The Turbine-Powered Car

A few days ago, I found myself thinking about how turbine engines work. I had the opportunity a couple of weeks ago to watch Troy Giles, a Utah Highway Patrol officer, fly his Bergen Turbine helicopter. Troy helped start the UHP R/C helicopter aerial photography program for traffic accident forensics. He does AP work in his spare time now and as a weekend business. The helicopter, apparently, pays for itself.

It was really impressive. Although heavy (because it was designed to carry more than its own weight in aerial photography payload), it had massive amounts of thrust and horsepower available. The fuel cost was also minimal compared to comparable alcohol-fueled aircraft (often called “glow” or “nitro” motors). There were practically no vibration issues, while piston-powered helis usually have large amounts of vibration.

Two sixteen-ounce aluminum bottles held the fuel — kerosene mixed with just a hint of turbine oil in this case — strapped to the side of the helicopter. It can burn just about anything, though. The motor isn’t really dependent on a particular type of fuel, but kerosene is safe, readily available, and doesn’t have the smell of diesel or gasoline. For a given amount of fuel, it can run two or three times longer than alcohol. The massive blades on this beast held an enormous amount of inertia, and the kerosene seemed to burn clean, hot, and with substantially less smoke than that created by piston-powered helicopters.

Basically, the way a turbine-powered helicopter like this works is that there is no direct connection between the turbine engine and the drive shaft. A squirrel fan, much like that found in swamp coolers and some window fans, sits in the thrust of the engine and is spun thereby. A shaft attaches this fan to a clutch; when the shaft reaches a certain RPM, the clutch expands enough to engage the clutch lining and clutch bell, which starts the rotors turning. It’s a nifty little system.

A really cool aspect is that the cost of small turbine engines has dropped radically over the past ten years. The advent of CNC — Computer Numerically Controlled — machining has made the production of fans which spin at a million RPM feasible on a small scale without enormous costs. Sure, the motors are expensive for a model — around $2,000-$5,000 instead of the $1000 which is typical for a glow or gasoline engine this size — but all things considered, they really aren’t terribly out of line.

It would seem to me that a turbine-powered automobile would have similar benefits. Clean operation. Quieter power, although a turbine does produce quite a roar without muffling. Very little exhaust smoke. Multiple fuel options without modification. Very light motor compared to piston power. Power to weight is superior to a piston engine, which means you can use a smaller engine for the same job and have better fuel economy in many cases. Almost no vibration. Reduced complexity. Much longer service life than piston motors.

The chief issues with using a gas turbine for a car were discovered by Chrysler in their attempt to create a turbine-powered car from the 1950’s through the 1970’s. In fact, the Dodge Charger was originally slated to be powered by a gas turbine. The problems are:

• Lots of excess heat. This was partially solved by re-using heat for pre-ignition heat, which dramatically improves fuel economy and reduces exhaust heat to tolerable levels. Even with that, the thought of 50,000 automobiles producing twice the heat of piston-powered cars idling in the summer sun in Los Angeles makes me shudder.
• High fuel consumption at idle… but better fuel consumption than piston vehicles at highway speeds.
• “Throttle Lag”. From the moment you push the pedal down to the moment the vehicle responds is variable, from as good as perhaps a second and a half to as bad as seven seconds. Not very good off the line, and drivers are really annoyed by the lack of instant power.
• High repair costs. The fact is, machining turbine blades designed to turn 250,000 RPM in 1977 was very expensive. So, too, was manufacturing bearings for such high RPMs, and the lack of strong computing power made a reliable solution for managing RPMs and heat involve a lot of expensive machinery.

I drive a Honda Insight to and from work every day. It carries a highly-optimized, all-aluminum piston engine. I get approximately 54-57 MPG with an automatic transmission, and I don’t drive carefully to conserve fuel (when I do, my average is about 10MPG higher). The key ingredient, after the very light weight of the vehicle (1800 lbs), aerodynamics, and low-rolling-resistance tires, is the hybrid approach. The internal combustion motor is optimized for running at high RPMS, but the electric motor and NiMH battery pack provide about 1/3 of the torque and horspower (about 75HP) required to run the vehicle during acceleration and deceleration. This approach also allows the engine to run extremely cleanly, without the plumes of smoke commonly associated with a heavily-loaded piston engine during acceleration.

What if there were a turbine-powered hybrid?

Stick with me here a moment. Look at the advantages.

• Turbines don’t care what type of fuel feeds them. Natural gas, propane, kerosene, gasoline, diesel, biodiesel, hydrogen… they will burn it all without any modifications to the engine or timing. An on-board computer just manages the heat and RPMs to keep them within bounds. Piston-powered aircraft have to change compression settings, among other things, to make for fuel conversions, which involves opening the engine and installing shims or changing cylinder properties. An ECU for a turbine just modifies the speed of the compressor fan for the same result.
• If run at their optimum RPM range, turbines are very efficient. They have to be kept spinning and kept hot in order to produce power, and that complaint about burning lots of fuel it idle really does matter. What if that “idle” burn was being harnessed to charge batteries rather than wasted?
• Although I have a teeny little engine in my Insight — small enough, in fact, that I could lift it out of the engine compartment and it would be lighter than the cases full of tapes I sling around every day at work — the electric motor acts like a booster and eliminates throttle lag almost completely. It provides a substantial amount of torque at very low RPMs
• Compared to a pure electric vehicle, you eliminate weight, range, and recharge time requirements. For anything other than a commuter car, these concerns are a big deal.
• CNC machining and high-performance electronics allow turbines to operate in safe ranges at all times without tinkering, tuning, or expensive mechanical solutions. A cheap $400 computer with a few sensors will keep a turbine engine running in-spec, all the time.
• Ceramic bearings are ubiquitous and cheap today. This was a big part of the way Chrysler tried to reduce up-front cost, which increased repair costs: using lower-quality bearings.

This hybrid system I imagine would target a state-of-charge of around 50% on the batteries at all times. It would use Lithium-based batteries, probably based on the A123 M1 technology for extremely long life and robustness. These are the same cells used in DeWalt 36V cordless power tools. I own some of these tools, and the power density and safety of these cells is simply awesome. The turbine engine could be reduced to low idle when the batteries are above 50% SOC, and increased when above.

In fact, since there is no direct connection between the turbine and the drive shaft anyway, why not only have the turbine power the generator exclusively? This is the way big trains work: the Diesel turbines power electric generators. The primary thing stopping cars from working this way is the cost of the turbine motors, and the dramatic reduction in machining cost for small turbines might just fuel such a revolution. This would eliminate the complexity of a fully hybrid drive train, allow the turbine to operate at peak efficiency almost all the time, and let you keep the battery pack very small and light since the turbine is providing most of the juice to keep your car running while the batteries just help out during acceleration and deceleration to keep things efficient.

The U.S. government gave Chrysler a loan during the late 1970s in order to keep the company afloat. One of the restrictions on the loan was that they abandon their turbine car program. Chief reasons? The throttle lag and higher cost reduced demand for the vehicle, the high idle fuel consumption was contrary to US energy policy and consumer interest, and repair costs for turbines were much higher than internal combustion engines (largely due to the machining cost). The “alternative fuels” advantage was hardly on the collective US radar during the 1970s… just reducing emissions and fuel consumption for existing fuels. Each of these looks like “solved problems” today using a hybrid approach and CNC machining.

What do you think? Is such a thing feasible? Is it even desirable?

I think of a hydrogen-powered turbine hybrid… and think I see the most perfectly non-polluting, energy-efficient personal automobile one could drive. And I could do it using off-the-shelf, commodity battery packs, turbines, computers, sensors, and existing auto frames.