METHOD FOR PREDICTING UREA CRYSTAL BUILD-UP IN AN ENGINE SYSTEM

Abstract

A method for predicting urea crystal build-up in an engine system when operating according to an intended drive cycle. The method includes providing data representing engine operational conditions for the internal combustion engine during the intended drive cycle, wherein the data comprises values for at least engine speed and engine torque distributed over a time period representing the intended drive cycle; determining values and time variation for at least one exhaust parameter during the time period of the intended drive cycle when the engine system is operated according to the engine operational condition data; providing a reference relation between values and time variation for the at least one exhaust parameter and an expected urea crystal build-up in the engine system when operating the engine system at different engine operational conditions, predicting urea crystal build-up in the engine system when operating according to the intended drive cycle by comparing the determined values and time variation for the at least one exhaust parameter with the reference relation.

Claims

1. Method for predicting urea crystal build-up in an engine system when operating according to an intended drive cycle, wherein the engine system comprises an internal combustion engine and an exhaust gas aftertreatment system provided with an urea solution dosage arrangement, the method comprising: providing data representing engine operational conditions for the internal combustion engine during the intended drive cycle, wherein the data comprises values for at least engine speed and engine torque distributed over a time period representing the intended drive cycle; determining values and time variation for at least one exhaust parameter during the time period of the intended drive cycle when the engine system is operated according to the engine operational condition data; providing a reference relation between values and time variation for the at least one exhaust parameter and an expected urea crystal build-up in the engine system when operating the engine system at different engine operational conditions, predicting urea crystal build-up in the engine system when operating according to the intended drive cycle by comparing the determined values and time variation for the at least one exhaust parameter with the reference relation; wherein the exhaust parameter is at least one of: an exhaust gas temperature, an exhaust gas mass flow rate, and/or an exhaust gas energy ratio reflecting an energy content of the exhaust gas in relation to the energy required to evaporate dosed urea solution.

2. Method according to claim 1, wherein the data representing engine operational conditions during the intended drive cycle are based on real engine operational data collected during a drive cycle corresponding to the intended drive cycle.

3. Method according to claim 1, wherein the method comprises: determining values and time variation for at least two, preferably all three, exhaust parameters during the time period of the intended drive cycle when the engine system is operated according to the engine operational condition data.

4. Method according to claim 1, wherein the step of determining values and time variation for the at least one exhaust parameter during the time period of the intended drive cycle comprises determining values for the at least one exhaust parameter at a plurality of points of time distributed over the time period representing the intended drive cycle.

5. Method according to claim 1, wherein the exhaust gas temperature and/or the exhaust gas mass flow rate is/are obtained from an engine calculation model using engine speed and engine torque as input data.

6. Method according to claim 1, wherein the exhaust gas energy ratio is obtained from: i) a numerator that depends on at least the exhaust gas temperature and the exhaust gas mass flow rate, and ii) a denominator that comprises a term dependent on the amount of urea solution dosage.

7. Method according to claim 4, wherein the step of determining values and time variation for the at least one exhaust parameter during the time period of the intended drive cycle comprises determining values and time variation for the exhaust gas energy ratio, wherein the method further comprises: selecting, from a pre-set relation between engine operational conditions and amount of urea solution dosage, an amount of urea solution dosage that corresponds to the engine operational conditions that apply at the corresponding point of time.

8. Method according to claim 1, wherein the reference relation is based on a plurality of tests of the engine system where the engine system has been operated according to various drive cycles followed by checking the magnitude of actual urea crystal build-up.

9. Method according to claim 1, wherein the reference relation comprises a threshold value for the exhaust parameter and a corresponding minimum portion of the total time period of the intended drive cycle, wherein the threshold value and the minimum portion of time are set so that, if the determined values and time variation for the at least one exhaust parameter during the intended drive cycle are such that the exhaust parameter threshold value is exceeded during at least the minimum portion of the total time period, the predicted amount of urea crystal build-up in the engine system is zero or below a threshold level for the urea crystal build-up.

10. Method according to claim 1, wherein the method comprises the step of determining suitability of the engine system for the intended drive cycle, and further comprising determining whether the engine system is suitable for the intended drive cycle with regard to the build-up of urea crystals in the exhaust gas aftertreatment system.

11. Method according to claim 10, wherein the method comprises determining suitability of a plurality of engine systems for an intended drive cycle, wherein each engine system comprises an internal combustion engine and an exhaust gas aftertreatment system provided with an urea solution dosage arrangement, and wherein the internal combustion engine and/or the exhaust gas aftertreatment system differ(s) between the plurality of engine systems; and comparing the suitability of the plurality of engine systems with regard to the build-up of urea crystals in the exhaust gas aftertreatment system.

12. Method according to claim 1, wherein the internal combustion engine is of the compression-ignition type, such as a diesel engine.

13. Method according to claim 1, wherein the exhaust gas aftertreatment system comprises an SCR-unit.

14. A computer program product comprising program code for performing the steps of claim 1 when said program is run on a computer.

15. A computer readable medium carrying a computer program comprising program code for performing the steps of claim 1 when said program product is run on a computer.

16. A control unit for controlling a method for determining suitability of an engine system for an intended drive cycle, the control unit being configured to perform the steps of the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

[0043] In the drawings:

[0044] FIG. 1 shows a plot of data representing engine operational conditions during an intended drive cycle.

[0045] FIG. 2 shows, schematically, an illustrated of a method according to this disclosure.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0046] FIG. 1 shows a plot of data representing engine operational conditions during an intended drive cycle. Each data point shows engine speed and engine torque at a certain time period element of the entire drive cycle time period.

[0047] The different lines in FIG. 1 indicate full-load curves for different engine systems of different size where the uppermost line represents the largest engine and the lowest line represents the smallest engine. As indicated in FIG. 1, the largest engine seems to be unnecessarily large, it will have to operate with a load that probably is too low for the intended drive cycle, whereas the smallest engine is too small, although it might be sufficient for an average load/torque it cannot provide sufficient torque for a great portion of the time period elements of the intended drive cycle. FIG. 1 thus indicates suitability of various engine systems for an intended drive cycle based on engine speed and engine load, but it does not include suitability with regard to EATS performance.

[0048] An example of the method of this disclosure is schematically illustrated in FIG. 3 and may be described as follows:

[0049] S10—providing data representing engine operational conditions for the internal combustion engine during the intended drive cycle, wherein the data comprises values for at least engine speed and engine torque distributed over a time period representing the intended drive cycle.

[0050] An example of such data is shown in FIG. 1. The data may be obtained by collecting operational data from the (old) engine system used presently in the application in which it is intended to replace the engine system for a new engine system (for which the suitability is to be determined and for which the urea crystal build-up is to be predicted). If the internal combustion engines of the new and old engine systems are of the same size and type one may use the same engine speed and torque values. If the new internal combustion engine is of (significantly) different size and type, the original speed and torque vales may be adapted (e.g. to give the same power output) before determining values and time variation for the exhaust parameter(s).

[0051] S20—determining values and time variation for at least one exhaust parameter during the time period of the intended drive cycle when the engine system is operated according to the engine operational condition data.

[0052] The principles of an example for how to carry out step S20 can be described as follows:

[0053] Data points as exemplified in FIG. 1 form input data to a calculation model, i.e. data on engine speed and engine torque at different points of time of the intended drive cycle. Exhaust gas temperature and exhaust gas mass flow rate downstream a turbocharger turbine of the engine system subject to the calculations are obtained from look-up tables. The look-up tables are obtained from operation of the engine system at all engine speeds from idling to maximum speed and at all loads from zero to maximum load. (This operation may be done in a previous phase, such as when developing the engine.) Two alternative look-up tables are used depending on the operating mode of the engine, one table for cool EATS and one for warm/hot EATS. Which table to use depends on the simulated EATS temperature at that point in time. The EATS is assumed to be cool when starting the engine.

[0054] The data on exhaust gas temperature and mass flow rate obtained for a certain point of operation are then fed to a numerical model of a pipe extending between the turbine and the EATS. The numerical model provides for a delay of any temperature change and also a decrease of temperature due to heat conduction away from the pipe. Downstream the pipe, a diesel oxidation catalyst (DOC) and a DPF are thermodynamically simulated as thermal inertia. A further numerical model simulates a further pipe and downstream that further pipe an SCR-unit (selective catalytic reduction) may be simulated in a similar way as the DOC and the DPF. The calculated temperature of the outgoing exhaust gas is used to select look-up table for the next operational data point (i.e. the next time period element).

[0055] A further look-up table is provided for obtaining amount of urea solution dosage for each time period element. This table provides the amount of urea solution dosage as function of engine speed and torque. The amount of urea solution dosage is then used, together with e.g. exhaust gas temperature and exhaust gas mass flow rate, to calculate the exhaust gas energy ratio for each time period element, for instance according to the following:

Energy ratio=(exhaust gas mass flow+exhaust gas temperature−heat capacity for air), divided by (amount of urea solution dosage−heat capacity for water.Math.(100° C.—temperature in ° C. of urea solution when dosed into the EATS)+(amount of urea solution dosage.Math.heat of evaporation for water).

[0056] Output from these calculations are then values for each of the exhaust parameters for each operational data point. Since these points are distributed over the drive cycle time period one obtains a determination of the values and time variation for all three exhaust parameters during the time period of the intended drive cycle when the engine system is operated according to the engine operational condition data.

[0057] S30—providing a reference relation between values and time variation for the at least one exhaust parameter and an expected urea crystal build-up in the engine system when operating the engine system at different engine operational conditions.

[0058] As mentioned previously, various reference relations are possible. Further, the reference relation may differ between different engine systems. In an example there are threshold values and corresponding minimum time fractions set for each of the exhaust parameters so it can be said that if the value of a certain exhaust parameter is at least X during at least Y % of the total drive cycle time period, then no (or only very little) urea crystal build-up is expected.

[0059] S40—predicting urea crystal build-up in the engine system when operating according to the intended drive cycle by comparing the determined values and time variation for the at least one exhaust parameter with the reference relation.

[0060] The comparison is relatively easy if all time period elements have the same length and if the reference relation comprises threshold values and corresponding minimum time fractions for each of the exhaust parameters as explained in relation to step S30. One may then, for each exhaust parameter at a time if desired, check whether the exhaust parameter values are above X for Y % of the time period elements. If this is the case for a first of the exhaust parameters, it may be concluded that the predicted urea crystal build-up in the engine system when operating according to the intended drive cycle is negligible or acceptable. If this is not the case for the first exhaust parameter, a second (and if necessary also a third) exhaust parameter can be subject to a similar assessment. Another procedure may be more suitable depending on the structure of the reference relation.

[0061] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.