Aviation and clean technology leaders launch Midwest Aviation Sustainable Biofuels Initiative
IEA: Global CO2 emissions up by 1.0 Gt (3.2%) in 2011 to record high

Orbital to supply FlexDI spark-ignited heavy fuel engines to AAI in $4.7M contract

Orbital’s air-assisted direct injection can deliver similar droplet sizes for all size fuels. Spray shape is not affected by fuel type. Source: Orbital. Click to enlarge.

Australia-based Orbital Engine has been contracted to supply spark-ignited heavy fuel engines for use in AAI Unmanned Aircraft Systems’ (AAI) Aerosonde Small Unmanned Aircraft System (SUAS). AAI, an operating unit of Textron Systems, a Textron Inc. company, recently won military contracts from the US Navy and Special Operations Command to provide SUAS fee-for-service operations utilizing the newest configuration of its Aerosonde SUAS.

This new engine and system uses Orbital’s FlexDI Engine Management system (earlier post) to enable spark ignition operation of heavy fuels such as JP5 (naval operations) and JP8 (land-based operations) satisfying a US Department of Defense initiative to eliminate gasoline fuels for safety and logistic reasons—the “one fuel” policy.

...spark ignition heavy fuel engines can retain the desirable features of the gasoline engine in terms of power/weight and packaging size, and operate on a wider range of fuels than the traditional compression engine.

—Cathcart et al. (2005)

Orbital direct injection system schematic. Source: Orbital. Click to enlarge.

Orbital’s Air Assist direction injection technology uses compressed air to atomize the fuel. This assists spark ignition of heavy fuels via injection attributes such as low penetration; very small droplet size; oxygen enrichment around the droplets to assist combustion initiation; and ability to control the air/fuel ratio profile of the injected fuel and air charge.

The small but powerful engine package has been designed to be lightweight, with size, weight and fuel efficiency being key factors to provide the required range and payload capability for this aircraft. One key advantage of the Orbital technology is extended range; the improved fuel efficiency can increase the range on a typical mission by 40% over current technology, or can allow AAI to increase the payload.

Orbital is contracted to supply engines up to a value of approximately $4.7 million throughout 2012.

Orbital’s FlexDI technology has been proven in more than 650,000 engine applications in the recreation, marine, motorcycle consumer markets.


  • Geoffrey Cathcart, Gavin Dickson, Steven Ahern (2005) The Application of Air-Assist Direct Injection for Spark-ignited Heavy Fuel 2-Stroke and 4-Stroke Engines. (SAE 2005-32-0065)


The comments to this entry are closed.