Diesel engine with a diesel particulate filter

Abstract

Various embodiments include a diesel engine comprising: an exhaust gas line; a diesel particulate filter arranged in the exhaust gas line; a first NO sensor arranged in the exhaust gas line upstream of the diesel particulate filter; and a second NO sensor arranged in the exhaust gas line downstream of the diesel particulate filter.

Claims

1. A diesel engine comprising: an exhaust gas line; a diesel particulate filter arranged in the exhaust gas line; a first NO sensor arranged in the exhaust gas line upstream of the diesel particulate filter; a second NO sensor arranged in the exhaust gas line downstream of the diesel particulate filter; a diesel oxidation catalyst arranged in the exhaust gas line upstream of the diesel particulate filter and between the first NO sensor and the second NO sensor; and an SCR catalyst; wherein the diesel oxidation catalyst, the diesel particulate filter, and the SCR catalyst are arranged in the exhaust gas line successively in the flow direction; the first NO sensor and a first NO2 sensor are arranged between the diesel oxidation catalyst and the diesel particulate filter; and the second NO sensor and a second NO2 sensor are arranged between the diesel particulate filter and the SCR catalyst.

2. The diesel engine as claimed in claim 1, further comprising an NO2 sensor arranged in the exhaust gas line upstream of the diesel particulate filter.

3. The diesel engine as claimed in claim 1, further comprising an NO2 sensor arranged in the exhaust gas line downstream of the diesel particulate filter.

4. The diesel engine as claimed in claim 1, further comprising an NOx sensor in the exhaust gas line upstream of the diesel oxidation catalyst.

5. A method for operating a diesel engine including an exhaust gas line and a diesel particulate filter arranged in the exhaust gas line, the method comprising: measuring a first NO concentration and a first NO2 concentration in the exhaust gas line upstream of the diesel particulate filter; measuring a second NO concentration and a second NO2 concentration in the exhaust gas line downstream of the diesel particulate filter; and calculating a first difference between the first NO concentration and the second NO concentration and a second difference between the first NO2 concentration and the second NO2 concentration to determine the quantity of particles reduced by the diesel particulate filter.

6. The method as claimed in claim 5, further comprising: measuring a NOx concentration upstream of the diesel particulate filter; and determining a NO2/NOx ratio downstream of the diesel particulate filter based on the measured NOx concentration.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The teachings of the present disclosure are explained in detail hereunder by means of exemplary embodiments in conjunction with the drawings. The drawings show:

(2) FIG. 1 a schematic illustration of an exhaust gas line of a diesel engine incorporating teachings of the present disclosure;

(3) FIG. 2 a depiction of a second embodiment of an exhaust gas line incorporating teachings of the present disclosure; and

(4) FIG. 3 a depiction of a third embodiment of an exhaust gas line incorporating teachings of the present disclosure.

DETAILED DESCRIPTION

(5) In some embodiments, a diesel engine comprises an exhaust gas line and a diesel particulate filter arranged in the exhaust gas line, which is characterized in that an NO.sub.2 sensor is arranged in the exhaust gas line upstream of the diesel particulate filter, and an NO.sub.2 sensor is arranged in the exhaust gas line downstream of the diesel particulate filter.

(6) The term “NO” used here means nitrogen monoxide, “NO.sub.2” means nitrogen dioxide, and “NO.sub.x” means nitrogen monoxide plus nitrogen dioxide. “CRT” means Continuous Regeneration Trap, i.e. the principle of a continuously regenerating particle trap. “DPF” means diesel particulate filter. The terms “DOC” (diesel oxidation catalyst) and “SCR” (selective catalytic reduction) and “SCR catalyst” (a catalyst using the SCR process) are also used below.

(7) Some embodiments include a method for operating a diesel engine which comprises an exhaust gas line and a diesel particulate filter arranged in the exhaust gas line, the method comprising: measuring the NO concentration in the exhaust gas line upstream of the diesel particulate filter; measuring the NO concentration in the exhaust gas line downstream of the diesel particulate filter; and using the obtained signals to form the difference between the NO concentration downstream and upstream of the diesel particulate filter in order to determine the quantity of particles reduced by the CRT effect.

(8) In some embodiments, a method comprises the following steps: measuring the NO.sub.2 concentration in the exhaust gas line upstream of the diesel particulate filter; measuring the NO.sub.2 concentration in the exhaust gas line downstream of the diesel particulate filter; and using the obtained signals to form the difference between the NO.sub.2 concentration downstream and upstream of the diesel particulate filter in order to determine the quantity of particles reduced by the CRT effect.

(9) In some embodiments, methods include determining the CRT efficiency of the diesel particulate filter by the arrangement of corresponding NO and/or NO.sub.2 sensors and by performing corresponding NO and/or NO.sub.2 concentration measurements with these sensors upstream and downstream of a diesel particulate filter. Furthermore, the efficiency values determined are used to control the active regeneration of the diesel particulate filter. The following procedure is applied:

(10) In some embodiments, when an NO sensor is used upstream and downstream of the diesel particulate filter, the rise in NO downstream of the diesel particulate filter is determined, namely the difference between the NO signal downstream of the diesel particulate filter and upstream of the diesel particulate filter. This value is used to establish how many particles (soot particles) have been reduced by the CRT effect.

(11) In some embodiments, both an NO sensor and an NO.sub.2 sensor are arranged in the exhaust gas line upstream of the diesel particulate filter. The NO.sub.2/NO.sub.x ratio downstream of the diesel particulate filter can thereby be determined as follows:
NO.sub.2_a/NO.sub.x_a=1−NO_a/(NO_b+NO.sub.2_b),
wherein:
NO.sub.2_a, NO_a=NO.sub.2 or NO concentration downstream of the diesel particulate filter,
NO.sub.2_b, NO_b=NO.sub.2 or NO concentration upstream of the diesel particulate filter.

(12) In some embodiments, in which an NO.sub.2 sensor is used upstream and downstream of the diesel particulate filter, the fall in NO.sub.2 downstream of the diesel particulate filter, i.e. the difference between the NO.sub.2 signal upstream and downstream of the diesel particulate filter, can be used to determine how many particles (soot particles) have been reduced by the CRT effect. Here too, as in the variant described above in which both an NO.sub.2 sensor and an NO sensor are arranged upstream of the diesel particulate filter, the NO.sub.2/NO.sub.x ratio downstream of the diesel particulate filter can be determined as follows:
NO.sub.2_a/NO.sub.x_a=NO.sub.2_a/(NO_b+NO.sub.2_b).

(13) In some embodiments, an SCR catalyst is arranged in the exhaust gas line downstream of the diesel particulate filter, wherein an NO sensor and an NO.sub.2 sensor are arranged upstream of the SCR catalyst. In these embodiments, the NO.sub.2/NO.sub.x ratio downstream of the diesel particulate filter can be determined, which is then used to control the correct SCR urea addition.

(14) In some embodiments, a diesel oxidation catalyst is arranged in the exhaust gas line upstream of the diesel particulate filter, wherein an NO.sub.x sensor is arranged upstream of the diesel oxidation catalyst, and either an NO sensor or an NO.sub.2 sensor is arranged upstream and downstream of the diesel particulate filter. In these embodiments, the soot particle reduction by the CRT effect can be determined in the same way as in the embodiment described above, in which an NO and/or an NO.sub.2 sensor is arranged upstream and an NO.sub.2 sensor or an NO sensor is arranged downstream of the diesel particulate filter. The total NO.sub.x concentration measured upstream of the diesel particulate filter is used purely to determine the NO.sub.2/NO.sub.x ratio. With this configuration, in addition the conversion efficiency of the diesel oxidation catalyst, from the NO or NO.sub.2 measurement upstream of the diesel particulate filter in comparison with the NO.sub.x upstream of the diesel oxidation catalyst, can be used for supply gas diagnosis of the diesel oxidation catalyst.

(15) The NO.sub.2/NO.sub.x ratio upstream of the SCR catalyst may also be used for active temperature management of the diesel particulate filter and/or diesel oxidation catalyst. If the NO.sub.2/NO.sub.x ratio is too high (i.e. above 50%), the temperature of the diesel oxidation catalyst should be reduced, for example by a reduction in EGR (exhaust gas recirculation) or via a shift in the combustion centre point towards a higher combustion efficiency. If the NO.sub.2/NO.sub.x ratio is too low (i.e. below 20%), the temperature of the diesel oxidation catalyst should be increased, for example by an increase in EGR or by delaying the combustion centre point towards a lower combustion efficiency.

(16) In some embodiments, a diesel oxidation catalyst, a diesel particulate filter and an SCR catalyst are arranged in the exhaust gas line successively in the flow direction, wherein an NO sensor and an NO.sub.2 sensor in each case are arranged in the exhaust gas line upstream of the diesel oxidation catalyst, and between the diesel oxidation catalyst and the diesel particulate filter, and between the diesel particulate filter and the SCR catalyst.

(17) As shown in FIG. 1, the exhaust gas of a diesel engine is conducted from left to right in the figure via an exhaust gas line 1. The exhaust gas thus passes through a diesel particulate filter 2 which is formed in a suitable and known fashion. An NO sensor 3 and an NO.sub.2 sensor 4 are arranged in the exhaust gas line upstream of the diesel particulate filter 2. A further NO.sub.2 sensor 5 is arranged in the exhaust gas line downstream of the diesel particulate filter 2.

(18) By means of the two NO.sub.2 sensors 4 and 5, the reduction in NO.sub.2 in the exhaust gas line after passing through the diesel particulate filter is measured (difference between the NO.sub.2 signal upstream and downstream of the diesel particulate filter) in order to establish the quantity of particles (soot quantity) reduced by the CRT effect. In addition, the NO.sub.2/NO.sub.x ratio downstream of the diesel particulate filter is calculated.

(19) In the embodiment shown in FIG. 2, an NO sensor 3 and an NO.sub.2 sensor 4 are situated upstream of the diesel particulate filter 2, while an NO sensor 6 is arranged in the exhaust gas line downstream of the diesel particulate filter 2. This arrangement measures the rise in NO downstream of the diesel particulate filter (difference between the NO signal downstream and upstream of the diesel particulate filter), which is used to establish the quantity of particles reduced by the CRT effect. In addition, the NO.sub.2/NO.sub.x ratio downstream of the diesel particulate filter is determined by calculation.

(20) FIG. 3 shows an embodiment in which a diesel oxidation catalyst 7 is arranged in the exhaust gas line 1 upstream of the diesel particulate filter 2. Here, an NO.sub.x sensor 8 is arranged in the exhaust gas line 1 upstream of the diesel oxidation catalyst 7. Either an NO sensor or an NO.sub.2 sensor 9, 10 is arranged upstream and downstream of the diesel particulate filter 2. Here, the reduction in particle quantity by the CRT effect is determined in a similar manner to the procedure in FIGS. 1 and 2. The total NO.sub.x concentration measured upstream of the diesel oxidation catalyst 7 is used only to determine the NO.sub.2/NO.sub.x ratio. With this configuration, in addition the DOC conversion efficiency, from the NO or NO.sub.2 measurement upstream of the diesel particulate filter in comparison with the NO.sub.x upstream of the diesel oxidation catalyst, can be used for DOC supply gas diagnosis.