WO2007069994A1

WO2007069994A1 - Arrangement for a combustion engine

Info

Publication number: WO2007069994A1
Application number: PCT/SE2006/050525
Authority: WO
Inventors: Henrik Grenfeldt
Original assignee: Scania Cv Ab (Publ)
Priority date: 2005-12-13
Filing date: 2006-11-30
Publication date: 2007-06-21
Also published as: SE0502738L; SE529400C2

Abstract

The present invention relates to an arrangement for supplying a medium to an exhaust line (3) of a combustion engine (1). The arrangement comprises an exhaust line (3) for 5 leading exhaust gases out from the combustion engine (1), a turbine (4) arranged in the exhaust line (3) for converting energy of the exhaust gases to mechanical work, an injection means (13) arranged in the exhaust line (3) for injecting a liquid medium in the exhaust line (3), whereupon the liquid medium is intended to be heated and vaporised by the warm exhaust gases in the exhaust line (3). The injection means (13) 10 is fitted at such a position (3a) in the exhaust line that it injects the liquid medium upstream from the turbine (4) with respect to the direction of exhaust gas flow in the exhaust line (3). (Fig. 1) 15

Description

Arrangement for a combustion engine

BACKGROUND TO THE INVENTION, AND STATE OF THE ART

The invention relates to an arrangement for a combustion engine according to the preamble of claim 1.

At present, many combustion engines and the majority of diesel engines are provided with a turbo unit. A turbo unit comprises a turbine powered by exhaust gases and driving a compressor which compresses air in an inlet line to the combustion engine. Air is thus supplied at above atmospheric pressure to the combustion chambers of the combustion engine. A larger amount of air and fuel can thus be supplied to and burnt in the combustion engine. A combustion engine with a turbo can therefore deliver a significantly greater power output than a corresponding combustion engine without a turbo. The power which the turbine can derive from the exhaust gases to drive the compressor is substantially proportional to the pressure drop of the exhaust gases through the turbine.

Techniques used for reducing the discharges of nitrogen oxides from diesel engines include so-called SCR (Selective Catalytic Reduction), which involves adding a specified proportion of urea solution to the exhaust gases in the exhaust line of a diesel engine. Urea solution can be sprayed into the exhaust line, whereupon the finely divided urea solution is vaporised by contact with the hot exhaust gases, resulting in the formation of ammonia. The mixture of ammonia and exhaust gases is led thereafter through a catalyst in which chemical reactions take place. The nitrogen from the nitrogen oxides in the exhaust gases then reacts with the nitrogen in the ammonia, resulting in the formation of nitrogen gas. The oxygen from the nitrogen oxides reacts with the hydrogen in the ammonia, resulting in the formation of water. The nitrogen oxides in the exhaust gases are thus reduced in the catalyst to nitrogen gas and water vapour. With correct urea proportioning, the discharge of nitrogen oxides from the diesel engine can greatly be reduced. SUMMARY OF THE INVENTION

The object of the present invention is to provide an arrangement for a combustion engine which makes possible a more effective uptake of the energy content of the exhaust gases by means of a turbine than according to the state of the art.

This object is achieved with an arrangement of the kind mentioned in the introduction which is characterised by the features indicated in the characterising part of claim 1. According to the present invention, a liquid medium is thus injected into the exhaust line at a position upstream from the turbine. The medium is preferably injected in a finely divided state so that it is quickly heated and vaporised by the hot exhaust gases in the exhaust line. The vaporisation causes the added liquid medium to change to gaseous form. As a substance in gaseous form occupies a significantly greater volume than in liquid form, the vaporisation process results in a definite pressure increase in the exhaust line upstream from the turbine. As the pressure in the exhaust line downstream from the turbine is at a substantially constant value, a pressure increase in the exhaust line upstream from the turbine results in the possibility of using a greater pressure drop to drive the turbine in the exhaust line. The energy content of exhaust gases is related to their pressure and temperature. With a turbine it is substantially only possible to utilise the energy content in the pressure of the exhaust gases. The arrangement thus makes it possible for a liquid medium to be added to and vaporised by the warm exhaust gases upstream from the turbine. The high temperature of the exhaust gases is here utilised to raise the pressure in the exhaust line. The turbine can thus also take up part of the temperature-related energy content of the exhaust gases, thus making possible a more effective uptake of the energy content of the exhaust gases than according to the state of the art.

According to a preferred embodiment of the present invention, the injection means is fitted at such a position in the exhaust line that it injects the liquid medium at a distance upstream from the turbine with respect to the direction of exhaust gas flow in the exhaust line, said distance being so adapted that substantially all of the added liquid medium will be heated and vaporised by the exhaust gases before it reaches the turbine. An optimum pressure increase due to the added liquid medium in the exhaust line upstream from the turbine is thus made possible. With advantage, the arrangement comprises a control unit adapted to controlling the amount of liquid medium injected into the exhaust line. The amount of medium added can thus be so adjusted that all of it becomes vaporised before it reaches the turbine in substantially all operating states of the combustion engine.

According to another preferred embodiment, the arrangement comprises a pressure sensor which measures the pressure of the exhaust gases in the exhaust line upstream from the turbine, the control unit being adapted to receive information from said pressure sensor in order to control the amount of liquid medium injected into the exhaust line. The exhaust gases leaving the combustion engine will be at a pressure which varies inter alia with the load and speed of the combustion engine. The prevailing pressure in the exhaust line upstream from the turbine is an essential parameter for being able to estimate the amount of liquid medium which can be added to the exhaust line. The arrangement preferably also comprises a temperature sensor which measures the temperature of the exhaust gases in the exhaust line upstream from the turbine, the control unit being adapted to receiving information from said temperature sensor in order to control the amount of liquid medium injected into the exhaust line. The exhaust gases leaving the combustion engine will be at a temperature which likewise varies with the load and speed of the combustion engine. The temperature of the exhaust gases in the exhaust line upstream from the turbine is likewise an essential parameter for being able to estimate the amount of liquid medium which can be added in the exhaust line. The arrangement may comprise a pump device by which the control unit controls the amount of liquid medium injected. The pump device may deliver the medium via a line from a storage container for the medium to a spray nozzle in the exhaust line by which a desired amount of the medium is sprayed into the exhaust line.

According to another preferred embodiment, the arrangement comprises a compressor driven by the turbine. In this case the energy of the exhaust gases is converted to mechanical work to operate the compressor. The turbine and the compressor may here take the form of a conventional turbo unit. The compressor is adapted to compressing air in an inlet line which leads air to at least one combustion chamber of the combustion engine. The turbine's performance boost due to the extra pressure in the exhaust line upstream from the turbine provides the compressor with corresponding extra capacity for compressing the air in the inlet line. The air led to the combustion engine is thus provided with extra pressure, with the result that a larger amount of air and fuel can be supplied to the combustion chambers of the combustion engine. The combustion engine is thus provided with increased power.

According to another preferred embodiment, the liquid medium is a reducing agent which is injected into and mixed with the exhaust gases in a catalyst in order to eliminate undesirable substances. The catalyst is with advantage situated in the exhaust line at a position downstream from the turbine. A known way of reducing the amount of undesirable substances in exhaust gases, e.g. nitrogen oxides, is to add reducing agent in exhaust lines of vehicles. Such reducing agents in liquid form intended to be vaporised by the hot exhaust gases can also be used for raising the pressure in the exhaust line upstream from the turbine. In such cases the reducing agent is added to the exhaust line before the turbine instead of the otherwise usual practice of adding it after the turbine. A further advantage of adding the reducing agent upstream from the turbine is that the rotating turbine can be used for mixing the reducing agent and the exhaust gases. The result is an effective way of achieving a substantially homogeneous mixture of reducing agent and exhaust gases without using extra components. The catalyst may therefore be situated substantially immediately after the turbine. The length of the exhaust line can therefore also be reduced. The liquid medium is with advantage a urea solution. Urea solutions are used conventionally in vehicles to reduce discharges of nitrogen oxides. Urea solutions can with advantage also be used for raising the pressure in the exhaust line upstream from the turbine. A urea solution is usually stored in a tank in the vehicle and is added via an injection system controlled by an electrical control unit. A vehicle equipped with SCR (Selective Catalytic Reduction) is thus already provided with substantially all the equipment needed for adding a liquid medium to an exhaust line. Supplying the liquid medium to the exhaust line upstream instead of downstream from the turbine can therefore in most cases be achieved at a relatively small cost.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention is described below by way of example with reference to the attached drawing, in which:

Fig. 1 depicts a diesel engine provided with an arrangement according to the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Fig. 1 depicts a combustion engine in the form of a diesel engine 1. The diesel engine 1 may be intended to power a heavy vehicle. The exhaust gases from the cylinders of the diesel engine 1 are led via an exhaust manifold 2 to an exhaust line 3. The exhaust line 3 is provided with a turbo unit which comprises a turbine 4 and a compressor 5. The turbine 4 is intended to convert the energy of the exhaust gases in the exhaust line 3 to mechanical work for driving the compressor 5. The compressor 5 is intended to compress air which is led into an inlet line 6 to the diesel engine 1. A charge air cooler 7 is arranged in the inlet line 6 to cool the compressed air before it is supplied to the respective combustion chambers of the diesel engine 1 via a manifold 8.

The exhaust line 3 is here provided with catalytic exhaust cleaning by the method called SCR (Selective Catalytic Reduction) which involves adding a urea solution to the exhaust gases in the exhaust line 3 of the diesel engine. The urea solution is stored in a tank 9 and is led via a line 10 to the exhaust line 3. A control unit 12, which may be a computer unit with appropriate software 12a, controls the supply of urea solution by activation of a pump 11. The pump 11 transports urea solution to the injection means 13 which injects urea solution into the exhaust line 3. The control unit 12 may use information concerning specific engine parameters to calculate the amount of urea solution to be supplied for optimum reduction of the content of nitrogen oxides in the exhaust gases. The urea solution supplied is intended to be heated by the exhaust gases in the exhaust line 3 so that it vaporises and is converted to ammonia. The mixture of ammonia and exhaust gases is thereafter led on through the exhaust line 3 to a catalyst 14 in which chemical reactions take place. The nitrogen from the nitrogen oxides in the exhaust gases reacts here with the nitrogen in the ammonia, resulting in the formation of nitrogen gas. The oxygen from the nitrogen oxides reacts with the hydrogen in the ammonia, resulting in the formation of water. The nitrogen oxides in the exhaust gases are thus reduced in the catalyst 14 to nitrogen gas and water vapour which are led out to the surrounding air.

The injection means 13 is fitted at such a position 3a in the exhaust line 3 that it injects the urea solution upstream from the turbine 4 with respect to the direction of exhaust gas flow in the exhaust line 3. The injection means 13 injects the liquid medium at a distance L upstream from the turbine 4. The distance L is so adapted that substantially all of the urea solution supplied will be heated and vaporised by the exhaust gases before it reaches the turbine 4. A pressure sensor 15 is arranged in the exhaust line 3 to measure the pressure of the exhaust gases upstream from the turbine 4. The pressure sensor 15 is intended to send to the control unit 12 signals representing the pressure of the exhaust gases in the exhaust line 3 upstream from the turbine 4. A temperature sensor 16 is arranged in the exhaust line 3 to measure the temperature of the exhaust gases upstream from the turbine 4. The temperature sensor 16 is intended to send to the control unit 12 signals representing the temperature of the exhaust gases in the exhaust line 3 upstream from the turbine 4.

During operation of the diesel engine 1, the control unit 12 substantially continuously receives current information concerning, for example, fuel consumption and the pressure of the exhaust gases from the pressure sensor 15 and the temperature of the exhaust gases from the temperature sensor 16. Using, for example, such information, the control unit 12 can calculate the amount of urea solution to be added for substantially optimum reduction of the content of nitrogen oxides in the exhaust gases. The control unit 12 can at the same time also estimate the maximum amount of urea solution which can be supplied for ensuring that substantially all of the urea solution will be heated and vaporised by the exhaust gases over the distance L before the turbine 4. The control unit 12 can also estimate the maximum amount of urea solution which can be supplied without the exhaust gases reaching such a low temperature in the exhaust line 3 after the turbine 4 as to cause risk of substances condensing in the exhaust gases. However, the control unit 12 is primarily adapted to controlling the amount of urea solution injected so that a substantially optimum reduction of the content of nitrogen oxides in the exhaust gases is achieved. In certain operating situations, however, the control unit 12 can limit the calculated amount of urea solution if it exceeds any of the maximum values mentioned above.

The control unit 12 supplies the calculated amount of urea solution by means of the pump 11 which delivers the urea solution from the tank 9 via the line 10 to the injection means 13. The injection means 13 injects the calculated amount of urea solution in a finely divided form into the exhaust line at a position 3a situated at a distance L upstream from the turbine 4. The finely divided urea solution is heated quickly and vaporised by the hot exhaust gases in the exhaust line 3. The vaporisation causes the urea solution to change to gaseous form, inter alia in the form of ammonia. Since substances in gaseous form occupy a significantly larger volume than in liquid form, the vaporisation process results in a definite pressure increase in the exhaust line 3 upstream from the turbine. As the pressure in the exhaust line 3 downstream from the turbine 4 will be at a substantially constant value, the pressure increase in the exhaust line 3 upstream from the turbine 4 results in the possibility of using a larger pressure drop to drive the turbine 4.

The energy of the exhaust gases is converted by the turbine 4 to mechanical work which drives the compressor 5. The boost to the performance of the turbine 4 due to the extra pressure in the exhaust line 3 provides the compressor 5 with corresponding extra capacity for compressing the air in the inlet line 6. The air led to the combustion engine 1 is thus provided with extra pressure, with the result that a larger amount of air and fuel can be supplied to the combustion engine 1, which is thus provided with increased power. The rotating turbine 4 gives off a substantially homogenous mixture of ammonia and exhaust gases. The catalyst 14 can therefore be situated relatively close to the turbine 4 in the exhaust line 3. The mixture of ammonia and exhaust gases is thereafter led through the catalyst 14, in which the nitrogen from the nitrogen oxides in the exhaust gases reacts with the nitrogen in the ammonia, resulting in the formation of nitrogen gas. The oxygen from the nitrogen oxides reacts with the oxygen in the ammonia, resulting in the formation of water. The nitrogen oxides in the exhaust gases are thus reduced in the catalyst to nitrogen gas and water vapour. With correct urea proportioning, the discharge of nitrogen oxides from the diesel engine 1 can be greatly reduced.

The invention is not limited to the embodiment described above but may be varied freely within the scopes of the claims. In the example described, a urea solution is used to create extra pressure in the exhaust line 3 upstream from the turbine 4. The amount of urea solution added is here controlled so as to achieve optimum reduction of the nitrogen oxides in the exhaust gases. However, the magnitude of the extra pressure in the exhaust line 3 is related to the amount of urea solution added. The liquid medium need nevertheless not be a urea solution but may be substantially any liquid medium which vaporises at a suitable temperature. If such a liquid medium is used with the sole object of increasing the pressure in the exhaust line 3 upstream from the turbine 4, the control unit 12 can relatively freely control the amount of liquid medium supplied to the exhaust line 3. The control unit 12 has nevertheless to supply at most such an amount of liquid medium that substantially all of it will be heated and vaporised by the exhaust gases over the distance L before the turbine 4. The control unit 12 has also at most to supply such an amount of the liquid medium that the exhaust gases after the turbine 4 do not reach such a low temperature as to cause risk of substances in the exhaust gases condensing in the exhaust line 3.

Claims

1. An arrangement for a combustion engine (1) whereby the arrangement comprises an exhaust line (3) for leading exhaust gases out from the combustion engine (1), a turbine arranged in the exhaust line (3) for converting energy of the exhaust gases to mechanical work, an injection means (13) arranged in the exhaust line (3) for injecting a urea solution into the exhaust line (3), whereupon the urea solution is intended to be heated and vaporised by the warm exhaust gases in the exhaust line (3), characterised in that the injection means (13) is fitted at such a position (3a) in the exhaust line that it injects the urea solution at a distance (L) upstream from the turbine (4) with respect to the direction of exhaust gas flow in the exhaust line (3), and that the arrangement comprises a control unit (12) adapted to controlling the amount of urea solution injected into the exhaust line (3) so that substantially all of the urea solution supplied will be heated and vaporised by the exhaust gases over said distance (L) before it reaches the turbine (4).

2. An arrangement according to claim 1, characterised in that it comprises a pressure sensor (15) which measures the pressure of the exhaust gases in the exhaust line (3) upstream from the turbine (4), the control unit (12) being adapted to receiving information from said pressure sensor (15) in order to control the amount of urea solution injected into the exhaust line (3).

3. An arrangement according to claim 1 or 2, characterised in that it comprises a temperature sensor (16) which measures the temperature of the exhaust gases in the exhaust line (3) upstream from the turbine (4), the control unit (12) being adapted to receiving information from said temperature sensor (16) in order to control the amount of urea solution injected into the exhaust line (3).

4. An arrangement according to any one of the foregoing claims, characterised in that it comprises a pump device (11) by means of which the control unit (12) controls the amount of liquid medium injected.

5. An arrangement according to any one of the foregoing claims, characterised in that it comprises a compressor (5) driven by the turbine (4).

6. An arrangement according to claim 5, characterised in that the compressor (5) is adapted to compressing air in an inlet line (6) which leads air to at least one combustion space of the combustion engine (1).