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shushuwa (Mechanical) (OP)
15 Jun 07 16:52
What is the temperature of combustion for a normally aspirated gas engine under part-throttle and W.O.T conditions?


 
NickE (Materials)
15 Jun 07 17:08
EGT at the exhaust port on my 2.0L - FI - 4cyl @ 28psi MAP is between 1200-1600F.

There is going to be a big difference between combustion adn actual gas temp.
shushuwa (Mechanical) (OP)
15 Jun 07 18:45
Thank-you NickE

I was hoping that combustion temperatures would exceed 2500 C

shushuwa (Mechanical) (OP)
15 Jun 07 18:56
How about pre-EGR era engines with compression over 10:1 ??

I am investigating water injection, trying to "crack" water into it's elements in the combustion chamber...
reidh (Automotive)
15 Jun 07 20:12
The adiabatic combustion temperature for natural gas is approximately 2000 C.  I believe that gasoline engines have roughly the same combustion chamber temps, although this will vary depending on engine design.

-Reidh

Helpful Member!  Feric (Mechanical)
16 Jun 07 0:10
Hi there:

Here are a few plots for ideal and complete combustion of carbon, hydrogen, sulfur, coal, oil and gas at stoichiometric conditions:











Thanks,

Gordan Feric, PE
Engineering Software
http://members.aol.com/engware

crysta1c1ear (Automotive)
16 Jun 07 17:30


I was hoping that combustion temperatures would exceed 2500 C

You can see from the adiabatic flame temperature of oil that temperatures will fall short of 2500 kelvin rather than centigrade.

Exhaust temperatures are not an indication of combustion temperatures, as heat has been extracted to push the piston down.
kenvlach (Materials)
16 Jun 07 18:15
shushuwa,
What is your point? The most thermal energy you could recover by dissociating water to hydrogen and oxygen would be when it recombines as water. And, even if your combustion temperature were astronomically high enough to make water dissociate, you certainly would not want recombination to blow apart the exhaust system.

Consider the temperatures achievable with gas-oxygen torches:
2200°C = 3992°F, for Propane/Oxygen
2927°C = 5300°F, for MAPP Gas/Oxygen
2700°C = 4892°F, for Acetylene/Oxygen
3200°C = 5792°F, for Hydrogen/Oxygen
http://www.derose.net/steve/resources/engtables/flametemp.html

Of course, hydrogen/oxygen couldn't reach 3200°C if the reaction began to go backwards at 2500°C!!! It might also be a problem for NASA's liquid fueled rockets, too.

But as a practical matter, water injection was used on some supercharged fighter aircraft piston engines during WW II.  It allowed more power w/o burning up the engines by creating some steam power.
globi5 (Mechanical)
16 Jun 07 18:38
If understand the flame temperature diagram correctly, the temperature difference with oil is roughly 2200 C (2200 K) (starting at 298 K).

So, if one ends up with a temperature of 600 C at TDC just before ignition, the temperature should reach 2800 C after ignition.
Feric (Mechanical)
16 Jun 07 22:29
To All:

Here is another combustion plot that indicates how the flame temperature changes with an increase of the oxidant preheat temperature.



I should have indicated that the plots are valid when the oxidant is standard air -- on mole/volume basis standard air composition is 79% N2 and 21 % O2.

Thanks,

Gordan Feric, PE
Engineering Software
http://members.aol.com/engware

crysta1c1ear (Automotive)
16 Jun 07 23:50
globi5
Yes, sorry, you are right.
automotivebreath (Automotive)
17 Jun 07 3:26
Feric posted "flame temperature increase with an increase of
the oxidant preheat temperature". Several other factors
influence flame temperature including including cylinder
pressure (this raises oxidant temp.), residual gas, air/fuel
ratio and fuel type.

So yes, as the flame front progresses the pressure and
temperature ahead of the flame rises resulting in increased
flame temperature.

Try this link to see the influence various factors have on
flame temperatures.

http://www.wiley.com/college/mechs/ferguson356174/wave_s.html

In practice increasing the engines dynamic compression ratio
and or volumetric efficiency will have a direct impact on
flame temperatures.
Feric (Mechanical)
17 Jun 07 10:29
To All:

My plots are just for an ideal and complete combustion case.

The more time you spend dealing with the subject matter, the more you realize the complexity of the subject matter and that other factors that need to be considered and taken into consideration.

It is good to participate in such a forum and contribute as much as I can.

Thanks,  

Gordan Feric, PE
Engineering Software
http://members.aol.com/engware

automotivebreath (Automotive)
17 Jun 07 18:26
This is a highly complex subject with so many variables.
 
I have a personal interest in the effects of moisture
content on flame temperature and cylinder pressure.
Racing at night in Louisiana we see extreme levels of
humidity. I have seen several instances when it appeared
that cylinder pressure was increased with a rise in humidity
using auto-ignition as an indicator.  I’m not saying what
I saw was dissociating water to hydrogen and oxygen.  I
suppose we see enough humidity here to generate cylinder
pressure with steam.

Using the Wiley Adiabatic Flame Temperature Applet I
developed this chart of theoretical flame temperatures.

Fuel – Gasoline

Cylinder Pressure; variable 1200 kPa to 4800 kPa
(1200 being theoretical cranking compression and 4800 peak cylinder pressure)

Unburned gas temperature; variable 298K to 519K
(298 inlet A/F temperature and 519 the auto-ignition point of gasoline)

Air/Fuel equivalence ratio; constant at 1

Residual mass fraction; constant at .1

Cylinder Pressure (kPa)           1200    1600    2000    2400    2800    3200    3600    4000    4400    4800
Unburned gas temperature (K) 298.0    322.6    347.1    371.7    396.2    420.8    445.3    469.9    494.4    519.0
Flame Temperature (K)            2154    2172    2189    2207    2224    2241    2258    2275    2291    2308
crysta1c1ear (Automotive)
20 Jun 07 16:26
Residual mass fraction; constant at .1

10% unburnt fuel is quite a lot!
automotivebreath (Automotive)
20 Jun 07 18:40
Typically values of residual gas fraction are in the range 3% to 12% for the SI
engine. This can be higher depending on camshaft overlap, operating RPM and
other factors.

Recalculating the table with residual mass fraction constant at 0.01 generates
different results. What becomes apparent is we can control flame temperature
with engine design and operating conditions.

Cylinder Pressure (kPa)            1200    1600      2000    2400      2800      3200    3600     4000    4400      4800
Unburned gas temperature (K)  298.0    322.6    347.1    371.7    396.2    420.8    445.3    469.9    494.4    519.0
Flame Temperature (K)            2293    2311      2329    2346      2363     2380    2396     2412     2428      2445

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