To properly troubleshoot any suspected combustion issue with either a forced air furnace or a fuel-fired boiler, we need to have an idea of the chemical process that occurs when the fuels are consumed in the combustion process. Oxidation is a process in which a chemical substance changes because of the addition of oxygen. For our discussion purposes, it is the chemical reaction of combining oxygen and fuel (methane or propane) resulting in Carbon Dioxide (CO2) and Water (H2O) and the release of heat energy.
The air we breathe is comprised of approximately 21% oxygen, 78% nitrogen, and other trace gases. To have a controlled and predictable result of combustion, equipment must be designed to achieve complete combustion for efficiency and safety, meaning the fuel needs to completely oxidize.
When the ratio of fuel to air is rich, there is too much fuel in the mixture and not enough oxygen for complete combustion. Only partial oxidization will occur, and the unburned carbon will result in compounds that are harmful to the equipment and potentially hazardous to the occupants.
The results of having a ratio of too much air to fuel will reduce heat transfer to exchangers and reduce efficiency. In this instance Nitrogen Oxides (NOx) gases can form in the products of combustion. These are considered “Greenhouse gases” and are harmful to the environment. Combustion analyzation is the only way to ensure the equipment is achieving complete combustion and is safely operating.
Any combustion issue can be referred to as a D.A.M. problem — dirt, alignment, or mechanical problems can cause combustion-related issues.
Dirt in equipment can cause:
1.) Burners can plug or rust, disrupting the flame shape, causing possible delayed ignition and imbalance the composition of the fuel-air mixture.
2.) Will collect on the surfaces inside of the exchanger and insulate it from heat transfer.
3.) Potentially collect and obstruct or derogate the ventilation system.
4.) Additionally, any chemical compound that could be in the fuel-air mixture can/will lead the combustion issues.
Alignment refers to the position of the burners in the equipment and can cause:
1.) Flame impingement, where the flame touches the exchanger, produces an excessive amount of (CO) carbon monoxide in the flue gases.
2.) May cause damage to the exchanger due to excessive heat transfer.
3.) Could also result in flame rollout and damage to the equipment controls and safety devices.
Mechanical problems are mostly ventilation-related and can cause:
1.) Venting can become compromised, causing flue gases to recirculate into combustion air and incorrect mixture ratios.
2.) Poor draft or insufficient combustion air being drawn into the equipment (Either from natural draft hoods, induced draft, or power venting motors).
3.) Compromises in the integrity of the exchanger or ventilation system will result in hazardous conditions.
Proper inspection and testing of flue gases, manifold pressures, temperature rises, safety devices, and overall operation should be performed annually. This will help prevent any D.A.M. problems from affecting operations. If equipment is showing signs of combustion-related issues, be sure to address them immediately. Contact the B-Y Customer Assurance team with any questions on troubleshooting combustion issues.