Forced Air Diesel Fuel Burner

[Toymaker]

My plan is to use the burner shown here in a water tube boiler. At max output, the burner consumes 14 liters of diesel per hour. One liter of diesel produces 10.6 KWh of energy, therefore 14 liters = 148KWh. The slotted burner "cans" and the external housing are both made from stainless steel drinking cups. The brass colored nozzle is a siphon type and uses 1 to 7 psi air pressure to atomize the diesel fuel. A small cordless leaf blower (blue) forces air in between the outer shell and slotted burner cans; that air is guided through a ring of steel vanes which cause the air to swirl around the annular assembly, helping to cool both outer and inner stainless steel cans. Notice how the burning combustion gases are kept away from the inner metal structures.

 

[lathe nut]

That is a nice-looking unit, looks and should like a jet engine, that would make shop work comfortable.

 

[Toymaker]

That is a nice-looking unit, looks and should like a jet engine, that would make shop work comfortable.

Thanks lathe nut. Yep, my little marshmallow toaster does share some similarities with a torpedo style space heater. At full burn it should put out a little over 500,000 BTU/Hr.

 

[perko7]

Interesting..... There are a number of people in Australia making diesel heaters for caravan/camping hot water and heating. Typical examples on this site amongst others: Home Maybe they would have some details you could adapt? Maybe you already know all about these?

 

[Toymaker]

Interesting..... There are a number of people in Australia making diesel heaters for caravan/camping hot water and heating. Typical examples on this site amongst others: Home Maybe they would have some details you could adapt? Maybe you already know all about these?

I had not heard of the Australian diesel heaters before your post, so thanks for the link.

I'm actually satisfied with how my current burner is operating. The only future change I'm considering is to wrap a few turns of the aluminum fuel line inside the monotube / water tube boiler which will pre-heat the fuel, which will both heat the fuel and lower it's viscosity, both of which will improve vaporization of the fuel once it leaves the nozzle.

 

[Steamchick]

In Europe, many modern camper vans have diesel heaters. Very compact and typically about 5 kW output. Pretty cheap on e&@y. I thought about getting one , but bottle gas is fine and convenient for my use. One caution, is that you need enough flue area, (same CSA as the flame!) or the back pressure can richen the mixture and make the exhaust more toxic. Or develop blow-back!
K2

 

[Toymaker]

I have no knowledge of European or Australian diesel heaters, but I am familiar with those in the USA, where they're typically referred to as space heaters. US models using forced air are designed to mix lots of air with the super hot combustion gases, which both cools the output air and substantially increases the volume of the now pleasantly warm output air. This is great if you want to heat a large room to a pleasant temperature, but not so good if your intentions are to boil water.

Kerosene stoves, which are designed for cooking meals, do produce high enough temperatures to boil water but not nearly enough BTU or KWH for my needs. My burner generates 500,000 BTU/Hour which is roughly equal to 150 kW, or about 200 HP.

 

[Steamchick]

Just a bit bigger than my "single-figure kW" radiant gas burners! (Largest 8kW). !!!OMG!!! Are you powering a steam car? - Or generator or pump for industry?
And your handle is TOYmaker?
K2

 

[Toymaker]

Just a bit bigger than my "single-figure kW" radiant gas burners! (Largest 8kW). !!!OMG!!! Are you powering a steam car? - Or generator or pump for industry?

My goal is actually pretty simply; I plan to use the turbine to drive one of the larger sized centrifugal compressors, like the ones found inside the turbo charger on a large diesel engine. The "steam" turbine I'm building will be directly coupled to the compressor and spin at about 70,000 rpm which will compress roughly 200 lbs of air per minuet, to roughly 4 bar (59 psi).

And your handle is TOYmaker?
K2

Have you heard the old saying; "The only difference between men and boys is the price of their toys" ?
As my avatar suggests, I may be a 71 year old man on the outside, but on the inside, I'm still just a kid playing with toys

 

[Mechanicboy]

We has Webasto and Eperspächer heater for coolant who are connected to the engine in winter period to heat up the engine before start up. Same principle.

 

[Toymaker]

I've made a few mods to the burner since my last post in late Jan.
1) I'm now using my DIY small wobble plate air compressor to supply 4 to 8 psi air pressure to the fuel nozzle.
2) I shortened the burner assembly by about 4.5".
3) I added a stainless steel end plate to the exhaust end of the burner in an attempt to more completely burn the fuel.

The first video shows the thin stainless steel plate glowing red in the exhaust flames; measured temp is just over 500 C.
At higher fuel burn rates the plate changes color to reddish-Yellow (second video) and finally to yellow-whitish.

At lower fuel burn rates, there is no visible exhaust, but at higher fuel burn rates, yellowish flames can be seen exiting the exhaust, (second video). I'm running out of ideas to achieve more complete combustion and a blue flame.

 

[Steamchick]

Hi Toymaker, Yes, I agree, you are not getting enough air mixed in with the fuel - before combustion is completed. In both videos, the flames are yellow.
I think the target (your first post) of 148kWh of fuel energy - in 1 hour - needs a load more air than you are supplying. I'm not really sure of the various stages within the burner, but my first thought is that the atomisation needs MORE AIR = higher pressure and volume - to reduce the particle size of the fuel droplets in the spray... so you really get an almost gas-like vapour mixing with all the air. Then the increased surface area of the droplets will increase the combustion speed, and the increased air will provide the oxygen for better combustion and generation of the blue zones.
To re-iterate =how good combustion works - with adequate air and atomisation:
1 - The fuel is a gas or atomised to almost gas-like aerosol when injected.
2 - The initial combustion of hydrocarbons in air is when the hydrogen burns with the O2 (the light blue cone in the Bunsen flame).
3 - Within the breakdown of the molecules to release the hydrogen ions for combustion, some carbon ions combine with oxygen to form CO.
4 - IF ALL the C is burnt to CO in this initial light blue cone, then the CO and residual O ions burn to CO2 in the outer dark blue flame of the Bunsen flame.
5 - But, if not all the C is burnt in the initial phase to CO, then the C will glow yellow to white hot - but NOT burn. You must get more air entrained initially. (essentially you are too rich for stoichiometric combustion). 6 - Possible solutions? Double the initial air pressure, to double the first combustion air. If this works the flames will get better. If TOO much air, the flames will blow out.
7 - Keep increasing the air pressure, using a bigger compressor if required, until the flames eliminate the "yellow-white feathers".

Incidentally, Diesel engines in cars, etc. have become much cleaner with the increased fuel atomising pressure, because the aerosol has improve from just a spray of fuel in the last 120 years or so... These engines are not directly comparable to flame burners like yours, because they run on air compressed to high pressures and temperatures in excess of the stoichiometric balance. = LEAN. Yet were "Smokey" with carbon and high CO in the exhaust simply because the particle (droplet) size was too large. So now the injectors are at higher pressures (not more fuel) they deliver a finer atomisation, which mixes quicker with the air and burns fast enough to be much cleaner and hence more efficient than say 50 years ago.
But I guess you know all this.
Oh, you could try a smaller fuel jet? What size is yours?
Keep on trying, and you will get there.
K2

 

[Steamchick]

Toy maker: I am but a spring Chicken at 68... and have only really challenged myself a bit with burners in the last couple of years. My 8kW burner doesn't compare with the industrial 27kW equivalent... But I can't get their exotic hole patterns in the base metal pre-mix chamber, nor the knitted exotic metal wire coating that forms the combustion zone.
My 8kW propane burner: - It flashes back after 5~10 mins.

the commercial 27kW burner (cost £70 or so...) on propane (around 4kW in the picture): - very stable from low gas to full! The development took half a year or so, but finally a venturi close to the designed size gave adequate air for stable combustion without any failure modes. It was all about getting enough air flow.

But I am getting there - if slowly.
You will too, I am sure!
I have some sample calculations that I can try and re-work for diesel fuel at 150kW to get an indication of how much air you need... I feel you need to double or treble the air-flow through the injector nozzle... at a guess?
Look at a 200HP diesel car to see what size of turbo they have to get the air into the engine. That's what you need to burn the same fuel, and 80% should come through the injector with the fuel, and only 20% surround the outside? - But I am guessing, not "Engineering".
K2

 

[Steamchick]

In Europe, many modern camper vans have diesel heaters. Very compact and typically about 5 kW output. Pretty cheap on e&@y. I thought about getting one , but bottle gas is fine and convenient for my use. One caution, is that you need enough flue area, (same CSA as the flame!) or the back pressure can richen the mixture and make the exhaust more toxic. Or develop blow-back!
K2

Her's one from £&@y:
https://www.ebay.co.uk/itm/28492896...WfSk/Za5AIHHVnYSOn14c1ukM=|tkp:Bk9SR77b6u_UYAMade by Webasto. I am sure that searching across the net you can find your local equivalent? - But only 12kW. However, it can give you an idea of what you need, to increase the size by a factor of 12 or more for your heater!
K2

 

[SmithDoor]

My plan is to use the burner shown here in a water tube boiler. At max output, the burner consumes 14 liters of diesel per hour. One liter of diesel produces 10.6 KWh of energy, therefore 14 liters = 148KWh. The slotted burner "cans" and the external housing are both made from stainless steel drinking cups. The brass colored nozzle is a siphon type and uses 1 to 7 psi air pressure to atomize the diesel fuel. A small cordless leaf blower (blue) forces air in between the outer shell and slotted burner cans; that air is guided through a ring of steel vanes which cause the air to swirl around the annular assembly, helping to cool both outer and inner stainless steel cans. Notice how the burning combustion gases are kept away from the inner metal structures.
View attachment 133525 View attachment 133526 View attachment 133527

View attachment 133528
View attachment 133529

I have used oil burners off heaters for aluminum and brass furnaces.
I also had set for propane so go with best price.

Both can setup upto 500,000 BTU

Dave

 

[Steamchick]

Hi Toymaker,
Fudging some equivalent combustion calcs, on a spreadsheet I was given for a burner of 49,500BTU/hr, (1/10th of yours) suggests you need 450kgs/hr (of air through your burner for 150kW combustion of diesel fuel.
Knowing that, I reckon you can do the sums for "cu.ft.min" and pressure (density 0.67lbs/cu.ft. @100psi), and find you need a very big compressor... - I make it 25cfm @100psi.?
Can any experts help Toymaker here?
K2

 

[Steamchick]

As Dave suggested: Why the CB-5000 is the Best Waste Oil Heater ..??
Or this?
Ecoflam Max12 TC Burner, 60-130kw : Ecoflam Max12 TC Burner, 60-130kw, 3142918 - Buy at H.P.W.
Maybe this?
https://www.industrial-equipment.co.uk/online-tools-store/r096-6035-garage-heater-info.html
Here's the spec, giving AIR usage as well as other facts... which may help you size your compressor and blower satisfactorily?
Manufacturer: Thermobile
● Model: PSO 150 ERP
● Nominal heat output (High Setting): 150KW
● Nominal heat output (Low Setting): 105KW
● Air flow: 10368 M3/hr
● Air throw (approx.): 28m
● Number of discharge heads: 4
● Static Pressure: standard motor - 175Pa
● Fuel Consumption: 15.9 l/hr
● Fuel connection: 3/8" Rc
● Main fan start/run current: 32.5A/5.1A
● Flue diameter: 7 inch
● Combustion air spigot diameter: 150mm
● Noise level: 62dB(A) @ 5m
● Nett weight: 390kg
● Voltage: 400V

I hope some of this is helpful?
K2

 

[Toymaker]

Hi Toymaker, Yes, I agree, you are not getting enough air mixed in with the fuel - before combustion is completed. In both videos, the flames are yellow.
I think the target (your first post) of 148kWh of fuel energy - in 1 hour - needs a load more air than you are supplying. I'm not really sure of the various stages within the burner, but my first thought is that the atomisation needs MORE AIR = higher pressure and volume - to reduce the particle size of the fuel droplets in the spray... so you really get an almost gas-like vapour mixing with all the air. Then the increased surface area of the droplets will increase the combustion speed, and the increased air will provide the oxygen for better combustion and generation of the blue zones.
To re-iterate =how good combustion works - with adequate air and atomisation:
1 - The fuel is a gas or atomised to almost gas-like aerosol when injected.
2 - The initial combustion of hydrocarbons in air is when the hydrogen burns with the O2 (the light blue cone in the Bunsen flame).
3 - Within the breakdown of the molecules to release the hydrogen ions for combustion, some carbon ions combine with oxygen to form CO.
4 - IF ALL the C is burnt to CO in this initial light blue cone, then the CO and residual O ions burn to CO2 in the outer dark blue flame of the Bunsen flame.
5 - But, if not all the C is burnt in the initial phase to CO, then the C will glow yellow to white hot - but NOT burn. You must get more air entrained initially. (essentially you are too rich for stoichiometric combustion). 6 - Possible solutions? Double the initial air pressure, to double the first combustion air. If this works the flames will get better. If TOO much air, the flames will blow out.
7 - Keep increasing the air pressure, using a bigger compressor if required, until the flames eliminate the "yellow-white feathers".

Incidentally, Diesel engines in cars, etc. have become much cleaner with the increased fuel atomising pressure, because the aerosol has improve from just a spray of fuel in the last 120 years or so... These engines are not directly comparable to flame burners like yours, because they run on air compressed to high pressures and temperatures in excess of the stoichiometric balance. = LEAN. Yet were "Smokey" with carbon and high CO in the exhaust simply because the particle (droplet) size was too large. So now the injectors are at higher pressures (not more fuel) they deliver a finer atomisation, which mixes quicker with the air and burns fast enough to be much cleaner and hence more efficient than say 50 years ago.
But I guess you know all this.
Oh, you could try a smaller fuel jet? What size is yours?
Keep on trying, and you will get there.
K2

First, thanks for all the detailed info and ideas.

The siphon type fuel nozzle I'm using produces a fog-like cloud of fuel-air mixture with droplets so fine they literally float away in a light breeze. This photo shows the un-ignited fuel mist:

I don't think fuel atomization is a problem.

The leaf blower supplying forced air into the combustion chamber is capable of blowing so much air that it will blow the fame out on lower and medium fuel flows. So, I don't think limited air flow is the problem.

My guess at this moment is the flames inside the combustion chamber are exiting so fast they don't have time to reach complete combustion temperatures.

 

[Toymaker]

Toy maker: I am but a spring Chicken at 68... and have only really challenged myself a bit with burners in the last couple of years. My 8kW burner doesn't compare with the industrial 27kW equivalent... But I can't get their exotic hole patterns in the base metal pre-mix chamber, nor the knitted exotic metal wire coating that forms the combustion zone.
My 8kW propane burner: View attachment 139320 - It flashes back after 5~10 mins.

the commercial 27kW burner (cost £70 or so...) on propane (around 4kW in the picture): View attachment 139318 - very stable from low gas to full! The development took half a year or so, but finally a venturi close to the designed size gave adequate air for stable combustion without any failure modes. It was all about getting enough air flow.

But I am getting there - if slowly.
You will too, I am sure!
I have some sample calculations that I can try and re-work for diesel fuel at 150kW to get an indication of how much air you need... I feel you need to double or treble the air-flow through the injector nozzle... at a guess?
Look at a 200HP diesel car to see what size of turbo they have to get the air into the engine. That's what you need to burn the same fuel, and 80% should come through the injector with the fuel, and only 20% surround the outside? - But I am guessing, not "Engineering".
K2

Instead of comparing my burner to a car engine, I think my little burner is very close in design to a common torpedo style space heater, like the one in this photo; the main difference being my burner is designed to produce a relatively small volume of extremely hot exhaust while space heaters are designed to produce very large volumes of pleasantly warm air. My burner uses the same siphon type fuel nozzle found in torpedo space heaters, and the same air pressures are used to drive the fuel nozzles. Both units use an electric motor driven fan to produce the forced air for the burner.

Viewing a few YouTube videos like this one, shows yellow flames exiting the exhaust. These space heaters are intended to keep a large room warm enough for people to comfortably work in, and for safety reasons, they cannot produce large volumes of toxic unburned exhaust gases.

This leads to the question: can complete combustion of kerosene or Diesel be attained without producing a blue flame? Blue flames are required for complete combustion in non-forced air burners (like wick stoves & Bunsen burners), but in forced air burners where large volumes of air are forced into the flame, is the higher temperature (indicated by a blue color) still necessary for complete combustion to occur?

Anyone know the answer?

 

[Steamchick]

Hi Toymaker, Yes there are a few answers. But these are my knowledge, and a proper burner engineer may have better answers. It does look like you have good atomisation, but I think you need more air within the cloud. (The mixture ratio is too rich).
My SIMPLE understanding is as below: (I say simple, because I am NOT a combustion engineer, just picked-up a few bits on the way, and I am probably incorrect in some of this?!)
The initial Fuel air mix must be heated to a point where the hydrocarbons begin to breakdown into ions, so the fuel ions (carbon, Hydrogen, and simple paraffins, butanes, etc.) can combine with the O2 => Oxygen ions from the air. So, because of the mix of Oxygen and Nitrogen making-up air, and the natural combinations of carbon and hydrogen in the hydrocarbons we are burning, you need about 15 times more air than fuel to balance most of the fuels we are burning here.
In flames, the hydrogen ignites and burns first, as it is so reactive, elevating the fuel and ionised gas temperature of the "Mass" of the mixture. This can be initiated in a small local zone by a spark (electrical, flint, iron, or whatever!), where the "gas temperature" to make the first ions to start the combustion is a few thousand degrees C. Once initiated, the heat released from the first few burning ions rapidly ionises the rest of the mixture nearby until a sustainable flame occurs. The heat at the flame front: where fresh mixture meets the combustion zone, keeps ionising more fuel which mixes with ionised O2 from the air to permit more combustion. This is my "simple layman's model of the flame.
When the hydrogen has been ripped off some molecules of fuel, the carbon ions mixing with Oxygen ions combust around 500degrees C or higher (?) forming CO. But there can be free carbon that is "quite big" relatively in molecular/ion size within the fuel gas mix, if there is insufficient air (oxygen) in this initial mix of fuel and air. This free carbon must be heated to glowing (over 700 degrees C?) with more air in order to burn to CO.
In a third phase, all the remaining CO and C burns with the remaining air (a darker blue flame, tinged with yellow or orange where there is free carbon). But as the flame is rapidly expanding, and, because of gas laws, that means cooling, when the temperature drops below around 700degrees C the carbon stops burning (leaving free soot), and when it drops below about 350 degrees C the CO stops burning.
A crazy thing I found is that when I get enough air into the mixture initially, the flames get smaller and more compact (actually are hotter as they burn faster). When you reach a stage close to "good" complete combustion, the "yellow feathers" reduce to an orange glow in the flame, and then disappear leaving just the 2 blue Bunsen cones we are familiar with.
So I still think you need MORE air in the jet nozzle.
I.E. use a smaller fuel jet and a higher air pressure, until you get a better mixture here.
You are pumping 14L of fuel per hour through the jet: This is 14 x 0.8 /60 = 187gms of fuel per minute.
Which means you need 15 x 187 = 2.8 kg. of air per min. = 6.172lbs of air per min.
Dry air at 0�C has a density of 12.417423770565761 cubic feet per pound. So you need 76.65CFM at atmospheric pressure. At 100 psi from your compressor, that equates to 9.82cfm.
What pressure are you delivering at the jet? What air flow rate do you have at the jet?
When we understand the Mixture is correct, then we can tackle any "flame dynamics" to resolve any issues. But I think your blower and nozzle outer giving the swirl pattern is probably good.
An idea: Can you fit a jet of maybe 3/4 the diameter (size) of your jet, and increase the air pressure to 1 1/2 times the current pressure? Then let us see what that does?
If my help is "no help", just tell me to stop. I am no expert, just a meddler in this subject.
K2