The Duke engine is a four stroke "axial" reciprocating engine. "Axial" because the axis of each cylinder is aligned with the axis of the output/crank shaft. Axial engines are sometimes called 'barrel' and 'Z-crank' engines. The former refers to the cylindrical shape of the Cylinder Group whilst the latter alludes to the shape of the Crankshaft. The Barrel shape is a result of the pistons being spaced evenly around the central Crankshaft and aligned parallel to the Crankshaft axis. The 'Z' in the crank provides the journal surfaces upon which the combustion loads (via conrods and then a swashplate, or the case of the Duke engine a 'Reciprocator') act to provide the driving torque of the engine. The uniqueness of the Duke Engine is the combining of these two motions in a counter-rotating configuration which results in a myriad of mechanical and performance advantages.
So far the prototype and developmental engines have run on petrol of various octane levels (91 through 98 octane) and kerosene based Jetfuel without modification and can be readily modified to run on diesel, or indeed any of the alternatives currently proposed as replacements for petroleum-based fuels, such as Bio-Fuels, Hydrogen, LPG, CNG, etc. In fact there are certain features such as the relative coolness of the Combustion Chamber walls during the combustion phase that give the spark ignition Duke Engine advantages for working on low octane fuels, such as kerosene. This feature has some manufacturers very excited as it offers the opportunity for a lightweight, high output engine operating on jetfuel – a fuel typically requiring a heavier, bulkier Diesel engine to be specified.
The most immediately obvious advantages of the Duke Engine are its size and weight when compared to late model conventional internal combustion engines. Duke purchased two current production 3-litre automobile engines (one European and the other Japanese) for measurement to provide true 'apples with apples' comparisons. The current prototype Duke 3-litre engine is up to 19% lighter than those two engines, despite being far from optimised for minimum weight. For example, the significant weight contributed by the many fasteners in the developmental engines would not be present in a production version. The Duke's size advantage is even more impressive, being as little as one third of the shipping box volume - the crate size that would accommodate the engine - of the 3-litre comparison engines. Similarly, a 'shrink wrap' measurement of the volume of the comparison engines showed the Duke has up to a 36% smaller volume.
• Valveless porting, reduces the parts count and size of the engine and gives much greater freedom with the design of the combustion chamber shape.
• Internal geometry generating increased power strokes per crank rotation (compared to a conventional 4-stroke engine). Dynamically the current 3-litre version displaces 3.6L for 2 revolutions of the output shaft, making it equivalent to a conventional 3.6 litre engine. A Duke engine can have any odd number of cylinders, with the optimum being 5 for space utilisation, the number of cylinders in turn determining how many power strokes are delivered per crank rotation.
• A greater range of design freedom due to its small cylindrical package size
• Reduced number of combustion 'banks' - the current 5 cylinder engine has only 3 sets of inlet ports, sparkplugs, exhaust ports and associated manifolds, with each cylinder generating a 4 stroke cycle as it passes each of the 3 'banks' - leading to overall weight, volume and parts cost savings.
• An almost perfectly sinusoidal piston motion leads to a near absence of secondary and higher-order unbalanced piston/conrod forces.
• Counter-rotating cylinder groups and crankshart provide cancellation of torque reactions and gyroscopic forces during engine speed flutuations and vehicle maneuvers.
• Power output versatility with the option of utilising high torque/low speed when using the cylinder group as the power take-off point as well as, or instead of the usual crankshaft output.
Even at the current non-optimised stage in the engine's development, the Duke Engine is delivering superior torque to the comparison engines mentioned above. Specific fuel consumption (a power independent comparison measure of the fuel economy of an engine) has shown a strong downward trend as the design has developed, being already competitive with with modern high end automotive engines operating a similar combustion cycle (gasoline, port injected, spark ignition). More detail
The design has come a long way since the Duke engine concept was first turned into hardware, yet optimisation of its features has barely begun. Despite this, the Duke engine is favourably comparable to modern conventional designs.
Mechanical and other main characteristics (Seal lubrication, combustion, performance, port timing, port shape, manifold geometry, reciprocating to rotary conversion mechanism etc) are performing satisfactorily at prototype stage, but all will no doubt benefit from concerted R&D effort.
Axial engines are challenging to make practicable at typical engine operating speeds. The technical innovations of Duke Engines have been aimed at overcoming these challenges.
All V3i gasoline and Jet A1 testing to date (March 2012) has been completed with a single set of prototype seals which remain in good condition. These seals will be reassembled into an engine for further testing without modification or repair.
Duke challenges in seal development are much less than in a 2-stroke or in the Wankel engine due to lower sliding velocity and a flat monoplane sealing surface (Wankel has 3 seal faces, 1 curved, that meet at a corner, seals). So far, our sliding seal challenges are proving to be modest in reality.
Duke Engines Limited PO Box 879
Shortland Street - Auckland 1015
T.+64 021 250 4494
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