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Combustion
Oil Fired Equipment
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OIL
• Combustion of oil fired equipment has the same basics
of gas.
• Remember, Oil is a liquid and this must be converted to
gas first.
• Oil also does not flow freely, it must be piped.
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Oil
• Oil equipment uses an oil burner to pump the fuel from
the tank.
• The pump then pumps the fuel to the nozzle at a
standard 100 psi.
• The nozzle meters the fuel and sprays it into an air
stream that is also caused by the burner.
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Oil
• This mixes the fuel and the air and the fuel is atomized,
it is a fine mist as it comes out of the burner.
• The atomized fuel is then ignited. The first source of
ignition is the igniters. The continued heat for
combustion comes from the fire itself.
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Oil
• The amount of time oil vapor has to combust, this is the
amount of time it resides in the burning zone in front of
the burner has been improved in recent years with
Flame Retention burners.
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Oil
• Flame retention burners violently spin the air fuel
mixture. This results in a better mixing and
reduces the amount of excess air needed to ensure
that each droplet of fuel is surrounded by oil.
• Increasing the pump pressure from a standard of
100 psi to 140 psi also results in finer atomization
of oil droplets
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Oil
• As the pump pressure is increased the nozzle size must
be reduced to compensate for the higher pressures.
• Every oil nozzle is sized based on 100 psi of oil
pressure.
• Example is a 1.50gph nozzle. This nozzle will provide
100 gallons per hour at 100 psi.
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Oil
• If the pump pressure on a 1.25 nozzle is increased to
140 psi the nozzle is now delivering 1.48 gph of oil.
• To maintain the 1.25gph at the high pump pressure the
nozzle size must be dropped to 1.05.
• See chart on page 73 of manual.
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Controlled Combustion
• With oil you can control the:
– Amount of Oil
– The amount of air
– The amount of draft
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Oil
• Oil contains 140,000 BTU of fuel. So burning 1 gallon
of fuel in 1 hour produces 140,000 BTU/Hr.
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Fuel Delivery
• Check and make sure all fittings are tight.
• Make sure vent and fill pipes are not clogged.
• Mae sure all fittings are not leaking. Remember the
pump is sucking oil from the tank, the leak may allow
air in.
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Fuel Delivery
• On every furnace cleaning you must check the pump
pressure. Verify it is at the manufactures recommended
pressure and verify the correct nozzle size.
• The name plate or data plate will give you this
information.
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Fuel Delivery
• In oil - Never use compression fittings. Always
use hard piped flare fittings.
• As a part of oil burning we must verify and
maintain draft over the fire. It is impossible to
control the amount of air being delivered if the
draft over the fire is not correct and stable.
• The barometric damper (or draft control) is there
for this purpose.
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The combustion Process
• As with Natural Gas, nitrogen is introduced into the
combustion process.
• For every percent increase of oxygen in the combustion
process you have 3.76% more nitrogen and flue gas.
• In most situations this results in Nitric Oxide (NO) or
Nitrogen Dioxide (NO2)
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The Combustion Process
• Both NO and NO2 are toxic substances and controlled
in many areas.
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Oil Combustion
• Burning:
– 1 Pound Pure Oil
• Requires
– 14.36 pounds (188 Cubic Feet) of Air
• Plus
– 7.18 Pounds (94 Cubic Feet) of Excess Air
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Oil Combustion
• Results in:
– 1.18 Pounds Water
– 56.1% Nitrogen (11.02 Pounds) (150 ft3)
• Plus
– 10.2% Carbon Dioxide (3.16 Pounds/27.2ft3)
• Plus
– 33.8% Excess Air (7.18 Pounds or 94 ft3)
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Oil Combustion
• Some levels of excess air are needed to ensure
complete combustion it will also reduce the safe
efficient operation of the heating system.
• This is why we do combustion and efficiency testing
yearly.
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Types of Efficiencies
• Combustion Efficiency is a calculated measurement of
how well the heating equipment is converting a set
amount of fuel into useable heat.
• Roughly looks at the known heat of oil, and the
temperature and composition of the flue gas.
• Compares this number with perfect combustion.
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Efficiency Testing
• 100% combustion efficiency is not possible due to the
stack loss and boiler shell loss.
• There are efficiencies from 0% to 95% available.
• Remember that in fuels with a large Hydrogen to
Carbon ratio more excess air must be provided. Oil has
more Carbon.
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Efficiency Testing
• When fuel is burning those fuels with the lowest
amount of Carbon produce the lowest amount of
Carbon Dioxide. In most cases this would be Natural
Gas.
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NOx
• The primary nitrogen pollutants produced by
combustion are nitric oxide and nitrogen oxide.
• Increasing evidence exists that nitric oxide has a direct
negative effect on the respitory system.
• Also NOx reacts with moisture in the air and forms
acid rain and ozone.
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NOx
• Instruments that measure NO usually read them in
PPM.
• NO readings must also be adjusted for excess air.
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Oxides of Nitrogen
• NO is formed in one of three ways:
– Thermal NO - produced when nitrogen and oxygen
combustion air supply combine at high temperatures. This is
normally produced during the combustion of gases and fuel
oils.
– Fuel NO is produced when nitrogen in the fuel combines with
the excess oxygen in the combustion air and is only a problem
with fuel oils containing fuel bound nitrogen.
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Oxides of Nitrogen
– Prompt NO is formed during the early, low temperature states
of combustion and is insignificant.
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Control of NO
• There are several ways NO can be controlled.
– Reducing the amount of O2 that is available to bind with
nitrogen during combustion. This means properly tuning the
burner or furnace.
– Burning low nitrogen fuel oils - bio-fuels.
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Control of NO
– Injecting water or steam into the flame to reduce the
flame temperature thus lowering overall NO production
as much as 80% for gas. (Note: This lowers boiler
efficiency as much as 10% depending on the amount of
steam or water injected.)
– Recirculating flue gas back into the combustion process
as combustion air. This effectively “re-burns” the fuel.
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Control of NO
• All control of NO must be done per local, state and
federal code.
• Also refer to equipment manufacturers specifications
prior to making any changes.