GB2452980A

GB2452980A - A separator

Info

Publication number: GB2452980A
Application number: GB0718519A
Authority: GB
Inventors: Jamie Archer; Adrian Mincher; Mark A Glynn
Original assignee: Parker Hannifin AB; Parker Hannifin Corp
Current assignee: Parker Hannifin AB; Parker Hannifin Corp
Priority date: 2007-09-22
Filing date: 2007-09-22
Publication date: 2009-03-25
Also published as: GB2465514A; GB201003420D0; GB0813939D0; GB2465514B; WO2009037496A2; GB2465514A8; WO2009037496A3; GB0718519D0

Abstract

A separator for separating contaminants from a fluid stream comprises a chamber 20, a first inlet 6 for receiving a first fluid stream into the chamber including a convergent nozzle 18 for accelerating the first fluid stream, a second inlet 2 for receiving a second fluid stream including entrained contaminants into the chamber (20;58), the second inlet 2 being arranged relative to the first inlet 6 such that the first fluid stream can entrain and accelerate the second fluid stream forming a combined fluid stream within the chamber (20;58). The separator further comprises a surface (36, 50) coupled to the chamber (20;58) arranged such that the surface (36;50) can cause a deviation in the course of the combined fluid stream incident upon it such that contaminants are separated from the combined fluid stream. Advantageously the separator may be used instead of a filter to separate particulate, liquid and aerosol contaminants from blow-by gas stream in a reciprocating engine.

Description

A separator The present invention relates to a separator. In particular, the present invention relates to a separator for separating particulate, liquid and aerosol contaminants from a fluid stream.

Certain embodiments of the present invention relate to a separator for separating particulate, liquid and aerosol contaminants from a blow-by gas stream within a reciprocating engine.

Blow-by gas within a reciprocating engine is generated as a by-product of the combustion process. During combustion, some of the mixture of gases escape past piston rings or other seals and enter the engine crankcase outside of the pistons. The term "blow-by" refers to the fact that the gas has blown past the piston seals. The flow level of blow-by gas is dependent upon several factors, for example the engine displacement, the effectiveness of the piston cylinder seals and the power output of the engine. Blow by gas typically has the following components: oil (as both a liquid and an aerosol, with aerosol droplets in the range 0.1 l.Lm to I OItm), soot particles, nitrous oxides (NOx), hydrocarbons (both gaseous hydrocarbons and gaseous aldehydes), carbon monoxide, carbon dioxide, oxygen, water and other gaseous air components.

If blow-by gas is retained within a crankcase with no outlet the pressure within the crankcase rises until the pressure is relieved by leakage of crankcase oil elsewhere within the engine, for example at the crankcase seals, dipstick seals or turbocharger seals. Such a leak may result in damage to the engine.

In order to prevent such damage, and excessive loss of oil, it is known to provide an outlet valve which allows the blow-by gas to be vented to the atmosphere. However, with increasing environmental awareness generally, and within the motor industry in particular, it is becoming increasingly unacceptable to allow blow-by gas, which is inevitably contaminated with oil and other contaminants from within the crankcase, to simply be vented to atmosphere. Furthermore, such venting increases the speed at which crankcase oil is consumed.

Consequently, it is known to filter the blow-by gas. The filtered blow-by gas may then either be vented to the atmosphere as before (in an open ioop system), or it may be returned to an air inlet of the engine (in a closed loop system). The filtering may be performed by passing the blow-by gas through a filtering medium, or another known form of gas contaminant separator. For a closed loop system, filtration is required in order to remove oil, soot and other contaminants to protect engine components from fouling and any resultant reduction in performance or failure of a component.

There is an increasing demand for higher efficiency cleaning of blow-by gas in both open and closed loop systems. For instance, separation efficiency of greater than 85% measured by mass (gravimetric) for particles greater than or equal to O.3m is required by many engine manufacturers.

Separation using filter mediums is undesirable as such filters have a finite lifespan before they become clogged and must be replaced. Engine manufacturers and end users in general prefer to only use engine components that can be fitted and remain in place for the life of the engine. While fit for life separators are known, typically only driven centrifugal separators have hitherto been able to achieve the required levels of separation efficiency.

Such a driven centrifugal separator is cumbersome and has moving parts which may be prone to failure. Impactor separators (where separation occurs as a contaminated gas stream is incident upon an impactor plate transverse to the gas flow) are not usually able to achieve the required separation efficiency.

It is an object of embodiments of the present invention to obviate or mitigate one or more of the problems associated with the prior art, whether identified herein or elsewhere.

Specifically, it is an object of embodiments of the present invention to provide a high efficiency, fit for life separator for separating contaminants from a fluid stream that is not dependent upon moving parts.

According to an aspect of the present invention there is provided a separator for separating contaminants from a fluid stream, comprising: a chamber; a first inlet for receiving a first fluid stream into the chamber including a convergent nozzle for accelerating the first fluid stream; a second inlet for receiving a second fluid stream including entrained contaminants into the chamber, the second inlet being arranged relative to the first inlet such that the first fluid stream can entrain and accelerate the second fluid stream fonning a combined fluid stream within the chamber; and a surface coupled to the chamber arranged such that the surface can cause a deviation in the course of the combined fluid stream incident upon it such that contaminants are separated from the combined fluid stream.

An advantage of the present invention is that contaminants can be removed from a fluid stream without the need for driven or moving parts, and still achieve high separation efficiency. The present invention is particularly suitable for separating contaminants from a gas stream. More particularly, the present invention is suitable for removing contaminants from a blow-by gas stream derived from an internal combustion engine.

Such a separator may be a fit for life separator owing to the absence of moving parts that may fail or filter mediums that would be prone to clogging and require periodic replacement. Advantageously, the separator provides for high separation efficiency and low or no pressure drop across the system between the blow-by gas inlet and the blow-by gas outlet. Furthermore, separators in accordance with embodiments of the present invention are relatively small, simple and cost effective to manufacture and have a small number of parts.

The surface may comprise an impaction plate. The impaction plate is positioned in a plane at approximately 900 to the combined fluid stream, such that the impaction plate can cause a deviation in course of the combined fluid stream of approximately 90°. The separator may further comprise a gap extending about at least a portion of the periphery of the impaction plate at the end of the chamber remote from the convergent nozzle, arranged such that the combined fluid stream can pass through the gap into a collection space. The gap may further comprise a bend operable to cause a further deviation in the course of the combined fluid stream.

Alternatively, the surface comprises an interior surface of a cyclone chamber arranged to receive the combined fluid stream.

The separator may further comprise a fluid outlet allowing the cleaned fluid stream to exit the separator. The separator may further comprise a drain positioned to allow contaminants to drain from the separator.

The convergent nozzle may comprise a convergent-divergent nozzle. The convergent nozzle may comprise a tube including a restricted central portion. The chamber may be generally cylindrical and the chamber diameter proximate to the convergent nozzle may be between 2 and 5 times larger than the diameter of the narrowest diameter of the convergent nozzle. The convergent nozzle may be arranged to generate a region of reduced pressure within the chamber about the first inlet operable to draw in the second fluid stream from the second inlet.

The separator may further comprise an annular second nozzle surrounding the first inlet, the second nozzle being in communication with the second inlet such that the second fluid stream can flow through the second nozzle. The second inlet may communicate with an annular space surrounding the chamber, the annular space in turn communicating with the annular second nozzle. The annular second nozzle may be arranged such that the second fluid stream can flow into the chamber generally parallel to the first fluid stream from the first inlet.

The chamber may be generally formed as a cylinder, the diameter of the chamber reducing towards the surface.

The fluid streams may comprise gas streams. The separator may be operable to separate particulate, liquid andlor aerosol contaminants from the combined gas stream. The separator may be operable to separate greater than 95% of particles greater than O.3im in diameter from the combined fluid stream.

In another aspect of the present invention there is provided an internal combustion engine including a separator as described above, wherein the second inlet is arranged to receive blow-by gas derived from a crankcase. The first inlet may be arranged to receive a pressurised gas stream derived from a turbocharger and the separator may be operable to separate crankcase oil from the combined gas stream, the separator being arranged to return separated crankcase oil to the crankcase.

The internal combustion engine may further comprise a vacuum limiting valve coupled to a gas outlet. The internal combustion engine may further comprise a pressure regulation valve coupled to the second inlet. The internal combustion engine may further comprise a check valve coupled to a contaminant drain arranged to prevent contaminants being drawn into the separator through the contaminant drain.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a separator in accordance with a first embodiment of the present invention; Figure 2 is a cross sectional view through the separator of figure 1; Figure 3 is an enlarged portion of the cross sectional view of figure 2; Figure 4 is a graph illustrating the variation of engine output power with engine speed for an exemplary engine firstly without a separator fitted, and secondly with a separator in accordance with an embodiment of the present invention fitted to extract contaminants from a blow-by gas stream; Figure 5 schematically illustrates a separator in accordance with embodiments of the present invention used in a closed loop application in combination with a reciprocating engine; Figure 6 is a perspective view of a separator in accordance with a second embodiment of the present invention; Figure 7 is a first cross sectional view through the separator of figure 6 illustrating the relative arrangements of the gas inlets; and Figure 8 is a second cross sectional view through the separator of figure 6 in a plane that is perpendicular to the plane illustrated in figure 7, illustrating the relative arrangement of the gas outlet and the contaminant outlet.

Referring first to figure 1, this is a perspective view of a separator in accordance with a first embodiment of the present invention for separating liquid, aerosol and particulate contaminants from a blow- by gas stream. The separator comprises a blow-by gas inlet 2, a cleaned blow-by gas outlet 4, a boost gas inlet 6 and an oil drain 8. The boost gas comprises a pressurised gas source, which may be either pressurised air (for instance from a turbocharger) or exhaust gas. The boost gas need not be at a high velocity on entering the boost gas inlet. The boost gas could be static, though under pressure. Optionally, the boost gas could be obtained from the exhaust or the turbocharger and stored in a separate holding chamber or collector prior to being passed to the boost gas inlet. The oil drain 8 allows separated oil and other contaminants to be extracted, either to be returned to the engine crankcase or stored in another chamber. Each of the inlets and outlets are suitable for connection to hoses for transfer of the various fluids to or from the engine or other devices.

Flanges 10 are provided on each inlet or outlet to assist in attaching hoses.

Referring to figure 2, this illustrates in cross section the separator of figure 1 through a plane passing through the axis of each inlet or outlet. The separator is formed from three parts: an inlet assembly 12, an outlet assembly 14 and an impactor assembly 16. The three parts are indicated by differing hashed lines for each part. The three parts may be formed from a polymeric material, for example glass filled nylon, formed by injection moulding. It will be appreciated that the separator could be formed in other embodiments from a differing number of components, and other suitable materials and production techniques are well known to the skilled person. For instance, the inlet assembly 12, or just the nozzle 18 could be made from sintered or injection moulded metal. The three parts are joined together using appropriate known fixing techniques, such as bolts, adhesive or welding.

Seals 28 may be required between each part in order to prevent leakage.

Pressurised boost gas enters the separator via boost gas inlet 6. When used on a turbocharged engine the pressurised gas may be derived from the intake manifold.

Alternatively, the pressurised gas could be derived directly from the turbocharger, however it is preferable to derive the air from the intake manifold as at this stage the turbocharger gas has passed through a heat exchanger (alternatively referred to as an intercooler) so that it is cooled from approximately 180-200°C to 50-60°C. Using cooler boost gas allows the separator to be formed from lower cost materials which do not need to be resistant to such high temperatures. Alternatively, exhaust gas derived from before or after the turbocharger maybe used as the boost gas. The boost gas typically is at a pressure of between IBar and 4Bar.

The boost gas passes through nozzle 18, which accelerates the boost gas (and causes a consequent reduction in pressure). The nozzle 18 is formed as a convergent nozzle. In particular, the nozzle may be a convergent-divergent nozzle, such as a de-Lavaal nozzle, which is well known in the art. Other suitable nozzle shapes are known. The boost gas is accelerated to a high velocity, for instance between 100-500ms', with the boost gas typically exceeding mach 1 at least in the region of nozzle 18. A convergent nozzle advantageously accelerates the boost gas to very high speeds, which consequently entrains the blow-by gas and accelerates the blow-by gas to high speeds. Furthermore, use of convergent nozzle advantageously results in a high degree of intermixing between the boost gas and the blow-by gas, resulting in improved separation of contaminants from the blow-by gas.

The resultant high speed boost gas jet passes into chamber 20 along the axis of the device indicated by line 22, which passes through the centre of boost gas inlet 6. The high velocity boost gas jet causes a region of reduced pressure within the chamber 20 in the vicinity of the nozzle 18. Pressure is reduced by up to 1 5OmBar relative to external atmospheric pressure. This reduction in pressure allows contaminated blow-by gas to be drawn in though annular nozzle 24, which surrounds nozzle 18. Annular nozzle 24 is in communication with annular space 26, that surrounds chamber 20 and is in turn in communication with blow-by gas inlet 2. Therefore, blow-by gas is sucked into chamber 20 through annular nozzle 24, which provides an annular flow of blow-by gas about the high speed boost gas jet. The blow-by gas flow is parallel to the boost gas flow, which aids the entrainment of the blow-by gas The relatively low speed blow-by gas is entrained by the high speed boost gas jet, intermixing with the boost gas and accelerating to approach the speed of the boost gas. Annular nozzle 24 assists the entrainment, mixing and acceleration of the blow-by gas by surrounding the high speed boost gas jet which results in a greater proportion of the gas streams being in contact with one another.

Advantageously for use within an engine, the contaminated blow-by gas is actively drawn out of the crankcase and into the separator, allowing for control of the pressure within the crankcase. The pressure within the crankcase is thus typically controlled to within +1- 5OmBar relative to external atmospheric pressure. The generated suction may be separately controlled by providing a pressure control valve connected to the blow-by gas inlet 4, or elsewhere connected to the engine. Alternatively, if the separator keeps the pressure within the crankcase too low then an impaction stage may be provided in the blow-by inlet 4 to reduce the pressure drop in the crankcase. The additional impaction stage may simply comprise an additional 900 turn within the blow-by inlet 2 or annular space 26.

Referring now to figure 3, this is an enlarged portion of the cross sectional view of figure 2, illustrating the nozzle 18 and chamber 20 in greater detail. The boost gas nozzle 18 and annular blow-by gas nozzle 24 are generally constructed as for ajet pump, as is known in the art. In order to achieve satisfactory entrainment and acceleration of the blow-by gas, preferably the diameter of chamber 20 indicated by arrow 30 should be between 2 to 5 times greater, preferably 3 to 4 times greater, than the critical diameter (typically, the smallest diameter) of boost gas nozzle 18 indicated by arrow 32. The position of the critical diameter (alternatively referred to as the throat of the nozzle) may vary from the narrowest point of the nozzle due to aerodynamic effects, as is known in the art of nozzle design.

The chamber 20 is generally formed as a cylinder, however side waIls 34 are not straight for the whole of their length. It can be seen from figure 3 that sides walls 34 taper inwardly towards the end of the chamber remote from nozzle 18. This tapering assists in controlling the direction of flow and mixing of the combined gas flow. In order for separators in accordance with embodiments of the present invention to efficiently separate contaminants from blow-by gas, it is desirable that the degree of intermixing of the gas flows is maximised.

The tapering additionally serves to create a vortex within the combined gas flow as entrained blow-by gas and boost gas passes back along the side waIls 34 of chamber 20 towards the annular nozzle 24. The vortex appears within the curved section of the chamber as a result of the flow conditions. The boost gas jet is in an axial direction along the centre of chamber 20 towards the impaction plate 36. Blow-by gas entering through annular nozzle 24 is entrained and drawn towards the boost gas jet as a result of the pressure drop around nozzle 18. However, due to the viscosity of the blow-by gas this motion sets up a rotating vortex. Even if the side walls of the chamber 20 are straight, a vortex may appear, however the strength of the vortex is affected by the geometry of the chamber, and increased by curved side walls. The vortex is occurs within planes that include the axis of the separator passing through the boost gas nozzle towards the impaction plate. This differs from the plane of the vortex within a centrifugal or cyclone separator known in the art which typically is in a plane transverse to the axis of the gas entering a cyclone chamber and rotating about a central axis of the device.

The vortex further encourages the gas streams to mix arid increases the acceleration of the blow-by gas allowing the blow-by gas portion of the combined gas flow to approach the speed of the boost gas jet. It has been observed that the vortex results in the contaminants beginning to separate within chamber 20. There may also be some initial separation of contaminants as a result of the mixing of the high speed boost gas and the lower speed blow-by gas stream.

The combined gas flow is incident upon impaction plate 36 at the end of chamber 20 remote from nozzle 18. The impaction plate 36 is transverse to the flow of gas, and preferably at approximately 90° to the gas flow. The combined gas flow is forced to turn through 90° to pass round impaction plate 36 to pass through annular space 38. This turning causes particulate and liquid contaminants to be impacted on the surface of the plate. The gas passing through annular space 38 then undergoes a second 90° bend passing around impaction plate 36 into collection space 40 (see figure 2). The second 90° bend also serves to separate out contaminants. The contaminants then flow under gravity towards oil drain 8 where they can be extracted. The oil can be returned to the crankcase, or stored separately. The cleaned gas stream passes out of the separator through blow-by gas outlet 4. The degree of separation is significantly higher than that encountered for blow-by gas streams incident upon an impaction plate without acceleration using a boost gas. While impaction plate 36 is illustrated as being flat (at least in the surface facing nozzle 18) this need not necessarily be the case. For instance, the impaction plate may be curved such that it presents a convex or a concave surface towards nozzle 18. A curved surface may increase the separation efficiency for certain embodiments of the present invention.

Oil within the gas stream as an aerosol is coalesced by impaction on the impaction plate 36.

Additionally oil is coalesced on the outer wall of the collection space at the second 90° bend. The second 90° bend contributes significantly to the efficiency of the separator as determined by the percentage of oil within the blow-by gas stream that is removed. When the gas passes into collection space 40 coalesced oil is encouraged to drain away to oil drain 8 by being flung against curved wall 42. A check valve may be provided in oil drain 8, as is commonly found in conventional oil separators. Similarly, a pressure regulator connected to the blow-by gas outlet 4 may be provided before passing back to the engine air intake manifold.

Separators according to the above described embodiments of the present invention have been observed to provide gravimetric separation efficiency in the range 95-98% for particles greater than or equal to 0.3m. It is possible that smaller particles still may be efficiently filtered.

Embodiments of the present invention adapted to filter contaminants from blow-by gas in a closed loop system typically operate with a flow of blow-by gas of 50-800 11mm. For higher flow rates within this range it can be desirable to combine two or more separators to achieve the required flow rate. Increased flow rates can be accommodated by increasing the size of the nozzle 18 and chamber 20.

The flow of boost gas through nozzle 18 when using boost gas derived from the turbocharger of an engine typically comprises less than 1% of the total engine gas flow, so as to have a negligible effect on engine performance. Referring to figure 4, this is a graph illustrating the variation of engine output power with engine speed for an exemplary engine firstly without a separator fitted (the line indicated by diamonds), and secondly with a separator in accordance with an embodiment of the present invention fitted to extract contaminants from a blow-by gas stream (the line indicated by squares). it can be seen that there is a negligible difference between the two plotted lines, the difference between the two lines being less than the measurement error for the power measurements. As an example, a 6 litre diesel engine consumes approximately 19800-22700 litres per minute (700-800 cubic feet per minute -CFM) of air when running at maximum rated power and speed. The maximum rated power is the engine speed at which the engine develops the maximum power. For such an engine, nozzle 18 typically varies between 0.5 and 15mm according to the amount of blow-by gas to be cleaned.

Referring now to figure 5 this schematically illustrates a separator 50 in accordance with an embodiment of the present invention used in a closed loop application in combination with a reciprocating engine in order to extract contaminants from blow-by gas derived from a crankcase. Air filter 52 draws in external air (line 54) and filters the air before passing the air to a turbocharger 56 (line 58). The turbocharged air then passes to intercooler 60 (line 62) where it is cooled before passing to the air intake manifold of engine 64 (line 66).

Exhaust gases from engine 66 are passed back to the turbocharger 56 (line 68) where they are used to drive the turbocharger 56. Blow-by gases from the crank case of engine 64 pass to separator 50 (line 70). Separator 50 also receives a small volume of air from the turbocharger 56 (line 72) which serves as the boost gas. Cleaned blow-by gas is returned to the air intake of turbocharger 56 (line 74) and the separated oil is returned to the crankcase of engine 64 (line 76). In alternative embodiments of the present invention the cleaned blow-by gas may be returned to the intake of air filter 52 such that the blow-by gas is subjected to further filtering prior to being passed to the air intake manifold of engine 64.

In accordance with embodiments of the present invention, a vacuum limiting valve may be coupled to a gas outlet from the separator in order to prevent cleaned gas from being drawn back into the separator. Additionally, a pressure regulation valve may be coupled to the blow-by gas inlet to prevent gas being drawn out of the separator into the crankcase.

Furthermore, a check valve may be coupled to the oil drain to prevent oil being drawn into the separator from the crankcase, or wherever the separated oil is stored, through the oil drain.

It will be appreciated that the system illustrated in figure 5 may be modified. For instance, the boost gas may be derived from the exhaust of engine 64 (line 68). Cleaned blow-by gas may similarly be passed to be combined with the exhaust gases (line 68). Separated oil may be stored separately and not returned to the crankcase of engine 64. Other possible configurations will be readily apparent to the appropriately skilled person.

Referring first to figure 6, this is a perspective view of a separator in accordance with a second embodiment of the present invention for separating liquid, aerosol and particulate contaminants from a blow- by gas stream. Where the separator illustrated in figure 6 shows features corresponding to those identified for the separator illustrated in figure 1, the same reference numerals have been used.

The separator comprises a blow-by gas inlet 2, a cleaned blow-by gas outlet 4, a boost gas inlet 6 and an oil drain 8. The boost gas comprises a pressurised gas source, which may be either pressurised air (for instance from a turbocharger) or exhaust gas. The oil drain 8 allows separated oil and other contaminants to be extracted, either to be returned to the engine crankcase or stored in another chamber. Each of the inlets and outlets are suitable for connection to hoses for transfer of the various fluids to or from the engine or other devices. Flanges 10 are provided on each inlet or outlet to assist in attaching hoses. The separator further comprises a cyclone main body 50 and a cyclone lid 52, as will be described in greater detail below.

Referring to figure 7, this illustrates in cross section the separator of figure 6 through a plane passing through the axis of each gas inlet. That is, the cross section of figure 7 is in a plane that is positioned passing transversely through the main cyclone body 50 underneath the cyclone lid 52. The separator is formed from three parts: a boost gas inlet assembly 54, a blow-by gas and cyclone assembly 56 and the cyclone lid 52 (not illustrated in figure 7).

The separator parts are indicated by differing hashed lines for each part. The separator may be formed from similar materials and using similar production techniques as those described above in connection with the first embodiment of the separator illustrated in figures Ito 3.

Pressurised boost gas enters the separator via boost gas inlet 6, derived from the same sources as described above for the first embodiment of the separator.

The boost gas passes through nozzle 18, which accelerates the boost gas (and causes a consequent reduction in pressure). The nozzle 18 is formed as a convergent nozzle. In particular, the nozzle may be a convergent-divergent nozzle, such as a de-Lavaal nozzle, which is well kn own in the art. Other suitable nozzle shapes are known. The boost gas is accelerated to a high velocity, for instance between 100-SOOms', with the boost gas typically exceeding mach 1 at least in the region of nozzle 18.

The resultant high speed boost gas jet passes into mixing chamber 58 along the axis of nozzle 18 indicated by line 60, which passes through the centre of boost gas inlet 6. The high velocity boost gas jet causes a region of reduced pressure within the chamber 58 in the vicinity of the nozzle 18. Pressure is reduced by up to l5OmBar relative to external atmospheric pressure. This reduction in pressure allows contaminated blow-by gas to be drawn in though annular nozzle 24, which surrounds nozzle 18. Annular nozzle 24 is in communication with annular space 26, that surrounds chamber 20 and is in turn in communication with blow-by gas inlet 2. Therefore, blow-by gas is sucked into chamber through annular nozzle 24, which provides an annular flow of blow-by gas about the high speed boost gas jet. The blow-by gas flow is parallel to the boost gas flow, which aids the entrainment of the blow-by gas The relatively low speed blow-by gas is entrained by the high speed boost gas jet, intermixing with the boost gas and accelerating to approach the speed of the boost gas.

As for the first embodiment of the separator, the contaminated blow-by gas is actively drawn out of the crankcase and into the separator, allowing for control of the pressure within the craniccase. The pressure within the crankcase is thus typically controlled to within +/-5OmBar relative to external atmospheric pressure. As before, the generated suction may be separately controlled by providing a pressure control valve connected to the blow-by gas inlet 4, or elsewhere connected to the engine or an impaction stage in the blow-by inlet 4 to reduce the pressure drop in the crankcase.

As for the first embodiment, the boost gas nozzle 18 and annular blow-by gas nozzle 24 are generally constructed as for ajet pump, as is known in the art. In order to achieve satisfactory entrainment and acceleration of the blow-by gas, preferably the diameter of chamber 58 indicated by arrow 62 should be between 2 to 5 times greater, preferably 3 to 4 times greater, than the critical diameter (typically, the smallest diameter) of boost gas nozzle 18 indicated by arrow 64 The position of the critical diameter (alternatively referred to as the throat of the nozzle) may vary from the narrowest point of the nozzle due to aerodynamic effects, as is known in the art of nozzle design.

The chamber 58 is generally formed as a cylinder, however side walls 34 need not be straight for the whole of their length. Tapering may assist in controlling the direction of flow and mixing of the combined gas flow. The tapering can additionally serve to create a vortex within the combined gas flow as entrained blow-by gas and boost gas passes back along the side walls of chamber 58 towards the annular nozzle 24.

The combined gas flow passes into cyclone chamber 66, defined by cyclone body wall 50 and cyclone lid 52. The curved inside surface of cyclone body wall 50 cause the combined gas flow to change direction and spiral towards the bottom of the cyclone, as indicated by the arrows 68. This change in direction causes particulate and liquid contaminants to be impacted on the inside surface of cyclone body wall 50. As the combined gas jet enters the cyclone chamber 66 it is still travelling at a high speed (generated by nozzle 18). This high speed gas jet creates a significant increase in separation efficiency, compared to conventional cyclone separators. As the combined gas stream passes further into the cyclone and spirals downwards the energy in the gas stream dissipates partly and the gas stream slows.

Referring now to figure 8, this illustrates the separator of figure 6 is cross section through the cyclone 66 and the gas outlet 4 and contaminant outlet 8. The combined airstream passes into cyclone 66 and spirals downwards. Cleaned gas then passes upwards through passage 70 that connects with gas outlet 4. Gas outlet 4 may connect with that engine air intake. Contaminants that have been separated from the gas stream by impacting upon the main cyclone body wall 50 then flow under gravity towards oil drain 8 where they can be extracted. The oil can be returned to the crankcase, or stored separately. The degree of separation is significantly higher than that encountered for blow-by gas streams entering a cyclone without acceleration using a boost gas.

Oil within the gas stream as an aerosol is coalesced by impaction on the cyclone body wall 50. A check valve may be provided in oil drain 8, as is commonly found in conventional oil separators. Similarly, a pressure regulator connected to the blow-by gas outlet 4 may be provided before passing back to the engine air intake manifold.

When used in connection with separating contaminants from a blow-by gas stream derived from an internal combustion engine the separator illustrated in figures 1 to 3 or 6 to 8 may be modified by providing the separator with suitable attachments for connecting to an engine. Alternatively, the separator may be integrated with part of an engine, for instance an air intake manifold or the oil drain. Means for coupling the separator to an engine will be readily apparent to the appropriately skilled person.

The separator described above may be modified by adding further bends through which the gas must pass after impaction plate 36, if further separation is required. Similarly, to increase the separation efficiency, other features may be provided such as further impaction plates and curved walls or spiral inserts within chamber 20 to encourage centrifugal separation. Providing an open filter medium (which is not subject to clogging due to the degree of openness) within collection space 40 or within the cyclone chamber 66 can improve separation efficiency by providing a surface on which the oil can coalesce, and reducing the amount of re-entrainment of separated contaminants. For applications in which an extremely high degree of separation (greater than 99%) is required, a tighter filter medium can be provided in collection space 40. Such a tighter filter medium may require periodic replacement.

Although particular embodiments of the present invention described above relate primarily to the use of the described separator for separating particulate and liquid aerosol contaminants from a blow-by gas stream within a reciprocating engine, the present invention is not limited to this. Indeed, the separator can be used to separate contaminants from a gas stream derived from other forms of internal combustion engine. More generally, the present invention can be applied to separate contaminants from any gas stream, such as compressed air lines, separating cutting fluid from gas streams in machine tools and separating oil mist in industrial air compressors. More generally still, the present invention can be used to separate contaminants from any fluid stream, that is it may also be applied to liquid streams. The separator may be advantageously used to separate contaminants from an oil or a fuel stream within an internal combustion engine. The separator can be used in both open loop systems where the cleaned fluid stream is vented to the atmosphere, or in closed loop systems where the cleaned fluid stream is reused.

The boost gas can be derived from any source of pressurised gas, for instance exhaust gas, compressed gas from a turbocharger or an engine intake manifold, compressed gas from a vehicle braking system or other sources.

Embodiments of the present invention described above relate to an impaction plate or a cyclone. However, the present invention is not limited to these two examples. In its broadest sense, as defined by the claims, the invention comprises means for accelerating a fluid stream using a second fluid stream which passes through a convergent nozzle which accelerates the second fluid stream. The accelerated jet of the second fluid entrains and accelerates the first fluid stream, intermixing with the first fluid stream. The combined fluid stream is then incident upon some form of surface which causes a change in direction in the combined fluid stream, resulting in separation of contaminants due to a centrifugal effect. Separation efficiency is increased relative to separator assemblies known in the art due to the high degree of acceleration provided by the nozzle assemblies described above.

The separator may comprise a stand alone device. Alternatively, it may readily be integrated into other engine components, for example an engine valve cover, timing cover, crankcase, cylinder head, engine block or turbocharger. The separator may be mounted directly on the engine, or mounted away from the engine.

Further modifications and applications of the present invention will be readily apparent to the appropriately skilled person, without departing from the scope of the appended claims.

Claims

CLAIMS: I. A separator for separating contaminants from a fluid stream, comprising: a chamber; a first inlet for receiving a first fluid stream into the chamber including a convergent nozzle for accelerating the first fluid stream; a second inlet for receiving a second fluid stream including entrained contaminants into the chamber, the second inlet being arranged relative to the first inlet such that the first fluid stream can entrain and accelerate the second fluid stream forming a combined fluid stream within the chamber; and a surface coupled to the chamber arranged such that the surface can cause a deviation in the course of the combined fluid stream incident upon it such that contaminants are separated from the combined fluid stream.
2. A separator according to claim 1, wherein the surface comprises an impaction plate.
3. A separator according to claim 2, wherein the impaction plate is positioned in a plane at approximately 900 to the combined fluid stream, such that the impaction plate can cause a deviation in course of the combined fluid stream of approximately 9�0
4. A separator according to claim 2 or claim 3, further comprising a gap extending about at least a portion of the periphery of the impaction plate at the end of the chamber remote from the convergent nozzle, arranged such that the combined fluid stream can pass through the gap into a collection space.
5. A separator according to claim 4, wherein the gap further comprises a bend operable to cause a further deviation in the course of the combined fluid stream.
6. A separator according to claim 1, wherein the surface comprises an interior surface of a cyclone chamber arranged to receive the combined fluid stream.
7. A separator according to any one of the preceding claims, further comprising a fluid outlet allowing the cleaned fluid stream to exit the separator.
8. A separator according to any one of the preceding claims, further comprising a drain positioned to allow contaminants to drain from the separator.
9. A separator according to any one of the preceding claims, wherein the convergent nozzle comprises a convergent-divergent nozzle.
10. A separator according to claim 9, wherein the convergent nozzle comprises a tube including a restricted central portion.
11. A separator according to claim 9, wherein the chamber is generally cylindrical and the chamber diameter proximate to the convergent nozzle is between 2 and 5 times larger than the diameter of the narrowest diameter of the convergent nozzle.
12. A separator according to any one of the preceding claims, wherein the convergent nozzle is arranged to generate a region of reduced pressure within the chamber about the first inlet operable to draw in the second fluid stream from the second inlet.
13. A separator according to any one of the preceding claims, further comprising an annular second nozzle surrounding the first inlet, the second nozzle being in communication with the second inlet such that the second fluid stream can flow through the second nozzle.
14. A separator according to claim 13, wherein the second inlet communicates with an annular space surrounding the chamber, the annular space in turn communicating with the annular second nozzle.
15. A separator according to claim 13 or claim 14, wherein the annular second nozzle is arranged such that the second fluid stream can flow into the chamber generally parallel to the first fluid stream from the first inlet.
16. A separator according to any one of the preceding claims, wherein the chamber is generally formed as a cylinder, the diameter of the chamber reducing towards the surface.
17. A separator according to any one of the preceding claims, wherein the fluid streams comprise gas streams.
18. A separator according to claim 17, wherein the separator is operable to separate particulate, liquid andlor aerosol contaminants from the combined gas stream.
19. A separator according to any one of the preceding claims, wherein the separator is operable to separate greater than 95% of particles greater than O.3m in diameter from the combined fluid stream.
20. An internal combustion engine including a separator according to claim 19, wherein the second inlet is arranged to receive blow-by gas derived from a crankcase.
21. An internal combustion engine according to claim 20, wherein the first inlet is arranged to receive a pressurised gas stream derived from a turbocharger and the separator is operable to separate crankcase oil from the combined gas stream, the separator being Is arranged to return separated crankcase oil to the crankcase.
22. An internal combustion engine according to any one of claims 20 to 21, further comprising a vacuum limiting valve coupled to a gas outlet.
23. An internal combustion engine according to any one of claims 20 to 22, further comprising a pressure regulation valve coupled to the second inlet.
24. An internal combustion engine according to any one of claims 20 to 23, further comprising a check valve coupled to a contaminant drain arranged to prevent contaminants being drawn into the separator through the contaminant drain.