Combustion start and end time

MMatt · May 7, 2020, 02:41

How would one define when the combustion should start and end in a PFI gasoline engine? I mean how this should be setup in Converge. I've set these to -17°CA (start) and 138°CA (end), but that's based on what I could find on the internet.

If the HR-rate is not 0 when the combustion end point is reached, should I make the combustion last longer? I understand that the start and end points are just to use the SAGE model (in my case).

Thanks!

MFGT · May 7, 2020, 09:09

If you are not interested in emissions, I would say end SAGE as soon as possible to reduce computaional effort, which means after combustion is over and HRR is close to zero.

Typically I use 120 °CA.

Start time seems to be less important, as long as its before spark obviously. I have it at -50°CA.

MMatt · May 8, 2020, 02:09

Right. There doesn't seems to be a correlation between time step and use of the SAGE model, as the time step varies between about 1E-7 to 6e-6 during combustion, so I will try to increase the end time of combustion since I am interested in emissions, however I don't want the simulation to last much much longer. I will give it a try!

May 7, 2020, 02:41	Combustion start and end time	#1
MMatt Member MMatt Join Date: May 2013 Posts: 59 Rep Power: 13	How would one define when the combustion should start and end in a PFI gasoline engine? I mean how this should be setup in Converge. I've set these to -17°CA (start) and 138°CA (end), but that's based on what I could find on the internet. If the HR-rate is not 0 when the combustion end point is reached, should I make the combustion last longer? I understand that the start and end points are just to use the SAGE model (in my case). Thanks! Last edited by MMatt; May 7, 2020 at 04:55.

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May 7, 2020, 09:09		#2
MFGT Senior Member Tobias Join Date: May 2016 Location: Germany Posts: 284 Rep Power: 11	If you are not interested in emissions, I would say end SAGE as soon as possible to reduce computaional effort, which means after combustion is over and HRR is close to zero. Typically I use 120 °CA. Start time seems to be less important, as long as its before spark obviously. I have it at -50°CA.

May 8, 2020, 02:09		#3
MMatt Member MMatt Join Date: May 2013 Posts: 59 Rep Power: 13	Right. There doesn't seems to be a correlation between time step and use of the SAGE model, as the time step varies between about 1E-7 to 6e-6 during combustion, so I will try to increase the end time of combustion since I am interested in emissions, however I don't want the simulation to last much much longer. I will give it a try!