Meet “The Neverending Article.” It seems like a pretty straightforward proposition, right? Compare and contrast the major motivators out there today. No problem. And it probably wouldn’t have been, if we’d just stopped at Part I of this article, which focused almost exclusively on powertrain options available for the last 20 years or so. But here in The Future, the minute you think you’re done writing about one kind of powertrain, you’re right back to recycling the intro from the last article to open the next one.

But hasn’t that been the way of the automotive industry for the last century or so? Slightly modifying a product that was mediocre to begin with so it seems relevant compared to similarly mediocre products? The next iteration is rarely about net improvement so much as it is keeping up with the neighbors. It’s a Sisyphean task indeed, not recycling the same crap from last year; over-using the same tired approaches for decades, and pretending as though “new and improved” weren’t a suspiciously relative compliment at best.

In Part II of our Powertrain Showdown, we’re going to go over some of the “weirder” technologies out there. Though probably the weirdest thing about a lot of them is how recycled they actually are. Sure, taken out of context, some of these ideas seem a little bit out there in left field; but a lot of them have been around at least as long as today’s powertrains. It’s just that they, like hybrid and electric technologies, have languished in under-development from the century-long scourge of cheap gasoline.

But, you have to give antiquated piston-engine technology this: it did make writing about powertrains a pretty straightforward endeavor for a while. At least when you were done talking about gas and diesel, you were done talking. Unlike today, where our Neverending Article continues with Part II, and our boulder rolls right back down the hill again.

Turbine Engines

Turbine engines are effectively jet engines, the same kind used in your favorite airliner. Many manufacturers have experimented with turbines over the years, most notably Chrysler in the 1950s. And the results were pretty predictable: turbine engines make absolutely no sense in terms of driving the wheels, unless all you’re looking for is massive, sustained high-rpm horsepower.

Imagine the highest-revving motorcycle engine in the world, then multiply that by 10. Turbine engines are incredibly light, compact, simple, and make tons of power at high rpm. How high? Over 120,000 rpm, usually.

That normally wouldn’t be a problem, since you could say the same of a lot of compact electric motors. The difference is, those motors don’t have to idle at 80,000 rpm, and they actually make some torque below that.

This isn’t to say they don’t have a place in the automotive world; Chrysler’s Turbine cars, Jay Leno’s Y2K Jet bike and the M1A1 Abrams tank would beg to differ. But those are all, shall we say, kind of "niche applications." Jet engines are amazing in terms of sustaining power output, and they’re almost unparalleled in applications where outright power trumps acceleration from a standstill. A jet engine could push a tank uphill at 100 mph with no problem…once it gets to 100 mph. But that could take a while.

Apart from sustaining high power output, a turbine engine’s diesel-like fuel flexibility is its biggest trump card. Its primary drawback: the turbine engine uses a LOT of that fuel for the amount of power delivered if it’s not in its (often pretty narrow) peak efficiency zone. Once it’s in that zone, the turbine engine can be extremely efficient; but again, it’s a matter of getting it and keeping it there. Even in the M1 Abrams tank, a diesel engine with more power than the turbine would be 14 percent cheaper to operate per mile. And that’s not counting idle time or red lights. Then again, it’s probably cheaper to spend an 88 mm cannon shell on a red light than to idle the M1A1 for 30 seconds. It’s all about strategy.

It’s probably cheaper to spend an 88 mm cannon shell on a red light than to idle the M1A1 for 30 seconds

So, if turbine engines are all but useless for automobiles, why mention them at all? Freak factor? Nope. There’s some real application here…at least Jaguar and its new parent company Tata think so. You might remember back in 2010, Jag introduced a concept car called the C-X75, a mid-engine exotic powered by a pair of “micro-turbines.” Ultimately, Jag opted not to use them in production over concerns about reliability; but they’re still working on them with U.K-based Bladen Jets Engineering Center.

The fact that Jag used turbines at all is interesting…but not as interesting as the way they used them. The C-X75 is a hybrid sports car, along the same lines as the McLaren P1. Difference being, this design is a pure series hybrid, with the micro-turbines used as generators to power the car’s primary electric motors. In testing, Jag found that its micro-jets were more efficient than the 1.6-liter Ford four-cylinder they wound up using.

In this application, using them as generator motors, Jag really capitalized on what turbines do best: provide a lot of constant power within a fairly narrow rpm range. Using it as a generator, you can keep the jet at an almost constant rpm, and engineer it to work perfectly at that rpm without compromise. It’s an elegant solution, and shows that turbines have some potential if they’re used in the right application. That’s not something Jag figured out, though. They’re just taking a cue from another industry where these engines are routinely used as generator motors: natural-gas powerplants. But natural-gas powerplants utilize a very particular type of jet engine…one that comes by its efficiency using another technology long thought abandoned for use in automobiles.

Steam

Put aside your face-palming recollections of the Stanley Steamer and Doble. Those early steam engines were renowned for their incredible (some would say "locomotive-like") torque. Next to an electric motor, nothing will give you the kind of "hand of God" shove that steam will. Those early steam engines obviously had some problems though. They’d go through water pretty quickly; less so for "condenser" cars like the Doble, but still about a gallon every 15 to 20 miles or so. They were fairly efficient in terms of fuel use for the day, but nowhere near modern-day standards.

Next to an electric motor, nothing will give you the kind of "hand of God" shove that steam will

So, why not just make steam engines better? The water isn’t that big a deal, but why not apply a century’s worth of development to just making them more fuel efficient? Partially because of something called "Carnot efficiency." Basically, Carnot is the theoretical wall on how efficient a steam engine can be, given a certain temperature of steam and a certain temperature of outside air. The closer the steam and air in the expansion chamber are in temperature, the less efficient the engine is. Or, to put it another way: really hot steam plus cold outside air makes for more efficiency. Cooler steam and hotter outside air means lower efficiency. To get past the Carnot wall of those older engines, you’d need to burn a lot more fuel, much faster and hotter than those old tea kettles ever could.

Enter: The Turbine.

"Combined-cycle" engines are essentially a hybrid of jet and steam engines. They recapture some of the heat from the jet and use it to super-heat water to potentially thousands of degrees. Turn that into super-heated steam, and you’ve blasted past the Carnot wall of those old Stanleys and Dobles. These “hybrid,” combined-cycle, steam/jet engines lay at the heart of most natural-gas powerplants. These engines are proven performers when it comes to squeezing every last drop of electricity from every ounce of fuel. Of course, they’re not 100 percent efficient, since Carnot still has some say…but combined-cycle engines are still in an entirely different league in terms of power and efficiency than either jet or steam engines alone.

Right now, the only real limitation on combined-cycle engines in this application have to do with size, weight and complexity. But ultimately, there’s no real technical reason you couldn’t make a combined-cycle powerplant much smaller for use it in a parallel or series hybrid. It’s kind of like Jeff Bridges said in the first Iron Man movie, while pointing at Stark’s prototype arc reactor: “The technology is right there. I’ve simply asked you to make it smaller.”

Once that happens, turbines and steam engines could combine to make a real contender for the hydrocarbon-burning hybrid of the future. Well, assuming hydrocarbons have a future at all. But we’ve already been over that.

These “hybrid,” combined-cycle, steam/jet engines lay at the heart of most natural-gas powerplants.

As of now, nobody’s really made the developmental leap to miniaturize combined-cycle engines for use in cars…or, more accurately, made much of an effort to. But the industry is on its way there, one way or the other. BMW, along with a few other companies, have been working on thermal recapture systems that may move us in that direction in the near future.

BMW’s Steam Assist Drive (“turbosteamer”) is essentially a bunch of steam tubes wrapped around the exhaust manifold and catalytic converter. The steam generated there goes to a turbine, which adds some power to help move the car. Effectively, it’s about a half of a combined cycle engine. Combine that half with Jag’s micro-turbine, and boom…you’ve got yourself a fully formed, miniaturized combine-cycle engine.

Granted, there are crucial developmental steps to be made between one and the other, but nothing technologically ridiculous at this point. It’s only a matter of time before BMW’s peanut butter meets Jaguar’s chocolate, and one delicious combined cycle gas generator emerges. We can call it “The Reese’s Drive.”
Then again, the Reese’s Drive might just be an academic thing. It may not happen at all, no matter what Jag and BMW do. Not because it’s not a good idea, but simply because there might be better options available by then. Battery technology is accelerating daily, and once manufacturers get real and start standardizing replaceable battery packs…well, you can probably wave goodbye to the automotive internal combustion engine altogether. Even the most efficient gas generator on Earth isn’t as efficient as your average cordless power drill. So, the Reese’s Drive may end up being the Me-262 of internal combustion – a great idea, but perhaps too little, too late to win the war.

And then it will be the Messerschmitt Drive.

We’ll see.

Then again, batteries and electric motors aren’t perfect, either. No matter how efficient or convenient the motor, battery or generator, it all still requires converting energy from one form to another. Which as you already know is wasteful business. What if, instead of converting kinetic energy to mechanical to chemical to mechanical and back to kinetic, you could skip a few steps and store kinetic energy directly? Wouldn’t that be even better?

Hydraulics, Pneumatics and Springs — Oh, My!

And now, the final roll of our Sisyphean boulder — kinetic energy storage devices. Cars driven with hydraulic power, compressed air and even wound-up clocksprings might seem very different, but ultimately they all work the same way: by storing and releasing kinetic energy.

Hydraulic (aka Hydrostatic) Drives

These are a lot more common than you might think. Like most others here, this idea isn’t new…but unlike the others, it’s already in widespread use today. Just look to your nearest bulldozer or "zero-turn" lawnmower. In these applications, you’ve got an engine to drive a variable-displacement hydraulic pump. That pump sends fluid to the hydraulic "motors," which directly power the wheels.

Just look to your nearest bulldozer or "zero-turn" lawnmower for hydrostatic drives.

Pros
1) Allows for precise and independent control of wheel speed and direction, which is what allows "zero-turn" lawnmowers to spin around on their own axis.
2) Can handle massive amounts of power, with zero internal friction and "infinite slip" between wheels and engine.
3) Can be extremely efficient, particularly since most come with a variable-displacement main pump. The VDP acts like a continuously variable transmission, but without the efficiency losses or slippage many CVTs have.
4) Can utilize spring-loaded "Hydraulic accumulators" to store energy like that recovered from braking, and release it with little to no loss in energy.

Cons
1) Heavy and complicated: This is a big reason why you usually only see these systems in heavy construction equipment. Hydraulic systems as a rule are very heavy, and so are the beefy parts and motors needed to handle the immense pressures involved.
2) Not usually efficient at speed or under cruise: These systems work well at low speed, but under sustained load the fluid heats up, thins out and pressure starts leaking internally. It’s not an insurmountable obstacle, but it’s one hydraulic systems face right now.

Pneumatic Drive

In terms of operation, everything that’s true about hydraulic drive is true of pneumatic, or compressed-air drives. Difference being, they’re worse in almost every way, especially in terms of energy efficiency, and not just because air is a terrible medium for power delivery, since it’s thin and leaks past seals even worse than hot hydraulic fluid. Mostly, pneumatic systems are worse because air compresses, and gets hot when it does.

It's worth noting that compressed-air cars are actually currently in use as taxi cabs in countries like India.

The Ideal Gas Law says that when you compress air, you cause it to heat up. Heat is waste; so, you’re going to lose energy just in compressing it. And even past that, you get into problems of compressor and motor efficiency, temperature variables, and a whole host of other issues.

It’s worth noting that compressed-air cars are actually currently in use as taxi cabs in countries like India. It’s also worth noting that people absolutely hate them, because they’re loud, annoying and about as subtle as the elephant god Ganesha in a room full of field mice. It’s a cute idea, but nowhere near as applicable in the real world as a hydraulic drive...which itself has issues.

The very LAST thing on our list, though...may have some surprising applications in the future.

Clockspring Cars

The image above is from a 1933 issue of Modern Mechanix Magazine. In the early 1930s, Japan was a blossoming industrial powerhouse, with ambitions of quickly catching up to the West. Only problem was, they didn’t have a steady supply of oil like the rest of the world. That oil shortage (or more pointedly, the U.S. embargo of oil in 1940) was one of the direct causes of Japan’s joining the Axis powers and getting into WWII.

The idea of using wind-up clocksprings or even coil-type accumulators to recapture brake energy isn't new.

Point is, the Japanese were among the very first people in the world to experience the pain of fuel shortages and chronic high gas prices. That forced some pretty heavy outside-the-box thinking, and made for a lot of innovative ideas. One of them was, you guessed it, clockspring-powered cars.

For the most part, nobody ever really took the full-sized wind-up car seriously as a viable transportation solution, because it isn’t one...so you can trust I’m not going to end The Neverending Article on that suggestion.

In the real world, clocksprings just can’t store enough energy to keep a car going down the road any length of time. You’d have to start winding your car up at 3 a.m. before work every day, and probably then stop to rewind it twice on the way there. But there is a real-world application here.

One of the major drawbacks to the average hybrid’s brake regen system is that it only recaptures about 25 to 70 percent of the energy that goes out. That high-end figure isn’t bad, but it’s laughable compared to the almost 100 percent efficiency rate of a simple spring. And then there’s the fact that in order to have that electric brake regen, you have to own a hybrid or electric vehicle in the first place.

The idea of using wind-up clocksprings or even coil-type accumulators to recapture brake energy isn’t new — but maybe, like hybrid and electric cars, it’s an idea whose time has come. Even a couple hundred years after the first wind-up cars, very little compares favorably with a wound-up spring in terms of efficiency and cost per unit of energy storage. It’s not a "drive system" in itself, but ye olde spring does have some real potential in terms of a supplementary regen system for electric and non-electric vehicles alike.

Summary

So, there it is…after two articles and the best part of 5,000 words, this boulder has finally settled. For now. And these are just the powertrains on offer; we didn’t even get into the various fuel sources available, which is an entirely separate subject.

It’s a neverending story of trial and error, change and adaptation.

I do want to hear from you on whether you want to see a comparison of fuels or other technologies.

It’s a brave new world…same as the old one. It’s a neverending story of trial and error, change and adaptation. Some ideas are good for a while, and some move in straight lines to tomorrow. But when tomorrow comes, even the best of yesterday’s ideas are old news.

Then we’re right back to the beginning, again.

What do you think?
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