METHOD FOR OPERATING A HYDROGEN FUELLED COMBUSTION ENGINE

Abstract

Method for operating a hydrogen fuelled combustion engine 1 comprising the steps of providing an internal combustion engine 1 having at least one cylinder 2 and a piston 3 supported at a crankshaft 5 for repeated reciprocal movement in the cylinder 2 so as to define a main combustion chamber 21, the internal combustion engine 1 further having an ignition device 4 arranged in said cylinder 2 with an igniter portion 42 and a hydrogen fuel injector 43 which are both arranged at a pre-chamber 41, wherein the pre-chamber 41 has a plurality of orifices 44 for providing fluid communication between said pre-chamber 41 and the main combustion chamber 21; and operating the engine in cycles comprising the following steps: introducing hydrogen fuel in the pre-chamber 41; introducing hydrogen fuel in the main combustion chamber 21; and igniting the introduced hydrogen fuel in the pre-chamber 41 for combusting the introduced hydrogen fuel in the main combustion chamber 21.

Claims

1. Method for operating a hydrogen fuelled combustion engine comprising the steps of: providing an internal combustion engine having at least one cylinder and a piston supported at a crankshaft for repeated reciprocal movement in the cylinder so as to define a main combustion chamber, the internal combustion engine further having an ignition device arranged in said cylinder with an igniter portion and a hydrogen fuel injector which are both arranged at a pre-chamber, wherein the pre-chamber has a plurality of orifices for providing fluid communication between said pre-chamber and the main combustion chamber; and operating the engine in cycles comprising the following steps: introducing hydrogen fuel in the pre-chamber; introducing hydrogen fuel in the main combustion chamber; and igniting the introduced hydrogen fuel in the pre-chamber for combusting the introduced hydrogen fuel in the main combustion chamber.

2. Method according to claim 1, wherein the step of introducing hydrogen fuel in the pre-chamber is conducted after the step of introducing hydrogen fuel in the main combustion chamber.

3. Method according to claim 1, wherein the step of introducing hydrogen fuel in the pre-chamber and the step of introducing hydrogen fuel in the main combustion chamber are conducted at least partially overlapping

4. Method according to claim 1, wherein the step of introducing hydrogen fuel in the pre-chamber comprises that a portion of the hydrogen fuel introduced into the main combustion chamber enters the pre-chamber.

5. Method according to claim 4, wherein the step of introducing hydrogen fuel in the pre-chamber comprises that a portion of the hydrogen fuel introduced into the main combustion chamber enters the pre-chamber during a compression stroke of the piston in the cylinder.

6. Method according to claim 4, wherein the step of introducing hydrogen fuel in the pre-chamber comprises that a portion of the hydrogen fuel introduced into the main combustion chamber enters the pre-chamber partially during an intake stroke of the piston in the cylinder.

7. Method according to claim 1, wherein the step of introducing hydrogen fuel in the pre-chamber comprises that hydrogen fuel is injected into the pre-chamber by the hydrogen fuel injector.

8. Method according to claim 7, wherein the step of introducing hydrogen fuel in the pre-chamber comprises multiple injections of hydrogen fuel via the fuel injector in the pre-chamber.

9. Method according to claim 1, wherein the amount of introduced hydrogen fuel in the pre-chamber is chosen so that the air/hydrogen fuel ratio λ inside the pre-chamber is within the range 0.25≤λ≤0.4 at the time of igniting the injected hydrogen fuel in the pre-chamber.

10. Method according to claim 1, wherein the amount of introduced hydrogen fuel in the pre-chamber is chosen so that the air/hydrogen fuel ratio λ, inside the pre-chamber is within the range 1.4≤λ≤2.5 at the time of igniting the injected hydrogen fuel in the pre-chamber.

11. Method according to claim 10, wherein the step of introducing hydrogen fuel in the pre-chamber is carried out so that the air/hydrogen fuel ratio λ inside the pre-chamber is maintained at 1.4≤λ during the steps of introducing hydrogen fuel in the pre-chamber until igniting the introduced hydrogen fuel in the pre-chamber.

12. Hydrogen fuelled internal combustion engine comprising at least one cylinder and a piston supported at a crankshaft for repeated reciprocal movement in the cylinder so as to define a main combustion chamber, the internal combustion engine further having an ignition device arranged in said cylinder with an igniter portion and a hydrogen fuel injector which are both arranged at a pre-chamber, wherein the pre-chamber has a plurality of orifices for providing fluid communication between said pre-chamber and the main combustion chamber, and the hydrogen fuelled internal combustion engine being operated by the method according to any one of the preceding claims

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The advantages of the invention are described in the following in connection to the drawings. In the following:

[0025] FIG. 1 is a vertical cross-section of an internal combustion engine using hydrogen fuel having an ignition device for turbulent jet ignition;

[0026] FIG. 2 is a block diagram describing the steps of a method for operating an internal combustion engine using hydrogen fuel;

[0027] FIG. 3 is a plot that shows the pre-chamber combustion duration versus pre-chamber lambda at time of ignition (spark timing);

[0028] FIG. 4 is a plot that shows the early burn duration in the main combustion chamber versus pre-chamber combustion duration;

[0029] FIG. 5 is a plot that shows simulated peak combustion temperature of contents interior to the pre-chamber versus pre-chamber lambda at time of ignition (spark timing);

[0030] FIG. 6 is a plot that shows the constant-volume adiabatic flame temperature and the flame speed versus lambda λ.

DETAILED DESCRIPTION

[0031] Hydrogen fuel refers to hydrogen fuel blends containing more than 50% hydrogen by volume. The use of an (actively hydrogen fuelled) pre-chamber combustor (active jet ignition) decouples the λ in the pre-chamber from the λ in the main combustion chamber. This allows tuning λ in the pre-chamber for an optimal spark event to occur in the pre-chamber, the highly reactive products of which subsequently initiate the second combustion event in the main combustion chamber. The λ in the main combustion chamber can be tuned independently from the λ in the pre-chamber in such a way that both abnormal combustion in the pre-chamber and in the main combustion chamber are mitigated.

[0032] Specifically, the step of introducing hydrogen fuel in the pre-chamber is conducted after the step of introducing hydrogen fuel in the main combustion chamber. This allows for separately controlling the air/hydrogen fuel mixture (and 2) in the pre-chamber and the main combustion chamber.

[0033] Alternatively, the step of introducing hydrogen fuel in the pre-chamber and the step of introducing hydrogen fuel in the main combustion chamber are conducted at least partially overlapping. This allows improved simultaneous controlling of the air/hydrogen fuel mixture in the main combustion chamber and the pre-chamber.

[0034] It is particularly preferred, when the step of introducing hydrogen fuel in the pre-chamber comprises that a portion of the hydrogen fuel introduced into the main combustion chamber enters the pre-chamber

[0035] According to a preferred aspect, the step of introducing hydrogen fuel in the pre-chamber comprises that a portion of the hydrogen fuel introduced into the main combustion chamber enters the pre-chamber during a compression stroke of the piston in the cylinder.

[0036] According to another preferred aspect, the step of introducing hydrogen fuel in the pre-chamber comprises that a portion of the hydrogen fuel introduced into the main combustion chamber enters the pre-chamber partially during an intake stroke of the piston in the cylinder.

[0037] Advantageously, the step of introducing hydrogen fuel in the pre-chamber comprises that hydrogen fuel is injected into the pre-chamber by the hydrogen fuel injector. This allows to reduce the air/hydrogen fuel ratio 2 in the pre-chamber and to compensate for a lean lambda of the hydrogen fuel entering the pre-chamber from the main combustion chamber.

[0038] According to an advantageous aspect, the step of introducing hydrogen fuel in the pre-chamber comprises multiple injections of hydrogen fuel via the fuel injector in the pre-chamber. This allows for adding more hydrogen fuel and, hence, to provide a rich mixture to be ignited in the pre-chamber which improves flammability of the hydrogen fuel-air mixture.

[0039] A particularly preferred aspect relates to the amount of injected hydrogen fuel in the pre-chamber being chosen so that the air/hydrogen fuel ratio λ inside the pre-chamber is within the range 0.25≤λ≤0.4 at the time of igniting the injected hydrogen fuel in the pre-chamber. This range of λ is selected to reduce the combustion temperatures within the pre-chamber to mitigate abnormal combustion (e.g. pre-ignition, knock) in the pre-chamber. Furthermore, this range of λ is selected for optimal pre-chamber combustion duration to mitigate abnormal combustion (e.g. pre-ignition, knock) in pre-chamber and in the main chamber.

[0040] According to another preferred aspect the amount of injected hydrogen fuel in the pre-chamber is chosen so that the air/hydrogen fuel ratio λ inside the pre-chamber is within the range 1.4≤λ≤2.5 at the time of igniting the injected hydrogen fuel in the pre-chamber. This range of λ is selected to reduce the combustion temperatures within the pre-chamber to mitigate abnormal combustion (e.g. pre-ignition, knock) in the pre-chamber. Furthermore, this range of λ is selected for optimal pre-chamber combustion duration to mitigate abnormal combustion (e.g. pre-ignition, knock) in the pre-chamber and the main chamber.

[0041] It is particularly preferred that the injection of hydrogen fuel in the pre-chamber is carried out so that the air/hydrogen fuel ratio λ inside the pre-chamber is maintained at 1.4≤λ during the steps of injecting hydrogen fuel in the pre-chamber until igniting the injected hydrogen fuel in the pre-chamber. This applies in conjunction with achieving a range of 1.4≤λ≤2.5 at the time of igniting the injected hydrogen fuel in the pre-chamber. This allows to reduce the likelihood of abnormal combustion (e.g. pre-ignition, knock) to occur in the pre-chamber.

[0042] In FIG. 1, an example for internal combustion engine 1 using hydrogen fuel is given which shows in the present illustration one cylinder 2 and a piston 3 supported at a crankshaft 5 for repeated reciprocal movement in the cylinder 2. Cylinder 2 and piston 3 define a main combustion chamber 21. The internal combustion engine 1 has an ignition device 4 arranged to face the combustion chamber 21. The ignition device 4 has an igniter portion 42 and a hydrogen fuel injector 43 which are both arranged at a pre-chamber 41 so as to form a part of the inner volume of the pre-chamber 41. The pre-chamber 41 has a plurality of orifices 44 for providing fluid communication between the inner volume of pre-chamber 41 and the inner volume of main combustion chamber 21.

[0043] According to the invention, the hydrogen fuel is introduced in main combustion chamber 21. Subsequently, hydrogen fuel is introduced in the pre-chamber 41 in such a way that hydrogen fuel enters the pre-chamber 41 from the main combustion chamber 21 during a compression stroke of the piston 3 in the cylinder 2. More hydrogen fuel is introduced in the pre-chamber 41 by injecting hydrogen fuel into the pre-chamber 41 by the hydrogen fuel injector 43. The introduced hydrogen fuel is ignited in the pre-chamber 41 via the igniter portion 42. The resulting pressure increase in the pre-chamber 41 causes this chemical energy to be rapidly transferred to the main combustion chamber 21 in the form of jets, which are formed when the contents flow through the orifices 44 to the main combustion chamber 21 for combusting the introduced hydrogen fuel in the main combustion chamber 21.

[0044] The method for operating a hydrogen fuelled combustion engine (as shown in FIG. 1) is illustrated by the block diagram of FIG. 2. The reference numbers of FIG. 1 and FIG. 2 correspond to each other so that in the following the reference numbers shown in FIG. 1 are used for the description of FIG. 2.

[0045] Step A relates to introducing hydrogen fuel in the main combustion chamber 21.

[0046] In step B hydrogen fuel is introduced in the pre-chamber 41 in such a way that hydrogen fuel enters the pre-chamber 41 from the main combustion chamber 21 during a compression stroke of the piston 3 in the cylinder 2.

[0047] In step C hydrogen fuel is injected into the pre-chamber 41 via the hydrogen fuel injector 43. This allows to reduce the air/hydrogen fuel ratio 2 in the pre-chamber 41 and to compensate for a lean lambda of the hydrogen fuel entering the pre-chamber 41 from the main combustion chamber 21. The present example comprises multiple injections (Step C, Step C, Step C, . . . ) of hydrogen fuel via the hydrogen fuel injector 43 in the pre-chamber 41. The provided air/hydrogen fuel mixture in the pre-chamber 41 will become richer after every injection which improves flammability of the hydrogen fuel-air mixture.

[0048] The introduced hydrogen fuel is ignited in the pre-chamber 41 via the igniter portion 42 in step D. By the resulting pressure increase in the pre-chamber 41 chemical energy is rapidly transferred to the main combustion chamber 21 in the form of jets, which are formed when the contents flow through the orifices 44 to the main combustion chamber 21 for combusting the introduced hydrogen fuel in the main combustion chamber 21.

[0049] FIG. 3 is a plot that shows the pre-chamber combustion duration versus pre-chamber lambda at the time of igniting the injected hydrogen fuel in the pre-chamber, i.e. at spark timing. For optimal combustion performance the amount of injected hydrogen fuel in the pre-chamber is chosen so that the normalized air/hydrogen fuel ratio λ inside the pre-chamber is within the range 0.25≤λ≤0.4 or within the range 1.4≤λ≤2.5 at the time of igniting the injected hydrogen fuel in the pre-chamber, i.e. at spark timing. Furthermore, these ranges of λ are selected for optimal pre-chamber combustion duration to mitigate abnormal combustion (e.g. pre-ignition, knock). Outside these regions overly slow pre-chamber combustion leads to a high likelihood of poor engine performance, e.g. because of unacceptable combustion instability or misfires in either the pre-chamber or main chamber, or excessively fast pre-chamber combustion leads to abnormal combustion in the pre-chamber, e.g. knocking.

[0050] FIG. 4 is a plot that shows the early burn duration in the main combustion chamber (duration in crank angle degrees of the time it takes the main chamber to consume from 0% to 10% of the fuel mass present) versus pre-chamber combustion duration. Region A identifies the area where overly slow pre-chamber combustion produces overly slow early combustion in the main chamber, leading to a high likelihood of poor engine performance, e.g. unacceptable combustion instability or misfires in the pre-chamber or main chamber. Region B identifies the area where an excessively fast pre-chamber combustion event can lead to abnormal combustion in the pre-chamber, e.g. knocking.

[0051] FIG. 5 is a plot that shows simulated peak combustion temperature of contents interior to the pre-chamber versus pre-chamber lambda 2 at the time of igniting the injected hydrogen fuel in the pre-chamber, i.e. at spark timing. High combustion temperatures within the range 0.4≤λ≤1.4 increase the likelihood of abnormal combustion, e.g. pre-ignition or knock, occurring in subsequent engine cycles.

[0052] For optimal combustion performance the amount of injected hydrogen fuel in the pre-chamber is chosen so that the normalized air/hydrogen fuel ratio λ inside the pre-chamber is within the range 0.25≤λ≤0.4 or within the range 1.4≤λ≤2.5 at the time of igniting the injected hydrogen fuel in the pre-chamber, i.e. at spark timing. Both ranges of λ are selected to reduce the combustion temperatures within the pre-chamber to an extent to mitigate abnormal combustion, e.g. pre-ignition or knock.

[0053] FIG. 6 is a plot that shows the constant-volume adiabatic flame temperature and the flame speed versus lambda λ. The plot serves to indicate a general relationship of hydrogen fuel properties to lambda, applicable for example to optimize the normalized air/hydrogen fuel ratio λ inside the pre-chamber at the time of igniting the injected hydrogen fuel in the pre-chamber, i.e. at spark timing.

[0054] For optimal combustion performance the amount of injected hydrogen fuel in the pre-chamber is chosen so that the normalized air/hydrogen fuel ratio λ inside the pre-chamber is within the range 0.25≤λ≤0.4 or within the range 1.4≤λ≤2.5 at the time of igniting the injected hydrogen fuel in the pre-chamber, i.e. at spark timing, in order to take into account both the constant-volume adiabatic flame temperature and the flame speed which influence the combustion behavior. For example, under lean conditions, the high flame temperature at λ=1.4 is somewhat balanced out by slower chemical reactions, followed by low flame speed, which leads to lower peak combustion pressure in the pre-chamber.

[0055] For this reason, the optimal λ range for good pre-chamber and subsequent main chamber combustion do not need to be symmetric about λ=1, but instead are shifted to richer values.