Diesel Overrun at Sea

[GILow]

Originally Posted by a64pilot

I think my 44 HP is 2.5L? If so then at 3000 RPM it’s over 30 liters per second if I do the math right.

Well the maths is probably sound but this is predicated on the assumption that the cylinders get their full 2.5 litres with each cycle. In practice, because of the restriction of the valve intake port, I believe it is about 30% of that at high revs. Unless you have a turbo. Then it depends on the boost.

[Taipe]

Originally Posted by thinwater

I've never experienced this on a boat, just an industrial generator and a large pump.

How hard is it to put a plastic bag over the air intake? Worked on the generator. Even if it does not shut it down completely, the odds of serious damage are considerably reduced with the engine running slower. Seems like you should be able to get there in seconds. The pump engine was damaged before the crew got to it.

I don't think you understand the tremendous suction at the air intake of a runaway diesel. Your plastic bag will get sucked into the engine and melt on the exhaust valve seat in the blink of an eye, and along with as many fingers as you have on the end of your hand!

[thinwater]

Originally Posted by Taipe

I don't think you understand the tremendous suction at the air intake of a runaway diesel. Your plastic bag will get sucked into the engine and melt on the exhaust valve seat in the blink of an eye, and along with as many fingers as you have on the end of your hand!

Yup, I've worked around vac hoses. 14 psi is a good pull and you keep your hands at least 6 inches away and to the side. In fact, Suppose it could crush an air cleaner. Let's also remember that most sailors have little baby engines.



I suspect what they used was a supper sac, since there were some lying nearby. They could stand that pressure.


Then the takeaway is to have something appropriate nearby that fits the intake.

[Diamond Life]

Thank you for all your ideas and suggestions, some have been very helpful.

I would like to show a picture of the engine so that you can understand the complexities in controlling an overrun in the very limited time period available to you.

This engine is accessible by lifting the stairs, good access but you will notice from the yellow arrow that the air intake is at the rear of the engine. The air intake hose points downwards and the hose opening is approximately 50cm below the level of the engine you can see. There is also very little room to put your hand (if you would even want to) or anything like a nearby bread board down into the area. Remember the engine is roaring and already unbelievably hot, plus you are waiting for something to shoot through the engine casing. You would have to have your upper body completely in the engine bay to enable access to the hose.

There are small side access hatches but these are too far forward to assist with access.

The only way to access the area is from the rear lockers, on the port side there are batteries and engine hoses. On the starboard side access may be achieved BUT being a delivery this was filled with racing sails (remember this was a delivery).

We had a very good look at the boat prior to departure, checking all the normal systems and getting an understanding of where all the emergency equipment was. You imagine all possibilities but you can only rely on experience for the unexpected.

The idea of the original message was to give everyone an understanding that the unexpected happens. If you are not aware of an engine overrun then you should run the remote possibility through, it may save you an engine. Remember we only had 30 - 45 seconds from the start to the end, not a lot of time. Once I realised I couldn't safely block the air intake my primary concern was fire so time was spent shutting off the fuel and having fire extinguishers ready if required. In addition to that I can still tell you exactly how many NM off a well known land point we were and in what direction just in case we had to make a call.

Regarding the engine, it was not to blame. The problem started with seawater entering the fuel tank via the fuel breather. From there problems flowed further down the line....

[skipperpete]

Well done with the safety management and planning, the most important thing is to keep the crew safe.
I'm not really clear about how the seawater caused this, normally water in the fuel causes an engine to just stop or at least falter. The white smoke is puzzling too. Is the photo a before or after, its a very tidy installation. If you send the pump to a fuel injection shop they will tell you what caused the overspeed.
Pete

[a64pilot]

Originally Posted by GILow

Well the maths is probably sound but this is predicated on the assumption that the cylinders get their full 2.5 litres with each cycle. In practice, because of the restriction of the valve intake port, I believe it is about 30% of that at high revs. Unless you have a turbo. Then it depends on the boost.

The volumetric efficiency of a Diesel is near 100%, because there is no throttle plate.
It’s why they have no vacuum, and if you have a diesel car that has vacuum operated accessories like power brakes etc., you have a vacuum pump. It is possible if you tune the intake tract during design and take advantage of the mass and velocity of the incoming air to exceed 100%, at certain RPM, but I doubt that is done on a Diesel.
A turbo motor as you point out is well over 100%

[sanibel sailor]

I am aware of runaway, but a new concern occurs to me. I'd be worried about the thing grenading and sending pistons, con rods, etc thru the hull. I've seen it blow thru the iron crankcase, a bit of fiberglass would be nothing. Not sure there is a reasonable solution other than hoping for seizure before disintegration. Race cars have a blanket and/or steel bellhousing to contain clutch/flywheel failure.

[a64pilot]

The shield is for a clutch and it’s called a scatter shield, clutches have flown apart at high RPM and of course that is right by your legs, and people have been hurt, before the scatter shields.
However it’s extremely uncommon for anything from a piston engine to actually escape the block with much force at all from an engine “blowing up”.
It’s possible, but exceedingly uncommon. I’ve never seen it in all my days at the drag strip, I’ve seen blowers blown off, even with sneeze valves, but we don’t have large overdriven roots blowers.
About the worst I have seen is a rod break, and the part that is still connected to the crank is no longer contained so it swings around wreaking havoc, knocking holes in the block, oil pan etc, but nothing comes flying out with great velocity.
I’d say a fire is more likely possible than knocking a hole in the hull, and even that isn’t real likely, depends I guess on if there is any fuel spilled, oil is very hard to ignite and keep burning.

[Jammer]

I have seen, with my own eyes, the hood of a truck with a piston-sized hole in it. It was at a body shop being repaired after throwing a rod, and as rare as it is, in this particular case it threw it right through the cylinder head and hood.


This was a gasoline engine, many years ago. I believe it had to have been a 6 cylinder engine as it went straight up vertically. This was before there were compact trucks with 4 cylinder engines.



I probably wouldn't have believed it if I hadn't seen it myself.

[sanibel sailor]

I saw a semi truck pulled over just after seeing the big piston laying in the road


When the broken con rod pokes a hole in the block, the block fragments could puncture the hull. Duct tape anyone?

[Island Time O25]

I had a MD5A run away on me during spring commissioning, while the boat was still on the hard. By the time I accessed the fuel shut off valve the engine was revving up like it wanted to fly. I managed to stop it but it was toast of course. The sludge that I pumped out from the oil fill looked like liquid gray putty.

The cost of a rebuild - parts and labor (even at a steep discount) was too much for a then 35 year old engine.

BTW I still have it under wrap in NH, near MA border. If anyone needs it for parts or as a mooring block (for free) PM me.

[Shaneesprit]

Running an engine only to charge the batteries will lead to cold pistons and cylinders / liners, this causes in very basic terms glazing of the bore then diesel collects on the cylinder and run into the oil sump. the same thing happens when you are running lightly loaded.
The engine manual will say something like, Do not operate at low loads for long periods usually more then 30 mins, Low normally being less than 50% throttle and a normal use is considered above 70%,
Not saying this caused the failure, but the sump is for oil, an occasional hour or so on high load, will help prevent this.

[Paradox111]

>The problem started with seawater entering the fuel tank via the fuel breather. <
All,
Can the fuel breather for the diesel tank be relocated inside the stern of the 31' sailboat? alternatives?

[wackerb]

How about using water through the air intake?

[a64pilot]

Originally Posted by wackerb

How about using water through the air intake?

That will destroy it in a hurry, it will stop the motor, instantly