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08/08 - Is there a Spark Ignited Heavy Fuel Engine in your future?

By Anthony J. Liberatore
Images courtesy www.sonexresearch.com

Imagine with today’s fuel prices, you are able to pull your aircraft up to the Jet A pump to save a little on your fuel bills. The concept is tantalizing, although I have been told it is nothing new. In order to help the war effort during WWII, some farmers would switch over to kerosene after getting the engine on their tractor warmed up. With a new war effort underway, a new military requirement has emerged that is a technology driver. This requirement is that all GPU’s, UAV’s, etc, with small engines, must run on JP-5 by 2010, in order to eliminate the logistics of carrying different fuel types into a theatre. 

This requirement is driving a number of manufacturers and     Two Stroke 100cc powered UAV converted to run entrepreneurs to use their creativity and come up            on JP-5 for the U.S. Marines.  
solutions to fill this need. Some of the current entries
with some unique solutions are Evan Guy Enterprises, Dan Gurney (of racing fame), Sonex Research Inc. (not to be confused with Sonex Ltd, the kitplane manufacturer), and Mercury Marine. While there are some true diesels such as the Deltahawk that are trying to fit in and fill a given role as an UAV engine, the thrust of many of these innovators is to modify existing engines to run on “heavy fuels”. With that said we might never see general aviation  applications for a long time  if at all. In fact with today’ s emission regulations, any application outside the military may never come to fruition. Nevertheless, the concept is so tantalizing we cannot help but dream of what an engine this would make for our aircraft. 

What they have created with these “spark ignited heavy fuel engines” is an engine that can burn a diesel type fuel without the high diesel compression ratios normally needed for the combustion process, and without the associated  high engine weight required for strength. It gets even more enticing; many of the engines they are converting are two strokes, which are even lighter than the small certified engines we are accustomed too.

With that said, I would like to discuss two of the entrants and their interesting technological solutions. One of the entrants is a company out of Annapolis, Maryland: Sonex Research Inc. Sonex’s unique and patented approach uses a design that can be applied to the cylinder head or the piston. This design utilizes a center chamber that has a series of smaller chambers surrounding it (see image to the right). The outer chambers are connected to the center chamber via individual passageways. A current application of Sonex’s technology in the field is a number of 2-Stroke 100cc powered UAV’s converted to run on JP-5 for the U.S. Marines. (see photo below) Sonex has two variations of there technology still in the R & D mode. With these variations, one is touted to make diesels run cleaner and the second

could allow the elimination of a spark source when direct fuel injection is used while at the same time allow heavy fuel use. Note this is a small and relatively new firm and many of these projects still may need some maturation.

Another interesting entry in this arena is the “Optimax JP” outboard engine by Mercury Marine. Mercury Marine is developing an outboard and a “jet” (both in the 200+hp class) for Navy “Seal” use. This Optimax JP is a derivative of their successful Optimax Series of outboard motors, which range from 75 hp up to 250 hp, and are direct injected two strokes. Direct injection applied to a two stroke gives the engine its inherent light weight, with 4-stroke fuel consumption and emissions, as well as a more robust lower end, since the crank and rods bearings are not exposed to fuel diluted oil. These direct injected two stokes utilize Orbital Engine’s air assisted direct injection technology which atomizes the fuel droplets down to 8 microns, which is the industry benchmark. The flexibility of this system allows Mercury Marine to convert the engine to heavy fuel while maintaining 95% part compatibility with their gas burning brethren.  

As you might garner, what is going on in this arena is definitely on the cutting edge. However, we as aviators and experimenters have always been on that edge when it comes to applying technologies. Perhaps a two stroke direct injected, spark ignited heavy fuel engine, with an excellent power to weight ratio and great fuel consumption specifics would drive a new generation of airframe designs. Not to mention it would be neat to taxi to the jet A fuel pump and filler up! 

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