Efficiency of today's internal combustion engines continues to improve, while pollution and cost continue to drop. Most applaud these trends in engine refinement, yet some want more. Truly significant improvements, they argue, demand a radical--not incremental--departure from traditional engine design. A Variable Combustion Ratio (VCR) engine from France, and a new rotary engine designed in the U.S. are recent examples. Do they warrant development and testing? Which offers the most promise? You decide.
Variable combustion ratio engine
Bernard Condamin believes there are too many engine types relative to the total number of cars produced in the world.
"Each year in Europe," claims the telecommunications engineer, "approximately ten automobile manufacturers build ten million personal vehicles equipped with 100 different engines." Assuming new engine development costs six billion FF, and manufacturers produce the engine for 20 years, Condamin contends amortization amounts to 3,000 FF--"an awful figure compared to manufacturing cost."
The VCR design, he says, makes better economic sense, since one engine covers a wide range of needs. This is because combustion chamber volume is proportional to load, resulting in constant compression pressure for maximum efficiency.
| Two shells forming the crankshaft block encapsulate the cylinder block.
Construction. Designed around traditional components, the VCR engine incorporates a crankshaft block and encapsulated cylinder block. Relative position of the two blocks varies due to a displacement set. Comprising nine eccentric crankpins, the displacement set is actuated by a hydraulic jack and computer-controlled solenoid valves.
| When displacement set swings 60 deg, crankshaft and cylinder blocks are relatively displaced 6 mm.
Engine and drive parameters govern solenoid valve operation. A kinematic transfer mechanism, designed to absorb variations in the distance between the camshafts and crankshaft due to relative displacement of the two blocks, drives the valve gear. This concept, Condamin says, can be applied on in-line or V-type engines.
Operation. Depending on load, the cylinder block moves up and down relative to the crankshaft axis. Compression ratio increases when the driver eases off the throttle. First, the engine management system orders the incoming solenoid valve open; fluid pressure then acts against the hydraulic jack, rotating the displacement set. As a result, the cylinder block slides down inside the crankshaft block to reduce combustion chamber volume.
Compression ratio decreases when the driver pushes the accelerator. Now, the computer orders the discharge solenoid valves open; the lever arm pushes the jack back, discharging fluid to a thrust chamber. The displacement set, in turn, rotates in the opposite direction. This allows the cylinder block to slide up inside the crankshaft block, increasing combustion chamber volume.
Benefits. Condamin claims the VCR engine offers several advantages over conventional internal combustion engines:
Maximum efficiency for all loads.
Like the VCR engine, Leo Kull's Peristaltic Vane engine features variable volume pressure chambers. Unlike the reciprocating motion of Condamin's VCR engine, Kull's design features concentric sets of rotating vanes.
| Variable volume pressure chambers and four 90-deg power strokes add up to 360-deg power consecutively applied to four vanes.
Kull, a life-long design engineer and holder of two dozen patents, has built kinematic models of the new engine. Presently, he is looking for a party to manufacture a working internal-combustion-driven prototype.
Construction. Differential linkage couples the two vane sets of Kull's design to an orbiting crankpin. Fixed on a 2:1 reduction gear, the pin follows an elliptical control path that forces the variable motion between vane sets. A 4:1 orbiting gear ratio, built into an "internal control" gear, changes the crankpin's elliptical control path to a "rounded square" control path. This power transmission linkup provides a positive translation between the variable-motion, alternately accelerating/decelerating vanes and the uniform rotation output shaft.
Valveless fuel input and exhaust ports reside in a distribution stator. Different configurations accommodate four- or eight-vane engines; synchronization with the internal control gear, via cam or crankarm, regulates timing between vanes and ignition.
Operation. Rotating the output shaft of a four-vane engine advances the outer set of vanes 135-deg. At the same time, it advances the inner set 45-deg. This variable motion creates a 90-deg volume increase between adjacent blades at the inlet port, and a 90-deg decrease at the outlet port.
| Differential linkage translates variable vane motion to a uniform rotation of the output shaft.
Similarly, an eight-vane engine exhibits eight opposing 45-deg power strokes. These volume changes, respective to the different port patterns, results in 2x360-deg of power consecutively applied to the engine's total number of vanes(16 45-deg power strokes per revolution in a double-acting model). Kull likens this phenomena to the peristaltic motion of a tube-and-roller pump.
Benefits. Believing his design allows for less-complicated sealing than Wankel and axial vane-type rotary engines, Kull says the Peristaltic Vane engine better realizes the inherent advantages of a rotary design:
Balanced rotors for quiet operation.
While Kull admits "it may be too optimistic to predict that our rotary engine will replace the vehicular piston engine," he says its advantages over the Wankel engine, and availability of five control options (see U.S. patent #5,501,182), make it suitable for a wide range of other applications. These vary from pumps and compressors to high-horsepower, low-speed direct propeller drives for marine diesel engines.