- Email: [email protected]
Filter performance as the engine sees it
Filter Performance as the Engine
SeesIt n this article, John Truhan, Fleetguard Corporation, USA describes heavy duty diesel engine tests currently being carried out at Fleetguard which aim to characterize filter performance in a more meaningful and responsible way: the way the engine sees it.
Performance tests which become industry standards are usually developed so that they may be carried out by a variety of laboratories with a reasonably high level of repeatability and in a relatively short period of time using relatively simple test stands. To achieve those characteris-
tics, compromises are made to the operating environment so that better control can be maintained. Industry-standard tests to establish filter performance characteristics such as efficiency, life, and capacity use a standard silica based dust contaminant in a hydraulic fluid. However, fil-
No. of Particles a 15 microns I ml WJU
350 300 250 2QO
Cellulose Full Flow Only 15 micron Efficiency = 66.7 Figure 1:The relationship duty diesel engine.The
Microglass Full Flow w Bypass 95%
between piston ring wear rate and lube oil cleanliness for a 1988 lab measured efficiencies for 15 micron particles are listed.
.
vintage
heavy
ters which have seen service on-engine, particularly lube and fuel filters, predominantly trap a complex mixture of organic contaminants in addition to inorganic contaminants, only a small part of which is silica dust. In most cases, the amount of organic contaminant is approximately 90% or more of the total contaminant trapped. The standard dust based tests will not predict how the filters will behave onengine, and more importantly, what effect the filters will have on engine durability and service requirements. As filter designers, we must balance the tradeoff between filter efficiency and life. Achieving high efficiency is not a challenge, but high efficiency filters in service do not live long before they become excessively plugged. Since customers are demanding longer service intervals as a way of reducing operating costs, the challenge for the filter designer is to provide the necessary protection to the engine from wear over longer servicing periods. This tradeoff is impossible to determine using current standardized lab tests, and determining this tradeoff by field testing is both impractical and expensive.
B
l
l
l .
.
.
. .
.
.
. .
. .‘.:$.: ‘7 2 52
a
t% -0
vintage
engines.The
newer
engines
PI 2 -. 2
l B 8 3 4 7 E; 8 l ‘-u 2 CD z E;
. .
. .
.
ENGINE-MEASURED FILTER EFFICIENCY
Figure 2:The sensitlvity of the piston ring to oil cleanliness for various are more tolerant of particulate contamination than the older ones.
.
.
.
* .
.
0 1
Filter efficiency is related to the filter’s ability to remove particulate contamination from a fluid resulting in lower engine wear. Surface (or thin) layer activation (SLA) has been used in our laboratory to measure the effect of fluid condition on engine wear since 1988. Critical engine parts such as piston rings, cylinder liners, and valve train parts are made radioactive by bombardment in a particle accelerator. The isotopes
. .
.
. *
.
*
.
* .
.
.
. .
.
.
I .
. .
.
.
. .
I
.
. .
.
.
.
. .
.
.
I .
. .
.
*
l .
.
.
.
.
.
.
. .
.
.
.
l
. l
.
.
. ,
. .
l
I
. .
. .
. .
r
No. of Particles . 5 microns / ml
Erasion Rate ~Gh~nge
3500 1
1i
/ h) O.E t
ra
i
1
None
Cellulose
5 micron Efficiency =O
Stratified Porosity
55%
88%
Figure 3:The relationship between injector erosion rates and fuel cleanliness for different levels of filtration.The lab measured efficiencies are listed.
0.7 1.
0 -.
Figure
_
4:
-.
Erosion Rate (% Change / h ) 1
1 2 3 No. of Particles / ml > 5 micron (thousands) . . .
. .
-.
.
_
.
.
.a..
4
. .
1ne senslervlry or uqeoror erosion Cares 10 ruei cieaniiness.
that are produced depend on the particles being used for bombardment and the target material. For example, when deuterons are used, to bombard a chromium plated piston ring, the Cr transmutes to Mn54, a gamma ray emitting isotope with a half life of about 300 days. Each of the isotopes emit gamma rays with energies specific to the isotope so that if a gamma ray spectrum is measured, multiple parts can be tracked simulta-
neously. The activity profile for each part is determined by removing material from a similarly irradiated part in successive layers measuring the surface activity at each increment. The activity profiles serve as calibration curves relating the loss of activity in the part due to wear to the depth of wear in the part. The irradiated parts are installed in the engine and a gamma ray detector is placed external to the engine as close as practical so that the loss of
activity due to wear can be measured directly. Although this method has been used primarily to measure wear in the lubricating system, we have applied the technique to measure wear and erosion in the fuel system as well. Examples of wear related to fluid cleanliness for both systems follow. Figure 1 shows the relationship between piston ring wear rate and oil cleanliness as measured by a screen obstruction techni-
que. The standard dust efficiencies for both full flow filters are given below. The data was collected from a 1986 vintage engine which shows a greater sensitivity to oil cleanliness than newer engines. In this case, there is a clear tie between filter efficiency, oil cleanliness and ring wear. This tie becomes less apparent for the newer engines. Figure 2 shows the relationship between ring wear and oil cleanliness as measured by the concentration of particles greater than 15 microns. The data shown in Figure 1 was taken from the curve representing the 1986 engine. The newer engines have both a lower overall ring wear rate and less sensitivity to contamination until the particle concentration becomes exceedingly high. This concentration was achieved in the test cell by the deliberate addition of dust into the sump and far exceeds concentration levels in normally filtered systems. This tolerance to contamination is in line with current field experience with engine life. Ten years ago, the typical life to rebuild was about 800K kilometers, but today, 1600K kilometers is becoming common for heavy duty onhighway use. Building excessive efficiency into these more durable engines, particularly at the expense of filter life, would not achieve the longer service intervals nor would the engines live noticeably longer. A similar argument can be made for the fuel system. Higher efficiency filtration is more typical here due to the closer tolerances in the fuel injectors and the higher operating pressures that they experience, but there is still a tradeoff between efficiency and life. Figure 3 shows the relationship between fuel cleanliness and erosion rate in the injector with the standard efficiencies given along the bottom of the figure. As was the case for the lube system, the higher efficiency filter reduced both the particle concentration and the erosion rate as measured by SLA. Figure 4 shows the
Differential Pressure (kPa)
150.0 100.0 50.0 0.0 0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
Running Time (h)
i Figure
I:The
pressure
differential
sensitivity of the injector to fuel cleanliness similar to Figure 2. As in that case, if the cleanliness can be kept at an acceptable level, erosion rates are low and installing a higher efficiency filter would buy little in extension of part life. ENGINE-MEASURED FILTER LIFE The effective life of a filter in service is defined as the time it takes to reach a predetermined pressure differential across it. Higher flow restrictions present a substantial parasitic pumping loss and, in the case of the lubricating system, prevent oiling from occurring in critical areas. In the laboratory, dust is used as the test contaminant to plug the filter. In actual service, however, dust constitutes less than 1% of what a filter takes out in the lube or fuel system for on-highway applications. On engine, a lube filter takes out sludge, resins, combustion byproducts, and, in severe service, oxidation products. Microscopic examination of a filter removed from the engine shows a tar-like substance coating the fibres compared to a dust test in which the fibres act essen-
buildup
across
various
filters
are shown
tially as strainers. Thus the mechanisms of filter plugging are different between the lab and engine test. Attempts were made in the late 1950s to isolate the organic contaminants from the oil and use them in a laboratory test to plug the filter the same way. This contaminant was termed
-..
tiefative
during
the MilFPT
SOFTC-1, but was later discarded in favour of the synthetic SOFTC9A currently in use. It proved impossible to obtain consistent contaminant to carry out long term tests. This attempt was duplicated in our laboratories recently with similar results. It was determined that the only
way to duplicate what was happening in the engine was to run controlled engine tests. Fleetguard has adapted the Cummins Ml1 High Soot Test (MllHST) to study filter plugging and to determine relative lives among the various lube filter products. The Ml 1HST has become an oil industry standard test to measure a lube oil’s ability to disperse the soot, sludge, and resins that buildup with use and measure the amount of wear that the soot can cause. The test is run with retarded timing and overfueling conditions to produce soot and sludge at an accelerated rate. Fleetguard has adapted the first half of the MilHST, by fixing the oil to a special formulation with poor dispersancy and varying the filter for testing. We are currently referring to this as the Ml1 Filter Plugging Test (MllFPT). This test will take a new oil and filter to plugging in 72 hours or less without changing the basic plugging mechanism. Figure 5 shows the pressure differential buildup with time for several different filters running the MllFPT cycle. An arbitrary B.... * . . . . . . I . . * , . . . . . . .
.._
Life
8
.
.
.
.
l . . . * . . . .
2 2 S s
l ii? zi 3 z 7 G 8 l 9
with
.
% s -I
. .
. .
9
7’
. *
.
. .
P
are normalized
.
*
.
. .
.
.
E
lives
.
.
.
., .
. .
.
2
by the MllFPT.The
. *
.
. .
.
.
Ei
as measured
. .
.
l .
.
.
‘7
filters
. .
,
, .
.
.
.
Figure &The relative lives for different respect to the reference filter.
. . *
.
l .
. .
.:.:_?.:.:
Reference
*
. .
.
. . .
.
800 11 Dust Capacity
1
300 200 100 nw
Figure 7:The on engine.
relationship
Refsrenccs between
terminal differential pressure across the full flow section of the filter is set at 207 kPa (30 psi), so that the time to reach the terminal restriction can be defined as the filter life. Since this test is an arbitrary cycle, we more frequently refer to a relative life which is normalized against the same reference filter used in the MIIHST. In this manner, comparisons can be made on-engine among various current and new products. Figure 6 shows the relative life for a variety of new products designed for extended service intervals. The higher capacity new products can result in a filter life approximatelydouble that of current products. These comparisons, we feel, will be a more valid way for determining the optimum service interval for those customers wishing to extend it. ENGINE-MEASURED FILTER CAPACITY As was the case for determining filter life in the laboratory, filter capacity is determined by challenging the filter with the
lab measured
bF3000SP dust
capacity
and engine
standard test dust and capacity is defined as the amount of dust the filter can hold at its terminal restriction. Again, the MllFPT can be employed to determine how much of the real world contaminant the filter can hold at the same differential pressure. Figure 7 shows a comparison between lab-measured and engine measured dust capacity for several of the previous filters. Since the material buildup rate was found to be linear, all of the capacities listed here have been corrected to the same pressure differential. It is evident that the dust capacity measured in the laboratory is a poor predictor of the actual amount of sludge that can be retained. At least part of the reason for this is that the dust tends to build up as a cake on the outside of the filter material and full use is not made of the depth of the material. Since the sludge coats the fibre, the effective fiber diameter increases and the mean pore size decreases and the full use is made of the material’s capacity.
LFQOOO
LFQOOI measured
capacity.The
lab tests
SUMMARY As customers are demanding longer servicing intervals for their engines as a way of reducing operating costs and increasing their utilization rate, the challenge for the filter designer is to provide sufficient protection for the engine hardware without sacrificing engine life. A high efficiency filter is not difficult to manufacture, but a high efficiency filter that will last a long time is a problem. Standard laboratory based filter performance testing is not a direct predictor of performance in the actual engine environments. Since it is impractical to develop this data base solely from field testing, we are left with engine testing under controlled operating conditions such as would be obtained in a test cell. As this study implies, far more attention has been paid to the lubricating system although some work has gone on in the fuel system. Additional test development needs to be carried out in the other fluid systems to provide meaningful engine tests. The standard performance characteristics are
do not predict
what
will happen
efficiency, capacity and life. We have developed surrogate engine tests for these common laboratory tests to describe filter performance in engine terms. The tradeoffs between efficiency and capacity can be determined and designers of new filtration products have a better method to balance the product for its actual operating environment. A substantial additional benefit is a better communication of filter performance to the customer of our products and a more reasonable way of determining what the customer’s requirements are for various applications. ACKNOWLEDGEMENT This paper is based on a presentation given at the First International Conference on Filtration in Transportation, Stuttgart, Germany. November 4-5, 1997. Filter Media Consulting, Inc., USA. Fleetguard Corporation Cookeville, TN 38506, USA. Tel: f 1 931-526-9551. Fax: + 7 937 528 9583. E-mail: [email protected]
SeesIt n this article, John Truhan, Fleetguard Corporation, USA describes heavy duty diesel engine tests currently being carried out at Fleetguard which aim to characterize filter performance in a more meaningful and responsible way: the way the engine sees it.
Performance tests which become industry standards are usually developed so that they may be carried out by a variety of laboratories with a reasonably high level of repeatability and in a relatively short period of time using relatively simple test stands. To achieve those characteris-
tics, compromises are made to the operating environment so that better control can be maintained. Industry-standard tests to establish filter performance characteristics such as efficiency, life, and capacity use a standard silica based dust contaminant in a hydraulic fluid. However, fil-
No. of Particles a 15 microns I ml WJU
350 300 250 2QO
Cellulose Full Flow Only 15 micron Efficiency = 66.7 Figure 1:The relationship duty diesel engine.The
Microglass Full Flow w Bypass 95%
between piston ring wear rate and lube oil cleanliness for a 1988 lab measured efficiencies for 15 micron particles are listed.
.
vintage
heavy
ters which have seen service on-engine, particularly lube and fuel filters, predominantly trap a complex mixture of organic contaminants in addition to inorganic contaminants, only a small part of which is silica dust. In most cases, the amount of organic contaminant is approximately 90% or more of the total contaminant trapped. The standard dust based tests will not predict how the filters will behave onengine, and more importantly, what effect the filters will have on engine durability and service requirements. As filter designers, we must balance the tradeoff between filter efficiency and life. Achieving high efficiency is not a challenge, but high efficiency filters in service do not live long before they become excessively plugged. Since customers are demanding longer service intervals as a way of reducing operating costs, the challenge for the filter designer is to provide the necessary protection to the engine from wear over longer servicing periods. This tradeoff is impossible to determine using current standardized lab tests, and determining this tradeoff by field testing is both impractical and expensive.
B
l
l
l .
.
.
. .
.
.
. .
. .‘.:$.: ‘7 2 52
a
t% -0
vintage
engines.The
newer
engines
PI 2 -. 2
l B 8 3 4 7 E; 8 l ‘-u 2 CD z E;
. .
. .
.
ENGINE-MEASURED FILTER EFFICIENCY
Figure 2:The sensitlvity of the piston ring to oil cleanliness for various are more tolerant of particulate contamination than the older ones.
.
.
.
* .
.
0 1
Filter efficiency is related to the filter’s ability to remove particulate contamination from a fluid resulting in lower engine wear. Surface (or thin) layer activation (SLA) has been used in our laboratory to measure the effect of fluid condition on engine wear since 1988. Critical engine parts such as piston rings, cylinder liners, and valve train parts are made radioactive by bombardment in a particle accelerator. The isotopes
. .
.
. *
.
*
.
* .
.
.
. .
.
.
I .
. .
.
.
. .
I
.
. .
.
.
.
. .
.
.
I .
. .
.
*
l .
.
.
.
.
.
.
. .
.
.
.
l
. l
.
.
. ,
. .
l
I
. .
. .
. .
r
No. of Particles . 5 microns / ml
Erasion Rate ~Gh~nge
3500 1
1i
/ h) O.E t
ra
i
1
None
Cellulose
5 micron Efficiency =O
Stratified Porosity
55%
88%
Figure 3:The relationship between injector erosion rates and fuel cleanliness for different levels of filtration.The lab measured efficiencies are listed.
0.7 1.
0 -.
Figure
_
4:
-.
Erosion Rate (% Change / h ) 1
1 2 3 No. of Particles / ml > 5 micron (thousands) . . .
. .
-.
.
_
.
.
.a..
4
. .
1ne senslervlry or uqeoror erosion Cares 10 ruei cieaniiness.
that are produced depend on the particles being used for bombardment and the target material. For example, when deuterons are used, to bombard a chromium plated piston ring, the Cr transmutes to Mn54, a gamma ray emitting isotope with a half life of about 300 days. Each of the isotopes emit gamma rays with energies specific to the isotope so that if a gamma ray spectrum is measured, multiple parts can be tracked simulta-
neously. The activity profile for each part is determined by removing material from a similarly irradiated part in successive layers measuring the surface activity at each increment. The activity profiles serve as calibration curves relating the loss of activity in the part due to wear to the depth of wear in the part. The irradiated parts are installed in the engine and a gamma ray detector is placed external to the engine as close as practical so that the loss of
activity due to wear can be measured directly. Although this method has been used primarily to measure wear in the lubricating system, we have applied the technique to measure wear and erosion in the fuel system as well. Examples of wear related to fluid cleanliness for both systems follow. Figure 1 shows the relationship between piston ring wear rate and oil cleanliness as measured by a screen obstruction techni-
que. The standard dust efficiencies for both full flow filters are given below. The data was collected from a 1986 vintage engine which shows a greater sensitivity to oil cleanliness than newer engines. In this case, there is a clear tie between filter efficiency, oil cleanliness and ring wear. This tie becomes less apparent for the newer engines. Figure 2 shows the relationship between ring wear and oil cleanliness as measured by the concentration of particles greater than 15 microns. The data shown in Figure 1 was taken from the curve representing the 1986 engine. The newer engines have both a lower overall ring wear rate and less sensitivity to contamination until the particle concentration becomes exceedingly high. This concentration was achieved in the test cell by the deliberate addition of dust into the sump and far exceeds concentration levels in normally filtered systems. This tolerance to contamination is in line with current field experience with engine life. Ten years ago, the typical life to rebuild was about 800K kilometers, but today, 1600K kilometers is becoming common for heavy duty onhighway use. Building excessive efficiency into these more durable engines, particularly at the expense of filter life, would not achieve the longer service intervals nor would the engines live noticeably longer. A similar argument can be made for the fuel system. Higher efficiency filtration is more typical here due to the closer tolerances in the fuel injectors and the higher operating pressures that they experience, but there is still a tradeoff between efficiency and life. Figure 3 shows the relationship between fuel cleanliness and erosion rate in the injector with the standard efficiencies given along the bottom of the figure. As was the case for the lube system, the higher efficiency filter reduced both the particle concentration and the erosion rate as measured by SLA. Figure 4 shows the
Differential Pressure (kPa)
150.0 100.0 50.0 0.0 0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
Running Time (h)
i Figure
I:The
pressure
differential
sensitivity of the injector to fuel cleanliness similar to Figure 2. As in that case, if the cleanliness can be kept at an acceptable level, erosion rates are low and installing a higher efficiency filter would buy little in extension of part life. ENGINE-MEASURED FILTER LIFE The effective life of a filter in service is defined as the time it takes to reach a predetermined pressure differential across it. Higher flow restrictions present a substantial parasitic pumping loss and, in the case of the lubricating system, prevent oiling from occurring in critical areas. In the laboratory, dust is used as the test contaminant to plug the filter. In actual service, however, dust constitutes less than 1% of what a filter takes out in the lube or fuel system for on-highway applications. On engine, a lube filter takes out sludge, resins, combustion byproducts, and, in severe service, oxidation products. Microscopic examination of a filter removed from the engine shows a tar-like substance coating the fibres compared to a dust test in which the fibres act essen-
buildup
across
various
filters
are shown
tially as strainers. Thus the mechanisms of filter plugging are different between the lab and engine test. Attempts were made in the late 1950s to isolate the organic contaminants from the oil and use them in a laboratory test to plug the filter the same way. This contaminant was termed
-..
tiefative
during
the MilFPT
SOFTC-1, but was later discarded in favour of the synthetic SOFTC9A currently in use. It proved impossible to obtain consistent contaminant to carry out long term tests. This attempt was duplicated in our laboratories recently with similar results. It was determined that the only
way to duplicate what was happening in the engine was to run controlled engine tests. Fleetguard has adapted the Cummins Ml1 High Soot Test (MllHST) to study filter plugging and to determine relative lives among the various lube filter products. The Ml 1HST has become an oil industry standard test to measure a lube oil’s ability to disperse the soot, sludge, and resins that buildup with use and measure the amount of wear that the soot can cause. The test is run with retarded timing and overfueling conditions to produce soot and sludge at an accelerated rate. Fleetguard has adapted the first half of the MilHST, by fixing the oil to a special formulation with poor dispersancy and varying the filter for testing. We are currently referring to this as the Ml1 Filter Plugging Test (MllFPT). This test will take a new oil and filter to plugging in 72 hours or less without changing the basic plugging mechanism. Figure 5 shows the pressure differential buildup with time for several different filters running the MllFPT cycle. An arbitrary B.... * . . . . . . I . . * , . . . . . . .
.._
Life
8
.
.
.
.
l . . . * . . . .
2 2 S s
l ii? zi 3 z 7 G 8 l 9
with
.
% s -I
. .
. .
9
7’
. *
.
. .
P
are normalized
.
*
.
. .
.
.
E
lives
.
.
.
., .
. .
.
2
by the MllFPT.The
. *
.
. .
.
.
Ei
as measured
. .
.
l .
.
.
‘7
filters
. .
,
, .
.
.
.
Figure &The relative lives for different respect to the reference filter.
. . *
.
l .
. .
.:.:_?.:.:
Reference
*
. .
.
. . .
.
800 11 Dust Capacity
1
300 200 100 nw
Figure 7:The on engine.
relationship
Refsrenccs between
terminal differential pressure across the full flow section of the filter is set at 207 kPa (30 psi), so that the time to reach the terminal restriction can be defined as the filter life. Since this test is an arbitrary cycle, we more frequently refer to a relative life which is normalized against the same reference filter used in the MIIHST. In this manner, comparisons can be made on-engine among various current and new products. Figure 6 shows the relative life for a variety of new products designed for extended service intervals. The higher capacity new products can result in a filter life approximatelydouble that of current products. These comparisons, we feel, will be a more valid way for determining the optimum service interval for those customers wishing to extend it. ENGINE-MEASURED FILTER CAPACITY As was the case for determining filter life in the laboratory, filter capacity is determined by challenging the filter with the
lab measured
bF3000SP dust
capacity
and engine
standard test dust and capacity is defined as the amount of dust the filter can hold at its terminal restriction. Again, the MllFPT can be employed to determine how much of the real world contaminant the filter can hold at the same differential pressure. Figure 7 shows a comparison between lab-measured and engine measured dust capacity for several of the previous filters. Since the material buildup rate was found to be linear, all of the capacities listed here have been corrected to the same pressure differential. It is evident that the dust capacity measured in the laboratory is a poor predictor of the actual amount of sludge that can be retained. At least part of the reason for this is that the dust tends to build up as a cake on the outside of the filter material and full use is not made of the depth of the material. Since the sludge coats the fibre, the effective fiber diameter increases and the mean pore size decreases and the full use is made of the material’s capacity.
LFQOOO
LFQOOI measured
capacity.The
lab tests
SUMMARY As customers are demanding longer servicing intervals for their engines as a way of reducing operating costs and increasing their utilization rate, the challenge for the filter designer is to provide sufficient protection for the engine hardware without sacrificing engine life. A high efficiency filter is not difficult to manufacture, but a high efficiency filter that will last a long time is a problem. Standard laboratory based filter performance testing is not a direct predictor of performance in the actual engine environments. Since it is impractical to develop this data base solely from field testing, we are left with engine testing under controlled operating conditions such as would be obtained in a test cell. As this study implies, far more attention has been paid to the lubricating system although some work has gone on in the fuel system. Additional test development needs to be carried out in the other fluid systems to provide meaningful engine tests. The standard performance characteristics are
do not predict
what
will happen
efficiency, capacity and life. We have developed surrogate engine tests for these common laboratory tests to describe filter performance in engine terms. The tradeoffs between efficiency and capacity can be determined and designers of new filtration products have a better method to balance the product for its actual operating environment. A substantial additional benefit is a better communication of filter performance to the customer of our products and a more reasonable way of determining what the customer’s requirements are for various applications. ACKNOWLEDGEMENT This paper is based on a presentation given at the First International Conference on Filtration in Transportation, Stuttgart, Germany. November 4-5, 1997. Filter Media Consulting, Inc., USA. Fleetguard Corporation Cookeville, TN 38506, USA. Tel: f 1 931-526-9551. Fax: + 7 937 528 9583. E-mail: [email protected]