LP Gas Burner Calculation

Don't the holes in the burner take a mixture of air and gas? I assume there's gas jet of some sort. If you measure the jet diameter and make some assumptions about coefficient of discharge you could estimate gas flow.

From gas flow you can easily calculate heat output, as I'm sure you know.

I don't know if this is what you have, but there are "Jet burners" with a number of brass nozzles about 1.5 inches long, each of which contributes ~10,000 Btu/h. If you search on the term, you can find many pictures.

http://web.go-spi.com/sinclairdev-new/wp-content/themes/sinclair-supply/pdf/Gas-Orifice-Capacity-Chart.pdf

http://www.alabamapropane.com/propane-technical-pocket-guide/

https://www.instructables.com/id/How-to-Make-a-BBQ-Burner/

http://www.davegardner.org/GasInfo.html

-------------air to fuel ratio-----fuel by percentage

http://wiki.gekgasifier.com/w/page/6123822/Stoichiometric%20Combustion%20Ratios

L P gas and all L P appliances and related equipment, are very very dangerous, and should never be instructed on forums or u tube. Explosions and C O WILL kill you and/or mess you up for the rest of your life. If you need a flame in your house or in your covered B B Q , hire a qualified person who has enough insurance. If you are living at high altitude, (3,000-8,000') hire a double qualified older person who has double the insurance. In general terms, having L P gas appliances and their flues and piping in closed spaces, is not for everyone, especially in mountain towns. Luckily NAT has taken over. But remember, all gas appliances are built and tested at sea level and the air fuel ratio is rarely adjusted for altitude. And in fact, if you are living in the mountains using L P gas, your range/oven is putting out massive amounts of C O. Always VENTILATE. My old timers saying is "if C O had B O it would not be a problem"

Thanks to everyone for all of the great info and suggestions.

I have an old 30,000 BTU burner,and I will measure the hole diameter and count the number of holes to get a ball park figure for my mystery burner.

From that starting point,I can start with the 30,000 orifice,and adjust as needed to get the best performance.

I have a numbered drill bit set,and an orifice chart.

I can drill the orifice to suit.

Thanks again Guys!

If you need to make the oriface size smaller (As you do for altitude over 2,000' adjustment). heat and fill with hard solder, and drill (with drill press) oriface to new size. Adjust air ratio to a nice blue color.

So that means (according to the data I've seen) for propane at 11" wg an orifice of 1/32" would deliver 26,500 btu's which may well give you something to base your calcs on?

It has always surprised me how tiny LPG orifices are which has always given hassle in some cases where they (the orifices) get bunged up compared to Nat Gas nozzles!

That's interesting = same as here in the UK 11" WG applies to low pressure butane and propane is 14" WG which of course gives a higher calorific value than butane. Propane = red bottles.

There are two gasses re low pressure =butane and propane. My previous post embraces all the data. The main item is to get the appropriate regulator correct.

You may well have a low pressure regulator because I thought I saw in your first post the word LOW pressure stated which relates to 11" wg butane and 14"wg propane. These pressures are fixed at the regulator but there are regulators which are adjustable for at least propane such as cutting gear (LP) and blowlamps (HP)..... There is one safety aspect re both those gasses in that they are heavier than air........ Quite a nasty surprise if there is a lot about near the floor in any room or garage & the low lying gas ignites ===== Wooosh.....

I measure the BTU output of gas burners by taking one litre of water and measuring the time it takes to raise the temperature to the point where it is either 90 degrees C or you view the bubbles. I then compare the time with a kettle of 2400 watts and put the value on the data sheet for the cook-top.

I see that an orifice of 1/8" will deliver 109,150 btu's at 11" wg! However propane in the UK is 14" wg after the pressure reduction gauge on the bottle for low pressure use as in our static holiday caravan. You probably know that the air has to be adjusted to give the correct blue neutral flame.

You will no doubt see that a calculation can be done to enable you to choose the nozzle you require to supply the propane you need to emit from your burner that you have. I made my burner in stainless on our barbeque but had to hand several 'injectors'/ jets/nozzles to try in as you say a bit hit and miss but finally got a nice blue flame without too much experiment re the orifice size!

Enlighten me, please.

Why can you not just put larger jets in now (If you think the current jets are too small) and then simply adjust the heat to the proper flame to cook whatever you're cooking that day, with the valve? Or, does your grill not have a thermometer?

Cooking ONLY with Mesquite wood, _{(the only true way to smoke or grill)} I never have to worry about jet size.

You don't want to change the air/fuel mix ratio.

The BTU will be determined by the mass flow rate of the fuel. The air mass flow should be varied to maintain a constant air fuel mix ratio. If you vary the air fuel mix, you will reduce the heat output by either chilling the flame with excess air or by choking the flame with unburned fuel.

Among other terms, the perforated burner plate is referred to as a flame holder. It basically placed the combustion locations where you want them and prevents the flame from backflashing into the air/fuel mixing chamber. As I recall the flame speed for back propagation is about 3 meters per second. If the air fuel mix is slower, then the flame has a potential to run up the air/fuel supply until it either hits a zone flowing at 3 meters per second or reaches the flame holder. That is when the burner backfires. If the velocity is greater than the 3 meters per second, it carries down the flow until it slows to the back propagation speed, or just blows out.

The sizing and spacing on the burner plate holes is set up to quench the flame to prevent backfires and to avoid exceeding the back burn propagation velocity to avoid having the flame blown out. You can easily have an excess of holes so that you have many smaller flames rather than a few large flames.

You are dead right bvecause if the nozzle is over pressure as when we used Nat gas in the early years we saw boiler burners that had the flame off the burner and occasionally blowing out due to the nozzle/nozzles not having enough flow rate. Propane could be worse with very tiny or rather smaller orifices used in low pressure burners.......

High pressure supplies to such as blow lamps consequently have minute orifices

and are therefore prone to clogging. There are tables with various nozzles and the applicable outputs which one would think that hopefully the gas speed is taken into consideration when the tables were formed?

The propane gas speed should be correct re the 105.500 btu's emitting from the 1/8" orifice @ 11" water column so the 1/8 divided by three should give about a third of the 105 500 @ same water gauge pressure and adjust the air to obtain a blue flame (no yellow) that is not jumping off the burner.

Natural gas has blue flame no yellow, propane has blue flame fringed with yellow....

Propane will burn all blue if the air mix is right. I suspect that if you have a yellow fringed flame, the burner is actually optimized for methane or compromised for dual fuel and has a slightly low or incomplete air mix. The mix ratio for methane is 3:1 air to fuel and propane is 7:1 air to fuel. Usually the burner uses fuel pressure in a jet to induce air using a venturi and the lower volume of propane gas used has more difficulty inducing enough air in a venturi originally set up for natural gas. Burners set up for both fuels are a compromise in the orifice and venture and the methane tends to run with excess air while the propane can't quite get enough air.

https://www.charbroil.com/help/gas/flames-blow-out-because-excess-flow-valve-tripped

They always told me that for natural gas (roughly same as pure methane)ratio should be 10:1 (air to fuel) because each (mole, cubic foot, cubic meter)of methane needs 2 ( ) of oxygen {CH4+2O2=CO2+2H2O} [and 8 ( ) nitrogen comes along]. Air and fuel are both at about same pressure (atmospheric and SLIGHTLY above).

You're right, I neglected the nitrogen. If my math works, then propane would be 17.5:1.