Why does incomplete combustion occur

Typically warm-air furnace manufacturers require checking of the gas flow and gas pressure upon initial start-up and allow no over-firing. To find and correct problems caused by excess gas flow it is important to check gas flow, gas pressure, orifice sizing, and carbon monoxide concentrations in combustion products.

Large holes in a heat exchanger are dangerous. Air forced through holes by the circulating fan increases the production of CO by disrupting the flame. The air flow increases the amount of combustion products spilling into the living quarters by disrupting the air flow through the appliance vent flue.

In most natural draft and induced draft furnaces, high pressure on the furnace blower side of the heat exchanger prevents combustion products from flowing directly into the circulation air. Usually combustion products enter the house because of vent failure or spillage.

In power vent and pulse combustion furnaces high pressures on the combustion side can force combustion products directly through holes into the circulating air and the house. Combustion products contain large amounts of carbon monoxide and water vapor, which can smother flames or lead to increased rust and corrosion of the heat exchanger. Flame roll-out occurs in severe cases.

Holes in heat exchangers can be found by direct observation, using either mirrors or by disassembling the unit. Some direct vent sealed combustion units can be tested by sealing the inlet and outlet and pressure testing. Smoke bombs, odor tracing and salt sprays have been used, but have not been totally acceptable. The American Gas Association has developed a heat exchanger test method using tracer gases which they have determined to be more reliable and accurate.

Observation of flame disruption when the furnace blower turns on will reveal large holes. Measurement of carbon monoxide in flue products using CO analyzers reveals incomplete combustion caused by air flow through holes.

Combustion gases should be sampled before draft hood dilution. In natural draft appliances the flue passages chambers at the top of the appliance can usually be reached, with a probe, through the draft diverter or hood.

For equipment with several burners and separate flue passages chambers , each burner must be checked separately by inserting the probe into the top of each chamber. It is important to insert the probe a sufficient distance into the flue chambers to ensure undiluted combustion products are being sampled.

Sealed combustion units can often be sampled most easily at the outdoor exhaust outlet. Locations that will not give an accurate reading of combustion gases include: the perimeter of the draft hood this will represent room air , directly above the flame sampling here may give an erroneous high reading , and at furnace air outlets which contain a mixed sample. There are many potential causes of carbon monoxide production and spillage of combustion products into living areas. Many causes are accidental and unpredictable; i.

To protect against accidental carbon monoxide poisoning, the U. Heating appliances should be inspected and maintained yearly by a qualified heating contractor. For example, with alkanes, the ones with an even number of carbon atoms are marginally harder than those with an odd number!

Your first draft would be:. Counting the oxygen atoms leads to a slight problem - with 13 on the right-hand side. The hydrocarbons become harder to ignite as the molecules get bigger. This is because the bigger molecules do not vaporize so easily - the reaction is much better if the oxygen and the hydrocarbon are well mixed as gases.

If the liquid is not very volatile, only those molecules on the surface can react with the oxygen. Bigger molecules have greater Van der Waals attractions which makes it more difficult for them to break away from their neighbors and turn to a gas. Provided the combustion is complete, all the hydrocarbons will burn with a blue flame.

However, combustion tends to be less complete as the number of carbon atoms in the molecules rises. Engineers try to maximize the energy output with respect to oxygen gas intake, and size of the cylinder or furnace.

Diesel engines as well as petrol engines still produce quantities of carbon monoxide, and carbon as particulate soot. Why does incomplete combustion occur? Chemistry Stoichiometry Limiting Reagent.

Dec 3, Explanation: Insufficient oxygen, an improperly stacked fire, a poorly designed furnace; all of which can limit egress of oxygen to the centre of the pile of fuel.

Does this address your question? Related questions How do you determine how much of the excess reactant is left over?