Another 100 Years?

Another 100 years?

TDC

Kevin Cameron

Is THE PISTON ENGINE THE “FOREVER powerplant” for motorcycles, cars and trucks? Or is something new just around the corner, ready to sweep away our familiar technology?

In 1940, railroad executives believed that the steam locomotive was set for another hundred years. And in 1950, the planners at Wright Aero were convinced that their 18-cylinder piston engine could soldier on “for years and years” as a mainstay of air transportation. Both groups were wrong. The diesel put an end to steam loco construction by 1956, and the gas turbine completely eliminated the piston engine from commercial aviation by the mid-1960s.

Yet here we are, working harder and harder to get smaller and smaller gains from our 100-year-old concept, the internal-combustion engine. Are we set for another hundred years?

Right now, many believe that electric vehicles are about to take over a major share of ground-transport duty. We’ll just cruise home from work, plug our sensibly sized commuter electrics into the charger and forget it. No more nasty, evaporating, incomplete-burning gasoline, no more emissions, no more problems. Neat. But the rumblings of dissent are loud.

At well-promoted electric-car races, advanced battery prototypes explode, spewing highly reactive electrolytes. At a recent conference on alternative transportation, many of the battery people said out loud that batteries cannot for the foreseeable future compete even remotely in energy-storage density with liquid fuels. Many of the proposed battery technologies require replacement of the entire battery set at short intervals-like every 20,000 or 40,000 miles.

But wait, there’s more. The electricity that will power these zero-pollution electric vehicles must be generated somewhere-perhaps in a low-population state where it’s not so hard or so expensive to obtain permits to burn oil or coal, or to operate a nuclear system. The generating plant has an efficiency of 30-50 percent. Then the power goes out over the electric grid, suffering radiation and resistance losses. There are further losses as the high-transmission voltage is stepped down at the substation, then stepped down again from the local

line to your home. Next, the voltage is stepped down once more in your electric car’s charger. Conversion of electric power into chemical energy, to be stored in the battery, takes its cut, too.

Finally, chemical energy is reconverted into direct current at a furtherefficiency loss. Depending on what kind of motor and control system are in the car, this power may have to be further processed, cut into pulses, switched and what-have-you. After all this, what overall efficiency will this system actually deliver?

It’s because the figures don’t look especially good that many automotive engineers have turned toward hybrid vehicles. Because we have already invested huge treasure to make local burning of liquid fuel clean and relatively efficient, it makes sense to continue using it. Therefore, hybrid vehicles carry an internal-combustion engine to provide sustainer power for highway cruising, hillclimbing and general highpower use. But to enter the city, where social legislation and common sense may require use of zero-pollution vehicles, the hybrid switches to a small battery pack. Once outside the city again, the sustainer IC engine cuts in and begins to both drive the vehicle and to recharge the onboard battery.

Volvo built such a vehicle and showed it last year: A turbo-electric car propelled by a 90,000-rpm gas turbine driving a direct-coupled alternator. There have been attempts to build turbinepowered cars before, but the problem is flexibility. A piston engine’s ability to

compress, burn and expand its charge depends upon its sealing ability-bikes have engines that idle at 1000 rpm and run fine all the way to 12,000. But a turbine’s ability to do all this depends upon the square of the speed at which its blades are moving. Essentially, drop the rpm of a 90,000 turbine to 80,000 and you have lost all your power and efficiency. Volvo’s hybrid design neatly gets around this problem. The turbine runs at a steady 90,000 rpm or it is shut off altogether and the car runs on battery. In either state, the car is driven by an electric motor, and load is altered by sending more or less fuel to the constant-speed turbine.

The big problem with turbines remains expense. At present, turbine technology requires advanced heat-resistant metals and fancy cooling techniques that hold the price at something like $250 per pound of engine weight. Auto engines are currently priced at more like $4-10 per pound, and motorcycle engines at $15-20 per pound. Even if a turbo-electric powerplant were quite light, the battery, motors and controls would surely bring all-up weight to figures near those for IC engines. A sportbike engine weighs close to 200 pounds, so let’s do the numberswe get $50,000 as a suggested retail for our dream engine. Fortunately, the hybrid concept still looks good built around a piston IC engine. That piston engine remains a reasonable combination of efficiency, price and weight/ bulk. Present-day emissions technology has made auto engines essentially pollution-free except for a few seconds during start-up. We have a long-established system for making these engines, and another fair-sized system that provides fuel for them. To change all that, even to an engine type as cheap as the IC engine itself, would require billions in worldwide re-tooling. Consequently, the piston IC engine will be with us for a while yet.

On the other hand, there is all that steady development in high-temperature ceramics that we read about. A simple, molded turbine wheel made of such “pottery” could lower turbine costs a lot. And then there is the fuel cell, some types of which have demonstrated direct fuel-to-electricity efficiencies of 50 percent.

Another hundred years?