Air Cars! Very exciting stuff?!

 

I read about these briefly about six months ago, but the topic has come up again in some of the environmental press and I have had a chance to look properly into the concept of air powered cars. I have to say, from what I have read, I am excited! There are questions about the hype of it all, but even only half of it turns out to be true, these things will be a lethal weapon in the fight against peak oil, and in a smaller part, climate change. My findings;

MELBOURNE is set to be the manufacturing home base for a car that operates with zero emissions and can run solely on compressed air. Guy Negre, who used to design engines for Formula One team Renault, has spent the past 15 years developing the air engine and says the first manufacturing plant will be established in Melbourne with cars expected to go on sale next year.  Compressed air, not petrol, pushes the engine’s pistons, which can then take the vehicle up to 110 kilometres an hour. Running on compressed air alone, the car can travel 150 kilometres, but when the air is heated externally and incorporated with a fuel source, such as ethanol or diesel, it is possible to travel from Perth to Brisbane without refuelling. Dr Arnoux said the car would be economically and environmentally friendly. He said the first small car would retail for less than $8000 and running costs would be 80% lower than current comparable vehicles. IT MDI-Energy aims to reduce car emissions in Australia over the next 10 years by 20%. The company says that more than 7000 new jobs will be created over the next five years. The car can be refuelled by plugging it into the compressed air supply that is found at most service stations. Dr Arnoux said the air engine technology could also be used to power homes. [Source]

Sounds good doesn’t it! $8000 is super, super cheap for a car, and for a while anyway, you would be able to essentially steal free fuel in the form of petrol station refilling. 110km/h and a range of 150km on air alone between refills really is more than enough for most people. I know that if those amost too good to be true claims deliver, I will be seriously considering one…

So you have heard the hype, now how do they really stack up? The Oil Drum have posted a very, very comprehenisve overview of everything to do with this idea, which is very well worth the read for anyone who cares about the future. Here are the very interesting calculations they got;

If I remember my high school physics and chemistry right, the energy E required to compress air at 25C is,E = 110,000 x ln (P1/P2) /m3/mol

There are about 45mol air in 1m3, so,E = 110,000 x ln (P1/P2) /m3

This howstuffworks article tells us that an air car tank might have 300lt at 4,561psi, which is 29,999,087.707 – call it 30,000 kPa.

Atmospheric pressure is 101.3kPa.

300lt at 30,000kPa will be 90,000lt at atmospheric pressure, or 90m3.

And so we get,E = 110,000 x ln (30,000 / 101.3) x 90= 110,000 x 5.69 x 90= 56,331,000J

which is 15.6kWhr

However, a company which supplies air compressors tells us that “Most systems typically waste 25 to 50 percent of the energy required to generate compressed air that actually provides useful work.“

Let’s be optimistic and assume that with lots of air cars zooming around, service stations will buy the most efficient (expensive) compressors. So we get just a 25% loss.

This brings us to 20.9kWhr.Let’s round it up to 21kWhr to refill the tank.

Again, this isn’t the air car referred to in the article, but it gives us an idea of the order of magnitude.

21kWhr to travel 200km.

A regular small city car gets about 10km/lt. Petrol costs about $1.30/lt, and causes 2.32kg CO2e/lt. So to go 200km in a regular car would cost $26 and cause 46.4kg CO2e in emissions.

Electricity from coal cost $0.1355/kWh and 1.21kg CO2e/kWh, so the 200km journey would cost $2.85 and cause 34.9kg CO2e in emissions.

Electricity from wind costs $0.19/kWh and causes 0.04kg CO2e/kWh. So the 200km journey would cost $3.99 and cause 0.84kg CO2e in emissions.

The average Australian car is driven 15,000km annually. That’d be 75 refills, or 1,575kWh energy in all. That’s not bad when the average household uses 6,000kWhr annually.

Presumably service stations could do things better than we could at home, since they can buy the big heavy and efficient equipment; if service stations supply so much compressed air, they’ll start charging more for it, more than the power costs. Still, it seems that running it on compressed air will be significantly cheaper in money terms.However, if the air is compressed by electricity got from coal, the greenhouse gas emissions will be comparable to simply burning petrol in the car.Again, not perfect calculations, but the best we can do with the data we’ve got, and they give us an order of magnitude idea of the numbers involved. [Source]

Very, very interesting indeed. If this proves to be true, we are in for some very exciting times in the world of sustainability and energy generation.