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Different fuels and blow backs
Posted by: Nick Howell (---.147.51.84.dyn.plus.net)
Date: October 21, 2015 12:21PM

After finally working out that steam automatic was on the wrong side of the vapoursing tube (after 4 years) I am now starting all over again with main jets, vapourising tube lengths,fuels and superheating coil otions. What fun!! ?.

I have come to the conclusion that no one solution suits all burners and as the other UK Toledo's all run cleanly on hexane and I wince at the price and danger of using it I am trying to use get fired up with kerosene, or more accuarately paraffin extra, or a mix of it with and some forecourt fuel for convenience sake on rallies.

The pilot light is a Toledo design and the, new, burner has an Ottoway jet layout of 5400 or so Number 54 drill bit jets but with a 48mm inlet tube underneath the burner plate, entering in the centre (also a la Toledo).

There are two vapoursing tubes, one for the pilot and one for the main jet, both going through 10mm OD, 5.85mm ID, 316 tube and fuel supply for both is at 30 psi.

On top of the vapourisors is the superheating coil, so quite a lot of piping above the burner grate.


Attachments: IMG_2757.jpg (158kB)  
Re: Different fuels and blow backs
Posted by: Nick Howell (---.147.51.84.dyn.plus.net)
Date: October 21, 2015 12:59PM

Er, continuing after accidently posting......

On firing up with straight unleaded petrol the flames were nice and blue on both the pilot and main burner. Changing to straight hexane and after adjusting the main jet,the result was the same so back to petrol. The pilot light vapourising coil was glowing orange for a lot of its length when teh main fire was on and sure enough after ten miles it started to carbon up inside; after twenty miles is was almost blocked up completely with low pressure to the pilot, yelllow and ble flames and from there of course more yellow flames on the main burner because of a weak pilot.

Plan two involved using straight kerosene --if the vapoursor was too hot for petrol I thought it would be fine for kerosen and making up a shorter vapourisor to the pilot and curled a little further away from the flames so as not to get too hot; now one hot spot next to the pilot, glowing orange, but not quite vapourising the kero enough. Plan 3, back to making a longer vapouriser, going around the midddle of the burner to be hot enough. Result, blue flames with a few yellow tips on the pilot when warming up, all blue when the main burner was on which was also nice and blue. But....when the pressure is up and the burner plate is hot and the steam automatic has cut off, when it cuts back in the main jet just keeps blowing back (igniting from the main jet). Adding 25% hexane made no difference.

Something is igniting the fuel vapour before it gets above the burner plate. I now have the burner out and have cleaned out the inside of any rusty flakes, which were very few, filed down a raised speck inside the inlet tube in case that was glowing hot, and there are no breaks in between jets on teh plate that could cause ignition below.

Does anyone have any suggestions as to what can cause ingnition aty the main jet?

Nick

Re: Different fuels and blow backs
Posted by: Old timer (86.112.221.---)
Date: October 21, 2015 01:31PM

Hi Nick,
One other thought, if you have any leaks between the boiler and burner, this can cause blowbacks, usually when the fire shuts down though, as the extra air causes the fire to burn below the grate.
Best Wishes
George

Re: Different fuels and blow backs
Posted by: Mike L Clark (---.colc.cable.ntl.com)
Date: October 21, 2015 03:52PM

Nick how thick is the burner plate?

I know little about the Ottway burner so you need to find someone who does, however here are few thoughts from my Stanley experience. All of this assumes that you have no gas leaks to the mixing chamber around the burner plate and no obvious hot spots below the plate.

Think of the process going on in the burner holes as a race between the gas going up the hole and the flame front trying to go down the hole against the gas flow.

The relative gas pressure in the mixing and combustion chambers and the diameter and number of holes in the plate determines the velocity of gas going up, while the velocity of the flame front going down is a property of the gas/air mixture. The length of the hole (thickness of the burner plate) determines, along with the temperature of the plate itself, whether the flame can retain enough heat as it goes down against the gas flow to still be burning at the bottom of the hole to ignite the contents of the mixing chamber. A thicker plate would be better than a thin one, more smaller holes are better than fewer big ones.

The problem you have may be that for a few seconds as the main burner relights, the volume of gas passing through is less than when on full fire, letting the flame win the race. If you have a steam stack blower you could possibly prove the point as the slight suction produced by the stack blower should assist the gas flow and hold the flame above the plate. At the expense of higher water consumption, you could fit a stack blower and leave it slightly open to improve draught and reduce the pressure in the combustion chamber until you find better solution.

Alternatively you could attack the problem from the other end by raising the fuel pressure to induce more air and boost the gas pressure below the burner plate. You mention a fuel pressure of 30psi - sounds very low in Stanley terms. Could you increase this to get a faster gas flow? It would not mean more fuel being used as the fiercer fire would be on for shorter periods. You need to talk to an Ottway expert on this, what pressure do they normally run at? I appreciate that changing the fuel pressure may need more changes to the fuel system of the car but the Ottway, like the Stanley will have a range of parameters within which it needs to work and these may be different to the original Toledo set up.

It is perhaps surprising to realise that the gas flow does have a cooling effect on the underside of the burner plate. I once put a thermometer into the mixing chamber through the mixing tube of my Stanley. Although the vapour was leaving the jets at over 300deg C, by the time it had got to the far end of the mixing tube it was down to 90 deg C, at which temperature some of the higher boiling point fractions of the petrol, and much of the diesel must have been back to the condition of a fog rather than a gas. The cooling effect of gas expansion is significant. It could be that a stronger fire might actually keep the burner plate cooler.


Mike








Edited 1 times. Last edit at 10/21/15 03:54PM by Mike L Clark.

Re: Different fuels and blow backs
Posted by: Old timer (86.112.221.---)
Date: October 21, 2015 04:22PM

Hi Mike,
Our 1900 Mobile has an Ottaway burner, running at 40PSI. This is for a 14" Burner/boiler (15.5" O.D of boiler). All the Locomobile I know running Ottaways are running around this pressure. However, I believe Nick's boiler and burner are quite a bit bigger-so your idea about higher fuel pressure might do the trick.
Best Wishes
George

Re: Different fuels and blow backs
Posted by: Old timer (86.112.221.---)
Date: October 21, 2015 04:22PM

Hi Mike,
Our 1900 Mobile has an Ottaway burner, running at 40PSI. This is for a 14" Burner/boiler (15.5" O.D of boiler). All the Locomobile I know running Ottaways are running around this pressure. However, I believe Nick's boiler and burner are quite a bit bigger-so your idea about higher fuel pressure might do the trick.
Best Wishes
George

Re: Different fuels and blow backs
Posted by: Nick Howell (---.147.51.84.dyn.plus.net)
Date: October 22, 2015 02:34AM

Thanks Mike and George, I'll be in the workshop in a minute investigating your suggestions.

Firstly I will check out the flue and boiler tubes to see if the earlier runs have produced too much soot and resticted the air flow; these blow backs didn't occur for the first 15 miles or so on straight unleaded fuel, they started as the vapourising tube gradually got blocked up --which would have reduced the airlow.

I have just fiited an stack blower Mike and linked it to a steam whistle inside the exhaust across the top of the car so I will try opening that at times as well.

The other half is off to France today so that's chef and main bottle washer gone for three weeks, tut! But then getting up at some dreadfully early hour to get in the workshop won't disturb anyone either!

London to Brighton next week is awfully close...are you in it this year George or is your Dad with Richard?

Nick

Re: Different fuels and blow backs
Posted by: Old timer (86.112.221.---)
Date: October 22, 2015 02:55AM

Hi Nick,
Yes Dad and I are taking the 1900 Mobile this year, with Richard as back-up. We too are finding it is getting close- with still a few things to do on the car.
Best Wishes
George

Re: Different fuels and blow backs
Posted by: Nick Howell (---.147.51.84.dyn.plus.net)
Date: October 22, 2015 03:38AM

Mike, that burner plate is 2.5mm thick 4130 alloy steel and there are 4548 jets (not 5400 odd as I salid earlier). Spacing 1/4" btween each on the y axis, a la Ottoway, and on a 60 degree matrix on the x axis. Though the burner fits tightely around the base of teh boiler casing there is a 70mm sealed hole in the burner which takes teh pilot; I wonder what that does to airflow! I do have a loosly fitting cover over the base of the pilot which seals most of it up; maybe I should make sure it seals it completely to get the airflow.



Attachments: IMG_3154.jpg (159kB)  
Re: Different fuels and blow backs
Posted by: Steamcarbob (---.range86-134.btcentralplus.com)
Date: October 22, 2015 05:10AM

Hello Nick,
When you have the burner off, check also that you have no evidence of steam leaks blowing down onto the burner as even a small one can cause the blowbacks too. I presume that this is the "reverse stack vent effect" as Mike suggests slowing the gas flow through the burner plate.
I have had to raise the pressure on the 1902 and 1903 Whites from 30 to 40 psi and reduce the jet size with adding paraffin to the unleaded petrol.
Regards Bob

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