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.

Comments

My car gets 40 hectares to the hogs head

[Anonymous Coward]

and that's how I likes it.

(you knew this one was coming)

Safety Equipment?

[Hallowed]

What kind of gas mileage will they get when they are loaded up with 1000+ pounds of DOT required safety equipment?

Re:Safety Equipment?

[barawn]

Going at 15 mph, there's not much safety equipment required.

Fuel efficiency is a difficult thing to deal with - engines have the highest efficiency (power out/fuel in) basically at the minimum point in the power band. Yes: this means that a common engine is getting terrible gas mileage if you're moving along at ~15 mph normally. This is why a car's maximum fuel efficient speed is complicated (and is rarely 55 mph, regardless of what hundreds of websites with terrible math will tell you!) and depends very strongly on the car's gearing. Many cars with overdrive will actually have a "two hump" fuel efficiency curve - that is, they'll be most efficient at about 30 mph or so if you're in 3rd gear, but also have another efficiency peak at 65-70 mph that's lower than the first (but still higher than going 55 mph in the overdrive gear).

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.

Note the details of these cars - slow speed (15 mph), massively underpowered engine (3-4 hp), and very light chassis.

Here is a very good explanation.

(As an aside, most websites are crap at explaning this. See here, where they state that going from 100 kph to 120 kph increases the fuel consumption by 20%. Since you're moving 20% faster, a 20% increased fuel consumption means exactly the same gas mileage.)

Re:Safety Equipment?

[John Courtland]

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).

Re:Safety Equipment?

[barawn]

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.

New hummer?

[aiyo]

Somehow I dont think a styrofoam hummer will take off..unless there is a gust of wind.

A more realistic challenge

[pio!pio!]

How about the most fuel efficient 4 door seating for 4 w/ trunk space, radio, air conditioning, that meets federal safety and crash tests?

Than watch those MPG numbers plummet. Add to that must have respectable performance numbers (ie it must not be so slow accelerating as to cause a hazard on public roads)

That's a real contest.

Re:A more realistic challenge

[ZeroGee]

No one is implying that "Big Car Companies could provide 23k mpg cars, but just aren't." Instead, competitions like these might come up with a teeny-tiny thought that will eventually lead to the development of a revolutionary technology. Even more importantly, it encourages young engineers to start thinking about these types of problems, and it only requires One Bright Idea(tm) to cause massive changes that could better any speed-happy motorist's life.

Re:A more realistic challenge

[rzbx]

"... it only requires One Bright Idea(tm)..."

A little optimistic when it comes to the better ideas winning. You ever read any books whatsoever? Heard of Tesla and Edision? How about the old steam engine wars? Why not look at the history of automobiles in general? The history of suppression of good ideas goes back as far as history itself. In a world of patents, copyright, reputation, various intellectual property laws, egoism, and other factors, the better idea doesn't always triumph. In fact, the opposite is true for the most part. It will take more than an idea to improve the automobile, there are plenty of those to go around. The technology exists to make automobiles many times more efficient. It is obvious that there are many factors that are not allowing these "ideas" to be used. The question is not what the next technological solution is, but what is the solution to bring out the tech that already exists without collapsing the economy and convincing/forcing/etc. the rich and powerful to go along with it. It will also take some education of the general population, which the wealthy and powerful don't care to do. The people have a say in this as well, but in general we appear to be happy for now.

High Mileage Cars

[Lordofohio]

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.

Re:High Mileage Cars

[Carnildo]

Unless you feed the gas into a fuel cell, you aren't going to get much above 30% efficiency. There's a fundamental limitation on the efficiency of heat engines, based on the operating and environmental temperatures, and modern automobiles are getting quite close to that limit.

Re:High Mileage Cars

[Rich0]

The Carnot engine is the basis of the 3rd law of thermodynamics. I think you can put that in the theoretically sound category.

The actual efficiency is 1-Tc/Th. From wikipedia.

In this equation, Tc is the temperature of the heat sink, and Th is the temperature of the engine's heat source. For a 40% efficient engine, your hot engine gases have to be about 1.75 times hotter than the atmosphere that you discharge your exhaust into.

That doesn't sound like much - but remember you have to use absolute temperature. Room temperature is about 300K. So you need a 500K heat source - which is 230C, which is actually fairly hot. And of course you have all kinds of non-idealities in a real engine.

The only way to get anywhere near 100% efficiency is to get the hot part really hot and the cold part really cold. That is why metal-cooled reactors are fairly efficient - you have liquid sodium metal (very hot) coupled with river water (reliably cold).

If you run the math backwards it tells you what the maximum efficiency of an air conditioner is as well. As the temperature difference between hot and cold grows the efficiency drops accordingly. Of course, in real life you also have to deal with the fact that as delta-T grows your walls also start leaking heat like a sieve...

Re:High Mileage Cars

[LS]

Umm, I think you are attacking some unrelated generalization you've heard in the past, not the actual poster's comment. He made no statement about hydrogen or solving fossil fuel dependancy.

But, since you are on that topic, there are a number of avenues besides fossil fuel for generating the electricity or heat or whatever for creating hydrogen:

Bacteria. Some scientist at UCLA did some calculations, and determined that a decent sized canyon in the Mojave desert covered 2 feet of water and a sheet to collect the hydrogen produced by the bacteria would be enough for all of Southern California.

Geothermal

Photovoltaics

Tidal

Convection

Fission

Fusion

Biomass Fuels

Solar Thermal

Wind

Hydroelectric

So, who are you swinging your fists at? Certainly not the original poster?

LS

Re:High Mileage Cars

[Graff]

a gallon of diesel fuel has about twice the energy as a gallon of gasoline. (Of course I'm not counting the energy used in refining, gasoline needs a lot of energy to create)

This is simply not true. There is a bit of variation between the different types and grades of diesel and gasoline but it pretty much comes down to they are fairly equal in the amount of energy that each fuel contains. If you look at this web site you will see the following numbers:

gasoline - 35 MJ/liter
diesel - 36.4 MJ/liter

Diesel has a bit more energy than gasoline but by no means does it have twice the energy!

Re:High Mileage Cars

[Virtex]

but 1500 mpg is a bit out of reach

640 MPG should be enough for anybody. (sorry, couldn't resist)

Re:High Mileage Cars

[line.at.infinity]

1. Burning fuel and turning it directly into mechanical power. 20 percent efficiency.

2. Burning fuel; converting it into electricity (40% at a power plant); storing the electrical voltage in a battery (possibly a fuel cell) (90%); convert the battery power into mechanical power (72%). .40 x .90 x .72 = 26 percent efficiency.

It's close. One thing's for certain: fossil fuel cars are inseperably tied to oil. I'm for fuel cell cars, because that would mean more options for the consumer, and more competion.

reference

People could do this hundreds of years ago

[harlows_monkeys]

I'm not impressed. The Spanish in the 15th century in their voyages to the New World and back were getting thousands of miles per galleon.

Re:Funny, I get more each day.

[cft_128]

I only walk and ride my bicycle. In the last 4 years (since I gave up driving) I haven't used any gasoline (hydrogen, natural gas, or electricity) while going from point A to point B.

When I can buy a car with that kind of effencieny I'll look into it, but until then, a walkin' I a' go.

Must be a bitch to take that shiny new 21 inch monitor home from the store.

What about aircraft?

[jcr]

This article makes me wonder: just how fuel-efficient can an aircraft be?

-jcr

Re:What about aircraft?

[Have Blue]

It's not really a fair question, as aircraft are so very different from cars. Their handling and common behaviors are different, as are the tasks to which they are put- An airliner may be less efficient than a car on paper, but if you try to move 300 people across the US with both of them, the plane may still come out on top.

Also, planes can use propulsion systems much more exotic than a reciprocating mechanical engine.

Driving Styles

[powerpuffgirls]

It's important to note that MPG has a lot to do with driving style. While my car cannot get 1700 MPG, a bit of predictive driving (i.e. know when to start slowing down, when to build up momentum) will greatly increase the MPG.

Re:street legal?

[drinkypoo]

It depends on where you are, but in the US the NTHSA and the DOT would strongly disagree with you. Vehicles sold in the US have to meet certain standards of crashworthiness in order to be allowed to be sold here for street use. This has kept a lot of cars from being imported here, because they would require significant modification. It is a result of all the big old cars (and big new cars) we have on our roads, of course. In Japan, where large vehicles are relatively rare (you have delivery vehicles, and tiny vehicles, and not much in between) you can have lots of little beer can vehicles because they can't do nearly as much damage to one another, whereas here in the US you have scads of two-ton-plus vehicles, even passenger cars with that kind of weight.

As far as acutal street legal vehicles go

[TheNarrator]

You can get 125 miles per gallon all ready with one of these little mopeds, And they're cheap and street legal too.

Re:Haha

[D-Cypell]

we'd all be a lot healthier if we followed Fred's example

I suspect the cardio vascular benefits of using your legs to power your car would be dwarfed in comparison to the damaged caused by eating one of those ribs that toppled said car.

your calculations are a little screwy

[SeXy_Red]

Your saying that your car can drive 4305564.16 Square Feet for every 52.5 gallons? First of all how do you calculate how many square feet a car drives? You would have to take the width of the car and multiply it by the length the car has driven. I will assume for the sake of easy math that your car is 10 feet wide; If you divide 10 4305564.16 by 10 you get 430556.416 feet, which converts to about 81.5 miles. That means that your car gets 1.55 miles to the gallon, which is pretty bad unless of coarse you are driving a canyonaro. :P

Some thoughts for you

[jd]

Air is about 79% nitrogen, and slightly under 20% oxygen. Nitrogen "burns" - that's how you get all those nitrogen-based pollutants out the exhaust.

There's one catch. Nitrogen is very stable. Almost any chemical reaction will take more energy than it releases. When it comes to engine efficiency, this is Not Good.

Ideally, what you'd want to do is separate the oxygen and nitrogen, so that the oxygen ratio in the engine is much higher. Since you're losing less energy through the nitrogen, you would (by implication) get more useful energy out.

Ok, so how to do this, without reducing the energy you're getting from the oxygen at the same time?

That's tough. However, it may be possible. Nitrogen, as mentioned, doesn't react easily. The electrons in the outer shell are tough to displace. With oxygen, the reverse is true. Oxygen reacts very easily, and electrons are displaced with considerably less effort.

You can certainly use this to separate oxygen and nitrogen. Just set up an electrically charged grid, such that the charge will convert O2 into O2+, but leave nitrogen (N2) electrically neutral. Set up a second grid, with the reverse charge. The oxygen will be attracted towards it, the nitrogen won't.

If you picture the first grid at the entrance to a y-shaped tube, and the second grid at the fork splitting off of the long section of tube, you can see how the nitrogen will travel straight on, whilst the oxygen will be diverted.

Now, here's the tricky bit. The oxygen is one electron short (it's charged), and you've got to put quite a bit of energy into a device like this to charge the grids up enough. Will you get a net gain in efficiency?

That part, I can't answer.

Would it be worth doing anyway? Maybe. Well, it'll cut out a major air pollutant. The oxides of nitrogen that you get off will react with water to produce nitric acid. Not really something I want to be breathing in, if I don't have to.

Are there better solutions? Not using a conventional piston engine. We're almost at the limits for those, given a standard air mix. A rotary engine might get you a better theoretical limit (you don't have to keep reversing mechanical devices), but they're costly to make (they develop far higher pressures) and you have to develop one that's large enough that the increased surface area to volume is no longer a factor.

For ultimate fuel efficiency, I suggest a small fusion reactor. Though you may need to wait a while for them to be approved for use in cars.

4 cylinder engine

[k4_pacific]

The SAE competition in the link requires a four cylinder engine. This kind of rules out other types of power such as steam, fuel cell, and stirling engine. Although, I suppose with enough modification, the provided Briggs and Stratton engine could be converted into a steam engine (not that this is necessarily more efficient). Let's see, new camshaft, a means to adjust the valve cutoff, maybe one of those cool looking fly-ball governors... Since a steam engine can apply power in each cylinder on every revolution, this makes it equivalent to a V-8. If you seal off the crankcase into a separate compartment for each cylinder, you can use both sides of the piston and make the equivalent of a V-16. Of course, details like, how to water from condensing in the oil will have to be addressed.

Also, since the peak horsepower of a car is rarely needed except in rapid acceleration, I would think that the key to reducing engine size, and thus, improving efficiency would be to use a small engine with some kind of storage system. Since batteries are bad for the environment, maybe two flywheels rotating in opposite directions (to cancel out precession) under the floor can be used, along with an electric motor/generator to transfer power to/from them. Extra power generated by the engines, as well as from braking, can be used to accelerate the flywheels. This would also improve handling because the gyroscopic effects would keep the car perfectly level on fast turns.

Also, I would think that the car would be cheaper to engineer and produce if you could eliminate most of the mechanical parts. How about a gasoline fired generator, a flywheel battery, and an electric motor on each axle?

Ceramic engines

[Moderation abuser]

Can increase the efficiency over metal based ones. The temperatures they can withstand are far higher, raising the efficiency substantially over conventional ones.

They're also much lighter, the materials don't expand/contract and can be machined to closer tolerances and they wear out much slower than metal ones.

Re:Ceramic engines

[qwasty]

I'm a machinist, and I've dealt with automotive engine blocks before. I think the big problem is going to be manufacturing costs. When machining a ceramic, it tends to chip very easily, which could raise costs due to high waste, and special manufacturing procedures that hamper productivity. However, since it's non-ferrous, you can use diamond tooling instead of the traditional carbide tooling, which will save a fortune on tooling costs

Ceramics are also very abrasive, which might drive up maintenance costs due to the need to frequently replace piston rings. The engine block itself should wear much more slowly than a normal cast iron block, however.

Ceramics can be pretty resilient even when faced with temperature stresses, but I don't know how well a car that needs to be running one moment, and parked the next would fare. I doubt people would put up with the need for a 5 minute warm up period, especially if failure to do so would destroy their car.

Another issue is that a ceramic block would be impossible to repair, and would probably be a good deal larger than a regular cast iron engine to provide strength at every location on the block that feels stresses. But, if it's possible to build ceramic handguns, I'm sure it's possible to build a durable ceramic engine block.

I doubt there's very many manufacturing experts who read slashdot, but I would be very curious to see solid numbers on the costs of ceramics manufacturing compared to traditional cast iron. I haven't done much work with ceramics, so much of the above is just educated speculation. Treat it as such.

Sheesh, tough crowd

[Concerned Onlooker]

Some students do something cool in a contest and all most people are saying is "yeah, call me when it's really a car." Criminy. Articles on case mods get friendlier comments than this, and this is something that I would have thought geeks would have found interesting. Or nerds. Or whatever we are.

how about cars vs. trains vs. planes

[SuperBanana]

How about the most fuel efficient 4 door seating for 4 w/ trunk space, radio, air conditioning, that meets federal safety and crash tests?

How about comparing modern day cars, trains, busses, and planes, on a per-passenger basis?

According to Top Gear a few nights ago, trains get worse mileage than the average car, per passenger(I'm trying to find any info about the study online to see if that's based on maximum capacity of each type of vehicle or real-world average passenger counts) and a high speed train gets worse mileage than a jumbo jet! Personally I'm kind of curious about a subway train as well. Both averages(ie based on typical # of people in them) and maximum figures would be interesting for all vehicles.

When they asked the UK "Green Party" for a statement, they said "the best choice is the journey not taken". Um...okay.

Oh, and ever watched a diesel locomotive idling or at speed, belching lots of blue/black smoke? How about a city bus? Here in Boston, they're downright filthy, and in neighborhoods near the bus depots and garages, asthma rates are much higher, and studies have repeatedly shown diesel soot causes both cancer and asthma.

Re:how about cars vs. trains vs. planes

[RedWizzard]

How about comparing modern day cars, trains, busses, and planes, on a per-passenger basis?

According to Top Gear a few nights ago, trains get worse mileage than the average car, per passenger(I'm trying to find any info about the study online to see if that's based on maximum capacity of each type of vehicle or real-world average passenger counts) and a high speed train gets worse mileage than a jumbo jet!

Top Gear were probably talking about the Lancaster University study (news article). So it's certainly not clear that trains are better for passengers. Then again you have to take the results with a grain of salt considering the fuel efficiency of cars varies by a factor of two or more from model to model.

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.

Fuel cell != Hydrogen fuel cell

[DarkMan]

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.

4 cycle - not 4 cylinder

[zerofoo]

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

Something a little more practical...

[ajdecon]

There's a University competition sponsored by Ford and the DOE to build environment-friendly, fuel-efficient vehicles called FutureTruck. The catch? They have to modify Ford Explorers, not create go-cart sized vehicles, maintain existing performance, and remain fairly manufacturable. (In other words, Ford is using college teams for their R&D.)

There've been amazing results: the winning team, from University of Wisconsin Madison, built a hybrid Explorer that got somewhere over 40 mpg. (Different sources disagree as to the exact number.) For reference, stock Explorers are rated at merely 15/19 mpg for city and freeway driving. They also scored well in emissions and made a vehicle which could probably be manufactured and sold for about the same price as a stock vehicle.

So it's not 1700 mpg. It's still pretty darn impressive for an SUV!