Building a ceramic burner

Hopefully I can spread a little light on the subject.
I actually designed a burner for the C18 and made a prototype using the two jet principal which works for me. Channing sent my drawings to China and they tried to replicate it but when their prototype arrived, it was not workable so they decided to go with their original design. I was sad that they weren't able to use my design and was hopeful that theirs would work.

First lets talk about ceramic material. There are two types of material I have used. The first one is shown above and in the Bic burners . It is hard and has small ridges and holes. It burns fine but it also gets very hot throughout the plate and will cause a combustion under the plate which will ruin the burner. The second material is softer with pronounced pyramids and larger holes, This material is bullet proof and will handle any temperature. I was getting it from Bruce Engineering in the UK but they are no longer carrying it.

Now to the design.
Accucraft is using a drafted design in the C18 which id not very efficient for ceramic burners. It draws air around the burner then through the tubes and out the stack. This design is great for coal and alcohol where the air is used for combustion but where a ceramic burner gets all of its combustion air from the holes in the jet holder, the additional air drawn in just cools things down.
To have a proper drafted system, the smokebox must be sealed and the firebox needs to have air passages around the burner box. This limits the size of the burner box.

My design uses a sealed firebox where the burner fills the entire bottom of the firebox and is sealed around the edges. The smokebox is vented at the bottom similar to poker burner engines. My larger engines have had burners as large as 15 square inches. Needles to say they produce more steam than would ever be necessary.

As for your tests, the blue flame tells me that the oxygen level is low, This could be caused by the tube length to diameter is off. the length to id should be 6:1 to get the proper venturi effect. A red glow means too low a fuel to plate area and a bright yellow glow is perfect,
Here are photos od the good ceramic and a strong operating burner.

I try to get 1/2" of space under the ceramic plate.
I don't know why the Accucraft burner flame is blue. It should be dull red on low and bright orange. I looked up my Quad build which was done with the Accucraft style plates and here are the photos of the burner, with it on low and high.



As you can see the old style ceramic plate burns just fine, it just is subject to the under plate combustion.
I can't remember what causes the blue flame but I do remember that I did have that problem when I first started testing burners. I think it may be caused by the jet tube length.

here is a graph showing the pressure/temp

I just checked my files and I do have a drawing of the burner I designed for Accucraft, the measurements are metric.

I have a little time this afternoon and reread the postings.
Tyler, looking at your burner, it doesn't look like it is hot enough to pre ignite. The burner needs to be air tight including around the plate and jets. Also you could be getting some flame being forced back and into the jet air holes.
For my system to work, the burner box must be the same size as the bottom of the firebox and then sealed off with high temp RTV (Permatex brand is sold at auto stores) The smokebox then needs an air hole at the bottom at least 1/2" in diameter. This allows the combustion gas to easily flow through the tubes and out the stack without a blower.
There should not be an arch or any other blockage between the ceramic plate and the crown sheet as this is where the majority of the radiant heat is absorbed.
The gas jet stream is a cone that has 6:1 ratio. Most jets have an outside diameter of 5/16" which is the inside diameter of the tube so 6 x 5/16 is 30/16 or just under 2". Any less that this and the cone will not contact the inside of the tube and there will be little or no venturi effect.
All of this must happen for this system to work. When I designed the system for Accucraft, I was expecting to see an engine that could pull 20 or more cars at top speed with the gas valve turned down. As mentioned here, mechanically, it is perfectly designed. As you can see the boiler design has changed from the original plan.

On the plate material, I have never had pre ignition with the Bruce Engineering product but they are no longer selling it. Accucraft attempted to source some but were unsuccessful. I only had the pre ignition a few times with the harder material and still have some engines running with it with no problems. Assuming everything is sealed up, the only problems seem to be when the burner is pushed past its limit by using fuel mixture or too hot of a water bath.

I haven't seen a C18 yet but it looks like there is space around the burner and it may have an arch between the burner and the crown sheet. The smoke box is sealed and it is drafted by a blower valve and exhaust nozzle. Startup is with a stack fan. Not drafting the system will cause the flames to come out the bottom of the firebox and could go into the burner box through the jet air holes.

If I were to redo the boiler, I would either make a new box the size of the firebox (Preferred) or seal off the sides of the existing box to make it air tight at the bottom. I would drill out the bottom of the smokebox and then replace the jet tube with one of the proper length. The arch would need to be removed if it has one. I would also remove the exhaust nozzle which would reduce the drafting.

This is an interesting topic. I am currently building and posting on the Trojan and will try to spend more time on the boiler and burner build which may help.

Sam
I have never done an alcohol burner so I have no idea but I would think so. In speaking with friends it seems that getting a meth burner to steam properly can also be a problem.

Here is a draft of the conversion I did

ACCUCRAFT C 18 CONVERSION TO RADIANT
INTRODUCTION
The C 18 is currently set up as a convective boiler where the firebox and tubes are heated from the hot fumes from the ceramic burner. There is some conductive heating but that is absorbed by the stainless steel arch which deflects the heat back into the firebox. The ceramic burner is very small, less than one inch in width and uses a #4 jet which has a hole diameter of .010” which is sufficient. The arch design dates back to the first coal fired locomotive style boilers where brick arches were installed to keep the hot fumes in the firebox longer. The arch absorbed some of the radiant heat from the coal fire thus blocking it from the crown sheet but the net effect was better steaming. The current burner has a jet holder which has a length of about 1/2” past the jets which allows some air in with the butane gas but the majority of the mixture which goes through the burner is butane and the combustion occurs after the ceramic plate. To convert it to radiant, we need to extend the jet tube so we have at least a six to one length to diameter which will create a venturi situation causing more air to mix with the gas and have the combustion at the top of the plate. Below is the current burner on a test stand. The photo doesn’t pick up all of the blue flames but it does show the ceramic plate which is unchanged from its normal look.

Here is the same burner-and-jet with a longer jet holder Note how the ceramic plate is almost white hot and the orange flames are abundant.

And here it is in the boiler

CONVERSION

The conversion can be done by a hobbyist with average skills. The tools needed are as follows:
1. Small Phillips screwdriver (high quality)
2. Propane torch and soft solder
3. Standard hacksaw blade – fine tooth
4. Small slot screw driver and pliers or small vice grip
The parts required are:
1. K&S 5/16” outside diameter brass tubing cut to 1.7” long
2. New Accucraft ceramic plate or cut one to fit from larger plate
3. Permatex high temp RTV (from Auto Stores)
4. Small sheet of metal to cover a 3/8” hole Burner removal Here is a drawing from Accucraft of the top view of the burner mounted in the frame. It shows the two front burner screws and the jet screws on the outside of the frame which need to be removed

T
To remove the burner, remove the two front screws and the horseshoe cap holding the jet tube down with two long screws. The curved tube jet holder needs to be removed by taking out the two screws on the outside of the frame. The lower half or the buffer is held in with a screw on each end and the shoulder bolt holding the tender connector needs to be removed also. The shoulder bolt has a very narrow slot so if you don’t have a driver to fit it, you can break it loose by grabbing it with a small vice grip or pliers and then removing it with a small screwdriver





BURNER CONVERSION

The ceramic material is soft and glued into the box which makes it almost impossible to remove it without damaging it. It should be dug out with a screwdriver and the sides of the box cleaned with an Exacto knife or similar tool.

Inside the box you will see two studs which are soldered in to holes in the bottom of the box. You can see the bottom of them in the photo above. The one nearest to the jet needs to be desoldered in order to add the tube extension. The hole can be covered with a plug soldered in like this or just a small, thin plate soldered on top

The tube extension can be installed after the stud is removed. Cut a piece of K&S 5/16” outside tubing to 1.7” long. Coat the end with the high temp RTV and slide it into the tube till it is just to the air hole in the tube and is not covering it. A ¼” wide of strip brass can be bent and positioned as shown which evens the gas distribution by diverting some of it back toward the jet.

Once the box is converted like this, a new ceramic plate can be set in place and sealed around the top with RTV. Below is the original ceramic plate which was broken out and a piece of new material. The material should be cut slightly oversize on a band saw or by hand and then sanded to a perfect fit.


The arch removal was also documented if anyone is interested

Tyler
You answered my question while I was writing it.
Here is how I removed the arch. somewhat crude. Maybe you have a better way

Arch removal
The removal of the arch is a simple but tedious job. The arch is a very hard stainless alloy which is about an inch wide and 1/32” thick. It is too hard to drill through and not accessible enough for a Dremel cutoff tool. It can be cut with a bi-metal fine tooth hack saw. I used a medium blade here as that is what I had at the time. The blade is too thick to fit in the space so I split it in half. I used a cutoff blade on my Shop smith but a Dremel will work too


Here is the blade after trimming. I trimmed both sides so I could try it with the cut on the push and the pull. I found that the push worked best for me. You will only have short strokes at the tip of the blade. The cut off on the left was to remove a portion with worn teeth and expose fresh ones.


I wrapped a couple of paper towels around the blade as a make-shift handle
Here the arch is being cut. The dark grey arch is on the right and the cutting is seen on the left of it. At this point the cut is about ¾ down and the saw blade is just above the bottom of the cut. The white on the left is the paper towel handle.

This is very hard material and with the limited stroke clearance it will take about a half hour to cut through so don’t get discouraged.

And here is the firebox with the arch gone

With no water in the tender, any butane engine will eventually run out of steam as the gas escaping from the tank will bring the tank temperature down so low that there is no gas pressure even on a mild summer day. At 33 degrees that would be exaggerated. Even room temperature water will cool down during a run and it will get worse as the level in the tender gets lower. The ideal tender water temperature seems to be about 70 - 90 F. It looks like Tyler's engine was doing fine at that temp.

As far as the diverter goes it is basically trial and error. Sometimes I burner will only glow at one end without something to divert the flow of the gas and sometime it is fine. the diverter shape I showed seems to work best but it cant be too high.
I usually make it about half as high as the tube and then move it around to get the best burn. I hold it in place with RTV while testing and then set it in RTV for a permeant bond. Once in the firebox, the glow evens out so it doesn't need to be perfect on the bench.

Early on I tried the springs, steel wool, screens etc. and they really didn't do much. Of coarse the Bruce Engineering ceramic made everything much better but for now it is no longer available. I emailed the new owners and they said they are considering stocking it again.

Tyler seems to have his engines running as well as possible with the drafted system and small ceramic burners.
A little of my history on air hole collars.
I first started using them on my poker burner engines to quiet the howling. I actually set them up with a handle which could adjust the position while the engine was running. I found that the collars worked best about half covered preventing the howling but inhibited the steam production. After things warmed up, I was able to slid them back without the howling and better poker burn and steam production
Back in the olden days, carburetors needed to be designed for the correct air/fuel mixture (I think it was 27-1). Now we have fuel injection where we always want more air so the mixture is not an issue. On our turbocharged diesel engines, the power is increased just by increasing the fuel volume with no concern for the air as there is always enough air and never too much. I feel our gas fired burners are the same here, In other words, unless you are restricting the air because of howling, you are limiting steam production. It is hard to determine if adjustments to the collar are working from boiler to boiler or even from run to run. I have tested ceramic burners with collars in the past and just to make sure, I did it again yesterday and they only decrease the burn, On my burners I have four 7/32" holes which is the largest I can get in. Like I said you can't have too much air.

Just my two cents