Smoke Rings

[ianfolland]

I was running my 7/8ths Hunslet in the still, warm, late afternoon air, of a sunny hot winter's day recently, and it produced "smoke" rings at the same spot on two successive trips. Lurking behind a linside bush with a camera for a third run, and since, to capture this phenomenom has produced nothing.

Has anyone else seen this? The Hunslet is fitted with a chuff pipe, and produces definite "chuffs".

[TonyW]

My Roundhouse Fowler (no chuff pipe) does it occasionally, but it is the only loco of mine that does.

[DolwyddelanLightRail]

My edrig has done that before and that has a chuff pipe and so has my mamod, but that doesn't have one. I found they only did it when the oil "popped" in the smokebox, however, my edrig usually produces blue ones

[Sir haydn]

Our Tom Rolt makes them, that doesnt have a chuffer and is the only one of our locos known to do it

[laalratty]

Don't think I've ever seen anything 16mm scale make them, but I've seen it from 7 1/4 locos a few times, and also one of the diesels at Ravenglass....

[Dr. Bond of the DVLR]

One of the locos at EARM does it quite a bit, has it something to do with a long tall chimney?

[Pretoria]

Both my locos (below) regularly blow smoke rings (to which I make no claim of merit).

I believe that it can only occur when the blast pipe arrangement and nozzle is directly in line with the centre-line of the funnel. And exactly in line, not just nearly.

[George]

my edrigs done it a few times, and moving to standard gauge i saw J15 at NNR do it twice last year

[Crayfish]

Smoke rings can be made by any circular opening, it just takes a momentary burst of pressure through the hole. This video explains it quite well:

http://www.youtube.com/watch?v=4b2SV3ASUxY

Skip to about a minute in if you are impatient to see the smoke rings being made.

I guess the circumstances by which they are produced by engines is mostly to do with how quickly the pressure changes in the smoke box.