predicted and measured ring pack performance of a diesel ... - Ricardo

PREDICTED AND MEASURED RING PACK
PERFORMANCE OF A DIESEL ENGINE
Jinglei Chen
Federal-Mogul Corporation
Ann Arbor, Michigan
D. E. Richardson
Cummins Engine Company
Columbus, Indiana
ABSTRACT
Piston ring pack performance is very critical to
diesel engine blow-by and oil consumption. As
structural analysis tools such as Finite Element
Analysis and Boundary Element Analysis can be
used to ensure the piston structural integrity,
cylinder kit dynamics models are being used to
predict power cylinder system performance. In
this paper, detailed comparisons of engine test
measurements and model predictions under
various operating conditions and with different
ring pack configurations are presented. The
cylinder kit model used in this project is Ricardo
– RINGPAK V3.1.1.
INTRODUCTION
Due to the complexity of the cylinder kit
modeling, it is very important to validate the
program against test results. Normally, one will
only measure blow-by and oil consumption
results during the engine test. The inter-ring gas
pressure and ring motions are rarely measured.
However, to have a thorough understanding of
the model, it is important to get into the details
of ring motion and inter-ring gas pressure. These
are the fundamental results of the modeling
work, while blow-by is the final end result.
Cummins Engine Company has conducted a
series of engine tests with the purpose of
measuring not only the blow-by value but also
the ring motion and pressure between the rings
(Cummins Technical Report). A wide range of
engine speed and loading conditions are tested
with different combinations of ring pack
configurations. Hence, a complete database
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consisting of inter-ring gas pressures, ring
motions, and blow-by results is available. This
database is ideal for benchmarking different
cylinder kit models/programs.
The validation results presented in this paper are
part of the joint cylinder kit modeling project
carried out by the Cummins Engine Company
and Federal-Mogul Corporation. Overall six
different programs, commercial or universitydeveloped
codes, have been evaluated. Ricardo-
RINGPAK is one of these programs. Two sets of
results from RINGPAK are presented in this
paper. The first set of results was generated
without any calibration work. The second set of
results was obtained by changing only one
parameter according to the engine running
conditions. Further, the new bore distortion
feature implemented in RINGPAK v 3.1.1 [1]
has also been used in the second iteration.
A significant amount of work has been done
developing and validating cylinder kit models [2-
6]. Usually the focus of validation will be on oil
consumption and blow-by predictions. Very few
papers deal with inter-ring gas pressure [6] and
ring motion validation due to the difficulty of
obtaining such detail measurement data. This
work is quite unique in its attempt to have a
complete review of the simulation program with
detailed fundamental test data.
Experimental Setup
The experimental work was carried out by
Cummins Engine Company. The tests were
conducted with the intention of improving
analytical tools – cylinder kit models. Overall
eight ring pack configurations have been tested
at different engine operating conditions.
With one of the cylinders in the engine
instrumented, the following measurements were
taken in addition to the blow-by values.
• Inter-ring Pressure – 2 nd land, Major and
Minor thrust. (Faulty Transducer)
• Ring motion – Top and 2 nd rings, Major and
Minor thrust; Oil ring, Major thrust. (Motion
Sensors mounted on the sides of grooves)
• Cylinder pressure – Standard measurement
More details on the tests and instrumentation can
be found in the Cummins Technical Report.
RINGPAK Model
To construct a RINGPAK model input set, one
needs to have information on engine operating
conditions, piston land and groove dimensions,
ring dimensions, cylinder gas pressure and gas
temperatures, temperatures of piston and rings,
surface and material properties, lubrication oil
properties, liner distortion or thermal expansion
of rings and piston, etc. These items are obtained
through drawings, material specifications,
measurement data, and reasonable estimations or
extrapolations. Also, there are a few parameters
in the RINGPAK program that are so-called
calibration factors – parameters that can be
changed to improve the match between model
predictions and test data. Most of these variables
are determined according to Federal-Mogul and
Cummins experience on using the RINGPAK
program. RINGPAK model is based mainly on
mathematical models rather than empirical
relations. Most of the input parameters in the
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Ricardo model have physical significance. Hence
one does not need to rely heavily on the
empirical coefficients.
Results from five case studies are discussed in
this paper, the configurations of which are
summarized in the following table.
Table One: Cases Simulated with RINGPAK
Case Engine
speed
Load Ring 1
Twist
Ring2
Twist
Gap ratio
R1 : R2
1 Medium Full + + 1:3
2 Medium Full + - 1:1
3 Low Partial + - 1:1
4 Low Full N + 1:1
5 High Full + - 1:3
Note: + positive twist, - negative twist, N no twist.
All the simulations were run on a HP C160 Unix
workstation. Typical running time is between 20
to 35 minutes.
Results and Discussions
There are two kinds of results that can be
obtained from the RINGPAK program. One of
the two are results such as blow-by, and oil
consumption, which are critical end results that
people want to know. The other kind of results
are more detail-oriented such as inter-ring
pressure traces, ring axial motions, ring twist etc.
These results are more useful for people to
understand the modeling fundamentals of the
program. Hence, both kinds of results are
important for the model evaluation and
validation.
Blow-by
Shown in Figure One are the blow-by
predictions and the corresponding measurement
data. As can be seen, predicted blow-by values
are fairly close to the corresponding measured
data except that of case 1. For case 1 the blowby
prediction is significantly higher than the test
measurement. More importantly, it does not
follow the trend of the measurement. However,
almost all programs evaluated by Federal-Mogul
and Cummins tend to over predict the blow-by
for case 1. Further, as shown in a later section,
RINGPAK gives very good predictions of interring
pressure and ring motions for case 1. Hence,
there is a possibility that the test data for case 1
might not be accurate. Overall, one can conclude
that blow-by predictions obtained through
RINGPAK simulation are satisfactory.
Inter-ring pressure and ring motion
Two sets of results of inter-ring pressure and ring
motions are presented in this paper. The first set
of results (iteration 1) was obtained without any
attempt to improve the correlation. In the second
iteration, the new bore distortion feature of the
RINGPAK program was used. Further, the ring
groove surface properties were also modified to
reflect the worn engine conditions. RINGPAK is
a 2-D program and no piston tilt effects are
considered in this project. In Figures Two to
Eleven ring motion a and b of the test results
refer to measurements in Major and Minor thrust
sides, while ring motion a and b of the
simulation results are locations of ring OD and
ID. In all cases the “tuning/calibration”
parameters are kept the same.
Inter-ring pressure
Overall, for results of iteration 1, the predicted
peak 2 nd land pressures are quite close to the
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measurements. However, the predicted pressure
traces do not always closely follow the measured
pressure traces, especially in case 5. The pressure
results from the second iteration provide much
better match with the test data. In all cases, the
predicted pressure traces are much closer to the
measured pressure curves throughout the entire
engine cycle. Overall, the peaks are also quite
close to measured data in the second iteration.
Only in case 4, the pressure prediction of
iteration 2 seems worse than that of iteration 1.
However, a close examination of the pressure
trace shows that the pressure trace is actually
better except the region in the vicinity of the
peak pressure.
Ring motions
Axial motions of all three rings are plotted along
with the corresponding pressure traces in Figures
Two to Eleven. Due to the improved pressure
trace prediction, the overall predicted ring
motions of iteration 2 agree better with the
measurements than those of iteration 1. Ring
motion results from iteration 2 are summarized
as follows. In case 1, all predicted ring motions
are very close to the measurements. Only the oil
ring lifting near the Firing TDC is later and
lifting period is shorter. This is also true for
cases 3 and 4. For case 2, the simulation predicts
that the top ring lifts and stays at the top of the
ring groove while the measurement shows that
top ring is fluttering. The 2 nd and oil ring motion
predictions are quite good except an extra lift of
the oil ring near the end of the intake stroke. The
simulation shows that the top ring lifts at the
same time as the measurement in case 3.
However the top ring goes down earlier due to
the lower predicted 2 nd land pressure. The 2 nd lift
of the top ring during the exhaust stroke has also
been captured by RINGPAK simulation. In case
4, the top ring lifts earlier due to the higher
predicted inter-ring pressure, while the 2 nd ring
and oil ring predictions are good. One important
ring motion features of case 5 is the 2 nd ring lift
(fluttering) right before FTDC. This is not
captured by the RINGPAK model. The predicted
top ring and oil ring motions are close to the
measurement in case 5.
Conclusions
♦ RINGPAK predictions on engine blow-by
correlate well with the measurements in
most cases.
♦ Overall, the inter-ring pressure calculations
are quite close to the measured pressure
traces. It has been noticed that a small
difference in pressure predictions can
sometime cause completely different ring
motions.
♦ Many of the actual ring motion
characteristics have been captured in the
RINGPAK simulations. However, there are
some discrepancies between the simulations
and measurements.
♦ RINGPAK has been found to be one of the
best programs available on the market. It
produces reasonably good results without
requiring too much effort on “tuning” or
calibrating the model.
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Recommendations
It has been found through the evaluation process
that all ring pack performance simulation
programs including RINGPAK have areas that
need to be further improved. Indeed, most of the
program developers have detailed plans to
develop and implement new features. Giving the
complexity of the model, it is very critical for
users to validate these new features. The
developers should also commit adequate
resources to the continuation of the program
development.
ACKNOWLEDGEMENTS
The first author wants to express his great
appreciation toward the Cummins Engine
Company for conducting this series of engine
tests without which this evaluation project will
not be possible.
REFERENCES
1. PISTON RINGPACK ANALYSIS –
Documentation/User’s manual Version 3.1.1,
1999.
2. Namazian, M., and Heywood, J. B., “Flow
in the Piston-Cylinder-Ring Crevices of a Spark-
Ignition Engine: Effect on Hydrocarbon
Emissions, Efficiency and Power,” SAE Paper
820088, 1982.
3. Gulwadi, S. D., “A Mixed Lubrication and
Oil Transport Model for Piston Rings Using a
Mass Conservation Algorithm,” ASME Journal
of Engineering for Gas Turbines and Power,
Vol. 120, 1998, pp.199-208.
4. Gulwadi, S. D., “Analysis of Tribological
Performance of a Piston Ring Pack,” to be
presented at the STLE/ASME International
Tribology Conference to be held in Oct. 1999.
Under review for publication in Tribology
Transactions.
5. Kuo, T., et al., “Calculation of Flow in the
Piston-Cylinder-Ring Crevices of a
Homogeneous-Charge Engine and Comparison
with Experiment,” SAE Paper 890838, 1989.
6. Richardson, D. E., “Comparison of
Measured and Theoretical Inter-ring Gas
Pressure on a Diesel engine,” SAE Paper
961909, 1996.
5

0.0
Ricardo Simulation
Test Data
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
case1 case2 case3 case4 case5
Figure One: Blow-by Predictions and Measurements
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Comparions of Inter-Ring Gas Pressure and Ring Motion
Predicted Ring Motion "a"
Predicted Ring Motion "b"
Actual Ring Motion "a"
Actual Ring Motion "b"
Cylinder Pressure - Model
Predicted Inter-ring Pressure
Cylinder Pressure
Actual Inter-Ring Pres.
24
16
8
Pressure
Ring Motion (Up/Down)
Up
Down
Up
Down
Up
Oil
Ring
Down
-24
-360 -270 -180 -90 0 90 180 270 360
Crank Angle (degree)
0
Top
Ring
-8
2nd
Ring
-16
Figure Two: Inter-ring Pressure and Ring Motion Case 1 – Iteration 1
Comparions of Inter-Ring Gas Pressure and Ring Motion
Predicted Ring Motion "a"
Predicted Ring Motion "b"
Actual Ring Motion "a"
Actual Ring Motion "b"
Cylinder Pressure - Model
Predicted Inter-ring Pressure
Cylinder Pressure
Actual Inter-Ring Pres.
24
16
8
Pressure
Up
Down
Up
Down
Up
Oil
Ring
Down
-24
-360 -270 -180 -90 0 90 180 270 360
Crank Angle (degree)
0
Top
Ring
-8
-16
2nd
Ring
Figure Three: Inter-ring Pressure and Ring Motion Case 1 – Iteration 2
7

Comparions of Inter-Ring Gas Pressure and Ring Motion
Predicted Ring Motion "a"
Predicted Ring Motion "b"
Actual Ring Motion "a"
Actual Ring Motion "b"
Cylinder Pressure - Model
Predicted Inter-ring Pressure
Cylinder Pressure
Actual Inter-Ring Pres.
24
16
8
Pressure
Ring Motion (Up/Down)
Up
Down
Up
Down
Up
Oil
Ring
Down
-24
-360 -270 -180 -90 0 90 180 270 360
Crank Angle (degree)
0
Top
Ring
-8
2nd
Ring
-16
Figure Four: Inter-ring Pressure and Ring Motion Case 2 – Iteration 1
Comparions of Inter-Ring Gas Pressure and Ring Motion
Predicted Ring Motion "a"
Predicted Ring Motion "b"
Actual Ring Motion "a"
Actual Ring Motion "b"
Cylinder Pressure - Model
Predicted Inter-ring Pressure
Cylinder Pressure
Actual Inter-Ring Pres.
24
16
8
Pressure
Ring Motion (Up/Down)
Up
Down
Up
Down
Up
Oil
Ring
Down
-24
-360 -270 -180 -90 0 90 180 270 360
Crank Angle (degree)
0
Top
Ring
-8
2nd
Ring
-16
Figure Five: Inter-ring Pressure and Ring Motion Case 2 – Iteration 2
8

Comparions of Inter-Ring Gas Pressure and Ring Motion
Predicted Ring Motion "a"
Predicted Ring Motion "b"
Actual Ring Motion "a"
Actual Ring Motion "b"
Cylinder Pressure - Model
Predicted Inter-ring Pressure
Cylinder Pressure
Actual Inter-Ring Pres.
24
16
8
Pressure
Ring Motion (Up/Down)
Up
Down
Up
Down
Up
Oil
Ring
Down
-24
-360 -270 -180 -90 0 90 180 270 360
Crank Angle (degree)
0
Top
Ring
-8
2nd
Ring
-16
Figure Six: Inter-ring Pressure and Ring Motion Case 3 – Iteration 1
Comparions of Inter-Ring Gas Pressure and Ring Motion
Predicted Ring Motion "a"
Predicted Ring Motion "b"
Actual Ring Motion "a"
Actual Ring Motion "b"
Cylinder Pressure - Model
Predicted Inter-ring Pressure
Cylinder Pressure
Actual Inter-Ring Pres.
24
16
8
Pressure
Ring Motion (Up/Down)
Up
Down
Up
Down
Up
Oil
Ring
Down
-24
-360 -270 -180 -90 0 90 180 270 360
Crank Angle (degree)
0
Top
Ring
-8
2nd
Ring
-16
Figure Seven: Inter-ring Pressure and Ring Motion Case 3 – Iteration 2
9

Comparions of Inter-Ring Gas Pressure and Ring Motion
Predicted Ring Motion "a"
Predicted Ring Motion "b"
Actual Ring Motion "a"
Actual Ring Motion "b"
Cylinder Pressure - Model
Predicted Inter-ring Pressure
Cylinder Pressure
Actual Inter-Ring Pres.
24
16
8
Pressure
Ring Motion (Up/Down)
Up
Down
Up
Down
Up
Oil
Ring
Down
-24
-360 -270 -180 -90 0 90 180 270 360
Crank Angle (degree)
0
Top
Ring
-8
2nd
Ring
-16
Figure Eight: Inter-ring Pressure and Ring Motion Case 4 – Iteration 1
Comparions of Inter-Ring Gas Pressure and Ring Motion
Predicted Ring Motion "a"
Predicted Ring Motion "b"
Actual Ring Motion "a"
Actual Ring Motion "b"
Cylinder Pressure - Model
Predicted Inter-ring Pressure
Cylinder Pressure
Actual Inter-Ring Pres.
24
16
8
Pressure
Ring Motion (Up/Down)
Up
Down
Up
Down
Up
Oil
Ring
Down
-24
-360 -270 -180 -90 0 90 180 270 360
Crank Angle (degree)
0
Top
Ring
-8
2nd
Ring
-16
Figure Nine: Inter-ring Pressure and Ring Motion Case 4 – Iteration 2
10

Comparions of Inter-Ring Gas Pressure and Ring Motion
Predicted Ring Motion "a"
Predicted Ring Motion "b"
Actual Ring Motion "a"
Actual Ring Motion "b"
Cylinder Pressure - Model
Predicted Inter-ring Pressure
Cylinder Pressure
Actual Inter-Ring Pres.
24
16
8
Pressure
Ring Motion (Up/Down)
Up
Down
Up
Down
Up
Oil
Ring
Down
-24
-360 -270 -180 -90 0 90 180 270 360
Crank Angle (degree)
0
Top
Ring
-8
2nd
Ring
-16
Figure Ten: Inter-ring Pressure and Ring Motion Case 5 – Iteration 1
Comparions of Inter-Ring Gas Pressure and Ring Motion
Predicted Ring Motion "a"
Predicted Ring Motion "b"
Actual Ring Motion "a"
Actual Ring Motion "b"
Cylinder Pressure - Model
Predicted Inter-ring Pressure
Cylinder Pressure
Actual Inter-Ring Pres.
24
16
8
Pressure
Ring Motion (Up/Down)
Up
Down
Up
Down
Up
Oil
Ring
Down
-24
-360 -270 -180 -90 0 90 180 270 360
Crank Angle (degree)
0
Top
Ring
-8
2nd
Ring
-16
Figure Eleven: Inter-ring Pressure and Ring Motion Case 5 – Iteration 2
11