The DEW Line

The US Air Force has just issued a rather innocuous-looking notice for a new technology called "active combustion control". But this is quite a momentous development, and here's why.

Today, the air force has two kinds of warplanes that can survive in modern and future combat, in which fighters and bombers have to compete with integrated air defenses as well as increasingly sophisticated enemy fighters.

One kind is the Northrop Grumman B-2A bomber. It's relatively slow, but super-stealthy. It can fly for a long time and drop a lot of weapons.

The other kind is like the Lockheed Martin F-22A. It's extremely fast and also super-stealthy. But it doesn't fly for very long without refuelling and can carry only a couple of strike weapons (okay, eight if you're talking about the Small Diameter Bomb).

The missing link is a single aircraft as nimble as the F-22, as long-range as the B-2 and as at least as stealthy as both. In short, it's the dream warplane for every gadget-hearting air force general.

And it is the basic concept for what the air force now calls the Next Generation Long Range Strike aircraft. It's supposed to be ready to enter service by 2018 to 2020.

The trick to meeting this schedule is for some company to come up with the next breakthrough in aircraft engine technology. The breakthrough is called active combustion control, which is just a fancy name for integrating a fuel injector into an aircraft's propulsion system.

Aircraft engines using active combustion controls should be able to fly longer distances at a lower rate of fuel consumption.

With today's engine technology, the flow of gas into the combustion chamber is fairly unrestricted, which is not very efficient. Many years ago, the automotive industry fixed this problem with fuel injectors, and now the aerospace industry wants to make a similar leap -- although at a far greater level of sophistication.

It's a new spin on old concept. In the past, aircraft designers used variable-geometry wings (think: F-111, F-14 and B-1) to be more efficient in high-speed and cruise-speed. With active combustion controls, the goal is to reconfigure the engine instead of the airframe to be optimal in both states.

After DefenseTech.org picked up my post about Active Combustion Controls for aircraft engines, a reader named Neil asked this question:

I wonder, why has it taken this long to be able to try enabling this advance? I would think, real fuel injection for jets and not just the same afterburner stuff we've had for decades, would be already in the bag.

Good question!

First, inventing an afterburner is a cinch compared to a fuel injector, especially one with "active" controls that precisely sense the measure of fuel needed at any given moment.

But the biggest reason for the delay is because the military customer has never asked for it -- until now, that is.

Engine companies still like to make money, and that means they do what the customer tells them to do. Until very recently, that meant finding ever-increasing ways to make military jet engines more powerful. The embodiment of that trend is the Pratt & Whitney F135, the 40,000lb-thrust monster powering the F-35 Joint Strike Fighter.

Efficiency hasn't been completely ignored in the process, but nor has it been embraced.

Back in the late-1980s, the air force started up a program called Integrated High Performance Turbine Engine Technology (IHPTET), with a major goal to improve fuel efficiency by a wide margin. Many study and design contracts followed, but when the JSF program decided to go primarily with the F135, which is just an improved version of the F-22's F119, the IHPTET community was forced to wait a few more years.

Then comes along the next-generation long range strike concept, and, voila, the military suddenly needs both a super-powerful and a super-efficient kind of engine. Although the IHPTET program no longer exists, it has provided the baseline for continued research on improving engine efficiency. IHPTET's successor is another program with an equally awkward name: Versatile Affordable Advanced Turbine Engines (VAATE). Under this new funding account, a new program exists called Project Advent (an acronym for Advanced Versatile Engine Technology), and this is the likely demonstration vehicle for the active combustion control concept.

Hope that answers your question, Neil.

The US military needs oil -- about 300,000 barrels a day, in fact -- to fight.

Lots of oil comes from the same places where the military actually is fighting today, or may be fighting sometime in the not so distant future (Iran, are you listening?)

Oh, the irony!

It should come as no surprise then that the Department of Defense is giving very serious thought to oil independence. The notion is that the nation -- and particularly the military -- must have assured access to energy, and oil isn't such a safe bet any more.

Champions of this concept are known to include John Young, DOD's director for defense research and enginneering; Ron Sega, under secretary of the air force and -- on Capitol Hill -- New York Republican Representative Steve Israel and Maryland Republican Representative Roscoe Bartlett.

There's been some press about a highly-touted air force experiment using a sythentic base fuel (derived from natural gas pumped in from Oklahoma) to power one of the B-52's eight engines.

But that's just kid-stuff, really.

It's very clear that a much broader vision exists within DOD to really go ... all .. the ... way, and fast.

The vision can be found in this master's thesis by air force Lt Col Michael J. Hornitschek, who originally published the document for the Air University's Center for Strategy and Technology. It has since been republished in the air force Journal of Logistics. It's a thesis, but it often reads like a very good Popular Science article.

Here's a quick excerpt that explains the vision:

"A directed-energy based, highly-automated force, capable of generating a majority of its own power in a distributed fashion from local and environmental sources, could theoretically provide that future. The potential efficiency, environmental ubiquity, universality and convertibility from one form to another of this configuration, make strong arguments that the force of 2050 can be powered almost exclusively by electricity and hydrogen.   

Setting aside conventional paradigms allows one to imagine a conceptual 2050 force. All navy ships might employ nuclear-powered direct-electric drives, lightweight nanoengineered hulls, and directed energy armament. All army and marine corps future combat system land vehicles (many of which are unmanned) are designed for modular upgrades with plug-in electric hybrid or fuel-cell power, lightweight carbon nanotube-based armor and directed energy weaponry. Today's vulnerable tanker fuel trucks are replaced with smaller hybrid or fuel-cell powered trucks carrying stable, solid hydrate-based hydrogen batteries or combat safety-engineered liquid hydrogen containers. Individual soldiers are outfitted with pocket hydrogen fuel cells to power 10-15 onboard electric systems. Virtually all combat fighter aircraft are small, unmanned or single-seat, and powered by liquid or even nano-engineered solid hydrogen-based fuels. Ultra-efficient aircraft designs eliminate the need for tanker aircraft. All imagery (sic), surveillance and reconnaissance (ISR) platforms are either space-based or unmanned vehicles, orbiting for weeks at a time exclusively on solar-generated power while peering through weather from above."

Who says the top minds of the Department of Defense aren't focused on energy policy?

I give you James L. Jones, retired US Marine Corps general (as in, four stars), former head of US European Command and Supreme Commander Allied Powers Europe, ex-commandant of the Marine Corps and (trivia alert) veteran of the siege at Khe Sanh.

Mr. Jones is now the president and chief executive officer of the Insitute for Energy, of the US Chamber of Commerce. His new job description reads:

"... to increase the variety of the U.S. energy supply and associated infrastructures, to advance international cooperation on energy issues, to protect national energy security, to promote better understanding of changes to the global climate and its effects on the environment, and to expand economic opportunities wherever possible."

Count on Mr. Jones to look into the Fischer-Tropsch production system, which can turn any carbon-based form of energy into synthetic oil. The most attractive energy form in the US is coal shale, which is attractive becasue it is abundant and there's a whole bunch of states that have got nothing else to do with it. The Department of Defense is signed on to generate at least 200 million gallons of Fischer-Tropsch fuel to demonstrate its viability in aircraft engines, including the B-52 and all 707-based aircraft in the air force fleet (KC-135, RC-135, E-3, E-8C, etc).