Hey, would you like to see a really dumb piece of science TV?
Sure you would!
Yes, the narrator appears to have no idea what "ironically" means, but never mind that. I find it pretty impressive that the voiceover proudly announces that it will cost nothing to fill up an air car, even as the guy they're interviewing explains that the engine runs on air that has been compressed somehow, and explicitly states that the air is just an energy carrier, not an energy source. (See also "hydrogen wells, nonexistence thereof".)
At the end of the clip, the voiceover grudgingly admits that it will take "some energy" to compress the air... and then immediately boldly postulates an absolutely classic, in-as-many-words perpetual-motion machine, in which the car carries around its own compressed-air-powered air-compressor.
Seriously. That's what he says. In a science show.
That's right - this clip is not from some podunk local news station, or promotional material from some scam artist. It's from an episode of the Discovery Channel's "NextWorld" series.
Which spurs me to ask, "How the fuck did this ever make it to air?"
(As usual, The Onion says it best.)
Setting aside the gibbering idiots who apparently now pass for science journalists in the USA, the vehicle they're talking about is the good old MDI Air Car, which for some years now has been right about to make it to market.
MDI first claimed to be right about to start producing cars in 2000. They've made similar claims several more times over the intervening years. I puzzled over the Air Car in 2006. But no cars have yet rolled off a production line.
Apparently the Tata Motors MDI-powered car will be going into production at the end of this year. I am assured of this.
MDI's most recent technological advancement is to change the name of the Air Car. It's now called Xe Altria FlowAir.
The FlowAir's claimed performance remains highly questionable. It seems that the massive range numbers that MDI have trumpeted these last ten years were arrived at by taking an actual tested range of less than ten kilometres, and applying a bunch of fudge-factor multipliers to take into account the great improvements that MDI promise to make when they actually make a working car.
Oh, and one of the MDI car's big features is that it's supposed to have some sort of heater doodad that boosts the air pressure going into the engine to give long highway range. So in order to get the "200 miles on one tank" the Discovery voiceover guy was so impressed about, you have to burn a fuel to run the heater. Which means that not even the minor claim that the car makes no emissions when driving around is actually true.
But don't worry - I'm sure there's some chemically trivial way to get the heater to run a little machine that makes more heater fuel.
24 February 2010 at 8:30 am
Speaking of credulous media treatments of snake oil... http://www.cbsnews.com/stories/2010/02/18/60minutes/main6221135.shtml
24 February 2010 at 8:55 am
I remember screaming at my TV when this first aired. That was the day I decided that this show was not worth my time.
24 February 2010 at 8:58 am
This was a really cringe-worthy segment of the (I think) "FutureCar" series which overall isn't too terrible. I remember yelling at the TV, "You have to run the air compressor using some other energy source!" when I first saw this. I think compressed air could play a role as a sort of "hybrid" system where you engage an air compressor that runs off the wheels as a form of regenerative breaking as Dan mentioned back in 2006. There was a Ford concept truck that had a similar system but used a hydraulic rather than pneumatic system.
These pneumatic systems can't physically store a whole lot of energy compared to typical gasoline or diesel fuel either. The amount of energy stored goes like the natural log of the pressure difference between the tank and atmospheric pressure, that gives horrible scaling. From the wikipedia page on compressed air energy storage http://en.wikipedia.org/wiki/Compressed-air_energy_storage even advanced carbon composite bottles would only have the energy density of lead acid batteries (which you don't see in modern electric/hybrid vehicles due to their low energy density).
The key is the rate at which energy can be added to the system; batteries don't like to be charged or discharged really quickly and internal combustion engines lose a lot of efficiency when you push them hard but a pneumatic system is much less limited in this respect so they'd be excellent to recover energy through regenerative breaking and then use that to ease the load on the main engine/motor during initial acceleration when those engines/motors won't be functioning near their peak efficiency. As a primary energy storage system pneumatics would perform poorly but as a supplemental system they could be quite good.
24 February 2010 at 9:09 am
Good grief, I just listened to the end of this and that "perpetual motion" bit at the end is COMPLETELY egregious. I bet the people who are actually working on this vehicle had to just shake their heads in disgust if they ever actually heard this.
Another issue with a car that carries so little energy is that you have to make it very light-weight so I can't see this vehicle doing very well in crash tests. It seems to be mostly made of "composite"-read as fiberglass-materials with a bit of a metal frame on the bottom.
There's another segment from this series talking about aerodynamics and they interview a quite eccentric Italian designer who is quite entertaining and seems to make some good points. He's a bit over-the-top though so I'm not sure how true some of his statements about how much vehicles can be improved are. Trucks, particularly big rigs in the US seem to only put a modicum of effort into streamlining though.
24 February 2010 at 12:17 pm
Working on pneumatic aerospace actuators gave me a healthy respect (read: fear) of compressed air. It's anxious and excited to be STP gas, just like chemical explosives, but without the courtesy to require activation energy.
Rather like the somewhat-associated fear of being in a crash in a metal-bodied super-duper electric car. Gasoline is so magnificently safe and pleasant, both in an absolute sense and compared to the alternatives.
24 February 2010 at 12:24 pm
Speaking of which, Derek Lowe has a new Things I Won't Work With!
[Yep! -Dan]
24 February 2010 at 4:38 pm
Remember children, Thermodynamics is a company in Alaska that makes heaters. It has nothing at all to do with making cars...:P
24 February 2010 at 11:55 pm
My first boss at my first job told me about his plan to get free electricity at his house. He was going to fill his basement with a bunch of car batteries.
I said, "Car batteries are recharged by an alternator which itself is powered by a gasoline powered motor. Do you plan on having an 8 cylinder motor running in your basement?!"
He replied, "No, the batteries will be charged by other batteries."
I asked, "What will charge those batteries?"
He was getting pretty angry and snapped, "I'll need a lot of batteries, OK."
Being my boss and all, I dropped it.
25 February 2010 at 2:41 am
http://www.engineair.com.au/airmotor.htm
I wonder what ever happened to that dude. I live literally a 10 minute walk away but have never bothered to see if they're still in business.
25 February 2010 at 2:40 pm
I agree that this seems like a pointless idea. I can sort of get it in the sense of an eco-friendly way to store electricity, in the same way as pumping water into a tower, or spinning up a centrifuge. But I didn't hear what he was saying as a claim that it was somehow getting more energy, or even close to the same energy out of refilling the tanks from energy derived from the onboard air. It sounded like you'd be carrying air and batteries (for some reason), then using the batteries to run engine in reverse (I think) to convert the onboard electrical energy into compressed air. That still seems pretty stupid, but I don't see a reason why it wouldn't work, at least for awhile.
25 February 2010 at 6:57 pm
It's not that using onboard batteries to run an electric motor to turn a compressor to compress air to run the motor wouldn't work. It's just that it would be stupid. Just attach the electric motor to the wheels.
My favorite idea(I should patent it) since good heatpumps can produce 3-4 times as much heat on their hot side as the electricity you use to run them, so 400% efficiency depending on how you look at it. If you could get a peltier or similar on the hot side that has an efficiency of 25-33% Then you spend 100 watts to feed 400 watts to the Peltier generator making 100 watts to power the heatpump. Any more and PROFIT! :) Lol.
27 February 2010 at 2:04 am
The only place I could even see a compressed air engine being of use would be in short distance service vehicles (think stuff like forklifts). But, even there, batteries can hold more power AND give more torque off the motor. The only benefit air has is you can charge the tank faster than batteries. But if you have enough battery power for a shift and can take the downtime, charging isn't bad. And if you need to run the thing 24/7, then you could just have a drop-and-swap battery pan to quickly put in fully charged ones.
So, yeah, no idea where this would be better than available alternatives.
28 February 2010 at 10:03 am
"The only place I could even see a compressed air engine being of use would be in short distance service vehicles (think stuff like forklifts). But, even there, batteries can hold more power AND give more torque off the motor. The only benefit air has is you can charge the tank faster than batteries."
Compressed air engines are of value in some 'dangerous' environments - think of a chemical plant, fuel depot or anywhere there are dangerously flammable vapours in the air. By eliminating potential ignition sources (ignition sparks from internal combustion engines, or stray sparks from the contactors in battery powered machinery) you can achieve a vehicle that could operate relatively safely in an environment from which other vehicles would have to be excluded. But of course there would have to be no other electrical equipment on the vehicle.
1 March 2010 at 2:28 pm
Hmm. While compressing air is certainly an inefficient process, all of the inefficiency is in the form of local heat generation.
Compressors get hot, just from the act of compressing air. Is there anything that this waste heat can be used for? Heating water to use for keeping buildings warm in cold climates, or industrial uses, seems like one perfectly reasonable use.
If the compressor can be designed to run at a high-enough temperature, it could generate steam power to run a turbine, which in turn could drive anything else mechanical.
If the compressor itself is a steam turbine, it gets even more interesting -- it's own waste heat can be used to pre-heat the water before it gets to the boiler.
It's naive (or at least just plain stupid) to say that compressed air cars are totally efficient and non-polluting, but it's equally naive to presume that there is nothing that can be done to increase the overall efficiency.
3 March 2010 at 10:13 pm
My electric car design has a wind generator on the roof that recharges the batteries as I drive!
Where's *my* spot on Discovery?
5 March 2010 at 5:46 am
Ah - Podunk doesn't have a News Station...
Podunk NY http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Podunk+NY&sll=37.0625,-95.677068&sspn=37.136668,55.634766&ie=UTF8&hq=&hnear=Podunk,+Tompkins,+New+York&t=h&z=14