AN AUTOMOTIVE EXAMPLE

It should be recalled that the jet plane was invented, on paper, in the last century; what was new about it in WW II was a metal that could withstand the heat without melting.

The efficiency of the current automobile engine is about 20%; a gas turbine using superalloys to work at 1900øF would double that to 40%. If a temperature of 2,500øF could be achieved, the efficien-cy would be pushed up to 50%. Apart from fuel savings, the engine would be smaller, lighter, and could burn alternative fuels (coal dust, for example).

What has been achieved in the lab is turbines with rotors made of CMCs running at temperatures above 2,000øF. A rotor that can spin at 100,000 rpm at 2,500øF is not yet here, but will eventually be realized, presumably in Japan, which is the leader in the field.

Meanwhile cars with diesel engines and CMC parts are already being tested on Japan's roads. The first level will leave the (tur-bocharged) diesel engine essentially unchanged, but will use CMCs for parts such as the turbocharger, valve train components and prechamber. The next level will use CMCs for the cylinders and a striking novelty: no cooling system at all, not even air cooling. The ceramic can take the heat.

Isuzu has reported 300 miles of road testing and is projecting production next year. Toyota plans to produce an all-ceramic diesel by 1992.

Automobile bodies will be given increased strength at far lighter weights, which in turn will increase fuel efficiency. Ford has built a prototype graphite fiber-reinforced plastic reducing the total body weight to 50%. What this means for safety is not altogether clear. Composites are far superior to metals in absorbing the energy of small projectiles, but in a collision it is the total weight of each car that determines the sudden deceleration, so that for this aspect small weight is no advantage.

In PMCs America apparently leads Japan. The Pontiac Fiero has an all-PMC exterior, the Ford Econoline van has a drive shaft manufactured by filament winding of graphite and glass fibers in a polyester resin, and springs made of glass fiber-reinforced plastics, used in the Corvette and other models, are now produced at a rate of 600,000 per year.

The main drawback of composites at present seems to be their manufacturing cost, which would explain why they were pioneered in the three fields where cost is not an overriding issue: space, defense, and health (biotechnology). The last of these now uses stainless steel for fermenters in which cell and bacterial cultures are grown. The cultures can be contaminated with metal ions; this and other disadvantages are eliminated by CMCs.

An interesting application of PMCs is armor. The stronger and lighter fiber-glass reinforced plastics absorb the energy of projec-tiles better than metals, and if they are pierced, do not give rise to fatal shards. Characterizing tanks by their weights may become a thing of the past: eventually the PMC tank will be to the metal tank as a bullet-proof vest is to a medieval knight's armor.

[More: "Advanced Materials by Design," OTA Report E-351, June 1988, $14 from Govt. Printg. Off., Wash., DC 20402, stock no. 052-003-01095-0. Apart from the inevitable palaver about government policies, this is a highly informa- tive and commendable report, quite unlike much of the bilge the OTA has been putting out at times.]