Is The Compressed Air Car A Viable Alternative?

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Alternative energy vehicles are a hot market and Zero Pollution Motors (ZPM) aims to bring a new kind of car to the US.  The AirPod is a 500 pound micro car that is powered by a compressed air motor and backed up with 5000 PSI air tanks that supposedly give it an 80 mile range.

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The AirPod has popped back up on the radar after an investment deal with Robert Herjavec on the ABC show Shark Tank.  ZPM was represented by interim CEO Ethan Tucker and recording artist Pat Boone and they were able to score a $5 million deal for a 50% stake in the company and the rights to future US expansion.  Herjavec has a passion for cars and racing and has competed in the Ferrari Challenge and owns many exclusive cars including a LaFerrari.  This passion may have persuaded him to invest in ZPM but it may also separate him from his money.

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The compressed air motor works much like an impact wrench and converts air pressure to mechanical energy.  The first compressed air motors showed up in the 1840s and have found some niche uses in early versions of torpedoes and trains.  Most of these power trains have been replaced by more efficient internal combustion or electric engines.  In the 1990s, former Renault engineer Guy Nègre founded Motor Development International (MDI) with the aim of producing a compressed air commuter car.  The first news of this showed up in 2000 stating that ZPM had made a deal with MDI to start producing the car in South Africa but production never started.

The concept bounced around with different companies for the next 9 years but none of the versions were brought to market.  MDI also tried their hand the at X Prize competition but were not able to make it out of the early stages.  In 2009, MDI reached an agreement with Tata motors to license the technology for the OneCAT vehicle to be produced in India.  Tata integrated the technology and reported in 2013 that they would be ready for market by the end of that year but as of this writing still have not shown a working product or any concrete sales plans.  ZPM is now trying their hand at bringing the car to the US market by presenting a plan to build the micro car in Hawaii and sell it for $10,000.

The AirPod seems like an interesting idea but when you get down to basic thermodynamics, it fails to prove its efficiency.  The biggest roadblock to the compressed air engine is the loss of energy due to heat created by compression process.  This presents a high loss of energy when the tank is loaded and is only the start of the issues.  In order to power the vehicle, the compressed air must be released quickly which leads to the second issue of extreme cooling which can cause issues for the engine or even freeze the supply lines.  This principle can be seen easily by how cold a pneumatic air tool or compressed air spray can gets once in use.

MDI has tried to counter some of these issues by using staged carbon fiber air tanks that drop the line pressure but the overall efficiency is still low.  The updated system drops the pressure from 5000 PSI in the main tank down to 290 PSI in the secondary tank.  This resolves some of the freezing issues but it also causes almost half of the energy to be wasted.  According to the figures provided by MDI, this should still provide the AirPod with around 80 miles of range but experts argue that process only leaves 1.9kWh of usable energy which only allows for 42 miles of range.  Things get even bleaker when you look at the efficiency of the compressor unit which MDI states is 58% efficient.  Once you take the charging cycle into account the AirPod ends being only 23% efficient overall which is very low compared to electric cars that are three times as efficient.

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The carbon fiber air tanks provide another hurdle as they are expensive to manufacture and still largely unproven.  The only vehicle on the market that uses a similar tank design is the hydrogen powered Toyota Mirai but the tanks on that vehicle cost almost as much as this whole car.  The safety of the air tanks due to their position and the overall safety of the entire vehicle has not been proven yet as crash tests have not been conducted.  The micro car also has many legislative issues ahead of it which other small-car companies like Elio Motors are facing right now.  The price of the vehicle is fairly high for the limited space and range it provides and the large air compressors needed to complete a fast charge are power hogs and use gobs of energy.  The proposed home charging solution on a standard outlet can take upwards of 6 hours and use just as much energy as an electric car recharge.

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The AirPod is an interesting concept but in the end, it’s a small plastic car that is powered by a motor that is highly inefficient.  Due to the multiple times the energy is converted it sounds more like a perpetual motion machine then an actual marketable product.  The only hope I see for the technology might be in a hybrid system where it assists a traditional ICE engine like we see in some buses but with battery technology getting cheaper by the day, that may be a lost proposition.

[Photo Credit: MDI]

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Robert Allen
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Robert Allen
1 year 3 months ago

I think time will prove this a benefit to energy. Hopefully more investors will financially help out along with ideas from developers. It’ll take time, but this will work.

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