The Care and Feeding of Diesel-Fueled Aircraft Engines

Written by Steve Ells
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September 2015

Three diesel engine experts explain what’s required to keep a diesel engine running well.

No spark plugs, no plug wires, no magnetos; no wonder diesel engines require less service than an Avgas engine.

In spite of the fact that these engines have a lot of advantages over an Avgas-fueled engine, today in the United States only one OEM sells a diesel-powered airplane. (Cessna Aircraft stopped taking orders for its 182 JT-A diesel engine Skylane last spring, and the project appears to be on hold. —Ed.)

Diesels are more fuel efficient, require less maintenance and are more dependable since there are far fewer moving parts. And because Jet-A fuel is a lubricant rather than solvent, internal engine rust is eliminated.

I interviewed John Weber, the diesel engine service expert on the 155 hp liquid-cooled CD-155 at Continental Motors; Thierry Saint Loup, chief of North American support for the SMA 230 hp SR305-230 oil- and air-cooled engine; and Dennis Webb, president and CEO at DeltaHawk Engines to learn what it takes to keep a diesel engine running well.

They all said essentially the same things. Critical maintenance items include observing the best clean-room techniques possible when dealing with diesel fuel systems and keeping the induction filter clean.

Saint Loup mentioned that maintenance procedures on an SMA diesel are more akin to servicing a turbine powerplant, and that as long as the fuel system and inlet air filter are kept operating-room clean, “a diesel engine will run a long, long time.”

Saint Loup also told me that SMA estimates that maintenance man-hour costs are 50 percent less than the costs to maintain an Avgas-fueled engine.

Data logging
The CD-155 and the SR305-230 diesels are equipped with data logging (a request for this information from DeltaHawk wasn’t received by press time); the CD-155 sports a cluster of data sensors that gather information to monitor and control systems such as the turbocharging, fuel injection, fuel pressure, propeller rpm and others.

The SR305 records engine hours and fault modes. At each inspection these engines are connected to a laptop computer and an engine operations text file is downloaded. This data can be applied to MS Excel to compare engine performance with earlier downloads. The files can also be sent to service centers when troubleshooting help is needed.

Service intervals for the SMA SR305-230

Every 100 hours
(100/200/300/400, etc.):
Change engine oil and filter; check
magnetic sump plug for metal; run up engine and download data. Conduct a thorough visual inspection for condition and external corrosion. Clean inlet air
filter. Estimated labor man-hours: three.

Every 200 hours
(200/400/600/800, etc.):
Conduct 100-hour maintenance listed above. Replace spin-on fuel filter and remove and clean turbocharger oil return check valve. Estimated labor man-hours: four.

Every 600 hours
(600/1,200/1,800, etc.):
Conduct 100- and 200-hour maintenance above. Perform cylinder compression test; remove and replace fuel injectors (exchange); check and adjust as necessary setting on fuel injection pump; replace pin in turbocharger if axial play of main shaft exceeds limits.

Every 1,200 hours:
Conduct 100-, 200-, and 600-hour maintenance. Replace turbocharger and remove and replace electronic control unit (ECU). Estimated labor man-hours: 10.5.
At 2,400 hours:
Exchange engine for new
or rebuilt engine.

Service Intervals for Continental Motors (formerly Thielert and Superior Air Parts) CD-155:

At first 100 hours and every
100 hours thereafter:
Change engine oil and filter and gearbox oil.

At first 200 hours and
every 200 hours thereafter:
Conduct 100-hour maintenance,
plus change engine air filter.

At first 600 hours and
every 600 hours thereafter:
Major inspection. Conduct 100- and 200-hour maintenance plus exchange gearbox; inspect dual mass flywheel (DMF); exchange electric pressure fuel pump; exchange common rail fuel
control valve; exchange alternator.

Every 900 hours:
Conduct appropriate hour interval maintenance, plus change camshaft timing chain.

Every 1,200 hours:
Conduct appropriate 100-,
200- and 600-hour maintenance.
Change V-rib belt; exchange
fuel feeder pump.

Every 1,500 hours:
Exchange engine and install
new motor mounts.

At this point, all aircraft diesel engines are serviced with Aeroshell Diesel Ultra fully synthetic multi-grade oil. Shell recommends 100-hour oil change intervals.
Cost is about $10 a liter versus $7 a quart for Aeroshell 15W-50 multi-grade Avgas engine oil. (One liter equals 1.056 U.S. quarts. An equivalent price in quarts for the diesel oil is $9.46. —Ed.)

Service intervals on DeltaHawk’s V4 engine

According to a service interval document supplied by Webb, DeltaHawk’s plan for the V4 is very similar to the other two engines except a few of the intervals are shorter, including 50-hour oil changes—and in addition to the engine oil change, oil is also changed on the fuel pump and supercharger.

Diesel engines haven’t been widely used, but interest in the technology—due in part to recent auto-industry improvements that offer higher power-to-weight ratios more suitable for an aircraft application—is growing.

Diesel’s significant benefits, including increased fuel efficiency, decreased maintenance and more dependability are being welcomed by many in the General Aviation industry.

In addition to the three companies highlighted here, many other manufacturers have diesel engines in development.

Steve Ells has been an A&P/IA for 43 years and is a commercial pilot with instrument and multi-engine ratings. Ells is a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. He owns Ells Aviation (EllsAviation.com) and lives in Templeton, Calif. with his wife Audrey. Send questions and comments to editor.

Resources
CD-155 engine (155 hp)
Continental Motors Group
continentaldiesel.com

SR305-230 engine (230 hp)
SMA
smaengines.com

V4 multi-fuel engine (160 to 200 hp)
DeltaHawk Engines, Inc.
deltahawkengines.com