Piston Slap: Depressurizing Compressed Air Engines?

Sajeev Mehta
by Sajeev Mehta
piston slap depressurizing compressed air engines

Maxim writes:

Just saw your post about running out of questions. Just wanted to say that you have a fan in Montreal, Canada! Love the subjects you guys talk about!

Everyone is talking about electrification and hybridization, but battery cost is a big negative point. PSA (group Peugeot Citroen) has developed a hybrid air system using compressed air as an alternative to electricity. A very smart and cost effective system. Where is that system now?

Why are the manufacturers not using tech like this to reduce their fleet MPG?

Sajeev answers:

The answer is almost always money, honey.

Peugeot isn’t risking it because they’d take a bath. Without the government incentive, why would a manufacturer put their eggs — ANY eggs — in a Hybrid-Air system basket?

The R&D costs, the durability and safety testing of components/subsystems/the whole vehicle, production/marketing of the final product must all be considered. I reckon this “moonshot” is a dangerous investment: only Tesla has the juice (and dat market cap) to make cars while often losing money.

There’s nothing wrong with moonshots: the Toyota Prius is proof. Between a Federal [s]boondoggle[/s] Partnership for a New Generation of Vehicles that (not?) surprisingly produced zilch for would-be buyers, the California ZEV initiative, and whatever Jim Press was alluding to, Toyota had ample reason to give their hybrid system a shot in Japan and the USA.

I’m not gonna speculate to the validity of Hybrid Air Systems in the real world of motoring: it’d be awesome to see it hit the road to see the pros and cons firsthand.

But follow the money and you’ll totally see why it had to die.

[Image: Shutterstock user Syda Productions]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.


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  • Vehic1 Vehic1 on Sep 29, 2018

    golden2husky: Oh, yeah - them thar smarty-paints sah-in-tists is a-gittin' rich, pickin' on them POOR fossil-fuel comp'nies, whut ain't got NO muney! A ex-purt with orange har, done tole me!

  • Makuribu Makuribu on Sep 30, 2018

    As Scotty might say, "Ye cannae change the laws of thermodynamics, Jim!" The energy efficiency involved in compressing and expanding air is very low. In the bottom of a mine where you might run in to pockets of methane, you can operate vehicles by running an air hose down from a honking big compressor, and plugging it in to a modified ICE engine. It's not efficient, but it avoids explosions. Your bulldozer or pickup truck is tethered to a hose, but it's in a mine, not driving on streets. Compressed air engines, like fuel cells, are only applicable to very limited applications where overall thermodynamic efficiency and cost is superseded by some other requirement, like operating in explosive atmospheres or outer space.

  • Dave M. Although the effective takeover by Daimler is pooped upon, this is one they got right. I wasn't a fan of the LHs, mostly due to reported mechanical, NVH and build quality issues, but I though Chrysler hit it out of the park with the LXs. The other hyped release that year was the Ford Five Hundred, which, while a well-built car with superior interior space, couldn't hold a candle to the 300.
  • Art Vandelay I always liked those last FWD 300's. Been ages since I've seen one on the road though. Lots of time in the RWD ones as rentals. No complaints whatsoever.
  • Cardave5150 I've had 2 different 300's - an '08 300SRT and an '18 300C. Loved them both a LOT, although, by the time I had the second one, I wasn't altogether thrilled with the image of 300's out on the street, as projected by the 3rd or 4th buyers of the cars.I always thought that the car looked a little stubby behind the rear wheels - something that an extra 3-4" in the trunk area would have greatly helped.When the 300 was first launched, there were invitation-only meet-and-greets at the dealerships, reminding me of the old days when new model-year launches were HUGE. At my local dealer, they were all in formalwear (tuxes and elegant dresses) with a nice spread of food. They gave out crystal medallions of the 300 in a sweet little velvet box (I've got mine around the house somewhere). I talked to a sales guy for about 5 minutes before I asked if we could take one of the cars out (a 300C with the 5.7 Hemi). He acted like he'd been waiting all evening for someone to ask that - we jumped in the car and went out - that thing, for the time, seemed to fly.Corey - when it comes time for it, don't forget to mention the slightly-stretched wheelbase 300 (I think it was the 300L??). I've never found one for sale (not that I've looked THAT hard), as they only built them for a couple of years.
  • Jkross22 "I’m doing more for the planet by continuing to drive my vehicle than buying a new one for strictly frivolous reasons."It's not possible to repeat this too much.
  • Jeff S Got to give credit to Chrysler for putting the 300 as a rear wheel drive back on the market. This will be a future classic.
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