Example EATR

Hybrid External Combustion Engine  (Source:

Energetically Autonomous Tactical Robot finds its own fuel

A robot that forages its own fuel might sound like a work of science fiction. However, that is exactly what is coming out of Defense Advanced Research Projects Agency or DARPA.

The robot, called Energetically Autonomous Tactical Robot or EATR for short, will be able to forage for biofuel during a long-range mission. This could then be used to recharge its electrical devices, carry troop equipment (MULE concept) or even transport the soldiers themselves.

In addition to vegetation, EATR can also use conventional or unconventional fuels (e.g., heavy fuel, gasoline, natural gas, diesel, kerosene, propane, coal, solar, algae, cooking oil).

Unlike internal combustion engines, the Cyclone engine which powers EATR uses an external combustion chamber to heat a separate working fluid (de-ionized water) which expands to create mechanical energy by moving pistons or a turbine (i.e., Rankine cycle steam engine). Combustion is external so engine can run on any fuel (solid, liquid, or gaseous). So far, a 100HP engine prototype has been developed.

The Cyclone engine offers several other important benefits, including lower combustion temperatures and pressures create less toxic and exotic exhaust gases as the uniquely configured combustion chamber creates a rotating flow that facilitates complete air and fuel mixing, and complete combustion, so there are virtually no emissions and less heat released (hundreds of degrees lower than internal combustion exhaust). It also does not need a catalytic converter, radiator, transmission, oil pump or lubricating oil (water-lubricated). 

The EATR uses a robotic arm to gather and prepare vegetation, which it feeds through a shredder into a centrifugal combustion chamber, where it is ignited and then heats a series of coils. The coils contain deionized water (to stop them from furring up like a kettle). As the water inside the coils is superheated, the steam is piped to a radial steam engine, which consists of six pistons. The steam rotates the pistons, driving a generator which produces electricity. This is stored in batteries that power the electric motors which drive the EATR along. 

The steam engine is designed to be a “closed-loop” system, in which water escaping from the cylinders through the exhaust ports is captured and cooled in a condensing unit. This turns the steam back into water, which is then returned to the combustion chamber.

Image-recognition software linked to a laser and camera would allow EATR to recognize plants, leaves and wood. Robert Finkelstein, Robotic Technology’s president, estimates that about 68 kilograms (150 pounds) of vegetation would provide enough electricity for the machine to travel around 160km (100 miles). The company recently received EATR’s engine, which has been developed by Cyclone Power Technology of Florida. The next stage is to integrate the EATR technology into a military vehicle to prove that the idea works. The type of vehicle that will be used has not yet been decided, although it could be a HMMWV modified to drive itself under robotic control. After a period of testing, Dr Finkelstein is confident that a fully working EATR prototype vehicle that acts autonomously could be fielded by around 2013.

A detailed PDF outlining the program can be found here.


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