Diesel carburettor backfires?

[dk]

Very strange explanation for the fire at Burton Waters marina in the YBW news story. The diesel carburettor backfired! New one on me! Never heard of one or of it backfiring.

 

[michael_w]

Dreadful sub editing, bit like Yachting Monthly.

 

[Topcat47]

Diesels don't have Carburettors. Both my old Volvo and my current Yanmar have started backwards when they were't swung hard enough but they didn't continue to run and apart from smoke in the inlet tract, there was no burning of fuel outside the combustion chamber. A petrol engine backfire is often accompanied by a jet of flame from the inlet tract and the has been know to ignite fumes in engine bays, but I've not heard of this happening on Diesels. Diesel fuel has a much higher flashpoint than petrol (which means it's more difficult to ignite). The accompanying video isn't much help

 

[Cantata]

Quite amused at the report, which says the boats were gutted. Usually the gutter press says that anyone remotely unhappy is gutted.

 

[CAPTAIN FANTASTIC]

Ha, ha; diesel engines don't have carburetors.

 

[Iliade]

http://www.radiocontrolmodels.co.uk/EngineGallery/English/Page1713.htm

I had a single cylinder one. I think I managed to start it once...

 

[macd]

Ha, ha; diesel engines don't have carburetors.

Now why didn't anyone else think of that?

(And believe it or not, some diesels -- although nothing likely to have been on the boat in question -- do have carbs). Edit: I see SAPurdie got there first

 

[DanTribe]

Well if it wasn't the carburetor, perhaps it was the sparking plugs or distributor.
Any way, someone has been deprived of earning that boat.

 

[superheat6k]

This thread explains why you lot hoist main engines !

I'll get my coat.

 

[vyv_cox]

My BMC 2.2 diesel has a device that looks very much like a carburettor, including a butterfly valve that controls engine speed. It has injectors as would be expected but uses a vacuum take-off downstream of the butterfly. There is no mention of it in the manual, which describes a more conventional arrangement with the speed control at the injection pump.

 

[mjcoon]

My BMC 2.2 diesel has a device that looks very much like a carburettor, including a butterfly valve that controls engine speed. It has injectors as would be expected but uses a vacuum take-off downstream of the butterfly. There is no mention of it in the manual, which describes a more conventional arrangement with the speed control at the injection pump.

Perhaps it is one of those notorious emissions-cheating devices? ;-)

Mike.

 

[vyv_cox]

Perhaps it is one of those notorious emissions-cheating devices? ;-)

Mike.

If so, it doesn't work - the engine smokes like a chimney when first started

 

[Norman_E]

My BMC 2.2 diesel has a device that looks very much like a carburettor, including a butterfly valve that controls engine speed. It has injectors as would be expected but uses a vacuum take-off downstream of the butterfly. There is no mention of it in the manual, which describes a more conventional arrangement with the speed control at the injection pump.

Obviously an engine designed for vehicle use, with a butterfly valve connected to the accelerator so that when the driver brakes a manifold vacuum is created to work the brake servo. I doubt that the butterfly valve actually controls engine speed, as that is done by the amount of fuel injected. There are some diesel vehicle that have done away with the butterfly valve and use either an electric or engine driven vacuum pump to power the brake servo. You can even buy brake vacuum pump conversion kits for some vehicles that allow you to remove the butterfly valve, claimed advantages are more powerful brakes and less smoke from the engine as the closed valve leads to incomplete combustion in some engines.

 

[duncanmack]

image: http://www.ybw.com/forums/images/ybw/misc/quote_icon.png
Quote Originally Posted by vyv_cox

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My BMC 2.2 diesel has a device that looks very much like a carburettor, including a butterfly valve that controls engine speed. It has injectors as would be expected but uses a vacuum take-off downstream of the butterfly. There is no mention of it in the manual, which describes a more conventional arrangement with the speed control at the injection pump.
Obviously an engine designed for vehicle use, with a butterfly valve connected to the accelerator so that when the driver brakes a manifold vacuum is created to work the brake servo. I doubt that the butterfly valve actually controls engine speed, as that is done by the amount of fuel injected. There are some diesel vehicle that have done away with the butterfly valve and use either an electric or engine driven vacuum pump to power the brake servo. You can even buy brake vacuum pump conversion kits for some vehicles that allow you to remove the butterfly valve, claimed advantages are more powerful brakes and less smoke from the engine as the closed valve leads to incomplete combustion in some engines.


Not quite.
Same arrangement as the old little Bedford TK 4 cyl lorries.
The throttle pedal is connected to the butterfly (push pedal down to open) and when the butterfly is closed there is lots (ahem, relatively speaking) of vacuum. The vacuum pipe just downstream of the butterfly is connected to a diaphragm on the end of the injector pump. The diaphragm controls the rack in the pump. Vacuum pulls the rack back against a spring to the idle stop. Butterfly open = no pull on diaphragm so spring on rack opens it . Engine off = no vacuum = full throttle - start position.
If the control rod falls off the butterfly (or the vacuum pipe fractures or falls off) then you get full throttle with no governor. If the strangler linkage then falls off - which it usually will because of the increased vibration of the almost runaway engine , it is quite incredible how fast this little 7.5 tonne truck will go, even with a large ice-cream van on the back!
Yes, T-shirt!

 

[vyv_cox]

Not quite.
Same arrangement as the old little Bedford TK 4 cyl lorries.
The throttle pedal is connected to the butterfly (push pedal down to open) and when the butterfly is closed there is lots (ahem, relatively speaking) of vacuum. The vacuum pipe just downstream of the butterfly is connected to a diaphragm on the end of the injector pump. The diaphragm controls the rack in the pump. Vacuum pulls the rack back against a spring to the idle stop. Butterfly open = no pull on diaphragm so spring on rack opens it . Engine off = no vacuum = full throttle - start position.
If the control rod falls off the butterfly (or the vacuum pipe fractures or falls off) then you get full throttle with no governor. If the strangler linkage then falls off - which it usually will because of the increased vibration of the almost runaway engine , it is quite incredible how fast this little 7.5 tonne truck will go, even with a large ice-cream van on the back!
Yes, T-shirt!

Yes, I'm pretty sure that is how mine works, thanks for the confirmation. There is no positive connection between the butterfly housing and the fuel system other than the vacuum pipe. I can confirm that without the control rod fitted the engine runs at maximum revs. Photo here.

 

[Norman_E]

It sounds like an unnecessary complication with a full on fail dangerous mode! Most diesels have seem to have nothing to throttle the airflow and speed control by increasing the fuelling against a spring that is trying to reduce it.

 

[Topcat47]

Now why didn't anyone else think of that?

(And believe it or not, some diesels -- although nothing likely to have been on the boat in question -- do have carbs). Edit: I see SAPurdie got there first

You'll not get a model Diesel engine like that one running on pump fuel. It's mostly Ether and castor oil.

 

[JumbleDuck]

Diesels don't have Carburettors.

Some do!

 

[macd]

Some do!

Jumble: beware the witching hour.
Post #6, #7.

And just in passing, Honda once made what amounted to a carburetted hybrid spark ignition/compression ignition two-stroke dirt bike. Googling "Honda EXP-2" should find it.

 

[vyv_cox]

It sounds like an unnecessary complication with a full on fail dangerous mode! Most diesels have seem to have nothing to throttle the airflow and speed control by increasing the fuelling against a spring that is trying to reduce it.

I agree it seems not to be ideal. However, it has been working for 45 years so I suppose that says something.