Method and Apparatus for Monitoring Lubricating Oil Condition

Abstract

A system for monitoring the condition of lubricating oil from a piece of equipment comprises a lubricating oil sample reservoir 19, a solvent fluid reservoir 78 connected to a solvent fluid flow path 80, a microfluidic device comprising a diffusion extractor; wherein the microfluidic device comprises a first microfluidic channel 52 in fluid communication with the oil sample flow path and a second microchannel 54 in fluid communication with the solvent fluid flow path; a control system configured to pass luboil and / or solvent fluid through the microfluidic device under stable flow conditions; and a detector 98 for measuring a characteristic of the fluid flowing through the microfluidic device. The detector may measure Total Acid Number (TAN), Total Base Number (TBN), insoluble content, viscosity, iron content, oil cleanliness (particle count) or water content of the oil sample. The microfluidic device may comprise a diffusion channel (figure 2) configured to transfer an analyte present in the lubricating oil sample into the solvent in the diffusion channel.

Description

The present invention relates to monitoring the performance of equipment and in particular to monitoring oil condition in equipment and / or machinery. Aspects of the invention relate to apparatus and methods to monitor the condition of lubricating oil in equipment and / or machinery and equipment. Background to the Invention Lubricating oil is a fluid substance that is used to reduce friction between moving surfaces in contact with each other. Lubricating oils are used to minimise wear between the moving surfaces. Lubrication is essential to improve the overall performance of machines, engines and tools, and equipment components. During use lubricating oils may become contaminated by debris from wear of the moving surfaces including mechanical erosion spalling, pitting, fatigue or corrosion of the component or its surfaces. Lubricating oils over time may become degraded by chemical or water infiltration or the chemical composition of the oil may change due to conditions such as heat, entrained air, incompatible gases, moisture, internal or external contamination, process constituents, radiation and inadvertent mixing of a different fluid. To maintain the performance and efficiency of machinery or engines and avoid damage, the quality of the lubricating oil must be monitored for contamination, degradation, and wear. The detection of high levels of wear particles or degradation of lubricating oil conditions may give advance warning of possible machinery malfunction, allowing early remedial action to be taken. Lubricating oil can be analysed using different techniques such as elemental measurements, particle counting and chromatography. These analysis methods give an indication of the health of the machinery and its components. However, these methods can be prohibitively complex, slow and cumbersome for a wide range of oil condition monitoring applications. Summary of the Invention It is an object of an aspect of the present invention to obviate or at least mitigate the disadvantages of prior art oil condition monitoring apparatus and methods. It is an object of an aspect of the present invention to provide a robust, reliable and compact apparatus suitable for monitoring the health and condition of a piece of machinery by analysing the products of wear, degradation and contamination in lubricating oil. It is another object of an aspect of the present invention to provide a reliable and portable apparatus for monitoring the condition of lubricating oil condition in equipment and / or machinery on site. It is a further object of an aspect of the present invention to provide a method and system for stabilising flow of co-flowing fluids through the apparatus to improve the accuracy of measuring and / or monitoring the condition of lubricating oil condition. It is another object of the invention to provide a portable system and method of use for detecting analytes and / or parameters of analytes in lubricating oil which may be indicative of machinery wear or corrosion and allow high-throughput oil analysis. Further aims of the invention will become apparent from the following description. According to a first aspect of the invention, there is provided a system for monitoring the condition of lubricating oil from a piece of equipment comprising: a lubricating oil sample reservoir connected to an oil sample flow path; a solvent fluid reservoir connected to a solvent fluid flow path; a microfluidic device comprising a diffusion extractor; wherein the microfluidic device comprises a first microchannel in fluid communication with the oil sample flow path and a second microchannel in fluid communication with the solvent fluid flow path; a control system configured to pass lubricating oil and / or solvent fluid through the microfluidic device under stable flow conditions; and a detector device configured to detect or measure at least one characteristic of the fluid flowing through the microfluidic device. By passing the lubricating oil and / or solvent fluid through the microfluidic device under stable flow conditions accurate, repeatable and reproducible measurements may be taken, or captured in a deterministic way. The detector device may be configured to detect or measure at least one analyte in the lubricating oil sample. The detector device may be configured to detect the presence, absence or measure a level of analyte such as naphthenic acid, sulphuric acid, components conferring an alkaline reserve and detergency e.g., sulphonates, phenates, salicylates etc., and / or organic solids in the lubricating oil sample. The detector device may be configured to detect the presence, absence or measure a level of analyte such as naphthenic acid, sulphuric acid, components conferring an alkaline reserve and detergency e.g., sulphonates, phenates, salicylates etc., and / or organic solids extracted from the lubricating oil sample into the solvent fluid. The detector device may be configured to measure changes in solvent fluid. The detector device may comprise at least one sensor. The at least one sensor may be selected from the group comprising a spectrometer, camera, Charge Coupled Device (CCD), Complementary Metal Oxide Semi-conductors (CMOS) and / or another photosensitive device. The at least one sensor may be configured to sense, measure and / or record a spectrum from the at least one analyte and / or a component of the lubricating oil. The at least one sensor may be configured to sense, measure and / or record an absorbance spectrum from the at least one analyte and / or a component of the lubricating oil. The detector device may be configured to measure at least one background and / or dark spectra of the solvent fluid. The detector device may be configured to measure at least one transmission spectrum of the solvent fluid. The detector device may be configured to measure at least one transmission spectrum of the oil sample fluid. The detector device may be configured to measure at least one transmission spectrum of the solvent with diffused analytes or components from the oil sample fluid. The at least one sensor may be configured to detect and / or measure UV-absorption. The detector device may be configured to detect analyte by measuring a difference in UV-Vis and IR Absorption. The detector device may be configured to detect or measure a level of analyte to determine Total Acid Number (TAN), Total Base Number (TBN), insolubles content, viscosity, iron content and / or water content of the oil sample. The presence, absence or measurement at a threshold level may be indicative of the condition or health of the piece of machinery. The detection of the presence, absence or measurement level of at least one other component of the oil sample may determine the presence, absence or measurement level of analyte in the lubricating oil. The detector device may be configured to detect the presence and / or measure the modal properties of at least one analyte or at least one component in the sample. Analysis of the modal properties of the at least one analyte or at least one component may be indicative of the condition of the machinery lubricating oil. The detector device may be located in, on, above, below or adjacent to the first and / or second microchannel. The microfluidic device may be a microfluidic chip. The diffusion extractor may be a H-cell or a H-cell-filter. The microfluidic device may comprise a first fluid inlet connected to the first microchannel in fluid communication with the oil sample flow path. The microfluidic device may comprise a second fluid inlet connected to the second microchannel in fluid communication with the solvent flow path. The microfluidic device may comprise a diffusion channel. The first fluid inlet, first microchannel, second fluid inlet, second microchannel may be in fluid communication with the diffusion channel. The microfluidic device may comprise a first outlet and a second outlet. The first outlet and / or the second outlet may be in fluid communication with the diffusion channel. The first and second inlets, diffusion channel and first and second outlet may have a generally H-shaped geometry or profile. The first outlet and / or second outlets may be in fluid communication with a waste reservoir. The first outlet may be in fluid communication with an oil sample waste reservoir. The second outlet may be in fluid communication with a solvent waste reservoir. The diffusion channel may be configured to diffuse, pass, or transfer at least one analyte or component present in the lubricating oil sample into the solvent in the diffusion channel. The first and / or second microchannel may comprise at least one observation well or interrogation site. The system may comprise a light source. The light source may be selected to provide light in the UV, VIS and / or IR range. The at least one observation well or interrogation site may be located between a light source and the detector device. The light source and detector may be located at the opposing sides of the at least one observation site. The light source and detector may be positioned such that light passes from the light source through the observation site and onto the detector during use. The oil sample flow path and the solvent fluid flow path may be two or more independent flow circuits. The oil sample flow path may be an oil sample flow circuit. The solvent fluid flow path may be a solvent fluid flow circuit. The at least one control unit may be configured to control the flow of oil sample from the oil sample reservoir to and / or through the microfluidic system. The at least one oil sample flow path may be configured to control the stable flow of oil sample to and / or through the microfluidic system. The at least one control unit may be configured to control the flow of solvent to and / or through the microfluidic system. The at least one solvent flow path may be configured to control the stable flow of solvent from the solvent reservoir to and / or through the microfluidic system. The oil sample flow path may comprise at least one-pump. The at least one pump may be a pneumatic pump. The at least one pump may be an air pump. The at least one pump may be an electric pump. The at least one pump may be a piezoelectric pump. The at least one pump may be configured to control the flow rate of the oil sample through the oil sample flow path. The at least one pump may be configured to control the flow rate of the oil sample to and / or through microfluidic device. The at least one pump may be configured to control the flow rate of the oil sample to and / or through diffusion extractor. The oil sample flow path may comprise at least one flow meter. The oil sample flow path may comprise two or more flowmeters. The oil sample flow path may comprise a plurality of flowmeters. The plurality of flowmeters may be arranged to control the flow rate of the oil sample in the system. The at least one flowmeter may be configured to control the flow rate of the oil sample through the oil sample flow path. The at least one flowmeter may be configured to control the flow rate of the oil sample to and / or through microfluidic device. The at least one flowmeter may be configured to control the flow rate of the oil sample to and / or through diffusion extractor. The oil sample flow path may comprise at least one valve. The oil sample flow path may comprise two or more valves. The oil sample flow path may comprise a plurality of valves. The plurality of valves may be arranged to control the flow of the oil sample in the system. The at least one valve may be configured to control the flow of the oil sample through the oil sample flow path. The at least one valve may be configured to control the flow of the oil sample to and / or through microfluidic device. The at least one valve may be configured to control the flow of the oil sample to and / or through diffusion extractor. The solvent flow path may comprise at least one pump. The at least one pump may be a pneumatic pump. The at least one pump may be an air pump. The at least one pump may be an electric pump. The at least one pump may be a piezoelectric pump. The at least one pump may be configured to control the flow rate of the solvent fluid through the solvent fluid flow path. The at least one pump may be configured to control the flow rate of the solvent fluid to and / or through microfluidic device. The at least one pump may be configured to control the flow rate of the solvent fluid to and / or through diffusion extractor. The solvent flow path may comprise at least one flow meter. The solvent flow path may comprise two or more flowmeters. The oil sample flow path may comprise a plurality of flowmeters. The plurality of flowmeters may be arranged to control the flow rate of the oil sample in the system. The at least one flowmeter may be configured to control the flow rate of the oil sample through the oil sample flow path. The at least one flowmeter may be configured to control the flow rate of the oil sample to and / or through microfluidic device. The at least one flowmeter may be configured to control the flow rate of the oil sample to and / or through diffusion extractor. The solvent flow path may comprise at least one valve. The solvent flow path may comprise two or more valves. The solvent flow path may comprise a plurality of valves. The plurality of valves may be arranged to control the flow the oil sample in the system. The plurality of valves may be arranged to control the stability of flow the oil sample in the system. The at least one valve may be configured to control the flow rate of the solvent fluid through the solvent fluid flow path. The at least one valve may be configured to control the flow rate of the solvent fluid to and / or through microfluidic device. The at least one valve may be configured to control the flow rate of the solvent fluid to and / or through diffusion extractor. The solvent fluid may be cyclohexane, isopropyl alcohol or other organic solvent. The solvent fluid may be an extraction solvent fluid. The selection of the extraction solvent may be designed to mitigate or minimise compounds (solute), e.g., organic solids like insolubles or soot held in suspension to come out of the solution and be deposited (drop out) in the microfluidic device. The lubricating oil may be a mineral oil. The lubricating oil may be a semi-synthetic oil. The lubricating oil may be a synthetic oil. The system may be a portable system. The system may be designed for onsite measurements. According to a second aspect of the invention, there is provided a method of monitoring the condition of lubricating oil comprising providing a microfluidic system comprising: a lubricating oil sample reservoir connected to an oil sample flow path; a solvent fluid reservoir connected to a solvent fluid flow path; a microfluidic device comprising a first microchannel in fluid communication with the oil sample flow path and a second microchannel in fluid communication with the solvent fluid flow path; a control system; and a detector device; passing lubricating oil and / or solvent fluid through the microfluidic device under stable flow conditions; and detecting or measuring at least one characteristic of the fluid flowing through the microfluidic device. The method may comprise extracting the lubricating oil sample from a piece of equipment to be tested. The method may comprise preparing the lubricating oil sample by diluting the sample with a dilutant fluid. The method may also comprise introducing an undiluted sample of the lubricating oil. The method may comprise diluting the lubricating oil sample with dilutant fluid at a ratio of 100:1 dilutant: oil sample. The method may comprise diluting the lubricating oil sample with dilutant fluid at a ratio of 40:1 dilutant: oil sample. The method may comprise diluting the lubricating oil sample with dilutant fluid at a ratio of 20:1 dilutant: oil sample. The method may comprise diluting the lubricating oil sample with dilutant fluid at a ratio of 10:1 dilutant: oil sample. The method may comprise diluting the lubricating oil sample with dilutant fluid at a ratio of 5:1 dilutant: oil sample. The method may comprise diluting the lubricating oil sample with dilutant fluid at a ratio of 4:1 dilutant: oil sample. The method may comprise diluting the lubricating oil sample with dilutant fluid at a ratio of 3:1 dilutant: oil sample. The method may comprise diluting the lubricating oil sample with dilutant fluid at a ratio of 2:1 dilutant: oil sample. The method may comprise diluting the lubricating oil sample with dilutant fluid at a ratio of 1:1 dilutant: oil sample. The dilutant may be an organic solvent such as cyclohexane. The method may comprise storing the diluted lubricating oil sample in a reservoir. The method may comprise flushing the oil sample flow path with a solvent. The method may comprise flushing the oil sample flow path with a solvent to remove air and / or contaminants in the oil sample flow path. The method may comprise flushing the oil sample flow path with a solvent for a desired period of time. The method may comprise flushing the oil sample flow path with dilutant. The method may comprise fully or partially flushing the oil sample flow path with a solvent. The method may comprise removing air and / or contaminants from the oil sample flow path, The method may comprise priming the solvent fluid flow path. The method may comprise pumping solvent into the solvent fluid flow path at a desired flow rate. The method may comprise pumping solvent fluid into the microfluidic device only at a desired flow rate. The method may comprise pumping solvent into the solvent fluid flow path for a desired period of time. The method may comprise performing at least one spectra readings of solvent fluid flow through the microfluidic device. The method may comprise performing at least one background or dark spectra readings of solvent fluid flow through the microfluidic device. By “dark” it is meant that the light source is not activated. The method may comprise actuating a light source and performing a spectrum and / or at least one group of spectra readings of solvent fluid flow through the microfluidic device. The method may comprise pumping oil sample into the oil sample flow path at a desired flow rate. The method may comprise pumping oil sample into the oil sample flow path for a desired period of time. The method may comprise pumping oil sample into the oil sample flow path at a flow rate in the range of 1gl / min to 10Ofxl / min. The method may comprise purging the oil sample flow path with diluted oil sample. The method may comprise pumping oil sample into the oil sample flow path at a first flow rate. The method may comprise pumping solvent into the solvent fluid flow path at a second flow rate. The first flow rate may be substantially equal to the second flow rate. The first flow rate may be lower than the second flow rate. The first flow rate may be higher than the second flow rate. The method may comprise controlling and / or adjusting the first and / or second flow rates to stabilise flow of the co-flowing diluted oil sample and / or solvent through the microfluid device. The method may comprise controlling and / or adjusting the first and / or second flow rates to stabilise flow at desired flow rates of the diluted oil sample and / or solvent thorough the microfluid device. The method may comprise controlling and / or adjusting the first and / or second flow rates to pump the diluted oil sample and / or solvent through the microfluidic device as coflowing streams. The method may comprise controlling and / or adjusting the first and / or second flow rates to pass the diluted oil sample and / or solvent thorough the microfluid device as linear flow streams. The method may comprise controlling and / or adjusting the first and / or second flow rates to adjust the residence time of the diluted oil sample and / or solvent through the diffusion channel of the microfluid device. Controlling the residence time of the diluted oil sample and / or solvent thorough the diffusion channel may control the amount of components of interest diffusing across a fluid barrier from the diluted oil sample to the solvent based on the molecular weight of these components. The method may comprise performing at least one spectra readings of solvent fluid flow through the microfluidic device. The method may comprise detecting or measuring at least one extracted component from the diluted oil sample. The method may comprise measuring a spectrum and / or at least one group of spectra readings of solvent fluid comprising extracted components from the diluted oil sample. The method may comprise measuring at least one group of spectra reading of diluted oil sample in the microfluidic device. The method may comprise measuring a spectrum and / or at least one group spectra readings using an infrared light source and a spectrometer. The method may comprise pumping diluted oil sample only into the microfluidic device. The method may comprise pumping diluted oil sample into the microfluidic device at a desired flow rate. The method may comprise pumping diluted oil sample into the microfluidic device at a high flow rate. The method may comprise pumping diluted oil sample into the microfluidic device at a flow rate in the range of 1 p,l to 1OOpJ. The method may comprise pumping diluted oil sample into the oil sample fluid flow path for a desired period of time. The method may comprise taking at least one spectra readings of diluted oil sample flow through the microfluidic device. The method may comprise actuating a light source and performing at least one spectra readings of diluted oil sample flow through the microfluidic device. The method may comprise cleaning or flushing the oil sample flow path. The method may comprise cleaning or flushing the oil sample flow path by pumping solvent such as cyclohexane into and through oil sample flow path. The method may comprise a first cleaning operation where solvent such as cyclohexane is pumped into and through oil sample flow path. The solvent bypasses the microfluidic device. The method may comprise a second cleaning operation where solvent such as cyclohexane is pumped into and through the cleaned oil sample flow path and into and through the microfluidic device. The method may comprise measuring the viscosity of the at least one undiluted lubricating oil sample. The method may comprise storing the undiluted oil sample in a reservoir. The method may comprise heating the undiluted oil sample. The method may comprise heating the undiluted oil sample to a temperature of between 30°C and 50°C . The method may comprise heating the undiluted oil sample to a temperature of 40°C. The method may comprise pumping, at constant pressure, the undiluted sample from a first known location to a second known location. The method may comprise pumping, at constant pressure, the undiluted sample from the reservoir to a location of known distance to the reservoir. The method may comprise monitoring the distance travelled by the undiluted sample as a function of time. The method may comprise determining the viscosity based on the distance travelled by the undiluted sample as a function of time. The method may comprise a multi-stage process. The method may comprise sequentially passing solvent, extraction solvent and / or diluted oil to and / or through the microfluidic system. The method may comprise sequentially passing solvent, extraction solvent and / or diluted oil to and / or through the microfluidic system at known or desired flowrates. The method may comprise performing and / or capturing spectra readings of the solvent, extraction solvent and / or diluted oil passing through the microfluidic system. The method may comprise controlling the flow rate of the solvent, extraction solvent and / or diluted oil such that a sliver of diluted oil enters the extraction channel during a predetermined extraction phase. The method may comprise performing and / or capturing spectra readings of n-alkane insoluble\organic solids -free fraction and the whole oil. The method may comprise determining the presence or quantification of insoluble\organic solids by analysing the difference between the spectra readings of n-alkane insoluble\organic solids -free fraction and the whole oil. The method may comprise determining the presence or quantification of n-alkane insoluble\organic solids by analysing the difference between the spectra readings of n-alkane insoluble\organic solids -free fraction and the whole oil. Embodiments of the second aspect of the invention may include one or more features of the first aspect of the invention or its embodiments, or vice versa. According to a third aspect of the invention, there is provided a portable microfluidic system for monitoring the condition of lubricating oil from a piece of equipment comprising: a lubricating oil sample reservoir connected to an oil sample flow path; a solvent fluid reservoir connected to a solvent fluid flow path; a microfluidic device; wherein the microfluidic device comprises a first microchannel in fluid communication with the oil sample flow path and a second microchannel in fluid communication with the solvent fluid flow path; a control system configured to pass lubricating oil and / or solvent fluid through the microfluidic device under stable flow conditions; and a detector device configured to detect or measure at least one characteristic of the fluid flowing through the microfluidic device. The microfluidic device may be diffusion extractor. The microfluidic device may be a microfluidic chip. The diffusion extractor may be a H-filter. The microfluidic device may comprise a first fluid inlet connected to the first microchannel in fluid communication with the oil sample flow path. The microfluidic device may comprise a second fluid inlet connected to the second microchannel in fluid communication with the solvent flow path. The microfluidic device may comprise a diffusion channel. The first fluid inlet, first microchannel, second fluid inlet, second microchannel may be in fluid communication with the diffusion channel. The microfluidic device may comprise a first outlet and a second outlet. The first outlet and / or the second outlet may be in fluid communication with the diffusion channel. The first and second inlets, diffusion channel and first and second outlet may have a generally H-shaped geometry or profile. Embodiments of the third aspect of the invention may include one or more features of the first or second aspect of the invention or its embodiments, or vice versa. According to a fourth aspect of the invention, there is provided a portable microfluidic system for monitoring the condition of lubricating oil from a piece of equipment comprising: a lubricating oil sample reservoir connectable to a piece of equipment and a dilutant reservoir; wherein the lubricating oil sample reservoir is connected to an oil sample flow path; a solvent fluid reservoir connected to a solvent fluid flow path; a microfluidic device; wherein the microfluidic device comprises a first microchannel in fluid communication with the oil sample flow path and a second microchannel in fluid communication with the solvent fluid flow path; a control system configured to pass lubricating oil and / or solvent fluid through the microfluidic device under stable flow conditions; and a detector device configured to detect or measure at least one characteristic of the fluid flowing through the microfluidic device. Embodiments of the fourth aspect of the invention may include any of features of the first to third aspects of the invention or their embodiments, or vice versa. According to a fifth aspect of the invention, there is provided a microfluidic system for monitoring the health of a piece of machinery by analysing the condition of lubricating oil comprising: a lubricating oil sample reservoir connected to an oil sample flow path; a solvent fluid reservoir connected to a solvent fluid flow path; a microfluidic device comprising a diffusion extractor; wherein the microfluidic device comprises a first microchannel in fluid communication with the oil sample flow path and a second microchannel in fluid communication with the solvent fluid flow path; a control system configured to pass lubricating oil and / or solvent fluid through the microfluidic device under stable flow conditions; and a detector device configured to detect or measure at least one characteristic of the fluid flowing through the microfluidic device. By passing the lubricating oil and / or solvent fluid through the microfluidic device under stable flow conditions accurate, repeatable and reproducible measurements may be taken or captured. Embodiments of the fifth aspect of the invention may include any of features of the first to fourth aspects of the invention or their embodiments, or vice versa. According to a sixth aspect of the invention there is provided a microfluidic device for a microfluidic system, the microfluidic device comprising: a microfluidic device comprising a microfluidic chip; wherein the microfluidic chip comprises a first microchannel in fluid communication with a lubricating oil sample flow path and a second microchannel in fluid communication with a solvent fluid flow path. The solvent may be an extraction solvent. The solvent may be selected from the group comprising organic solvents such as cyclohexane or isopropyl alcohol. The microfluidic chip may comprise a diffusion extractor. The diffusion extractor may comprise a diffusion channel. The diffusion channel may be dimensioned to allow the at least one component or analyte to diffuse out of the oil sample into the solvent. The diffusion channel may be dimensioned to allow steady state or stable flow of oil sample and / or solvent through the diffusion channel. Embodiments of the sixth aspect of the invention may include one or more of any of features of the first to fifth aspects of the invention or their embodiments, or vice versa. According to a seventh aspect of the invention, there is provided a method of monitoring the condition of lubricating oil comprising providing a microfluidic system comprising: a lubricating oil sample reservoir connected to an oil sample flow path; a solvent fluid reservoir connected to a solvent fluid flow path; a microfluidic device comprising a first microchannel in fluid communication with the oil sample flow path and a second microchannel in fluid communication with the solvent fluid flow path; a control system; and a detector device; diluting a sample of oil sample from a piece of equipment to be tested and storing the lubricating oil sample in a lubricating oil sample reservoir; passing lubricating oil and / or solvent fluid through the microfluidic device under stable flow conditions; and detecting or measuring at least one characteristic of the fluid flowing through the microfluidic device. Embodiments of the seventh aspect of the invention may include one or more of any of features of the first to sixth aspects of the invention or their embodiments, or vice versa. Brief Description of the Drawings There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which: Figure 1 is a schematic view of a microfluidic system circuit in accordance with an embodiment of the invention; Figure 2 is an enlarged view of a microfluidic chip showing stable flow of a diluted oil sample and solvent through the chip; Figure 3 is graphical representation showing the flowrates of the diluted oil sample and solvent at various stages of operation of the system of Figure 1. Figures 4A, 4B and 4C are graphical representations of absorbance spectra for three repeated measurements respectively of an oil sample from an engine tested on the same microfluidic system. Figure 5A and 5B are graphical representations of absorbance spectra for an oil sample from an engine tested on two different microfluidic systems respectively. Figure 6A is a graphical representation of absorbance spectra for a sample of new (fresh) oil from an engine tested on a microfluidic system, and Figure 6B is a graphical representation of absorbance spectra for a sample of used oil from an engine tested on the same microfluidic system. Figure 7 is graphical representation of absorbance spectra for a diluted whole oil sample from an engine and a solvent extract with target components extracted as obtained from the same microfluidic system. Detailed Description Referring firstly to Figure 1, there is shown a microfluidic system 10 for monitoring the condition of lubricating oil. The microfluidic system controls the flow rate of two co-flowing liquids in linear laminar flow (flow where there is no physical mixing) ensuring that target components can be extracted from a diluted oil sample fluid from a piece of equipment into an extraction solvent fluid through diffusion. Both fluids can then be analysed for their components using optical spectroscopy. The system 10 comprises a sample measurement flow circuit 16 and an extraction solvent fluid circuit 18. As shown in Figure 1 the sample measurement flow circuit 16 is shown connected to a sampling reservoir 19. The system is designed to be portable and to allow for samples to be taken from an engine and analysed using the system 10. The sample measurement flow circuit 16 comprise a system of valves and flowlines. A representative oil sample is extracted from a target machinery and prepared for introduction in the microfluidic system 10. In this example, the sample preparation comprises diluting the sample at ratio of 1 ml oil sample with 3ml of dilutant. In this example the dilutant is cyclohexane, a non-polar cycloalkane. The prepared sample is stored in the sample reservoir 19. A flushing solvent in this case is stored in a reservoir 21. The sample line is prepared by flushing with the flushing solvent for a prescribed duration to clear the sample line of air and / or any other contaminants. The sample measurement flow circuit 16 comprises a pump 40 and a system of valves and flowlines. In this example when a flushing operation is required three-way valves 22, 24 are moved to a first valve position to open a pathway between the flushing solvent and the sample lines 33, 37 and 38. Pump 40 is actuated to pump air from atmosphere. The pumped air is passed along flow line 26, through non-return valve 28, through valve 22 along flow line 31 into the flushing solvent reservoir 21, pressurising the reservoir. Flushing solvent is displaced out of the flushing solvent reservoir 21 at a target flowrate into flow line 33 where it passes through valve 24, through valve 34 along flow line 38 into flow meter 40. Flushing solvent flows from flow meter 40 along flow line 42. Three-way control valves 44 and is actuated to open flow path between flowlines 42 and 46. Flushing solvent flows from flow line 46 into one of a first microchannel inlet 52 of a microfluidic chip 60. The flushing solvent passes through the microfluidic chip outlet 90 and into a waste reservoir 92. During the flushing operation pump 72 is actuated and set to a target flowrate of zero; this ensures that the extraction solvent line 55 in the microfluidic chip is pressurised and that no backflow of flushing solvent occurs from the sample line 53 in the microfluidic chip to the solvent line 55 in the microfluidic chip. Upon completion of the flushing operation, the extraction solvent fluid circuit 18 is primed. The priming process comprises actuating Pump 72 to pump air from atmosphere, through check valve 74, T-piece 75 and three-way valve 76 into an extraction solvent reservoir 78, pressurising it. In this example the extraction solvent is isopropyl alcohol. The extraction solvent is pushed out of the pressurised reservoir 78 into flowline 80 at a target flowrate. The extraction solvent flows through check valve 82 into flowmeter 84. The extraction solvent flows through valve 86 into a second microchannel inlet 54 into flow channel 55 of the microfluidic chip 60. A dark spectrum of the solvent is captured in the microfluidic chip. “Dark” spectrum implies that a light source is not activated. The dark spectra is a measure of the background noise of the spectrometer photo sensor array. Following capture of the dark spectra a light source 91 is activated and three background spectra of the solvent are captured. The dark spectra data is subtracted from the light spectra data to remove noise from the readings and facilitate accurate readings. Upon completion of priming the extraction solvent fluid circuit the pump 72 is switched off and the light source 91 is deactivated. The control of flowrate of solvent through the microfluidic chip prior to introducing the sample to enables the capture of background or dark spectra. By performing preparation of the sample line and microchip prior to measurement may facilitate accurate measurement By flushing the sample line any air or residue from previous sampling is removed from the system prior to commencement of chemical analyses. This mitigates contamination of the samples and facilities stable flow thorough the sample line. In sample measurement operation the three-way valves 22, 24 are moved to a second valve position to open a flow path between the diluted oil reservoir 19 and the flow line 37. Pump 40 is actuated to pump air from atmosphere. The pumped air passed along flow line 26, through non-return valve 28, through valve 22 along flow line 30 into the sample reservoir 19, pressurising the reservoir. A fluid sample of oil is pushed out of the sample reservoir 19 into flow line 32 where in passes through valve 24, through valve 34, along flow line 38 into flow meter 40. The fluid sample flows from flow meter 40 along flow line 42. Three-way control valves 44 is actuated to open flow path between flowlines 42 and 46. The fluidic sample flows from flow line 46 into one of a first microchannel inlet 52 of a microfluidic chip 60. The sample is purged with the sample at a high flowrate for a prescribed duration in this example 30 seconds. In the extraction solvent flow circuit 18, pump 72 pumps air from atmosphere, through check valve 74, T-piece 75 and three-way valve 76 into an extraction solvent reservoir 78, pressurising it. In this example the extraction solvent is isopropyl alcohol. The selection of the extraction solvent and / or relative flowrates of sample and extraction solvent through the microfluidic chip ensures that there is no drop out of insolubles that could result in blockages in the microfluidic chip. This maintains a stable flow through the microfluidic chip and accurate measurements. The extraction solvent is pushed out of the pressurised reservoir 78 into flowline 80 at a target flowrate. The extraction solvent flows into flowmeter 84. The extraction solvent flows through valve 86 into a second microchannel inlet 54 of the microfluidic chip 60. The chemical extraction and measurement process commences when the fluid sample and extraction solvent co-flow through the microfluidic chip at prescribed flowrates, achieving target resident times for the sample and extraction solvent in the main channel 57 of the microfluidic chip 60. In the microfluidic chip, components of interest diffuse across the fluid barrier from the dilutant oil sample to the extraction solvent based on their molecular weight with low molecular weight components diffuse across at a faster rate than higher molecular weight components. During the extraction analysis, the relative target flowrates of the diluted oil sample and extraction solvent are adjusted and tuned to ensure a target resident time of the diffusion boundary between the co-flowing liquids in the chip is achieved to obtain the desired stable extraction and to capture accurate oil sample spectra data. Figure 2 shows an image of optimised flow through a microfluidic chip. The fluidic sample passes through the microfluidic chip outlet 90 and into a waste reservoir 92. The extraction solvent passes through observation sites 94 in the microfluidic chip 60 and into a waste reservoir 92. A detector device 98 in this example a spectrometer is positioned at the microfluidic chip observation sites 94 and analyte detected by measuring UV absorption. It will be appreciated that alternatively or additionally the detector device may comprise a light source and / or fibre-optic cable. In this example, three spectra of the solvent “loaded” with diffused components of interest are captured using an UV-Vis light source and spectrometer. Upon completion of the extraction process, pump 72 is stopped and pump 40 continues to pass oil sample only through the microfluidic chip at high flowrate. The UV-Vis light source and spectrometer capture diluted oil sample spectra, in this example three diluted oil sample spectra are measured. The diluted oil sample line is cleaned by repeating the flushing operation described above. However, in this case valve 44 is actuated to redirect the flushing solvent to flow line 62 to bypass the microfluidic chip, with flushing solvent proceeding directly to waste. Once the diluted oil sample line is cleaned the microfluidic chip is cleaned by repeating the flushing operation described above. By separating the cleaning of the sample line and microchip into two separate processes it minimise the exposure of the microfluidic chip to large amounts of debris in the sample line. Figure 1 shows an additional flow line to carry out a viscosity analysis of a lubricating oil sample. To determine a viscosity measure of a sample the system may monitor the time required for a sample, at a reference temperature, to pass between two fixed points. When a viscosity measurement is required a representative sample of the lubricating oil is introduced to the device at sampling reservoir 71. In this example the sample is undiluted. A heating device 73 heats the sample to a temperature of 40°C. Pump 72 is actuated to pump the oil sample from sampling reservoir 71 at a known constant pressure. A measurement of the time taken from the front of the oil sample to reach a known distance to the flowmeter 41. Using the distance travelled by the oil sample and the time taken, the viscosity is determined. Figure 3 is graphical representation 100 of the flow rate control for the oil sample and the extraction solvent at the sample line preparation stage 110, solvent line preparation stage 112, extraction and measurement stage 114, sample analysis stage 116 and cleaning stage 118. As shown in Figure 3, the flow rate of the solvent during the solvent spectra capture 120 in solvent analysis stage 112 is stable. The flow rate of the diluted oil sample and solvent through the system during the extraction spectra capture 122 in extraction analysis stage 114 is stable. The flow rate of the diluted oil sample and solvent through the system during the diluted oil spectra capture 124 in diluted oil analysis stage 116 is stable. Figures 4A to 6Bs show absorbance spectra from which the chemical composition parameters of interest for example TAN, TBN, insoluble etc., are determined. For instance TAN / TBN are determined by obtaining the absorbance value from a weighted combination of absorbance numbers between two wavelength ranges. The absorbance value is then imputed into an algorithm derived from the correlation of increasing TAN / TBN values for a range of oil samples as determined by a laboratory and their corresponding absorbance spectra to give the calculated TAN / TBN value. Figures 4A, 4B and 4C shows normalised absorbance spectra for a gas oil sample analysed three times at different times on the same apparatus. As can be seen from the absorbance spectra in each of Figure 4A, 4B and 4C, the stable flow through the microfluidic chip produces a high degree of repeatability and consistency in the result curves. Figures 5A and 5B shows absorbance spectra for a gas oil sample analysed on two different apparatus to test the reproducibility of results between apparatus. As can be seen from the absorbance spectra in Figures 5A and 5B, the stable flow through the microfluidic chip produces a high degree of reproducibility and consistency in the result curves. In addition, for different oils, or for the same oil at different stages of degradation, variations in the absorbance spectra based on different levels of contaminants can be used to determine the degree of degradation. Figures 6A and 6B shows the difference in absorbance spectra for a fresh (new) oil (Figure 6A) and a used sample of the same oil (Figure 6B). Figure 7 shows absorbance spectra for a diluted gas oil sample and an extraction from the same oil sample. As can be seen from the absorbance spectra in a diluted oil a clear absorbance curve is obtained and data of the condition of the oil obtained. In the extraction, only target components have been extracted (i.e., diffused across) from the diluted oil and as such the solvent used for extraction has a different spectral profile to reflect that only certain components have been fractionated from the diluted oil sample. Without a stable flow regime, the replicates shown in the figures could not be achieved. The invention may provide a system and method for monitoring the condition of lubricating oil from a piece of equipment. The system may comprise a lubricating oil sample reservoir connected to an oil sample flow path and a solvent fluid reservoir connected to a solvent fluid flow path. The system may comprise a microfluidic device comprising a diffusion extractor wherein the microfluidic device comprises a first microchannel in fluid communication with the oil sample flow path and a second microchannel in fluid communication with the solvent fluid flow path. The system may comprise a control system configured to pass lubricating oil and / or solvent fluid through the microfluidic device under stable flow conditions and a detector device configured to detect or measure at least one characteristic of the fluid flowing through the microfluidic device. Embodiments of the invention may allow early detection of contaminated lubricating oil facilitating detection of wear or damage in equipment and machinery. This may mitigate failure of key components, downtime for repairs and replacement, casualties, and incidents in many industries such maritime, power generation, processing, and manufacturing. Embodiments of the invention may provide accurate measurement analysis of lubricating oil samples by controlling the stable flow of oil samples through the microfluidic apparatus to obtain consistent absorbance spectra. This may allow a high degree of repeatability and reproducibility. This may also allow comparisons of different oil types or oil at different stages of degradation over time to be determined and measured. Embodiments of the invention may provide accurate measurement analysis of oil samples by controlling and adjusting the flow rate, dilution of sample, and / or solvent type to optimise extraction from the oil sample in the microfluidic device diffusion channel. The ability of the system to deliver repeatable and reproducible results is dependent on achieving a stable flow regime at all stages of the analysis workflow. Throughout the specification, unless the context demands otherwise, the terms 'comprise' or 'include', or variations such as 'comprises' or 'comprising', 'includes' or 'including' will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers. Furthermore, relative terms such as “up”, “down”, “above”, “below”, “top”, “bottom”, “upper”, “lower”, “upward”, “downward”, “horizontal”, “vertical”, “and the like are used herein to indicate directions and locations as they apply to the appended drawings and will not be construed as limiting the invention and features thereof to particular arrangements or orientations. Likewise, the term “outlet” or “output” shall be construed as being a location or connection type which, dependent on the direction of power, signal or charge may also serve as an “inlet” or “input”, and vice versa. Various modifications to the above-described embodiments may be made within the scope of the invention, and the invention extends to combinations of features other than those expressly claimed herein.

Claims

1. A system for monitoring the condition of lubricating oil from a piece of equipment comprising:a lubricating oil sample reservoir connected to an oil sample flow path;a solvent fluid reservoir connected to a solvent fluid flow path;a microfluidic device comprising a diffusion extractor;wherein the microfluidic device comprises a first microchannel in fluid communication with the oil sample flow path and a second microchannel in fluid communication with the solvent fluid flow path;a control system configured to pass lubricating oil and / or solvent fluid through the microfluidic device under stable flow conditions; anda detector device configured to detect or measure at least one characteristic of the fluid flowing through the microfluidic device.

2. The system according to claim 1 wherein the detector device is configured to detect or measure at least one analyte in the lubricating oil sample and / or measure changes in the solvent fluid.

3. The system according to claim 1 or claim 2 wherein the detector device comprises at least one sensor selected from the group comprising a spectrometer, camera, Charge Coupled Device (CCD), Complementary Metal Oxide Semi-conductors (CMOS) and / or another photosensitive device.

4. The system according to any preceding claim wherein the detector device is configured to measure at least one background spectra or dark spectra of the solvent fluid.

5. The system according to any preceding claim wherein the detector device is configured to measure at least one transmission spectrum of the solvent fluid and / or oil sample fluid.

6. The system according to any preceding claim wherein the detector device is configured to detect or measure a level of analyte to determine Total Acid Number (TAN), Total Base Number (TBN), insolubles content, viscosity, iron content and / or water content of the oil sample.

7. The system according to any preceding claim wherein the microfluidic device is a microfluidic chip.

8. The system according to any preceding claim wherein the microfluidic device comprises a diffusion channel configured to diffuse, pass, and / or transfer at least one analyte or component present in the lubricating oil sample into the solvent in the diffusion channel.

9. The system according to any preceding claim wherein the at least one control unit is configured to control the stable flow of oil sample from the oil sample reservoir to and / or through the microfluidic system.

10. The system according to any preceding claim wherein the at least one control unit is configured to control the stable flow of solvent to and / or through the microfluidic system11. The system according to any preceding claim wherein the oil sample flow path comprises at least one pump, a plurality of valves, and as least one flowmeter operable to control the flow and flow rate of the oil sample through the oil sample flow path, through microfluidic device and / or through the diffusion extractor.

12. The system according to any preceding claim wherein the solvent flow path comprises at least one pump, a plurality of valves, and as least one flowmeter operable to control the flow and rate of the solvent through the solvent flow path, through microfluidic device and / or through the diffusion extractor.

13. The system according to any preceding claim wherein the solvent fluid is cyclohexane, isopropyl alcohol or an organic solvent.

14. The system according to any preceding claim wherein the lubricating oil is a mineral oil, semi-synthetic oil and / or synthetic oil.

15. The system according to any preceding claim wherein the system is a portable microfluidic system configured to be connectable to a piece of equipment and / or receive at least one sample of oil from a piece of equipment.

16. A method of monitoring the condition of lubricating oil comprisingproviding a microfluidic system comprising:a lubricating oil sample reservoir connected to an oil sample flow path;a solvent fluid reservoir connected to a solvent fluid flow path;a microfluidic device comprising a first microchannel in fluid communication with the oil sample flow path and a second microchannel in fluid communication with the solvent fluid flow path;a control system; anda detector device;passing lubricating oil and / or solvent fluid through the microfluidic device under stable flow conditions; anddetecting or measuring at least one characteristic of the fluid flowing through the microfluidic device.

17. The method according to claim 16 comprising extracting and / or transferring a sample of lubricating oil from a piece of equipment to be tested to the lubricating oil sample reservoir.

18. The method according to claim 16 or 17 comprising preparing the lubricating oil sample by diluting the sample with a dilutant fluid.

19. The method according to any of claims 16 to 18 comprising pumping solvent into the solvent fluid flow path at a desired flow rate and / or for a desired period of time.

20. The method according to any of claims 16 to 19 comprising performing at least one background or dark spectra readings of solvent fluid flow through the microfluidic device.

21. The method according to any of claims 16 to 20 comprising pumping oil sample into the oil sample flow path at a first flow rate and pumping solvent into the solvent fluid flow path at a second flow rate.

22. The method according to any of claims 16 to 21 comprising controlling and / or adjusting the first and / or second flow rates to stabilise flow of the co-flowing diluted oil sample and / or solvent through the microfluid device.

23. The method according to any of claims 16 to 22 comprising measuring at least one group of spectra readings of solvent fluid flow and / or diluted oil sample flow through the microfluidic device.

24. The method according to any of claims 16 to 23 comprising detecting or measuring at least one extracted component from the diluted oil sample.

25. The method according to any of claims 16 to 24 comprising measuring the viscosity of the at least one undiluted lubricating oil sample.27

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