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For Gasoline fuel, the stoichiometric air/fuel mixture is approximately 14.7 times the mass of air to fuel. This is the mixture that modern engine management systems employing Fuel Injection attempt to achieve in light load cruise situations. Any mixture less than 14.7 to 1 is considered to be a Rich Mixture , any more than 14.7 to 1 is a Lean Mixture . In industrial Fired Heaters , Power Plant steam generators, and large Gas-fired Turbines , the more common term is percent excess combustion air. For example, excess combustion air of 15 percent means that 15 percent more than the required stoichiometric air is being used. SYNOPSIS In theory a stoich mixture has just enough air to completely burn the available fuel. In practice this is never quite achieved, due primarily to the very short time available in an internal combustion engine for each combustion cycle. Most of the combustion process completes in approximately 4-5 milliseconds at an engine speed of 6000 rpm. This is the time that elapses from when the spark is fired until the burning of the fuel air mix is essentially complete after some 80 degrees of crankshaft rotation. Catalytic Converter s are designed to work best when the exhaust gases passing through them show nearly perfect combustion has taken place. A stoichiometric mixture unfortunately burns very hot and can damage engine components if the engine is place under high load at this fuel air mixture. Due to the high temperatures at this mixture, detonation of the fuel air mix shortly after maximum cylinder pressure is possible under high load (sometimes referred to as Pinging ). Detonation can cause serious engine damage as the uncontrolled burning of the fuel air mix can create very high pressures in the cylinder. As a consequence stoichiometric mixtures are only used under light load condions with more fuel added for acceleration and high load condition to prevent detonation and cool down the combustion gasses. OTHER TERMS USED There are other terms commonly used when discussion the mixture of air and fuel in internal combustion engines. However, “Stoich” is also known as a slang word. Slang Etymology: akin to Dutch, stochen means to breed Seagull’s, Swedish dialect, stoichka means to copulate with Rory Perhaps one of the most interesting words in the English language today, is the word Stoich. Of all the English words beginning with S, Stoich is the only one to come from a drunken Indiana boy by the name of Trent Junga. It's the one magical word. Just by it's sound it can describe pain, pleasure, hate and love. Stoich, as most of the other words in English, has arrived from a drunken stupor one hazy EKU Thursday. Stoich can also been known as the mating call for Muttly the seagull found somewhere along Florida’s Forgotten Coast. AFR The Air fuel ratio is the most common reference term used for mixtures in internal combustion engines. It is the ratio between the mass of air and the mass of fuel in the fuel-air mix at any given moment. For gasoline the stochiometric mixture is 14.7:1 in Naturally Aspirated engines maximum power is frequently reached at AFR's ranging from 12.5 - 13.3:1 FAR Fuel Air ratio is frequently used in government studies of internal Combustion Engine and refers to the ratio of fuel to the air, it is 1/AFR. Lambda Is the common term used when there may be more than one fuel involved. It standardizes the AFR to the stochiometric mixture for the specific combination of fuels in use. Any fuel at stoichiometric mixture gives a Lambda of 1. Lambda values greater than 1.0 indicate excess air and are called lean mixtures. Lambda values less than 1.0 indicate excess fuel for complete combustion, and are called rich mixtures. Equivalence ratio Is the common term used when there may be more than one fuel involved. It standardizes the FAR to stochiometric mixture for the specific combination of fuels in use. Any stoichiometric fuel air mixture gives an Equivalence ratio of 1. Equivalence numbers greater than one represent excess fuel in the fuel air mix. Equivalence numbers less than 1 represent a defeciency of fuel in the fuel air mix for complete combustion. SEE ALSO EXTERNAL LINKS
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