Chemists recognize several fuels capable of acting as oxidants for combustion. Therefore, it is important that the technician completely understands how each of the subsystems affects the chemical reaction called combustion. This could be introduced into the appliance after the point of combustion through a draft diverter or as excess air which goes completely through the combustion process. Depending on the type of furnace, a certain amount of heat must go out of the flue to prevent the gasses from condensing. During the combustion process, as the fuel and oxidizer are turned into exhaust products, heat is generated. If excess air is not provided we will not have the complete conversion of carbon to CO2, and will end up with the formation of partially oxidized compounds, such as carbon monoxide and aldehydes. Each type of fuel has specific measurable heat content. heat to the room air determine how well the heat produced by the combustion process is utilized. For maximum combustion efficiency low excess air is desirable. Gross combustion efficiency calculations assume that the energy contained in the water vapor is not recovered. While ideal operating range for burners is not as efficient as stoichiometric combustion, it does provide us with an additional factor of safety. Please tell us where you read or heard it (including the quote, if possible). For complete combustion to occur, we have to have excess air, or air supplied in excess of what is needed typically because of poor mixing of the fuel and air during the combustion process. These include impingement for example from an improperly placed pilot, excess air from a cracked heat exchanger, insufficient combustion air due to tight construction or improper ventilation, an improperly installed venting system, or incorrect orifices. Heat removed from the flue gasses on a condensing furnace is latent or hidden heat. With high efficiency furnaces, condensing is desirable because of the additional heat extracted from the flue gasses. For maximum combustion efficiency low excess air is desirable. Net combustion efficiency calculations assume that the energy contained in the water vapor (which is formed as a product of combustion) is recovered and is not exhausted from the flue or stack. For example, if methane reacts with oxygen and produces only carbon dioxide and water, the process is complete combustion. These substances are called exhaust gasses. Typically, energy must be supplied to initiate the reaction. Usually, larger exhaust sources (higher BTU systems) are targets of NOx and SO2 regulations. This leads them to suggest that fuel pressures be raised to provide the net heat output that the manufacturer has published. In the most general sense, combustion involves a reaction between any combustible material and an oxidizer to form an oxidized product. If the natural gas is burned with air, which contains 21% oxygen, 78% nitrogen and 1% trace gasses, the exhaust can also include carbon monoxide (CO), oxides of nitrogen (NOX, nitrogen + oxygen) and if sulfur is present in the fuel, sulfur dioxide, SO2 (Sulfur + oxygen). By not taking this discrepancy into account, some in the industry have suggested that fuels are being delivered with low BTU levels. When the activation energy for the reaction is available, the cellulose (a carbohydrate) in wood reacts with oxygen in the air to produce heat, light, smoke, ash, carbon dioxide, water, and other gases. In reality, in the HVAC industry we are striving not for stoichiometric combustion, but complete combustion in which all hydrogen and carbon in the fuel are oxidized to H2O and CO2. he thermal efficiency of a condensing appliance and combustion efficiency will be different. The percentage of excess air required is based upon several things including, Equipment application (commercial, residential, industrial), Expected variations in fuel properties (wobble numbers), Combustion air supply rates and air density, Degree of operator supervision required or available (summer winter adjustments). (NOTE: This calculation does not affect the AFUE numbers, which are derived by a different means.) It is the service technician’s responsibility to determine if combustion problems are caused by improper adjustment, incorrect installation, component failure, or equipment defect. What made you want to look up combustion engine? The only way to calculate the actual thermal efficiency of an appliance is to measure the exact airflow across the heat exchanger and the change in air temperature across the heat exchanger and input the measured values into the sensible heat formula to calculate the heat energy input into the conditioned air. If excess air is not provided we will not have the complete conversion of carbon to CO2, and will end up with the formation of partially oxidized compounds, such as carbon monoxide and aldehydes. Gasoline and air are both present in your automobile fuel tank; but combustion does not occur because there is no source of heat. Other factors can affect the combustion process. Since heat is both required to start combustion, and is itself a product of combustion, we can see why combustion takes place very rapidly. Due to the readings achieved on their analyzer. Combustion efficiency is a measurement of how well the fuel being burned is being utilized in the combustion process. Combustion is considered an exergonic or exothermic chemical reaction. Delivered to your inbox! Incomplete oxidation of a fuel may also occur. Combustion efficiency is a measurement of how well the fuel being burned is being utilized in the combustion process. Singular Nonbinary ‘They’: Is it ‘they are’ or ‘they is’? As a service technician, unless a component has failed, there are only three things can be adjusted on a gas/oil appliance that will affect the combustion process. Stack loss is a measure of the heat carried away by dry flue gases and the moisture loss. This is true of all analyzers currently manufactured. Soot, which is incompletely burned fuel, is a form of solid exhaust that occurs in some combustion processes. Gasoline and air are both present in your automobile fuel tank; but combustion does not occur because there is no source of heat. [1]Manufacturers use differing forms of combustion equations. Some manufacturers have chosen to use a combustion calculation that does not extrapolate the thermal efficiency values of flue gasses below the dew point, as those values are not representative of the heat that is removed from the flue gasses during the condensing process. Although terms of thermal and combustion efficiency are often used interchangeably on non-condensing units, they cannot be used in the same manor on condensing appliances. Can you spell these 10 commonly misspelled words? Combustion efficiency is a valuable part of the system evaluation, but it is only one part of the evaluation process and cannot be used as the sole reason or justification for keeping or replacing existing equipment. Net combustion efficiency calculations assume that the energy contained in the water vapor (which is formed as a product of combustion) is recovered and is not exhausted from the flue or stack. So, although energy is absorbed in the reaction, it is released when the stronger bonds are formed to make carbon dioxide (CO2) and water (H2O).