Patent Description:
The water in fuel may be problematic in fuel systems of internal combustion engines. Water in fuel may damage fuel injectors due to corrosion or vaporization during combustion. For example, damage to injectors may cause various problems in operation of the engine, such as failing to be able to comply with jurisdictional emission standards. Fuel injector damage may require repair or maintenance. Reduced operating time may be particularly costly for commercial or industrial vehicles.

Sensors, such as water-in-fuel (WIF) sensors, have been proposed to detect water in fuel. One type of sensor is a float system, which uses material with density between water and fuel. Another type of sensor is a conductivity sensor. Both of these types of sensors are subject to problems over time as dirt or debris collects on the surfaces. In particular, conductive WIF sensors may be susceptible to corrosion and electrochemical plating over time. In-line flow sensors on fuel systems have been proposed using light sources at near infrared wavelengths to detect water in fuel. Some systems are designed to have path lengths between the light source and detector on the order to centimeters to be suitable for detecting water. Such systems may be ineffective at distinguishing from dissolved water and water droplets, which may have different impacts on the injectors. Further, such system may provide inaccurate sizing information when multiple water droplets are present in the detector.

There is a need for improved sensors to mitigate fuel injector damage and to improve the performance of internal combustion engines over time.

<CIT> discloses an apparatus for determining water content in liquids based on oil.

Document <CIT> discloses a fluid analyzer including an optical source and an optical detector.

Document <CIT> discloses methods for assessing characteristics or properties of a microfluidic droplet within a microfluidic channel.

A system according to the invention is disclosed in any one of claims <NUM>-<NUM>. A use of said system according to the invention is disclosed in claim <NUM>. An engine system according to the invention is disclosed in claim <NUM>.

Various aspects of the present disclosure relate to droplet sensors configured to detect liquid in a different fluid using a sensing channel, specifically to detect liquid droplets dispersed in a different fluid using a microfluidic channel, as per the invention according to claim <NUM>. In some embodiments, the droplet detection sensors may be configured to detect water droplets dispersed in a hydrocarbon fluid, such as fuel, which may be described as a microfluidic water-in-fuel (WIF) sensor. Infrared light may be used by the droplet sensors to measure light absorbance through the microfluidic channel and determine whether or how much of a liquid droplet is present in the fluid. The droplet sensor may be configured to differentiate, or distinguish, between liquid droplets dispersed in fluid and dissolved liquid in fluid as the fluid flows through the microfluidic channel. Information from the sensor may be used to determine one or more of the concentration of liquid in the fluid, the liquid droplet size, or the liquid droplet rate of flow through the microfluidic channel. A water level may also be measured using the sensor.

The present invention relates to a system including a microfluidic channel configured to receive a flow of a first fluid and a second fluid dispersed in the first fluid. The second fluid has a different composition than the first fluid. The system also includes a light source configured to direct a light beam in a frequency band along a path through the microfluidic channel. The frequency band is selected to have a higher absorbance by the second fluid than by the first fluid. The system further includes an aperture element defining a light aperture positioned in the path of the light beam from the light source. The system further includes a light detector positioned to receive the light beam in a sensing area after passing through the microfluidic channel and the light aperture. The light detector is configured to provide a signal representing an amount of light in the frequency band that remains after passing through the microfluidic channel. The system further includes a controller operably coupled to the light detector and configured to determine whether the second fluid is in droplet form based on the signal.

In another aspect not forming part of the claimed invention, the present disclosure relates to a system including a fuel and water separator having a housing defining a water collection volume. The water collection volume is fluidly connected to an engine fuel line and fluidly connected to a water drain outlet. The system also includes a light source configured to direct a light beam in a frequency band along a path through the water collection volume. The frequency band is selected to be absorbed by water. The system further includes a light detector positioned to receive the light beam in a sensing area after passing through at least part of the water collection volume. The light detector is configured to provide a signal representing an amount of light in the frequency band. The system further includes a controller operably coupled to the light detector and configured to determine whether water is detected based on the signal.

In yet another aspect, the present disclosure relates to a system including a microfluidic channel configured to receive a flow of hydrocarbon fluid. The microfluidic channel has a cross-sectional area sized to receive one water droplet at a time when a water droplet of a predetermined size is dispersed in the hydrocarbon fluid. The system also includes a light source positioned outside the microfluidic channel configured to generate light in a selected frequency band such that the water droplet has a higher absorbance than the hydrocarbon fluid in the selected frequency band. The system further includes a light detector sensitive to the selected frequency band positioned outside the microfluidic channel and configured to provide a signal representing an amount of light remaining after passing through the microfluidic channel. The system additionally includes a light aperture positioned between the light source and the light detector, wherein light from the light source passing through the light aperture forms a light beam defining a beam axis that extends through the light source, the microfluidic channel, and the light detector. The system still further includes a controller operably connected to the light detector and configured to detect one or more water droplets dispersed in the flow of hydrocarbon fluid based on the signal from the light detector representing the amount of light from the light source remaining after passing through the microfluidic channel and the light aperture.

In still another aspect, the present disclosure relates to a sensor including a microfluidic channel sized to receive a flow of fluid. The microfluidic channel has a cross-sectional area sized to receive one liquid droplet at a time when a liquid droplet of a predetermined size is dispersed in the fluid. The sensor also includes a light source positioned outside the microfluidic channel configured to generate light in a selected frequency band such that the droplets have a different absorbance than the different liquid in the selected frequency band. The sensor further includes a light detector sensitive to the selected frequency band positioned outside the microfluidic channel and configured to provide a signal representing an amount of light remaining after passing through the microfluidic channel. The sensor additionally includes a light aperture positioned between the light source and the light detector, wherein light from the light source passing through the light aperture forms a light beam defining a beam axis that extends through the light source, the microfluidic channel, and the light detector. A width of the light aperture and the light detector define a sensing area. The sensor still further includes a controller operably connected to the light detector and configured to determine a droplet rate through the sensing area of the microfluidic channel based on the signal from the light detector representing the amount of light from the light source remaining after passing through the microfluidic channel and the light aperture.

In a further aspect, the present disclosure relates to a water droplet sensor including a microfluidic channel defining a cross-sectional area less than <NUM><NUM>. The sensor also includes a light source positioned outside the microfluidic channel configured to generate light in a near infrared frequency band. The sensor further includes a light detector sensitive to the selected frequency band positioned outside the microfluidic channel and configured to provide a signal representing an amount of light remaining after passing through the microfluidic channel. The sensor additionally includes a light aperture positioned between the light source and the light detector, wherein light from the light source passing through the light aperture forms a light beam defining a beam axis that extends through the light source, the microfluidic channel, and the light detector. The aperture has a width less than <NUM>. The sensor still further includes a controller operably connected to the light detector and configured to detect one or more water droplets dispersed in the flow of hydrocarbon fluid based on the signal from the light detector representing the amount of light from the light source remaining after passing through the microfluidic channel and the light aperture.

Various embodiments of the disclosure are illustrated in the drawings, which are summarized as follows:.

This disclosure relates to sensors configured to detect or characterize liquid droplets dispersed in a different fluid using one or more sensing channels, such as microfluidic channels. Although reference is made herein to water droplet sensors to protect engine fuel systems, such as water-in-fuel (WIF) sensors, the sensors and related techniques may be used to detect or characterize any liquid-in-fluid for which the absorbance of the liquid is different than the fluid, as well as various vehicular or non-vehicular applications. A non-limiting example of another application includes detecting water-in-oil. An example not forming part of the claimed invention includes detecting water in fuel tanks used for bulk fuel storage. In another example not forming part of the claimed invention, a water level may also be measured using the sensor. Various other applications will become apparent to one skilled in the art having the benefit of this disclosure.

In applications related to engine fuel systems, different forms of water may have different effects on various components of the fuel system. For example, water that is not dissolved in the fuel, which may be described as free water, water droplets, or dispersed water, can cause damage to engine systems by causing rust, encouraging microbial growth, damaging fuel injectors, or causing poor ignition performance.

It may be beneficial to provide a sensor configured to precisely detect water droplets, or free water, instead of treating all forms of water equally. For example, the sensor may be substantially more sensitive to detecting water droplets, such as emulsified water in fuel, compared to dissolved water in fuel. It may be beneficial to provide sensors that may require less maintenance than existing sensors, such as float sensors or conductive WIF sensors. Further, it may be beneficial to provide a sensor that can be used to characterize the water droplets in the fuel.

The present disclosure provides droplet sensors that may be configured to use light, such as near infrared (NIR) wavelengths of light, to detect and size water droplets in a stream of hydrocarbon fluid, such as fuel or oil, using one or more microfluidic channels. The microfluidic channel may have a cross-sectional area that is a square, rectangle, circle, oval, half-circle, or any other suitable geometric shape. The microfluidic channel limits the path length of light across the channel that is used to detect water droplets in the fuel. Advantageously, the limited path length provided by the microfluidic channel may reduce the occurrence of some water droplets being hidden behind other water droplets in a sensing area of the droplet sensor, thereby facilitating a sensitivity for detecting water droplets higher than for detecting dissolved water, which may facilitate accurate and precise characterization of the droplets.

In some applications, the width or depth of the microfluidic channel may be sized comparably to water droplets of interest. For example, droplets in a range from <NUM> up to <NUM> micrometers in diameter may be detected and sized using a microfluidic channel having a width of <NUM> micrometers. In other words, a droplet diameter down to one-tenth the width or depth of the microfluidic channel may be detected and sized. Smaller droplets may be detected and sized using a smaller channel, such as a width of <NUM> micrometers, a more precise alignment, or a more sensitive electronic detector.

The absorbance of water to NIR light may be substantially different than the absorbance of fuel. For example, water may have an absorbance greater than <NUM>, whereas hydrocarbon fluid, such as fuel, may have an absorbance of less than <NUM> for a <NUM>-millimeter path length. In one or more embodiments, a sensor includes an NIR light source centered at approximately <NUM> nanometers, a circular aperture aligned with the channel, and a light detector. In some embodiments, the sensor may contain no focusing optics, and many parts of the droplet sensors, such as the light source and light detector, do not need to physically contact the water or fuel to detect water droplets using light, which may facilitate the robust operation of the sensor electronic, for example, due to less risk for corrosion compared to a conductive WIF sensor. In some embodiments, only the microfluidic channel may contact the water or fuel. Further, the droplet sensor may be designed using low-power usage parts and without moving parts, which may facilitate fewer maintenance events and longer operational times.

As used herein, the term "light" refers to energy at one or more wavelengths in the electromagnetic spectrum. Non-limiting examples of "light" include solar energy, infrared (IR) light, visible light, or ultraviolet (UV) light. Infrared light may include wavelengths in a range from <NUM> micrometers up to <NUM> micrometers.

As used herein, the term "near infrared" or "NIR" light includes wavelengths greater than or equal to <NUM> or <NUM> micrometers and less than or equal to <NUM> or <NUM> micrometers.

As used herein, the term "or" is generally employed in its inclusive sense, for example, to mean "and/or" unless the context clearly dictates otherwise. The term "and/or" means one or all the listed elements or a combination of at least two of the listed elements.

Reference will now be made to the drawings, which depict one or more aspects described in this disclosure. However, it will be understood that other aspects not depicted in the drawings fall within the scope of this disclosure. Like numbers used in the figures refer to like components, steps and the like. However, it will be understood that the use of a reference character to refer to an element in a given figure is not intended to limit the element in another figure labeled with the same reference character. In addition, the use of different reference characters to refer to elements in different figures is not intended to indicate that the differently referenced elements cannot be the same or similar.

<FIG> shows system <NUM> with droplet sensor <NUM> that is configured to detect liquid dispersed in a different fluid. In the illustrated embodiment, system <NUM> is an engine system including engine <NUM>, fuel system <NUM>, and computer <NUM>. Engine <NUM> may be an internal combustion engine. Droplet sensor <NUM> may be configured to detect water droplets in fluid. The fluid may be hydrocarbon fluid, such as a fuel or oil. In the illustrated embodiment, the fluid is fuel <NUM>. Non-limiting examples of fuel <NUM> include gasoline and diesel. Fuel <NUM> is stored and provided to engine <NUM> by fuel system <NUM>. System <NUM> may be used on a vehicle for on-road or off-road applications, such as trucking or mining. In such applications, computer <NUM> may be a vehicle computer, such as an engine control module (ECM) or other on-board computer.

As illustrated, fuel system <NUM> includes droplet sensor <NUM>, fuel tank <NUM>, fuel pump <NUM>, fuel line <NUM>, fuel filter <NUM>, and injection system <NUM>. Fuel tank <NUM> is in fluid communication with fuel pump <NUM>, fuel line <NUM>, and injection system <NUM>. Fuel <NUM> is stored in fuel tank <NUM> and pumped by fuel pump <NUM> when system <NUM> is in operation combusting fuel <NUM> in engine <NUM>. Fuel pump <NUM> is configured to provide a flow of fuel <NUM>, or fuel flow, to one or more fuel injectors of injection system <NUM>. Fuel line <NUM> is configured to deliver fluid to injection system <NUM>. Fuel <NUM> enters fuel line <NUM> at fuel pump <NUM> and exists fuel line <NUM> at injection system <NUM>. Injection system <NUM> may include a pressurized fuel rail and one or more fuel injectors. Injection system <NUM> is configured to provide a pressurized spray of fuel <NUM> into one or more combustion cylinders of engine <NUM>.

Fuel filter <NUM> is positioned, or disposed, along fuel line <NUM>. Fuel <NUM> may contain water. Fuel filter <NUM> is configured to remove water from fuel <NUM>. Fuel filter <NUM> may be a fuel-water separator (FWS), for example, as used in some on-vehicle diesel engine systems. Water in fuel <NUM> may cause damage to various components of system <NUM>. For example, water may cause damage to one or more injectors of injection system <NUM>. In particular, water droplets in fuel <NUM> may cause damage to one or more injectors of injection system <NUM> when vaporized in the combustion cylinder. Dissolved water in fuel <NUM> may not cause similar damage.

Droplet sensor <NUM> may be positioned, or disposed, along fuel line <NUM> to detect water in fuel <NUM>. Droplet sensor <NUM> may be configured to be more sensitive to detecting water droplets in fuel <NUM> than dissolved water in fuel <NUM> to provide reliable indication of potential damage to any injectors of injection system <NUM>.

Droplet sensor <NUM> includes one or more detection assemblies <NUM>. Each detection assembly <NUM> may be configured to receive a flow of fuel <NUM> for measuring water droplets. Fuel <NUM> from fuel line <NUM> may flow through each detection assembly <NUM>. Fuel <NUM> may be returned to fuel line <NUM> after measurement. Fuel <NUM> may enter each using the flow of fuel <NUM> through fuel line <NUM> provided by fuel pump <NUM>. In other words, fuel <NUM> may enter some or all detection assemblies <NUM> passively.

In some embodiments, droplet sensor <NUM> may include one or more separate pumps (not shown), different than fuel pump <NUM>, to actively provide a flow of fuel <NUM> from fuel line <NUM> to some or all detection assemblies <NUM>. The separate pumps, or sampling pumps, may be positioned downstream of any sensing channel or microfluidic channel so that the pump does not affect measurement of droplets. For example, a pump may have the effect of "chopping up" some water droplets.

As used herein, the term "downstream" refers to a direction along fuel line <NUM> toward fuel pump <NUM>. The term "upstream" refers to the opposite of downstream, or a direction along fuel line <NUM> toward injection system <NUM>.

In the illustrated embodiment, fuel pump <NUM> is positioned upstream of fuel filter <NUM>. In other embodiments (not shown), fuel filter <NUM> is positioned upstream of fuel pump <NUM>. In some embodiments (not shown), system <NUM> includes two or more fuel filters <NUM>. For example, one fuel filter <NUM> may be positioned upstream and one fuel filter <NUM> may be positioned downstream of fuel pump <NUM>. Each fuel filter <NUM> may be the same or different. In some embodiments, water may be removed from fuel at the upstream fuel filter <NUM>, the downstream fuel filter <NUM>, or both.

Each detection assembly <NUM> may include a microfluidic channel configured to receive a flow of fuel <NUM> from fuel line <NUM>. Each microfluidic channel may be positioned adjacent or proximate to a main flow of fuel <NUM> along fuel line <NUM>. In some embodiments, some or all microfluidic channels of detection assembly <NUM> are in parallel fluid communication with fuel line <NUM>. In some embodiments, some or all microfluidic channels of detection assembly <NUM> are disposed in the main flow of fuel line <NUM>, such that some of or all the main flow is directed through one or more microfluidic channels.

Depending on the application, droplet sensor <NUM> may be positioned at one or more locations along fuel line <NUM>, such as upstream, downstream, or at the location of fuel filter <NUM>. In some embodiments (not shown), droplet sensor <NUM> is located on a fuel return line (not shown) in fluid communication between injection system <NUM> and fuel tank <NUM>. In some embodiments (not shown), droplet sensor <NUM> may be built into, or integrated with, one or more injectors of injection system <NUM>. In other words, the droplet sensor <NUM> may be directly integrated into the fuel injector or the injection system <NUM>.

In one embodiment, droplet sensor <NUM> includes one detection assembly <NUM>. The one detection assembly <NUM> may be positioned downstream of fuel filter <NUM>. Alternatively, the one detection assembly <NUM> may be positioned at fuel filter <NUM> or upstream of fuel filter <NUM>. In some embodiments, droplet sensor <NUM> includes a combination of detection assemblies <NUM> positioned at one or more locations selected from upstream, downstream, or at the location of fuel filter <NUM>. One or more detection assemblies <NUM> may be positioned at the same location along fuel line <NUM>.

Positioning detection assembly <NUM> downstream of, or at, fuel filter <NUM> may be used to provide information used to determine the quality of water-fuel separation by fuel filter <NUM>, which may be used to indicate that fuel filter <NUM> is operating correctly or may need maintenance or replacement. Positioning detection assembly <NUM> upstream of, or at, fuel filter <NUM> may be used to provide information used to determine the quality of fuel <NUM> stored in fuel tank <NUM> or being provided along fuel line <NUM>, which may be used to indicate that fuel tank <NUM> is operating correctly or may need maintenance or replacement or that fuel <NUM> provided to fuel tank <NUM>.

As fuel <NUM> approaches injection system <NUM>, fuel <NUM> may reach a high temperature, for example, due to the proximity to injection system <NUM> or engine <NUM>. In some embodiments, detection assembly <NUM> may be positioned upstream from injection system <NUM> a sufficient distance to prevent the high temperature of some injection systems from substantially impacting the performance of certain droplet sensors <NUM>.

Droplet sensor <NUM> may include sensor controller <NUM>. Sensor controller <NUM> may be operably connected, or coupled, to one or more detection assemblies <NUM>. Each detection assembly <NUM> may make measurements and provide information characterizing water droplets detected in fuel <NUM> to sensor controller <NUM>. Information may be provided in the form of a signal, such as an electrical signal. Examples of electrical signals include a current signal, voltage signal, and power signal. Information from detection assemblies <NUM> may be used by sensor controller <NUM> to determine various characteristics corresponding to the water droplets in fuel <NUM>, such as droplet size, droplet rate, or the amount of water in fuel <NUM> (for example, a concentration).

Sensor controller <NUM> may be operably connected to computer <NUM>. Computer <NUM> may be used to control various aspects of fuel system <NUM>, such as flow rate of fuel <NUM> or injection timing for injection system <NUM>. Sensor controller <NUM> and computer <NUM> are part of a control system of system <NUM> and may be separate components. In some embodiments, the functionality of sensor controller <NUM> and computer <NUM> may be integrated into a single component, such as a single controller or computer.

Droplet sensor <NUM> may be configured to detect a predetermined size of liquid droplet, or droplet size. As used herein, "droplet size" may be described interchangeably using a volume or using a spherical diameter corresponding to the volume of a liquid droplet when shaped as a sphere. In other words, the volume of a liquid droplet of any shape may be described by a spherical diameter of the same droplet when re-shaped into a sphere. In this manner, droplet size may be described as a volume corresponding to a specified spherical diameter.

In some embodiments, droplet sensor <NUM> is configured to detect or characterize a droplet size greater than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> micrometers. In some embodiments, droplet sensor <NUM> is configured to detect or characterize a droplet size less than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> micrometers. In some embodiments, droplet sensor <NUM> is configured to detect or characterize a droplet size in a range from <NUM> up to <NUM> micrometers. In one or more embodiments, droplet sensor <NUM> is configured to detect or characterize a droplet size in a range from <NUM> to <NUM> micrometers.

In fuel system applications, droplet sizes less than <NUM> micrometers may not be considered liquid droplets that negatively impact the operation of injection system <NUM> of system <NUM>. In particular, such water droplet sizes may be considered unstable below <NUM> micrometers and may not substantially contribute to damaging fuel injectors. Further, water in fuel that passes through typical fuel pumps <NUM> tend to form droplets of at least about <NUM> micrometers.

In general, one or more of the components, such as controllers, sensors, detectors, or computers, described herein may include a processor, such as a central processing unit (CPU), computer, logic array, or other device capable of directing data coming into or out of the sensor. The controller may include one or more computing devices having memory (which may include storage drives), processing, and communication hardware. The controller may include circuitry used to couple various components of the controller together or with other components operably coupled to the controller. The functions of the controller may be performed by hardware and/or as computer instructions on a non-transient computer readable storage medium.

The processor of the controller may include any one or more of a microprocessor, a microcontroller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), and/or equivalent discrete or integrated logic circuitry. In some examples, the processor may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, and/or one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to the controller or processor herein may be embodied as software, firmware, hardware, or any combination thereof. While described herein as a processor-based system, an alternative controller could utilize other components such as relays and timers to achieve the desired results, either alone or in combination with a microprocessor-based system.

In one or more embodiments, the exemplary systems, methods, and interfaces may be implemented using one or more computer programs using a computing apparatus, which may include one or more processors and/or memory. Program code and/or logic described herein may be applied to input data/information to perform functionality described herein and generate desired output data/information. The output data/information may be applied as an input to one or more other devices and/or methods as described herein or as would be applied in a known fashion. In view of the above, it will be readily apparent that the controller functionality as described herein may be implemented in any manner known to one skilled in the art.

<FIG> shows various components of droplet sensor <NUM> including detection assembly <NUM> and sensor controller <NUM> that may be used with system <NUM> of <FIG>. In the illustrated embodiment, detection assembly <NUM> includes microfluidic channel <NUM>, light source <NUM>, light aperture <NUM>, and light detector <NUM>. Sensor controller <NUM> is operably connected to light detector <NUM> and may also be operably connected to light source <NUM>.

Microfluidic channel <NUM> is configured to receive a flow of fluid <NUM>. Microfluidic channel <NUM> may include an inlet to receive the flow of fluid <NUM> and an outlet to discharge the flow of fluid <NUM>. The droplet sensor <NUM> may be configured to detect and characterize liquid droplets <NUM> in the flow of fluid <NUM> may also flow through microfluidic channel <NUM> in a forward direction toward the outlet or even in reverse direction toward the inlet.

Liquid droplets <NUM> may be dispersed in fluid <NUM> in microfluidic channel <NUM>. For example, liquid droplets <NUM> may be suspended in fluid <NUM> in a separate phase. In other words, liquid droplets <NUM> are not dissolved in fluid <NUM>.

In general, microfluidic channel <NUM> is sized to receive one or more liquid droplets <NUM> at a time. In some embodiments, microfluidic channel <NUM> has a cross-sectional area sized to receive one liquid droplet <NUM> of a predetermined size at a time. In particular, the cross-sectional area of microfluidic channel <NUM> may be about the same size as a cross-sectional area of liquid droplet <NUM>, which may facilitate counting one liquid droplet <NUM> at a time to facilitate accurate counting and sizing of liquid droplet <NUM>.

The cross-sectional area may be defined orthogonal to the direction of the flow of fluid <NUM>. In other words, the cross-sectional area may be described as transverse to a longitudinal flow of fluid <NUM>. In some embodiments, microfluidic channel <NUM> has a cross-sectional area less than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM><NUM>. In some embodiments, microfluidic channel <NUM> has a cross-sectional area greater than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM><NUM>. For example, the cross-sectional area of a <NUM> x <NUM>-micrometer microfluidic channel <NUM> would be <NUM><NUM>.

Cross-sectional area may be defined as a channel depth multiplied by a channel width. Both channel depth and channel width may be orthogonal to the direction of the flow of fluid <NUM>. In some embodiments, the channel depth is less than or equal to the channel width. Using a shallow channel depth may prevent liquid droplets <NUM> from stacking, or hiding behind one another, as the liquid droplets flow through microfluidic channel <NUM>.

In some embodiments, the channel width is less than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> micrometers. In some embodiments, the channel width is greater than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> micrometers. In one or more embodiments, the channel width is <NUM> micrometers. In one or more embodiments, the channel width is <NUM> micrometers.

In some embodiments, the channel depth is less than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> micrometers. In some embodiments, the channel depth is greater than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> micrometers. In one or more embodiments, the channel depth is less than or equal to <NUM> micrometers. In one or more embodiments, the channel depth is less than or equal to <NUM> micrometers.

In the illustrated embodiment, light source <NUM> is positioned outside microfluidic channel <NUM>. Light aperture <NUM> is positioned between light source <NUM> and light detector <NUM>. In some embodiments, light aperture <NUM> is positioned before microfluidic channel <NUM>, for example, between light source <NUM> and microfluidic channel <NUM>. In some embodiments, light aperture <NUM> is positioned after microfluidic channel <NUM>, for example, between microfluidic channel <NUM> and light detector <NUM>.

Light source <NUM> is configured to direct light <NUM> through light aperture <NUM> to form light beam <NUM>. Light beam <NUM> is directed to pass through microfluidic channel <NUM>. Light beam <NUM> may be collimated or substantially collimated by light aperture <NUM>, at least for the path length of light beam <NUM> through microfluidic channel <NUM>. Light beam <NUM> may define a beam axis extending through the microfluidic channel <NUM>. The walls of microfluidic channel <NUM> may be formed of a light transparent material, at least to light <NUM> provided by light source <NUM>. The path of light beam <NUM> intersecting with microfluidic channel <NUM> defines sensing area <NUM>, which may also be described as a sensing volume, in which liquid droplets <NUM> may be detected. After light beam <NUM> passes through microfluidic channel <NUM>, light beam <NUM> is received by light detector <NUM>, which is positioned outside of microfluidic channel <NUM> in the illustrated embodiment. When liquid droplet <NUM> and fluid <NUM> are in sensing area <NUM>, light detector <NUM> may be used to determine an absorbance of light beam <NUM> by liquid droplet <NUM> and fluid <NUM> to detect, size, or otherwise characterize liquid droplet <NUM>.

As used herein, the term "path length" refers to the distance that light from light source <NUM> travels in fluid to be measured. In some embodiments, the path length may be equal to a width or depth of microfluidic channel <NUM>. The path length may be small to improve sensitivity to liquid droplets <NUM>. In some embodiments, the path length is less than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> micrometers. In one or more embodiments, the path length is less than or equal to <NUM> micrometers.

Light source <NUM> is configured to generate light in a selected frequency band such that liquid droplet <NUM> has a different absorbance than fluid <NUM> in the selected frequency band. In one or more embodiments, liquid droplet <NUM> has a higher absorbance than fluid <NUM> when the liquid is water and fluid <NUM> is a hydrocarbon fluid. In fuel system applications, for example, light source <NUM> may generate light <NUM> in at least the NIR frequency band. In some embodiments, NIR light <NUM> may include an emission peak in, or at least include frequencies in, a range from <NUM> to <NUM> nanometers. In particular, NIR light <NUM> may include an emission peak centered at or near <NUM> nanometers. In some embodiments, NIR light <NUM> may include an emission peak in, or at least include frequencies in, a range from least <NUM> to <NUM> nanometers. In particular, NIR light <NUM> may include an emission peak centered at or near <NUM> nanometers.

Light source <NUM> may include any suitable type of light source capable of providing light <NUM> in a selected frequency band. In some embodiments, light source <NUM> is a light-emitting diode (LED). The LED light source <NUM> may be a low-power LED. In some embodiments, the LED light source emit omnidirectionally or in all directions from the light-emitting junction. In some embodiments, the LED light source emits primarily in one direction. In some embodiments, light source <NUM> may be paired with or include a fiber optic cable that directs light to microfluidic channel <NUM>. Light aperture <NUM> may be used to allow a narrow light beam <NUM> through microfluidic channel <NUM>, which may facilitate eliminating noise or false signals, for example, due to scattering and reflectance.

Light aperture <NUM> includes an opening in an aperture element <NUM>. As used herein, "aperture" refers to the opening, or void, within the aperture element. Light aperture <NUM> has a width that is sized relative to microfluidic channel <NUM> and light detector <NUM> to facilitate optimal sensitivity for detecting liquid droplets <NUM> in fluid <NUM>. In some embodiments, the width of light aperture <NUM> is the same or substantially the same as the channel width of microfluidic channel <NUM>.

Additionally, or alternatively, light aperture <NUM> may be sized relative to a predetermined droplet size of interest. For example, in some embodiments, the width of light aperture <NUM> may be designed to be less than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> times the droplet size of interest. In some embodiments, the width of light aperture <NUM> may be designed to be greater than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> times the droplet size of interest.

Light aperture <NUM> may have any suitable geometric shape. In some embodiments, light aperture <NUM> has a round or circular shape, such as a circle or oval. In some embodiments, light aperture <NUM> has a polygonal shape, such as a triangle, square, trapezoid, or rectangle. Light aperture <NUM> may have a length, which may extend along the same direction as the flow of fluid <NUM>. In one or more embodiments, the length of light aperture <NUM> may be the same or substantially the same as the width of light aperture <NUM>.

In some embodiments, light aperture <NUM> has a width less than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> micrometers. In some embodiments, the width of light aperture <NUM> is greater than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> micrometers. In one or more embodiments, the width of light aperture <NUM> is <NUM> micrometers. In one or more embodiments, the width of light aperture <NUM> is <NUM> micrometers.

Light detector <NUM> may be any suitable type of photodetector sensitive to the selected frequency band, which may be an NIR frequency band. Light detector <NUM> is also configured to provide a signal representing an amount of light from light beam <NUM> remaining after passing through microfluidic channel <NUM>. In particular, light detector <NUM> may be configured to generate an electrical signal, such as a current, voltage, or power signal, in response to receiving light in the selected frequency band. Non-limiting examples of types of photodetectors include indium-gallium-arsenide (InGaAs) or germanium (Ge) photodiodes. For example, an InGaAs photodiode may be sensitive to light <NUM> in a frequency band from <NUM> to <NUM> nanometers. A Ge photodiode may have a peak sensitivity at <NUM> nanometers.

Sensor controller <NUM> is configured to detect, size, or otherwise characterize one or more liquid droplets <NUM> dispersed in the flow of fluid <NUM> based on the signal from light detector <NUM>. In some embodiments, sensor controller <NUM> may be configured to detect one liquid droplet <NUM> at a time dispersed in the flow of fluid <NUM>, particularly liquid droplets <NUM> of a predetermined size. The signal may be used to determine an amount of liquid (e.g., water) per unit volume of fluid <NUM> (e.g., hydrocarbon fluid) excluding liquid dissolved in fluid <NUM>.

In some embodiments, sensor controller <NUM> is configured to determine a droplet rate through sensing area <NUM>. For example, a change in absorbance detected based on the signal from light detector <NUM> may indicate that liquid droplet <NUM> is entering or is leaving sensing area <NUM>. Alternatively, or additionally, sensor controller <NUM> may be configured to determine a droplet size. In some embodiments, sensor controller <NUM> may determine a droplet rate or a droplet size based on at least one of: a magnitude of a pulse contained within the signal, a width of a pulse contained within the signal, a first threshold signal level for detecting a minimum size droplet in the sensing area, a second threshold signal level for detecting a droplet that fills the sensing area, and a threshold signal level crossing rate, which are described herein in more detail with respect to <FIG>. Sensor controller <NUM> may determine an amount of liquid <NUM> in droplet form per unit volume of fluid <NUM>, such as a droplet concentration, based on droplet rate, droplet size, or both. In some applications, such as non-engine applications, when a droplet rate is regular or substantially regular, the droplet rate may be used to estimate or determine a droplet size or concentration.

In fuel systems applications, sensor controller <NUM> may be configured to provide a maintenance signal in response to detecting water in fuel. For example, a maintenance signal may be provided under certain conditions, such as when detecting a droplet above a threshold size, detecting a number of droplets above a threshold size, detecting a threshold number of droplets, determining a threshold volume of water based on detected droplets, detecting a threshold rate (or frequency) of droplets, or detecting a threshold concentration of water in fuel. These conditions may also be used for other liquid droplets in fluid.

<FIG> show various sizes of liquid droplets <NUM>, <NUM>, <NUM> that may be detected using a single microfluidic channel in detection assembly <NUM> of <FIG>. In particular, <FIG> are various illustrations showing when liquid droplet <NUM> with a large droplet size (e.g., a plug shape) greater than channel width <NUM> of microfluidic channel <NUM> flows through sensing area <NUM>. <FIG> are various illustrations showing when liquid droplet <NUM> with a medium droplet size (e.g., a spherical shape) equal to channel width <NUM> flows through sensing area <NUM>. <FIG> are various illustrations showing when liquid droplet <NUM> with a small droplet size (e.g., a small spherical shape) less than channel width <NUM> flows through sensing area <NUM>.

In the illustrated embodiments, channel depth <NUM> of the cross-sectional area <NUM> of microfluidic channel <NUM> is equal to channel width <NUM>. In other words, microfluidic channel <NUM> has a square shaped cross-sectional area <NUM>. Also, in the illustrated embodiments, sensing area <NUM> is in the shape of a cylinder, which may be provided by a light aperture in the shape of a circle. As described herein, various characteristics of liquid droplets <NUM>, <NUM>, <NUM> may be determined based on signals <NUM>, <NUM>, <NUM> detected, for example, in response to various liquid droplets <NUM>, <NUM>, <NUM>.

As used herein, a "plug shape" may be used to describe a liquid droplet that has been squeezed into a microfluidic channel and may have a shape similar to two spherical caps connected by a cylinder.

<FIG> shows a snapshot of large liquid droplet <NUM> flowing through microfluidic channel <NUM> when a center of liquid droplet <NUM> is aligned with a center of sensing area <NUM> of microfluidic channel <NUM>. <FIG> shows cross-sectional area <NUM> of microfluidic channel <NUM> at the center of sensing area <NUM> when liquid droplet <NUM> is positioned as shown in <FIG>. As can be seen, when liquid droplet <NUM> is constrained in microfluidic channel <NUM>, width <NUM> of liquid droplet <NUM> is the same as channel width <NUM> and channel depth <NUM>. When liquid droplet <NUM> is not constrained by microfluidic channel <NUM>, liquid droplet <NUM> may have a spherical shape. For comparison, <FIG> shows a top-down view of liquid droplet <NUM> as visible in sensing area <NUM>, also, when liquid droplet <NUM> is positioned as shown in <FIG>. As can be seen, liquid droplet <NUM> fills sensing area <NUM> as liquid droplet <NUM> flows through sensing area <NUM>.

<FIG> shows plot <NUM> of one example of a signal from light detector <NUM> (<FIG>). Plot <NUM> of signal <NUM> shows electrical voltage V versus time t. Signal <NUM> may be inversely related to absorbance of liquid in sensing area <NUM>. In other words, as light-absorbing liquid enters sensing area <NUM>, signal <NUM> may drop and, as light-absorbing liquid leaves sensing area <NUM>, signal <NUM> may rise. In other embodiments, signal <NUM> may be directly related (e.g., the opposite to inversely related) to absorbance of liquid in sensing area <NUM>, for example, depending on the particular type of light detector used.

Various thresholds may be used to characterize liquid droplet <NUM>. In the illustrated embodiment, before liquid droplet <NUM> enters sensing area <NUM>, signal <NUM> exceeds first threshold <NUM>. As light-absorbing liquid droplet <NUM> begins to fill sensing area <NUM>, signal <NUM> drops. After liquid droplet <NUM> completely fills sensing area <NUM>, signal <NUM> falls below second threshold <NUM>. As liquid droplet <NUM> begins to leave sensing area <NUM>, signal <NUM> rises and exceeds second threshold <NUM>. After liquid droplet <NUM> completely leaves sensing area <NUM> signal <NUM> may once again exceed first threshold <NUM>.

<FIG> shows a snapshot of medium liquid droplet <NUM> flowing through microfluidic channel <NUM> when a center of liquid droplet <NUM> is aligned with a center of sensing area <NUM> of microfluidic channel <NUM>. <FIG> shows cross-sectional area <NUM> of microfluidic channel <NUM> at the center of sensing area <NUM> when liquid droplet <NUM> is positioned as shown in <FIG>. As can be seen, when liquid droplet <NUM> is in microfluidic channel <NUM>, width <NUM> of liquid droplet <NUM> is the same as channel width <NUM> and channel depth <NUM>. For comparison, <FIG> shows a top-down view of liquid droplet <NUM> as visible in sensing area <NUM>, also, when liquid droplet <NUM> is positioned as shown in <FIG>. As can be seen, liquid droplet <NUM> fills sensing area <NUM> as liquid droplet <NUM> flows through sensing area <NUM>. In other words, both the large droplet size of liquid droplet <NUM> (<FIG>) and the medium droplet size of liquid droplet <NUM> (<FIG>) entirely fill sensing area <NUM>.

<FIG> shows plot <NUM> of signal <NUM> from light detector <NUM> (<FIG>). Like <FIG>, plot <NUM> of signal <NUM> shows electrical voltage V versus time t. The same thresholds <NUM>, <NUM> shown in <FIG> are shown here. In the illustrated embodiment, before liquid droplet <NUM> enters sensing area <NUM>, signal <NUM> exceeds first threshold <NUM>. As light-absorbing liquid droplet <NUM> begins to fill sensing area <NUM>, signal <NUM> drops. Like <FIG>, after liquid droplet <NUM> completely fills sensing area <NUM>, signal <NUM> falls below second threshold <NUM>. As liquid droplet <NUM> begins to leave sensing area <NUM>, signal <NUM> rises and exceeds second threshold <NUM>. After liquid droplet <NUM> completely leaves sensing area <NUM> signal <NUM> may once again exceed first threshold <NUM>. In contrast to <FIG>, the duration between signal <NUM> falling below second threshold <NUM> and subsequently exceeding second threshold <NUM> is substantially lower. As can be seen in <FIG>, the duration between crossings of second threshold <NUM> looks like a flat or substantially flat line, whereas signal <NUM> of <FIG> looks like a "V" or sharp valley. Further, the duration between signal <NUM> crossing first threshold <NUM> is shorter compared to signal <NUM> of <FIG>.

<FIG> shows a snapshot of small liquid droplet <NUM> flowing through microfluidic channel <NUM> when a center of liquid droplet <NUM> is aligned with a center of sensing area <NUM> of microfluidic channel <NUM>. <FIG> shows cross-sectional area <NUM> of microfluidic channel <NUM> at the center of sensing area <NUM> when liquid droplet <NUM> is positioned as shown in <FIG>. As can be seen, when liquid droplet <NUM> is in microfluidic channel <NUM>, width <NUM> of liquid droplet <NUM> is less than channel width <NUM> and channel depth <NUM>. For comparison, <FIG> shows a top-down view of liquid droplet <NUM> as visible in sensing area <NUM>, also, when liquid droplet <NUM> is positioned as shown in <FIG>. As can be seen, liquid droplet <NUM> does not fill sensing area <NUM> as liquid droplet <NUM> flows through sensing area <NUM> in contrast to the large droplet size of liquid droplet <NUM> (<FIG>) and the medium droplet size of liquid droplet <NUM> (<FIG>).

<FIG> shows plot <NUM> of signal <NUM> from light detector <NUM> (<FIG>). Like <FIG> and <FIG>, plot <NUM> of signal <NUM> shows electrical voltage V versus time t. The same thresholds <NUM>, <NUM> shown in <FIG> and <FIG> are shown here. In the illustrated embodiment, before liquid droplet <NUM> enters sensing area <NUM>, signal <NUM> exceeds first threshold <NUM>. As light-absorbing liquid droplet <NUM> begins to fill sensing area <NUM>, signal <NUM> drops. In contrast to <FIG> and <FIG>, after liquid droplet <NUM> completely enters sensing area <NUM>, signal <NUM> does not fall below second threshold <NUM>. As liquid droplet <NUM> begins to leave sensing area <NUM>, signal <NUM> rises. After liquid droplet <NUM> completely leaves sensing area <NUM> signal <NUM> may once again exceed first threshold <NUM>. In contrast to <FIG> and <FIG>, signal <NUM> does not cross second threshold <NUM>. Further, the duration between signal <NUM> crossing first threshold <NUM> is shorter compared to signal <NUM> of <FIG> and signal <NUM> of <FIG>. Signal <NUM> looks like a flat or substantially flat line when below first threshold <NUM>, similar to <FIG> but unlike <FIG>. The flat line may be attributed to the length of liquid droplet <NUM> being shorter than the length of sensing area <NUM> such that the entire liquid droplet <NUM> is in sensing area <NUM> for a longer duration than as shown in <FIG>.

With reference to the various patterns observed in signals <NUM>, <NUM>, <NUM>, various liquid droplets <NUM>, <NUM>, <NUM> may be identified and characterized. A droplet rate or droplet size may be determined based on a magnitude of a pulse contained within the signal from light detector <NUM> (<FIG>). As used herein, the term "pulse" refers to a time when the signal falls below first threshold <NUM>. A greater magnitude drop of the pulse may indicate a larger droplet size or slower droplet rate. Further, qualitatively, if the signal crosses first threshold <NUM> twice but does not cross second threshold <NUM> in between, then the droplet size may be determined as less than channel width <NUM>. Vice versa, if the signal crosses second threshold <NUM> in between first threshold <NUM> crossings, then the droplet size may be qualitatively determined as at least the size of channel width <NUM>.

In some embodiments, a droplet size may be determined based on the magnitude of the pulse contained within the signal when the signal level does not cross the second threshold. When the signal does not cross the second threshold, the droplet size may be determined to be less than channel width <NUM>. In such cases, the droplet size may be determined based on the magnitude drop of the signal during the pulse. In general, the larger the magnitude drop, the larger the droplet size.

Additionally, or alternatively, a droplet rate or droplet size may be determined based on a width of a pulse contained within the signal from light detector <NUM>. A greater width of the pulse, between first threshold <NUM> crossings, between second threshold <NUM> crossings, or both, may indicate a larger droplet size or slower droplet rate.

In some embodiments, a droplet size may be determined based on the width of the pulse contained within the signal when the signal level crosses the second threshold. When the signal crosses the second threshold, the droplet size may be determined to be at least the size of channel width <NUM>. in such cases, the droplet size may be determined based on the time between crossings of the signal with one or both thresholds <NUM>, <NUM>, which may be used to indicate the width of the pulse. In general, the larger the width, the larger the droplet size.

First and second thresholds <NUM>, <NUM> may be empirically determined and stored by sensor controller <NUM> (<FIG>) for a particular application. A first threshold <NUM> may be set to detect a minimum size liquid droplet in sensing area <NUM>. In general, the lower first threshold <NUM> is set, the larger the minimum size of liquid droplet detection. A second threshold <NUM> may be set to detect a liquid droplet that fills sensing area <NUM>, such as liquid droplet <NUM> (<FIG>) or liquid droplet <NUM> (<FIG>), which may have a droplet size greater than or equal to channel width <NUM>. A droplet rate or droplet size may be determined based on whether the signal crosses first threshold, second threshold, or both.

A droplet rate or droplet size may be determined based on a threshold signal level crossing rate, or how quickly the signal crosses first threshold <NUM>, second threshold <NUM>, or both. For example, the crossing of the signal from above to below first threshold <NUM> or second threshold <NUM> may be measured, or vice versa. In some embodiments, the crossing of the signal across one threshold <NUM>, <NUM> may be used. For example, if the signal falls below first threshold <NUM>, the next time the signal falls below first threshold <NUM>, the signal must have risen above first threshold <NUM>. Therefore, a droplet rate may be determined using only one type of threshold crossing.

In some embodiments of the present disclosure, more than one microfluidic channel may be used in a droplet sensor. For example, at least another microfluidic channel may be included in each detection assembly. The sensor controller operably connected to light detector <NUM> (<FIG>) may be further configured to detect one or more liquid droplets dispersed in a flow of fluid through another microfluidic channel based on the signal from the light detector. The sensor controller may be configured to distinguish between liquid droplets flowing through each of the microfluidic channels.

<FIG> show additional embodiments of detection assemblies <NUM>, <NUM>, which may be used with system <NUM> of <FIG>. In the illustrated embodiments, each detection assembly <NUM>, <NUM> includes a plurality of microfluidic channels <NUM>. Each microfluidic channel <NUM> may share one inlet <NUM> and may share one outlet <NUM>. The fluid connections between microfluidic channels <NUM>, inlet <NUM>, and outlet <NUM> are shown schematically with dashed lines. In some embodiments (not shown), microfluidic channels <NUM> may be in fluid communication with different inlets <NUM> and may be in fluid communication with different outlets <NUM>. Inlet <NUM> and outlet <NUM> may be in fluid communication with a main fluid flow, for example, in fuel line <NUM> of system <NUM>. As illustrated, microfluidic channels <NUM> are in parallel fluid communication with fuel line <NUM>. Each detection assembly <NUM>, <NUM> includes light detector <NUM> and an opposing light source (not shown). Microfluidic channels <NUM> may share one light detector <NUM> and one light source.

Each microfluidic channel <NUM> may have the same or different cross-sectional area. In some embodiments, the cross-sectional areas of each microfluidic channel <NUM> may be differently sized to detect different droplet sizes. Using a plurality of microfluidic channels <NUM> may be used in various applications to allow more fluid to be sampled at the same pressure drop compared to using a single microfluidic channel, allow a higher flowrate of fluid through the detection assembly, or lower the pressure drop for the same amount of fluid sampled. For example, using a plurality of microfluidic channels <NUM> may be used in-line with a main flow of fluid through fuel line <NUM>.

Detection assembly <NUM> may include a plurality of light apertures <NUM>. Each light aperture <NUM> corresponds to one microfluidic channel <NUM>. Light apertures <NUM> may be used to define multiple light beams, which in turn define one sensing area per microfluidic channel <NUM>. As liquid droplets flow through each microfluidic channel <NUM>, light detector <NUM> will detect different levels of absorption corresponding to liquid droplets flowing through microfluidic channels <NUM>. Light apertures <NUM> may have the same or different widths, which may facilitate sensitivity to the different droplet sizes. Each light aperture <NUM> may have any suitable shape, such as a circular shape.

Detection assembly <NUM> may include a single light aperture <NUM>. Single light aperture <NUM> corresponds to the plurality of microfluidic channels <NUM>. In other words, the plurality of microfluidic channels <NUM> share one light aperture <NUM>. Light aperture <NUM> may have any suitable shape, such as a rectangular shape. In some embodiments (not shown), light aperture <NUM> may have different widths along each microfluidic channel <NUM>.

In some embodiments (not shown), more than one light detector <NUM> may be used. For example, each microfluidic channel <NUM> may have a corresponding light detector. Each light detector may be operably connected to the same or a different sensor controller.

<FIG> shows a layout of sensor controller <NUM> that may be used with droplet sensor <NUM> (<FIG> and <FIG>). As illustrated, sensor controller <NUM> includes input interface <NUM> and output interface <NUM>. Sensor controller <NUM> may be operably connected to light detector <NUM> or optional flow sensor <NUM> using input interface <NUM>. Sensor controller <NUM> may be operably connected to computer <NUM> or light source <NUM> using output interface <NUM>. Each interface <NUM>, <NUM> may be operably connected to processor <NUM>, memory <NUM>, or both. Processor <NUM> may be operably coupled to memory <NUM> to store and retrieve information or data, such as signal <NUM>, threshold <NUM>, droplet rate <NUM>, droplet size <NUM>, or droplet amount <NUM>.

In the illustrated embodiment, processor <NUM> may be configured to receive signal <NUM> from light detector <NUM> using input interface <NUM>. One or more thresholds <NUM> may be determined by processor <NUM> based on signal <NUM> or retrieved from memory <NUM>. Various modules of processor <NUM> may be executed based on signal <NUM> and threshold <NUM>. For example, signal <NUM> and threshold <NUM> may be compared using comparator <NUM> executed on processor <NUM>. Based on the comparison, processor <NUM> may determine whether a liquid droplet has been detected using droplet detector <NUM>. Further, various characteristics of the liquid droplet may be determined using droplet characterizer <NUM>. Non-limiting examples of droplet characteristics that may be determined include droplet rate <NUM>, droplet size <NUM>, and droplet amount <NUM>. In some embodiments, processor <NUM> may determine to provide a maintenance signal <NUM> to output interface <NUM>.

A flow rate of fluid from flow sensor <NUM> may be used to determine some characteristics. In some embodiments, the flow meter or flow sensor <NUM> may be positioned in, upstream of, or downstream of the sensing channel or microfluidic channel. In general flow sensor <NUM> is positioned and configured to determine a flow rate of fluid through the microfluidic channel, which may also be described as a sensing channel.

<FIG> shows a flowchart describing method <NUM> that may be used with droplet sensor <NUM> of <FIG> or sensor controller <NUM> of <FIG>. Method <NUM> may include monitoring a signal <NUM>. If the monitored signal falls below a first threshold <NUM>, method <NUM> may continue and determine that a liquid droplet has been detected <NUM>. Otherwise, the signal may continue to be monitored <NUM>.

After a droplet has been detected <NUM>, if the signal exceeds the first threshold <NUM>, for example, without falling below the second threshold, method <NUM> may continue and determine a droplet size or rate <NUM>. For example, the droplet size may be determined to be less than a channel width of a microfluidic channel. As another example, a droplet rate may be determined based only on crosses of the first threshold. After the droplet size or rate is determined, the signal may continue to be monitored for another droplet <NUM>. If the signal has not yet exceeded the first threshold <NUM>, method <NUM> may continue and determine whether the signal has fallen below a second threshold <NUM>.

If the signal falls below the second threshold <NUM>, for example, before exceeding the first threshold, method <NUM> may determine droplet size or rate based on a pulse width <NUM>. As described herein above, a signal below the second threshold may indicate that the droplet size is greater than or equal to the channel width of the microfluidic channel, and the pulse width may indicate the droplet size or rate. After determining droplet size or rate <NUM>, the signal may continue to be monitored for another droplet <NUM>.

Otherwise, if the signal does not fall below the second threshold <NUM>, for example, before exceeding the first threshold, method <NUM> may determine droplet size based on a pulse magnitude <NUM>. As described herein above, a signal above the second threshold may indicate that the droplet size is less than the channel width of the microfluidic channel, and the pulse magnitude may indicate the droplet size. After determining droplet size <NUM>, the signal may continue to be monitored for another droplet <NUM>.

The droplet sensor may be integrated with the main flow line as described in claim <NUM> in any suitable manner. Controlling piping dimensions (e.g., length or hydraulic diameter) and observing the impact of minor pressure head losses (e.g., expansions or contractions in hydraulic diameter) may allow pressure losses in the overall system to be controlled. In some cases, the droplet sensor may be integrated in a manner to reduce overall pressure or energy loss, for example, facilitating a shorter microfluidic channel length.

The microfluidic sensor is in parallel fluid communication with a main flow branch. In some embodiments, the microfluidic channel may be configured to accept a bypass flow from the main flow. In some embodiments, the microfluidic channel may be at least partially disposed within the main flow.

<FIG> shows one example of a droplet sensor that may be used with system <NUM>. Droplet sensor <NUM> includes microfluidic channel <NUM> positioned to receive a bypass flow from main flow channel <NUM>. One or both of main flow channel <NUM> or microfluidic channel <NUM> may include a bend to separate the bypass flow from the main flow.

In the illustrated embodiment, microfluidic channel <NUM> forms a straight path with main flow inlet <NUM> and main flow outlet <NUM> of main flow channel <NUM>. The straight geometry may prevent water drops or bubbles from being caught in microfluidic channel <NUM>. The main flow follows a different path along main flow branch <NUM>. As illustrated, main flow branch <NUM> is shown as a simple loop, but any suitable shape may be used to balance pressure and flow through the microchannel.

In some embodiments, microfluidic channel <NUM> may include a converging-diverging nozzle or converging-diverging nozzle design. The nozzle may improve pressure recovery, or otherwise control pressure losses, for example, by reducing the length of microfluidic channel <NUM>. In the illustrated embodiment, the nozzle may be defined by inlet portion <NUM>, sensing portion <NUM> (which may also be described as a throat of the nozzle), and outlet portion <NUM>. In other embodiments, sensing portion <NUM> may be incorporated into the inlet portion <NUM> or the outlet portion <NUM>.

In the illustrated embodiment, inlet portion <NUM> and outlet portion <NUM> each have widths that are variable, or that change, along their length. Length of microfluidic channel <NUM> is defined along an axis that extends along the direction of flow through microfluidic channel <NUM>. Width of microfluidic channel <NUM> is generally orthogonal to length. Sensing portion <NUM> may have a width that does not change along its length, for example, when sensing portion <NUM> is not incorporated into inlet portion <NUM> or outlet portion <NUM>.

Inlet portion <NUM> may taper in the direction of fluid flow, or flow direction, through microfluidic channel <NUM>. The taper may be linear or non-linear (e.g., curved). Inlet portion <NUM> may define a contraction angle, which is a measurement that may represent the angle of a linear taper or may represent an average measurement representative of multiple measurements of angles in a non-linear taper. An angle may be measured from any suitable axis, such as an axis aligned to the direction of bypass fluid flow through microfluidic channel <NUM>. Inlet portion <NUM> may be described as a contracting inlet portion.

Outlet portion <NUM> may flare in the direction of fluid flow, or flow direction, through microfluidic channel <NUM>. The flare may be linear or non-linear (e.g., curved). Outlet portion <NUM> may define an expansion angle, which may be calculated in a similar manner to the contraction angle. An angle may be measured from any suitable axis, such as an axis aligned to the direction of bypass fluid flow. Outlet portion <NUM> may be described as an expanding outlet portion.

Inlet portion <NUM> and outlet portion <NUM> may also be described using a contraction ratio and an expansion ratio. As used herein, "contraction ratio" refers to the ratio of the cross-sectional area at the nozzle inlet (widest cross-sectional area of inlet portion <NUM> or at the widest opening of the inlet portion) and the throat (the smallest cross-sectional area, such as in the sensing portion <NUM>). The "expansion ratio" refers to the ratio of the cross-sectional area at the nozzle outlet (widest cross-sectional area of outlet portion <NUM> or at the widest opening of the outlet portion). For example, a channel cross-sectional area that goes <NUM> micrometers down to <NUM> micrometers and back to <NUM> micrometers would have a contraction ratio of <NUM> and an expansion ratio of <NUM>.

The lengths and corresponding angles of inlet portion <NUM> and outlet portion <NUM> may be the same or different. In some embodiments, the length of contracting inlet portion <NUM> is shorter than the length of the expanding outlet portion <NUM>, or vice versa. In some embodiments, the contraction angle of inlet portion <NUM> may be greater than the expansion angle of outlet portion <NUM>. In some embodiments, the expansion and contraction ratios may be the same or different. For example, the expansion ratio and the contraction ratio may be the same even though the corresponding lengths and angles are the different.

In the illustrated embodiment, main flow <NUM>, or main fluid flow, enters from the left side of the illustration into microfluidic channel <NUM> from main flow inlet <NUM>. The main flow <NUM> splits between main flow branch <NUM> and microfluidic channel <NUM>. The bypass flow enters microfluidic channel <NUM> at inlet portion <NUM> and increases in fluid velocity, while flow rate remains the same, as the cross-section decreases in inlet portion <NUM> causing the static pressure head to decrease. After the bypass flow passes from inlet portion <NUM> and sensing portion <NUM> and enters outlet portion <NUM>, the reverse occurs and the fluid velocity decreases, while flow rate remains the same, causing the static head pressure to increase. In other words, the fluid velocity may decrease, and the static head pressure may increase, after a minimum diameter of microfluidic channel <NUM> is encountered by the bypass flow. The bypass flow may then rejoin in the main flow after passing through outlet portion <NUM>.

By controlling the contraction and expansion rates, the amount of pressure recovery may be controlled, for example, by minimizing flow separation within the system. In properly engineered devices, minimizing flow separation may lead to sustainably less pressure drop at a given channel length compared to a constant cross-sectional area channel length. The converging-diverging nozzle design of microfluidic channel <NUM> may be used to control the pressure drop through droplet sensor <NUM>. A lower pressure drop may lead to additional flow through droplet sensor <NUM>.

System <NUM> may include a flow restrictor to facilitate fluid flow through droplet sensor <NUM>. In the illustrated embodiment, flow restrictor <NUM> may be positioned along the main flow channel <NUM>, for example, in main flow branch <NUM>. Flow restrictor <NUM> may facilitate driving more flow through microfluidic channel <NUM> compared to a system without flow restrictor <NUM>. In some cases, without flow restrictor <NUM>, less than or equal to <NUM> % of the main flow may enter microfluidic channel <NUM>, for example, when a width or diameter of microfluidic channel <NUM> is <NUM> micrometers and a width or diameter of main flow channel <NUM> is <NUM> millimeters. In general, the relative width of microfluidic channel <NUM> is much smaller compared to main flow channel <NUM> than illustrated (e.g., at least one order of magnitude). In some embodiments, at least <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or even <NUM> % of the main flow may enter microfluidic channel <NUM>, for example, when the converging-diverging nozzle or flow restrictor <NUM> is included.

Optical components may be used to increase the signal-to-noise ratio of droplet sensor <NUM>, for example, by increasing the intensity of light from light source <NUM> directed at light detector <NUM>. In one or more embodiments, droplet sensor <NUM> may include one or more optical components, such as focusing optics or a lens <NUM>. One or more lenses <NUM> may be positioned generally between light source <NUM> and light detector <NUM>. As illustrated one lens <NUM> is positioned between light source <NUM> and microfluidic channel <NUM>, and another lens <NUM> is positioned between microfluidic channel <NUM> and light detector <NUM>.

The microfluidic channel may be at least partially or fully submerged in the main flow of the fuel line. In some embodiments, an inlet of the microfluidic channel is positioned in the main flow or main flow channel. <FIG> show various examples of positioning an inlet of the microfluidic channel to sample the main flow from the main flow channel. Main flow <NUM> through main flow channel <NUM> may be sampled by the droplet sensor from near the wall of main flow channel <NUM> (e.g., near the wall of the pipe) or from inside main flow channel <NUM> (e.g., inside the pipe). If main flow <NUM> is sampled from the middle of main flow channel <NUM>, the main flow <NUM> may be sampled from a straight section of pipe or from a bend in the pipe. Inlet portion <NUM> of microfluidic channel <NUM> may include opening <NUM> positioned to capture a representative fluid sample for the droplet sensor, a sample in which the water drops are concentrated, or a sample in which water drops are diluted. In general, the center of main flow channel <NUM> may provide a representative fluid sample of main flow <NUM>.

The opening <NUM> may have the same cross-sectional dimensions as microfluidic channel <NUM> or may be larger or smaller. Larger sensor inlet dimensions may be advantageous due to a lower pressure drop.

<FIG> shows droplet sensor <NUM>, which includes opening <NUM> at a distal end of inlet portion <NUM> extending from a side of main flow channel <NUM> toward a center of main flow channel <NUM> to position opening <NUM> near the center of main flow channel <NUM>. In the illustrated embodiment, main flow channel <NUM> extends linearly, or straight, and microfluidic channel <NUM> extends linearly, or straight, orthogonal to the direction of main flow <NUM>.

Main flow channel <NUM> may extend linearly or non-linearly. In some embodiments, one or more droplet sensor embodiments may also be used with a main flow channel having a bend or other non-linear geometry. <FIG> shows droplet sensor <NUM>, which includes opening <NUM> at a distal end of inlet portion <NUM> extending from bend <NUM> in main flow channel <NUM> to a center of main flow channel <NUM> to position opening <NUM> near the center of main flow channel <NUM>. In the illustrated embodiment, main flow channel <NUM> is non-linear. Microfluidic channel <NUM> enters into main flow channel <NUM> at bend <NUM>.

Inlet portion <NUM> of microfluidic channel <NUM> may be straight or include a taper (or converging nozzle). <FIG> shows droplet sensor <NUM>, which includes opening <NUM> at a distal end of inlet portion <NUM> extending from bend <NUM> to a center of main flow channel <NUM> to position opening <NUM> near the center of main flow channel <NUM>. Inlet portion <NUM> is at least partially tapered and opening <NUM> is larger compared to droplet sensor <NUM> (<FIG>). In the illustrated embodiment, main flow channel <NUM> extends linearly, or straight, and microfluidic channel <NUM> extends linearly, or straight, along the direction of main flow <NUM>.

The microfluidic channel may be entirely submerged in the main flow channel. In particular, the inlet and the outlet of the microfluidic channel may be positioned in the main flow of the main flow channel. In some embodiments, the droplet sensor may be in an annular flow configuration, in which the microfluidic sensor channel is contained within the main flow channel. The microfluidic channel may be located at the center of the main flow channel or away from the center.

The microfluidic sensor channel runs parallel to the direction of fluid flow. The light source and detector may be submersed in the main flow channel, encapsulated and submersed, or coupled to the microfluidic channel with fiber optics, light guides, waveguides, or the like. The microfluidic channel may have a constant cross-sectional dimension (e.g., width) or may vary along its length. Varying the microfluidic sensor channel dimensions may be advantageous by lowering pressure drop or increasing sampling volume.

<FIG> show various examples of microfluidic channels submerged in a main flow channel, which may facilitate having fewer bends in the path of fluid flow. <FIG> show one example of a droplet sensor with the light source and light detector submerged in a main flow channel. Droplet sensor <NUM> includes light source <NUM>, light detector <NUM>, and microfluidic channel <NUM>. In particular, inlet <NUM> (e.g., opening or inlet portion) and outlet <NUM> (e.g., opening or outlet portion) of microfluidic channel <NUM> are submerged in main flow channel <NUM>. Microfluidic channel <NUM> may be described as being surrounded by a wall, or interior surface, of main flow channel <NUM>.

To hold a substrate forming microfluidic channel <NUM> in the main flow, one or more supports <NUM>, or support structures, may be coupled to main flow channel <NUM>. In the illustrated embodiment, one support <NUM> is coupled between light source <NUM> and a wall of main flow channel <NUM>. Another support <NUM> is coupled between light detector <NUM> and a wall of main flow channel <NUM> and may be on the opposite side of main flow channel <NUM> or microfluidic channel <NUM> than the other support. The substrate forming microfluidic channel <NUM> may be coupled to light source <NUM> or a first support <NUM> and may be coupled to light detector <NUM> or a second support <NUM> to be held, for example, near a center of the main flow. Supports <NUM> may be made of any suitable material to mechanically couple different components of the droplet sensor <NUM>.

Microfluidic channel <NUM> may be formed from a substrate or defined between two or more optical components, for example, instead of being formed only from a substrate. In some embodiments, microfluidic channel <NUM> may be defined between two or more optical components, such as a light source, light detector, light aperture, light channel, lens, and separate microfluidic channel substrate. In some embodiments, microfluidic channel <NUM> may be formed of a glass tube as the substrate.

One example of a light channel is a fiber optic channel, or a channel formed by fiber optics. Use of fiber optics may allow certain optical components of the droplet sensor to be positioned outside of the main flow channel. <FIG> show one example of a droplet sensor with fiber optics at least partially submerged in a main flow channel that form a microfluidic channel. Droplet sensor <NUM> includes light source <NUM>, light detector <NUM>, and fiber optics <NUM>. In the illustrated embodiment, light source <NUM> and light detector <NUM> are positioned outside of main flow channel <NUM> and optically coupled to the interior of main flow channel <NUM> through fiber optics <NUM>. The microfluidic channel <NUM> may be defined in length and width by end portions of optical fibers of fiber optics <NUM>, for example, instead of a separate microfluidic channel substrate.

Various combinations of optical components may also be used to form the microfluidic channel. In some embodiments, a light source and a fiber optic channel may be used to define the microfluidic channel. In other embodiments, a light detector and a fiber optic channel may be used to define the microfluidic channel. In still further embodiments, the light source and light detector may be contained within main flow channel and define the microfluidic channel.

Optical components forming the microfluidic channel may be described as forming a virtual microfluidic channel between the two components. That is, the path length between the two components creates the microfluidic channel. The light detector or light source may be coupled to, or positioned relative to, a light aperture to define the virtual microfluidic channel.

In general, one or both of the light source and detector may be outside the main flow channel, where fiber optics, light guides, waveguides, or the like may be used to bring the light into or out of the main flow channel to or from the virtual microfluidic channel. Utilizing the virtual microfluidic channel may reduce pressure drop relative to using a separate substrate only to form the microfluidic channel.

Sensors similar to the droplet sensors described herein may also be used to detect water without a microfluidic channel. In some embodiments, such a sensor may be used to detect when a water volume or water level (e.g., based on height) has reached a certain threshold or used to monitor water level continuously. In some trucking applications, for example, understanding water height may help a truck operator understand when to drain water from the fuel system because a certain water volume has been collected. Existing water sensors in trucking applications utilize a mechanical float, which may be prone to fouling, or a resistive or conductive probe, which may also be prone to fouling through electroplating or deposits.

<FIG> show various examples sensors that do not form part of the claimed invention, such as water level sensors, used without a microfluidic channel in a fuel water separator or fuel filter, such as fuel filter <NUM> (<FIG>). When water is removed from a fuel system using a filter, the water may be collected in the bottom of a housing <NUM> of fuel water separator <NUM> in a water collection volume <NUM>, or bowl, after fuel is filtered. The water collection volume <NUM> may be fluidly connected to an engine fuel line (e.g., main flow channel) fluidly connected to filter element <NUM> and water drain outlet <NUM> to selectively drain water when water has reached threshold water level <NUM>. In general, the water collection volume <NUM> may be upstream of filter element <NUM> or downstream of filter element <NUM>.

Sensor <NUM> may be positioned at a height of water collection volume <NUM> corresponding to detect water reaching threshold water level <NUM>. Sensor <NUM> may include light source <NUM>, which may be a near-infrared light source. Sensor <NUM> may also include light detector <NUM>, which may be a photodetector. Light source <NUM> and light detector <NUM> may be positioned to define threshold water level <NUM> in the water collection volume <NUM>. The distance or space between lights source <NUM> and light detector <NUM> may define path length <NUM>.

A controller (which may be similar to controller <NUM> of <FIG>) may be operably coupled to light detector <NUM> and optionally light source <NUM>. The controller may be configured to determine that water in water collection volume <NUM> has reached threshold water level <NUM> in response to the signal from light detector <NUM>. In general, when water is present between light source <NUM> and light detector <NUM> along path length <NUM>, in response, the controller may determine that the water volume has reached threshold water level <NUM>.

Various configurations of sensor <NUM> may be used to measure the water level. <FIG> shows sensor <NUM> having light source <NUM> and light detector <NUM> positioned outside of water collection volume <NUM> and housing <NUM>. In other embodiments, one or both of light source <NUM> and light detector <NUM> may be positioned inside water collection volume <NUM> or housing <NUM> and may be submersible in water.

<FIG> shows another example of a sensor configuration. Sensor <NUM> is similar to sensor <NUM> and further includes optical components <NUM>, or fiber optics. Optical components <NUM> may be used to couple light from light source <NUM> or light detector <NUM> into or out of water collection volume <NUM>. In the illustrated embodiment, light source <NUM> is positioned outside water collection volume <NUM> and is optically coupled to optical component <NUM> to direct a light beam into water collection volume <NUM> and toward light detector <NUM>. Light detector <NUM> is positioned inside water collection volume <NUM> to receive the light beam and is optically coupled to another optical component <NUM> to direct the light beam outside of water collection volume <NUM>. Path length <NUM> may be defined between optical component <NUM> coupled to light source <NUM> and light detector <NUM>.

<FIG> shows yet another example of a sensor configuration. Sensor <NUM> is similar to sensor <NUM> and is oriented to measure a water level by defining path length <NUM> in a direction to measure rising water levels (e.g., vertically). In particular, light source <NUM> and light detector <NUM> are positioned to measure a water level in water collection volume <NUM> and the controller (which may be similar to controller <NUM> of <FIG>) is configured to determine the water level in response to the signal. As the water level rises along path length <NUM>, the absorptivity detected by light detector <NUM> will increase, and the controller may determine the water level, for example, in proportion to the increase in absorptivity. In the illustrated embodiment, light source <NUM> and light detector <NUM> are positioned inside water collection volume <NUM> and housing <NUM>. In other embodiments, light source <NUM> and light detector <NUM> may be positioned outside water collection volume <NUM> or housing <NUM>.

In general, a near-infrared light source and detector may be placed outside the water collection bowl. If the near-infrared light source and detector are outside the water collection volume, they may be coupled with fiber optics, wave guides, light guides (or similar) to bring the incoming light into the bowl, and to collect the transmitted light and bring it back out of the bowl. In some embodiments, one of the light source and detector may be in the water collection volume, while the other component may be outside the water collection bowl connected by a fiber optic, wave guide, or light guide. In other embodiments, both the light source and detector may be in the water collection volume.

The path length of the light may consist of a portion of the water collection volume width or height or may include the entire water collection bowl width or height. If the path length of light is the entire water collection volume width or height, the housing of the fuel water separator may be made from a material transparent to near-infrared light (e.g., glass) such that the light source and detector are outside the housing. If the sensor is oriented with the water collection bowl width, the sensor can act as a trigger once the water has reached the height of the sensor. If the sensor is oriented with the water collection bowl height (or at an oblique angle), the sensor can act as a continuous water level sensor as a decrease in transmitted light may indicate an increase in water height.

<FIG> shows one example of a fuel water separator including a filter head. In the illustrated embodiment, various positions for a sensor or droplet sensor <NUM> are shown within fuel water separator <NUM>. In some examples, one or more droplet sensors <NUM> may be positioned in filter head <NUM>. Filter head <NUM> may include an inlet and an outlet in fluid communication with a main flow channel and the filter element. Droplet sensor <NUM> may be positioned to sample along inlet <NUM>, along outlet <NUM>, between inlet and outlet, or even along or within filter element <NUM>.

In general, a microfluidic water sensor, or droplet sensor, may be integrated directly into the filter head. The sensor could be placed in the inlet or outlet of the filter head. The sensor could be a bypass to the filter connecting the inlet and outlet directly. The sensor may be incorporated directly into a replaceable filter element.

While the present disclosure is not so limited, an appreciation of various aspects of the disclosure will be gained through a discussion of the specific examples and illustrative embodiments provided below. Various modifications of the examples and illustrative embodiments, as well as additional embodiments of the disclosure, will become apparent herein.

In Example <NUM>, detection assembly <NUM> was provided as shown in <FIG>. Detection assembly <NUM> included a near-infrared light-emitting diode (LED) <NUM>, which was centered at <NUM> (available from Thorlabs, Newton, New Jersey). LED <NUM> was driven by commercially-available 5V power source <NUM> connected using a Universal Seral Bus (USB) port. LED <NUM> was connected in series with a commercially available 51Ω resistor <NUM>. Light from LED <NUM> was not focused by an optics. LED <NUM> was brought into close proximity to microfluidic device <NUM>, made of poly(dimethylsiloxane) (PDMS) (available under trade name DOW CORNING SYLGARD <NUM>) and glass, which defined a microfluidic channel. Microfluidic device <NUM> included a T-Junction droplet generator that fed water drops into the microchannel of microfluidic device <NUM>. The microchannel, or microfluidic channel, had a width of <NUM> micrometers and a depth of <NUM> micrometers. The channel was aligned with <NUM>-pinhole light aperture <NUM> (available from Thorlabs). Light from LED <NUM> was directed through the light aperture <NUM> and the microfluidic channel of microfluidic device <NUM> to be detected by a PDA30B germanium (Ge) transimpedance amplified light detector <NUM> (available from Thorlabs, Newton, New Jersey). The output signal was transferred via a <NUM>Ω BNC cable to a TDS 2014C oscilloscope (available from Tektronix, Beaverton, Oregon).

A flow of fuel at <NUM> microliters per minute and a flow of water at <NUM> microliters per minute were provided to detection assembly <NUM> using syringe pumps (available from Harvard Apparatus, Holliston, Massachusetts), which resulted in the formation of water droplets. As determined from signal analysis, the water droplets had a diameter of <NUM> micrometers at a droplet rate of <NUM> droplets per second. Measurements were taken using the TDS 2014C oscilloscope set at a probe attenuation of 10x. <FIG> shows plot <NUM> of voltage (V) versus time (s) of signal <NUM> from the TDS 2014C oscilloscope. Each dip in signal <NUM> corresponded to a droplet moving through a sensing area defined by detection assembly <NUM>.

In Example <NUM>, a detection assembly was fed with drops smaller than the dimensions of the microchannel of a microfluidic device to test whether the detector response would correspond, or correlate, to droplet diameter. The detection assembly was the same as detection assembly <NUM>, except that the microfluidic device used a flow focusing droplet generator was used instead of a T-Junction droplet generator was used to feed the microchannel and the oscilloscope was set at a 1x attenuation. From signal analysis, droplet frequency and size were determined. As illustrated in <FIG>, plot <NUM> shows the output voltage drop of the detector in millivolts (mV) for various droplet sizes (µm or micrometers). As can be seen, the greater voltage drops correspond to greater droplet diameters when the droplet is smaller than the width of the microchannel.

Thus, various embodiments of the DROPLET SENSORS FOR FUEL SYSTEMS are disclosed. Although reference is made herein to the accompanying set of drawings that form part of this disclosure, one of at least ordinary skill in the art will appreciate that various adaptations and modifications of the embodiments described herein are within, or do not depart from, the scope of this disclosure. For example, aspects of the embodiments described herein may be combined in a variety of ways with each other. Therefore, it is to be understood that, within the scope of the appended claims, the claimed invention may be practiced other than as explicitly described herein.

Herein, the terms "up to" or "less than or equal to" a number (e.g., up to <NUM>) includes the number (e.g., <NUM>), and the term "no less than" a number (e.g., no less than <NUM>) includes the number (e.g., <NUM>).

The terms "coupled" or "connected" refer to elements being attached to each other either directly (in direct contact with each other) or indirectly (having one or more elements between and attaching the two elements). Either term may be modified by "operatively" and "operably," which may be used interchangeably, to describe that the coupling or connection is configured to allow the components to interact to carry out at least some functionality (for example, sensor controller may be operatively connected to vehicle computer to send and receive data).

Terms related to orientation, such as "top," "bottom," "upstream," and "downstream," are used to describe relative positions of components and are not meant to limit the orientation of the embodiments contemplated.

As used herein, "have," "having," "include," "including," "comprise," "comprising" or the like are used in their open-ended sense, and generally mean "including, but not limited to. " It will be understood that "consisting essentially of," "consisting of," and the like are subsumed in "comprising," and the like.

Claim 1:
A system comprising:
a microfluidic channel (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>) configured to receive a flow of a first fluid and a second fluid dispersed in the first fluid, wherein the second fluid has a different composition than the first fluid;
a light source (<NUM>; <NUM>; <NUM>; <NUM>) configured to direct a light beam in a frequency band along a path through the microfluidic channel (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>), wherein the frequency band is selected to have a higher absorbance by the second fluid than by the first fluid;
an aperture element (<NUM>) defining a light aperture (<NUM>; <NUM>; <NUM>) positioned in the path of the light beam from the light source (<NUM>; <NUM>; <NUM>; <NUM>);
a light detector (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>) positioned to receive the light beam in a sensing area after passing through the microfluidic channel (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>) and the light aperture (<NUM>; <NUM>; <NUM>), the light detector (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>) configured to provide a signal representing an amount of light in the frequency band that remains after passing through the microfluidic channel (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>); and
a controller (<NUM>) operably coupled to the light detector (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>), wherein the controller (<NUM>) is configured to determine whether the second fluid is in droplet form based on the signal,
characterized by the fact that the system comprises an engine fuel line (<NUM>), wherein the microfluidic channel (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>) is in parallel fluid communication with a main flow of said engine fuel line (<NUM>).