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Duke Engine

Duke Engines, New Zealand

The Duke Engine is an advanced internal combustion engine delivering high thermodynamic efficiency, complete fuel flexibility, (runs on any suitable spark ignition fuel), negligible 1st and 2nd order vibration with huge weight and size savings, which is ideal in general aviation or experimental aircraft.

It is a considerably less complex internal combustion engine and is suitable for marine (inboard and outboard), light aircraft, generator/utility and military drone applications.

Duke Engines are in an advanced stage of developing an unique high-speed, valve-less 5 cylinder, 3 injector axial internal combustion engine with zero first-order vibration, significantly reduced size and weight, very high power density and the ability to run on multiple fuels and bio-fuels

The Duke's unique counter rotation, 3 dimensional, almost vibration free motion and the innovative methodology employed to achieve this, addresses previous limitations that have prevented the commercialisation of axial piston engines to date, especially at higher power and speed.

On these pages we discuss this unique engine design that will definitely change a lot in aviation in years to come!

Design Technology

Duke Engine Internals

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 swash plate, 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.


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.

Design Optimizations

Duke Engine Internals

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 utilization, 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, which makes it ideal in light aircraft. Reduced number of combustion 'banks' - the current 5 cylinder engine has only 3 sets of inlet ports, spark plugs, 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/connecting rod forces. Counter-rotating cylinder groups and crankshaft provide cancellation of torque reactions and gyroscopic forces during engine speed fluctuations and vehicle maneuvers. This reduces vibrations resulting in longer life of the aircraft frame.

Power output versatility with the option of utilizing high torque/low speed when using the cylinder group as the power takeoff point as well as, or instead of the usual crankshaft output.

Company information

Duke Engines can be contacted at the following addresses:

Duke Engines Limited
PO Box 879, Shortland Street
Auckland, 1015 New Zealand
+64 021 250 4494
[email protected]

Text and images used with permission of Duke Engines Ltd.

Written by EAI.

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