Popular Mechanics
The radial piston engine long has been recognized as a space-efficient design, and it's been the powerplant of choice for general aviation. A new approach to the radial design—a four-cylinder layout with connecting rods linked to a circular drive-plate type of crankshaft—is being promoted by Markel Motor Espana, a Spanish engineering company. This engine is a radial, but it's also a rotary—the entire cylinder block spins. It's a two-stroke engine, delivering a fuel-air mixture (from a carburetor) through the crankcase into ports adjacent to the cylinders, and it delivers power on each downstroke. The two-stroke cycle reduces vacuum, so there isn't enough vacuum to fill the cylinder. Therefore, the engine is supercharged.
Most conventional engines operate like a bicycle in that pedaling turns the crank and the road wheels. In this engine, however, the power strokes of the pistons impart rotary motion to the crankshaft plate, and the plate transfers rotary motion (through the rods and pistons) to the radial block. Because both the engine block and crankshaft turn, the two transfer power to a common gear drive in a transmission, for a combined power output.
Each cylinder has a spark plug, but because the block spins, there's no wiring directly to the plugs. Instead, this mechanism is much like the free-ride brass-ring holder at the edge of a carousel. As the block rotates, each spark plug passes within 2mm (0.08 in.) of an ignition terminal and the high-voltage electricity "jumps" the small gap to the plug. You can see the external spark as the engine operates.
The engine resembles a four-stroke in that each cylinder has an overhead exhaust valve operated by a pushrod (from a cam drive on a fixed portion of the engine). And the reaction from the escape of the exhaust gas adds a small amount of rotational "push" to the engine block.
Because the block rotates, it is inherently air-cooled. Of course, the rotating block has to be shielded, and unless a machine has an engine housing (such as a lawnmower), one would have to be added. In addition, there would have to be good isolation of the ignition spark from the exhaust, just in case there was a lot of unburned gasoline in the exhaust stream, such as from a misfire. At this stage, there isn't much of an exhaust system in the design.
Markel is claiming very high efficiency and what seems like high performance (80 hp from 24 cu. in.). The output actually is reasonable for a supercharged two-stroke, but there's a long way to go to produce a practical powerplant that can meet emission regulations. At this point, all we know for sure is that the experimental engine definitely runs, as was demonstrated at the recent exposition of the Society of Automotive Engineers.
The design is unlike anything we've ever seen, although it combines elements of many engines. In an era in which the two-stroke was given up for dead, the Markel engine demonstrates that there are engineers who think it can come back. The Markel engine is barely out of the womb, and the automobile industry needs sophisticated maturity. Markel recognizes this, and is hoping that engineers with less-demanding applications, such as stationary powerplants, can see enough potential to help with the development.
Page 1 of 1
