When Good Ideas Don’t Work Out

It’s unwise to plan a future of scheduled breakthroughs.

Jay Leno with Motorsport Turbine Technologies Y2K
Efficiency wasn’t a selling point for comedian Jay Leno when he bought a Motorsport Turbine Technologies Y2K, a Roll-Royce M250-powered motorcycle geared for 266 mph. “I have steam cars, electric cars, and I’ve always been fascinated by turbines,” he told Cycle World in 2001. “I don’t know how practical it is, but I love it.”Cycle World

One of our readers very reasonably proposed that waste heat from internal-combustion engines could be used to raise steam and recover otherwise wasted power, calling this a “no-brainer.” And I do recall that some trials of such a system in heavy long-distance trucks have been made. A spark-ignition four-stroke gasoline engine on a motorcycle at best applies 30 percent of its fuel to the task of turning its crankshaft. The rest goes out the exhaust or cooling system as waste heat.

Waste-heat recovery can work very well in systems under constant, 24-hours-per-day load, such as the base-load combined-cycle gas turbines that are generating an ever-increasing percentage of US electricity. The six or more hours it takes to get such a system—part gas turbine, part Rankine cycle steam turbine—operating at rated power is a tiny fraction of the 11 months a year duty cycle of such machines. But in a commuter vehicle, the time taken to get a steam bottoming cycle up to operating temperature would seldom be reached in operation, and the system’s efficiency would fall from the extra work of carrying the equipment around. This is why heat recovery has been first applied to big trucks, steadily droning at rated power on long hauls. Even there, with trucking as competitive as it is, it’s questionable whether the resulting fuel savings will pay back first cost plus maintenance of the extra machinery.

Steam rail locomotives were highly inefficient, as toward the end of their era 6 percent efficiency was considered excellent. Therefore, every imaginable fuel-saving scheme was tested. One such scheme was compounding, sending the exhaust steam from a high-pressure cylinder to do more work in a larger low-pressure cylinder. In marine engines, it was relatively easy to place three such compounded cylinders on a common crankcase, presenting relatively easy plumbing from high-to-medium to low-pressure cylinders. When applied to locomotives, whose cylinders are necessarily located where they can directly drive the wheels through crosshead and side rods, the added compound plumbing added flow and expansion losses. Trying for a maximum fuel savings with three stages forced placement of the third cylinder under the boiler, driving a crank axle between drive wheels. This, by limiting service access, increased the labor cost of keeping such locomotives on the road enough that fuel savings were eaten up by increased maintenance.

Yet a much-simpler system of reducing fuel consumption, that of “superheating” steam on its way to conventional single-expansion cylinders, added so little to maintenance costs while saving significant fuel that it was widely adopted. Good ideas that succeed in one application may fail in another. At sea, triple-expansion piston steam engines were successful. Pounding over the rails, they were generally not.

Gas turbine
Gas turbines have been manufactured under General Electric license in Belfort, France, for more than 60 years. GE claims 64 percent combined-cycle efficiency for its 50-Hz 9HA models, which are further hailed as the “world's largest gas turbine.”GE

A similar case was the application of the steam turbine to railroading. In a classic example of “disruptive technology,” the smoothness and efficiency of the steam turbine swept aside vibrating-piston steam at sea and in electrical generation, both of which applications allowed the machinery to operate for long periods at rated power. But when steam-turbine rail locomotives were built and tested that efficiency disappeared in the necessary periods of operation at lower-than-rated power. Turbines are dynamic machines, so their efficiency falls rapidly as they are operated at reduced powers. The same effect is seen in airliner turbofan engines in which thrust-specific fuel consumption throttled back in cruise might be 0.6 pound of fuel burned per pound of thrust per hour (lb/lbt-hr), but drop to 0.35 during full-power takeoff.

So the steam turbine, excellent as it was in full-power applications, could not pay its way on the railroads, which climb and descend grades, stop and accelerate away from stations, and slow for turns.

Wright Aeronautical looked at the problem of flying large piston-engined aircraft across the Atlantic and decided to recover some of the energy being lost as exhaust. Engineers arranged three “blowdown” turbines at 120 degrees behind each engine’s two rows of nine cylinders, piping the exhaust from six cylinders to each turbine. They kept the plumbing short so that the high velocity of escape from the cylinders could be maintained all the way to the spinning turbine blades; no inefficient conversion of velocity into pressure, then pressure back into velocity as on wartime aircraft turbocharger systems. This was neat, direct, and light in weight. And it worked well, reducing cruise-specific fuel consumption enough to permit direct flights New York to London. No more flying the long way, up the coast to refuel at Gander, Newfoundland, then across the water.

Will the engineering experience from F1 trickle down to become more efficient hybrid consumer automobiles?

It has been normal for years to divert part of the exhaust of large marine diesels to spin a turbine driving the ship’s electrical system. And the present hybrid internal-combustion V-6s in Formula 1 use unneeded exhaust flow to generate electricity to charge a battery. That stored electric power can either eliminate turbo lag by spinning up the engine’s turbocharger as the driver accelerates off turns or sent to power the wheels via an electric motor.

Will the engineering experience from F1 trickle down to become more efficient hybrid consumer automobiles? As with compound-steam locomotives, it will be a matter of working out all the costs to see if this technology, effectively operating as a “business,” can earn a profit for the car owner. If the numbers are wrong, buyers will look elsewhere. Tech costs money to develop, and that development cost has to be handed on to the consumer. Hardware costs money, and the more of it there is, the higher the maintenance cost becomes.

The tall foreheads don’t always get it right either. Space shuttle was originally planned to fly 50 to 60 times a year, but because refurbishing it after each flight turned out to be much costlier than hoped, and because of program interruptions caused by two major accidents, in its 30 years of operation, it flew only 135 times, an average of 4-1/2 times a year.

Bill Lear of Learjet fame planned to power America’s cars and trucks with a radical steam cycle.

No sooner did jet engines take to the air than a bright future for high-tech turbine cars was predicted. But, as with other turbines, in applications where there is frequent operation at less than rated power, efficiency is disappointing. And the smaller the turbine is made, the greater the loss from turbine blade-tip leakage, an effect noted before 1910 by Charles Parsons, the man who originally made the steam turbine a success.

Driving to a West Coast roadrace national in the 1970s, I was passed by an experimental turbine bus. I felt a surge of optimism, but automotive turbines didn’t have the flexibility required by surface vehicles.

When I read about the latest breakthrough in the often-hyperventilating tech press, I make a note in the appropriate file and will check back later. In real life, not every good idea can be made successful.