Accidental diesel in Rotax 912
 

I accidentally added 20 lt of diesel to 20 lt of avgas in the tank and flew a circuit at the end of which the oil pressure had fallen to the red line and the temperature was rising rapidly. After the tank, lines and carburettors had been flushed and the oil changed the cruising oil pressure dropped from 4 to 2 bar, the oil consumption rose from 1 lt per 22 hrs (45 ml per hour) to 1 lt per 6 hrs (167 ml per hour) and there was some debris in the filter, whereas previously there had been none. Subsequently the differential cylinder pressures proved to be below the Rotax minimum of 65 psi on a reference of 86 psi. I understand that the introduction of diesel can reduce the amount of blow by gasses and thus reduce the return of oil to the reservoir.

I should much appreciate any advice or information about similar experiences experienced by other Rotax owners.

The engine is very nearly scrap.......... you don't want to be flying behind it when it finaly turns to scrap.

My advice would be to get the thing into the hands of the UK Rotax agent and he might and I say might be able to save something from your engine.

The engine has undoubtly suffered from massive detonation. I amazed that

1) You continued to fly the engine

2) You have not become an accident statistic

There is lots of information on the web on what happens to gasoline engines when fed Diesel or Jet A/B (hint it is all really,really bad). I highly recommend you do some research

Bottom line: You are one lucky guy.....

Big Pistons Forever, diesel fuel does not detonate in a petrol engine. The engine is probably damaged but not to such a dire extent as to require a full replacement. Most likely, the engine is badly fouled with soot and sludge, hence the debris in the filter (unless this debris is metal shavings, in which case it's a lot more serious). The spark plugs are definitely fouled up. Some scouring of cylinder walls is also possible. There may also be remnants of diesel fuel still circulating in the oil - when you change oil, you cannot drain 100% of it.
However, whatever the situation is, I second A&C's advice to consult a factory representative and definitely not to fly it until fully diagnosed.

dimona

What did an engineer "do" after your refuel incident and flight to clear the aircraft for further flight? Or if a Permit, what did your LAA inspector ensure you did, and coutnersign for? i.e. what do the worksheets say?

In the unlikely event that no engineer / inspector was involved, and you just "decided" to flush the lines and go flying again, I suggest you remove your post PDQ before the CAA/LAA come after you :=

NoD

This is from the Textron Lycoming Engine web site. It is a reprint of maintainance recommendations.

Quote "Turbine fuel, or a mixture of turbine and aviation gasoline, has
proven to be a particularly ruinous fuel for piston engines. As a
result, if the engine has been operated with this unspecified fuel,
qualified maintenance personnel must make a detailed inspection
of the engine with particular attention to the combustion chambers.
If detonation has been severe enough, further damage will
occur to crank pins and main bearings, counterweights and valve
train components. In view of possible damage, disassembly and
inspection of the engine parts is the only safe recommendation
that can be made after the engine has been operated with improper
fuels. If it has been determined that the engine has been run on
unspecified fuel, do not continue to operate it unless it has been
inspected and certified to be airworthy by competent maintenance
personnel.
Lycoming Service Bulletin No. 398 is the latest reference concerning
Lycoming engines which have been operated with
unspecified fuel" Unquote

I would suggest this advice is equally relavent to the ROTAX 912 (note jet fuel and diesel fuel are esssentially equivalent for the purposes of this discussion)

What is the mechanism which would cause an avgas/avtur mixture to trash the compression?

Detonation (I have no idea if that happens in this case) would eventually cause various damage but would not, AIUI, cause cylinder scoring.

It would overheat the valves (exhaust valves especially) and mess up the compression that way - that I can see.

Peter, decreased compression may be a result of stuck piston rings caused by carbon deposits. The same would lead to cylinder scoring, further decreasing compression.

Detonation
 

I have no exp of aero engines but a fair bit by way of preparing motorcycle race engines ( 2 & 4 stroke) and have witnessed the destructive powers of detonation and many a ruined bore (usually caused by the use of regular pump fuel instead of a racing 'brew').
What generally happens is that the detonation nibbles away at the thin land above the top ring,eventually leaving the ring unsupported,bits break off and start engraving the bore.
Loss of compression can also be caused by the piston crown cracking right through.
I wouldn't dream of sending someone out on a motorbike in this condition,let alone an aeroplane:ugh:


MM

Anton K

Please provide some references to support your contention that "carbon deposits" , "soot", and "sludge" are the principal effects of diesel/jet fuel use in a gasoline engine. Is this something you "think" or do you have resaech to back up your information. I have personally seen nothing in the technical literature that supports your post. Everything I have read indicates it is the extremely high cylinder pressures/temperatures generated by the improper combustion of the deisel/contaminaed fuel, which damage the engine. If I am wrong I would be very interested in a better explanantion from a technically reliable source.

Big Pistons Forever, detonation would undoubtedly be ruinous to the engine, but I have a strong doubt the mixture in question would detonate. Unfortunately, I have no direct experience with that, so can only provide an educated guess that
- low compression (on a diesel scale)
- rich mixture (when flying a circuit)
- the diesel part in the mixture remaining mostly in liquid phase, as opposed to quickly evaporating avgas
would mostly suppress detonation. Whoever has seen this situation in practice, please correct me if I'm wrong!

That's correct. The 912, AFAIK, uses a mechanism whereby the blow-by from the cylinders causes enough pressure to develop in the crankcase to push the oil into the separate oil reservoir.

If the diesel fuel has somehow impeded this blow-by (soot on the cylinder walls maybe?), you might actually have been running the engine "dry", with all the oil collecting in the crankcase and not making its way (via the external tank and oil pump) towards all the bits and pieces that need lubrication. That would explain the dropping oil pressure and rising oil temperature: a lack of circulating oil.

The resulting wear on all the surfaces might then be the reason for your increased oil consumption afterwards, and for the debris in the filter.

As others have said, contact the importer (Skydrive I think) and have them do a detailed inspection.

dimona,

If what you wrote is true at face value, you are an entirely unsuitable person to hold a pilot's licence.

The post does seem a little strange, the gross error of refilling with diesel followed by the detailed logging of the engine data.

How did this happen, was it Jet-A1 from a pump? If hand-filled the fuel is so different in smell and viscosity it's hard to see how you would keep on filling after the first few seconds.

Agree, the initial post seems very strange. Too much info and data, how were the figures (Oil consumption etc) obtained...... Note this is the first post by the individual aswell

A couple of things...

Firstly, everyone makes mistakes. Unfortunately this one is likely to cost him serious coinage. A phone call to the manufacturer immediately upon discovery of fuel contamination would be my preferred route, but hindsight is great innit.

Secondly, he doesn't state that he flew it again (which I surmise as being the inferred source of your criticism).

Shunter...

I said, 'at face value'. How did the OP assess the

Quote:

---

cruising oil pressure

---

without flying it?

Yes, everyone makes mistakes. Some make mistakes of such gravity that they demonstrate that they are not fit to be trusted with an aircraft.

I'm not sure which makes me more cross, some of the stupid acts I come across in GA, or the bizarre pack-animal behaviour of those who step in when anyone makes a bold and entirely correct statement about an individual's incompetence. Perhaps this is borne out of a failure to appreciate the gravity of the mattter, perhaps from a desire to justify past indiscretions of their own.

Looks like he may have flown it again.

As I said above this engine needs inspecting by a Rotax expert and I think the best guy to takel it is the UK rotax agent.

ConAir Sports Ltd About Us

“If what you wrote is true at face value, you are an entirely unsuitable person to hold a pilot's licence.”

It is very common to put the wrong fuel in cars, so not suitable for a driving licence?

“the detailed logging of the engine data.”

Most uncertified LAA engine info systems will log engine parameters for later download.

Contact Conrad ASAP.

Rod1