Combustion And Performance – Flashcards
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| Properties of Gas |
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| Gases are Hydrocarbons React readily with Oxygen Known as Combustion 3 diff groups (family of gases) |
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| 1st Family of Gas |
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| Manufactured Gas Any gas produced through industrial process coke gas, coal gas and towns gas phase out og general use |
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| 2nd Family of Gas |
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| Natural Gas. formed from decomposition of organic material. Main component Methane in UK 82-97% of total volume of gas |
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| 3rd Family of Gas |
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| Liquid Petroleum Gas (LPG) LPG is a by product from extraction of natural gas. LPG can be either Propane or Butane |
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| Odour and Colour of Gases |
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| Nat gas,propane and Butane all colourless and odourless Odorants are called Thiols Nat gas-methyl LPG-t butyl mercaptan,ethyl mercaptan |
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| Toxicity of Gases |
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| Nat gas and LPG do not contain Co still a risk of asphyxiation due to gas displacing Oxygen. |
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| Specific Gravity (Relative Density) |
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| Air S.G = 1 Nat Gas = 0.6-0.7 (lighter than air) Propane =1.5 Butane= 2 (Heavier than air) |
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| Calorific Value |
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| Is the amount of energy released when a specific quantity of gas is burnt under standard ref conditions |
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| Wobbe Number |
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| Is an indication of the heat which can be produced from a burner using a particular gas |
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| Flammability Limits |
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| is the range of concentration of gas mixed with air. |
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| Ignition Temperature of natural gas |
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| ignition temps Methane -632*C-704*C Propane- 493*C-547*C Butane-413*C-527*C |
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| Combustion |
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| Combustion is a chemical reaction between the fuel gas and oxygen which produces 2 main gases Carbon Dioxide CO2 Water Vapour H2O |
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| CH4+2O2=CO2+2H2o |
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| The Chemical equation for complete combustion of Methane |
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| CH4 |
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| Chemical Symbol for Methane. |
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| Stoichiometric Combustion |
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| A theoretical concept which can only be achieved under strict laboratory conditions |
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| Equation for IN-COMPLETE combustion of natural gas |
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| CH4 + 1.5O2= CO + 2H2O |
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| The Flame speed of natural gas |
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| 0.36m/s |
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| Explosive limits of natural gas |
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| 5% to 15% Gas in Air |
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| Chemical produced by burning natural gas |
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| 1.Alcohol 2.Aldehyde |
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| What % of O2 is required to sustain life |
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| Between 19%-21% |
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| . What is the approximate volume of air required to completely burn 5 m3 of natural gas? |
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| 50m3 |
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| Causes of Incomplete Combustion Inadequate Ventilation |
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| Supply of combustion air to the appliance burner has become restricted or contaminated |
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| Causes of Incomplete Combustion Vitiation of Atmosphere |
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| Where the air used to supply the appliance becomes DEFICIENT IN OXYGEN |
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| Causes of Incomplete Combustion Contamination Of Burner |
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| Debris deposits build up creating a restriction to the air floe to the burner |
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| Causes of Incomplete Combustion Poor Flueing |
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| POCs not being removed will re enter the area and re-circulate into the appliance combustion chamber. As the air has already been burnt its O2 has been reduced and no longer support complete combustion |
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| Causes of Incomplete Combustion Blocked Flueways |
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| Flueways are the path that POCs pass through,when this is restricted the POCs re enter the chamber affecting combustion |
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| Causes of Incomplete Combustion Flame Chilling |
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| Hitting a surface cooler than temp of ignition. No longer supports complete combustion This can happen when flame touches a heat exchanger. |
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| Causes of Incomplete Combustion Flame Impingement |
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| When one flame touches another or cold surface Incomplete combustion is created by one flame robbing the other of secondary air or by chilling |
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| Causes of Incomplete Combustion Gas Rich Mixture |
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| Supplying too much gas (over gassing) Too much gas will create a "reducing flame" |
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| Causes of Incomplete Combustion Lean Gas Mixture |
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| Created either by supplying not enough gas(under gassing). or correct amount of gas but too much air too much air creates an "Oxidising" flame |
