AN AIR HYBRID---WHAT'S THAT?--Carl Schwab

Tata Corporation claims to be planning to introduce into the world car market, a hybrid car based upon compressed air technology. When you stop laughing, read on. Frankly in reading about the Tata Air car, some call it an "out and out fraud", ---others say its claims are grossly exaggerated. So for the purpose of this blog, the writer will try to apply logic to project what things have to be done.

The Tata Nano (and there are others) claims to use an ICE to drive an air compressor and stores the compressed air in a tank or plenum. Air from this plenum is used to drive an air motor and thence to the vehicle wheels. The air motor that powers the vehicle wheels can be operated as air compressor during braking to put air back into the storage plenum. On the surface this sounds simple enough BUT there have to be some real problems or somebody would already be doing it. First the working fluid in this case is a gas, compressed air, and as such follows the gas laws of PV=KT where P is pressure in
lbs/in^2, V is volume in in^3 and T is measured in Kelvin. K is a constant that numerically can be calculated for the experiment. Tata has claimed that their Air Car prototype has produced 52mpg at 60 mph and has a range of 250 miles on a full tank.

SOME BACKGROUND—At the end of the 19th and beginning of the 20th century quite a lot of effort was expended into building pneumatically powered trains for mining operations. The French did a good bit of this. The air-powered engine was safe in mining operation where methane gas and other explosive mixtures were common. For the mine operations the plenum was filled with compressed air at the surface and the train engine pulled the cargo cars down into and back up to the surface. Some of these actually used a form of regenerative braking i.e. the air pump/motor pumped air back into the plenum.
Also before electric power for a subway train was perfected, a pneumatically powered shuttle car was used in Paris replacing a horse drawn shuttle. As electric power was perfected the pneumatic ideas were displaced. BTW the pneumatic engines were conversions of steam engines and were double and triple expansion and 2 cylinder sets so that the engines could reliably start under full load. Around 1910 a White steam car converted to pneumatic drive drew attention. At one point it had an ICE/compressor to
refill the plenum. BTW a White Steam car in 1910 cost about $4500, (in 2011 dollars $4500 becomes $108,000!!) and was popular with government officials. It was THE luxury car.

WHAT'S NEEDED? ----First we will need a compressed air motor/pump, preferably electrically controlled from the car computer. According to Tata they DO have such a unit. Second we need an efficient ICE driven compressor to supply air to the storage plenum. BTW I feel this plenum not only has to withstand up to 5000psi; this plenum has to be thermally insulated sufficiently that the compressed gas temperature does not change for upwards to 10s of minutes due to ambient temperature.

AN ASIDE—Tata says that the exhaust (just air at a lowered temperature) will be used as they say, for "free air-conditioning". The writer is not sure how "free" it will be <G>.

So we have to see what Tata has up their sleeve besides their arm<G>.

Interesting!

Comments

[david pacholok]

Carl:
Since they have an ICE on board, it might make sense to use some of its waste heat to increase the temp/pressure of the working fluid, pressurized air to acheive a "free" increase in the energy content thereof. If a cycle first pressurizes "cold" air (adiabatic heating to 5000 PSI is not practical with present materials - they would melt - heat must be dissipated between compressor stages)and then uses scrap stored heat to increase/maintain pressure as compressed air is used later in the cycle an increase in eff may well result.
I cannot think of a way to do this inexpensively, however.

[Howard Edelman]

Internal combustion is an air compressor/motor where instead of adding air under pressure at the right moment, some fuel mixed in with the air is ignited to add temperature at the right moment. PV=NRT still works.

BTW What kind of ice are you referring to.

[Carl Schwab]

Comment to David P.--
In thermodynamics, an adiabatic process or an isocaloric process is a thermodynamic process in which the net heat transfer to or from the working fluid is zero. Such a process can occur if the container of the system has thermally-insulated walls or the process happens in an extremely short time, so that there is no opportunity for significant heat exchange. I think the isocaloric is a better term to describe what I thought Tata had to solve to make a practical hybrid.
There are some attractive features. ----Carl Schwab

[value garage equipment]

There are hand-powered air compressors, but most are powered by either electricity or natural gas. Natural gas air compressors usually are more cost effective. If the air compressor is used in a small, enclosed area, however, an electric model might be more desirable in order to avoid gas fumes.