Crevice

hamedc · February 27, 2018, 15:32

Hi,

I conducted a simulation by a geometry which is included crevice that is attached in bowl profile.
I also conducted another simulation which is not included crevice, but i have used a crevice model (Heywood & Namazian) instead.
I set specified compression ratio in both of cases using compression ratio calculation.
In case of Crevice, i saw that the amount of in-cylinder pressure was too high.
In case of crevice model, i saw that the amount of in-cylinder pressure was close the experimental.
In the case of crevice, I reduce the compression ratio to a value of 0.9 from the specified compression ratio, then i saw that in-cylinder pressure was close to the another one (crevice model).
What is the reason?
Does not calculate the volume associated with the crevice in CR calculation?

thank you in advance.

Regards,

yli · March 2, 2018, 12:46

Hi, Hamed,
It is quite normal that two of your simulations not match. The first one you include the crevice shape in the geometry but there is no leakage path. And the second one you used the crevice model (with many user-defined parameters to define the crevice characteristics) where there is mass leakage. So if you check the total cylinder mass they are different and that's why there is pressure trace difference.

Pramod B · March 5, 2018, 15:07

Hi,
I have a question regarding Crevice model. What should be Initial Pressure and Temperature to be specified in the volumes 2,3,4 in the crevice model if I'm starting the simulation before IVO? And also what should be given be initial position of the rings?

Thanks.

SamWijey · March 5, 2018, 16:45

Hi Pramod,

These input quantities are engine case specific and needs to be known via available engine data. Please read section 20.8 in CONVERGE version 2.4 Theory manual for more details.

Thanks,

hamedc · March 6, 2018, 15:25

Hi,

Thank you for your answer.
Another question that remains to me is: Is it correct the reduction of compression ratio (i mean geometric CR) when you have crevice shape in your geometry?

Regards,
Hamed

Quote:

Originally Posted by yli

Hi, Hamed,
It is quite normal that two of your simulations not match. The first one you include the crevice shape in the geometry but there is no leakage path. And the second one you used the crevice model (with many user-defined parameters to define the crevice characteristics) where there is mass leakage. So if you check the total cylinder mass they are different and that's why there is pressure trace difference.

SamWijey · March 7, 2018, 13:12

Hi Hamed,

This is usually correct if you calculate CR=Volume @ BDC / Volume at TDC

Thanks,

Pramod B · March 11, 2018, 05:57

We do not know the pressure in the regions 1,2,3 for the crevice model from experiments. Also the ring positions change with crank angle. So, my question is what would be a good approximation for these values.
This is what I'm specifying for the simulation starting at IVO.
The initial Pressure in these regions are given same as the pressure in the cylinder at that crank angle obtained from experiments. For the ring positions, I'm considering the Top ring to be in contact with groove upper surface and the bottom ring to be in contact with the groove lower surface.
Is this correct?

Thanks.

February 27, 2018, 15:32	Crevice	#1
hamedc New Member Hamed Join Date: May 2017 Posts: 26 Rep Power: 8	Hi, I conducted a simulation by a geometry which is included crevice that is attached in bowl profile. I also conducted another simulation which is not included crevice, but i have used a crevice model (Heywood & Namazian) instead. I set specified compression ratio in both of cases using compression ratio calculation. In case of Crevice, i saw that the amount of in-cylinder pressure was too high. In case of crevice model, i saw that the amount of in-cylinder pressure was close the experimental. In the case of crevice, I reduce the compression ratio to a value of 0.9 from the specified compression ratio, then i saw that in-cylinder pressure was close to the another one (crevice model). What is the reason? Does not calculate the volume associated with the crevice in CR calculation? thank you in advance. Regards,

March 2, 2018, 12:46		#2
yli Member Yanheng Li Join Date: Jan 2016 Location: Convergent Science, Madison WI Posts: 33 Rep Power: 10	Hi, Hamed, It is quite normal that two of your simulations not match. The first one you include the crevice shape in the geometry but there is no leakage path. And the second one you used the crevice model (with many user-defined parameters to define the crevice characteristics) where there is mass leakage. So if you check the total cylinder mass they are different and that's why there is pressure trace difference. __________________ Yanheng Li Research Engineer-Applications CONVERGECFD

March 5, 2018, 16:45		#4
SamWijey Senior Member Sameera Wijeyakulasuriya Join Date: Jan 2016 Location: Convergent Science, Madison WI Posts: 117 Rep Power: 10	Hi Pramod, These input quantities are engine case specific and needs to be known via available engine data. Please read section 20.8 in CONVERGE version 2.4 Theory manual for more details. Thanks, __________________ Sameera Wijeyakulasuriya Principal Engineer, Applications CONVERGECFD

March 7, 2018, 13:12		#6
SamWijey Senior Member Sameera Wijeyakulasuriya Join Date: Jan 2016 Location: Convergent Science, Madison WI Posts: 117 Rep Power: 10	Hi Hamed, This is usually correct if you calculate CR=Volume @ BDC / Volume at TDC Thanks, __________________ Sameera Wijeyakulasuriya Principal Engineer, Applications CONVERGECFD

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March 5, 2018, 15:07		#3
Pramod B New Member Pramod Borado Join Date: Sep 2017 Posts: 6 Rep Power: 8	Hi, I have a question regarding Crevice model. What should be Initial Pressure and Temperature to be specified in the volumes 2,3,4 in the crevice model if I'm starting the simulation before IVO? And also what should be given be initial position of the rings? Thanks.

March 11, 2018, 05:57		#7
Pramod B New Member Pramod Borado Join Date: Sep 2017 Posts: 6 Rep Power: 8	We do not know the pressure in the regions 1,2,3 for the crevice model from experiments. Also the ring positions change with crank angle. So, my question is what would be a good approximation for these values. This is what I'm specifying for the simulation starting at IVO. The initial Pressure in these regions are given same as the pressure in the cylinder at that crank angle obtained from experiments. For the ring positions, I'm considering the Top ring to be in contact with groove upper surface and the bottom ring to be in contact with the groove lower surface. Is this correct? Thanks.