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TwoSeven
18th June 2006, 19:31
Ok, given a fuel flow rate of 36.68lb/hr I want to calculate the btu/hr and from that the final hp. I'm expecting a number above 77hp but dont seem to get it.

Anyone have an ideal formula to do it ?



Biggest problem I am having is finding correct values for btu of petrol and a formula that actually works.

boomer
18th June 2006, 19:38
Forty Two..

cowpoos
18th June 2006, 20:45
Ok, given a fuel flow rate of 36.68lb/hr I want to calculate the btu/hr and from that the final hp. I'm expecting a number above 77hp but dont seem to get it.

Anyone have an ideal formula to do it ?



Biggest problem I am having is finding correct values for btu of petrol and a formula that actually works.
depends sooo much on the efficiency of the engine....bettr to track down a HP rate using cfm of air flowed....as your engine is real just an air pump....not a fuel burner....


ps: why do you want to know this....it seems very much like fairy bullshit to me...

TwoSeven
18th June 2006, 21:02
If you want v.e use 0.85 and if you need airflow, just assume 12.5:1 mix. - but those are not important to the formula, just modifiers.

I need the energy of the fuel in brake mean HP, hence the question :)

cowpoos
18th June 2006, 21:16
I need the energy of the fuel in brake mean HP, hence the question :)

thats why I think it fairy bullshit for you asking....how efficient is your engine??? theres a massive difference between a OHV briggs and stratton and lambourghini V12....theres forces to drive....weight of engine parts....thick-ness of the oil...abient temp....shit loads of variables....

the end result is your gunna get a figure which is meaning-less !!! their will be different hp figures for two engines coming off the producton line next to each other...

Motu
18th June 2006, 22:12
When I was a 2nd year apprentice I sat in a cold prefab in St Pauls St on tuesday nights and did calculations about btu's - I didn't have a clue what it was about then,nor do I now.But I remember a gallon of petrol weighs 1 lb,that was the only easy bit.....

Ixion
18th June 2006, 22:24
Uh, treacherous thing, memory, isn't it , as we get older.

The calorific value of petrol (no idea what octane etc) is about 19000 BTU per pound weight, if that's any help.

However , the conversion from BTU/hr to watts is 0.2931. Which would give a figure of about 272 hp. Which sounds rather optimistic?

bobsmith
18th June 2006, 23:05
When I was a 2nd year apprentice I sat in a cold prefab in St Pauls St on tuesday nights and did calculations about btu's - I didn't have a clue what it was about then,nor do I now.But I remember a gallon of petrol weighs 1 lb,that was the only easy bit.....

Uhhhh a US gal of fuel weighs about 5.99lbs.. and british gallon isn't that much smaller....

Ixion
18th June 2006, 23:12
Uhhhh a US gal of fuel weighs about 5.99lbs.. and british gallon isn't that much smaller....

Imperial gallon is bigger than US one. 4.5 litres versus 4 litres roughly. Yanks are behind the times, in 1766 they opted to stick with the obsolete Winchester measurerments , instead of the later London ones.

A gallon (Imp) of water weighs ten pound. Petrol is lighter but not that much lighter. About 7 lb, roughly.

ZeroIndex
18th June 2006, 23:15
Forty Two..
by that, I gather you have recently watched the Hitchhikers Guide to the Galaxy

bobsmith
18th June 2006, 23:22
Imperial gallon is bigger than US one. 4.5 litres versus 4 litres roughly. Yanks are behind the times, in 1766 they opted to stick with the obsolete Winchester measurerments , instead of the later London ones.

I say the americans and the brits are both fucking slow. the rest of europe knew that the metric is the only way to go... I can't believe seeing american textbooks that has values for things like gravitational acceleration and specific mass of water in imperical units.... Oh and the unit of mass is pounds and the unit of force is.... oh also pounds... WTF!!!!!!!!!

bobsmith
18th June 2006, 23:29
Ok so I just looked up all the constants and:

Specific gravity of vehicle petrol = 737.22kg/m^3 = 0.73722kg/Litre
1 Imperical gallon = 4.54609188 litre
1 Kg = 2.20462262 pound

so:

1 Imperical gallon of fuel is:

4.546 * 0.737 * 2.2 = 7.4 lb (2s.f)

right... now everyone can go to sleep now...

Ixion
18th June 2006, 23:32
Metrichumbug. Woz the deal with a system where everythings a kilosummit. What's wrong with ells and firkins and leagues and minims and perches anyway. Rot set in when they made us give up our real money and settle for this danged funny money. Never bought as much. Petrol used to be 3/4d a gallon then. Look at it now, all on account of meddling with the money and measures.

Motu
18th June 2006, 23:41
The USA has actualy signed up for Systems International (suposed to be in French,but can't be arsed tooking it up) so in theory they are as metric as any other country in the world.But they will never force their populace to change to metric,that old free will thing again.They like having that last Imperial yoke apon their shoulders.Good grief...seven sixtyfourths and three thirthyseconds...talk about making it hard for yourself....

bobsmith
18th June 2006, 23:46
it is strange though, I thought they would at least publish their textbooks in metric if they are indeed supposed to be going SI

Ixion
18th June 2006, 23:58
so how come the UK speed limits are still in mph? As are the speedos on Pommie vehicles? I blame the Welch. It's all Biff's fault.

Kickaha
19th June 2006, 07:02
so how come the UK speed limits are still in mph? As are the speedos on Pommie vehicles? I blame the Welch. It's all Biff's fault.

Everything is Biffs fault :yes:

marty
19th June 2006, 07:30
they can't change to metric - i'd have to buy a completely new tool box. at least i won't have to unless i work on those french fly-boy thingies...

imdying
19th June 2006, 09:13
by that, I gather you have recently watched the Hitchhikers Guide to the GalaxyHush young pup! It was a great book long before it was an average movie...

F5 Dave
19th June 2006, 09:42
You mean Books: 5 in an increasingly misnamed trilogy.


So by the logic applied with measuring fuel; does this make my old Victor 3.3 I had as a teenager heinously powerful? as it used to suck like an Ethiopian hooker. But it used to go through almost as much oil, so. . . :scratch: Does anyone know the calorific value of oil. I could add that to the fuel used & get a real big number.

Another revelation: getting a tune-up reduces power!! :gob:


Hey! This is a conspiracy!

Ixion
19th June 2006, 09:49
I think that what is calculated is the theoretical 100% efficiency horsepower. If you supplied that amount of fuel to a magically 100% efficient engine, you would get that horsepower.

As we all know, the internal combustion engine is horribly inefficient.

So in reality the actual horsepower , as measured on a dyno, will be much much less.The ratio between theoretical or actual being the overall heat efficiency of the engine .

In the example case , about 77 / 272 = 28% efficiency roughly. The "missing" 195 horsepower is lost through the zorst, as noise, as waste heat in the radiator, as friction etc.

Or maybe it doesn't mean anything. I'm not quite sure what is being measured here.

Fooman
19th June 2006, 09:50
Ok, given a fuel flow rate of 36.68lb/hr I want to calculate the btu/hr and from that the final hp. I'm expecting a number above 77hp but dont seem to get it.

Anyone have an ideal formula to do it ?



Biggest problem I am having is finding correct values for btu of petrol and a formula that actually works.

I'll do it in S.I. units and then convert to hp:

Flow rate = 36.68lb/hour = 16.63777 kg/hour = 0.004622 kg/sec

Calorific value of petrol ~ 43500 kJ/kg

Therefore 0.004622*43500 = 201 kJ/s = 201 kW = 269.6 hp

I'm not sure if the calorific value is the low (net) calorific value, but it shouldn't make too much difference. The difference between my answer and >77hp is either:

1. I cocked it up.

2. The overall thermal efficiency of the engine in question.

If you want to go the BTU/hp route, I get 18701 BTU/lb for petrol, converted from the value above ( 1 btu/lb = 2.3260 kJ/kg). Also, 1 BTU/sec = 0.70678 hp:

36.68 lb/hr = 685974 BTU/hr = 190.55 BTU/sec = 269.6 hp.

Sources: Bosch Automotive Handbook, 3rd ed.

Also, if you have access to Microsoft Excel, the "CONVERT" function can convert between a lot of imperial and S.I. units, e.g. =CONVERT(50000,"W","HP") will convert 50 kw into HP. You have to string a few together if there is no direct conversion (e.g. BTU/hr to kW has to go BTU/hr to BTU/sec to J/sec to J/sec*1000 to get kW)

Hope this helps.

FM

Ixion
19th June 2006, 09:57
Ok

So, two different people, different methods , different sources, come up with the same answer (difference between my 272 and your 269hp being the difference bewteen my 19000 btu/lb and your 18700 - prolly varies with octane, brand too). So , either that IS the answer, or we're answering the wrong question. Over to original poster.

Fooman
19th June 2006, 10:09
Ok

So, two different people, different methods , different sources, come up with the same answer (difference between my 272 and your 269hp being the difference bewteen my 19000 btu/lb and your 18700 - prolly varies with octane, brand too). So , either that IS the answer, or we're answering the wrong question. Over to original poster.

Yup. The real simple answer is 1 lb/hour of petrol = 7.35 hp ( x the thermal efficiency of the motor).

What's really interesting is this quote I found in the Bosch Automotive Handbook:



Calorific value of air-fuel mixture

The calorific value of the air-fuel mixture determines the engine output. Assuming a constant stoichiometric ratio, this figure remains roughly the same for all liquid gases and fuels (approx. 3500 - 3700 kJ/cubic metre).


Which sort of makes sense. To get more power, stick in more air/fuel, rather than a specific type of fuel.

FM

bobsmith
19th June 2006, 10:15
I think you two are on the right track. Referring to :

http://ffden-2.phys.uaf.edu/102spring2002_Web_projects/Z.Yates/Zach's%20Web%20Project%20Folder/EICE%20-%20Main.htm

for effiency of internal combustion engines:

thermal effiiciency: ~ 26%
Mechanical efficiency: ~94%
so Overall efficiency: 0.26 * 0.94 = 24%

So multiply 270hp by 24% = 65hp... much closer to 77hp

ZeroIndex
19th June 2006, 10:26
Hush young pup! It was a great book long before it was an average movie...
yes i did read the book.. I even have it on AudioBook format.. I happen to think the movie was quite a good attempt at the book.. just like Fight Club..

imdying
19th June 2006, 10:30
Oooh, audio book... and ahh, how big would that be.. :innocent:

ZeroIndex
19th June 2006, 11:10
Oooh, audio book... and ahh, how big would that be.. :innocent:
44MB.. it's 5 hours long.. I'll upload it onto a download site, and post the link on this thread and also PM you the link..

Firefight
19th June 2006, 11:16
just like Fight Club..




Bloody hell, you mean there's a book and a movie out about us ???

hear that Rendy, Paco and Co we are famous !!!


Fight Club of 22 rules !!!!


F/F

ZeroIndex
19th June 2006, 11:25
Bloody hell, you mean there's a book and a movie out about us ???

hear that Rendy, Paco and Co we are famous !!!


Fight Club of 22 rules !!!!


F/F
the movie left out some interesting stuff that is in the book/audiobook.. the audiobook is quite more involved, more anarchistic and in a more 'audibly' violent way than the movie.. it is 86MB and about 5 hours too.. if you ask nicely, I might upload that audiobook next..

Two Smoker
19th June 2006, 11:28
Bahahahahahahaha!!!! :killingme

imdying
19th June 2006, 11:31
the movie left out some interesting stuff that is in the book/audiobook.. the audiobook is quite more involved, more anarchistic and in a more 'audibly' violent way than the movie.. it is 86MB and about 5 hours too.. if you ask nicely, I might upload that audiobook next..
/me asks nicely :D

ZeroIndex
19th June 2006, 11:37
/me asks nicely :D
shall do it then.. my upload of Hitchhiker is uploading at a lousy 7KB/s (and says 1 hour 20 minutes approx.. so I'll start uploading Fight Club after that (if i'm in front of my computer)

Motu
19th June 2006, 11:47
Sources: Bosch Automotive Handbook, 3rd ed.
FM

Ah,3rd edition - you lucky bugger.I had the 4th edition,it was my Bible and went everywhere with me...in a quiet moment I could take it out and read chapter and verse,a fantastic book.But one day I didn't take it with me and it was stolen from my car.So I got the 6th edition for a replacement - just got to be even better eh? WRONG!! The whole book has changed,there is nothing from the old book in this one,and it's all written in incomprehensable ''new speak'' - it's made for some engineer who has come out of the modern schools,not for hands on engineers who want simple formulas,data and guidance....I hate my 6th edition Bosch Automotive Handbook.

Btu is not mentioned at all,only in the Units of Energy conversion chart.There is talk about the p-V diagram,the thermodynamic cycle,and the T-S diagram,or temerature entropy diagram....um then the Carnot Cycle.Ah! I understand none of it!

Firefight
19th June 2006, 13:16
the movie left out some interesting stuff that is in the book/audiobook..





I am not aware that a movie was made about us !


F/F

ZeroIndex
19th June 2006, 13:22
I am not aware that a movie was made about us !


F/F
the fight club where brad arm-pitt laughs at someone hitting him in the face repeatedly.. the same fight club that edward norton throws himself down several flights of stairs..

Fooman
19th June 2006, 13:36
Ah,3rd edition - you lucky bugger.I had the 4th edition,it was my Bible and went everywhere with me...in a quiet moment I could take it out and read chapter and verse,a fantastic book.But one day I didn't take it with me and it was stolen from my car.So I got the 6th edition for a replacement - just got to be even better eh? WRONG!! The whole book has changed,there is nothing from the old book in this one,and it's all written in incomprehensable ''new speak'' - it's made for some engineer who has come out of the modern schools,not for hands on engineers who want simple formulas,data and guidance....I hate my 6th edition Bosch Automotive Handbook.

Btu is not mentioned at all,only in the Units of Energy conversion chart.There is talk about the p-V diagram,the thermodynamic cycle,and the T-S diagram,or temerature entropy diagram....um then the Carnot Cycle.Ah! I understand none of it!

Yeah, it's a great wee book. I got it at the start of my 1st professional year at uni on the recommendation of a classmate - He had to get it ordered in especially, as it's not too common. Used in heaps, more so for the general engineering data than the automotive stuff. The fact that it is translated from German does make it a bit obscure at some stages.

As for thermodynamic cycles, the stuff I'm involved in use the Brayton and Rankine cycles, rather than the Carnot...good stuff!

FM

ZeroIndex
19th June 2006, 16:32
shall do it then.. my upload of Hitchhiker is uploading at a lousy 7KB/s (and says 1 hour 20 minutes approx.. so I'll start uploading Fight Club after that (if i'm in front of my computer)
having problems with uploading, but am still persisting with it..

ZeroIndex
20th June 2006, 16:34
alrighty.. here's the link for my AudioBooks post: http://www.kiwibiker.co.nz/forums/showthread.php?p=655384#post655384

have a look, and post replies etc..