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Posted by Bob Chilcoat on March 19, 2006, 7:51 am
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I've been converting a 150,000 BTU natural gas salamander heater to propane.
I finally got everything together Friday, and turned it on. Basically I
have produced an afterburner. Way too much gas flow -- sounds like an F-16.
BIG flame and it cycles on the overheat safety, not the thermostat.
OK, so I didn't calculate the resized orifices correctly. The jet block
consists of a cylindrical brass piece with ten radial #40 drill holes. I
machined a new one with #50 holes, based on the cross sectional area of the
holes and the relative heat content of natural gas vs. propane (because I
left the NG regulator inside, the pressure supplying this jet block is the
same as it was for NG). I figured that this would be a good first attempt.
Clearly not even close to the right size. I can deal with that, but there
is an interesting conundrum here. In trying to tame the flame, I throttled
it down with the propane tank valve, and got down to a more reasonable flame
size. For safety, I've put a CO detector in the garage during these
experiments, and with the BIG flame, it detects no CO. However, with the
throttled flame, the CO level rises fairly rapidly, and there is obviously
something in the air that strongly irritates the nose and throat.
I would have thought that the opposite would happen. The air flow is fixed
by the electric blower, so with too much gas there should be incomplete
combustion. There is quite a bit of yellow tips on the flames with the full
gas flow, which seems consistent with this hypothesis. However, with less
gas, there should be more complete combustion. There are fewer yellow
flames when I throttle back the gas flow, but I begin to get a lot of CO,
and that irritating byproduct.
Is my logic wrong here? I'm confused. With the gas throttled back, there
is very little yellow, the heater cycles on the thermostat, not the safety
cutout, and all seems fine except that it's trying to kill me. Thoughts
from you experts?
--
Bob (Chief Pilot, White Knuckle Airways)
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Posted by ATP* on March 19, 2006, 9:11 am
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> I've been converting a 150,000 BTU natural gas salamander heater to
> propane. I finally got everything together Friday, and turned it on.
> Basically I have produced an afterburner. Way too much gas flow -- sounds
> like an F-16. BIG flame and it cycles on the overheat safety, not the
> thermostat.
>
> OK, so I didn't calculate the resized orifices correctly. The jet block
> consists of a cylindrical brass piece with ten radial #40 drill holes. I
> machined a new one with #50 holes, based on the cross sectional area of
> the holes and the relative heat content of natural gas vs. propane
> (because I left the NG regulator inside, the pressure supplying this jet
> block is the same as it was for NG). I figured that this would be a good
> first attempt.
>
> Clearly not even close to the right size. I can deal with that, but there
> is an interesting conundrum here. In trying to tame the flame, I
> throttled it down with the propane tank valve, and got down to a more
> reasonable flame size. For safety, I've put a CO detector in the garage
> during these experiments, and with the BIG flame, it detects no CO.
> However, with the throttled flame, the CO level rises fairly rapidly, and
> there is obviously something in the air that strongly irritates the nose
> and throat.
>
> I would have thought that the opposite would happen. The air flow is
> fixed by the electric blower, so with too much gas there should be
> incomplete combustion. There is quite a bit of yellow tips on the flames
> with the full gas flow, which seems consistent with this hypothesis.
> However, with less gas, there should be more complete combustion. There
> are fewer yellow flames when I throttle back the gas flow, but I begin to
> get a lot of CO, and that irritating byproduct.
>
> Is my logic wrong here? I'm confused. With the gas throttled back, there
> is very little yellow, the heater cycles on the thermostat, not the safety
> cutout, and all seems fine except that it's trying to kill me. Thoughts
> from you experts?
>
I wouldn't assume the NG regulator is OK for propane, given the difference
in inlet pressure.
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Posted by Bob Chilcoat on March 20, 2006, 9:40 am
Please log in for more thread options The NG regulator is a final reduction with a 1/2" inlet pressure and a lower
outlet pressure (haven't measured it). Since the pressure from the propane
regulator at the tank is 11", and 1/2 psi is 14", the NG regulator should
just drop the propane pressure to whatever the normal NG pressure is to the
orifice block. So I need to figure out the equivalent orifice size for LP
at the same pressure as the NG. If I took out the NG regulator, I could
just use the proper LP jet (which is supplied at 11"), which I can get from
the manufacturer, or machine one with the same size holes. I'm trying to
save the hassle of putting in a length of tubing where the NG regulator is
(between the orifice supply tube and the solenoid valve). OTOH, it might be
a lot easier to do that in the long run, but perhaps not as interesting.
Drilling ten radial holes in my shop-built orifice block involved using the
indexing head that I've only used once before. Kinda fun (HSM content).
--
Bob (Chief Pilot, White Knuckle Airways)
>
>> I've been converting a 150,000 BTU natural gas salamander heater to
>> propane. I finally got everything together Friday, and turned it on.
>> Basically I have produced an afterburner. Way too much gas flow --
>> sounds like an F-16. BIG flame and it cycles on the overheat safety, not
>> the thermostat.
>>
>> OK, so I didn't calculate the resized orifices correctly. The jet block
>> consists of a cylindrical brass piece with ten radial #40 drill holes. I
>> machined a new one with #50 holes, based on the cross sectional area of
>> the holes and the relative heat content of natural gas vs. propane
>> (because I left the NG regulator inside, the pressure supplying this jet
>> block is the same as it was for NG). I figured that this would be a good
>> first attempt.
>>
>> Clearly not even close to the right size. I can deal with that, but
>> there is an interesting conundrum here. In trying to tame the flame, I
>> throttled it down with the propane tank valve, and got down to a more
>> reasonable flame size. For safety, I've put a CO detector in the garage
>> during these experiments, and with the BIG flame, it detects no CO.
>> However, with the throttled flame, the CO level rises fairly rapidly, and
>> there is obviously something in the air that strongly irritates the nose
>> and throat.
>>
>> I would have thought that the opposite would happen. The air flow is
>> fixed by the electric blower, so with too much gas there should be
>> incomplete combustion. There is quite a bit of yellow tips on the flames
>> with the full gas flow, which seems consistent with this hypothesis.
>> However, with less gas, there should be more complete combustion. There
>> are fewer yellow flames when I throttle back the gas flow, but I begin to
>> get a lot of CO, and that irritating byproduct.
>>
>> Is my logic wrong here? I'm confused. With the gas throttled back,
>> there is very little yellow, the heater cycles on the thermostat, not the
>> safety cutout, and all seems fine except that it's trying to kill me.
>> Thoughts from you experts?
>>
> I wouldn't assume the NG regulator is OK for propane, given the difference
> in inlet pressure.
>
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Posted by ATP* on March 20, 2006, 5:47 pm
Please log in for more thread options
> The NG regulator is a final reduction with a 1/2" inlet pressure and a
> lower outlet pressure (haven't measured it). Since the pressure from the
> propane regulator at the tank is 11", and 1/2 psi is 14", the NG regulator
> should just drop the propane pressure to whatever the normal NG pressure
> is to the orifice block. So I need to figure out the equivalent orifice
> size for LP at the same pressure as the NG. If I took out the NG
> regulator, I could just use the proper LP jet (which is supplied at 11"),
> which I can get from the manufacturer, or machine one with the same size
> holes. I'm trying to save the hassle of putting in a length of tubing
> where the NG regulator is (between the orifice supply tube and the
> solenoid valve). OTOH, it might be a lot easier to do that in the long
> run, but perhaps not as interesting. Drilling ten radial holes in my
> shop-built orifice block involved using the indexing head that I've only
> used once before. Kinda fun (HSM content).
>
> --
> Bob (Chief Pilot, White Knuckle Airways)
>
Maybe there's a reason why the manufacturers have it set up without the NG
regulator. I think there are a lot of potentially complicated combustion
engineering issues here and the stakes are very high.
>>
>>> I've been converting a 150,000 BTU natural gas salamander heater to
>>> propane. I finally got everything together Friday, and turned it on.
>>> Basically I have produced an afterburner. Way too much gas flow --
>>> sounds like an F-16. BIG flame and it cycles on the overheat safety, not
>>> the thermostat.
>>>
>>> OK, so I didn't calculate the resized orifices correctly. The jet block
>>> consists of a cylindrical brass piece with ten radial #40 drill holes.
>>> I machined a new one with #50 holes, based on the cross sectional area
>>> of the holes and the relative heat content of natural gas vs. propane
>>> (because I left the NG regulator inside, the pressure supplying this jet
>>> block is the same as it was for NG). I figured that this would be a
>>> good first attempt.
>>>
>>> Clearly not even close to the right size. I can deal with that, but
>>> there is an interesting conundrum here. In trying to tame the flame, I
>>> throttled it down with the propane tank valve, and got down to a more
>>> reasonable flame size. For safety, I've put a CO detector in the garage
>>> during these experiments, and with the BIG flame, it detects no CO.
>>> However, with the throttled flame, the CO level rises fairly rapidly,
>>> and there is obviously something in the air that strongly irritates the
>>> nose and throat.
>>>
>>> I would have thought that the opposite would happen. The air flow is
>>> fixed by the electric blower, so with too much gas there should be
>>> incomplete combustion. There is quite a bit of yellow tips on the
>>> flames with the full gas flow, which seems consistent with this
>>> hypothesis. However, with less gas, there should be more complete
>>> combustion. There are fewer yellow flames when I throttle back the gas
>>> flow, but I begin to get a lot of CO, and that irritating byproduct.
>>>
>>> Is my logic wrong here? I'm confused. With the gas throttled back,
>>> there is very little yellow, the heater cycles on the thermostat, not
>>> the safety cutout, and all seems fine except that it's trying to kill
>>> me. Thoughts from you experts?
>>>
>> I wouldn't assume the NG regulator is OK for propane, given the
>> difference in inlet pressure.
>>
>
>
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Posted by Fred R on March 19, 2006, 9:35 am
Please log in for more thread options Bob Chilcoat wrote:
> I've been converting a 150,000 BTU natural gas salamander heater to propane.
> I finally got everything together Friday, and turned it on. Basically I
> have produced an afterburner. Way too much gas flow -- sounds like an F-16.
> BIG flame and it cycles on the overheat safety, not the thermostat.
>
> OK, so I didn't calculate the resized orifices correctly. The jet block
> consists of a cylindrical brass piece with ten radial #40 drill holes. I
> machined a new one with #50 holes, based on the cross sectional area of the
> holes and the relative heat content of natural gas vs. propane (because I
> left the NG regulator inside, the pressure supplying this jet block is the
> same as it was for NG). I figured that this would be a good first attempt.
>
> Clearly not even close to the right size. I can deal with that, but there
> is an interesting conundrum here. In trying to tame the flame, I throttled
> it down with the propane tank valve, and got down to a more reasonable flame
> size. For safety, I've put a CO detector in the garage during these
> experiments, and with the BIG flame, it detects no CO. However, with the
> throttled flame, the CO level rises fairly rapidly, and there is obviously
> something in the air that strongly irritates the nose and throat.
>
> I would have thought that the opposite would happen. The air flow is fixed
> by the electric blower, so with too much gas there should be incomplete
> combustion. There is quite a bit of yellow tips on the flames with the full
> gas flow, which seems consistent with this hypothesis. However, with less
> gas, there should be more complete combustion. There are fewer yellow
> flames when I throttle back the gas flow, but I begin to get a lot of CO,
> and that irritating byproduct.
>
> Is my logic wrong here? I'm confused. With the gas throttled back, there
> is very little yellow, the heater cycles on the thermostat, not the safety
> cutout, and all seems fine except that it's trying to kill me. Thoughts
> from you experts?
>
Sounds like fun! Good first approximation approach on the orifice size,
except that for small nozzles the flow is not linear with area. It
involves voodoo and math that made my head hurt.
Regarding the incomplete combustion, my WAG is that with low pressure
the gas mixture is too lean to keep all of itself at combustion
temperature. You might try throttling the air intake; although a waste
gate would be better it is a lot of fooling around for a trial.
--
Fred R
"It doesn't really take all kinds; there just *are* all kinds".
Drop TROU to email.
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> propane. I finally got everything together Friday, and turned it on.
> Basically I have produced an afterburner. Way too much gas flow -- sounds
> like an F-16. BIG flame and it cycles on the overheat safety, not the
> thermostat.
>
> OK, so I didn't calculate the resized orifices correctly. The jet block
> consists of a cylindrical brass piece with ten radial #40 drill holes. I
> machined a new one with #50 holes, based on the cross sectional area of
> the holes and the relative heat content of natural gas vs. propane
> (because I left the NG regulator inside, the pressure supplying this jet
> block is the same as it was for NG). I figured that this would be a good
> first attempt.
>
> Clearly not even close to the right size. I can deal with that, but there
> is an interesting conundrum here. In trying to tame the flame, I
> throttled it down with the propane tank valve, and got down to a more
> reasonable flame size. For safety, I've put a CO detector in the garage
> during these experiments, and with the BIG flame, it detects no CO.
> However, with the throttled flame, the CO level rises fairly rapidly, and
> there is obviously something in the air that strongly irritates the nose
> and throat.
>
> I would have thought that the opposite would happen. The air flow is
> fixed by the electric blower, so with too much gas there should be
> incomplete combustion. There is quite a bit of yellow tips on the flames
> with the full gas flow, which seems consistent with this hypothesis.
> However, with less gas, there should be more complete combustion. There
> are fewer yellow flames when I throttle back the gas flow, but I begin to
> get a lot of CO, and that irritating byproduct.
>
> Is my logic wrong here? I'm confused. With the gas throttled back, there
> is very little yellow, the heater cycles on the thermostat, not the safety
> cutout, and all seems fine except that it's trying to kill me. Thoughts
> from you experts?
>