Ian,

I don't think we can answer your latest question yet but I can tell you that between Mark and I, and with the mathematical and musical help of Chris Busk there is quite a lot going on which we hope will provide a proper scientific explanation of burner howling. Patience please!

As far as whether it is good or bad, as you say many people say it is good - but whether it is in itself good, producing more heat in the burner, or is just a sign that the burner is being pushed I can't say. There is an argument that vibrating gas in the boiler tubes may be disturb the otherwise smooth linear flow of gas and thereby increase heat transfer to the tube wall, or on the water side disturb the layer of steam on the tube wall thus exposing water more to the tubes. If howling does produce more steam I guess it is through one of these mechanisms.

Mike

Hello Mike
If it helps or adds to the howling question the Boiler on my latest car is a Bolsover with no tubes & has a large area of exhaust gas space
it is side entry ,running on petrol at 80 psi, But at speeds above 45 mph it howls & more as speed increases .I like it to howl on relighting as the older one gets the more help you need with the hearing.
Gerry

Gerry - I didn't know you were using a Bolsover - look forward to seeing how it goes and hearing it howl at Tiverton. The new car looks fantastic.

Following Sssteamer's comments on the deeper howl of bigger burners Chris Busk brought along a musician's frequency meter to play with. We found that the usual howl of my Model H is between 310 and 330Hz. There is an indication that the howl increases in pitch as the burner gets hotter which is as would be expected because the speed of sound also increases with temperature. As it happens this frequency corresponds pretty well to the calculated frequency for a 2ft long pipe and guess what - the distance from the mouth of the venturi to the back of the mixing chamber is - 2ft.

So Gerry you have to anticipate a visit from the frequency inspectors at Tiverton where we hope to have a good opportunity to try to relate howling frequency to burner size. I found that recording the sound with a microphone about a couple of feet in front of the venturi intake makes it much easier to analyse the howl which may just happen for a few seconds.

This brings me to an interesting question - if a burner is fired up out of the car does it howl with the same pitch as when it is mounted under the boiler? If the pitch of the howl is unchanged by putting it back under the boiler then clearly most of the acoustic resonance is happening in the venturi and mixing chamber. If the pitch changes then the parts above the fire are also contributing. If anyone has a chance of doing this experiment and recording it on tape with a commentary as to what is being done we would be able to check the pitch from the tape and might learn something useful. Any volunteers? If not I will do it when the boiler inspector comes next month.

As part of this acoustic experiment I put a thermocouple probe into the mixing chamber about 3 inches beyond the end of the venturi. Quite a surprise - although the gas exiting the jets is at nearly 300C, by the time it gets out of the other end of the venturi it is down to under 100C.
The temperature in the mixing chamber is affected by the outside air temperature and whether the burner is on or off. It drops to the low 40's when coasting down hill but mostly runs in the region of 75-90C when the burner is firing. The significance of this is that at such low temperatures the nicely vaporised fuel has probably condensed into a fog of droplets before it gets to the burner - heaven knows what that means. When the car stops with the burner off the temperature of the probe rises from heat soak and radiant heat coming back from the burner plate. Usually I see about 130-150C when stopping after a run but once after firing up to 600psi and turning the burner off without driving away the temperature went up to 425C - clearly the airflow through the venturis has an enormous cooling influence.

Mike

A thought accrued to me concerning burner noise and the high pitch some burners make.
I was drawing up the venturi tubes for my burner. I was always lead to believe the tube diameter to length should be 6.5 X diameter.
I checked two original Stanley burners I have and one has 1-5/8 diamenter by 13.5 long tubes, that’s 8.3 X diamenter another has 1-1/4 diamenter by 10.5 long tubes that’s 8.4 X diamenter
I did a drawing on an baker burner that one of our SACA members has appart and the tubes were 2-1/2 diamenter by only 13 inch long and that’s only 5.2 X diamenter. Very short tube length.
I was woundering if the higher pitch noise on some burners is do to a short tube length to diamenter.
When you make steam whistle the longer the length the deeper the tone, the shorter the higher pitch.
Rolly