CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > CONVERGE

Heat Release vs. Apparent Heat Release // Comparison with GT Power

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 14, 2016, 07:01
Default Heat Release vs. Apparent Heat Release // Comparison with GT Power
  #1
Senior Member
 
Tobias
Join Date: May 2016
Location: Germany
Posts: 238
Rep Power: 9
MFGT is on a distinguished road
Hi all,

currently i am working on a file with GT Power inputs and compare resulting cylinder pressure. Next step followed by that is the burn rate, however, there is no variable named like that in CONVERGE. This may or may not lead to confusion if comparing to 1D GT Power or experimental data.

Allie wrote in another Thread:
Quote:
Originally Posted by alemoine View Post
The heat release rate that is present in thermo.out does not include any losses due to heat transfer. If you are interested in looking at the heat transfer rate across a boundary (such as between the combustion chamber wall and gases), then you will want to look at bound*-wall.out.
Basically, in theory, we have:
"Integrated Heat Release (Burn Rate * LHV) - total Heat Transfer = Apparent Integrated Heat Release"

Integrated Heat Release is column 11 from thermo.out file, total Heat Transfer can be calculated as sum from column 17 of all bound*-wall.out files attatched to cylinder region. To get the Apparent Heat Release we use the Apparent Heat Release Calculator in Studio, that takes the pressure trace, gamma and geometric volume from cylinder region into account.

In a complete combustion the Integrated Heat Release is equal to the burnt fuel mass times lower Heating value: QB=mB * Hu

In GT Power we have variables called Burn Rate and Apparent Heat Release Rate.
It seems like they are equal to the Heat Release Rate divided my LHV and Apparent Heat Release Rate of CONVERGE.

Regards,
Tobias

Last edited by MFGT; July 18, 2016 at 04:01.
MFGT is offline   Reply With Quote

Old   July 15, 2016, 08:35
Default
  #2
Senior Member
 
Tobias
Join Date: May 2016
Location: Germany
Posts: 238
Rep Power: 9
MFGT is on a distinguished road
Q1: Is there an overview of species properties that CONVERGE uses, especially the lower Heating value of the different species? Depending on where i look i find different values for the species.

Q2: If the Heat Release Rate is actually the Burn Rate, would it be possible and sensful to rename the column in the thermo.out file if Engine Simulation is used?
MFGT is offline   Reply With Quote

Old   July 15, 2016, 11:14
Default
  #3
Member
 
Dan Probst
Join Date: Jan 2016
Location: Convergent Science, Madison WI
Posts: 38
Rep Power: 8
dprobst is on a distinguished road
The LHV of the fuel is calculated using property data in therm.dat. If you do not want to calculate it from the therm.dat data, you can get the calculated LHV of the fuel as an output from Converge. To get the LHV as an output, you will run a simple test case:
- create a hidden.in file with the following line:
1 lhv_flag
- create a file called lhv.in with the following lines:
2.0 lhv_value LHV VALUE TO BE ACHEIVED IN J/kg
1 lhv_num_species NUMBER OF FUEL SPECIES TO BE MODIFIED FOR LHV
c8h18 1.0 massfrac RELATIVE FRACTION OF EACH FUEL SPECIES


Run this test case for a short time - a file called lhv_info.out file will contain the calculated LHV as the second line (LHV SURROGATE). As this is a new feature, it is still in trial mode and has not been moved to a regular file input, and you will need a recent version of v2.3.

The chemical heat release rate, as named in thermo.out, is a precise and well understood term for engine research. Calculated burn rates & apparent heat release rates use different methods and assumptions.
__________________
Dan Probst
Principal Engineer
CONVERGECFD
dprobst is offline   Reply With Quote

Old   July 18, 2016, 03:57
Default
  #4
Senior Member
 
Tobias
Join Date: May 2016
Location: Germany
Posts: 238
Rep Power: 9
MFGT is on a distinguished road
Thanks Dan, that worked pretty well. The values i had previously were a bit different lower and i already wondered why my calculated mFuel*LHV was less than integrated Heat Release.

And to be precise, with Burn Rate i obviously meant fuelmass times LHV to get an Energy value as well. So shouldnt be the chemical heat release rate equal to the rate how fuel is burned multiplied with its LHV?
MFGT is offline   Reply With Quote

Old   July 18, 2016, 16:16
Default
  #5
Member
 
Dan Probst
Join Date: Jan 2016
Location: Convergent Science, Madison WI
Posts: 38
Rep Power: 8
dprobst is on a distinguished road
If you are considering the burn rate to be the fraction of fuel burned and the fuel is reacting completely to products, than the chemical heat release would equal the energy content of the consumed fuel. There are several factors that can affect the energy balance in combustion, however: incomplete combustion, heat transfer, unburnt fuel.
The reason we call it chemical heat release is because it is precise and understandable, as I said above.
Energy calculated from a burn rate can be different than chemical heat release, for example when the mixture is rich and there is significant CO in the products.
Furthermore, there are different experimental methods to calculate apparent heat release, burn rate, etc... which may introduce errors that show up in comparison to chemical heat release.
__________________
Dan Probst
Principal Engineer
CONVERGECFD
dprobst is offline   Reply With Quote

Old   July 29, 2016, 04:06
Default
  #6
Senior Member
 
Tobias
Join Date: May 2016
Location: Germany
Posts: 238
Rep Power: 9
MFGT is on a distinguished road
Quote:
Originally Posted by dprobst View Post
The LHV of the fuel is calculated using property data in therm.dat. If you do not want to calculate it from the therm.dat data, you can get the calculated LHV of the fuel as an output from Converge. To get the LHV as an output, you will run a simple test case:
- create a hidden.in file with the following line:
1 lhv_flag
- create a file called lhv.in with the following lines:
2.0 lhv_value LHV VALUE TO BE ACHEIVED IN J/kg
1 lhv_num_species NUMBER OF FUEL SPECIES TO BE MODIFIED FOR LHV
c8h18 1.0 massfrac RELATIVE FRACTION OF EACH FUEL SPECIES

Run this test case for a short time - a file called lhv_info.out file will contain the calculated LHV as the second line (LHV SURROGATE). As this is a new feature, it is still in trial mode and has not been moved to a regular file input, and you will need a recent version of v2.3.
If i run a simulation with this hidden.in and lhv.in file, will it then use the specified LHV value instead of the LHV surrogate?
Code:
LHV SPECIFIED             = 4.222000e+007
LHV SURROGATE             = 4.465837e+007
LHV FRACTIONAL CORRECTION = -5.460048e-002

LHV_SPECIES         OLD_LOW_A6      NEW_LOW_A6         fractional change
C8H18       -2.9944688e+004      -6.3447372e+004       1.1188190e+000
Or would i need to modify the therm.dat file Low_a6 value of my species manually and the method described previously is just an info output?
MFGT is offline   Reply With Quote

Old   August 1, 2016, 10:17
Default
  #7
Member
 
Dan Probst
Join Date: Jan 2016
Location: Convergent Science, Madison WI
Posts: 38
Rep Power: 8
dprobst is on a distinguished road
Yes, this allows you to modify the LHV.
__________________
Dan Probst
Principal Engineer
CONVERGECFD
dprobst is offline   Reply With Quote

Old   August 1, 2016, 13:51
Default
  #8
Senior Member
 
Tobias
Join Date: May 2016
Location: Germany
Posts: 238
Rep Power: 9
MFGT is on a distinguished road
Thank you Dan.

I really like the hidden, secret features
MFGT is offline   Reply With Quote

Old   August 15, 2016, 08:38
Default
  #9
Senior Member
 
Tobias
Join Date: May 2016
Location: Germany
Posts: 238
Rep Power: 9
MFGT is on a distinguished road
Hey Dan, quick question from my side again.

I have a simulation where i slightly reduced the LHV of my PRF (92% IC8H18, 8% C7H16) from 4.467920e+007 to 4.256100e+007, which is -4.74%.

Compared to a simulation, where i didnt make any changes, this had a quite drastic impact on mean pressure and temperature (e.g. peak firing pressure dropped from 45bar to 31bar). Also, the rate at which the fuel was consumed was significantly reduced.

I will rerun this to double check the result, but i simply expected only a minimal reduce in power output.
MFGT is offline   Reply With Quote

Old   August 16, 2016, 15:03
Default
  #10
Member
 
Dan Probst
Join Date: Jan 2016
Location: Convergent Science, Madison WI
Posts: 38
Rep Power: 8
dprobst is on a distinguished road
Reducing the energy content by ~5% is showing to be quite significant, as the lower heat release translates to less temperature gain, and hence slower combustion.
But also, you may want to run a 2nd and even 3rd cycle of each case to before drawing conclusions.
__________________
Dan Probst
Principal Engineer
CONVERGECFD
dprobst is offline   Reply With Quote

Old   August 17, 2016, 02:38
Default
  #11
Senior Member
 
Tobias
Join Date: May 2016
Location: Germany
Posts: 238
Rep Power: 9
MFGT is on a distinguished road
Sure, at the moment i am running from two cycles from -520 to 900 and the values i mentioned were from 2nd cycle.
MFGT is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
heat power per unit area in heatfl.f or heatob.f boesendorfer FLOW-3D 0 April 26, 2014 09:44
combustion heat release Anna_p Main CFD Forum 0 June 20, 2013 11:40
Water subcooled boiling Attesz CFX 7 January 5, 2013 03:32
Comparison of radiation and convection heat transfer panos_metal FLUENT 0 December 5, 2011 21:04
How to measure total Heat Power myyahaha ANSYS 8 November 17, 2010 08:47


All times are GMT -4. The time now is 12:29.