Says Concerns Cited Are Already Addressed By FAA Regs

The crew at DeltaHawk Engines, Inc. knows a thing or two about developing piston powered diesel-fueled engines for aviation applications... and joined Diamond Aircraft this week in responding to ExxonMobil Aviation's position that jet fuel should not be used in those powerplants.

As ANN reported, ExxonMobil shocked the aviation world last month in a missive to its fuel distributors, stating the company did not approve fueling diesel-powered aircraft with Jet-A. For the moment, those distributors are still allowed to sell Jet-A to pilots flying diesel-engine aircraft... but customers must sign an indemnity agreement before doing so, waiving ExxonMobil of liability should something go wrong.

Diamond Aircraft -- the largest provider of diesel-powered planes, most notably the Thielert-powered DA42 Twin Star -- responded shortly after to ExxonMobil's statements... saying it was as "surprised" as owners were to hear the news.

While conceding the technical reasons cited by ExxonMobil were "valid general concerns for operation of diesel engine powered aircraft," Diamond added "in the case of TAE and Diamond, all listed reasons, specifically ignition quality, freezing point and lubricity, have been addressed as part of the engine and aircraft certification process and approved by the responsible airworthiness authorities."

Those sentiments were echoed by DeltaHawk, which is working to certify its V-4 aerodiesel engine for aviation applications. "ExxonMobil is correct in stating that the FAA is working on this matter. Indeed, all three technical issues raised by ExxonMobil are already specifically included as analysis and test items during the diesel engine FAA Type Certification process," DeltaHawk said Wednesday.

"All three are readily-addressed issues for any diesel engine appropriately engineered for aviation use and being certified and distributed under current aviation safety standards. They will also be a part of the high altitude Technical Readiness Level (TRL) testing to be done with the DeltaHawk engine by the US Navy."

DeltaHawk addressed each of ExxonMobil's cited concerns as follows:

• Freezing Point. "Many jet fueled aircraft which do not fly at "speeds that cause heating of the fuel in the wing due to friction caused by airflow" have been operating safely for years. The Beech King Air aircraft is one example, along with the many turboprop conversions of piston aircraft. Even those aircraft which do fly at high Mach speeds may also have active fuel heating systems. The use of a fuel additive such as PRIST Hi-Flash is also common. So, DeltaHawk-powered diesel aircraft will address this issue in the same way used by all aircraft today: published operating limitations plus fuel heating systems in specific aircraft installations to extend operating limits. The DeltaHawk diesel engine is ideally suited for use in such installations by virtue of our built-in heated fuel recirculation and engine liquid cooling systems."
• Lubricity. "Fuel lubricity is an issue only if you use the fuel as a lubricant for your fuel pumps. The DeltaHawk diesel engine fuel pump and injectors do not. All testing to date has been done with jet fuel, and the Type Certification test plan will document the engine's ability to operate satisfactorily with worst case fuel lubricity. As evidence that lubricity is not an issue, Jet A has been used in airport ground support equipment diesel engines for many years with no problems. DeltaHawk plans to certify use of multiple fuels, and we anticipate that #1 road diesel will actually produce the worst case lubricity case due to its tighter sulfur specs."
• Ignition Quality. "The lack of a cetane specification in jet fuel is the one truly unique technical issue for jet fuel powered aircraft diesels. Difficult cold weather starting is the primary effect of extraordinarily low cetane on diesel engines, but once running, the engine will perform within normal engine limits. This is not a safety of flight issue. Further, DeltaHawk engines were specifically designed to handle low cetane levels, and the DeltaHawk FAA Type Certification program will test and document engine performance with worst case cetane fuel."

DeltaHawk CEO Diane Doers echoed sentiments of Diamond CEO Peter Mauer, in questioning what appears to be a snap overreaction on the part of ExxonMobil.

"We wonder what 'extensive technical review' could have been conducted by ExxonMobil without extensive technical discussions with either Diamond or DeltaHawk," Doers said. "It seems that broad generalizations have been relied upon, when specific dialogues could have provided reassurance that the issues were being appropriately addressed.

"Diesel engines for aircraft bring significant benefits by reducing both usage of leaded fuel and total fuel consumption," she added. "They also will improve safety, especially in areas of the world where on spec 100LL is not available. In a time when bottom line costs and becoming 'green' are ever more important, DeltaHawk's innovative engines are in demand worldwide for both general aviation and military applications. Diesel power will be an important contributor to a vibrant, cost-effective aviation industry. We look forward to working with ExxonMobil for the good of our mutual customers."

FMI: www.deltahawkengines.com, www.diamondaircraft.com, www.exxonmobil.com