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Duke Engine

Duke Aircraft 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.

This engine is the world's only viable axial, 4 stroke, spark ignited piston engine. It is lightweight, small, valveless, vibration-free, has very high power density, and runs on most fuels, including kerosene/jet fuel. The Duke engine is a great fit for aerospace applications, including ultralight, experimental and UAV platforms.

Aviation Platform Technology

Duke Engine Internals

The Duke engine is in advanced stages of development, with prototype engines operational. The 5 cylinder, 4-stroke internal combustion engine platform offers numerous benefits in aerospace applications:

  • Aerodynamically friendly cylindrical shape, with output shaft on centre line
  • Installation in small cowlings with lower drag
  • Low weight
  • Small package size
  • Near perfect mechanical balance for very low vibration
  • Direct drive low-power or geared high-power options
  • High power density potential - over 0.7 hp/lb installed weight in direct drive option or over 1.0 hp/lb @ 2700 - 3300 RPM output shaft speed in geared option
  • Multi fuel options. Automotive gasoline with low octane requirements. Compatible with 100LL AVgas
  • No cam drive train or valves
  • Low parts count compared to classic engines
  • Simplicity of design – 3 injectors & 3 manifold connections for 5 cylinder engine
  • Multi-point spark ignition simply achieved
  • Partial cancellation of gyroscopic effects from slow speed counter rotation of cylinder group
  • Suitable for 50hp to 350+ hp


Cooling is achieved with conventional water jackets around the cylinders and ported areas. Seals around concentric flow passages allow the coolant to enter and leave the rotating cylinder group. The coolant is then circulated in a conventional manner through radiators mounted on the airframe, using a pump.

Thermodynamic efficiency

The absence of hot valves in the favorably shaped combustion chamber allows high compression ratios for efficient operation on low octane fuels. Current engines operate on 91 octane gasoline detonation free at compression ratios above 12.5:1.

Fuel flexibility

Development will allow operation on all appropriate fuels, including ethanol/methanol and blends, bio-ethanol, LPG, CNG, hydrogen, kerosene and diesel. Spark ignited Duke engines are currently successfully running on 91 octane gasoline and kerosene/jet-A1.

Less complexity

Duke Engine Internals

The much lower part and component count (only 3 sets of spark plugs, injectors and ports for 5 cylinders with no valve train), coupled with ease of repair and maintenance and potentially lower production costs, offer potential for savings in manufacturing and operation. While the Duke uses existing materials and manufacturing processes in its construction, there is considerable scope for the use of light weight materials as appropriate.

Engine Prototypes

Duke Aircraft Engine #1 is a 2.0 Ltr – 3300 RPM with 103 hp @ 3300 RPM and weighs 101 lbs (no gearbox required). Size: Length: 17.3 in x Diameter: 11.6 in.

Duke Aircraft Engine #2 is also 2.0 Ltr but at 6250 RPM with 180 hp @ 6250 RPM with equal weight: 101 lbs (needs a gearbox) Size: Length: 17.3 in x Diameter: 11.6 in.

Text used with permission.

Written by EAI.

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