Power Transmission

10-99

Technical Feature

Rotary turbine torques up more power

Mark Fletcher casts his eye over an engine design that claims to combine the advantages piston and rotary engines

What do you get if you cross a skating rink with a rotary engine? Before you start envisaging a new form of skidoo, read on. A new engine concept from Canada, known as the Quasiturbine, offers a design similar to that of a rotary engine but with the advantages of a gas turbine – all within the confines of chamber based on the shape of a Saint-Hilaire skating rink profile.

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The profile offers the rotary components of the engine a bigger, more uniform radial path, enabling maximum torque to be reached more efficiently than a normal combustion engine. A fixed centre of rotation offers significantly less dynamic vibration, while continuity is provided by continuous ignition (like a turbine) through ignition transfer slots.

The method of operation allows the engine to be extremely flexible. The developer claims that it is possible to use it for pneumatics, hydraulics, steam, petrol, natural gas and hydrogen. This flexibility immediately opens up the application base for what looks to be an extremely compact power source. A combustion version has been built and fitted to a trial design of chainsaw. The developer is also working on a steam engine that runs on saturated vapour for co-generation and an air compressor for use in the pneumatic industry.

Its ability to deliver high torque at low speeds can realise certain savings due to an increase in efficiency. According to the developer, gearboxes can typically consume between 8 and 12 per cent of the energy output from an engine. Good low-speed torque characteristics could remove the need for a gearbox and the infrastructure associated with it.

The internal mechanism manages to follow the internal 'ice-rink' profile of the chamber by using a series of carriages which in turn ride on a four-element variable shape rotor. As the engine turns, the variable shaped rotor exhibits a square configuration when two opposing elements are in the 0 and 180 positions. After further rotation (45 ) it elongates to exhibit a lozenge shape (due to the shape of the chamber) and then back to a square. Where the rotor elements meet they form four pivot points on which the four centrally pivoted carriages ride. These carriages can contain a continuous contact with the inner profile of the chamber due to the variable shape of the rotor.

The Quasiturbine incorporates few moving parts and as it has no oil pan it can be operated in completely submerged conditions. Due to shorter high-pressure confinement times its method of operation also claims to reduce both heat transfer to the engine block and the creation of nitrogen oxides. A compressed air prototype or steam prototype has been built using two parallel expansion circuits of 200cc per revolution each; a total intake of only 12 cubic feet/min is needed at 1,000rpm.

The ‘Saint-Hilaire’ profile allows the fastest possible transition around the top dead centre. The prototype demonstrates a rate of change in its radius of 0.42 per cent per degree of rotation; this compares to 0.3 per cent for an elliptical profile and 0 to 0.15 for a piston engine. The greater rate of change enables the engine to reach 50 per cent of its maximum torque after a rotor movement of just 10{{degrees}}.

Unlike other rotating devices, in which torque increases progressively until a maximum is reached), the Quasiturbine rapidly reaches the maximum diameter and then follows it accurately along its entire length. Traditional rotary engine designs also present a dilemma when it comes to specifying compression ratios. If the compression ratio is to be increased, the intake volume must decrease to an unacceptable level. This imposes dimensionally on the engine. The Quasiturbine permits the construction of a compact detonation or diesel engine. Its asymmetric shape allows a higher compression to be reached, for maximum energy extraction, and offers an extended expansion cycle.

Rotary engines are often prone to wear and leakage around the tips of the rotor. One reason for this is because the seals interact with the internal profile of the chamber at a variety of angles. The Quasiturbine's variable-shaped rotor, however, ensures that the tips are always in perpendicular contact with the engine profile. It is also not prone to the same vibrational forces that are a feature of the off-centre rotating ‘piston’ of rotary engines.

The lesser complexity of the engine permits it to run with far fewer peripheral devices such as pumps, cam shafts, push rods and valves – all of which lower the mechanical efficiency of what is already an inefficient process (certainly lower than 50 per cent). The Quasiturbine’s empty centre area allows for the inclusion of an electric motor/generator – a principle that will appeal to designers of hybrid devices.

Recent advances in more traditional engines have identified hydrogen as a potential future power source for vehicles. According to the developers of this engine the Wankel engine was always a good candidate for the use of hydrogen as a fuel because of its stratifiable intake chamber. The Quasiturbine also exhibits the fundamental criteria necessary to use hydrogen as a fuel source. These include cold intake area, stratified intake, reduced confinement time, low sensitivity to detonation, less pollutant, robustness and energy efficiency.

Another grievance of many internal combustion designs is noise. For comparable power, the Quasiturbine claims to be quieter than a piston engine. This is due to the fact that it splits each expansion and evacuates the gases more gradually.

Details of the engine can be found on the internet at www.quasiturbine.com. One section shows various animations including a Realvideo or Windows Media file of the engine being run. To get the full benefit of how the carriages and the variable-shaped rotor interact with the internal profile there is an impressive 3D animation showing the engine cycling.

The engine exhibits similarities of both rotary and turbine engines with some of the advantages of both

By using a special profile the engine reaches a higher torque level much more quickly than other designs

A prototype has already been fitted to a chainsaw, which is being further developed

Claimed to be quieter and with less dynamic vibration, the engine can be directly linked to an electric motor – opening up applications for hybrid power plants

Design Pointers

The engine exhibits similarities of both rotary and turbine engines with some of the advantages of both

By using a special profile the engine reaches a higher torque level much more quickly than other designs

A prototype has already been fitted to a chainsaw, which is being further developed

Claimed to be quieter and with less dynamic vibration, the engine can be directly linked to an electric motor – opening up applications for hybrid power plants

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