Maybe a silly Q but - how does one stop a Diesel Engine running ?

Poignard said:
Covering the air intake stops them.
Click to expand...
But don't put your hand over the air intake ( unless you want to risk loosing skin and flesh).
Lots of big diesels have wooden bungs adjacent to the air intakes, so that they can be hammered in in an emergency e.g. when engine over runs due to sucking in engine oil and running on that.
 
Bav32 said:
But don't put your hand over the air intake ( unless you want to risk loosing skin and flesh).
Lots of big diesels have wooden bungs adjacent to the air intakes, so that they can be hammered in in an emergency e.g. when engine over runs due to sucking in engine oil and running on that.
Click to expand...
Yes, I guess it is a good idea to 'have a plan' and the items needed for this rare but ( frightening in my case!) eventuality When 'messing' with my engine now I have the air filter off and a handy bung to close off the intake..
 
BlowingOldBoots said:
Positive Air Shut-off devices are fitted from small single cylinder water pump diesel engines to massive power station diesel engines. Some manufactures are Pyroban, Amot, Rig Saver, Chalwyn. They operate via various techniques, overspeed sensors, high airflow or manual trip levers. They are there to prevent the diesel engine running away under gas in air intake or sucking up their own oil. Some countries require them by law e.g. USA on offshore vessels, many commercial diesel engines fit them as standard for oil and gas market.

Chalwin and Pyroban are very common on small diesel engines and can easily be retrofitted with no significant effort: -

Chalwyn-Categories
Click to expand...


These are required on all offshore rigs in the UK as well. Something I had never seen at sea but Rig Saver along with Donkey's Dicks and other quaint expressions soon became part of my vocabulary when I got involved with Semi subs and Jack Ups. As you say all the diesels on the rigs had these and they were automatically actuated by overspeed.

I once saw pictures of a medium speed marine diesel of about 10,000HP that had run away. Luckily no one was hurt but the physical damage was excessive due to parts breaking free in the crankcase. This was caused by a failure of the governor drive causing excessive over fueling. The engine thought is was slowing down) was not clutched in so took off like a formula 1 engine:)
 
Boater Sam said:
Which engine do you have Popeye? There are several very different ways that the engine normally stops.

In emergency loosening the pipes to the injectors will stop any diesel, mess but fool proof.
Click to expand...
Zing said:
From what little info you have given it’s probably a stop solenoid that is activated by the key. It will be activated to most likely release fuel pressure preventing fuel from going through the injectors.
Click to expand...

Hi there Mr B and Mr Z I ask the Q because some one asked me and I did not know the answer; I ask a Motoring Friend who talks Car Engine Performance and he hummed and arred quite a bit, so thought I know will post an ask on there; at present I have Pet /oil outboards but considering buying a Yacht with small Inboard Diesel soon so am keen to know the answers; Am used to them Old Types with a half ton flywheel and decompressors fitted plus mandatory Hand Cranking but those with a keyed switch i have just used /driven but not understaood at all; silly me thought it was like a Petrol Car I assumed and turned the Key to off.

Well thank you all's, now I know far more about what to ask and look for when considering a Boat with a Diesel engine; yes many years ago I had a Kelvin TVO / Petrol 800rpm inboard that I could (and needed to) clean the carbs (2) whilst still motoring along, that was fun, turning off the fuel to a pair of cylinders with one carb and removing the Fuel bowl to clean it out; replacing the Bowl and turning on again the fuel whilst on Petrol when running OK turning over to TVO (Parrafin sometimes) and back to full throttle; yes I was far more adventurous in them far off days {:-)# but I survived so did Crew (Wife) cripes what risks I took what ignorance I had
 
Rogershaw said:
The vacuum created in the cylinders with the air supply cut of is massive

Ok so the is a vacuum in the cylinder that could/will suck oil into the cylinder from the sump.

For the diesel/sump oil to burn it need oxygen from the air and heat from the compression of the air.

As there i a vacuum in the cylinder there is not enough oxygen to allow the oil to burn and not enough heat as no compression.

So how will combustion be sustained?
Click to expand...
From the crankcase, it is not airtight. The piston will allow air and oil to be sucked from the crankcase on the exhaust stroke, 4 stroke engine of course. Any breather in the manifold and crankcase will be under severe negative pressure on part of the cycle.
You don't have to believe me or understand how it happens, just accept that it does, frequently.
 
Reminds me many years ago, working on a Lister 2 cyl engine, fitted with a new hydraulic pump to power a small crane, unfortunately the pump had been supplied with the wrong rotation so when I operated the hydraulic control nothing happened - the seals blew in the pump and the engine started to run on the hydraulic fluid which had pumped into the sump - workshop filled with white smoke, engine going faster and faster and in desperation I yanked off the air cleaner and clapped my hand on the inlet pipe and fortunately it stopped. It was a heart stopping moment.
 
Boater Sam said:
You don't have to believe me or understand how it happens, just accept that it does, frequently.
Click to expand...

Well as an Professional Engineer I tend to look for proof and anm not into blind faith.

There has been sever posts where blocking the air inlet is a safety requirement and in some cases a legal requirement

So forgive me if I find it difficult to understand and believe you as its been considered an acceptable way of stopping a runaway diesel.

If you have a video of this happening I am willing to review and get comments from the wealth of knowledge on the forum
 
Bilgediver said:
... Donkey's Dicks ...
Click to expand...

Mostly replaced with strain gauge pressure sensors now. The young today have no idea about the names of stuff that used to be common place: The F*&% Stick, Cows C*&^, Poor Boy, Possum Belly, Worms, Kelly Cocks. Last year I was in USA, Permian area of West Texas. It was a time warp with old rigs and old ways of working, even the new rigs were built as if they had just time warped from the 1960's.
 
The stop solenoid on my engine is actually a run solenoid - activated to allow fuel to flow. When the key is turned to off, power is removed and a spring operates to cut off the fuel.
A few years ago the solenoid burned out and the engine stopped soon after leaving the marina.
Discussions over a long period led to a modified solenoid being fitted in which the spring allows fuel to flow and a push button operates the solenoid to stop the engine.
 
Rogershaw said:
Well as an Professional Engineer I tend to look for proof and anm not into blind faith.

There has been sever posts where blocking the air inlet is a safety requirement and in some cases a legal requirement

So forgive me if I find it difficult to understand and believe you as its been considered an acceptable way of stopping a runaway diesel.

If you have a video of this happening I am willing to review and get comments from the wealth of knowledge on the forum
Click to expand...
I speak from 50 years experience as an engineer, I don't have arguments on open forums.
 
I sort of get it... but wouldn’t the air available if only sucked in past the piston rings be progressively so little as to prevent combustion anyway (unless the rings were incredibly worn)?

In turn, if the rings were that worn, could there even be sufficient combustion for the engine to run at all?

Diesels in runaway at maybe 1.5 or 2 times max RPM must be sucking tons of air. Way more than I could imagine only coming in past the rings.

But I’m decidedly not an engineer... only curious!
 
dankilb said:
I sort of get it... but wouldn’t the air available if only sucked in past the piston rings be progressively so little as to prevent combustion anyway (unless the rings were incredibly worn)?

In turn, if the rings were that worn, could there even be sufficient combustion for the engine to run at all?

Diesels in runaway at maybe 1.5 or 2 times max RPM must be sucking tons of air. Way more than I could imagine only coming in past the rings.

But I’m decidedly not an engineer... only curious!
Click to expand...
You are correct. If there were sufficient air getting past the rings to allow combustion to run away, the compression would be so low that the engine would not run at all.

It's a catch 22 ..... you can't have one without the other.

Many engines also have a one-way PCV so there would be no way for air to get into the crankcase anyway so there would be very little in there to get past the piston rings anyway.

Richard
 
I'm remind of an old Stuart Turner single that we couldn't stop. The kill lever had rusted solid. a rubber ball placed over the air intake and operating the decompressor eventually worked. It took me three hours to free off the stop lever working with a tin of WD40, a small tap hammer and a mole grip.
 
Boater Sam said:
From the crankcase, it is not airtight. The piston will allow air and oil to be sucked from the crankcase on the exhaust stroke, 4 stroke engine of course. Any breather in the manifold and crankcase will be under severe negative pressure on part of the cycle.
You don't have to believe me or understand how it happens, just accept that it does, frequently.
Click to expand...

What absolute and utter nonsense, i've read some rubbish on this forum, this takes the biscuit.
 
You must log in or register to reply here.

Share this page

Top