A compressed air car

[duncan drennan]

It seems that engineers have managed to produce a car that runs on compressed air, and TATA will be manufacturing them.

Most importantly, it is incredibly cost-efficient to run – according to the designers, it costs less than one Euro per 100Km (about a tenth that of a petrol car). Its mileage is about double that of the most advanced electric car (200 to 300 km or 10 hours of driving), a factor which makes a perfect choice in cities where the 80% of motorists drive at less than 60Km. The car has a top speed of 68 mph.

[Dave A]

90m3 of compressed air is stored in fibre tanks.

Answers my kneejerk first question (weight) but raises the next.

90 cubic metres?? 3m x 3m x 10m. Or is that the volume at standard atmospheric pressure? Just has to be I guess.

Incredible! And the price tag looks OK too.

[Graeme]

Used to work fine in torpedos - maybe it still does. But how much energy is used to compress the air?

[duncan drennan]

But how much energy is used to compress the air?

I suppose the right question is how efficient is the engine. There has to be enough energy to do the actual work - say it requires 10kWh (kilowatt hours) to drive 100km, then there actually has to be 10kWh worth of energy stored in the compressed plus enough energy to cover the overheads (the inefficiencies).

It sounds like they make use of the energy in the air for a number of things, from driving the actual engine, to using the cold exhaust air for the air conditioning. They also recover energy when braking. You can find out more about the car on MDI's website. Unfortunately I couldn't find anything about the engine's efficiency.

What is nice when compared to other options (such as hydrogen) is that the infrastructure is already in place (compressed air is used for pumping tyres), there might just need to be an upgrade to accommodate the required pressure.

The energy has to come from somewhere, and it would be source from the power grid. Hopefully pollution due to power generation is lower than pollution from motor vehicle engines. I'm pretty sure power stations are more efficient at extracting energy from their fuel - it I remember correctly (don't quote me), internal combustion engines only extract about 30-40% of the energy from the fuel.

[Dave A]

I think we should bear in mind that a big part of fuel costs are taxes, often related to infrastructure costs such as roads. Currently there is no tax on compressed air, which might account for a big part of the apparent cost efficiency. Widespread uptake of compressed air vehicles might just change all that.