FI129299B

FI129299B - Internal combustion engine and method for operating the same

Info

Publication number: FI129299B
Application number: FI20175649A
Authority: FI
Inventors: Andreas Döring
Original assignee: Man Diesel & Turbo Se
Priority date: 2016-07-20
Filing date: 2017-07-05
Publication date: 2021-11-15
Also published as: FI20175649A; JP2018013123A; CN107642393A; CN107642393B; DE102016113382A1; JP6907053B2; KR20180010152A; KR102307828B1

Abstract

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Description

Internal combustion engine and method for operating the same The invention relates to a method for operating an internal combustion engine, in particular an internal combustion engine operated with gas, which comprises a gas combustion system and an exhaust gas aftertreatment system. The invention, fur- thermore, relates to an internal combustion engine, in particular an internal com- bustion engine operated with gas, which comprises a gas combustion system and an exhaust gas aftertreatment system.

From practice, internal combustion engines, which combust a gaseous fuel, such as for example natural gas, are known. Such internal combustion engines can for example be reciprocating piston internal combustion engines or turbomachines such as gas turbines. Accordingly, internal combustion engines are known for ex- ample from ship construction, which combust natural gas and for this purpose comprise a gas engine as gas combustion system. Furthermore, such internal combustion engines comprise an exhaust gas aftertreatment system in order to purify the exhaust gas which leaves the gas combustion system. US 9358503 B2 discloses emissions treatment systems for an exhaust stream having an ammonia-generating component, such as a NOx storage reduction _ (NSR) catalyst or a lean NOx trap (LNT) catalyst, and an SCR catalyst disposed O downstream of the ammonia-generating catalyst.

S S 25 US 2005137082 A1 discloses a catalyst for removing nitrogen oxides which is ca- E pable of keeping sufficient denitrification performance, i.e., a high removal rate of 3 nitrogen oxides in exhaust gas having a high NO2 content especially under condi- S tions where the ratio of NO2/NO in exhaust gas is 1 or higher, a catalyst molded N product therefor, and an exhaust gas treating method.

EP 3018314 A1 discloses An exhaust gas purification system of an internal com- bustion engine including: processing means for executing at least one of a process of increasing an air-fuel ratio of an air-fuel mixture burned in the internal combus- tion engine and a process of increasing EGR gas recirculated by an EGR appa- ratus, when increasing a NO 2 proportion in exhaust gas; and control means for controlling the processing means so that an increase in the air-fuel ratio becomes larger, and an increase in the EGR gas becomes smaller when a temperature of the exhaust gas purification apparatus is high as compared to when the tempera- ture of the exhaust gas purification apparatus is low.

When these internal combustion engines are operated with excess air, the propor- tion of NO? in the overall nitrogen oxides can increase significantly. When these internal combustion engines are operated as dual-fuel internal combustion en- gines, i.e. simultaneously with liquid and gaseous fuel, the NO2 proportion in- creases additionally. As already described, nitrogen oxides are created, inter alia, during the combus- tion of the gaseous fuel. For reducing nitrogen oxides in the exhaust gas, primarily so-called SCR catalytic converters are employed in exhaust gas aftertreatment systems known from practice. In an SCR catalytic converter, a selective catalytic reduction of nitrogen oxides takes place, wherein the reduction of the nitrogen ox- ides requires ammonia (NH3) as reduction agent. The ammonia (NH3) or an am- - monia precursor substance, such as for example urea, is introduced for this pur- O pose into the exhaust gas upstream of the SCR catalytic converter in liguid form, N 25 theammonia or the ammonia precursor substance being mixed with the exhaust 0 gas upstream of the SCR catalytic converter. j 3 Although nitrogen oxides in the exhaust gas can already be successfully reduced S with the SCR catalytic converters known from the prior art, there is a need for fur- N 30 ther improving the exhaust gas aftertreatment for internal combustion engines op- erated with gaseous fuels. This is necessary, among other things, since with these internal combustion engines the NO? proportion in the overall nitrogen oxides can exceed 50% which results in that the SCR reaction is significantly slowed down and the consumption of ammonia or ammonia precursor substance increases. Compared with the standard SCR reaction (Equation 1) this case is described as so-called slow SCR reaction (Equation 2) 2NO + 2NH3 + 0.5*02 --> 2N2 + 3H20 Equation 1 6NO2 + 8NH3 --> 7N2 + 12H20 Equation 2 — Starting out from this, the present invention is based on the object of creating a new type of method for operating an internal combustion engine which comprises a gas combustion system and an exhaust gas aftertreatment system, and a corre- sponding internal combustion engine. This object is solved through a method according to Claim 1. According to the in- vention, the exhaust gas for the reduction of an NO? proportion in the exhaust gas is conducted via at least one NO? decomposition catalytic converter of the exhaust gas aftertreatment system, wherein the exhaust gas conducted via the or each NO? decomposition catalytic converter is subsequently conducted via an SCR cat- — alytic converter. N As already described above, the invention is based on the realisation that for an

O . optimal nitrogen oxide reduction in an SCR catalytic converter a defined NOz2 pro- 7 portion in the exhaust gas upstream of the SCR catalytic converter is advanta- 9 25 —geous. In order to adjust a defined NO? proportion in the exhaust gas, the exhaust

I T gas is conducted via an NO2 decomposition catalytic converter upstream of the 3 SCR catalytic converter in order to ensure the desired, defined NO? proportion in 2 the exhaust gas aftertreatment system downstream of the NO2 decomposition cat- N alytic converter and thus upstream of the SCR catalytic converter.

Preferentially, the or each NO? decomposition catalytic converter is operated at a pressure between 2 bar and 20 bar and/or at a temperature greater than 400°C. Such operating parameters for the NO? decomposition catalytic converter allow a particularly decomposition of the NO: in the NOo decomposition catalytic converter to effective adjust the defined, desired NO? proportion upstream of the SCR cata- lytic converter. This is due to the fact that the thermodynamic equilibrium at high temperatures lies on the side of NO so that with the help of the catalytic converter a rapid adjustment of the equilibrium and thus a lowering of the NO? proportion be- comes possible without the addition of a reduction agent.

With its help, the ratio between NO? and NO is shifted to the side of NO: 2N02 -<-> 2NO + 202 Eguation 3 According to a further development, the decomposition is improved through the addition of a reduction agent, in particular CHa, upstream of the NO? decomposi- tion catalytic converter, wherein the actual NO? proportion in the exhaust gas is determined and the CH4 quantity utilised in the NO? decomposition catalytic con- verter is adjusted in such a manner that the actual NO? proportion is approximated to or corresponds to a set NO? proportion. To this end, the actual NO2 proportion in the exhaust gas aftertreatment system is measured or calculated. By way of this, a particularly advantageous adjustment of the NO? proportion in the exhaust N gas upstream of the NO? decomposition catalytic converter or upstream of the . SCR catalytic converter is possible. The quantity of the CH4 reduction agent uti- 7 25 —lised in the NO? decomposition catalytic converter can be regulated in this way so 7 that the actual NO? proportion in the exhaust gas is approximated to or corre- E sponds to the set NO? proportion. 2 © > NO2 + CH4 + Oz --> NO + 2H20 + CO Eguation 4

According to an advantageous further development, the exhaust gas upstream of the or each NO? decomposition catalytic converter and upstream of the SCR cata- lytic converter is conducted via a CH2O decomposition catalytic converter.

This fur- ther development is based on the realisation that in the NO2 decomposition cata- 5 lytic converter, which utilises CH4 as reduction agent, formaldehyde CH2O can de- velop via a side reaction.

Downstream of the NO? decomposition catalytic convert- er, the exhaust gas is preferentially conducted via the CH2O decomposition cata- lytic converter in order to decompose the formaldehyde that has been formed, namely upstream of the place of addition of the reduction agent (ammonia or an ammonia precursor substance) for the SCR catalytic converter or downstream of the SCR catalytic converter.

Preferred further developments of the invention are obtained from the subclaims and the following description.

Exemplary embodiments of the invention are ex- plained in more detail by way of the drawing without being restricted to this.

There it shows: Fig. 1: a schematic representation of a first internal combustion engine accord- ing to the invention; Fig. 2: a schematic representation of a second internal combustion engine ac- cording to the invention; Fig. 3: a schematic representation of a third internal combustion engine accord- N ing to the invention; and Fig. 4: a schematic representation of a fourth internal combustion engine ac- 10 25 cording to the invention. j 3 The invention relates to an internal combustion engine which comprises a gas S combustion system and an exhaust gas aftertreatment system, and to amethod N for operating such an internal combustion engine.

In the following, the invention is described on the example of internal combustion engines 10 making reference to Fig. 1 to 4, which as gas combustion system comprise a gas engine 11 with cylinders 12, wherein the cylinders 12 are supplied in particular with natural gas as fuel 14 and additionally to the gaseous fuel 14 combustion air 13 for the combustion of the same. Exhaust gas 15 created in the process is discharged from the gas engine 11 and conducted via an exhaust gas aftertreatment system 16. It is pointed out here that the invention is preferentially used with internal combustion engines which as gas combustion system utilise a reciprocating gas engine or Otto gas engine 12, the same however can also be employed with internal combustion engines whose gas combustion system 11 is provided by a turbomachine such as for example a gas turbine. The exhaust gas aftertreatment system 16 comprises an NO? decomposition cata- lytic converter 17 and downstream of the NO? decomposition catalytic converter 17, an SCR catalytic converter 18, so that the exhaust gas 15, which leaves the cylinders 12 of the gas engine 10, is initially conducted via the NO? decomposition catalytic converter 17 for reducing the NO? proportion in the exhaust gas 15 and accordingly for adjusting a defined NO2 proportion in the exhaust gas 15 and only following this via the SCR catalytic converter 18.

The NO? decomposition catalytic converter 17 is preferentially an NO? decomposi- tion catalytic converter, in which CH. as reduction agent is utilised for the decom- — position of NO». The reaction in the NO? decomposition catalytic converter 17 us- O ing CH4 as reduction agent takes place according to the Eguation 4 describe 5 25 above. 3 = - In order to make possible a particularly advantageous decomposition of the NO», 3 the NO2 decomposition catalytic converter 17 is preferentially operated at an abso- S lute pressure between 2 bar and 20 bar and a temperature of more than 400°C.

O N 30 In exhaust gas turbocharged internal combustion engines, these conditions are usually present upstream of the turbine of at least one exhaust gas turbocharger,

i.e. in this it is opportune to attach the NO? decomposition catalytic converter up- stream of at least one turbine of an exhaust gas turbocharger.

In the NO? decomposition catalytic converter 17, which is preferentially embodied as CH. oxidation catalytic converter, zeolite or perowcite and/or at least one ele- ment of the platinum metal group, in particular palladium and/or copper and/or ce- rium and/or calcium and/or titanium and/or aluminium is/are employed as active component.

— In particular when in the embodied NO? decomposition catalytic converter as ac- tive component at least one element of the platinum metal group is employed, the charge of the same with elements of the platinum metal group amounts to a max- imum of 1,765 g/m? (50 g/ft3), preferably maximally 882.5 g/m? (25 g/ft?), particu- larly preferably maximally 353 g/m? (10 g/ft3).

In addition to the NO2 decomposition catalytic converter 17 and the SCR catalytic converter 18 arranged downstream of the same, Fig. 1 shows an introduction de- vice 19, with the help of which ammonia or an ammonia precursor substance, such as for example urea, is introduced into the exhaust gas downstream of the NO? decomposition catalytic converter 17, wherein in the SCR catalytic converter 18 ammonia as reduction agent is utilised.

S Fig. 2 shows a further development of the internal combustion engine 10 of Fig. 1, 5 in which the same in addition to the exhaust gas aftertreatment system 16 com- S 25 prises an exhaust gas turbocharger system with an exhaust gas turbocharger 22. E There, the exhaust gas 15 leaving the cylinders 12 of the gas engine 11 according o to Fig. 2 is initially conducted via a turbine 20 of the exhaust gas turbocharger 22 O and only following this via the exhaust gas aftertreatment system 16. An advanta- > geous version (not shown here) consists in arranging the NO? decomposition cata- lytic converter 17 upstream of the turbine 20 in order to utilise the high tempera- tures and pressures that are present there. Energy extracted during the expansion of the exhaust gas 15 in the turbine 20 is utilised in a compressor 21 of the ex- haust gas turbocharger 22 in order to compress the charge air 13 to be fed to the cylinders 12 of the gas engine 11. The internal combustion engine 10 of Fig. 2 uti- lises a single-stage exhaust gas turbocharger system.

In contrast with this it is also possible that the internal combustion engine 10 utilises a two-stage exhaust gas turbocharger system consisting of a low-pressure exhaust gas turbocharger and a high-pressure exhaust gas turbocharger.

In this case, the exhaust gas aftertreat- ment system 16 is then preferentially placed between the turbine of the high- pressure exhaust gas turbocharger and the turbine of the low-pressure exhaust gas turbocharger.

During the decomposition of the NO: in the NO2 decomposition catalytic converter 17, CH4 can be decomposed into formaldehyde CH20 as side reaction, namely according to the following reaction equation:

CH4 +02 — CHO + HO The formation of formaldehyde however can be reduced when the NO, decompo- sition catalytic converter 17 comprises the above described charges with elements of the platinum metal group. = In the exemplary embodiment of Fig. 3 it is provided that downstream of the NO» N decomposition catalytic converter 17 and upstream of the SCR catalytic converter 5 18 a CH2O decomposition catalytic converter 23 is positioned, in order to decom- S 25 pose the formaldehyde formed in the NO2 decomposition catalytic converter 17 in E a defined manner.

Such a CHO decomposition catalytic converter 23 can be inte- O grated together with the NO? decomposition catalytic converter 17 and/or the SCR O catalytic converter 18 in a reactor chamber.

Such a CHO decomposition catalytic > converter 23 can obviously be utilised also with the internal combustion engine 10 of Fig. 2.

According to an advantageous further development of the invention, it is provided according to Fig. 4 to determine the actual NO2 proportion in the exhaust gas and dependent thereon regulate the operation of the NO? decomposition catalytic con- verter 17 embodied as CH4 oxidation catalytic converter in such a manner that the actual NO: proportion in the exhaust gas is approximated to or corresponds to a predetermined set NO» proportion, wherein for this purpose dependent on the ac- tual NO? proportion the CH4 quantity utilised in the CH. oxidation catalytic convert- er is adjusted.

According to Fig. 4 it is provided there to measure the actual NO» proportion in the exhaust gas downstream of the NO? decomposition catalytic converter 17 with the help of a sensor 24 and dependent thereon adjust the CH4 quantity utilised in the NO? decomposition catalytic converter 17. There it is provided that the set NO? proportion in the exhaust gas amounts to between 25% and 55%, preferably be- tween 30% and 50%, in particular approximately 50%, for example 50%+2%. The CH. quantity can be changed by varying the operating parameters of the in- ternal combustion engine. These are among others ignition timing, fuel/air ratio, valve timing (intake and/or exhaust valve/valve overlap, Miller cycle), injection tim- ing, charge pressure; charge air temperature, compression ratio, ratio between gaseous and liguid fuel. N In contrast with the detection of the actual NO2 proportion in the exhaust gas by 1 25 measurement with the help of the sensor 24 positioned downstream of the NO? I decomposition catalytic converter 17, the actual NO2 proportion in the exhaust gas > can also be determined by calculation, for example via a model. 3 S Furthermore, the actual NOz2 proportion can also be determined by determining the —SCR turnover in the SCR catalytic converter 18, in particular via the detection of the NOx quantity downstream of the SCR catalytic converter 18 with the help of a NOx sensor arranged downstream of the SCR catalytic converter 18. The NOx quantity that is present downstream of the SCR catalytic converter 18 can be tak- en into account as reference variable, since the NOx quantity that is permissible downstream of the SCR catalytic converter 18 is predetermined by way of emis- sion regulations and may not be exceeded.

The set NO? proportion in the exhaust gas is preferentially determined dependent on operating parameters of the gas engine 11 and/or of the exhaust gas after- treatment system 16, for example dependent on exhaust gas temperatures that are currently present, and/or ignition timings and/or valve timings and/or of a uti- lised exhaust gas recirculation if utilised.

It can be provided that the exhaust gas downstream of the NO? decomposition catalytic converter 17 is not only conducted via an SCR catalytic converter 18 but additionally via a particle filter and/or a NOx storage catalytic converter. This is the case in particular when not only gaseous fuel but also liquid fuels such as diesel, crude oil or residual oils are combusted (dual fuel engines).

In a particle filter, carbon-containing soot is retained. The carbon-containing soot can be converted with the help of nitrogen oxide into carbon monoxide, carbon di- oxide, nitrogen and nitrogen monoxide, namely according to the following reaction S equations:

S 3 25 2N02 +C — 2NO + CO z 2NO2+C — 2N0 + CO 2C + 2N02— N? + 2C02 =

N

Accordingly, it is proposed with the present invention to specifically reduce and accordingly specifically adjust the NO? proportion in the exhaust gas 15 upstream of an SCR catalytic converter 18 via an NO2 decomposition catalytic converter, in order to ensure an optimal SCR reaction in the SCR catalytic converter 18.

A defined NO: proportion in the exhaust gas is advantageous also for a particle filter and/or NOx storage catalytic converter which can be connected downstream of the SCR catalytic converter 18.

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List of reference numbers 10 Internal combustion engine 11 Gas combustion system 12 Cylinder 13 Combustion air 14 Fuel 15 Exhaust gas 16 Exhaust gas aftertreatment system 17 CH. oxidation catalytic converter 18 SCR catalytic converter 19 Introduction device 20 Turbine 21 Compressor 22 Exhaust gas turbocharger 23 CH2O decomposition catalytic converter 24 Sensor

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Claims

Claims

1. A method for operation an internal combustion engine (10), which comprises a gas combustion system (11) and an exhaust gas af- tertreatment system (16), wherein exhaust gas (15), which leaves the gas combustion system (11), is conducted via the exhaust gas aftertreatment system (16) for purifying, characterized in that the exhaust gas (15) for reducing an NO: proportion in the exhaust gas (15) is conducted via at least one NO? decomposition catalytic converter (17) of the exhaust gas aftertreatment system (16), and in that exhaust gas conducted via the or each NO2 decomposition catalytic converter (17) is subsequently conduc- ted via an SCR catalytic converter (18), and that the NOz2 proportion in the exhaust gas (15) is adjusted via the or each NO? decomposition cata- lytic converter (17) so that upstream of the SCR catalytic converter (18) the NO: proportion in the overall nitrogen oxides in the exhaust gas (15) amounts to between 25% and 55%, preferably between 30% and 50%.

2. The method according to Claim 1, characterized in that CH. as reduction agent is fed to the NO? decomposition catalytic converter (17).

3. The method according to Claim 2, characterized in that the actual NO? proportion in the exhaust gas is determined and the CH. quantity utilised in the NO? decomposition catalytic converter adjusted in N such a manner that the actual NO2 proportion is approximated to or cor- N responds to a set NO» proportion. 2 4. The method according to Claim 3, characterized in that the x 25 actual NO? proportion in the exhaust gas is measured or calculated. 3 5. The method according to any one of the Claims 1 to 4, char- S acterized in that the exhaust gas (15) downstream of the NO? decomposi- N tion catalytic converter (18) is conducted via the SCR catalytic converter

(18) and additionally via a particle filter and/or via a NOx storage catalytic converter.

6. The method according to any one of the Claims 1 to 5, char- acterized in that the or each NO? decomposition catalytic converter (17) is operated at a pressure between 2 bar and 20 bar.

7. The method according to any one of the Claims 1 to 6, char- acterized in that the or each NO? decomposition catalytic converter (17) is operated at a temperature greater than 400°C.

8. The method according to any one of the Claims 1 to 7, char- acterized in that as active component for the NO? decomposition at least one of the following components is utilised in the respective NO? decom- position catalytic converter (17): Zeolite Perowcite Iron Copper Cerium — Calcium

QA

O

N < Titanium o © 20 Aluminium = a o at least one element of the platinum metal group.

S

O 2 9. The method according to any one of the Claims 1 to 8, char- N acterized in that the exhaust gas downstream of the or each NO? decom- position catalytic converter (18) and upstream of the addition for the reduction agent (19) of the SCR catalytic converter (18) and/or down- stream of the SCR catalytic converter is conducted via a CH2O decompo- sition catalytic converter (23).

10. The method according to any one of the Claims 1 to 9, characterized in that the NO? decomposition catalytic converter (17) is ar- ranged upstream of at least one turbine (20) of an exhaust gas turbo- charge.

11. The method according to any one of the Claims 1 to 10, characterized in that the CH4 for reducing the NO» proportion is created through variation of operating parameters of the internal combustion en- gine.

12. An internal combustion engine (10), which comprises a gas combustion system (11) and an exhaust gas aftertreatment system (16), characterized in that the exhaust gas aftertreatment system (16) com- prises at least one NO? decomposition catalytic converter (17) and down- stream of the or each NO? decomposition catalytic converter (17) an SCR catalytic converter (18).

13. The internal combustion engine according to Claim 12, characterized in that the exhaust gas aftertreatment system (16) down- N stream of the or each NO2 decomposition catalytic converter (17) further- N more comprises a particle filter and/or a NOx storage catalytic converter. o 14. The internal combustion engine according to Claim 12 or I 13, characterized in that the exhaust gas aftertreatment system (16) a > 25 downstream of the or each NO2 decomposition catalytic converter (17) 3 and upstream of the addition for the reduction agent (19) of the SCR cat- = alytic converter (18) and/or downstream of the SCR catalytic converter N comprises a CHO decomposition catalytic converter (23).

15. The internal combustion engine according to Claim 12 to 14, characterized in that the NO? decomposition catalytic converter (17) is arranged upstream of the turbine (20) of an exhaust gas turbocharger.

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