Science: Help from Honda

While Detroit's automakers search for ways to reduce the polluting gases produced by the internal-combustion engine, a company best known for its motorcycles may well have found the answer. Japan's Honda Motor Co. plans to begin exporting to the U.S. a 1,600-lb., four-seat car that will easily meet the 1975 emission standards set by the Environmental Protection Agency.

The Japanese auto will be the first production-line car with a "stratified-charge" engine, a modified version of the standard auto engine. That modification, which does not require extensive retooling of production lines, allows the stratified-charge engine to run on mixtures of fuel that are considerably more "lean" (a high ratio of air to gasoline) than standard engines now burn. The result is more complete combustion in the engine's cylinders and the reduction of polluting exhaust gases escaping from the tail pipe.

In Honda's machine—as well as in versions under development by other companies—a mixture of fuel that would ordinarily be too lean to ignite in the cylinder is coaxed into burning by the ignition of an adjoining layer of much richer fuel. To accomplish this stratification of fuel, Honda's engineers added a small combustion chamber, to accommodate the richer mixture, at the top of each cylinder (see diagram); the chamber contains the spark plug and is equipped with its own intake valve.

Spreading Flame. With that addition, the cycle of the stratified-charge engine remains quite similar to the sequence in ordinary internal combustion engines: 1) As the piston descends, a rich fuel mix from one carburetor is injected into the small combustion chamber near the spark plug. A leaner mixture, from a second carburetor, is squirted into the rest of the cylinder. 2) Moving up, the piston compresses both charges, pushing back most of the richer mix that may have seeped into the main chamber. 3) The spark plug fires the rich mix. 4) The rich, burning mix ignites the adjoining lean mix, and the expanding gases push the piston down. 5) Moving up again, the piston forces the spent gases through the open exhaust valve.

Honda engineers insist that the extra carburetor and the additional parts needed to open and close the second intake valve on each cylinder will not add more than 10% to the basic cost of the 65-h.p. engine. Moreover, they point out that the engine does not require special servicing or changes of material to maintain low emission. By contrast, U.S. and other foreign engines will need expensive catalytic converters or thermal reactors to meet 1975 emission standards. The catalytic converters can easily be fouled, have tended to break down in tests and, in any case, must be periodically replaced.