet that I enter the value for temperature.
As stated in the description of the equation, it's close but not 100% accurate. Good enough for what...
Thanks berkeman. Gave 'em a look. Nothing clicked. Perhaps it will become more clear to me as I learn.
So, from what I've read, and this part is starting to make sense... The statement "how much water air can hold" is more of an over simplified point of view than a statement of fact. It...
Hi guys and gals. Hobbyist, not a student. I've had great input here in the past. Thank you in advance for any direction and help figuring this out.
-Seth-
1. Homework Statement
I'd like to learn how to calculate relative humidity, saturation, and dew point under differing pressures and...
I can fumble my way through equations, but can't claim any familiarity. I've tried using Bulk Modulus Elasticity and density to the power of 0.5 (Hooks Law), but the results don't seem linear with pressure.
The more layman you can convey it, the better. If I get stumped I'll take the time...
Thank you for the reply boneh3ad. Would I be off base to assume that mass flow through a convergent or conical nozzle would follow the same principal as a convergent-divergent nozzle? Also, how would I go about calculating mass flow at differing pressures and temperatures? For instance, a...
I'm interested in identifying mass airflow through a choked convergent or conical nozzle.
I've found some web info claiming that mass airflow through a nozzle becomes primarily a linear function of the inlet pressure, and doubling the inlet pressure doubles the flowrate.
Further research...
This isn't homework, I'm a hobbyist, not a student. Posting here because questions I've previously posted were moved to this section. My intent is to better understand humidity and it's role in compressed air for an automotive application. All help and direction is greatly appreciated. Thank...
Been trying to figure this out all day and the light bulb just came on. Just going to jot it down here for my future reference...
Figuring out pressure and pressure ratio with a known compression ratio/volume ratio.
Simple really. It's the ratio to the power of 1.4
10:1
10 to the...
Hey Cal,
Per the forum rules, I can not offer any help without proof that you've attempted to figure it out on your own. Perhaps you can share some specific details about your inquiry and particular steps you've taken to solve your question?
What is the total head?
Pipe ID?
Pipe length...
Woo Hoo! (doing a little victory dance) :biggrin:
In automotive engine vernacular, what you call volume ratio, is referred to as the compression ratio and is usually expressed as 3.15:1 (in this case). Until now, that's the only term I knew to use.
I was writing when you posted and missed your reply earlier. Thank you for the verification and input.
So, I can use the same equation to find the temperature upon decompression? Let's try it out!
k = 1.4 so the exponent is 0.286
P2 = 29.4 absolute (14.7 psig)
P1 = 73.5
T1 = 294...
If the above checks out, can I apply Charles's Law to find the volume once the heat of compression is removed?
If,
V1 = 31.75 cubic feet
T1 = 466
T2 = 294
Then, 31.75 / 466 x 294 = 20 cubic feet
So, the new compression ratio, assuming a constant pressure ratio of 5 is now 5:1...
Rap, I can't thank you enough.
Reading through Wikipedia and taking notes like a man on a mission, I came upon this equation which I believe converts the numbers I have so far into a volumetric compression ratio, or pressure ratio to compression ratio.
CR = T1 / T2 x PR
I checked it...
T1 = 70°F = 294.261kelvin
P1 = 14.7psi or 1 bar
P2 = 73.5 psi or 5 bar absolute pressure
I solved for the exponent first, 1.4 -1 = 0.4 / 1.4 = 0.286
Then solved the pressure ratio, 73.5 / 14.7 = 5
Pressure ratio of 5 to the power of 0.286 = 1.585
1.585 x 294.26 kelvin = 466 kelvin
Is...
Maybe it's appropriate for this to be in the homework area. I'm drawing on memory and can't seem to work the equation out in any way that makes sense. A little embarrassing to have to ask, but would one of you guys walk me through it? Please.
Thank you for your time. I went back to the reference I used to find the Heat Capacity Ratio, and you are completely correct. I mistakenly read Ar as Air. :rolleyes:
Is this the correct equation to use in finding temperature increase with compression?
T1 = 70°F = 294.261kelvin
P1 = 14.7psi or 1 bar
P2 = 73.5 psi or 5 bar absolute pressure
In reading about the value for k, I've found that most use 1.4, which is for dry air at 20°c. I've noted that...
Hello everyone. New guy, first post.
I typically frequent gasoline engine performance forums, but my inquisitive nature has led me beyond the scope of general knowledge available within that format. I appreciate any help in figuring out the following.
Thank you in advance!
If 100 cubic feet...