- #1

InquisitiveOne

- 36

- 1

**Hi guys, 42 year old engine hobbyist here, not a student. I've had great luck figuring out my questions in this portion of the forum in the past and look forward to your input. Keep in mind that I'm not formally educated, so if it's possible to dumb something down a bit I'd appreciate it.1. Homework Statement**

I want to calculate and compare the pressures that different air/fuel ratios may produce in an internal combustion engine if the piston were to stop at Top Dead Center and all the reactants combusted.

What pressure would a stoichiometic Air/Fuel ratio produce? What about richer or leaner ratios?

I don't need actual running engines pressures. A figure based on a static volume will be fine for my current purposes.

I want to calculate and compare the pressures that different air/fuel ratios may produce in an internal combustion engine if the piston were to stop at Top Dead Center and all the reactants combusted.

What pressure would a stoichiometic Air/Fuel ratio produce? What about richer or leaner ratios?

I don't need actual running engines pressures. A figure based on a static volume will be fine for my current purposes.

2. Homework Equations

In my research so far, I haven't found a direct way to calculate what I want. So, I've come up with a couple plans to use several calculative methods combined to produce the product I'm hoping for. Please review them and let me know if one is a better method than the other, or if there is another way that might be preferred for accuracy, ease of calculating, or whatever reason.

I also have some questions about the calculations/processes listed below which I'll list in #3 of this post.

Step 1) Calculate Adiabatic Flame Temperature

Step 2) Using Pv = nRT, calculate the new volume per given mass

Step 3) Use calculation for Adiabatic Compression, new volume and temperature from last step, compressed to known final volume to get final pressure and temperature.

Step 1) Identify a fuels BTU/lb or kJ/kg

Step 2) Calculate amount of thermal energy from the mass of fuel at stoichiometric per given mass of air.

Step 3) Average the Specific Heat Capacities of the gasses left after combustion

Step 4) Use the Isochoric Process to solve for a final temperature and pressure

Is there a better way, or is one of these two methods incomplete or otherwise not valid?

2. Homework Equations

In my research so far, I haven't found a direct way to calculate what I want. So, I've come up with a couple plans to use several calculative methods combined to produce the product I'm hoping for. Please review them and let me know if one is a better method than the other, or if there is another way that might be preferred for accuracy, ease of calculating, or whatever reason.

I also have some questions about the calculations/processes listed below which I'll list in #3 of this post.

__PLAN 1__Step 1) Calculate Adiabatic Flame Temperature

Step 2) Using Pv = nRT, calculate the new volume per given mass

Step 3) Use calculation for Adiabatic Compression, new volume and temperature from last step, compressed to known final volume to get final pressure and temperature.

__PLAN 2__Step 1) Identify a fuels BTU/lb or kJ/kg

Step 2) Calculate amount of thermal energy from the mass of fuel at stoichiometric per given mass of air.

Step 3) Average the Specific Heat Capacities of the gasses left after combustion

Step 4) Use the Isochoric Process to solve for a final temperature and pressure

Is there a better way, or is one of these two methods incomplete or otherwise not valid?

**3.**~~The attempt at a solution~~ Questions about the proposed plans

In PLAN 1, Step 1,

In PLAN 1, Step 1,

**Calculate Adiabatic Flame Temperature...**

All the examples I've been able to source for calculating flame temperature assume either stoichiometric ratios OR excess air, a lean condition. When using the calculation for a rich condition which would result in excess un-reacted fuel, how would I go about adding it into the equation?

The fuels I'd like to calculate for are gasoline (which seems to have wildly varying chemical compositions. Seems most just use Octane for calculating, C8H18), methanol, and ethanol. I'd also like to be able to account for humidity and/or water added to the combustion process.If you guys can point me in the right direction I'd appreciate it greatly.

Thank you,

-Seth-All the examples I've been able to source for calculating flame temperature assume either stoichiometric ratios OR excess air, a lean condition. When using the calculation for a rich condition which would result in excess un-reacted fuel, how would I go about adding it into the equation?

The fuels I'd like to calculate for are gasoline (which seems to have wildly varying chemical compositions. Seems most just use Octane for calculating, C8H18), methanol, and ethanol. I'd also like to be able to account for humidity and/or water added to the combustion process.If you guys can point me in the right direction I'd appreciate it greatly.

Thank you,

-Seth-

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