Although impending new rotary engine-powered Mazda Motor Corp. vehicles will be the flagships for the rotary engine community, they are not alone in the rebirth of interest in this segment of engine technology.

Mazda is the leading worldwide developer and producer of Wankel-type rotary engines — and its new rotary sports car, sources say, will be named RX8. That car, and a rotary powered sports sedan to follow, can be expected to focus new attention on unconventional internal combustion systems. Mazda will kick-off its new program in October at the Tokyo Motor show and is planning to show the RX8 in Detroit at the North American International Auto Show in January, 2000.

Other “rotary” engines worth noting at this time:

  • Rotary Wankel GmbH of Korb, Germany, the follow-on venture to Felix Wankel's original development effort, is starting production of direct-injection (DI), spark-ignited heavy fuel (diesel and Jet-A) versions for specialized uses such as military remotely piloted aircraft.

    Two of Rotary Wankel's latest offerings, in addition to its series of gasoline-fueled engines, are a single-rotor, 48-hp, 74.9-lb. (43-kg) engine and a companion twin-rotor version. At the recent Experimental Aircraft Assn. (EAA) event in Oshkosh, WI, the company's president, Juergen G. Bax, says that the single-rotor engine has proven to be of great interest in the military unmanned aircraft category and light experimental aircraft market (kit airplanes) due to its light weight and exceptionally smooth operation. He says initial deliveries also have been made for automotive, marine and industrial uses.

    Fuel consumption of the heavy fuel versions is in the 0.50 lb./hp/hr range.

  • An interesting new entry in the rotary field (see accompanying exhibit) is a 2-stroke diesel rotary (actually an oscillating vane) engine invented by Vladimir Shapovalov, an engineer at Sandia National Laboratory of Albuquerque, NM.

    Referred to as the VSD engine, claims for it are centered on its 1 hp/lb. output, small specific size, favorable power-to-cost ratio and 20% lower friction versus conventional Otto cycle piston engines (see Society of Automotive Engineers paper #1999-01-2888).

    As can be seen from the drawing, there are a total of four combustion chambers, resulting in two dual combustion events per complete oscillation of the vane, from which power is transmitted to the output shaft by a pendulum-like oscillating crank mechanism.

    The VSD requires a separate scavenging air blower at 1 atm. to 1.5 atm. of pressure. Engine compression ratio is 21:1. Claimed fuel consumption, presumably for a small 350-cc prototype, is 0.40 lb./hp/hr with output of 75 hp at 3,500 rpm.

    The VSD's vane oscillates 52 degrees for the equivalent of top- to bottom-dead-center, or 104 degrees, maximum travel of the vane.

    A downside to the design is the loss of lubricant swept along the cylindrical housing wall by the vane apex seals and directly out the exhaust port — but this might be minimized, as Mazda has done, by use of side exhaust porting. Although the surface-to-volume ratio may not be optimum for the least thermal loss, the remarkably small size of the VS diesel could be interesting for a variety of applications.

  • Another dark horse, but with interesting promise in the rotary category, is the Rand Cam system partially funded by NASA (see WEVTU — Aug. 1, '96, p.4). Its developer, Reg Technologies of Columbus, IN, announced at the EAA event that it has filed for patents on a simplified and more-effective sealing system for the multiple-vane compact diesel engine.

Depending on the number of vanes used, a single rotor/vane system has six or more combustion cycles per revolution of the output shaft, providing extremely smooth operation at low rpm. This is ideal for direct-drive aircraft uses, hybrid vehicles and many other applications.

A NASA spokesman says the overlapping torque pulse characteristics of the Rand Cam could translate into minimum propeller weight. And because the engine has a high power-per-pound output and does not require a scavenging air blower, these characteristics — in combination with expected fuel consumption of 0.30 lb./hp/hr — make it very interesting.

A unique feature of the Rand Cam system is its ability to switch the compression ratio at any time from 16:1 to 26:1 by controlling dual intake port openings (i.e., control intake timing at different positions of the compression stroke).

Separately, NASA indicated at the EAA event that the new-technology Williams turbine engine for light aircraft (approximately 700 lbs. [318 kg] of thrust and 500 hp) is scheduled for flight demonstration in a specially built aircraft being built by Scaled Composites at the 2000 EAA event next summer.

Targeted performance for the aircraft is 275 knots (316 mph) with 13.5 mpg fuel economy. Assuming 65% power at cruise, this translates into something between 0.40 and 0.45 lb./hp/hr consumption, considered very good for a turbofan engine. A NASA target for the turbine engine program is a 90% reduction in engine cost. Engine design details are being kept secret by NASA and Williams. Pressure ratio and turbine inlet temperature are on the “secret” list.