AEDC-led collaborative effort results in safer, ‘green’ alternative fluid for turbine flow measurement calibrators

  • Published
  • By Philip Lorenz III
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  With an uncertain economy and the possibility of deep cuts to national defense budgets looming on the horizon, it seems that good news is hard to find.

However, Dr. John Wright, the National Institute of Standards and Technology Fluid Flow Facility Group lead, is optimistic about the future.

A recent NIST Fluid Flow Facility-hosted workshop on turbine meters and hydrocarbon liquid flow measurement included a consensus to promote replacing toxic and flammable calibration liquids with benign ones.

"The decision to shift away from hydrocarbon-based fluids used in turbine meter calibrators to propylene glycol and water is a milestone that will have a significant impact on improving safety, protecting the environment and saving money," Dr. Wright said.

AEDC's Precision Measurement Equipment Laboratory, the Air Force Metrology and Calibration (AFMETCAL) organization, Army Test, Measurement and Diagnostic Equipment (TMDE) programs and the other representatives did more than advocate for this fluid change at the conference.

It was a collaborative effort between all of these organizations that made such an impactful decision not only possible, but with the support and backing from NIST, doable.

NIST is the federal technology agency that works with the Department of Defense (DOD) and industry to develop and apply technology, measurements and standards.

Dr. Wright said AEDC, like the Army, Navy, other Air Force ground testing facilities and industry, have faced the same challenge of finding a workable replacement for hydrocarbon-based calibrator fluids for decades.

Most laboratories that calibrate turbine meters for jet fuel applications have switched to Stoddard solvent, a surrogate that is less toxic and flammable than actual fuels.

"We've wanted to stop using it [Stoddard solvent] if possible because it irritates some people and may be toxic and harm the environment, it's flammable and has a lot of downsides," Dr. Wright said, "but it's better than jet fuel."

James Winchester, an AEDC PMEL senior metrology engineer, emphasized that AEDC took a different route to find a safer, less costly and greener alternative to jet fuel and never switched to Stoddard solvent to use in flow meter calibrators.

He said the significance of flow meter calibration needs to be understood before explaining what led to the consensus to switch fluid used in the calibrators.

"At AEDC, the most important application of turbine flow meters is [for] testing the turbine jet engines that are used on military aircraft," he said. "We do lots of performance testing [at AEDC] at lots of different conditions. Fuel flow rates and fuel consumption is a very important parameter for that testing.

"You can see how efficient the engine is at converting the thermal energy that's derived from combusting this fuel, to mechanical thrust."

Dr. Wright said the aerospace industry and DOD use NIST calibration services for hydrocarbon liquid flow to ensure agreement and quality of measurements of jet fuel flow and hydraulic oil flows.

AEDC and these other entities require accurate flow measurements to evaluate jet engines on test stands, actuators for ailerons on airplanes and turrets on tanks.

"Accuracy is critical," Winchester said. "This is where [our] Precision Measurement Equipment Laboratory (PMEL) comes into play. PMEL provides traceability to NIST. That's our number one job, to provide accurate calibrations with traceability, all the way back to NIST.

"By having traceability to NIST we then have international traceability as well, because NIST and other national metrology institutes regularly inter-compare to maintain agreement with each other. This is important because we have foreign customers who bring measurement systems to our test facilities that have been calibrated against foreign standards. Any disagreement with our measurements would raise doubt in test data.

AEDC PMEL engineers pioneered and implemented the propylene glycol and water combination as a surrogate fluid for the fuel flow meter calibrators.

Jeremy Latsko, AFMETCAL's chief of mechanical engineering section, learned about AEDC PMEL's transition to the benign calibrator fluid approximately seven years ago during a liquid flow conference held at Hill AFB, Utah.

Winchester and Latsko knew other DOD entities would benefit from this change, but those other organizations would have to test it in their own calibrators and inter-compare the data with everyone involved in the testing to validate its use beyond the Air Force.

AEDC PMEL and AFMETCAL had initiated an over-arching Calibration Coordination Group (CCG) project to accomplish several objectives, with the overall goal of finding "next generation" turbine flow meter calibrators. These new calibrators would be able to monitor thermal instabilities and be better suited for use with propylene glycol and water. The end goal is to ensure the availability of robust turbine meter calibrators that provide accurate, NIST traceable readings.

Over the past several years a working relationship has been forged between the AEDC PMEL; the U.S. Army Product Director Test, Measurement and Diagnostic Equipment (PD TMDE) and the U.S. Army TMDE Activity (USATA) that has proven to be mutually beneficial.

"We had been working with James Winchester and the folks up at Arnold, previously, on other projects, not flow projects, and just through conversations it turned out that we learned that they were working on this CCG project that was very closely related to what we were looking at," said John Ball, formerly the Army TMDE director and now their consultant and principal research scientist at the University of Alabama at Huntsville. "We became interested when we discovered that the Air Force (AEDC only) was already using propylene glycol and water to simulate fuel. We were [already] looking at studying the effect of using surrogate fluids instead of hazardous fluids for calibrating turbine flow meters in the Army."

Latsko said the Army's interest and support on the work underway, especially on the benign fluid, had a multiplying effect on drawing additional support for the effort.

"That's where the Army came in," he said. "That's where the joint part comes in; this project was already underway through these research funds, for the thermal instabilities."

Latsko said the Army's support for switching to food-grade propylene glycol and water for the turbine flow meter calibrator was the catalyst needed to gain wider acceptance.

"The Army came in and really pushed that, which was great, because [this] food-grade propylene glycol, it's extremely safe," he said. "The Army was a big part of making that happen and bringing that up to our national lab, NIST, who actually had made some conclusions about it being acceptable. Thanks to the Army's interest in this, it really changed the conversation."

Ball said the work with AEDC's PMEL is ongoing.

"The project will continue for another year, just data gathering at the Army Primary Laboratory and then they're going to be continuing correlations between us and the Air Force Lab," Ball said. "At the end of the time we're hoping to be able, at least to a large extent, to replace hydrocarbon calibrations for turbine flow meters in the Army with propylene glycol and water, [which is] non-toxic, non-explosive [and] good for the environment."

Judy Burden, senior engineer with the Army's Product Director for TMDE and Calibration Sets (Calsets) at Redstone Arsenal, said joint service projects make good sense fiscally and technically.

"It's been a great pleasure working with the Air Force group and we look forward to working with them in the future on other projects," she said. "[We're] trying to find more projects that are tri-service, to get more bang for the buck for all of the services and looking for those projects to pursue because money is so hard to come by in this tight economy.

"By doing something that gets the government three or four times its money's worth certainly is the way we have to go. And we are [working] toward that and I am personally willing to champion."

Winchester said that working with the Army PD TMDE/flow metrology team and AFMETCAL has proven to be an excellent approach.

"There is synergy amongst the team members and all have contributed," he said. "Testing and data inter-comparisons between the Army, AFMETCAL, NIST and other labs are ongoing to refine our understanding of turbine flow meter response mechanisms and performance limitations."

Counterparts at the Navy Primary Standards Laboratory (NPSL) have also been kept current on the collaborative work leading to the recent consensus (at the NIST-hosted conference) to switch to propylene glycol and water for turbine meter calibration.

David Giesenschlag, with the Navy Primary Standards Laboratory's (NPSL Mechanical Metrology/Calibration Branch, said, "At NPSL we have been watching the progress and discussions involving the implementation of propylene glycol and water in our test stands with much interest."

Giesenschlag said although it is premature to say what course the Navy will take, his group wants to talk about AEDC PMEL's experience using propylene glycol and water.

"We're seeking some ideas on what to do and what not to do, advantages and disadvantages, test stand prep and modifications needed for fluid change over, cleaning and preparations of flow meters after the calibration, propylene glycol and water supply sources, and any other recommendations that might be beneficial to fast tracking," he said.