CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/EP2018/068248, filed Jul. 5, 2018, which claims priority from Swedish Patent Application No. 1750935-7, filed Jul. 14, 2017, the disclosures of which are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a method for controlling the propulsion of a ship. Moreover, the present invention relates to a computer program, a computer readable medium, a control unit and a ship.

BACKGROUND

A controllable pitch ship propeller is designed such that the angle of attack of the blade can be continuously varied. In this manner, the torque of the main engine may be varied. A controllable pitch propeller is common for medium sized ships (50-150 m l.b.p.) with medium to high requirements on maneuverability.

Although a ship with a controllable pitch propeller can be maneuvered with an appropriated flexibility, contemporary ships often consume more fuel than necessary, for instance due to inappropriate operation settings of the ship's engine or the controllable pitch propeller.

SUMMARY

In view of the above, according to a first aspect of the present invention, an object of the present invention is to provide a method for controlling the propulsion of a ship wherein the engine of the ship is operated in appropriate operating conditions.

The above aspect is obtained by a method according to claim1.

As such, the first aspect of the present invention relates to a method for controlling the propulsion of a ship. The ship comprises an engine and a controllable pitch propeller, wherein torque and engine speed are adjusted to correspond to an output set point value. The adjustment is such that the ship is operated in an operating condition with an engine speed of the engine and a propeller pitch of the controllable pitch propeller such that the fuel consumption of the ship is brought and/or held within a desired fuel consumption range.

According to the first aspect of the present invention, the method comprises:determining a NO value indicative of a NO content in the exhaust gas produced by the engine andreducing the torque of the engine upon detection that the NOxvalue exceeds a NOxthreshold value.

As such, by virtue of the above method, a control of the propulsion of a ship is proposed wherein the engine is operated with an appropriate fuel consumption and wherein the NOxcontent also can be kept appropriately low. Thus, the above method implies an operating condition of the ship which is less harmful to the environment as compared to previously used operating conditions. Moreover, keeping the fuel consumption within the desired fuel consumption range implies cost reductions.

As used herein the term “NOxcontent” relates to the total content of nitrogen monoxide NO and nitrogen dioxide NO2. It should however be noted that this term is also intended to mean the content of nitrogen monoxide or nitrogen dioxide if measured separately.

By virtue of the above method, an actual NOxcontent in the exhaust gas produced by the engine may be taken into account when controlling the propulsion of the ship. Thus, instead of determining constraints on e.g. the torque from simulations and/or tests in a test environment in order to avoid high NOxcontent levels when operating the ship's engine, the above method implies that the actual NOxcontent may be taken into account. Purely by way of example, the amount of NOxproduced by the engine of a ship may vary throughout the life of the engine, for instance due to aging and/or wear, and such variations may be automatically accounted for in the above method.

Optionally, the ship comprises an exhaust gas system adapted to guide exhaust gases from the engine, the exhaust gas system comprising a NOxreduction assembly.

Optionally, the method comprises determining the NOxvalue by evaluating exhaust gas between, as seen in an intended direction of exhaust gas flow, the engine and the NOxreduction assembly in the exhaust gas system. Measuring the NOxcontent between the engine and the NOxreduction assembly implies that the NOxcontent measured is the NOxcontent in the exhaust gases produced by the engine. As such, the above method implies a rapid and stable control of the engine since the control is for instance not dependent on any changes of the capacity, for instance due to aging, of the NOxreduction assembly.

Optionally, the method comprises determining the NO value by evaluating exhaust gas downstream, as seen in an intended direction of exhaust gas flow, of the NOxreduction assembly in the exhaust gas system. Measuring the NOxcontent downstream of the NOxreduction assembly implies that the NOxcontent measured is the NOxcontent in the exhaust gas that will enter the environment ambient of the ship. As such, the above method implies that the engine can be controlled such that the NOxcontent does not exceed predetermined emission levels which for instance may be legal emission levels.

Optionally, the method comprises determining a geographical location of the ship and determining the NOxthreshold value on the basis of the thus determined geographical location. Different geographical areas of the world may be associated with different allowable emission levels. As such, the above method, being adapted to adjust the NOxthreshold value in dependence on the determined geographical location, implies that such different allowable emission levels may be taken into account when setting the NOxthreshold value. This in turn implies an appropriate operation of the engine with appropriate NOxemission levels as well as an appropriate fuel consumption.

Optionally, the engine speed of the engine is increased upon detection that the NOxvalue exceeds the NOxthreshold value. The speed increase implies that the ship may produce the requisite power, as indicated by the output set point value, whilst still producing exhaust gases with a NOxcontent lower than or equal to the NOxthreshold value.

A second aspect of the present invention relates to a method for controlling the propulsion of a ship. The ship comprises an engine and a controllable pitch propeller. The engine comprises least one cylinder. The torque and engine speed are adjusted to correspond to an output set point value, wherein the adjustment is such that the ship is operated in an operating condition with an engine speed of the engine and a propeller pitch of the controllable pitch propeller such that the fuel consumption of the ship is brought and/or held within a desired fuel consumption range.

According to the second aspect of the present invention, the method comprises:determining a top pressure value indicative of a top pressure in the at least one cylinder andreducing the torque of the engine upon detection that the top pressure value exceeds a top pressure threshold value.

Excessive top pressures may be harmful to the engine. As such, by virtue of the above method according to the second aspect of the present invention, the risk of damaging the engine may be kept appropriately low.

Optionally, the engine speed of the engine is increased upon detection that the top pressure value exceeds the top pressure threshold value.

Optionally, for the first and/or second aspects of the present invention, the feature of reducing the torque of the engine comprises reducing the propeller pitch of the controllable pitch propeller.

A third aspect of the present invention relates to a computer program comprising program code means for performing the steps of any one of the first or second aspects of the present invention when the program is run on a computer.

A fourth aspect of the present invention relates to a computer readable medium carrying a computer program comprising program code means for performing the steps of any one of the first or second aspects of the present invention when the program product is run on a computer.

A fifth aspect of the present invention relates to a control unit for controlling the propulsion of a ship. The ship comprises an engine and a controllable pitch propeller, wherein the control unit is adapted to receive a signal indicative of an output set point value. The control unit is also adapted to issue control signals to control the engine speed of the engine and the propeller pitch of the controllable pitch propeller in response to the output set point value. The control signals are determined such that the ship is operated in an operating condition, corresponding to the output set point value, with an engine speed of the engine and a propeller pitch of the controllable pitch propeller such that the fuel consumption of the ship is brought and/or held within a desired fuel consumption range.

According to the fifth aspect of the present invention, the control unit is adapted to:receive a NOxsignal with a NOxvalue indicative of a NOxcontent in exhaust gas produced by the engine and toissue a control signal to reduce the torque of the engine upon detection that the NOxvalue exceeds a NOxthreshold value.

Optionally, the ship comprises an exhaust gas system adapted to guide exhaust gas from the engine, the exhaust gas system comprises a NOxreduction assembly.

Optionally, the control unit is adapted to receive a signal with a NOxvalue indicative of the NOxcontent in the exhaust gas from a NOxsensor being located in a position between, as seen in an intended direction of exhaust gas flow, the engine and the NOxreduction assembly in the exhaust gas system.

Optionally, the control unit is adapted to receive a signal with a NOxvalue indicative of the NOxcontent in the exhaust gas from a NOxsensor being located in a position downstream, as seen in an intended direction of exhaust gas flow, of the NOxreduction assembly in the exhaust gas system.

Optionally, the control unit is adapted to receive a signal indicative of the geographical location of the ship, the control unit further being adapted to determine the NOxthreshold value on the basis of the thus determined geographical location.

Optionally, the control unit is adapted to issue a control signal to increase the engine speed of the engine upon detection that the NOxvalue exceeds the NOxthreshold value.

A sixth aspect of the present invention relates to a control unit for controlling the propulsion of a ship. The ship comprises an engine and a controllable pitch propeller. The engine comprises at least one cylinder. The control unit is adapted to receive a signal indicative of an output set point value. The control unit is also adapted to issue control signals to control the engine speed of the engine and the propeller pitch of the controllable pitch propeller in response to the output set point value. The control signals are determined such that the ship is operated in an operating condition, corresponding to the output set point value, with an engine speed of the engine and a propeller pitch of the controllable pitch propeller such that the fuel consumption of the ship is brought and/or held within a desired fuel consumption range.

According to the sixth aspect of the present invention, the control unit is adapted to:receive a top pressure signal with a top pressure value indicative of a top pressure in the at least one cylinder and toissue a control signal to reduce the torque of the engine upon detection that the top pressure value exceeds a top pressure threshold value.

Optionally, the control unit is adapted to issue a control signal to increase the engine speed of the engine upon detection that the top pressure value exceeds the top pressure threshold value.

Optionally, the control unit is adapted to issue a control signal to reduce the propeller pitch of the controllable pitch propeller in order to reduce the torque of the engine.

A seventh aspect of the present invention relates to a ship comprising a control unit according to the fifth or sixth aspect of the present invention.

