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- Stoichiometric Air-Fuel Ratio / Mixtures


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In the IL2 series the Engine Management is quite simple but this doesn't mean that the mixture should be, Since now the engine respond to the atmosphere and which is great ! The mixtures should be well detailed tuned ( sounds as well )  to give the Virtual pilot the tools to be good or bad with his skill of tuning his own aircraft, Heat/Cold/Dry/Humid/High or Low etc..

Thank you to the IL2 team to do their best for this great sim and theater.

 

==

 

http://flighttraining.aopa.org/students/solo/special/mixture.html

 

Interesting read for Virtual pilots that want to know more about Air-Fuel Ratio Mixture

 

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  • Calculating the Ratio

    The air to fuel ratio is the property of fuel and chemical composition of the fuel that defines the value for this ratio. Most of the fuels we use in internal combustion engines are hydrocarbons, and their burning will obviously result in the release of hydrogen and carbon as residuals, along with heat and pressure. Below is an example of the oxidation reaction of methane (natural gas) as a fuel.

    CH4 + 2(O2) → CO2 + 2(H20)

    If we look up the atomic weights of the atoms that make up octane and oxygen, we get the following numbers:

    Carbon © = 12.01

    Oxygen (O) = 16

    Hydrogen (H) = 1.008

    • So 1 molecule of methane has a molecular weight of: 1 * 12.01 + 4 * 1.008 = 16.042
    • One oxygen molecule weighs: 2 * 16 = 32
    • The oxygen-fuel mass ratio is then: 2 * 32 / 1 * 16.042 = 64 / 16.042
    • So we need 3.99 kg of oxygen for every 1 kg of fuel
    • Since 23.2 mass-percent of air is actually oxygen, we need : 3.99 * 100/23.2 = 17.2 kg air for every 1 kg of methane.

    So the stoichiometric air-fuel ratio of methane is 17.2.

     
     
  • When the composition of a fuel is known, this method can be used to derive the stoichiometric air-fuel ratio. For the most common fuels, this, however, is not necessary because the ratios are known:

    • Natural gas: 17.2
    • Gasoline: 14.7
    • Propane: 15.5
    • Ethanol: 9
    • Methanol: 6.4
    • Hydrogen: 34
    • Diesel: 14.6

    You may find it interesting that methanol and ethanol both have a very low air-fuel ratio, while the carbon chain length is comparable to methane and ethane. The reason for this is that alcohols like methanol and ethanol already carry oxygen themselves, which reduces the need for oxygen from the air.

     
     
  • The Bottom Line

    In order to be able to judge if an air-fuel mixture has the correct ratio of air to fuel, the stoichiometric air fuel ratio has to be known. If the composition of a fuel is known, this ratio can be calculated rather easily.

     

    Scources:

    http://www.lub.lu.se/luft/diss/tec432.pdf

    ftp://ftp.energia.bme.hu/pub/bsc/Interan%20Combsution%20Engines-Temp.pdf

     

    etc.. plenty of this online..

     

     

     

     

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+1

 

The above is only the beginning, because using leaner or richer mixtures has unique advantages and disadvantages, too. Leaner mixtures, for instance, are more fuel efficient, but burn hotter. Richer mixtures waste fuel, but cool the engine. Also engine power depends on the mixture, with the most power developed at a slightly rich mixture. Mixture in flight simulation games has never been given the importance it has in real aircraft, it would be very nice to see this changed. In particular as the Soviet aircraft mostly need to manually adjust, at least at high altitude, whereas the German aircraft have this automated, which was one of their historical advantages.

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  • 3 weeks later...

 

In the IL2 series the Engine Management is quite simple but this doesn't mean that the mixture should be, Since now the engine respond to the atmosphere and which is great ! The mixtures should be well detailed tuned ( sounds as well )  to give the Virtual pilot the tools to be good or bad with his skill of tuning his own aircraft, Heat/Cold/Dry/Humid/High or Low etc..

Thank you to the IL2 team to do their best for this great sim and theater.

 

==

 

http://flighttraining.aopa.org/students/solo/special/mixture.html

 

Interesting read for Virtual pilots that want to know more about Air-Fuel Ratio Mixture

 

  •  
  • Calculating the Ratio

    The air to fuel ratio is the property of fuel and chemical composition of the fuel that defines the value for this ratio. Most of the fuels we use in internal combustion engines are hydrocarbons, and their burning will obviously result in the release of hydrogen and carbon as residuals, along with heat and pressure. Below is an example of the oxidation reaction of methane (natural gas) as a fuel.

    CH4 + 2(O2) → CO2 + 2(H20)

    If we look up the atomic weights of the atoms that make up octane and oxygen, we get the following numbers:

    Carbon © = 12.01

    Oxygen (O) = 16

    Hydrogen (H) = 1.008

    • So 1 molecule of methane has a molecular weight of: 1 * 12.01 + 4 * 1.008 = 16.042
    • One oxygen molecule weighs: 2 * 16 = 32
    • The oxygen-fuel mass ratio is then: 2 * 32 / 1 * 16.042 = 64 / 16.042
    • So we need 3.99 kg of oxygen for every 1 kg of fuel
    • Since 23.2 mass-percent of air is actually oxygen, we need : 3.99 * 100/23.2 = 17.2 kg air for every 1 kg of methane.

    So the stoichiometric air-fuel ratio of methane is 17.2.

     
     
  • When the composition of a fuel is known, this method can be used to derive the stoichiometric air-fuel ratio. For the most common fuels, this, however, is not necessary because the ratios are known:

    • Natural gas: 17.2
    • Gasoline: 14.7
    • Propane: 15.5
    • Ethanol: 9
    • Methanol: 6.4
    • Hydrogen: 34
    • Diesel: 14.6

    You may find it interesting that methanol and ethanol both have a very low air-fuel ratio, while the carbon chain length is comparable to methane and ethane. The reason for this is that alcohols like methanol and ethanol already carry oxygen themselves, which reduces the need for oxygen from the air.

     
     
  • The Bottom Line

    In order to be able to judge if an air-fuel mixture has the correct ratio of air to fuel, the stoichiometric air fuel ratio has to be known. If the composition of a fuel is known, this ratio can be calculated rather easily.

     

    Scources:

    http://www.lub.lu.se/luft/diss/tec432.pdf

    ftp://ftp.energia.bme.hu/pub/bsc/Interan%20Combsution%20Engines-Temp.pdf

     

    etc.. plenty of this online..

     

     

     

     

  •  

 

 

A few corrections to your quoted source(s) cut/pasting there. You have brought out the general physical chemist in me, prepare yourself.

 

First, chemical measurements are meaningless without units, excepting very specific instances. Second, one must use the right measurements and values, or again the calculations are meaningless. The "molecules" in your calculations should be "moles", one of which is actually 6.022*10^23 molecules. Quite a difference.

 

But most importantly from a conceptual point of view, and for our purposes, the general formula for combustion, which you have shown above, is true for ANY carbon source. The "stoichiometric ratio" which you refer to is actually implicit in the calculation, and does not vary. Your adjustments for differing fuel sources, including the alcohols, are not adjustments to the stoichiometric ratio, but rather a measurement of the density of the fuel, and the number of carbon-carbon bonds availble to break per molecule. In fact, these "ratios", which are actually nothing more than rules of thumb, can vary with ambient temperature (which increases the density of oxygen per c.c. of air, as well as varying the density of the fuel mixture) as well as the refining techniques used in making the fuel (which are, after all, nothing more than simply sorting a liquid column based on density - and thus the length of the carbon chains).

 

As a side note, an fuel source's octane rating is simply a measurement of the quality of the refinement technique. Octane is simply a eight-carbon straight-chain alkane, and thus an octane rating is how much of the fuel is at the octane level of complexity.

 

Thank you for allowing me to use my undergraduate chemistry education once more.

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Old school.  Pull to lean to rough, push forward to smooth.....

 

Works extremely well.  Try it sometime with a engine analyzer with EGT's on each cylinder and a lean function.  Compare the results with the old school.  It will be within a few degrees EGT of each other every time.

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Something to consider, most WWII fighter designs incorporated an "auto-rich" and "auto-lean" control.  Auto rich was for maximum power and Auto lean for maximum range.  For example, cruise settings would be auto lean while climbing, take off, and combat on auto rich.

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Good suggestion GOZR, btw.  The skill in operating the engine IAW the operating instructions to get best performance should be a factor in squeezing out the best performance from the design.  One of the best things about CLOD was that mindset of having to operate the engine above the normal as well as extremely unrealistic "shove it to the firewall and go" mentality of previous games.  It would be a shame for the development team to take a step back.  Complex engine management is required is one of the defining characteristics of a World War II fighter.

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