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Can Your Car Get 1,700 MPG?
Xaroth writes "Given all the hubbub over EPA mileage ratings, I'm a little surprised that this one hasn't come up earlier. SAE apparently holds a contest each year to encourage students to design single-person, fuel-efficient vehicles. This year's winner achieved 1,747.4 MPG, with the press release that tipped me off pointing out that third got a 'measly' 1,194. There are more details on the competition over at SAE's site about the competition. Now, if only they could make these street-legal..." However, even the winner has nothing on top entries we mentioned in Shell's competition a few years back.
When I was working on a solar powered car in college there was one of those SAE cars next to our bay. I don't think they're all that plausible because they are little more than go carts. I think we should work toward some of the technologies they use, like superatomizing and mixing the fuel, and trying to get engines above their pathetic 30% efficiency, but 1500 mpg is a bit out of reach. Of course, I guess I should never say never.
These cars typically achieve their best mileage using a 'coast and burn' strategy. They run the engine full throttle until they reach ~20mph, then cut the engine. This way the engine is always operating at peak efficiency (no throttling losses). This driving technique could be a little impractical in stop-and-go traffic...
TERRE HAUTE, Ind., June 15 (AScribe Newswire) -- Engineering students at Rose-Hulman Institute of Technology designed a fuel efficient one-person vehicle that achieved 1,194 miles per gallon of gasoline in the Society of Automotive Engineers' Supermileage Competition, conducted last weekend near Detroit.
That performance placed third out of 24 teams in the collegiate division, a remarkable achievement for a first-year team in the competition, according to Tom Edelmayer, a technical specialist for Eaton Corporation's Engine Air Management Operations. Eaton hosted the annual engineering contest at the company's vehicle proving grounds in Marshall, Mich.
Rose-Hulman engineering students designed and constructed a one-person vehicle that is powered by a highly modified single cylinder 3.5 horsepower Briggs & Stratton engine. The vehicle is eight feet long, 26 inches wide and weighed approximately 80 pounds. It has two wheels that provide steering in the front and a single drive wheel in the middle of the back. The main structure of the vehicle is provided by a honeycomb carbon-fiber panel which rests approximately a half inch above the pavement.
The vehicle completed six laps around the proving grounds (9.6 miles) while maintaining a minimum average speed of 15 miles per hour. Edelmayer said that a typical 9.6-mile run burns an average of about 14 grams of fuel, which weighs about as much as 14 paper clips. Each team's fuel is measured before and after each run. The difference is calculated to determine the contest winner.
The University of British Columbia (Vancouver, Canada) finished first in the collegiate class with 1,747.4 mpg. The California State University-Los Angeles placed second at 1,615.5 mpg. There were 24 teams in the division this year from the United States, Canada, Puerto Rico and Mexico. Other colleges on the list included the University of California-Berkley, University of Toronto and Virginia Military Institute.
"People certainly took notice of our performance this year. Achieving over 1,000 mpg is quite an accomplishment, especially for the first year," stated Rose-Hulman Supermileage Vehicle Team President Matt Neisen.
Nine of the team's 25 members traveled to the competition. Joining Neisen were vice president Rob Lally, driver Brittney Elkins and members Tim Berowski, John Frey, Elliot Goodman, Michael Haughney, Joshua Persels, and faculty advisor Richard Stamper.
Rose-Hulman's team is supported by Caterpillar, Rose-Hulman Ventures and Rose-Hulman's Student Government Association.
http://www.solectria.com/products/accomp.html#sunr ise
And that was in 1997 with old NiMH batteries. Current LiONs would double that to around 700 miles and next generation Li-Ss should pretty much double that again to around 1,300 miles.
Government of the people, by corporate executives, for corporate profits.
Answer: To the end of the universe.
Unless you're one of those people who figures in friction from air resistance, rolling resistance, etc.
"Prefiero morir de pie que vivir siempre arrodillado!"
You can get 125 miles per gallon all ready with one of these little mopeds, And they're cheap and street legal too.
gasoline has energy content of 114,000 btu/gallon
With a Carnot engine, that means you get half of that, max, assuming perfect cooling (which doesn't really exist).
By the way, 114,000 btu == 33.41 kWh
"I assumed blithely that there were no elves out there in the darkness"
So, how much energy can you get from combusting a gallon of gas? If an engine was completely efficient, how far should it push 1ooo pounds?
This isn't an easy question to answer.
What sort of assumptions are you making on wind resistance? At 55 mph, most of the output of an engine goes into fighting wind resistance.
Which "completely efficient" are you asking about? A heat engine has a maximum potential efficiency that varies based on operating temperature, and is always (for reasonable conditions) much less than 100% of the heat energy being converted into mechanical energy.
What sort of track are you driving on? Rolling resistance is a significant factor at low speeds.
If you were driving on the moon (no air) on a perfectly flat maglev track (no rolling resistance), you could keep going almost forever on however much gas you wanted to use to get up to speed. In the real world, fuel economy seems to top out at around 50-60 mpg.
"They redundantly repeated themselves over and over again incessantly without end ad infinitum" -- ibid.
Except that's not combusting.
Gasoline that has not been oxygenated with MTBE or ethanol holds about 115,000 BTUs of energy per gallon, give or take depending on environmental conditions and a few things about the blend. Oxygenates typically reduce that value by about 3% or so.
You can never go home again... but I guess you can shop there.
With a Carnot engine, that means you get half of that, max, assuming perfect cooling (which doesn't really exist).
Sorry, that was bunk. With perfect cooling, you can get 100%. At reasonable temperatures for the hot and cold sides, the max is about 50%.
"I assumed blithely that there were no elves out there in the darkness"
Checking some classnotes there is approx 686 kcal/mol in glucose which gets converted to 219 kcal/mol of potential energy in ATP. Which means only 32% efficiency for converting glucose to the energy form used by about every cell operation inside a cell.
Now there is also inefficiency in getting glucose to those cells (and not all of it of course gets to them). Plus ATP isn't completely itself efficiently used so 10% is prolly around the correct figure for the amount of energy used of digested food.
The misquoted Simpsons line is "40 rods to the hogshead", which is about 0.0019 miles per gallon. Presumably, though, that horrendously low fuel economy is made up for by traveling more than 5 furlongs per fortnight.
Must be a bitch to take that shiny new 21 inch monitor home from the store.
If you're serious about riding as a way of life, get a Yak trailer. Light, easy to park, very little drag, and carries a lot more than they should.
The ______ Agenda
5.5 GPH at 120 knots: The brand new two-seater by Liberty Aircraft.p erformance. php
http://libertyaircraft.com/libertyxl2/
A knot being 1.15 mph, for the non-pilots here.
See subject line. I accept your rant, and raise you a hear-hear, in general.
However, you seemed to have invoked shades of a strawman - the grandparant did _not_ make any reference to a hydrogen fuel cell. It is, in principle possible to make a fuel cell that will convert fuels other than pure hydrogen into electricty (+ wastes).
That's not to say that they exist - most 'methonal' fuel cells are reformation style, where the carbon -> CO2 converstion is not used to produce power, but just to free up the hydrogen.
In principle, however, there is no theoretical barrier to a gasoline fuel cell, with high efficency (just a huge, _huge_, long list of practical ones). There _is_ a theoretical barrier to raising the efficency of an internal combustion engine.
Most of us in the metric world use litres per kilometre (actually, litres per hundred kilometres, but it's easy to convert in your head of course).
:)
I prefer this; it's easier to ask the question "how much fuel to I need to go distance x"
The submitter didn't catch this, and no one else seems to have pointed it out, but 1194.10 mpg (obtained by the Rose-Hulman team) was not the third highest mpg. Rose-Hulman was third amongst collegiate teams. If the high-school teams are included, Rose-Hulman drops to fifth place. Overall, Evansville Mater Dei (1352.58 mpg) was third, and Winamac (1235.33 mpg) was fourth. First and second remain Univ. of British Columbia, and Cal. State LA.
The PDF on the web site says the engine in question is a Briggs & Stratton Corporation (Model 091202 Type1016E1A1001). The engine is air cooled, four cycle, with a 2.61 kw (3.5 horsepower) rating at 3600 rpm.
It's a tiny 1 cylinder engine.
-ted
...if they can do it at 55MPH. Getting insane milage at 15MPH, while cool, doesnt seem very useful as a route toward replacing the current gas guzzlers in use. What ever happend to tinkering with things like the California Commuter ???
The way to get good fuel efficiency with a standard design engine is twofold - make the car light, make the engine underpowered, and go slow. If the engine is always struggling, it's always in the power band, and always efficient. Hence the reason that a Geo Metro gets great gas efficiency.
That's exactly opposite to what i've always heard. My recollection is that maximal efficiency is roughly at torque peak (ignoring such things as aerodynamics and gearing), and that underpowering a car kills the mileage. Case in point: a particular truck is offered in an economy V6 and a V8 trim. The V8 got better mileage because the V6 was always running full throttle (above the powerband).
Your Geo may get good mileage, but it's crap, and I won't drive one. I have an MR2 that gets 30 MPG and handles nicely, so I don't have to.
"We returned the General to El Salvador, or maybe Guatemala, it's difficult to tell from 10,000 feet"
If you look at a torque vs RPM graph, you'll see that torque rises then usually falls off, but on a naturally aspirated engine, it tends (not in all cases, due to VTEC, VVT-i, cam timings, etc) to plateau for a time. In that plateau is where your fuel efficiency is greatest. Get in gear and get to the point where your torque band starts, you win. This is the idea behind constantly variable transmissions. Keep the engine in its powerband and change the gearing constantly. Only problem is you can't put too much torque to them or they fall apart.
Also, you almost made a full connection there: horsepower will almost always rise with engine RPM as HP = (tq*RPM)/5252. The almost meaning if the torque band falls off dramatically, the HP may go down. Looking again at a Dynamometer readout, you will always see torque and HP cross at 5252. This is why even though a Honda may have 240HP and my car has a paltry 225HP, my 310ft/lbs+ of torque will "own" most any Honda (except the S2000, because that car weighs almost half of mine, but it still would be a pretty good race).
Slashdot is proof that Sturgeon's Law applies to mankind.
As a former supermileage team member, I can tell you, driving style and strategy are key to this competition. Basically, you floor it untill you get up to 25-30 mph, then coast a few laps. Start the engine up again only when necessary. This is because an engine is most efficient when working at full effort and within the optimal RPM range.
You're right. The engineers call it Brake Specific Fuel Consumption, commonly measured in pounds of fuel consumed per horsepower per hour. "The best (lowest) brake number always occurs at peak torque where the engine is most efficient."
The problem is that this is measured at full throttle, and cars don't need full throttle power at the torque peak to cruise at speed. Small throttle openings are less efficient because of pumping losses with the intake restriction (diesels don't have this problem). A single purpose car for this contest could be optimized for efficiency by having just enough power to maintain speed running full throttle at the torque peak in the highest gear, but it wouldn't be very practical. You'd have a little reserve power by revving over the torque peak (power peak is usually higher than the torque peak) but not much. Throw in a hill or a headwind, and you might not make the 15mph minimum speed requirement.
A gallon of gasoline has 121MJ, while a gallon of diesel has about 138MJ.
--
make install -not war
thats because your running closer to WOT. Thats what you want to be doing, since a throttle by definition is a energy waster.
I didn't look at that site, but Trucks do have better brakes then cars in the sense they are much bigger and more powerful.
You'd get the same mileage if the losses grew linearly with speed, but they dont. The rolling-resistance loss goes pretty linearly with speed, but the aerodynamic losses increase much more rapidly as speeds go up.
Another dirty little secret - since automobiles emissions are regulated in grams/mile, modern cars advance timing to increase power (and emissions) when you're in high gear. Our lab tested a Ford F150 on a dyno at highway speeds, and it emitted more particulate matter than a 7.2L heavy duty diesel at the same operating condition. - no biggy to the automakers since particulates aren't regulated for them, but it gives diesel people heartburn.
Diesel locos are electric trains, they just differ in where the electricity is produced. They act just as a hybird car does with regenerative braking and the like. Any smoke belching is due to improper maintenance.
Diesel locos are basically power plants on wheels, which is very useful for vast stretches of land that they need to cover. It'd be almost useless to run electric lines across the US to power trains, as the transmission losses would be huge.
"Why do you consent to live in ignorance and fear?" - Bad Religion
For freight there's no doubt that diesel locomotives are the winner. Diesel locomotives are hybrid vehicles: a 2-stroke diesel generator, but electric motors. They are very efficient at moving large loads, not so good at light loads due to the weight of the loco itself (something like 135 tons). That's why passenger trains tend to be purely electric - to keep the huge weight of the generator off the train.
Here are some links:
HowStuffWorks article on diesel locomotives.
A CN Railroad page claiming a diesel locomotive can travel 3.5 times further than a truck on a gallon of fuel (presumably pulling equivalent loads).
A BNSF Railroad page claiming fuel efficiency of approx. 750 GTM (gross ton miles) per gallon. Most high efficiency cars would probably weight a ton or less so a 50 MPG Prius would be about 50 GTM per gallon.
Lets hit RPM's from a different angle.
With a reciprocating engine, energy must be expended everytime the piston changes direction. Decelerate and accelerate the mass of the piston. So, higher RPM's mean more energy lost because the piston must change direction more frequently. This is why so called racing pistons are much lighter than standard ones. So, if you can make a lighter piston, use at lower RPM's with a deeper stroke for higher compression, combine with a fuel that tolerates higher compressions, and you are on the right track.
Now hook this motor to a generator, so it only runs at its ideal efficientcy/power, and use electric motors to drive the wheels as the driver desires. Yes, there is some energy lost in the conversion of mechanical-electric-mechanical however, since the engine always runs at its highest efficiency you still get a strong net gain in effciency.
You'll have to correct my figures below:
fuel -- compression ratio
gas -- 10:1
nat gas -- 12:1
propane -- 14:1
diesel -- 20+:1
----- If communism is a system where the government owns business, what do you call a system where business owns govern
My recollection is that maximal efficiency is roughly at torque peak (ignoring such things as aerodynamics and gearing), and that underpowering a car kills the mileage.
That's exactly what I said - though actually, efficiency is pretty constant in the power band, so maximum fuel efficiency is at the lowest point in the power band.
(Except for the last part, but that's addressed later...)
Case in point: a particular truck is offered in an economy V6 and a V8 trim. The V8 got better mileage because the V6 was always running full throttle (above the powerband).
Woah, woah - you're talking about two different situations here. Most cars are way overpowered for going at the speed where aerodynamic losses equal total residual losses - this is about 35 or 40 mph for most cars. So when I said underpower the engine, I meant underpower it compared to most cars, not underpower it compared to its needs.
You're exactly correct that a car that's running full throttle will have crap efficiency, but that's because it's past it's torque peak. You want to be at the torque peak, not above it (full throttle) or below it (going slow).
In your case, the aerodynamics and rolling resistance are so high because the weight is so high that the car is now not overpowered to go the speed that's efficient for aerodynamics. The V6 would get better gas mileage than the V8 if it went slower.
Your Geo may get good mileage, but it's crap, and I won't drive one. I have an MR2 that gets 30 MPG and handles nicely, so I don't have to.
I don't own a Geo. It is however a good example of a car that uses standard design principles to get high gas mileage. Small engine, light weight.
I assume it was air resistance that was making me get poor mileage.
:) )
At 130 mph??? Holy bleep yes! At 130 mph probably something like 80-90% of your power output was going to fight the aerodynamics. You want to be at the point where 50% of the power is going to aerodynamics, 50% to rolling resistance. More or less, that's about good.
The point I'm trying to make is that if you then attempt to go 60 mph in 5th, you'll get lower gas mileage than if you go 60 mph in 4th (assuming that in 4th it's in the 3000 rpm range, and the engine is designed with the torque peak). Most people won't believe it, because the engine sounds like it's struggling and it sounds like you're using more fuel.
(Then again, you are wearing the engine faster, so one way or another, you're spending money. The maintenance cost of a car is usually ~ equivalent to the fuel cost, so you're screwed either way.
What you are describing is more accurately termed a "diesel-electric" locomotive, for obvious reasons. There have been/are plain diesel locos.
Interestingly, here in Ireland, our newest diesel-electrics are required to supply three-phase 220v a/c to the carriages from the head-end power (HEP) unit. Being US locos (GM-EMD), it seems they were merely retrofitted for this. We now have ten-year old locos that are more unreliable than 40 year old ones (also GM-EMD)! In addition, due to the engine overload, three locos have burst into flames while pulling passengers.
Being Ireland, there's not much being done but rotating the locos to ensure even wear. (Only the cross-border Dublin-Belfast service, requiring 3 out of 34 locos, uses the HEP).
-- *~()____) This message will self-destruct in 5 seconds...
just one note: diesels are switching from 2-stroke to 4-stroke to meet emissions requirements. Improvements in engine technology allow this with little or no loss in power over the predecessors.