Technical field

The invention relates to an arrangement and a method for a dosing system for supply of a reducing agent in the exhaust flow according to the preambles of claim 1 and claim 5.

More specifically, the invention relates to a method and arrangement for identifying whether incorrect liquid is used as reducing agent and hence also for at least indirectly identifying that correct reducing agent is used.

Background The combustion of fuel in combustion engines or other combustion processes, e.g. power stations etc., results in the formation of residual products which leave the combustion installation via an exhaust system. Various factors, e.g. concern for the environment, have lec to the introduction of progressively more stringent limit values for the amounts of residual products allowed to be discharged from different types of combustion installations.

One of the residual products in the exhaust flow takes the form of nitrogen oxides, NOx emissions. One way of decreasing the NOx emissions in the exhaust flow is to inject into it a reducing agent, e.g. an aqueous solution of urea. The reducing agent reacts with the nitrogen oxides in the exhaust flow, resulting in the formation inter alia of nitrogen gas and water. The reducing agent is drawn from a separate tank and is injected by means of a dosing system in the exhaust flow.

It unfortunately happens that the reducing agent tank is sometimes filled, intentionally or unintentionally, with other liquids instead of the reducing agent for which it is intended, e.g. the tank may be filled with fuel instead of reducing agent. If fuel is put into the tank intended for reducing agent and is dosed in the exhaust line, there is considerable risk of damage to components of the exhaust post-treatment system, e.g. the dosing system, catalysts, pipes or neighbouring parts, and of simultaneous failure to achieve the desired decrease of emissions but instead an actual increase in the emissions from the engine.

Prior art which may be cited within this technical field is US 20100199644, which describes an arrangement and a method for diagnosing an exhaust post-treatment system. More specifically, it indicates how this may be used to indicate dosing of too diluted a reducing agent. A control unit is connected to temperature sensors situated before and after a catalyst. On the basis of information about amounts of reducing agent injected and temperatures before the catalyst, the control unit calculates an expected temperature after the catalyst, and if the temperature monitored after the catalyst is not as expected, a fault signal is generated. There is thus a need to make it possible to detect something other than the intended reducing agent having been put into the tank and being dosed in the exhaust line.

Summary of the invention The object of the present invention is to meet the above need. The object is achieved by an arrangement according to claim 1 and a method according to claim 5.

The arrangement according to the invention comprises a temperature sensor situated downstream of a catalyst. The temperature sensor is connected to a monitoring unit which compares the temperature measured in the exhaust flow downstream of the catalyst with a predetermined verified temperature range which may normally be expected when correct reducing agent is supplied to the exhaust flow. If the measured temperature does not fall within the range, this is an indication that some other agent than the intended reducing agent is being supplied to the exhaust flow by the dosing system.

In accordance with the invention, the supply of agent from the dosing system to the exhaust flow is halted if the measured temperature falls outside the predetermined range. This further enhances security against accidents and undesirable discharges in that the supply of medium via the dosing system is halted automatically when there is indication of incorrect agent.

In an advantageous embodiment of the arrangement, the temperature range within which the measured temperature should be is around 50° C. This range results in reliable measurements and allows necessary scope for temperature variations which occur because of variations in, for example, surrounding conditions, engine load levels and the like.

In an embodiment of the arrangement, the control unit is connected to an instrument panel in which a signalling unit shows whether some agent other than correct reducing agent is injected in the exhaust flow. This is a good solution for making an operator aware that there is a problem and that corrective action is required to rectify it.

In an embodiment of the arrangement, a filter is provided in the exhaust line downstream of the catalyst, and a temperature sensor is provided downstream of the filter. This makes it possible for the temperature sensor to be situated where there is appropriate space. It also makes it possible to use other types of temperature sensors which are effective within other temperature ranges. The invention relates also to a method which makes it easy to determine reliably whether the agent taken from the tank of the dosing system is not the intended reducing agent.

In accordance with the invention, the method comprises also the step of switching off the dosing of agent in the dosing system, with the consequent advantage that no manual switching off is required if incorrect agent is identified in the dosing system.

In an advantageous embodiment, the method comprises the further subsequent step, after the dosing has been halted, of comparing the temperature of the exhaust gases with temperatures expected when no dosing is taking place. If this temperature is within the expected range, it if an indication that other components of the dosing system are functioning correctly. This embodiment of the method makes it possible to determine whether the fault is a particular agent dosed or whether there is some other fault in the arrangement. The invention relates also to a computer programme containing programme code for implementing a method according to any of the embodiments described. The method may with advantage be applied by a computer programme which can continuously monitor prevailing temperatures downstream of the catalyst and/or the filter in order to verify that reducing agent is being dosed in the exhaust flow.

Brief description of drawings Fig. 1 depicts schematically an embodiment of the arrangement, and

Fig. 2 is a flowchart for a method according to the invention.

Detailed description of embodiments exemplifying the invention Fig 1 depicts a schematic arrangement according to the invention. The arrangement comprises a combustion engine 10 and an exhaust line 11 intended to lead combustion gases from the engine 10 to appropriate outlets. The size and configuration of the engine 10 may be varied in many ways to adapt it to the vehicle or application in which it is intended to serve as power source. The engine may therefore alternatively be used for marine purposes or take the form of a permanently installed engine for industrial purposes.

From the engine 10 the exhaust gases are led first to a turbo unit 12 which is driven by them. The turbo unit need not be part of the arrangement according to the invention and may therefore even be omitted without affecting the arrangement.

The arrangement comprises also a system for post-treatment of the exhaust gases from the engine with the object of reducing emissions such as nitrogen oxides. To this end, the arrangement comprises a dosing system 20 for dosing a reducing agent in the exhaust flow in the exhaust line 11. The dosing system 20 comprises a tank 21 intended to accommodate reducing agent which may be a suitable aqueous solution of urea usually marketed under the name AdBlue. The reducing agent is conveyed by a pump 22 which generates a pressurised flow in a supply line 23 in order thereafter to be dosed in the exhaust flow of a dosing unit 24 so situated that its orifice is in the exhaust line 11. There are also other types of reducing agent whose form and consistency may vary, in which case the parts concerned are adapted according to the reducing agent chosen. The dosing of reducing agent is controlled by a control unit (not depicted) which uses various parameters, e.g. engine load and/or other relevant factors, as a basis for determining the amount of reducing agent to be dosed. To ensure that the amount of reducing agent supplied to the dosing unit will always be sufficient, the pump 22 generates constantly a greater flow than is being dosed, and the resulting surplus is led back from the dosing unit 24 to the tank 21.

A catalyst 13 in which the reducing agent reacts with the nitrogen oxides in the exhaust gases and thereby cleans the exhaust flow is situated downstream of the dosing unit 24 in the exhaust line 11. Such a catalyst is often called SCR catalyst, the configuration of which is well-known prior art. Various types of filters may be provided in the exhaust line 11 to reduce the amount of particles in the exhaust gases, although no filters appear in the diagram. Other components may also be provided in the exhaust line to reduce emissions, e.g. an ammonia slip catalyst situated after the catalyst 13. The exhaust line may with advantage alsc incorporate a silencer to reduce noise. As these components are not necessary for

understanding the invention, they are not described in more detail.

A temperature sensor 14 for measuring the temperature T of the exhaust flow is provided downstream of the catalyst 13 and, in the present case, downstream also of a filter. The temperature sensor 14 measures the temperature T at chosen intervals and sends the results to a monitoring unit 15. If there are further components in the exhaust line, the temperature sensor 14 may be situated before or after them, what is important that it be downstream of the catalyst 13 irrespective of whether there are further components between the catalyst 13 and the temperature sensor 14. The monitoring unit 15 compares the measured temperature T with a predetermined temperature range Tmi _n - T _max arrived at by testing what temperatures should normally prevail in the exhaust flow during continuous operation of the engine 10 with correct dosing of reducing agent in the exhaust flow upstream of the catalyst 13. If the temperature T measured by the temperature sensor 14 in the exhaust flow falls outside the desired range determined, this is an indication that the agent being dosed by the dosing unit 24 is not the intended reducing agent.

An example which may be cited is that if the tank 21 is mistakenly (or intentionally) filled with diesel or some other fuel instead of reducing agent, the temperature T in the exhaust flow downstream of the catalyst 13 will increase and exceed the highest temperature T _max within the desired range determined. The difference between T _m i _n and T _max in this example is of the order of 50°, thus allowing scope for the normal variations which may occur during normal operation with correctly injected reducing agent. Temperature ranges in other applications may be significantly narrower, of the order of 10°, or significantly wider, of the order of 100°. How wide the temperature range should be is determined inter alia by where in the exhaust line the temperature sensor 14 is situated and whether there are other components between it and the catalyst 13.

If the temperature comparison by the monitoring unit 15 indicates that an incorrect reducing agent has been dosed in the exhaust line 11 , the arrangement comprises means which make it possible for this to be indicated to an operator on a signalling means intended for the purpose on an instrument panel. In addition, the monitoring unit 15 comprises means through its connection to the dosing unit 24 for being able to halt continued dosing of agent in the exhaust line 11 , and also means for being able to switch off the dosing system. Switching off the dosing system 20 may be done manually by an operator in response to indications that an incorrect agent has been dosed, but may also be done automatically by the monitoring unit 15 providing the dosing unit 24 with an appropriate signal.

The arrangement described above works on the basis of a method, an embodiment of which is illustrated in the flowchart in fig. 2.

The method comprises the following step:

a) The first step of the method is to determine whether the agent is being dosed by the dosing system 20, which is done by the monitoring unit 15 communicating with the control unit of the dosing system. If no agent is being dosed from the dosing unit 24, step a) is repeated, but if agent is being dosed the method moves on to step b);

b) The prevailing temperature T downstream of the catalyst 13 is then determined by means of the temperature sensor 14;

c) The temperature measured by the temperature sensor 14 is compared with a predetermined temperature range (Tmi _n < T < T _max ) which is normally applicable when correct reducing agent is being dosed in the exhaust flow; if the measured temperature T falls within the range, the intended reducing agent is being dosed and step a) is then repeated to verify again that such is the case, but if not the method moves on to step d);

d) The measured temperature T is outside the range, which means that incorrect agent is being dosed; dosing has therefore to be switched off. When it is found that incorrect agent has been dosed, this fact may be presented visually to an operator so that the dosing system 20 can be switched off manually or automatically. The fault can then be rectified.

In this type of arrangement it is of course also possible for other faults to occur, so the methoc may be further supplemented for greater precision in fault tracing. This is done by adding further steps as follows:

e) determining prevailing temperature T downstream of the catalyst 13 after the dosing has been switched off;

f) comparing the measured temperature T with some other predetermined

temperature range with reference values (T ^' _m i _n < T <T ^' _max ) for normally occurring temperatures when reducing agent is not being dosed; g) if the measured temperature T is then within the range, this indicates that other components in the arrangement are functioning as they should but that the reducing agent dosed was not the intended one; it is then appropriate for the whole dosing system to be switched off in order to prevent circulation of incorrect agent in the dosing system, and to take corrective action for ensuring that correct reducing agent is used before the dosing system is switched on again; h) if the measured temperature T does not fall within the range, this indicates that there is probably some other fault than dosing of incorrect reducing agent, e.g. faults in sensors or the like; the dosing may therefore be switched on again to reduce nitrogen oxides in the exhaust gases; the method is then repeated.

The invention is described above on the basis of embodiment examples which may of course be combined in various ways. An aqueous solution of urea has been cited as an example of a correct intended reducing agent. A correct agent need not be in liquid form but may alternatively be in solid or gaseous form. The invention has been mainly described in terms of how it can be used to indicate that an incorrect reducing agent is being used and that the tank has therefore been filled with, and contains, an incorrect reducing agent. The invention may of course also be used to indicate that a correct reducing agent is being used, which is thi case if the measured temperature in the exhaust flow is within the predetermined range. Such an indication may take the form of absence of a fault indication such as described above. Alternatively the arrangement may be supplemented by a signalling means, e.g. in the form ol an indicating lamp which shows when there is no fault.

A simplified form of the invention may be used if the only risk is that the tank might be filled with fuel or some other agent which might result in too high a temperature of the exhaust gases. In such a case the lower limit of the predetermined temperature range may be set so low that the temperature will in practice always be above it, with the result that the arrangement will in practice only indicate incorrectly injected agent if too high a temperature is measured in the exhaust gases. Similar problems and risks arise if an incorrect mixture of a reducing agent which in itself is correct is used for dosing, which may happen if a partly filled tank is filled up with only water.

In a similar way, the invention may therefore in an alternative simplified embodiment be used to discontinue dosing if the only risk is that the tank has been filled with water or some other agent which might prevent intended temperatures of the exhaust gases ever being reached. If the tank 21 happens to be filled with water, with the result that it contains an incorrect mixtun of reducing agent with too low a urea content in the solution, the intended temperature increase in the exhaust flow will not be achieved and the measured temperature T will be below the lowest temperature Tmi _n within the desired temperature range. In such a case the upper limit of the predetermined temperature range may be set so high that the temperature will in practice never rise to it, in which case the arrangement will in practice only indicate incorrectly injected agent if a predetermined low temperature is not measured in the exhaust gases. To be able to identify this type of incorrectly injected agent, the measured exhaust temperature needs to be compared with other values for the temperature range. As risk of damage due to too low exhaust temperatures is not as serious as that which might occur because of too high exhaust temperatures, the dosing in such a case may continue even after an incorrect reducing agent has been indicated. Although the exhaust post-treatment will then not be complete, it can still proceed with impaired function. It is then sufficient that this be indicated by suitable signalling means so that appropriate corrective action can be taken. Upon indication that an incorrect agent has been dosed in the exhaust line, one such appropriate corrective measure is that the tank be emptied of its contents and that they be replaced by a correct reducing agent.