# MDI's AIRPod coming to New Zealand



## John (Sep 11, 2007)

Powering a car on compressed air isn't a new idea, it’s an idea that has been around for quite a few decades. It's not an idea I like particularly as I know how horrendously inefficient air compressors and air motors can be. A piston compressor will compress air pretty much adiabatically where as it would be more efficient to compress air isothermally. You cannot generally compress air isothermally as this would require the air be compressed very slowly. So as the air is compressed it becomes hotter requiring greater pressure and hence power to achieve a given volume reduction. This heat and hence excess pressure is then lost as the air cools to ambient temperature in the air receiver. This can be mitigated to a degree by multistaging and intercooling the compressor. This of course still rejects heat (energy) from the system but achieves maximum compression for minimum power consumption. A similar if opposite problem occurs in the air motor. The now ambient temperature compressed air is expanded in the air motor adiabatically instead of the more ideal isothermal expansion and so becomes very cold and hence denser than if at ambient temperature hence not expanding as much as it could have and consequently not as much power is produced. Again multistaging and interwarming of the air would improve things. This is interesting though because the interwarming allows the motor to suck heat energy out of thin air and in doing so can provide a cooling source for the interior of the car. Not all of the energy the car uses is contained in the tank. The other problem with the air motor is how you throttle it efficiently. If you use any sort of flow restricting valve in the air circuit either before or after the motor you would not only be altering the dynamics of your multi expansion air motor but more importantly the valve would be dumping energy in the form of pressure loss. When supplied with the full available pressure the motor would basically be a constant torque device hence the power it produces will vary with RPM. The motor could basically be throttled with the transmission if it was joined to a transmission that could vary from zero RPM's. The other way would be a variable capacity motor. Another problem is what happens to the motors expansion rates and power as the tank is used up and the pressure declines. The torque that the motor could produce would decline in proportion to the tank pressure so as the tank is used up the cars preformance would deteriorate. The size and weight of the pressure vessel and just how critical the integrity of it is to the safety of those around it are some more issues. I wouldn’t like to guarantee its integrity in an accident situation. The main advantages of this concept I see as being that it is cheap as it doesn't contain any expensive elements like batteries, and quick refilling from cheap to produce infrastructure. No three hour plus charge times for this car.


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## linz (May 18, 2008)

If it stays a niche product, complementary to electric cars, then I dont suppose the inefficiency of compression will draw heavily on the grid and should still be much cheaper than petrol. I suppose the inefficiency of the air cooling in the motor can be compensated with combustion by adding fuel in their other models (this would obviously be tiny a fraction of that of an ICE fuel:air ratio). For a full-feature car electronic control could compensate cvt or similar for loss of power to match drivers input. Safety of the air-tank could be weighed against LPG and petrol tanks and what they can do in an accident. A big advantage would be the simplicity and how cheaply they could be made. They might be suitable for amphibious recreational type vehicles, no batteries to drown or exhaust or air intakes to flood, and there used to be air-power torpedo's. I dont think that it will replace alternatives like electric outside che, but its good to have a range of options.


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## KiwiEV (Jul 26, 2007)

linz said:


> From autoblog green-
> "Looking like just about every other three-wheeled, joystick-controlled, compressed air-driven car we've ever seen, the AIRPod by MDI will be available to lease in New Zealand soon. MDI has an agreement with IndraNet Technologies to market them in the land of the Māori and, according to an article in the New Zealand Herald, they could be arriving on the island before the end of the year..."
> 
> Looks like a niche vehicle that could be useful for quiet towns, golf courses, large campuses...
> ...


As much as I loathe the hypocrite Clive Matthew Wilson, I agree with some of what he says in this case. This was also on the front page of the Herald last weekend.
Interesting looking car but I wouldn't want to be doing 70km/h in it!


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## Andy Dutton (Oct 15, 2008)

Gidday all,

Might aswell do a little introduction before I start my rant:

Andy's the name, long(ish)-time reader first time blogger. I'm a first year Electrical Engineering Student at Victoria, soon to be second year at Canterbury (assuming the next 12 hours of exams go well enough. Groan!!). I've loved cars for years but when I saw "Who Killed the Electric Car?" It opened my eyes a little as to the lack of innovation in the industry in recent times. I hate the idea of modern society relying on fossil fuels in its daily function. I see it as an exploitation of resourses rather than a utilisation. Renewables have to be way of the not-too-distant-future, and New Zealand is the perfect place to start

Right, now that that's done...



KiwiEV said:


> Interesting looking car but I wouldn't want to be doing 70km/h in it!


I have to agree with you on this one Gav. This thing just does not look safe! Can you imagine taking evasive action at 50kph (let alone 70!!) in a 3-Wheeled car?? I'm picturing Air-Pods doing roly polies down Ghuznee Street at the first sign of the drunken Hobos wandering across the Cuba intersection without due attention. And am I alone in thinking that this thing actually looks like a children's toy? It should be 4 inches tall and getting bashed against the skirting board by 18month-old future EV driver.

Sorry MDI, but if I ever had the needs that your product meets, I'll buy a Segway and a raincoat.

Greetings again to everyone, specially you Hadz if your reading!!!


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## KiwiEV (Jul 26, 2007)

Andy Dutton said:


> ...this thing actually looks like a children's toy? It should be 4 inches tall and getting bashed against the skirting board by 18month-old future EV driver.


LOL
That was just the sort of thing I did at 18 months. Or probably more like 118 months in my case...

Hey Andy, and welcome by the way!


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