Crevice model

InzGS · May 25, 2019, 10:47

Hi,
I have a question regarding use of the crevice model for IC application: does it influence the compression ratio?
Example: if my engine CR is 18 (with the real geometry), but to simplify geometry for simulation I remove geometrical crevices, certainly CR increases, as the clearance volume decreases. In that case, I usually modify (increase) the squish height to obtain correct CR for simulation. However, increasing the squish height can influence the results, as spray targeting changes, etc. So, if I don't change the squish height, but instead use the crevice model, will it decrease CR?
Thank you in advance, I hope I made myself clear.

kbansal · May 30, 2019, 12:10

Hi,

When using the crevice model, it will not show any difference in CR in the studio since it is calculated based on the geometry. However, when the simulation is running, there will be a mass exchange between the cylinder region and modeled-crevice region that will account for the change in pressure/compression to simulate the presence of the crevice region. CONVERGE will output a file crevice.out which contains the mass in the crevice region.

Thanks,

InzGS · May 30, 2019, 12:20

Thank you for the answer!

May 25, 2019, 10:47	Crevice model	#1
InzGS New Member Join Date: Mar 2019 Posts: 4 Rep Power: 7	Hi, I have a question regarding use of the crevice model for IC application: does it influence the compression ratio? Example: if my engine CR is 18 (with the real geometry), but to simplify geometry for simulation I remove geometrical crevices, certainly CR increases, as the clearance volume decreases. In that case, I usually modify (increase) the squish height to obtain correct CR for simulation. However, increasing the squish height can influence the results, as spray targeting changes, etc. So, if I don't change the squish height, but instead use the crevice model, will it decrease CR? Thank you in advance, I hope I made myself clear.

May 30, 2019, 12:10		#2
kbansal New Member Join Date: Dec 2015 Posts: 27 Rep Power: 10	Hi, When using the crevice model, it will not show any difference in CR in the studio since it is calculated based on the geometry. However, when the simulation is running, there will be a mass exchange between the cylinder region and modeled-crevice region that will account for the change in pressure/compression to simulate the presence of the crevice region. CONVERGE will output a file crevice.out which contains the mass in the crevice region. Thanks, __________________ Karan Bansal Senior Research Engineer CONVERGECFD

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May 30, 2019, 12:20		#3
InzGS New Member Join Date: Mar 2019 Posts: 4 Rep Power: 7	Thank you for the answer!