Experimental and Numerical Investigation of Inter-Ring Gas Pressures and Blowby in a Diesel Engine 930792

Inter-ring gas pressures and blowby in a diesel engine were investigated analytically and compared to experimental data measured at three engine speeds. Coupled simulations of ring dynamics, ring lubrication and inter-ring gas dynamics were carried out using the RINGPAK software, a code for the integrated analysis of ring pack performance and tribology. Inter-ring pressures and ring dynamics are known to have an important effect on the “blowback” mechanism of in-cylinder oil consumption, i.e. that of oil-laden gas flow from the ring lands into the cylinder.
Predicted land pressures matched the experimental results very well qualitatively as well as quantitatively. The coupling between ring motions and inter-ring gas pressures and blowby, a key feature of the methodology, was seen to be crucial in obtaining agreement with detailed features of the land pressure data. Ring axial flutter and radial lift and collapse were found to be the second land pressure relief mechanisms which best explain the behavior of measured second land pressure during the power stroke. Simulations were also used to explain the observed effect of top ring bottom keystone angle and helped identify features of the experimental data which are questionable.
Some calibration of the simulations was necessary, but consisted of varying ring pack geometrical parameters (end gap dimensions, land volumes), mostly within tolerances. This reveals the very significant effect manufacturing tolerances may have on ring pack performance.
Good agreement was also obtained with the blowby mesurements associated with the land pressure data, by seeking correlation with inter-ring pressures only, without otherwise calibrating simulations for a best match of blowby measurements.


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