Verification Measurement of Laboratory Test Equipment for Evaluation of Technical Properties of Automotive Oil Filters

Abstract

By simulating the operating conditions, it is possible to verify and evaluate the technical properties of motor vehicle oil filters and the functionality of the designed equipment. Contaminated engine oil from operation was used with MANN W950/26 oil filter and a CNH Industrial 2992242 oil filter in the test circuit. Before use, the level of engine oil contamination in the test circuit was determined by evaluating the physicochemical properties. The laboratory test equipment also allows monitoring the technical life of oil filters, with variously contaminated engine oil, with the possibility of extending engine oil change service intervals depending on changes in the physicochemical properties of engine oil and filter efficiency. These laboratory tests can be performed in parallel in two hydraulic circuits, which can significantly reduce the testing time of the filter capabilities of oil filters, without the risk of engine damage, provided that the tests were performed under operating conditions. The results of the evaluation of the filtration capacity of oil filters can be used in the design of new filter materials, but also with a suitably determined methodology of oil filter replacement and engine oil change interval, it is possible to extend replacement intervals, which has a significant benefit not only from an economic but also ecological point of view. The result of the measurements is the confirmation of the functionality of the device with the possibility of simulating the operating conditions, at different degrees of oil contamination, at different operating temperatures and using different oil filters.

1. Introduction

We consider working fluids to be an important indicator of the correct operation of each hydraulic mechanism, while they have a fundamental influence on their elements. However, it is necessary to have knowledge and overview of their physical–chemical properties, which have a significant impact on the technical life of the components of the hydraulic circuit [1,2]. The authors [3,4,5] deal with the evaluation of working fluids and subsequent physical analysis. In the case of hydraulic circuits, the most accurate engineering production of its individual elements is important, where it is important to monitor the accuracy of CNC (computer numerical control) machine tools when using new methods in development and also planning future products. Equally important is the multicriterial diagnostics of CNC machines [6,7]. In terms of the choice of base oils and suitable additives that affect the properties and perfect lubrication, engine oils are among the most demanding working fluids in vehicles. Practice shows that the most serious source of machine failure is oil pollution [8,9]. The greatest progress in the theory of filtration was probably made by prof. Fitch of Oklahoma State University, author of ISO 16889: 2008 Hydraulic fluid power-Filters-Multi-pass method for evaluating filtration performance of a filter element, filter test to evaluate filtration capacity and capture capacity. Filtration ability is the ability of a filter to capture particles of a certain size. It is one of the most important criteria for filter selection. In general, a finer filter maintains a lower level of contamination, which significantly reduces wear on system components and increases service life.

In one of the standardized tests, foreign particles of different sizes are added to the test liquid. This mixture of foreign particles is aimed at the actual use of the filter on the mixture of particles in the test procedure, and still may not provide an accurate comparison of different types of filters, as only a weight comparison will be made. This equipment and test procedures do not offer an immediate indication of the filtration efficiency and do not offer plotting of the curve of efficient, and time use without using the averaging procedure [10].

The functionality of oils suffers when contaminated with particles. Filtration can play a key role in ensuring that hydraulic and lubricating systems are running effectively [11]. By means of the given proposed device, it is possible to test oil filters with different filtration capacities during simultaneous testing in two separate hydraulic circuits. To ensure that the filter is able to remove the required particle size, it has to be subjected to tests that can be destructive or nondestructive in nature. The pressure drop and particle size distribution form important aspects of the test results [12]. Additionally, according to [13], the physicochemical data corresponding to the interactions between the filter medium and the filtered liquid are of major importance to allow identifying the right filtration system.

Efficiency of the filter is the key, and only, factor for its installation. Be that as it may, brief scientific survey and practical experience show that the filter’s efficiency is influenced by all of the liquid, particle, and flow characteristics [14]. The device allows the simulation of operating conditions using oils with different degrees of contamination [15]. Operational measurements were performed on the Iveco Crossway intercity bus, which is supplied with a Man W950/26 oil filter, while contaminated engine oil together with the engine filter was removed from the bus after driving 80,744 km.

2. Materials and Methods

When designing the laboratory test equipment to evaluate the efficiency of engine oil filtration, we relied on the technical characteristics of oil filters, hydraulic pump, the used hydraulic elements in the test hydraulic circuit, and internal combustion engine characteristics and calculations [15,16,17].

The laboratory test equipment was designed for the evaluation of filters of various types with the possibility of simultaneously comparing the properties and operating capabilities of the original filter or a filter from another manufacturer—additionally, with the ability to simulate different operating conditions in terms of temperature, contamination, pressure, and oil type. The level and type of contamination is monitored by ferrography. At present, samples of engine oil used in buses in are monitored directly in operation, and the oil and the state of oil contamination and degradation are evaluated every 10,000 km. The proposed laboratory equipment has a Hydac EVS 3100 sensor, which, except for the standard temperature, pressure, and flow sensors (

Table 1. Basic data of flow, pressure, and temperature sensors [15].

Hydac Temperature Sensor ETS 4144-A-006-000
Parameter	Unit	Value
Protection class acc. to DIN 43650	IP	65
Supply voltage	V	8 ÷ 32
Output signal, permitted load resistance	mA	4 ÷ 20
Measuring range Accuracy of measuring	°C %	−25 ÷ 100 ≤±0.4
Response time acc. to DIN EN 60751	s	4
Hydac flow sensor EVS 3104-A-0060-000
Output signal, permitted load resistance	mA	4 ÷ 20
Measured range (flow)	dm3/min	6 ÷ 60
Measuring range (pressure) Accuracy of measuring	MPa %	40 ≤2
Supply voltage	V DC	10 ÷ 32
Fluid temperature range	°C	−20 ÷ 90
Operating temperature range	°C	−20 ÷ 70
Hydac pressure sensor HDA 4744-A-0250-000
Protection class acc. to DIN 43650	IP	65
Measuring range (pressure)	MPa	25
Accuracy of measuring	%	≤±0.25
Supply voltage	V DC	12 ÷ 30
Output signal, permitted load resistance	mA	4 ÷ 20

), can also be extended with HBL 1400 and CS 1000 sensors. HBL 1400 is a multifunctional sensor for online monitoring and online recording of standard and biological oils conditions in stationary and mobile applications. Online measurement provides data in terms of electrical parameters of the fluid, dielectric constant, relative conductivity, water saturation level. The CS 1000 sensor is a stationary particle sensor for continuous recording of the contamination of solid particles in fluids. The output of the cleanliness class can be selected to be in accordance with either ISO, SAE, or NAS. In addition, the laboratory test equipment is adapted for simple oil sampling for other diagnostic methods. The advantages of laboratory test equipment are, except for knowledge of the properties of filters in different conditions, also provide an economic benefit with the possibility of choosing a cheaper and at the same time reliable filtration equipment and extending the exchange interval. The hydraulic scheme (Figure 1) of the proposed device consists of two hydraulic circuits, where circuit A represents the reference measuring circuit, circuit B is the test circuit, and circuit C is the control circuit of the measuring devices [15].

The measurement of quantities in the hydraulic system is performed by means of combined sensors, which enable the simultaneous measurement of pressure, temperature, and fluid flow at different types of oil filters and the degree of contamination of engine oil simultaneously in circuit A and B (Figure 2).

The laboratory test equipment operates with an expanded measurement uncertainty, U, which is expressed as the standard measurement uncertainty multiplied by the overlap coefficient k = 2, which, under normal distribution, corresponds to a probability of coverage of approximately 95% and was set according to MSA 0104-97, respectively EA-4/02 M:2013).

Iveco Crossway intercity buses are supplied by the manufacturer with a MANN W950/26 oil filter. The second alternative oil filter tested was the CNH Industrial 2992242 filter. The technical specification of the filters is given in

Table 2. Parameters of oil filters.

MANN W950/26
Parameter	Unit	Value
Outer diameter	mm	93
Internal diameter 1	mm	62
Internal diameter 2	mm	71
Hight	mm	170
Nominal flow	dm3/min	60
Permissible operating pressure	MPa	1.4
CNH Industrial 2992242
Outer diameter	mm	93.7
Internal diameter 1	mm	63
Internal diameter 2	mm	72
Hight	mm	168
Nominal flow	dm3/min	60
Permissible operating pressure	MPa	1.4

. The bus used was an oil whose technical specification is listed in

Table 3. Technical specification of engine oil.

Manufacturer	Petronas
Type	Urania FE LS
Viscosity grade	5 W-30
API	CF
ACEA	E4/E6/E7
Density at 15 °C	855 kg/m3
Dynamic viscosity at −30 °C	6100 mPa.s
Kinematic viscosity at 100 °C	11.5 mm2/s1

.

The measurement of pressure, flow, and temperature in the hydraulic circuit of the device can be split into measurements of the main and secondary measured quantities. The sensors are located in front of and behind the oil filters. To measure the required quantities, measuring devices are used to set and control parameters and diagnose faults in the hydraulic circuit, where one group are measuring devices displaying the instantaneous value of the measured quantity (flow meter, pressure gauge, and thermometer) and the other group are measuring devices for recording the measured value, displayed on the timeline.

To verify the functionality of the device, the conditions of the verification measurement were determined, where we tested a reference oil sample, an original oil filter, and an alternative oil filter in the reference measuring circuit A. In test circuit B, we applied contaminated oil, as well as the original and alternative oil filter. Contaminated engine oil with an oil filter was taken from the new Iveco Crossway intercity bus, which had a mileage of 80,744 km.

Specified measurement conditions:

• measurement of pressure and flow characteristics of selected types of oil filters with uncontaminated and contaminated engine oil at a temperature of 30 °C;
• the hydraulic pump will not be loaded with pressure from the throttle valve during the test; the working pressure range in the reference and test circuit will be in the range of 0.2 to 0.5 MPa;
• comparison and evaluation of measured values of pressure and flow characteristics of oil filter MANN W950/26 and oil filter CNH Industrial 2992242;
• the laboratory equipment measurement setting shall not change during the test, the hydraulic pump speed shall correspond to the nominal engine speed under operating conditions, and the speed value shall not change after adjustment Δn = ± 1% or 10 rpm, whichever is greater.

3. Results

Verifying the measurement of the device for evaluating engine oil filtration in the length of 60 s in the interval of 0.02 s, we demonstrated the functionality of the proposed device and the ability to measure the required parameters in individual hydraulic measuring circuits, while from one measurement we recorded 3000 measured values for each measured quantity. For this reason, the measured parameters were transformed into graphs and the average values of main parameters are presented the

Table 4. Results from the laboratory test equipment measurement.

	MANN W950/26		CNH Industrial 2992242
Parameter	Uncontamined	Contamined	Uncontamined	Contamined
	Oil	Oil	Oil	Oil
Average Flow Gradient, ΔQ (dm3·min−1)	1.39	1.12	1.41	1.14
Average Pressure Drop, Δp (MPa)	0.22	0.08	0.21	0.05

. The recording of the values was started at least 10 min after the start of the device due to the mixing of the oils and reaching the set temperature. It is possible to see the stable values of the monitored parameters from the graphs, the time of 60 s is for verification measurements proved to be sufficient. The measurement lasts a longer period of time and because there were no changes, only the time period 60 s is shown on the graph. For the indication of a clogged filter with contamination particles, every filter should be equipped with a filter contamination indicator. The degree of filter clogging is assessed by indirect control of the pressure drop on the increasing hydraulic resistance represented by the filter element. Different designs are available. In principle, there are two options for measuring pressures. In the first case, it is a measurement of the pressure drop between the pressure on the side of the liquid inlet to the filter and the atmospheric pressure, and in the other case, the pressure drop is measured at the inlet of the liquid to the filter and the outlet of the liquid from the filter. For filters where the outlet of the fluid is into the tank, they used an indicator where the inlet pressure is compared with the atmospheric pressure. For other filters, such as pressure filters or filters built into the lines, the indicator measures the pressure drop on the filter. Figure 3 shows the oil pressure and Figure 4 shows the oil flow in front of the MANN W950/26 oil filter and behind the filter in question at an oil temperature of 30 °C in the reference measuring circuit A, in which the uncontaminated Urania FE LS engine oil has been applied.

Figure 5 shows the oil pressure and Figure 6 shows the oil flow in front of the alternative oil filter CNH Industrial 2992242 and behind the filter at an oil temperature of 30 °C in the reference measuring circuit A, in which uncontaminated Urania FE LS engine oil was applied.

The recorded values of pressure and flow in reference circuit A, when using uncontaminated oil at an operating temperature of 30 °C with the measurement of the values before and after the used oil filters, are not significantly different.

We used contaminated engine oil from the intercity bus in test circuit B and measured the pressure and flow with the original MANN W950/26 oil filter and the alternative CNH Industrial 2992242 oil filter (Figure 7, Figure 8, Figure 9 and Figure 10).

Figure 10 shows the small change in the plot of flow. In this case, it is a cheaper replacement of the monitored filters, whose filtration properties may have lower-quality properties than the original one; a small increase in flow may have occurred due to partial clogging of the filter element. During the continuous measurement, there was no further increase in the flow rate (Figure 10).

Figure 11 shows the resulting uncontaminated oil pressure values measured on the original MANN W95/26 oil filter and the CNH Industrial 2992242 alternative oil filter at an operating oil temperature of 30 °C in the reference circuit.

Figure 12 shows the resulting contaminated oil pressure values measured on the original MANN W950/26 oil filter and the CNH Industrial 2992242 alternative oil filter at an operating oil temperature of 30 °C in test circuit B.

During the verification measurement on the laboratory test equipment, 3000 values were obtained by the digital recording unit recorded from each value (pressure and flow rate) at the input and output of filters, which were processed for similar clarity into average values of main evaluation parameters (pressure drop and flow gradient), as shown in Table 4. During the laboratory test with new oil and with filter Mann W950/26, a value of average pressure drop Δp = 0.22 MPa and a value of average flow gradient ΔQ = 1.39 dm³ min⁻¹ were observed. With the CNH filter 2992242, the pressure drop Δp = 0.21 MPa and the flow gradient ΔQ = 1.41 dm³ min⁻¹ occurred. After the application of the used oil after 80,744 km, the pressure drop Δp = 0.08 MPa and the flow gradient ΔQ = 1.12 dm³ min⁻¹ occurred for the Mann W950/26 filter. The pressure drop for the CNH 2992242 filter was Δp = 0.05 MPa and the flow gradient was ΔQ = 1.14 dm³.min⁻¹. The filters did not show significant changes during the test. In this case, it is only a verification measurement; filters and oil will be evaluated in next laboratory test after obtaining more of the monitored parameters, where is also possible to change measurement conditions (contamination, pressure, operating speed) if it is necessary from the point of view of the characteristics, or type of measurements. Based on the verification measurement and the correct function of the laboratory test equipment, the test will continue with the application of more contaminated oil (more kilometres), with subsequent monitoring of changes in the physical–chemical properties and contamination of the used engine oil.

The parameters for expressing the filtration capacity are the filtration efficiency ƞ_x; the newer parameter is the filtration coefficient β_x and the degree of purity. The service life of the filter element is the time of operation of the filter element after reaching the maximum pressure drop at a viscosity of 35 mm²/s; this parameter is important because it indicates how often the element needs to be changed.

4. Discussion

It seems to be the case that no filtration theory manages to link the filtration efficiency with the media or cartridge operational conditions. However, experimental results commonly illustrate that changes in any of the characteristics of the particles (size, size distribution, shape factor distribution, electrical surface potential, hardness, concentration) and of the liquid (viscosity, pH, density, temperature, viscosity, electrical conductivity, ionic strength, surface tension, face velocity) directly impact the measured efficiency of any kind of media and, ultimately, the filters [14].

According to the authors [18,19,20,21], the basic precondition for the correct function and effective care of hydraulic fluids is a suitably chosen methodology for testing fluids with monitoring of the level of contamination of the working fluid. With an experimental set of pressure measurements with numerical simulation for engines in laboratory conditions, we reduce the time required to perform operational measurements [22]. By verification measurements and results, we demonstrated the suitability of the laboratory test equipment for testing oil filters and monitoring the effect of engine oil contamination on the filtering ability of the oiled filter, while changing the measured pressure and flow before and after oil filters. As stated [23], by analyzing lubricating oils during engine operation, it is possible to determine the probability of failure of lubrication of functional parts, determine the suitability of a given type of oil and the oil change interval, together with evaluation of technical condition of functional parts.

From all these mentioned aspects, the tribotechnical diagnostics of oils is important not only for monitoring the degradation of the oil itself, determining its current state or the intrusion of undesirable external substances. Diagnosis of the oil or oil level indicates oil contamination and contaminants, warns of possible faults, and allows faults to be prevented [18].

The construction of the laboratory test equipment was carried out based on knowledge from the design of test hydraulic equipment, which they dealt with in the work [15,16,24,25], which created a set of measuring laboratory equipment for testing hydrostatic elements and hydraulic fluids. During the test equipment, it was necessary to solve the question of the location of the oil filters in the hydraulic circuit A and B, together with the question of the service life of the oil filters. All these aspects must be harmonized to ensure the required level of engine oil contamination in the future, when testing the filterability of oil filters.

The laboratory test equipment makes it possible to evaluate the level of contaminants and the filtration efficiency of oil filters by monitoring the pressure and pressure drop, monitoring the flow and drop in flow through the inlet and outlet of the test device.

The primary reasons for needing pressure drop and particle retention information are that for a new filter medium, the pressure drop as a function of flow rate is used to give the medium permeability. Suppliers measure this using air as the fluid, and the data is helpful in their categorisation. The size of the smallest particle retained indicates it should have a lesser tendency to bleed upon first usage. Moreover, when a filter is in use, the pressure drop is a function of the flow rate through the filter and the amount of particles trapped in or on the surface. Critical for cartridge filters, for cloth-type media, it is important when assessing the likelihood to blind and the rate of cake growth [26].

Standard ISO 16889 “Hydraulic fluid power-Filters-Multi-pass method for evaluating filtration performance of a filter element” describes a multi-pass filtration performance test with continuous contaminant injection for hydraulic fluid power filter elements: a procedure for determining the contaminant capacity, particulate removal, and differential pressure characteristics. The standard is intended to provide a test procedure that yields reproducible test data for appraising the filtration performance of a hydraulic fluid power filter element. It is performed at prescribed contamination levels. The designed and measured verified laboratory test equipment can more accurately simulate the operating conditions, parameters of which were obtained from measurements in practice. It is possible to simultaneously simulate and monitor two identical or different types of filters under the same or different operating conditions (temperature, pressure, contamination level, different type of oils) based on the main parameters (inlet and outlet of pressure, pressure differences, flow) and additional parameters, analyses to which the laboratory stand is adapted (oil aging, oil contamination, viscosity, acid number, and water content). The literature also mentions the filter testing device US 3478601 A, for evaluating the efficiency of a filter insert, which evaluates the ability based on the gravimetric method, i.e., comparing the weight of the filter before and after the test. In designed laboratory equipment, it is possible too.

5. Conclusions

The laboratory test equipment allows to evaluate the use of the oil filter, its filtering ability when changing the fluid flow, and pressure change in the hydraulic circuit of the engine, with the possibility of extending engine oil change service intervals depending on changes in the physical–chemical properties of the engine oil and filter efficiency. The author [27] focuses on increasing the engine oil change interval in his work. Pollution mainly affects hydraulic fluids, which accelerates their degradation processes and affects their physical–chemical properties during operation [22,24]. According to the author [3,8], the properties of fluids and lubricants are also affected by the conditions under which the fluid or lubricant is used, as well as the evaluation of hydraulic fluids due to operational load and subsequent analysis of contaminants. According to the author [4], contamination of the hydraulic fluid results in accelerated wear of the hydraulic elements of the hydraulic system as well as corrosion of steel surfaces, oxidation of the oil, and a change in its physical and chemical properties.

The universality of laboratory testing equipment is that it is possible to test hydrostatic transducers and hydraulic fluids according to ASTM D 288200, a test method for indicating the wear characteristics of petroleum and non-petroleum hydraulic fluids in constant volume pumps. The results from the verification measurement of the functionality of the test equipment will be used in creating database files and simulation processes, and can be used as evaluation indicators for the development and production of oil filters, where we will also evaluate the efficiency of oil filters or change the volume of contaminants in test circuit B, according to conditions.

The purpose of the designed device is to verify the possibility of changing the extension of the service interval of engine oil change depending on the filtering ability of oil filters to capture contaminants and the stability of physical–chemical properties of engine oil. The extension of engine oil change intervals has a significant benefit not only from an economic point of view, but also from an ecological point of view, thus reducing the environmental impact of mobile energy products.