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Author Topic: Electronically controlled paraffin burner  (Read 5854 times)

TurboTyne

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Electronically controlled paraffin burner
« on: May 19, 2014, 02:43:04 pm »

 Since there have been some posts recently about LPG and paraffin burners in other threads I thought I’d post a description of my electronically controlled paraffin burner in case it might give someone an idea to develop themselves or in case someone has words of advice / warning regarding use of paraffin in model boats – bearing in mind that I have not yet built a boat although I aim to install my steam plant in one eventually.
It was the fascinating series of posts by Flashtwo about his “Flash steam plant control” that initially brought me to this forum and prompted me to have a go at building a similar system. Regarding burners I initially fiddled around and ended up with a working gas burner controlled with an electronically-controlled needle valve. However, when I came to operating the boiler (a horizontal double coil of ¼” diam copper tube) I found that all my electronic controls were useless because I could not boil water fast enough to produce steam unless the water feed pump was running ridiculously slowly. Even with only a No. 10 gas jet I experiencing problems with cooling of the butane or butane/propane bottles so, to increase burn rate I figured I would have to change my burner to some sort of liquid gas feed. At that point I decided to follow the comments of Oohyah/2 and try paraffin. Since boats such as Oohyah have paraffin pumped to the burner rather than using a pressurised fuel tank I decided to try an electrically driven fuel pump the speed of which could be accurately controlled since I am not looking for the flat-out performance of a speed boat.
First I made a paraffin burner - following valuable advice from Oohyah/2.  Initially I connected this to a small hand-operated boiler water feed pump that I’d made many years ago for an O-gauge railway loco. At first attempt this arrangement gave an amazingly impressive roaring flame that could also be reduced to a small flame by reducing the pumping rate. This convinced me that it was worthwhile to have a go at building an electrically powered pump. Burner and pump are shown in the photos.
Sizing the initial pump was informed guess-work. It is 3/16” bore by 3/8” stroke with twin opposed rams so as to give a more uniform fuel flow than a single ram – particularly important for avoiding erratic burning / flame failure at very slow pumping rates.   At slowest speeds the fuel flow is still rather too irregular since pump output varies continuously from max at mid-stroke to zero at the end of each stroke. To counter this, since I was using a stepper  motor, it was possible to make the step times vary throughout each pump stroke so that the rotation speed increases towards the end of the stroke and then slows down again towards mid-stroke. Currently the flame can be varied from a small stand-by yellowish flame (pump at 3 rpm, roughly 0.03 oz/min) up to a full roar blue flame (30 rpm, roughly 0.26 oz/min) that is more than sufficient to boil water even at my fastest feed-pump rate. 
I think that using a small bore higher speed pump would make it possible to use a single barrel pump powered by a normal DC motor with speed controller. I guess it might be possible to use a commercial electric boiler feed pump providing the seals are of suitable material.  I’d be happy to provide more details of my pump and burner if anyone wants them.
I like the idea of using paraffin because, in addition to the power of the flame, it seems to me to be a safer fuel than LPG, can be very accurately regulated, requires no pressure vessel, is easy to re-fill and the fuel tank can be made to fit anywhere – I guess. Also, I like the idea that it more closely resembles the fuel used in real ships such as the WW1 destroyer of which I hope to eventually build a model.  (The role of fuel oil in the navy was really brought home to me when we visited the Lyness naval museum on Scapa Flow with its vast storage tank(s) and huge steam pumps + boilers for moving the fuel oil around the surrounding pipelines).
But, since  I’ve not actually fitted this in a boat yet I wonder what problems lay ahead, so any advice will be gratefully received.
Regards  Mike

 
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flashtwo

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Re: Electronically controlled paraffin burner
« Reply #1 on: May 19, 2014, 04:18:50 pm »

Hi Mike,
I admire your double Scotch crank fuel pump – a fine piece of work (phosphor-bronze cylinders?)  and a good way of balancing the pump stresses. Where are the non-return valves located? Very clever to adjust the ram speed during the stroke!

I was also concerned about the safety of using an inverted gas cylinder for the liquid fuel, but it has (touch wood!) been fine for several years now. When I took out insurance for the new steam launch (see the Edwardian Steam Launch thread), I did declare to the insurance company that I was using an inverted gas cylinder and they didn’t query the method and issued me insurance.

I can understand the use of paraffin – it is cheaper, more powerful and, as you say, can be stored on the boat in a more convenient way.

My latest consumption figures with the D10 engine and monotube boiler are 3.8g/min for varied running, which gives 120min for a 460g gas cylinder.

Have you considered using a pressure accumulator for smoothing out the pressure fluctuations – much like a capacitor in a D.C. power supply? The accumulator need only be a vertical copper pipe (not a pressure vessel) close at the top end to trap a volume of air and located directly at the pump outlet but before the burner jet.

From the photo, it appears that you are using an Hall effect speed pick-up to give a speed feed-back signal to a PIC? Does the LED give a flash per rev?

I built a speed controller for SteamBoatPhil for use with an electric water pump.

It is making me think of converting to paraffin, although I’m wary of paraffin spots spreading on the pond it may not be a problem.

All the best

Ian
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TurboTyne

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Re: Electronically controlled paraffin burner
« Reply #2 on: May 19, 2014, 08:32:57 pm »

 Hi Ian
Thanks for the kind comments. Plenty of points to respond to. Yes they are phosphor bronze barrels - screwed into brass valve blocks – see attached part section diagram. This drawing is not complete or polished but it shows the key features of valves etc..
 
Hmm, insurance is something I’ve not thought about – or will need to think about for a long time I guess. But is your insurance to cover risk to 3rd parties or to cover loss/damage to your model?
 
It's interesting to see your latest fuel consumption figure. Translating my estimates into metric gives 0.7 to 7 gm / min and I find it reassuring that this covers the consumption that you use for butane. From what I can find out it seems that paraffin and butane have similar heating values expressed as KJ /Kg. My rates are not based (yet) on measurements but just estimated assuming 90% pump efficiency.

 
That’s an interesting idea to use a pressure accumulator. Actually I assume that the vaporising coil in the burner acts like such an accumulator to some extent. I assume that as the fuel is pumped into the hot coil it soon vaporises so that much of the coil is filled with pressurised vapour which then flows out of the jet at a rate proportional to the pressure. If I pump at speeds above about 6 rpm then the value of having the varying step time becomes insignificant and the burner operates virtually pulse-free anyway. I  would guess that an accumulator could be particularly useful if one were to attempt to use a single barrel pump where fuel flow becomes zero for half of each rotation time. But I wonder if there could be a risk of strange oscillations between the pressurised vapour in the coil and the pressurised air in the accumulator. If so, an increased coil capacity might give the desired buffering effect.

The Hall effect sensor (which I first learnt about from your posts) has two functions. Unlike the speed sensor I use for the boiler feed pump (based on your design)  where the magnet rotates on the crank shaft, in this pump the magnet is fixed in position and is located inside a mild steel ring with the sensor located just outside.  This ring has 2 slots milled in it – see attached photo. As you will have realised, the steel shields the sensor from the magnet except when a slot passes between them. (I think this was how the ignition worked in my old car). The slots are opposite each other and positioned to activate the sensor at mid-stroke of the pump. The LED, which is removable, is just there to help adjust the position of the steel timing ring relative to the pump. So it actually flashes twice per pump rev. The sensor output goes to the PIC and its key role is to tell the PIC when to start counting steps so the adjustment to stepping rate is synchronised with the pump ram movement. The other role is that the PIC counts the number of steps since the last Hall sensor event and if the count exceeds 24 then this indicates a missed step. If it exceeds a pre-set limit (e.g. 30) then it indicates that the pump has stalled. The present motor is a cheap and simple 48 step unipolar permanent magnet motor.I plan to upgrade to a 100 step bipolar motor which has more power - I've had fun learning about all this stuff - thank goodness for Microchip etc application  notes.

 
Your point about the risk of paraffin spots getting in the water is something I had not thought about. Now you've pointed it out I can see it is a serious concern that needs to be planned for. Maybe Oohyah/2 will comment from his experience of running a paraffin fired boat. I can imagine three ways of contaminating the pond water: From a capsize; During re-filling the fuel tank;   From droplets emiited up the funnel. 
I don’t think the last possibility is very likely.  When re-fuelling it would certainly be necessary to take careful precautions.  A capsize seems to have the potential to cause serious contamination so I think some sort of one-way valve on the air-vent of the fuel tank will be important. I doubt if much fuel would escape from the burner since the jet is so small and water would tend to be drawn in as the burner cooled down. 



Regards   Mike



 
 
 
 
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ooyah/2

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Re: Electronically controlled paraffin burner
« Reply #3 on: May 20, 2014, 12:03:35 am »

Mike & Ian,
There is no chance of exhaust fumes from a paraffin burner contaminating the pond water, when the burner gets going it's vaporized paraffin in a gaseous form that is burning.
The fuel that I use in my flashsteamer is a 4/1 mix of Paraffin/ petrol and on full bore the engine burns 1/2 pint of fuel per 4 min run, the petrol is to aid start up of the 3- burners and I must say that Paraffin is much safer than L.P.G. as it has a very much lower flash point.

There is more chance of oil contamination from engine exhaust even after using an oil separator as they are not 100% efficient.

If on the vent of a turn over there could be contamination but the same goes for the oil sloshing about in the bilges of a conventional boat.

I'm sorry that I can't comment on the electronic operations, after all I am only an old Clydeside hammer and chisel man.

Best of luck with your experiments.

George.
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TurboTyne

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Re: Electronically controlled paraffin burner
« Reply #4 on: July 11, 2014, 05:52:39 pm »

 Just a brief update on progress with the paraffin burner because I am so impressed by its latest performance.

I have replaced the unipolar stepper motor with a more powerful bipolar motor (see photo, Size NEMA17, about £12 new on Ebay). This has 200 steps per revolution compared to 48 steps with the first motor. The unipolar motor could be easily controlled by having the PIC microcontroller directly switching four power transistors (one for each motor winding). However, for the bipolar motor, it was necessary to design and make a more complicated controller board (see photo). The new motor requires a controller chip which limits the power passing though the motor coils and this limit can be adjusted by a simple potentiometer. With the old motor,  once the speed exceed about 30 rpm the motor started to miss steps and, at still higher speeds it would stall. I believe the cause of this was two-fold. As the pumping rate increases, the back-pressure in the vapouriser tube of the burner also increases, giving the motor more work to do. At the same time, for electrical reasons, as the speed of the unipolar motor was increased, it’s torque would have decreased significantly.  In contrast, the bipolar motor is more powerful and it maintains it’s torque even at higher speeds. Max current for this motor is 1.6A but even for speeds above 40 rpm, it drives the pump perfectly well with the current limit set at only about 0.5A. This can be reduced further at lower speeds. So far I have run the pump & burner at up to 60 rpm and the flame was then fearsome!  So  I can now easily generate steam at 80 psi with feed pump delivering over 40 ml water per min - with what is surely a very inefficient boiler. Furthermore,  for standby purposes, the burner keeps alight right down to about 1.5 rpm (about 0.5 ml per min).

Lighting the burner is quite easy and quick. The copper tray beneath the burner is there to catch drips of fuel when starting up. Inside this tray is a smaller copper trough filled with glass wool. I place a teaspoonful of meths in this trough and light it. Once the burner is hot I start pumping paraffin slowly and after a minute or two the flame starts to roar.
I’d be very happy to give details if anyone is interested in any aspect of this.

Regards,  Mike

 
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ooyah/2

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Re: Electronically controlled paraffin burner
« Reply #5 on: July 11, 2014, 11:37:51 pm »

Mike,
Glad to hear that you have the burner now working to your satisfaction, well done, if I may suggest that you try a fuel mix of 4/1 Paraffin to petrol, this is the mix that I use and it definitely helps on start up.
Just mix up a small amount to try it and see if you have any improvement.

What type of boiler are you going to use ?
If it's to be a Mono tube for the pressure that you will be working with I would suggest 1/4 " dia  copper, I think you will find that 80 p.s.i will be a little on the high side.

Make sure that the "O" rings on the pump ram are Black Viton, Paraffin melts  Silicone rings.

Any luck with hull drawings ?

I shall be away for the rest of next week, talk to you when I get back.

George.
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TurboTyne

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Re: Electronically controlled paraffin burner
« Reply #6 on: July 12, 2014, 11:12:02 pm »

Hi George.
Thanks for those words of advice. I shall try the petrol- paraffin mixture - if I can get hold of some petrol - my car is diesel. Do you have any idea how diesel fuel compares with petrol? Would it be suitable to add to paraffin?

The present boiler is 1/4" copper - a horizontal double layered coil. Why do you think 80psi might be a bit high? Is that because of the types of engines I have?

Yes, I now have the drawings of the WW1 destroyer - from National Maritime Museum. They are amazingly detailed.

Regards,  Mike
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ooyah/2

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Re: Electronically controlled paraffin burner
« Reply #7 on: July 20, 2014, 05:19:14 pm »

Hi George.
Thanks for those words of advice. I shall try the petrol- paraffin mixture - if I can get hold of some petrol - my car is diesel. Do you have any idea how diesel fuel compares with petrol? Would it be suitable to add to paraffin?

The present boiler is 1/4" copper - a horizontal double layered coil. Why do you think 80psi might be a bit high? Is that because of the types of engines I have?

Yes, I now have the drawings of the WW1 destroyer - from National Maritime Museum. They are amazingly detailed.

Regards,  Mike


Hi Mike, I wouldn't add Diesel to the Paraffin as it doesn't have as high a flash point, I suggested some petrol as it may help to keep the burner going at slow pump speeds.
I do know that the 4/1 mix in my flashsteamer helps to get the burners going.

George.
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Stoneflash

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Re: Electronically controlled paraffin burner
« Reply #8 on: May 26, 2015, 11:23:24 pm »

A long time dormant this thread but here are a few thoughts on kerosene, petrol and diesel.
from my experience with these fuels in a full size Stanley steam car.

Petrol was, in the early 1900’s, almost a waste product of the lighting oil industry in the USA and very cheap until petrol engined cars became so successful. Most early steam cars ran on petrol until about 1914 when petrol  became more expensive than kerosene. Stanley then modified their main burner to run on kerosene although they stuck to petrol for the pilot.

Nowadays most steam car owners with vaporising burners use a mixture of 50/50 petrol/diesel because it is available everywhere, unlike kerosene. Because both fuels are intended to work in a very sophisticated i.c. engine, be it petrol or diesel, they have to be very closely specified. The product is therefore consistent and one can fiddle with the proportions and the length of the vaporiser pipe to get good vaporisation without overheating the mix and making loads of carbon. Kerosene and 28 second central heating oil might be expected to work but because neither is intended for use in a situation where volatility is critical, it seems that the product sold is very variable - some would say any old rubbish!

So the main burner is generally fired on the 50/50 mix. The pilot does not like the mixture or straight kerosene as the normal vaporiser is too small for the heavier fuel. In fact even current petrol creates a problem because in the cold air around the front of the burner the vaporised fuel condenses before getting to where it is supposed to burn - the pilot being of the silent burner type as illustrated by Westbury and others. The reason being that petrol contains a rather wide variety of long chain hydrocarbons, with boiling points ranging from 40C up to even 200C. Unless the gas can be kept above about 90c, some will condense, leading to a reduced flow of induced air, a yellow flame and a vicious spiral as the vaporiser cools and the flame goes out. The answer to this for some is to use hexane instead of petrol as, being one compound, it boils at a consistant 69C. It is though highly inflammable, hard to buy and risky to store at home.

There is however another more closely specified kerosene (Jet 1) which has to work in jet engines which are in fact just monster vaporising burners with a few blades added. I have no experience of Jet 1 but there is every reason to think that it would work well in a steam car or in a model kerosene burner. I say this having heard that a friend, given the task of making the BRM Rover gas turbine racing car work after many years disuse made the mistake of trying it on ordinary kerosene which was quite hopeless, burning yellow and cause all kinds of problems which disappeared immediately once it was fed with Jet 1.

There were kerosene after-market pilot lights supplied for steam cars in the 20’s and the problem is mainly that of adding the just right amount of vaporising heat, adjusting the vaporiser length, its position in relation to the flame, and getting the proper air flow. With ordinary kerosene this might be tricky, but I reckon that with Jet 1 the job could be made much easier.

Just my thoughts
Another Mike
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TurboTyne

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Re: Electronically controlled paraffin burner
« Reply #9 on: May 27, 2015, 02:04:16 pm »

 Hi Mike
Those are very interesting thoughts. Your post started me wondering about what fuel and fuel pumps are used for model gas/jet turbines.
From information on this site (http://www.sportsturbine.com/) it seems commonly available kerosene is used but a proportion of turbine oil is mixed into this because it has to lubricate the bearings.
The pumps seem to be gear pumps and are lightweight. It seems such a pump might have been an alternative to the pump that I constructed since they can deliver fuel at up to over 100 psi (scroll down to fuel pump section on this page:  http://www.gtba.co.uk/engine_parts.php )
However, with a max flow rate (at 6V) of several hundred ml per min it might prove difficult to control them down at the rates of delivery appropriate for a model boat boiler. Also, they are rather expensive (e.g. http://www.wrenturbines.co.uk/spares-accessories/general-spares/fuel-supply ), although I guess £120 for a pump is in line with the cost of buying and running a miniature gas turbine.
I think a small boiler feed pump might make a simple, small and acceptable fuel pump for a paraffin burner since, for what it does, my pump is too large and complicated. However, it does the job and I enjoyed making it, especially playing with the stepper motor.
I am finding that the simple blowlamp-type burner is surprisingly flexible and can be controlled from what is virtually a stand-by flame up to a frightening roar that leads to steam that is far too hot for my needs.  A key aspect was making a jet with the correct proportions.

Regards 

Mike

 
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ooyah/2

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Re: Electronically controlled paraffin burner
« Reply #10 on: May 29, 2015, 12:53:58 pm »

Hi Mike,
They say that these pumps are good for up to 100 p.s.i.with the delivery  and suction connections being barbed, these are to take the Silicone fuel lines that are used in the turbines.
What they don't say is the working pressure of the turbine.
If these were to work at 100 p.s.i. I feel that the tubes would blow off of the connections at that pressure.
Ball valve pumps are capable of pressures in excess of 300 p.s.i. and are controllable for delivery using M.F.A. Como gear boxes if an electrical drive is required and are less expensive if you can't make them yourself.
The ball valves on my Flashsteamer , water and fuel, work in excess of 300 p.s.i. at approx 2500 stroke/min.



Another Mike.

I can assure you that using paraffin on a blow lamp burner does not produce a yellow flame working at pressure, in fact the 3- burners on my flassteamer produce a very light blue flame at the burners and even after travelling down the 15" long casing the flame is still not yellow at the exhaust outlet so I would stick with Paraffin.
Also I have been searching for small quantities of JET 1 and can't find any and if this fuel was better than paraffin I am sure that the guys that fly their flashsteamers around the pole at 130 m.p.h.would use it but they don't.

Have a look at the water and fuel pumps on my thread posted on page 2 of R &D ( OOYAH a FLASHSTEAMER.) the water and fuel pumps are made from the same block of Ali to prevent the fuel vaporizing before getting to the burners and and causing malfunction of the fuel pump.

Link to http://www.modelboatmayhem.co.uk/forum/index.php/topic,24568.0.html

George.
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rfurzer

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Re: Electronically controlled paraffin burner
« Reply #11 on: August 10, 2016, 12:14:46 pm »

I have had access to large quantities of Jet A1 and use it for my Tilley lamps. It is a little heavier than blue kero and takes a bit more preheating but is fine when up and running.


I consider that it is basically interchangeable for my purposes with the blue stuff. For the aviators, tho, it has a lower "cloud point" and wont make waxy deposits in the tanks and filters at stratospheric temperatures (i.e. cold). Other similar fractions are not guaranteed to perform in the same way.
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