THE RETURN OF JAMES WATT

In 1774, James Watt's invention of the steam engine ushered in the Industrial Revolution. For more than a century it reigned supreme. Then electric power and the internal combustion engine began replacing it, finally pushing it out from its last stronghold, the railroads.

The third point is one that cannot have worried James Watt very much: Pollution control in any external combustion engine is child's play compared with an ICE. It's not all that simple to make nitrogen oxides. You really have to compress the nitrogen (air) and then fire into it with an electric spark to produce them. The steam engine doesn't go out of its way to do that.

So why aren't we all driving steammobiles?

Because steam engines (and turbines) are big and heavy; they need a boiler and condenser as well as the actual engine. Which is fine for a power station, but not for a car. Many designers have tried to fit all three elements into a car, but they usually ended up with a bus. Even so, the Learbus (using a turbine) and other steam driven vehicles designed in the last few years have been less than a roaring success.

But now SAAB, the Swedish car and aircraft manufacturer, has come up with a steam engine that looks like a winner. It will have 250 HP, yet it weighs less and takes up less space than a conventional car engine plus radiator and transmission. The boiler consists of some 120 parallel discs of fine, spirally wound tubing. Liquid fuel (such as gasoline) is burned in the spaces between tubes, turning the water in the tubes into steam. This steam generator measures about 4 by 12 inches and weighs about 26 Ibs. The condenser is air cooled and not radically different trom a conventional radiator.

But the real breakthrough is the design of the steam engine itself. It has 9 vertical cylinders, in a circle inside a cylindrical block. The connecting rods are rigidly attached to the pistons and press down on a "wobble plate," whose action is like that of a coffee percolator lid lying upside down on its knob on a table. When you press one side, the other goes up, and when you press it consecutively going round its circumference, it will do a circular wobble. Under the consecutive action of the 9 connecting rods, the wobble plate wobbles in this way, pushing up the piston opposite the one that is pressing it down. It does not actually revolve, but it can make a crank perform a circular motion, and this motion can be converted to a rotary motion (of the drive shaft) by a bevel gear. (Fairly detailed drawings will be found in this month's Science & Mechanics.)

Reversing the car and preventing the water freezing when the engine is not running are minor problems, which have been solved. The entire engine is so compact that there is enough space left for an additional steam engine to run the car's auxiliary (electric) equipment. This engine runs even when the main engine is idle (e.g., in traffic jams) and contributes to lower fuel consumption. The gas mileage is described as "superior," though we could not get exact figures. SAAB expects to phase out its ICE production in favor of the new steamer over the next 15 years.

The Wankel engine and the Honda stratified charge engine are clever designs, but ultimately they are patch-ups of the internal combustion engine. The 1774 principle in the 1974 version could be more promising.