EP3788244A1

EP3788244A1 - A method for starting a four-stroke reciprocating internal combustion piston engine and a four-stroke reciprocating internal combustion piston engine

Info

Publication number: EP3788244A1
Application number: EP18726202.7A
Authority: EP
Inventors: Jörgen STRANDBERG; Thomas Hägglund; Magnus Sundsten; Edward Winter
Original assignee: Wartsila Finland Oy
Current assignee: Wartsila Finland Oy
Priority date: 2018-05-04
Filing date: 2018-05-04
Publication date: 2021-03-10
Anticipated expiration: 2038-05-04
Also published as: WO2019211508A1; EP3788244B1

Abstract

The disclosure relates to a method for starting a four-stroke reciprocating internal combustion piston engine. The present disclosure further concerns a four-stroke reciprocating internal combustion piston engine for implementing the method. The description is based on the idea of providing an airflow into the combustion cylinder during an instroke of the respective piston, so as to expel any remaining liquid from the combustion cylinder via the exhaust valve.

Description

A METHOD FOR STARTING A FOUR-STROKE RECIPROCATING INTERNAL COMBUSTION PISTON ENGINE AND A FOUR-STROKE RECIPROCATING

INTERNAL COMBUSTION PISTON ENGINE

FIELD OF THE DISCLOSURE

The present disclosure relates to four-stroke reciprocating internal combustion piston engines and more particularly to a method for starting such an engine. The present disclosure further concerns a four-stroke reciprocating internal combustion piston engine for implementing the method.

BACKGROUND OF THE DISCLOSURE

Depending on the structure and end-use of a reciprocating internal combustion piston engine, water or other liquids may in some instances accumulate within the combustion cylinder of the engine during a standstill in the case of four-stroke engines, this may lead to engine failure, if the liquid in the combustion cylinder is not discharged before starting the engine. This is because any liquids, being generally non-compressible, residing in the combustion cylinder results in a critically high cylinder pressure during a compression stroke of the engine when it is started.

BRIEF DESCRIPTION OF THE DISCLOSURE

An object of the present disclosure is to provide a method for starting a four-stroke reciprocating internal combustion piston engine in which any remaining liquid contents is expelled from the combustion cylinder, so as to prevent possible damage to the engine.

It is a further object of the present disclosure to provide a four-stroke reciprocating internal combustion piston engine in which any remaining liquid contents is expelled from the combustion cylinder, so as to prevent possible damage to the engine.

The object of the disclosure is achieved by a method and engine which are characterized by what is stated in the independent claims 1 and 13, respectively. The preferred embodiments of the disclosure are disclosed in the respective dependent claims.

The disclosure is based on the idea of providing an airflow into the combustion cylinder during an instroke of the respective piston, so as to expel any remaining liquid from the combustion cylinder via the exhaust valve.

An advantage of provided by the disclosure is that no separate purging valve is required for expelling the liquid. BRIEF DESCRIPTION OF THE DRAWINGS

In the following the disclosure will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Fig.1 shows an embodiment of an Internal combustion engine according to the present disclosure during an early stage of an instroke, depicted as a schematic illustration;

Fig. 2 shows an embodiment of an internal combustion engine according to the present disclosure during a late stage of an instroke, depicted as a schematic illustration;

Fig. 3 shows an embodiment of an internal combustion engine according to the present disclosure with the combustion piston in its TDC, depicted as a schematic illustration;

Fig. 4 shows an embodiment of an internal combustion engine according to the present disclosure during an early stage of an outstroke, depicted as a schematic illustration;

Fig. 5 shows an alternative embodiment of an internal combustion engine according to the present disclosure with the combustion piston in its TDC, depicted as a schematic illustration;

Fig. 8 shows variants of an exemplary embodiment of a safety actuator 7b provided on an internal combustion engine according to the present disclosure, depicted as a schematic illustration, and

Fig. 7 shows an alternative exemplary embodiment of a safety actuator 7b provided on an internal combustion engine according to the present disclosure, depicted as a schematic illustration.

DETAILED DESCRIPTION OF THE DISCLOSURE

According to a first aspect of the present disclosure, a method for starting a four-stroke reciprocating infernal combustion piston engine is provided.

In the method, a crankshaft is rotated and during an insfroke, i.e. during a movement away from the crankshaft, of a combustion piston 4 within a combustion cylinder 3, a respective exhaust valve 7 is maintained in an open position

During said instroke, an airflow is provided into said combustion cylinder 3 from an air valve 8, so as to expel any remaining liquid contents from said combustion cylinder 3 to an exhaust port past the exhaust valve.

Consequently, no separate purging valve is required, as the liquid contents is expelled via the exhaust valve. Although an exhaust valve is referred to throughout this disclosure, it foreseeable, that liquid contents may be expelled to the intake port via the intake valve, alternatively. However, expelling liquid contents to the exhaust port instead of the intake port removes the need to provide further arrangement in connection with the intake port in order to drain the liquid contents therefrom.

In the context of the present disclosure, the term liquid contents encompasses, among other, water contents, such as fresh water, salt water and water solutions including coolant liquid used in a coolant circulation of the engine.

Preferably, but not necessarily, said instroke is a compression stroke of the combustion piston 4. This is particularly advantageous, as the exhaust valve is not typically open during normal operation of the engine. That is, during a start-up of an engine, damage caused by liquid contents in the combustion cylinder 3 typically occurs during the compression stroke.

Preferably, but not necessarily, the exhaust valve 7 is operated with an independent exhaust valve actuator 7a. That is, the exhaust valve 7 may be operated independently from the position of the crankshaft, for example with a hydraulic or pneumatic actuator. Particularly, when an independent exhaust valve actuator 7 is used, the exhaust valve 7 may be maintained in in the open position at least until said combustion piston 4 reaches an uppermost clearance position.

This enables the exhaust valve 7 to be opened during any time of the piston movement, for example during the compression stroke. Moreover, maintaining the exhaust valve 7 open for as long as possible (without colliding with the combustion piston 4) ensures that maximum flushing effect by the airflow is achieved.

According to an embodiment of the first aspect, airflow may be provided starting from a movement of the combustion piston 4 immediately preceding the combustion piston 4 reaching the uppermost clearance position, said movement corresponding to a 1/2 stroke of the combustion piston 4, preferably 1/4 stroke of the combustion piston (4), more preferably 1/8 stroke of the combustion piston 4.

Several benefits follow; firstly, because the airflow is not provided for the entire instroke, less air is used. Moreover, less work needs to be done by the piston against the airflow pushing the combustion piston 4 against the direction of the instroke. Consequently, less energy is consumed for rotating the crankshaft 2. Finally, as the combustion cylinder 3 has a smaller volume the closer it reaches its TDC, the flushing effect of the airflow is further improved.

Preferably, but not necessarily, the uppermost clearance position is a position of the combustion piston 4 corresponding to a 1/5 - 1/10 stroke thereof preceding a point at which said combustion piston 4 would coincide with the exhaust valve 7 in an open position. This is particularly advantageous when the structure of the engine does not allow to maintain he exhaust valve 7 In an open position when the combustion piston 7 is in its TDC.

It has been considered that the above-mentioned range for the position of the upper clearance position provides the liquid content to be expelled most efficiently, while maintaining a sufficient clearance between the exhaust valve 7 and the combustion piston 4 in connection with engine structures not allowing to maintain the exhaust valve 7 open while the combustion piston 4 is in its TDC.

Alternatively, the uppermost clearance position may be the TDC of the combustion piston 4. This is particularly advantageous when the structure of the engine allows maintaining the exhaust valve 7 in an open position when the combustion piston 7 is in its TDC.

In an embodiment of the first aspect according to the present disclosure, the exhaust valve 7 may be moved to a safety position during said instroke, by retracting the independent exhaust valve actuator 7a and by extending, or maintaining extended, a safety actuator 7b

In such a case, the safety position of the exhaust valve 7 is configured such that the exhaust valve 7 remains partially open, while a clearance remains between the exhaust valve 7 and the respective combustion piston 4 in the TDC thereof.

This is particularly advantageous for engine structures not allowing the exhaust valve 7 to be fully open when the combustion piston 4 is in its TDC. Namely the safety actuator 7b allows the exhaust valve 7b to remain partially open for a longer period during the instroke, without risking collision with the combustion piston 4, thus improving the removal of liquid.

Exemplary embodiments of the safety actuator 7b are described at a further stage of this description with reference to Fig 8 and Fig. 7.

Preferably, but not necessarily, said exhaust valve 4 is maintained in the safety position when said piston 4 reaches the uppermost clearance position. This provides a longer time period for the airflow to flush liquid contents form the combustion cylinder 3

In another embodiment of the first aspect according to the present disclosure, said exhaust valve 7 may be closed when said piston 4 reaches the uppermost clearance position. This may be done regardless of whether a safety actuator 7b is provided or used.

In a further embodiment of the first aspect according to the present disclosure, the airflow into said combustion cylinder 3 is provided during either, or both, of a compression stroke and an exhaust stroke of the combustion piston 4. Preferably, but not necessarily, the airflow is a starting air flow and the air valve 8 is a starting air valve. In such a case the crankshaft 2 is rotated by providing a starting air flow to the combustion cylinder 3 during either or both of a power stroke and an intake stroke of said combustion cylinder 3.

This enables, that not separate air valve 8 is required for engines, in which initial start-up is done with compressed air.

Alternatively, or additionally, the crankshaft 3 may be rotated by a separate starter motor.

Furthermore, it should be noted, that the first aspect of the present disclosure encompasses the combinations of the embodiments discussed above and variations thereof.

According to a second aspect of the present disclosure, a four-stroke reciprocating internal combustion piston engine 1 is provided. The benefits and advantages of the embodiments and their variants discussed in connection with the first aspect of the present disclosure are equally applicable to the corresponding embodiment and their variants of the second aspect of the present disclosure.

The engine 1 comprises a crankshaft 2 and a crankshaft rotation means for rotating said crankshaft 2 without combustion.

The engine 1 further comprises at least a combustion cylinder 3 and a combustion piston 4 arranged within the combustion cylinder 3, said combustion piston being coupled to the crankshaft 2.

The engine 1 further comprises a cylinder head 5 equipped with at least an exhaust valve 7 corresponding the combustion cylinder 3 for selectively opening and closing a flow connection between the combustion cylinder 3 and an exhaust port, said exhaust valve 7 being equipped with a valve actuator 7a.

The engine 1 further comprises an air valve 8 configured for providing an airflow into the combustion cylinder 3, and a control means 9 operationally coupled at least to the valve actuator 7a for selectively opening and closing the exhaust valve. The control means 9 are further operationally coupled to the air valve 8 for selectively enabling and disabling an airflow to the combustion cylinder 3.

The control means 9 are further configured to, during an instroke of the combustion piston 4 within the combustion cylinder 3, operate the valve actuator 7a so as to maintain the exhaust valve 7 in an open position. The control means 9 are further configured to, during said instroke, operate the air valve 8 to provide an airflow into said combustion cylinder 3 so as to expel any remaining liquid contents from said combustion cylinder 3 to an exhaust port past the exhaust valve 7.

Preferably, but not necessarily, said instroke is a compression stroke of the combustion piston 4.

Preferably, but not necessarily, the valve actuator 7a is an independent valve actuator 7a for selectively opening and closing the exhaust valve 7 by extending and retracting said independent valve actuator 7a, respectively. That is, the exhaust valve 7 may be operated independently from the position of the crankshaft, for example with a hydraulic or pneumatic actuator. Particularly, when an independent exhaust valve actuator 7 is used, the exhaust valve 7 may be maintained in in the open position at least until said combustion piston 4 reaches an uppermost clearance position.

In such a case, the control means 9 are further configured to operate the valve actuator 7a to maintain the exhaust valve 7 in the open position at least until said combustion piston 4 reaches an uppermost clearance position.

According to an embodiment of the second aspect of the present disclosure, the control means 9 are further configured such that said airflow is provided starting from a movement of the combustion piston 4 immediately preceding the combustion piston 4 reaching the uppermost clearance position, said movement corresponding to a 1/2 stroke of the combustion piston 4, preferably 1/4 stroke of the combustion piston 4, more preferably 1/8 stroke of the combustion piston 4.

Preferably, but not necessarily, the uppermost clearance position is a position of the combustion piston 4 corresponding to a 1/5 - 1/10 stroke thereof preceding a point at which said combustion piston 4 would coincide with exhaust valve 7 in an open position. This is particularly advantageous when the structure of the engine does not allow to maintain he exhaust valve 7 in an open position when the combustion piston 7 is in its TDC.

In an embodiment of the second aspect according to the present disclosure, the exhaust valve 7 may further be equipped with a safety actuator 7b for limiting the movement of the exhaust valve towards a closed position into a safety position by extending said safety actuator 7b. In such as case the safety position of the exhaust valve 7 may be configured such that the exhaust valve 7 remains partially open, while a clearance remains between the exhaust valve 7 and the respective combustion piston 4 in the TDC thereof.

Furthermore, the control means 9 may further be configured, during said instroke, to move the exhaust valve 7 to a safety position by retracting the independent exhaust valve actuator 7a and by extending, or maintaining extended, a safety actuator 7b.

Preferably, but not necessarily the control means 9 are advantageously further configured to maintain the exhaust valve 7 in the safety position when said piston 4 reaches the uppermost clearance position.

In another embodiment of the second aspect according to the present disclosure, the control means 9 are further configured to close the exhaust valve 7 when said piston 4 reaches the uppermost clearance position by retracting the independent valve actuator 7a, or retracting the independent valve actuator 7a and the safety actuator 7b. This may be done regardless of whether a safety actuator 7b is provided or used.

In a further embodiment of the second aspect according to the present disclosure, the control means 9 are further configured to provide an airflow to the combustion cylinder 3 during either, or both, of a compression stroke and an exhaust stroke of the combustion piston 4.

Preferably, but not necessarily, the airflow is a starting air flow and the air valve 8 is a starting air valve in such a case, the crankshaft rotation means are implemented by the control means 9 being further configured to provide a starting air flow to the combustion cylinder 3 during either, or both, of a power stroke and an intake stroke of the combustion piston 4.

Alternatively, or additionally, the crankshaft rotation means comprise a separate starter motor.

Furthermore, it should be noted, that the second aspect of the present disclosure encompasses the combinations of the embodiments discussed above and variations thereof.

Fig.1 shows an embodiment of an internal combustion engine according to the present disclosure during an early stage of an instroke, depicted as a schematic illustration. That is, the crankshaft 2 of the engine 1 rotates and the combustion piston moves towards its TDC, thereby reducing the volume in the combustion cylinder 3. The cylinder head 5 is equipped with an exhaust port 6 for exhausting combustion fumes. The exhaust port is selectively opened or dosed by the exhaust valve 7, actuated by the exhaust valve actuator 7a, in turn controlled by the control unit 9, to which it is operationally connected. The cylinder head 5 is further equipped with an air valve 8 in connection with an intake port.

The situation of Fig. 1 may depict either an exhaust stroke or a compression stroke, in which the exhaust valve 7 is opened by the control unit 9 commanding the exhaust valve actuator 7a. No air is introduced into the combustion chamber via the air valve 8.

Fig. 2 shows an embodiment of an internal combustion engine according to the present disclosure during a late stage of an instroke, depicted as a schematic illustration. That is, the crankshaft 2 of the engine 1 still rotates and the combustion piston still moves towards its TDC, thereby further reducing the volume in the combustion cylinder 3.

Further in Fig. 2, differing from the situation of Fig. 1 , an airflow is introduced into the combustion cylinder 3 via the air valve 8. The introduced airflow flushes the combustion cylinder 3 and exhaust via the exhaust port 6, thus expelling any remaining liquid form the combustion cylinder 3.

Fig. 3 shows an embodiment of an internal combustion engine according to the present disclosure with the combustion piston in its TDC, depicted as a schematic illustration. That is, the piston has reached its position furthest away from the crankshaft, between the instroke and prior to the outstroke. Differing from the situations of Fig. 1 and Fig. 2, Fig. 3 further illustrates the exhaust valve 7 being closed and the airflow 8 being interrupted. It should be noted, however, that alternatively that the exhaust valve 7 may be maintained open or partially open, while the airflow' from the air valve 8 may be continued for a while during the beginning of the outstroke in order to maximize the flushing effect of the airflow.

Fig. 4 shows an embodiment of an internal combustion engine according to the present disclosure during an early stage of an outstroke, depicted as a schematic illustration. That is, the combustion piston 4 is moving towards the crankshaft 2.

The situation of Fig. 4 may depict either an intake stroke or a power stroke, in which an airflow via the air valve 8 is introduced to the combustion cylinder 3, while the exhaust valve 7 is maintained closed.

Although Fig. 1 - Fig. 4 illustrate the air valve 8 in connection with an intake port, it should be noted that the air valve 8 may be provided separately from the intake port, i.e. so as directly introduce an airflow into the combustion cylinder 3. This provides the additional benefit that an airflow may be provided into the combustion cylinder 3 even when the combustion piston 4 is in its TDC without further consideration to a possible collision of an intake valve with the combustion piston.

Fig. 5 shows an alternative embodiment of an internal combustion engine according to the present disclosure with the combustion piston in its TDC, depicted as a schematic illustration. Particularly in Fig. 5, the air valve 8 is provided separate from an intake valve.

Moreover, a safety actuator 7b, operationally coupled to the control unit 9, is provided is equipped with the exhaust valve. Furthermore, Fig. 5 show the exhaust valve in its safety position, actuated by the safety actuator 7b, while a safety clearance remains between the exhaust valve and the combustion piston 4. This enables flushing any remaining liquid with an airflow when the combustion cylinder is in its TDC, even when the construction of the engine would not otherwise enable opening the exhaust valve 7 with the combustion piston in its TDC position.

It should be noted that the alternate variations regarding the air valve 8 and the safety actuator 7b may also be provided independently from each other. Particularly, the air valve 8 configuration and safety actuator 7b shown in Fig. 5 may be introduced to the arrangement illustrated in Figs. 1 - 4, either separately or together.

Fig. 8 shows variants of an exemplary embodiment of a safety actuator 7b provided on an internal combustion engine according to the present disclosure, depicted as a schematic illustration. More particularly, Fig. 6 shows a cross-sectional view of a portion of a cylinder head 5 associated to an internal combustion piston engine 1 according to an embodiment of the present disclosure. The cylinder head 5 has two exhaust ports 8, each equipped with a respective exhaust valve 7 of the poppet type. Naturally, any other number of exhaust ports 6 may be provided per combustion cylinder 3, and other valve types may be used. Both of the overhead valves 7 are spring biased towards their respective closed positions, although other biasing means may naturally be used. Such biasing enables that the exhaust valve 2 only needs to be actuated towards its open position, while movement towards the closed position is achieved by the biasing when the exhaust valve 2 is not actuated.

The exhaust valve 7 on the left side is operationally coupled with an embodiment of a safety actuator 7b according to the present disclosure. This safety actuator comprises an operating piston chamber 10a, in which an operating piston 10b is movably arranged. The An end of operating piston 10b not facing the operating piston chamber 10a lies against the exhaust valve 7, thus enabling movement of the operating piston 10b to be directly transferred to the exhaust valve 2. An operating fluid channel 10c is provided for conducting operating fluid to the operating piston chamber 10a so as to actuate the operating piston 10b. A safety piston chamber 1 1 a, in which a safety piston 1 1 b is movab!y arranged, is provided above the operating piston chamber 10a and the operating piston 10b, i.e. in a direction away from the exhaust valve 7. Accordingly, a safety fluid channel 1 1 c is provided for conducting operating fluid to the safety piston chamber 1 1 a so as to actuate the safety piston 1 1 b. In the situation of Fig. 6, i.e. the exhaust valve 7 being in its dosed position, the operating piston 3b being in its first operating position and the safety piston 1 1 b being in its first safety position, a safety stem 1 1 d’ of the safety piston 1 1 b extends up to, and lies against, the operating piston 10b, so as to directly transfer movement of the safety piston 1 1 b to the operating piston 1 1 b. That is, movement of the safety piston 1 1 b actuates the exhaust valve 7 via the operating piston 10b.

The exhaust valve 7 on the right side, in turn, is operationally coupled with another embodiment of a safety actuator 7b according to the present disclosure. Particularly, the safety actuator arrangement on the right side differs from that on the left side by having a safety stem 1 1 d” extending through an opening in the operating piston 10b directly up to the exhaust valve 7, so that the safety stem 11 d” lies against the overhead valve. Accordingly, the movement of the safety piston actuates the exhaust valve 7 directly.

Although Fig. 6 shows, for illustrative purposes, different embodiments of a safety actuator 7b according to the disclosure, it is clear for the skilled person, that both overhead valves 7 may utilize identical safety actuators 7b, if multiple exhaust valve 7 are provided per cylinder. Moreover, either of the safety actuators of Fig. 6 may be used in an arrangement where only a single exhaust valve 7 is operationally coupled to a safety actuator 7b.

The safety actuator assembly of Fig. 8 also shows an operating control valve 13 selectively coupling the operating fluid channel 10c between an operating fluid supply and an operating fluid discharge. Correspondingly, a safety control valve 14 is provided to selectively couple the safety fluid channel 1 1 c between a safety fluid supply and a safety fluid discharge. Both the operating control valve 13 and the safety control valve 14 are shown as solenoid actuated valves biased to positions coupling the operating fluid channel 10c and the safety fluid channel 1 1 c to their respective discharges. Naturally, other types of valves may be used. Although Fig. 6 illustrates both safety actuators 1 coupled to a common operating control valve 13 and a common safety control valve 14, separate respective valves may be used for each safety actuator.

Moreover, the portion of the internal combustion piston engine illustrated in Fig. 6 has a control unit 9 operationally coupled to the operating control valve 13 and the safety control valve 14 so as to actuate them. Fig 7 shows an alternative exemplary embodiment of a safety actuator 7b provided on an internal combustion engine according to the present disclosure, depicted as a schematic illustration. Namely, Fig. 7 illustrates a similar arrangement to that of Fig. 6 with the exception of the safety actuator 7b being provided as one according to a further embodiment of the present disclosure. Particularly, the operating piston chamber 10a and the safety piston chamber 1 1 a, and their respective pistons 10b, 1 1 b, are arranged side by side. Moreover, a valve yoke 13 is situated between the overhead valves 7 and both the operating piston 10b and the safety piston 1 1 b. The end of the operating piston 10b not facing the safety piston chamber 10a, and respectively, the end of the safety piston 1 1 b, namely the safety stem 1 1 d, both lie against the valve yoke 13, so that movement of the pistons 10b, 1 1 b are transferred to the exhaust vaive 7 via the valve yoke 13.

The valve yoke 13 extends over the two overhead valves 7, such that a single safety actuator may be used for controlling both overhead valves 7. It should be noted, however, that a valve yoke 13 may be used to operationally couple a single safety actuator 7b to a single exhaust valve 7. That is, a or each exhaust valve 7 may be provided with a respective safety actuator 7b equipped with its respective valve yoke 13, thus enabling said or each exhaust valve 7b to be operated separately.

Although Fig. 6 and Fig. 7 illustrate the safety actuator 7b arranged in connection with the exhaust valve 7, it should be noted that a corresponding safety actuator may be provided in connection with an intake valve. This provides the additional benefit that, even if the structure of the engine does not allow to maintain an intake vaive its open position when the combustion piston 4 is in its TDC without risking collision therebetween, an airflow may be provided to the combustion cylinder 3 from an air valve 8 arranged in connection with the intake port via the intake valve in its safety position when the combustion piston 4 is in its TDC.

Claims

1. A method for starting a four-stroke reciprocating internal combustion piston engine (1 ), comprising the steps of:

rotating a crankshaft (2), and

during an instroke of a combustion piston (4) within a combustion cyiinder (3), maintaining a respective exhaust vaive (7) in an open position

characterized by, during said instroke, providing an airflow into said combustion cylinder (3) from an air valve (8), so as to expel any remaining liquid contents from said combustion cylinder (3) to an exhaust port (6) past the exhaust valve.

2. The method according to Claim 1 , characterized in that said instroke is a compression stroke of the combustion piston (4).

3. The method according to Claim 1 or 2, characterized in that the exhaust vaive is operated with an independent exhaust valve actuator (7a), and

wherein the exhaust vaive (7) is maintained in in the open position at least until said combustion piston (4) reaches an uppermost clearance position.

4. The method according to any of the preceding Claims 1-3, characterized in that said airflow is provided starting from a movement of the combustion piston (4) immediately preceding the combustion piston (4) reaching the uppermost clearance position, said movement corresponding to a 1/2 stroke of the combustion piston (4), preferably 1/4 stroke of the combustion piston (4), more preferably 1/8 stroke of the combustion piston (4).

5. The method according to any of the preceding Claims 1-4, characterized in that the uppermost clearance position is a position of the combustion piston (4) corresponding to a 1/5 - 1/10 stroke thereof preceding a point at which said combustion piston (4) would coincide with the exhaust vaive (7) in an open position.

8. The method according to any of the preceding Claims 1-4, characterized in that the uppermost clearance position is a TDC of the combustion piston (4).

7. The method according to Claim 8, characterized in that, during said instroke, the exhaust valve (7) is moved to a safety position by retracting the independent exhaust valve actuator (7a) and by extending, or maintaining extended, a safety actuator (7b), and wherein the safety position of the exhaust valve (7) being configured such that the exhaust valve (7) remains partially open, while a clearance remains between the exhaust valve (7) and the respective combustion piston (4) in the TDC thereof.

8. The method according to Claim 7, characterized by maintaining said exhaust valve (4) in the safety position when said piston (4) reaches the uppermost clearance position.

9. The method according to any of the preceding Claims 1-7, characterized by closing said exhaust valve (7) when said piston (4) reaches the uppermost clearance position.

10. The method according to any of the preceding Claims 1-9, characterized in that the airflow into said combustion cylinder (3) is provided during either, or both, of a compression stroke and an exhaust stroke of the combustion piston (4).

11. The method according to any of the preceding Claims 1-10, characterized in that the airflow is a starting air flow and the air vaive (8) is a starting air valve, and

wherein the crankshaft (2) is rotated by providing a starting air flow to the combustion cylinder (3) during either or both of a power stroke and an intake stroke of said combustion cylinder (3).

12. The method according to any of the preceding Claims 1-11 , characterized in that the crankshaft (3) is rotated by a separate starter motor.

13. A four-stroke reciprocating internal combustion piston engine (1 ) comprising:

- a crankshaft (2);

- a crankshaft rotation means for rotating said crankshaft (2) without combustion;

- at least a combustion cylinder (3);

- a combustion piston (4) arranged within the combustion cylinder (3), said combustion piston being coupled to the crankshaft (2);

- a cylinder head (5) equipped with at least an exhaust valve (7) corresponding the combustion cylinder (3) for selectively opening and closing a flow connection between the combustion cylinder (3) and an exhaust port, said exhaust vaive (7) being equipped with a vaive actuator (7a);

- an air valve (8) configured for providing an airflow into the combustion cylinder (3), and - a control means (9) operationally coupled at least to the valve actuator (7a) for selectively opening and closing the exhaust valve, the control means (9) being further operationally coupled to the air valve (8) for selectively enabling and disabling an airflow to the combustion cylinder (3),

wherein the control means (9) being configured to, during an instroke of the combustion piston (4) within the combustion cylinder (3), operate the valve actuator (7a) so as to maintain the exhaust valve (7) in an open position, and

characterized by the control means (9) being configured to, during said instroke, operate the air valve (8) to provide an airflow info said combustion cylinder (3) so as to expel any remaining liquid contents from said combustion cylinder (3) to an exhaust port past the exhaust valve (7). The engine according to Claim 13, characterized in that said instroke is a compression stroke of the combustion piston (4). The engine (1 ) according to Claim 13 or 14, characterized in that the valve actuator (7a) is an independent valve actuator (7a) for selectively opening and closing the exhaust valve (7) by extending and retracting said independent valve actuator (7a), respectively, and

wherein the control means (9) being further configured to operate the valve actuator (7a) to maintain the exhaust valve (7) in the open position at least until said combustion piston (4) reaches an uppermost clearance position. The engine according to any of the preceding Claims 13-15, characterized by the control means (9) being further configured such that said airflow is provided starting from a movement of the combustion piston (4) immediately preceding the combustion piston (4) reaching the uppermost clearance position, said movement corresponding to a 1/2 stroke of the combustion piston (4), preferably 1/4 stroke of the combustion piston (4), more preferabiy 1/8 stroke of the combustion piston (4). The engine (1 ) according to any of the preceding Claims 13-16, characterized in that the uppermost clearance position is a position of the combustion piston (4) corresponding to a 1/5 - 1/10 stroke thereof preceding a point at which said combustion piston (4) would coincide with exhaust valve (7) in an open position. The engine (1 ) according to any of the preceding Claims 13-16, characterized in that the uppermost clearance position is the TDC of the combustion piston (4)

19. The engine (1 ) according Claim 18 characterized by the exhaust valve (7) being further equipped with a safety actuator for limiting the movement of the exhaust valve towards a closed position into a safety position by extending said safety actuator (7b), wherein the safety position of the exhaust valve (7) being configured such that the exhaust valve (7) remains partially open, while a clearance remains between the exhaust valve (7) and the respective combustion piston (4) in the TDC thereof, and wherein the control means (9) being further configured, during said instroke, to move the exhaust valve (7) to a safety position by retracting the independent exhaust valve actuator (7a) and by extending, or maintaining extended, a safety actuator (7b).

20. The engine (1 ) according to any Claim 19, characterized by the control means (9) being further configured to maintain the exhaust valve (7) in the safety position when said piston (4) reaches the uppermost clearance.

21. The engine (1 ) according to any of the preceding Claims 13-19, characterized by the control means (9) being further configured to close the exhaust valve (7) when said piston (4) reaches the uppermost clearance position by retracting the independent valve actuator (7a), or retracting the independent valve actuator (7a) and the safety actuator (7b).

22. The engine (1 ) according to any of the preceding Claims 13-21 characterized, by the control means (9) being further configured to provide an airflow to the combustion cylinder (3) during either, or both, of a compression stroke and an exhaust stroke of the combustion piston (4).

23. The engine (1 ) according to any of the preceding Claims 13-22, characterized in that the airflow is a starting air flow and the air valve (8) is a starting air valve,

wherein the crankshaft rotation means are implemented by the control means (9) being further configured to provide a starting air flow to the combustion cylinder (3) during either, or both, of a power stroke and an intake stroke of the combustion piston (4).

24. The engine (1 ) according to any of the preceding Claims 13-23, characterized in that the crankshaft rotation means comprise a separate starter motor.