Rotary with a Twist

For some automotive experts, the most exciting exhibit at London's recent fall motor show was found not among the gleaming new Jaguars and Rolls-Royces on the floor of the main exhibition hall, but inside a back room where admission was by invitation only. There, away from the car-hungry crowds, a young American automotive whiz and part-time motorcycle racer named Bob Karol displayed small models of a bold new engine design that may some day challenge the much-bally-hooed Wankel.

Karol's machine, like the Wankel, works on the rotary principle; that is, the energy from its burning fuel is converted directly into rotary motion.* Yet unlike other rotaries, it retains many of the acknowledged advantages of conventional internal-combustion engines. In standard auto engines, for example, the reciprocating actions of cylindrical pistons successively suck in a mixture of gasoline and air, compress it, turn a crankshaft after an electric spark touches off the explosive vapors, then expel the burned fuel residues. In rotary engines like the Wankel, the same effect is achieved not by reciprocating pistons but by a turning rotor. As it revolves inside a specially shaped chamber, the rotor is able to perform all the basic strokes of a piston engine: induction, compression, ignition and exhaust. The new engine, originally conceived by Karol to get more performance out of motorcycles, combines what he considers the best of both systems: it consists of a large, partly spherical rotor that itself contains two side-by-side pistons sliding at right angles to each other.

Although the design looks like a machine-tooled Chinese puzzle, the engine works with remarkable simplicity. Unlike the pistons in ordinary engines, those in Karol's engine are double-ended and have entirely separate functions (see diagram). It is the job of one piston to draw in air. The other provides the power; all the explosions in the engine occur within its cylinder. Thus it is the movement of this second piston that actually turns the crankshaft (which passes through both pistons) and the rotor.

The cycle begins when one end of the air-pumping piston passes a vent in the engine casing and sucks air into its cylinder (1). At exactly the same moment, the other end of the piston is pushing the air that it has already captured and compressed into a passage at the opposite side of the engine casing. As the rotor turns, the air is forced through a transfer port into the cylinder of the power piston (2). Continuing its rotation, the power piston compresses the air even more (3). As the piston's cylinder moves past the fuel injector, the compressed air is mixed with a spray of gasoline (4). Then, as the cylinder edges by the spark plug, the fuel-air mixture is ignited (1). Pressed by the expanding gases, the piston begins the equivalent of the power stroke. All the while, it continues its rotary motion (2, 3 and 4). Finally, as the power piston's cylinder passes another opening in the engine casing, the burned gas is expelled (1), only to be quickly replaced by a fresh charge of air from the pumping piston (2). The design practically eliminates waste motion by either piston. Both ends of both pistons are at work in every cycle.

Richard Ansdale, a British rotary-engine specialist who is close to completing a working prototype of the engine, considers this division of labor by the pistons--or "split cycling," as he calls it--a distinctive feature. By relieving the power piston of the job of inducting air, it allows the engine to take in more air and burn its fuel during a much greater portion of each cycle than in conventional engines. Moreover, a blast of fresh air helps expel the exhaust gases before any more fuel is introduced. The net result, Ansdale explains, is not only a more efficient use of gasoline, but also less of the unburned chemical residue that is a major source of automotive pollution.

Vibration-Free. Like the Wankel and other rotaries, the Karol-Ansdale design has fewer moving parts (no potentially troublesome valves, for example). It is almost vibration-free and weighs much less than conventional engines with equivalent horsepower. Ansdale figures that a 145-h.p. model would be only 27 in. long and 18 in. wide. Finally, the design has a distinction that the Wankel cannot claim: because of the uncomplicated shape of its pistons and rotor, it can be built with familiar piston-engine techniques. In contrast, the Wankel has introduced many new engineering problems.

Detroit auto men who have seen the design are skeptical. They point out that a full-scale working model has not yet been completed or put into a car. But Pennsylvania's Anidyne Corp., which has bought the patent rights from Karol and is sponsoring the developmental work in Britain, is convinced that design can be turned into reality. "It can be hellishly complicated," admits Ansdale, who helped develop the Wankel, "but none of the problems are beyond the range of known technology."

* In the conventional reciprocating engine, combustion drives the pistons in straight-line up-and-down movement, which is converted into rotary motion by connecting rods and the crankshaft.

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