EP4643001A1

EP4643001A1 - Low carbon combustion engine

Info

Publication number: EP4643001A1
Application number: EP23833537.6A
Authority: EP
Inventors: Abraham Wessel Hakstege; Ignace Theodorus Maria VAN DEN HEUVEL
Original assignee: DAF Trucks NV
Current assignee: DAF Trucks NV
Priority date: 2022-12-30
Filing date: 2023-12-27
Publication date: 2025-11-05
Also published as: NL2033886B1; WO2024144399A1

Abstract

It is aimed to provide a hydrogen combustion engine 110 comprising downstream an exhaust gas after treatment system 250 is provided. The exhaust gas after treatment system 250 comprises a first catalytic NOx converter 251 immediately downstream of the combustion engine 110, said first catalytic NOx converter comprising a first catalyst. An oxidation catalyst 252 is provided immediately downstream of the first catalytic NOx converter 251. A second catalytic NOx converter 253 downstream of the oxidation catalyst 252 comprises a second catalyst and a dosing system 254 for providing a reductant and a particle filter 255 is provided downstream of the second catalytic NOx converter 253. A fuel control system is arranged for controlling the amount of unburnt hydrogen produced by the internal combustion engine; whereas the first catalytic NOx converter 251 is arranged for using the unburnt hydrogen as an NOx reducing agent and for increasing the temperature of the second catalytic NOx converter 253.

Description

TITLE: Low carbon combustion engine

DESCRIPTION

Field of invention

The invention relates to a low carbon fuel, in particular hydrogen combustion engine comprising an exhaust, wherein downstream the exhaust an exhaust gas after treatment system is provided.

Description of the prior art

Future combustion systems are required to have extreme low level of pollutant emissions and therefore be active almost instantiations after a (cold) start. The NOx emissions can be reduced in an engine aftertreatment system (EAS). Typical components of such an aftertreatment system include a catalytic NOx converter more specifically an SCR (Selective Catalytic Reduction) catalyst that converts NOx into harmless products also known as the deNOx process. In normal operation, the aftertreatment system can be heated by residual heat from the combustion engine, however, at very low loads, the temperature of the exhaust gas may be too low. The temperature may be influenced by an engine efficiency mode, which controls the efficiency of the engine and an engine out temperature. For high efficiency engine power settings, the temperature may be too low to accommodate a required NOx conversion efficiency of the catalytic NOx converter, in which case the engine aftertreatment system temperature should be increased to provide a better performance of the SCR system. Especially for a lean-burn engine, exhaust gas temperature may be too low at low loads for the chemical reaction in SCR-system to convert NOx. Lean -burn combustion technology is selected for low engine-out NOx and high efficiency, but

SUBSTITUTE SHEET (RULE 26) involves more intake air than necessary for the combustion, which can be problematic for NOx forming and for temperature control of the NOx conversion catalyst.

In strategies to reduce carbon emission, upcoming fuel concepts contemplate the use of carbon-free fuels, e.g. H2 or NH3 as a fuel source. For these combustion engines, small fractions e.g. 2-4% of injected fuel may remain unburnt due to the imperfectness of homogenous combustion. A traditional method to eliminate unburnt fuel that enters the exhaust, is by applying a ‘oxicat’ or oxidation catalyst. The oxicat may improve the temperature of the exhaust after treatment system, so that conversion efficiency of the NOx conversion catalysts improves.

The invention aims to provide an improved aftertreatment setup for a low carbon internal combustion engine that is optimized for cold start conversion, where the EAS is functional even at low exhaust temperatures.

Summary of the invention

In one aspect, it is aimed to provide a hydrogen combustion engine comprising an exhaust, wherein downstream the exhaust an exhaust gas after treatment system is provided. The exhaust gas after treatment system comprises a first catalytic NOx converter immediately downstream of the combustion engine, said first catalytic NOx converter comprising a first catalyst. A second catalytic NOx converter downstream of the first NOx converter catalyst comprises a second catalyst selective for NOx conversion and a dosing system for providing a reductant for the selective NOx conversion. A particle filter is provided downstream of the second catalytic NOx converter. A fuel control system is arranged for controlling the amount of unburnt hydrogen produced by the internal combustion engine; whereas the first catalytic NOx converter is arranged for using the unburnt hydrogen as an NOx reducing agent and for increasing the temperature of the second catalytic NOx converter.

By suitable control of the amount of unburnt fuel, the unburnt fuel is used in the first NOx converter both for NOx conversion in the lower temperature ranges and for fast increase of the temperature of the second NOx converter, to an optimized conversion efficiency at higher temperatures. By providing the particle filter downstream of the second catalytic NOx converter, the second catalytic NOx converter can be heated faster without losing thermal energy to thermal mass of the particle filter. The particle filter is specifically aimed at collecting particles from reductant, in particular urea fluid, that is not converted by the second catalytic NOx converter. In addition, the particle filter functions to also collect ash from lubrication oil and other hydrocarbon fluids. Furthermore the first catalytic NOx converter can be close coupled to the exhaust of the combustion engine, which will function to almost instantaneously at a suitable conversion efficiency even when the exhaust gases are relatively cool, e.g. in a range below 200 degrees Celsius.

The internal combustion engine may further comprise one or multiple sensors for measuring the amount of NOx and/or unburnt hydrogen in the exhaust, to provide sensor information to the fuel control system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further elucidated in the figures:

Figure 1 shows an embodiment of an internal combustion engine arranged for reducing the emission of unburnt fuel;

Figure 2 shows in more detail the EAS depicted in Figure 1. Figure 3 shows a further embodiment of an EAS. DETAILED DESCRIPTION

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs as read in the context of the description and drawings. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. In some instances, detailed descriptions of well-known devices and methods may be omitted so as not to obscure the description of the present systems and methods. Terminology used for describing particular embodiments is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "and/or" includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms "comprises" and/or "comprising" specify the presence of stated features but do not preclude the presence or addition of one or more other features.

While example embodiments are shown for systems and methods, also alternative ways may be envisaged by those skilled in the art having the benefit of the present disclosure for achieving a similar function and result. E.g. some components may be combined or split up into one or more alternative components. Finally, these embodiments are intended to be merely illustrative of the present system and should not be construed as limiting the appended claims to any particular embodiment or group of embodiments. Thus, while the present system has been described in particular detail with reference to specific exemplary embodiments thereof, it should also be appreciated that numerous modifications and alternative embodiments may be devised by those having ordinary skill in the art without departing from the scope of the present systems as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner and are not intended to limit the scope of the appended claims.

Any reference signs in the claims do not limit their scope; several "means" may be represented by the same or different item(s) or implemented structure or function; any of the disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

Turning now to Figure 1, there is illustrated an embodiment of an internal combustion engine 100 producing exhaust gas with an amount of unburnt fuel 201 in dependence of engine operating conditions. The internal combustion engine 100 comprises an air intake 120, a fuel intake 130, and a fuel control system 110. The fuel control system 110 is arranged for controlling the amount of unburnt hydrogen produced by the internal combustion engine.

The internal combustion engine 100 further comprises an exhaust 200 for transporting the exhaust gas from the internal combustion engine 100 through an engine after treatment system 250 (EAS), including selective catalytic reactor for removing NOx from the exhaust gases, to the environment.

The internal combustion engine 100 further comprises an engine management system 500 arranged to increase the amount of unburnt fuel 201 in the exhaust gas upstream of the EAS.

The ratio between the amount of unburnt fuel 201 and an amount of NOx produced in-cylinder may be adjusted by an engine management system 500 that controls the fuel control system 110 by engine operating conditions such as ignition and injection timing on fuel intake 130, air-fuel ratio and, in case of automatic transmission, engine load and running speed, e.g. by late post injection, to increase the amount of unburnt fuel delivered to the exhaust. In this way, the amount of unburnt fuel in the exhaust gas upstream of the SCR can be controlled Alternatively, the amount of unburnt fuel 201 could be increased by injecting additional fuel directly into the EAS

250 or into the exhaust 200 upstream of the EAS 250.

The requested amount of fuel for conversion can be determined in several ways:

Determination of both unburned fuel 201 & NOx quantities 202 produced by the internal combustion engine by a sensor that directly measures the unburnt fuel & NOx quantity. Alternatively either unburnt fuel and/or NOx quantity may be derived from look-up tables or models based on mapping of the engine states, based on other sensed variables, e.g. lambda sensor, exhaust gas temperature sensor to produce the amount of unburnt fuel as a function of the exhaust temperature. Figure 2 shows in more detail the exhaust gas after treatment system 250 depicted in Figure 1. The exhaust gas after treatment system 250 comprises a first catalytic NOx converter

251 immediately downstream of the combustion engine. The first catalytic NOx converter comprises a first catalyst, which may be platinum or any other suitable catalyst aimed at converting and thereby reducing NOx at lower exhaust temperatures in a first exhaust gas temperature range, mainly after a cold start or at engine operational conditions that result in a low exhaust gas temperature, for example, lower than 200 degrees Celsius, more specifically, in a range of 70-200 degrees Celsius. For example, for a NH3 based fuel combustion, the converter may be a selective catalytic reductor that can be close coupled to the engine and that, due to the close coupling and due to lack of thermal mass, can be heated fast to a suitable conversion temperature. Immediately downstream of the first catalytic NOx converter 251 an oxidation catalyst 252 may be provided for burning excess unburnt fuel that leaves the first catalyst for increasing the temperature of the exhaust gas, more specifically of second catalytic converter 253. The amount may be more than required for NOx conversion, in view of the oxidation catalyst that is able to oxidize excess NO that leaves the first catalytic NOx converter.

The oxidation catalyst 252 has a catalyst that may be platinum based or any other suitable material.

Figure 3 shows an embodiment where catalytic NOx converter 251 and oxidation catalyst 252 are combined in one single device that may comprise a platinum based substrate. In this embodiment the first catalyst comprises an oxidation catalyst for oxidizing NO to NO2, prior to conversion by second catalytic NOx converter. This provides synergy, since for a hydrogen based fuel combustion the same catalyst can be used both for NOx conversion and for oxidation and less components are needed in the EAS 250. When the temperature of the catalytic converter 251/252 is increased to a second temperature range above 200 degrees Celsius, the first catalyst may lose NOx conversion efficiency and the unburnt fuel is not used for reducing the NOx. However, meanwhile, when increasing the exhaust temperature to the second temperature range above 200 degrees Celsius, the second catalytic NOx converter 253 downstream of the first catalytic converter device 251/252, which may be suitable for converting larger volumes of exhaust gas at full temperature, becomes more efficient, since the catalytic NOx converter bed temperature is raised above 200 degrees Celsius. The first catalytic converter/oxidation catalyst device 251/252 is then only used for oxidizing the nitrogen oxide components to a suitable composition for the second catalytic converter 253 and for burning excess unburnt fuel that leaves the first catalyst for increasing the temperature of the exhaust gas, more specifically of second catalytic converter 253.

The second catalytic NOx converter 253 comprises a second catalyst selective for NOx conversion, which may be vanadium/copper-zeolite based or any other suitable catalyst aimed at converting and thereby reducing NOx at higher exhaust temperatures in a second exhaust gas temperature range above 200 degrees Celsius. The second catalytic NOx converter further comprises a dosing system 254 for providing a reductant. First catalytic NOx converter notably does not need an additional dosing system, since it uses excess unburnt fuel as a reducing agent.

Particle filter 255 is provided downstream of the second catalytic NOx converter 253, which effectively prevents particulates entering ambient atmosphere however, without burdening the NOx conversion by adding thermal mass to the EAS prior to converting the NOx from exhaust gas. The particle filter may comprise a reductant oxidation catalyst for converting excess NOx reductant of the second catalytic NOx converter. Preferably the particle filter is coated with an Pt/Pd-based oxicat washcoat, but where it is intended when used for carbon fuels to support NO2-make for passive soot conversion, in this low carbon application it is used to convert slipped ammonia (overdosed urea or NH3 formed from particles that are further decomposed at higher temperatures). For instance the reductant oxidation catalyst may be an ammonia slip catalyst (ASC), e.g. in case the internal combustion engine 100 is operated with a fuel comprising ammonia (NH3). This catalyst will also convert urea deposits that may be present, that will eventually be converted at higher loads at higher temperatures to ammonia. In addition, the particle filter functions to also collect ash from lubrication oil and other hydrocarbon fluids and can be regenerated by increasing the exhaust temperature.

In practice the exhaust gas after treatment system 250 functions as follows: At lower temperatures, in particular, in a first exhaust temperature range e.g. between 70 and 200 degrees Celsius the first catalytic NOx converter has a conversion efficiency higher than the second catalytic NOx converter. Since the low carbon fuel, especially hydrogen combustion engine will produce dominantly NO (the other fractions of NOx will be in the order of less than 5%) the use of a Pt based conversion is very effective, since the dominant conversion is 2 NO + 2 H2 -> N2+ 2 H2O. In this temperature range this NO(x) conversion may be performed primarily by the first NOx converter 251 close coupled to the engine. As the exhaust temperatures increase to exhaust temperatures in a second exhaust temperature range higher than the first range, e.g. with exhaust temperature range between 200 degrees and 400 degrees Celsius or above, the second catalytic NOx converter becomes more efficient than the first catalytic converter and the first catalytic NOx converter merely reduces unburnt fuel to water, substantially without converting the NOx. However, the heat that is involved in this reduction adds to the conversion efficiency of the second catalytic NOx converter, that is operated with an urea/ammonia dosing system 254 as known in the art. The second NOx converter is usually equipped with a Va and/or Cu-zeolite. This dosing system is operational at higher temperatures, where urea deposits can be prevented, and urea is suitably converted into ammonia, used as a reductant for NOx.

Figure 4 shows in more detail a temperature based control scheme for fuel control system 110 to increase the amount of unburnt fuel delivered to the exhaust. A temperature sensor 301 is provided at least at a location of the first catalytic NOx converter 251. In addition a further temperature sensor 302 may be provided at or closely coupled the second catalytic NOx converter 253. Preferably temperature 301 sensor is closely coupled to the first catalytic converter, in particular to be able to measure/ determine an operational condition of the first NOx converter 251, to be able to control a maximum temperature thereof and still achieve a fast warm up of the engine after treatment system. Fuel control system 110 controls the amount of unburnt fuel with a control scheme targeting a temperature value for the downstream engine after treatment system, e.g. at the location of the second catalytic NOx converter, using the information of the temperature sensors upstream and downstream of the engine after treatment system for determining the amount of unburnt fuel. The arrangement of the fuel control system 110 for the amount of unburnt fuel may be set up as a temperature control scheme 504 with a temperature target value for the engine after treatment system 250. The target value of the temperature control scheme may be compared to a reading of a temperature sensor 302 downstream of the engine after treatment system 250. A temperature control scheme may be using both values for determining an adaption of the amount of unburnt fuel via a feedback part of the temperature control scheme, as well that the temperature control scheme may use a reading of a temperature sensor 301 upstream of the engine after treatment system 250, as basis of a feedforward part of the temperature control scheme. The target value of the temperature control scheme may be chosen in such a way that a fast warm up of the of the engine after treatment system 250 can be achieved without excessively heating the first NOx catalytic converter. Accordingly the fuel control system is provided with control instructions based on engine management system 500 that controls fuel control system 110 to increase the amount of unburnt fuel delivered to the exhaust, at least based on a measured or determined temperature at the first NOx catalytic converter, whereas the amount of fuel is maximized to a maximum operational condition of the first NOx catalytic converter. The engine management system to this end may have a temperature control scheme 504 that aims to maximize a temperature increase of the second NOx catalytic converter, while keeping the first NOx catalytic converter below a maximum temperature threshold. The temperature control scheme 504 may have a feedback control that tunes the amount of unburnt fuel, based on A) keeping the first NOx catalytic converter at a maximum threshold temperature and B) tuning down the amount of unburnt fuel when a target temperature of the second catalytic converter is reached. The temperature control scheme 504 may further have a feedforward control derived from look-up tables or models based on mapping of the engine states, based on other sensed variables, e.g. lambda sensor, exhaust gas temperature sensor to produce the amount of unburnt fuel as a function of the exhaust temperature.

Claims

1. A low carbon fuel, in particular hydrogen internal combustion engine comprising an exhaust, wherein downstream the exhaust an exhaust gas after treatment system is provided, said exhaust gas after treatment system comprising:

- a first catalytic NOx converter immediately downstream of the combustion engine, said first catalytic NOx converter comprising a first catalyst;

- a second catalytic NOx converter downstream of the first catalytic NOx converter, comprising a second catalyst selective for NOx conversion and a dosing system for providing an NOx reductant for the selective NOx conversion;

- a particle filter downstream of the second catalytic NOx converter; and

- a fuel control system arranged for controlling the amount of unburnt fuel produced by the internal combustion engine;

- whereas the first catalytic NOx converter is arranged for using the unburnt hydrogen as an NOx reducing agent and for increasing the temperature of the second catalytic NOx converter.

2. The internal combustion engine according to claim 1, wherein the first catalyst comprises an oxidation catalystfor oxidizing NO to NO2, prior to conversion by second catalytic NOx converter.

3. The internal combustion engine according to claim 2, wherein the first catalyst comprises platinum.

4. The internal combustion engine according to any previous claim, wherein the first catalytic NOx converter has a conversion efficiency higher than the second catalytic NOx converter at exhaust temperatures in a first exhaust gas temperature range and wherein the second NOx converter has a conversion efficiency higher than the first catalytic NOx converter at exhaust temperatures in a second exhaust temperature range.

5. The internal combustion engine according to claim 3, wherein the first exhaust temperature range is between 70 and 200 degrees Celsius; and wherein the second exhaust temperature range is between 200 degrees and 400 degrees Celsius.

6. The hydrogen combustion engine according to claim 1, wherein the engine is a hydrogen combustion engine, and wherein the first catalyst comprises platinum.

7. The hydrogen combustion engine according to claim 1, wherein the engine is a ammonia combustion engine and the first catalyst comprises vanadium.

8. The internal combustion engine according to any previous claim, wherein the second catalyst comprises vanadium.

9. The internal combustion engine according to any previous claim, wherein the particle filter comprises an NOx reductant oxidation catalyst for converting excess NOx reductant of the second catalytic NOx converter.

10. The internal combustion engine according to any previous claims wherein the NOx reductant comprises ammonia.

11. Internal combustion engine according to any preceding claim, whereas the fuel control system is arranged for controlling the ignition timing and/or injection timing of the internal combustion engine.

12. Internal combustion engine according to any preceding claim, whereas the amount of unburnt fuel produced by the internal combustion engine is derived from a model of the internal combustion engine and/or from sensor output from the internal combustion engine, as input to the fuel controlsystem.

13. Internal combustion engine according to claim 12, wherein the fuel control system is arranged to produce the amount of unburnt fuel as a function of the exhaust temperature.

14. Internal combustion engine according to any of claims 12-13, wherein the exhaust temperature is determined at at least a location of the first catalytic NOx converter and the second catalytic NOx converter.