The invention provides a me as set out in Claim 1 and apparatus as set out
in Claim 18. Advantageous features are set out in the subsidiary claims.
Using an oil to condense onto the particulates effectively increases the diameter and the mass of each particulate. T13e increase is sufficient to ensure that the particles, now suspended within a droplet of condensed oil behave like the equivalent relatively large particles. They can therefore be efficiently separated, using suitable separation means, from the gas stream. The separation means can be centrifugal or another form of separator or a filter. The removal of the particulates from the oil and the recirculation of the oil for reintroduction means that the system can be made self-contained and therefore transportable. This allows the system to be applied to the exhaust of an internal combustion engine forming part of a vehicle. The vaporised oil preferably possesses the necessary qualities of a low vapour pressure liquid at relatively elevated temperatures. Preferably, the oil has a boiling point within the range of 250 - 350C at normal atmospheric pressure and is inert at these temperatures. Such an oil may be a mineral oil or vegetable oil. A system according to the invention is capable of significantly reducing the content of carbon particulates in a diesel exhaust prior to emission of the gas stream into the atmosphere without introducing unacceptable increases in the volume or cost of the exhaust system. This results in fewer pollutants entering the atmosphere with obvious beneficial results.
4 An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein:- Figure 1 is a schematic representation of apparatus according to the invention and shown connected to the exhaust of an internal combustion engine; Figure 2a shows, in cross section and on an enlarged scale, injection means forming part of the apparatus shown in Figure 1; Figure 2b and 2c show in cross section alternative injection means; Figure 3a shows, in cross section and on an enlarged scale, cooling and condensing apparatus forming part of the apparatus shown in Figure 1; Figure 3b shows an alternative cooling and condensing apparatus; Figure 4a shows in horizontal cross section a cyclonic separator forming part of the apparatus shown in Figure 1; Figure 4b shows in cross section a collecting chamber associated with the cyclonic separator shown in Figure 4; Figure 5 illustrates a filtration separator capable of replacing the cyclonic separator illustrated in Figure 4; Figure 6 illustrates in cross section filtration means forming part of the apparatus shown in Figure 1; Figure 7 is a schematic representation of test apparatus; Figures 8a and 8b show the particle distribution resulting from a first series of tests; and Figure 9 shows the particle distribution resulting from a second series of tests.
The apparatus shown in Figure I Wustrates how the invention can be utilized in aftertreatment of exhaust products containing unacceptable levels of particulates, for example in conjunction with an internal combustion engine in order to reduce the particulate content of the exhaust therefrom. The apparatus 10 is shown connected to the exhaust of an engine 20 via a conduit 2 1. The engine 20 can be any form of internal combustion engine, although it is envisaged that the invention will be particularly applicable to diesel engines or to other compressionignition engines.
The apparatus 10 essentially consists of a series of conduits connecting a plurality of elements together. The inlet conduit 21 carries the exhaust from the engine 20, in which carbon particulates are entrained, to injection means 30 in which an atomized oil is injected into the exhaust stream_ The atomized oil is then vaporised by the hot exhaust gas. Alternatively, the oil can be vaporised prior to injection into the exhaust stream. The exhaust stream is then carried via conduit 22 through cooling and condensing apparatus 40. The effect of the cooling and condensing apparatus 40 is to allow the vapour in the exhaust stream to condense on and around the carbon particulates entrained within the exhaust stream. The result is that a significant proportion of the carbon particulates leaves the cooling and condensing apparatus 40 suspended within a droplet of oil. This effectively increases the mass and diameter of the respective carbon particulate so that, when the exhaust stream enters a separator 50, for example a cyclonic separator, the relatively large droplets can be easily separated from the exhaust gas. The exhaust gas exits the cyclonic separator 50 via an outlet conduit 23 whilst the separated droplets, with the carbon particulates suspended therein, drop down into a collecting chamber 60 via a conduit 24. An outlet conduit 25 carries the collected oil, with the carbon particulates suspended therein, to a pump 70 which feeds the oil to filtration means 80. In the filtration means, the carbon particulates can 6 be effectively separated from the oil which is then recirculated back to the injection means 30 via a conduit 27 in order to be reintroduced into the exhaust stream and revaporised in order to effect further separation of carbon particulates.
Having described the apparatus and its manner of operation in broad terms, the individual components will now be described in more detail.
Figure 2a Wustrates in cross section the injection means 30 of the apparatus 10. The injection means 30 include a chamber 32 having a cross section area which is somewhat larger than that of the inlet conduit 21. The enlarged cross section of the chamber 32 allows the gases introduced thereinto to mix freely by ensuring a sufficient mixing length after injection. The inlet conduit 21 communicates with the chamber 32 on a first side thereof and the conduit 22 communicates with the chamber 32 on the opposite side thereof. Located on the lower side of the chamber 32 and projecting thereinto, is an injector nozzle 34. The injector nozzle is illustrated simply in the drawings and can take the form of an aerosol injector, a spray atomizer or an engine-type diesel injector. All three forms of injector are well known and require no flirther description here. All that is required is that the injector nozzle 34 is capable of introducing to the chamber 32 a fine mist or spray of the oil to be vaporised and ensuring good turbulent mixing to help reduce the length of mixing time required. The oil mixes with the exhaust gas within the chamber 32 and quickly vaporises before exiting via conduit 22. In Figure 0 2a, the carbon particulates entrained within the exhaust gas are illustrated using reference numeral 12. For illustrative purposes, the vaporised oil is illustrated using reference numeral 14. It will be understood that the oil may be introduced in the form of a very fine mist or a true vapour. The illustration is not intended to imply that droplets of oil must be introduced via the injector nozzle 34.
The oil which is introduced into the chamber 32 via the injector nozzle 34 is a mineral oil having a boilin.. point of around 30WC at atmospheric pressure. Other oils can be used. (It will be understood that the term "oil" is here used to mean any liquid having a 7 high boiling point and suitable for use in an application of this sort.) The oil is introduced to the chamber 32 via the nozzle 34 and is heated by the hot exhaust gas to effect vapourisation. In the event that the exhaust gas temperature is too low to evaporate the injected mist, the mist may be heated by an electric heater, for example, downstream of the injector to cause the mist to evaporate. Conversely, if the exhaust gas temperature is too high, this would cause the injected oil mist to bum rather than just vapourise. In these circumstances, it will be necessary to cool the exhaust gas prior to injecting the mist.
An alternative form of injection means 30 is illustrated in Figure 2b. In this embodiment, eight injector nozzles 34a are arranged around an annular support 36 and these nozzles are in direct communication with the conduit 27 by means of which the oil to be vaporised is carried to the injection means 30. The injector nozzles 34a surround a central chamber 32a which need not be any larger in cross section than the inlet conduit 21 or the conduit 22. Ilie fact that a plurality of injector nozzles 34a are provided, and their spacing around the chamber 32a, means that mixing of the vaporised liquid with the exhaust gas is swift and effective.
A further alternative form of injection means is illustrated in Figure 2c. In this embodiment, an injector nozzle 34 is arranged in the path of the conduit 12. The outlet of the injector nozzle 34 is directed downstream to improve the mixing of the mist and exhaust gas.
Figures 3a and 3b illustrate alternative cooling and condensing means 40. In Figure 3a, the conduit 22 is surrounded by a chamber 42 having an inlet 44 and an outlet 46. The chamber 42 is sealed around the conduit 22 so that a coolant 48 can be made to flow through the chamber 42 thus having a cooling effect on the contents of the conduit 22. The coolant 48 will pass through some form of second heat exchange device after leaving the exit 46 and before returning to the inlet 44. Any appropriate form of heat 0 exchange device can be used, including a simple array of air cooled fins. When the 0 8 apparatus 10 used in conjunction with the internal combustion engine of a vehicle, the vehicle's onboard cooling system can also be used.
The effect of cooling the exhaust stream flowing along conduit 22 is to encourage the vaporised oil to condense within the conduit 22. At least some of the vaporised oil will condense onto the carbon particulates also entrained within the exhaust stream. As the condensation proceeds, a significant proportion of the carbon particulates become surrounded by and suspended within droplets of the condensed oil. Each carbon particulate therefore increases its diameter and mass, effectively making it many times larger than its true size.
The same effect can be achieved by the provision of a cooling coil 42a wound around the conduit 22 as illustrated in Figure 3b. The coil 42a has an inlet 44 and an outlet 46 and carries the coolant 48. Again, some sort of heat exchange device is required to be positioned between the outlet 46 and the inlet 44 so that the recirculating coolant 48 enters the coil 42a at a lower temperature than that at which it leaves the coil.
A suitable coolant would be any water/glycol mix.
The conduit 22 carries the exhaust stream, with the carbon particulates suspended within droplets entrained therein, to the tangential inlet of a cyclonic separator 50. The cyclonic separator 50 is shown in horizontal cross section in Figure 4a. The tangential arrangement of the inlet 52 causes the exhaust stream to swirl around the conically tapering wall 54 and the consequent acceleration of the exhaust stream causes the droplets 16 to be separated from the exhaust stream. The exhaust stream passes towards the central axis of the cyclonic separator 50 and exits the cyclonic separator 50 via the outlet pipe 23. The separated droplets of oil with the carbon particulates suspended therein drop down under the force of gravity into the conduit 24 and fall into the collected chamber 60.
9 The collecting chamber 60 is illustrated in Figure 4b. It is essentially a simple container in which the oil 62 is collected. The oil 62 has carbon particulates suspended therein. The container 60 has an outlet 64 to which the conduit 25 is connected.
Use of a cyclonic separator will cause a certain loss of heat from the exhaust stream as well as losses along the length of the conduit. Therefore, a separate upstream heat exchanger as described above may not necessarily need to be provided.
It will be appreciated that the cyclonic separator 50 can easily be replaced by a simple filtration separator 50a such as that illustrated in Figure 5. The filtration separator 50a consists of a simple mesh or filter 52a through which the exhaust stream is directed. The droplets 16 collect on the mesh and subsequently fall into the collecting chamber 60 positioned beneath the filtration separator 50a. Periodic replacement of the mesh 52a may be required.
The conduit 25 carries the oil 62 to a pump 70 which is a simple pump and requires no further description. The pump 70 can be supplied with its own motor or, alternatively, it can be connected to a vehicle's onboard systems. The purpose of the pump 70 is to return the oil 62 to the injection means 30 via the filtration means 80. The conduit 26 carries the oil from the pump 70 to the filtration means 80.
The filtration means 80 are illustrated in Figure 6. The filtration means 80 consist of a chamber 82 having a filtration cartridge 84 suspended therein. The conduit 26 carries the oil 62 directly to the interior of the filtration cartridge. The carbon particulates 12 are then retained in the filtration cartridge 84 whilst the oil droplets 18 are returned via conduit 27 to the injection means 30. The filtration cartridge 84 is advantageously removable and replaceable in order that deposits of carbon particulates can be safely disposed of and so that the filtration efficiency of the filter cartridge 84 can be maintained. To remove the cartridge 84, the upper surface 82a of the chamber 82 can be made removable and the cartridge itself can be made releasable from the conduit 26.
It will be appreciated that the condensed oil is to be revaporised. The injection means 30 may therefore include means for heating and compressing the oil before it is injected into the exhaust stream or alternatively heating means can also be located in the conduit 27 separately from the injection means 30 to heat the atomized oil. Standard equipment can be used to achieve this.
It is widely recognized that the concentration of carbon particulates appearing in the exhaust of a diesel engine is dependent upon the loading of the diesel engine. Engines operated at high load produce more carbon particulates. It is therefore advantageous if the apparatus described above also incorporates means for adjusting the amount of oil injected into the exhaust stream in accordance with the expected concentration of carbon particulates. In a preferred embodiment of -the invention, therefore, either a manual adjusting device is included in the injection means, perhaps in the form of a calibrated valve for adjusting the rate of flow of the oil to the injection means 30, or else means are provided for detecting a parameter capable of indicating of the level of carbon particulates in the exhaust stream and for adjusting the amount of oil injected into the stream in response to that parameter. For example, a control system can be incorporated into a vehicle which monitors the loading of the engine and a signal can be passed directly to the injection means 30 in order to control the amount of oil injected into the exhaust stream. Other ways of monitoring the loading of the engine will be apparent to a reader skilled in the art and these too can be used to control the amount of injected oil.
It is envisaged that the oil which is vaporised and then condensed on and around the carbon particulates can be a mineral oil or even a simple vegetable oil. Many such oils boil and recondense at a temperature of around 300T. Internal combustion engines generally have exhaust temperatures of somewhere around 350C, although temperatures of around 500C can be reached with high loads. Assuming that the exhaust stream enters the conduit 21 at a temperature of approximately 350C, it is envisaged that the injected oil would be a suitable mineral oil which is atomized then 11 heated by the hot exhaust gas to vapourise it. In the event of high loads in which the exhaust gas is too hot and causes the atomized oil to bum, the exhaust gas is cooled prior to its introduction into the injection means 30. As the mixture of exhaust gases and vaporised oil passes through the cooling and condensing apparatus, the mixture is cooled to approximately 28WC, or approximately WC below the boiling point of the oil at atmospheric pressure. This is sufficient to ensure that substantially all of the vaporised oil is condensed thus allowing the oil to be separated from the gas stream and recirculated for further use.
Alternatively, an oil can be used which has a boiling point at atmospheric pressure which is substantially higher than the exhaust temperature of the engine. If the oil is heated under pressure to a temperature above its boiling point and then injected into the exhaust stream at that temperature, thus causing vapourisation, the mixing of the vapour with the cooler exhaust stream will cause the oil to condense. The presence of separate cooling and condensing means is then unnecessary.
Tests have been carried out to confirm that particulates can be "grown" in a manner as described above, using two different engines; a Perkins 4 litre, 4 cylinder turbocharged diesel engine and a Cummins 5.9 litre, 6 cylinder turbocharged direct injected diesel engine. The test apparatus is illustrated in Figure 7. The results of the tests are shown graphically in Figures 8a and 8b and Figure 9, respectively.
Tbe first series of tests were carried out on a Perkins 4 litre, 4 cylinder turbocharged diesel engine type 1004-4.
The test apparatus as shown in Figure 7 comprises the Perkins engine 101 which is loaded by an eddy current dynamometer 102 with water cooling. The exhaust pipe 108 of the engine 10 1 comprises a stainless steel pipe having a diameter of 75mm. Injection means 104 is provided downstream of the exhaust pipe 108 which atomizes oil fed from a reservoir 103 and introduces the atornized oil into the pipe 108. The injection means 12 104 comprises a Taylor scientific series smoke-aerosol generator for atomizing the oil. The oil droplets are then introduced into the exhaust gas stream by a Bird and Tolle type BTS 176 air ejector.
A sampler 106 is provided downstream of the injection means 104 approximately 2.2m from the point of injection. The sampler 106 comprises an isokinetic probe which is located centrally in the exhaust pipe and a PALAS dilution system which is set to dilute the sampled stream at 100 to 1. The sampler 106 is connected to a particle size measuring device 107 which is an electrical low pressure impactor manufactured by DEKATI. The impactor measures the particle diameter and numbers of particles in twelve bands from 30run to lOpm. The data is stored on a computer for later analysis. The exhaust gas is then fmally passed out into the atmosphere.
During the tests, the engine was operated at 75ORPM full torque with a load of 288n.M. This gave an exhaust gas flow of approximately 35 litrels. The temperature at the point of injection was measured and maintained at 382C The temperature at the sample point was 27WC. The drop in temperature from the point of injection to the sample point was a result of losses to atmosphere over the length of the pipe 108 from the injection point to the sample point. The drop in temperature was sufficient to condense the oil droplets and therefore a cooler 105, shown in Figure 7, was not requiredShell Ondina EL oil was used and injected into the exhaust gas stream at a rate of approximately 10Orng/hour.
The resulting particle distribution before and after oil injection is shown in the graphs of Figures 8a and 8b. As can be clearly seen, the distribution of the particle shifts so that there is an increase in the number of larger particles so that inertial separation will be more effective.
A second series of tests were carried out on a Cumn-tins 5.9 litre, 6 cylinder turbocharged direct injected diesel engine.
13 The test apparatus comprises a Cummins engine 101 connected to a load 102 which is a water brake. The exhaust gas from the engine 101 is carried through an exhaust pipe 108. The pipe 108 comprises a tee section 109 in which a portion of the exhaust gas is vented to the atmosphere under the control of valves so that a controlled flow rate of exhaust gas is passed through injection means 104 and a cooler 105. The flow rate is set to approximately 18 litrets. The exhaust pipe 108 is a stainless steel pipe having a diameter of 50mm.
The test apparatus fin-ther comprises injection means 104 inunediately downstream of the tee section 109 and further downstream a cooler 105. The length of the pipe 108 between the injection point and the exit of the cooler 105 is approximately 2.5m. The injection means 104 corresponds to that utilized in the first tests described above. The cooler 105 is of the type shown in Figures 3a and 3b and the coolant was water with a flow rate of approximately 10 litres per minute. Irrimediately downstream of the cooler 105, the exhaust gas passes into a Richard Oliver dilution tunnel from which a sample is extracted by an isokinetic probe. The sample is then passed to a particle size measuring device 107 as utilized in the first tests described above.
The oil droplets are generated by a plurality of proprietart nebulisers, for example 3 or 4 nebulisers, to provide a flow of 42 mg/hour. TIhe engine was operated at 120ORPM with a load of 540nM. The exhaust gas produced had a temperature at the injection point of 43CrC and a temperature at the sample point of 200-25TC. Shell Ondina EL oil was used and injected into the exhaust gas stream at a rate of 42rng/hour.
The resulting particle distribution before and after oil injection is shown in the graph of Figure 9. As can be clearly seen, the distribution of the particle shifts so that there is an increase in the number of larger particles so that inertial separation will be more effective.
14 CLAIMS 1. A method of removing particulates from the exhaust gas stream of an internal combustion engine comprising the steps of:
combining the exhaust gas stream with a vaporised liquid; cooling the gas stream and vaporised liquid so that the vaporised liquid condenses onto the particulates; passing the gas stream and condensed liquid through a separating device so that the condensed liquid and particulates are removed from the gas stream; removing the particulates from the condensed liquid; and recirculating the condensed liquid for reintroduction to the exhaust gas stream in order to effect removal of further particulates therefrom; characterised in that the liquid is an oil and all of the condensed oil is collected and recirculated for reintroduction into the gas stream so as to provide a transportable system suitable for use in motor vehicles.
2. A method as claimed in Claim 1, wherein the oil is introduced as a liquid to the gas stream at a point at which the temperature of the gas stream is above the boiling point of the oil so that the oil is vaporised on introduction of the oil to the gas stream.
3. A method as claimed in Claim 2, wherein the oil is introduced to the gas stream as an atomized spray.
4. A method as claimed in Claim 2 or 3, wherein the temperature of the gas stream is at least 2TC above the boiling point of the oil when the oil is introduced thereto.
- A method as claimed in any one of the preceding claims, wherein the amount of vaporised oil introduced to the gas stream is controlled in dependence upon the expected concentration of particulates in the gas stream.
6. A method as claimed in any one of the preceding claims, wherein the gas stream and vaporised oil are cooled to a temperature at least ITC below the boWng point of the oil.
7. A method as claimed in Claim 6, wherein the gas stream and vaporised oil are cooled to a temperature at least 20T below the boiling point of the oil.
8. A method as claimed in any one of the preceding claims, wherein the gas stream and vaporised oil are passed through a heat exchanger in order to effect cooling.
9. A method as claimed in Claim 8, wherein the coolant used to cool the heat exchanger is the same as the coolant used to cool the internal combustion engine.
10. A method as claimed in any one of the preceding claims, wherein the condensed oil and particulates are separated from the gas stream by means of a centrifugal separator.
11. A method as claimed in Claim 10, wherein the condensed oil and particulates are separated from the gas stream by means of a cyclonic separator.
12. A method as claimed in Claim 10 or 11, wherein the centrifugal separator acts as a silencer to reduce the acoustic energy of the gas stream.
16 13. A method as claimed in any one of the preceding claims, wherein the particulates are removed from the condensed oil by means of filtration.
14. A method as claimed in any one of Claims I to 12, wherein the particulates are removed from the condensed oil by means of a centrifugal separator.
15. A method as claimed in Claim 14, wherein the particulates are removed from the condensed oil by means of a liquid cyclone.
16. A method as claimed in any one of the preceding claims, wherein the oil has a boiling point of between 20WC and 400'C.
17. A method of removing particulates from the exhaust gas stream of an internal combustion engine substantially as hereinbefore described with reference to any one of the embodiments shown in the accompanying drawings.
18. Apparatus for removing particulates from the exhaust gas stream of an internal combustion engine comprising:
a flow path for carrying the gas stream between an inlet and an outlet; introduction means for introducing to the gas stream either a vaporised liquid or an atomized liquid which is subsequently vaporised; cooling means for cooling the gas stream and vaporised liquid so as to condense the vaporised liquid onto the particulates entrained within the gas stream; a separating device located downstream of the cooling means for separating the condensed liquid and particulates from the gas stream; 17 particulate removing means for removing the particulates from the condensed liquid; and recirculation means for recirculating the condensed liquid back to the introduction means; characterised in that the liquid is an oil and the recirculation means are adapted to recirculate all of the condensed oil back to the introduction means so that the apparatus is transportable.
19. Apparatus as claimed in Claim 18, wherein the introduction means comprise a spray atomizer.
20. Apparatus as claimed in Claim 18, wherein the introduction means comprise an aerosol injector.
21. Apparatus as claimed in Claim 18, wherein the introduction means comprise a diesel-type injector.
22. Apparatus as claimed in anyone of Claims 18 to 21, wherein the introduction means comprise a valve for adjusting the amount of oil introduced to the gas stream.
23. Apparatus as claimed in any one of Claims 18 to 22, wherein the cooling means comprise a heat exchanger surrounding the flow path.
24. Apparatus as claimed in Claim 23, wherein the heat exchanger contains a coolant comprising water, air, a water-glycol mixture or an ethanolwater mixture.
25. Apparatus as claimed in Claim 23 or 24, wherein the heat exchanger contains the same coolant as that which is used to cool the internal combustion engine.
18 26. Apparatus as claimed in any one of Claims 18 to 25, wherein the separating device is a centrifugal separator.
27. Apparatus as claimed in Claim 26, wherein the centrifugal separator is a cyclonic separator.
28. Apparatus as claimed in any one of Claims 18 to 27, wherein the separating device includes a collector for collecting the condensed oil and particulates separated from the gas stream.
29. Apparatus as claimed in Claim 28, wherein the recirculation means comprise a conduit for returning the condensed oil from the collector to the introduction means.
30. Apparatus as claimed in Claim 29, wherein the particulate removing means are located in the conduit.
31. Apparatus as claimed in any one of Claims 19 to 30, wherein the particulate removing means comprise a filter having at least one removable filter cartridge.
32. Apparatus as claimed in any one of Claims 18 to 30, wherein theparticulate removing means comprise a cyclonic separator.
33. Apparatus for removing particulates from the exhaust gas stream of an internal combustion engine substantially as hereinbefore described with reference to any one of the embodiments shown in the accompanying drawings.