btu's per hp
btu's per hp
(OP)
Is there a formula for figuring out how many btu's are consumed per horsepower. In other words, gas has 125,000 btu's per gallon, theoretically at 100 percent effiency how far would this take a 3500 vehicle rated at 200 hp. I realize friction among many other varibles come into play, just looking for ballpark, thanks





RE: btu's per hp
About 1/3 the total heat released by the fuel goes to the cooling system, about 1/3 to the flywheel and about 1/3 out the exhaust pipe.
Friction is relatively small with most being in the rings.
There is also a bit through windage in the crankcase and through driving the oil pump.
A little is lost in pumping air.
A little is lost to accelerating and decelerating reciprocating weight.
Other very variable losses are through ancillaries like alternator, power steering, air conditioning, water pump etc.
All of the above vary a lot with different engine size and fuel type.
Also, comparable products from various manufacturers vary to a lesser degree from individual design details.
For comparable engines, the main factors effecting thermodynamic efficiency are compression ratio, expansion ratio, cam timing, surface area to volume ratio of the surfaces contacting the charge during the compression and power strokes, coolant temperature and conductivity of the materials.
Regards
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RE: btu's per hp
A 3500 lb vehicle would only use 200Hp runnig at 150+ miles/hr if it has a low drag coefficient.
200HP is 1,500,000 BTU/hr If Gasoline has 125,000 BTU/gal, 12 gallons/hr. In 1 hour, you could travel 150 miles on 12 gallons, 12+ miles/gallon.
RE: btu's per hp
A 120 cid engine at WOT will pump about the same theoretic CFM as a 350 cid engine at 1/3 throttle opening, with only half the internal friction.
Just guessing the vehicle mileage through fuel BTU's is only a small fraction of the total equation.
Franz
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RE: btu's per hp
My real question is, is it mathematically possible for the likes of Charles Pogue, Fisher, Smokey Yunich to get over 100mpg. Is there enough energy in a gallon of gas to carry a vehicle that distance?
RE: btu's per hp
Reality:
For a conventional vehicle to get 100 mpg, it would barely run over idle, a real tiny engine (swept area), stripped of all inertia bound weight, coasting downhill with a strong tail wind, and a huge flywheel. I don’t really see how.
Pogue and the Fish carburetor guru groups are nothing but charlatans and never proven outside of questionable unsubstantiated non verifiable third party anecdotes.
They were never bought out by the oil companies, the government didn’t "lose the patents", they didn’t magically "disappear". Take one of these units plus their most vocal advocate and install it under recognized emission laboratory conditions with third party non-biased witnesses and lets see the actual results.
Our engines today are approaching their limits for thermal efficiency, dont expect any significant improvements over what they are currently. Any improvements will be in parallel energy storage (hybrid, kinetic, etc).
Franz
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RE: btu's per hp
If you want 100 mpg, buy a moped. If you want 50 mpg, buy a Japanese micro car like a very small Dihatsu or Suzuki
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RE: btu's per hp
Inside it was about as roomy as a Focus.
It was very light, had a high efficiency 3 cylinder, manual trans, and great aero.
Performance was pretty good due to the light weight and aero.
http:/
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: btu's per hp
There is a force resisting motion due to friction and air resistance, which is so and so many Newtons. Multiplying top and bottom by metres, the resistive force is so many N*m/m and N*m is an energy unit called Joules. So the resistive force can be measured in J/m or kJ/km.
What that means is the resistive force is just telling us the energy required to go a distance, and taking its reciprocal, the resistive force tells us how many km/kJ the vehicle is capable of.
In imperial units that is saying the (reciprocal of) the resistive force is just a measure of how many miles/BTU you can get.
So to get an MPG figure, now isn't difficult
Miles per gallon = miles per BTU * BTUs per gallon.
As others have said, the BTUs per gallon require some assumption of engine efficieny, eg BTUs per gallon for the vehicle might be 30% of the figure you gave for BTUs in the fuel.
I'm not going to do any calculations for force resisting motion, as what one person finds an acceptable vehicle might be considered a joke to somebody else. However its easy to estimate from frontal area, coefficient of drag, etc.
Volkswagen created a street legal prototype (the so called cigar car) which consumed 1 litre per 100 km, which is 235 MPG US. 100 MPG is achievable by combining
(1) an efficient engine
(2) a low coefficient of drag
(3) a low frontal area
(4) driving well
RE: btu's per hp
I came across a calculation I have done some time ago, assuming a more efficient engine put in a Loremo and travelling at constant speed.
For all I know, it could be full of mistakes, but something in it might be useful to somebody.
CODE
0.35 lbs of fuel per horsepower hour
equals 0.21 kg per kilowatt hour
which gives 4.69870971 kWh / kg of fuel used.
Rolling resistance
Mass 450 kilograms
Add Driver and multipy by gravity
Weight 5297.4 Newtons
Use Coefficient of rolling resistance just over 1%
Roll Force 55.6227 Newtons
Air resistance
Wind resistance (1/2) * airdensity * velocity * velocity * frontalarea * coefficientofdrag
eg Loremo (1/2) * 1.2 * 27 * 27 * 1.1 * 0.20
Air force 94.9662307 Newtons
Add air resistance and rolling resistance together
Air force 94.9662307 Newtons
Roll force 55.6227 Newtons
Total force 150.588931 Newtons
= 0.0418302585 kWh / km
which gives 23.9061396 km per kWh
Finally, let's assume a compact fuel, eg diesel, rather than a less dense fuel like petrol.
Fuel Density 0.86 kg / litre
Fuel economy
Now we just need to multiply things together:
How good the car is at getting miles from energy
how good the engine is at getting energy from a mass of fuel
and how dense the fuel is.
23.9061396 km per kilowatt hour
* 4.69870971 kWh / kg
* 0.86 kg / litre
Fuel economy = 96.6020889 km / litre
ie 272.272246 UK miles per gallon
RE: btu's per hp
Also Loremo won't achieve that Cd in practice. A looks low as well - draw a box 3.3 feet square and sit two people side by side in it.
Crr is a tad optimistic, for grooved tires.
And your final drive would appear to be at least 15 % less inefficient than any I've seen.
But yes, that's the way to do it.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: btu's per hp
Pat, I think that references to 50mpg (Imperial gallons?) only being achievable in 'micro cars' aren't all that fair.
The latest crop of diesel vehicles from Peugeot and Ford of Europe are proving that (shared engine technologies).
A c-class vehicle will achive 50mpg, no problem and CD class are approachng these levels.
As for petrol engine technology development, what about the introduction of direct injection and the possibility of increasing the performance of pistons and combustion chambers by ceramic coatings?
Bill
RE: btu's per hp
And that is, to be honest, easy.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: btu's per hp
I forgot about the recent developments of light weight high speed diesels in Europe. We don't see many of them here.
Last time I was in Europe (about 10 years ago) I had a Reno 2 litre diesel. It was a quite slow of the mark, a bit noisy, but performed OK on the autobahn. It seemed to use as much fuel of a more expensive fuel as something like a Suzuki Swift of the era.
I guess things have changed.
Regards
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RE: btu's per hp
I often think that the best way to market diesel vehicles in the USA would be to focus on this attribute. If the weather is nice, fill your car up. If it's really cold, wait until a warm day.
RE: btu's per hp
Calibrators are now able, using electronic control of turbo and fuel injection & timing, to dial-in fat torque curve, giving the driver a big-engine feel. These torques are also enabling quite high gearing for cruising. A 30mph/1000rpm top gear is not uncommon; accel is still capable due to the torques.
Check this, the writer notes a top speed of 124mph and 47mpg imperial:
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Bill
RE: btu's per hp
Hi Greg
I used the manufacturers quoted figures for the mass, area and drag for the Loremo, vieable at http://www.loremo.com/daten_en.php. If you cannot get two people side by side in that area, try putting them one behind the other like in a Jetcar (pictured above), and the area might still be achievable.
Point taken that there are no transmission losses in the calculation.
I used engine figures from a press article by John Mortimer.
A google search on
"lb/hp-hr" "city car" mortimer
will throw up a link for verification, but I think the article itself is pay-to-view.
The coefficient of rolling resistance was from a thread on eng-tips - if I remember rightly. I tried to take the lowest street legal figure achievable, so the figure is intended to be low: if the aim is best milage one has to push the limits of area, drag, mass, etc.
If I redo a similar calculation sometime I'll put some transmission losses in: gearbox and final drive. I guess I should find a reference for the rolling restiance or change the figures too, as you're given a hard time on eng-tips if you cannot support what you are saying, l.o.l!
RE: btu's per hp
On the other hand I knew propane had less btu's, but it is vaporized before it reaches the engine and these people sure aren't getting great milage. Looks like I'll be building that Joe cell after all, just kidding.
RE: btu's per hp
Prius engine efficiency average 33%, max 37%. You should be able to beat that with a diesel.
yes, I know Loremo are making some amazing claims. I like the idea, and even with more realistic numbers in it still makes sense. The Cd is achievable on a prototype, but will need a fair bit of stuff that is not realistic in a light production machine.
You have reminded me that Cd and A is a bit of a misnomer. In cars the surface area is really what matters, frontal area is not the most important parameter on a well deisgned car. That is, I can get lower overall aero with a larger A sometimes.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: btu's per hp
RE: btu's per hp
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: btu's per hp
As a side note, the US EPA has set a new standard for running the MPG tests that are posted on vehicles. The new test more closely mimics how people drive. The results are most cars will have a 8% reduction in MPG for city and 12% for highway. The high effiency vehicles ove 30 mpg will be hit 15% / 20%. The hybreds will get wacked 20%/30%. Again, hybreds are just a fad, you can't add 500 pounds of motors and batteries and get that much farther ahead.
RE: btu's per hp
He considered weight only, and considered maximum power. This indicates he knows very little about the subject, or meant to be very specific in looking at thermodynamics.
He did quote a BTU value for the fuel, so that should exclude all fuels not of that value.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: btu's per hp
RE: btu's per hp
Its not the fuel price, its, not anything we have control over. The US public wants a car that is bigger than their neighbors so if they collide, the neighbor will die and not him. Second, we want cars that will pull a 12,000 pound trailer (just in case we need to tow away or nieghbors car from a crash site), go 0 to 60 in under 6 seconds (just in case we have to evade our neighbors car), have every electric gadget known to man (because our neighbor does, at a cost of fuel), AC to chill us to the bone (never see the neighbors window down, heck the AC drops my milage by 10% when I run it). Its not the fuel, its peoples perception of what they think they need.
RE: btu's per hp
The reason for many linear engines is to have a longer power stroke than intake, then only operate the number required to propel the vehicle. No crankshaft engine will have the same efficiency at different loads and speeds. The power to the wheel varies from little to a lot depending on terrain, speed and if you are accelerating.
RE: btu's per hp
That would help if that were a major source of engine inefficiency, however it is not. Virtually all the fuel is burned and turned into heat well before the end of the power stroke. This means that any improvement can only be small as there is not much room for improvement. Like I said earlier, in a modern petrol engine, about 1/3 goes to the cooling system. Vapourising the fuel won't change that very much. About 1/3 goes out the exhaust. Vapourising fuel won't change that at all.
Vapourising fuel might give a slightly faster burn rate. This will require less timing advance to avoid detonation. This later ignition will give less time at higher cylinder pressures, so a little less will go to the cooling system, also less power will be consumed pushing against cylinder pressure on the late compression stroke and all available heat will be generated earlier in the power stroke so more work can be extracted, but at this stage it will also put more heat into the cooling system. There might be one or two percent in it. A long way short of 100 miles per US gallon.
Smokey might have obtained very high MPG figures, but it was not down to the fuel heating. He had many other significant mods, not the least of which was half an engine. I strongly suspect he used smoke and mirrors as a diversion from the real causes. While everyone focused on the fuel heater, no one noticed other features that do work.
State of the art very small engine, light weight, good aero, hard small tyres, constant low speed, simple light weight transmission are the secrets to low fuel consumption
Regards
eng-tips, by professional engineers for professional engineers
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RE: btu's per hp
I have a home heater that is 92% effcient, the exhaust of the heater leaves the house just 30 degrees warmer than the air intake to the burner, it condeses the water by preheating the air. So if we want cars that can achieve this kind of efficency, lets go back to the steam car, or put a combined cycle system where the exhaust gases are make steam that drives turbines to get energy.......
RE: btu's per hp
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: btu's per hp
RE: btu's per hp
RE: btu's per hp
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: btu's per hp
RE: btu's per hp
The trouble is that Carnot tells you what the max efficiency of the entire system is going to be, so until we can figure out how to extract all of the enrgy at high temperature, we are never going to see much better than 60%.
Of course, the reduction in fuel consumption is much greater in going from 20% to 40%, than 40% to 60%.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: btu's per hp
RE: btu's per hp
RE: btu's per hp
Caterpillar G16CM34
6100 bkW @720 RPM
7671 BTU/bkW-Hr
7909 BTU/ekW-Hr*
44% Efficiency
0.5 Gm/BHP-Hr NOx
power output 5.9 MWe
cylinders & arrangement 16Vee
cylinder output 380 kW/cyl
bore 340 mm
stroke 420 mm
speed 720/750 rpm
fuel Natural Gas Methane > 70
Fuel Cons 7909 BTU/ekW
RE: btu's per hp
RE: btu's per hp