DK180308B1

DK180308B1 - A large two-stroke uniflow scavenged gaseous fueled engine and method for controlling conditions in combustion chamber

Info

Publication number: DK180308B1
Application number: DKPA201970370A
Authority: DK
Inventors: Jensen Kim; Hoffmann Mark
Original assignee: Man Energy Solutions Filial Af Man Energy Solutions Se Tyskland
Priority date: 2019-06-13
Filing date: 2019-06-13
Publication date: 2020-10-28
Also published as: CN112081652A; JP2020200831A; KR20200143648A; KR102242378B1; JP7000501B2; DK201970370A1

Abstract

A large two-stroke turbocharged uniflow scavenged gas operated internal combustion engine with a plurality of combustion chambers, at least one controller (60) associated with the engine, a controller (60) configured to determine an average compression air excess ratio and a bulk compression temperature in the combustion chambers at time of combustion start, the controller (60) being configured to: - perform at least one compression air excess ratio increasing measure when the determined or measured average compression air excess ratio is below a lower compression air excess ratio threshold, - to perform at least one compression air excess ratio decreasing measure when the determined or measured average compression air excess ratio is above an upper compression air excess ratio threshold, - to perform at least one bulk compression temperature increasing measure when the determined or measured bulk compression temperature is below a lower bulk compression temperature threshold, and - to perform at least one bulk compression temperature decreasing measure when the determined or measured bulk compression temperature is above an upper bulk compression temperature threshold.

Description

. DK 180308 B1 A LARGE TWO-STROKE UNIFLOW SCAVENGED GASEOUS FUELED ENGINE

AND METHOD FOR CONTROLLING CONDITIONS IN COMBUSTION CHAMBER

TECHNICAL FIELD The disclosure relates to large two-stroke gaseous fueled internal combustion engines, in particular large two-stroke uniflow scavenged internal combustion engines with crossheads running on gaseous fuel injected from fuel valves arranged in the cylinder liner.

BACKGROUND Large two-stroke turbo charged uniflow scavenged internal combustion engines with crossheads are for example used for propulsion of large oceangoing vessels or as primary mover in a power plant. Not only due to sheer size, these two-stroke diesel engines are constructed differently from any other internal combustion engines. Their exhaust valves may weigh up to 400 kg, pistons have a diameter up to 100 cm and the maximum operating pressure in the combustion chamber is typically several hundred bar. The forces involved at these high pressure levels and piston sizes are enormous.

Large two-stroke turbocharged internal combustion engines that are operated with gaseous fuel that is admitted by fuel valves arranged medially along the length of the cylinder liner, i.e. engines that admit the gaseous fuel during the upward stroke of the piston starting well before the exhaust valve closes, compress a mixture of gaseous fuel and scavenging air in the combustion chamber and ignites the compressed mixture at or near top dead center (TDC) by timed ignition means, such as e.g. pilot oil injection.

, DK 180308 B1 This type of gas admission, using fuel valves arranged in the cylinder liner, has the advantage that a much lower fuel injection pressure can be used, since the gaseous fuel is injected when the compression pressure is relatively low, when compared to large two-stroke turbocharged internal combustion engines which inject gaseous fuel when the piston is close to its top dead center (TDC), i.e. when the compression pressure in the combustion chamber is at or close to its maximum.

The latter type of engine needs fuel injection pressures that are significantly higher than the already high maximum combustion pressure.

Fuel systems that can handle gaseous pressures at these extremely high pressures are expensive and complicated due to the volatile nature of the gaseous fuel and its behaviour at such high pressures, which include diffusion into and through the steel components of the fuel system.

Thus, the fuel supply and system for engines that inject gaseous fuel during the compression stroke are significantly less expensive when compared to engines that inject the gaseous fuel at or near TDC.

However, when injecting gaseous fuel during the compression stroke, the piston compresses a mixture of gaseous fuel and scavenging air and consequently there is a risk of pre- ignition.

The risk of pre-ignition can be reduced by operating with a very lean mixture, but lean mixture increases the risk of misfire.

Thus, there is a need for an improvement in control over the conditions in the combustion chamber during compression in

DK 180308 B1 such large two-stroke turbocharged internal combustion engines in order to overcome or at least reduce the problems relating to pre-ignition/diesel-knock. In order to prevent pre-ignition and misfires from happening the conditions in 5 the combustion chamber need to be controlled very accurately. During steady state running of the engine, the performance layout of the engine normally ensures that pre-ignition is avoided. This is achieved by careful selection of combustion chamber design, fuel injection timing and exhaust valve timing. However, tropical operating conditions and other external factors such as the engine not running stationary, are unavoidable and can cause conditions in the combustion chambers that lead to either pre-ignition or misfires.

EP2634398 discloses a two-stroke engine operating on fuel gas as a main fuel, according to the preamble of claim 1, with an air-fuel ratio controller configured to calculate an average air-fuel ratio inside the cylinders, and of controlling the average air-fuel ratio by adjusting an air flow volume which is supplied to the plurality of cylinders; and configured to calculate an air-fuel ratio inside each cylinder, and of controlling the air-fuel ratio by adjusting a closing timing of the exhaust valve). Thus, the air-fuel ratio can be kept within an upper and lower threshold. However, this is not sufficient for ensuring that pre-ignition is avoided during all operating conditions.

SUMMARY It is an object to provide an engine and a method that overcomes or at least reduces the problems indicated above.

2 DK 180308 B1 The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect, there is provided a large two- stroke turbocharged uniflow scavenged internal combustion engine configured to operate on gaseous fuel as a main fuel in a gaseous operation mode, said engine comprising: a plurality of combustion chambers, each delimited by a cylinder liner, a piston and a cylinder cover, scavenge ports arranged in the cylinder liner for admitting scavenge air into said combustion chamber, an exhaust gas outlet arranged in the cylinder cover and controlled by an exhaust valve, a variable timing exhaust valve actuation system, at least one controller associated with the engine, sald at least one controller being configured to determine and control the opening and closing timing of said exhaust valve, sald at least one controller being configured to determine and control the amount of gaseous fuel admitted to the combustion chambers, sald at least one controller being configured to determine or measure an average compression air excess ratio for the combustion chambers, the at least one controller being configured to determine or measure a bulk compression temperature in the combustion chambers at time of combustion start, the at least one controller being configured to perform at least one compression air excess ratio increasing measure

- DK 180308 B1 when the determined or measured average compression air excess ratio is below a lower compression air excess ratio threshold, the at least one controller being configured to perform at least one compression air excess ratio decreasing measure when the determined or measured average compression air excess ratio is above an upper compression air excess ratio threshold, the at least one controller being configured to perform at least one bulk compression temperature increasing measure when the determined or measured bulk compression temperature is below a lower bulk compression temperature threshold, and the at least one controller being configured to perform at least one bulk compression temperature decreasing measure when the determined or measured bulk compression temperature is above an upper bulk compression temperature threshold.

By providing a large two-stroke engine with a controller that keeps both the bulk compression temperature between an upper and lower threshold and the compression air excess ratio between upper and lower threshold by performing actions that adjust the bulk compression temperature and the air fuel ratio, respectively, it is ensured that the conditions in the combustion chamber during compression neither develop towards conditions that lead to pre-ignition nor to develop towards conditions that lead to misfire.

Thus, the large two-stroke engine with the controller configured as the defined above will operate with neither risk of pre-ignition nor risk of misfire substantially regardless of the operating conditions of the engine.

. DK 180308 B1 In a possible implementation form of the first aspect the at least one controller comprises or 1s connected to a compression air excess ratio observer for determining a momentary average compression air excess ratio in the combustion chambers. In a possible implementation form of the first aspect the at least one controller comprises or 1s connected to a bulk compression temperature observer for determining the average momentary bulk compression temperature for the combustion chambers.

In a possible implementation form of the first aspect the lower compression air excess ratio threshold, the upper compression air excess ratio threshold, the lower bulk compression temperature threshold and the upper bulk compression temperature threshold are engine load dependent parameters.

In a possible implementation form of the first aspect the at least one compression air excess ratio increasing measure is selected from the group comprising: - timing the closing of the exhaust valve earlier, - for engines comprising a scavenge bypass: closing or increasing throttling of the scavenge bypass, - for engines with hot cylinder bypass: opening or reducing throttling of a hot cylinder bypass control valve, - for engines with an auxiliary blower: activating the auxiliary blower, - for engines with a variable geometry turbine: reducing the effective turbine flow area,

_ DK 180308 B1 — for engines with turbocharger assist: speeding up the turbocharger for engines with exhaust gas recirculation, increasing the speed of the exhaust gas recirculation blower, for engines operating on both gaseous and liquid fuel, increasing the liquid fuel fraction.

In a possible implementation form of the first aspect the at least one compression air excess ratio decreasing measure is selected from the group comprising: - timing the closing of the exhaust valve later, - for engines comprising a scavenge bypass: opening or reducing throttling of the scavenge bypass control valve, - for engines comprising an exhaust gas recirculation conduit: activating or increasing the speed of an exhaust gas recirculation blower in the exhaust gas recirculation conduit, - for engines comprising an exhaust gas bypass: opening or reducing throttling of exhaust gas bypass control valve, - for engines with a variable geometry turbine: increasing the effective turbine flow area, - for engines with liquid fuel ignition, increasing the gaseous fuel fraction and increasing the liquid fuel fraction, - for engines with turbocharger assist: reducing assistance of the turbocharger.

In a possible implementation form of the first aspect the at least one bulk compression temperature increasing measure is selected from the group comprising:

2 DK 180308 B1 - for engines comprising a cylinder bypass: opening or reducing the throttling of the cylinder bypass control valve, - for engines with hot cylinder bypass: opening or reducing throttling of a hot cylinder bypass control valve, - for engines with cold cylinder bypass: opening or reducing throttling of cold cylinder bypass control valve, - for engines with a scavenge Air Cooler Bypass: opening the scavenge air cooler bypass control valve or reducing throttling of the scavenge air bypass control valve, - exhaust advancing closing of the exhaust valve.? In a possible implementation form of the first aspect the at least one bulk compression temperature decreasing measure is selected from the group of: - temporary preventing changing of the timing of the closing of the exhaust valve, - timing the closing of the exhaust valve later, - for engines with hot cylinder bypass: closing or increasing the throttling of the hot cylinder bypass control valve, - for engines with an auxiliary blower: activating the auxiliary blower, - for engines with water injection, injecting water into the combustion chamber during compression.

In a possible implementation form of the first aspect the at least one controller is configured to perform further compression air excess ratio increasing measure when the determined or measured average compression air excess ratio

; DK 180308 B1 is below a minimum compression air excess ratio threshold that is lower than the lower compression air excess ratio threshold.

In a possible implementation form of the first aspect the at least one controller is configured to perform further compression air excess ratio decreasing measure when the determined or measured average compression air excess ratio is above the maximum compression air excess ratio threshold that is higher than a maximum upper compression air excess ratio threshold, that is higher than the upper compression alr excess ratio threshold.

In a possible implementation form of the first aspect the at least one controller is configured to perform at least one further bulk compression temperature increasing measure when the determined or measured bulk compression temperature is below a minimum bulk compression temperature threshold that is lower than the lower bulk compression temperature threshold.

In a possible implementation form of the first aspect the at least one controller is configured to perform at least one further bulk compression temperature decreasing measure when the determined or measured bulk compression temperature is above a maximum bulk compression temperature threshold that is higher than the upper bulk compression temperature threshold.

In a possible implementation form of the first aspect one or more of gaseous fuel admission openings re arranged in the i DK 180308 B1 cylinder liner for admitting gaseous fuel received from a supply of pressurized gaseous fuel via a fuel admission valves into the combustion chamber.

In a possible implementation form of the first aspect liquid fuel is injected in the gaseous operation mode for igniting the air-fuel mixture in the combustion chamber.

In a possible implementation form of the first aspect the engine is configured to operate on a liquid fuel operation in a liquid fuel operation mode. In a possible implementation form of the first aspect the compression air excess ratio is a weight based ratio.

In a possible implementation form of the first aspect the controller terminates performing the at least one compression alr excess ratio increasing measure when the determined or measured average compression alr excess ratio rises above the lower compression air excess ratio threshold. In a possible implementation form of the first aspect the controller terminates performing the at least one compression alr excess ratio decreasing measure when the determined or measured average compression air excess ratio falls below the upper compression air excess ratio threshold. In a possible implementation form of the first aspect the controller terminates performing the at least one bulk compression temperature increasing measure when the

DK 180308 B1 determined or measured bulk compression temperature rises above the lower bulk compression temperature threshold, and In a possible implementation form of the first aspect the controller terminates performing at least one bulk compression temperature decreasing measure when the determined or measured bulk compression temperature falls below the upper bulk compression temperature threshold.

In a possible implementation form of the first aspect the controller controls the exhaust valve actuation system and the fuel admission valves in accordance with predetermined lookup tables that indicate the timing of the opening and closing of the exhaust valve and indicate the opening and closing of the fuel admission valves in relation to the engine load.

In a possible implementation form of the first aspect the gas admission openings are arranged substantially in the middle part in the longitudinal direction of the cylinder liner.

In a possible implementation form of the first aspect the engine is a unit flow scavenged engine.

In a possible implementation form of the first aspect the admission openings are directed to the center of the cylinder liner and is positioned above the upper end of the scavenging ports and in a variation above the top plate of the cylinder frame.

In a possible implementation form of the first aspect the engine 1s provided with an ignition system for initiating i. DK 180308 B1 ignition and controlled by the electronic control unit, preferably at or near TDC. The ignition system may be in electronic ignition system, such as e.g. comprising laser ignition. Alternatively, the ignition system may comprise the liquid fuel injection system which 1s electronically controlled to ignite the liquid fuel when the controller determines that ignition should be initiated. The ignition system may comprise a pre-chamber in which the liquid fuel is injected.

In a possible implementation form of the first aspect the minimum compression air excess ratio threshold, the maximum compression air excess ratio threshold, the minimum bulk compression temperature threshold and the maximum bulk compression temperature threshold are dependent on engine operating conditions, such as e.g. engine load, ambient temperature, ambient humidity, engine speed. D. In a possible implementation form of the first aspect the engine comprises a state observer for determining the compression air excess ratio, i.e. a system that provides an estimate of the compression air excess ratio in the combustion chamber, from measurements of the input and output of the engine. In an embodiment the state observer for determining the compression air excess ratio is computer-implemented. In a possible implementation form of the first aspect the engine comprises a state observer for determining the bulk compression temperature, i.e. a system that provides an estimate of the bulk compression temperature in the combustion chamber, from measurements of the input and output of the i.

DK 180308 B1 engine.

In an embodiment the state observer for determining the bulk compression temperature is computer-implemented.

According to a second aspect there is provided a method of controlling a large two-stroke turbocharged uniflow scavenged internal combustion engine, the engine being configured to operate on gaseous fuel as a main fuel in a gaseous operation mode, and the engine comprising:

a plurality of combustion chambers, each delimited by a cylinder liner, a piston and a cylinder cover, scavenge ports arranged in the cylinder liner for admitting scavenge air into the combustion chamber, an exhaust gas outlet arranged in the cylinder cover and controlled by an exhaust valve, a variable timing exhaust valve actuation system, at least one controller associated with the engine, with the at least one controller: determining and controlling the opening and closing timing of the exhaust valve, determining and controlling the amount of gaseous fuel admitted to the combustion chambers, determining or measuring an average compression air excess ratio for the combustion chambers, to determining or measuring a bulk compression temperature in the combustion chambers at time of combustion start, performing at least one compression air excess ratio increasing measure when the determined or measured average compression air excess ratio is below a lower compression air excess ratio threshold,

y DK 180308 B1 performing at least one compression air excess ratio decreasing measure when the determined or measured average compression air excess ratio is above an upper compression air excess ratio threshold, performing at least one bulk compression temperature increasing measure when the determined or measured bulk compression temperature is below a lower bulk compression temperature threshold, and performing at least one bulk compression temperature decreasing measure when the determined or measured bulk compression temperature is above an upper bulk compression temperature threshold.

These and other aspects will be apparent from the embodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed portion of the present disclosure, the aspects, embodiments and implementations will be explained in more detail with reference to the example embodiments shown in the drawings, in which: Fig. 1 is a front view of a large two-stroke diesel engine according to an example embodiment, Fig. 2 is a side view of the large two-stroke engine of Fig.

1, Fig. 3 is a first diagrammatic representation the large two- stroke engine according to Fig. 1, Fig. 4 is a sectional view of the cylinder frame and a cylinder liner of the engine of Fig. 1 with a cylinder cover and an exhaust valve fitted thereto and a piston shown both in TDC and BDC,

. DK 180308 B1 Fig. 5 a second diagrammatic representation of the engine of Fig. 1, Fig. 6 is a schematic representation of a compression temperature observer and a compression air excess ratio observer, Fig. 7 is a diagram illustrating with compression air excess ratio on the vertical axis and bulk cylinder temperature on the horizontal axis, showing a safe zone surrounded by a zone in which action needs to be taken to return to the safe zone, and Fig. 8 is a process illustrating an embodiment of a method of controlling a large two-stroke engine.

DETAILED DESCRIPTION In the following detailed description, an internal combustion engine will be described with reference to a large two-stroke low-speed turbocharged internal combustion crosshead engine in the example embodiments. Figs. 1, 2 and 3 show an embodiment of a large low-speed turbocharged two-stroke diesel engine with a crankshaft 8 and crossheads 9. Figs. 1 and 2 are front and side views, respectively. Fig. 3 is a diagrammatic representation of the large low-speed turbocharged two-stroke diesel engine of Figs. 1 and 2 with its intake and exhaust systems. In this example embodiment, the engine has four cylinders in line. Large low-speed turbocharged two-stroke internal combustion engines have typically between four and fourteen cylinders in line, carried by an engine frame 11. The engine may e.g. be used as the main engine in a marine vessel or as a stationary engine for operating a generator in a power station. The total output of the engine may, for example, range from 1,000 to 110,000 kW.

Cc DK 180308 B1 The engine is in this example embodiment an engine of the two-stroke uniflow scavenged type with scavenge ports 18 in the lower region of the cylinder liners 1 and a central exhaust valve 4 at the top of the cylinder liners 1. The scavenge air is passed from the scavenge air receiver 2 through the scavenge ports 18 of the individual cylinders 1 when the piston is below the scavenge ports 18. Gaseous fuel is injected from gaseous fuel injection valves 30 under control of an electronic controller 60 when the piston is in its upward movement and before the piston passes the fuel valves 30. The fuel valves 30 are preferably evenly distributed around the circumference of the cylinder liner and placed somewhere in the central area of the length of the cylinder liner 1. Thus, the injection/admission of the gaseous fuel takes place when the compression pressure is relatively low, i.e. much lower than the compression pressure when the piston reaches TDC.

A piston 10 in the cylinder liner 1 compresses the charge of gaseous fuel and scavenge air, compression takes place and at or near TDC ignition and is triggered by e.g. injection of pilot oil (or any other suitable ignition liquid) from pilot oil fuel valves 50 that are preferably arranged in the cylinder cover 22, combustion follows and exhaust gas is generated. Alternative forms of ignition systems, instead of pilot oil fuel valves 50 or in addition to pilot fuel valves 50, such as e.g. pre-chambers (not shown), laser ignition (not shown) or glow plugs (not shown) can also be used to initiate ignition.

- DK 180308 B1 When the exhaust valve 4 is opened, the exhaust gas flows through an exhaust duct associated with the cylinder 1 into the exhaust gas receiver 3 and onwards through a first exhaust conduit 19 to a turbine 6 of the turbocharger 5, from which the exhaust gas flows away through a second exhaust conduit via an economizer 20 to an outlet 21 and into the atmosphere.

Through a shaft, the turbine 6 drives a compressor 7 supplied with fresh air via an air inlet 12. The compressor 7 delivers pressurized scavenge air to a scavenge air conduit 13 leading to the scavenge air receiver 2. The scavenge air in conduit 13 passes an intercooler 14 for cooling the scavenge air.

The cooled scavenge air passes via an auxiliary blower 16 driven by an electric motor 17 that pressurizes the scavenge alr flow when the compressor 7 of the turbocharger 5 does not deliver sufficient pressure for the scavenge air receiver 2, i.e. in low- or partial load conditions of the engine.

At higher engine loads the turbocharger compressor 7 delivers sufficient compressed scavenge air and then the auxiliary blower 16 is bypassed via a non-return valve 15. Fig. 4 shows a cylinder liner 1 generally designated for a large two-stroke crosshead engine.

Depending on the engine size, the cylinder liner 1 may be manufactured in different sizes with cylinder bores typically ranging from 250 mm to 1000 mm, and corresponding typical lengths ranging from 1000 mm to 4500 mm.

In Fig. 4 the cylinder liner 1 is shown mounted in a cylinder frame 23 with the cylinder cover 22 placed on the top of the cylinder liner 1 with the gas tight interface therebetween.

DK 180308 B1 In Fig. 4, the piston 10 is shown diagrammatically by interrupted lines in both bottom dead center (BDC) and top dead center (TDC) although it is of course clear that these two positions do not occur simultaneously and are separated by a 180 degrees revolution of the crankshaft 8. The cylinder liner 1 is provided with cylinder lubrication holes 25 and cylinder lubrication line 24 that provides supply of cylinder lubrication oil when the piston 10 passes the lubrication line 24, next piston rings (not shown) distribute the cylinder lubrication oil over the running surface of the cylinder liner

1. The pilot fuel valves 50 (typically more than one per cylinder), or pre-chambers with pilot oil valves 50, are mounted in the cylinder cover 22 and connected to a source of pilot oil (not shown). The timing of the pilot oil injection is controlled by the electronic control unit 60. The fuel vales 30 are installed in the cylinder liner 1, with their nozzle substantially flush with the inner surface of the cylinder liner 1 and with the rear end of the fuel valve 30 protruding from the outer wall of the cylinder liner 1. Typically, one or two, but possibly as much as three or four fuel valves 30 are provided in each cylinder liner 1, circumferentially distributed around the cylinder liner 1. The fuel valves 30 are in an embodiment arranged substantially medial along the length of the cylinder liner 1. Further, Fig. 4 schematically shows the gaseous fuel supply system including a source of pressurized gaseous fuel 40 connected via a gaseous fuel supply conduit 41 to an inlet of each of the gaseous fuel valves 30.

0 DK 180308 B1 Fig. 5 illustrates is a schematic representation of the engine similar to Fig.2 however, with more details on the gas exchange infrastructure of the engine. Ambient air is taken in at an ambient air pressure and temperature 26 and transported through the air inlet 12 to the compressor 7 of the turbocharger 5. From the compressor 7 the compressed scavenge air is transported through the air conduit 32 to a distribution point 28.

The distribution point 28 allows branching off scavenge air through a hot cylinder bypass conduit 29 to a turbine connection 32 in the first exhaust conduit 19. The flow through the hot cylinder bypass conduit 29 is regulated by a hot cylinder bypass control valve 31. The hot cylinder bypass control valve 31 1s controlled electronically by the controller 60. The effect of opening the hot cylinder bypass 29 or reducing throttling of the control valve 31 in the hot cylinder bypass is an increase in the compression air excess ratio and an increase in the bulk compression temperature and vice versa. The air conduit 13 further includes a first scavenge air control valve 33 upstream of an intercooler 14. A second scavenge air control valve 34 is arranged downstream of the intercooler 14. The air conduit 13 continues to the scavenge alr receiver 2. A conduit comprising the auxiliary blower 16 is branched off from the intercooler 14.

A cold cylinder bypass conduit 35 connects the scavenge air receiver 2 to the turbine connection 32 in the first exhaust

>0 DK 180308 B1 conduit 19. The flow through the courts in the bypass 35 is regulated by the cold cylinder bypass control valve 36. The cold cylinder bypass control valve 36 1s controlled electronically by the controller 60. The effect of opening the cold cylinder bypass 35 or of reducing the throttling of the cold cylinder bypass valve 36 is an increase in the bulk compression temperature.

A cold scavenge bypass conduit 37 allows scavenge air to escape from the scavenge air receiver 26 the environment.

The flow through the cold scavenge bypass conduit 37 is controlled by the cold scavenge bypass control valve 38. The cold scavenge bypass control valve 38 is controlled electronically by the controller 60. The effect of opening the cold scavenge bypass control valve 38 or reducing throttling of the cold scavenge bypass control valve 38 is a decrease in the scavenge alr pressure and reduces the compression air excess ratio.

The cold scavenge bypass conduit 37 does not need to be branched off from the scavenge air receiver 2, but could just as well be branched off from the air conduit 13 at any position downstream of the intercooler 14. Fxhaust gas recirculation conduit 42 connects the exhaust gas receiver 3 to the scavenge air receiver 2 and comprises an exhaust gas recirculation control valve 45, and exhaust gas recirculation cooler 44 and an exhaust gas recirculation blower 43. The exhaust gas recirculation blower 43 and the exhaust gas recirculation control valve 45 are both used to regulate the flow through the exhaust gas recirculation conduit 42 under the electronic control of the controller 60. Under normal operating conditions no flow will occur through

> DK 180308 B1 the exhaust gas recirculation conduit 42 unless the exhaust gas recirculation blower 43 is active since the pressure in the exhaust gas receiver 42 is normally lower than the pressure in the scavenge air receiver 2 (hence, the exhaust gas recirculation control valve 45 needs to be closed when the exhaust gas recirculation blower 43 is not active). The exhaust gas recirculation conduit 42 does not need to connect from the exhaust gas receiver 3, but could just as well be connected at any point to the first exhaust conduit 19 and does not need to connect to the scavenge air receiver 2 and could just as well connect to any position on the air conduit 13 downstream of the intercooler 14. Activating or increasing the speed of an exhaust gas recirculation blower 43 in the exhaust gas recirculation conduit 42 reduces the compression air excess ratio and slightly reduces bulk compression temperature. An exhaust gas bypass 39 branches off from the exhaust gas receiver 3 or from the first exhaust conduit 19 and connects to the atmosphere 27 at a given back pressure 27. An exhaust gas bypass control valve 40 regulates the flow through the exhaust gas bypass conduit 39 and the electronic control of the controller 60.

Opening the exhaust gas bypass control valve 40 or reducing throttling of the exhaust gas bypass control valve 40, decreases the compression air excess ratio in the cylinders. In engines that are provided with a selective catalytic receiver (SVR) reactor and a reactor bypass valve (RVB)

> DK 180308 B1 regulates the fraction of the flow from the scavenge air receiver 3 to the turbine 6 of the turbocharger 5 that passes through the SCR reactor, under the electronic control of the controller 60.

All the above-mentioned components that are controlled by the controller 60 are connected to these components by signal lines that are indicated by the interrupted lines in Fig. 5. Fig. 6 illustrates the compression air excess ratio observer 46 and the bulk compression temperature observer 47. The compression air excess ratio observer 46 is a computer implemented algorithm that is in possession of information about the scavenge air pressure, the exhaust valve closing timing, the cylinder geometry, the stoichiometric air-fuel ratio and the injected gas amount. The compression air excess ratio observer 46 can be a part of the controller 60 or can be a separate computer or controller. The compression air excess ratio observer 46 provides an output that is an estimate of the compression air excess ratio of the (fully) compressed air-fuel mixture (when piston is at TDC) and sends it to the controller 60. The estimate is based on the ratio of the fresh air mass captured in the combustion chamber when exhaust valve 4 lands on its seat, divided by the mass of same fresh air necessary for stoichiometric combustion of the total injected gas mass. The bulk compression temperature observer 47 is a computer implemented algorithm that is in possession of information about the scavenge air pressure, the scavenge air temperature,

> DK 180308 B1 the exhaust valve closing timing and the crankshaft speed.

The bulk compression temperature observer 47 can be a part of the controller 60 or can be a separate computer or controller.

The compression air excess ratio observer 46 provides an output that is an estimate of Tcomp (Tc); the maximum bulk compression temperature in combustion chamber in the time window from start of gas injection to time of pilot injection.

The compression air excess ratio observer 46 sends the estimate to the controller 60. In an embodiment the Tcomp estimation refers to piston at TDC.

Fig. 7 is a graph setting out the bulk compression temperature Tcomp against compression air excess ratio (A). A normal running zone 51 is within the boundaries defined by a lower compression air excess ratio threshold, an upper compression alr excess ratio threshold, a lower bulk compression temperature threshold and an upper bulk compression temperature threshold.

In this normal running zone 51 the controller 60 provides the amount of fuel that is required for the present engine load and the controller 60 does not take any measures that change the bulk compression temperature and the compression air excess ratio.

However, when the conditions in the cylinder liners 1 threaten to leave the normal running zone 51 and enter the action zone 52, the controller 60 will take measures to prevent this from happening.

Hereto, the controller 60 is configured to: - perform at least one Compression Air Excess Ratio Increasing Measure (CAERIM) when the determined or

> DK 180308 B1 measured average compression air excess ratio is below a lower compression air excess ratio threshold, - to perform at least one Compression Air Excess Ratio decreasing measure (AERDM) when the determined or measured average compression air excess ratio is above an upper compression air excess ratio threshold, - to perform at least one Bulk Compression Temperature Increasing Measure (BCTIM) when the determined or measured bulk compression temperature is below a lower bulk compression temperature threshold, and - to perform at least one bulk compression temperature decreasing measure (BCTDM) when the determined or measured bulk compression temperature is above an upper bulk compression temperature threshold.

By performing these measures, the controller 60 keeps the conditions in the cylinder liners 1 inside the normal running zone 51, and at least only temporary allows the conditions to move outside the normal running zone 51 and enter the action zone 52. The action zone 52 is surrounded by a critical zone 53 where pre-ignition and/or misfire is likely to occur. The boundaries for the zones 51,52 and 53, can be defined by the upper and lower thresholds for the bulk compression temperature and the upper and lower limits for the compression alr excess ratio. These thresholds can be determined for a particular engine empirically by trial and error or through computer simulation of the engine cycle When the observers indicate that both the compression air excess ratio and the bulk compression temperature are outside

Je DK 180308 B1 the normal running zone 51, the controller 60 will take both measures to adjust the compression air excess ratio and the bulk compression temperature in order to move the conditions in the cylinder liners back to the normal running zone 51.

Opening the Exhaust Gas Bypass (EGB) conduit 39 (flow from TC turbine inlet to turbine outlet or ambient) by adjusting the exhaust gas bypass control valve 40 (moving the exhaust gas bypass control valve 40 to a more open position) causes significant reduction in scavenge air pressure, and therefore in captured air mass in combustion chamber. As a consequence, this measure is suitable for reducing Compression Air Excess Ratio, with only minor impact on compression bulk temperature. In cases where engine has more turbochargers, a single EGB can still be used from exhaust gas receiver, as long as its position is chosen according to other potential mixing points from other flows to the exhaust gas receiver. Opening the Hot cylinder bypass control valve 31 (flow from TC compressor outlet to TC turbine inlet) causes increase in Compression Air Excess Ratio and bulk compression temperature in combustion chamber. Opening the scavenge bypass control valve 38 creates flow from the scavenge air receiver 2 to compressor inlet or ambient and opening has similar qualitative effects as exhaust gas bypass on air compression excess ratio, but different impact on the scavenging process (and therefore on bulk compression temperature in the combustion chamber). The effects of opening the scavenge bypass control valve 38 on

De DK 180308 B1 combustion chamber conditions are faster when compared to exhaust gas bypass.

Opening the Cold Cylinder Bypass Valve 36 increases flow from scavenge air receiver to TC turbine inlet and causes increase in Bulk Compression Temperature, while having very small effect on Compression Air Excess Ratio.

Fxhaust Valve Closing Timing determines the ratio between compression and scavenge air pressure in combustion chamber Varying timing has significant effect om both compression air excess ratio and bulk compression temperatures in combustion chamber.

Exhaust Valve Opening Timing affects first phase of the scavenge process of the combustion chamber: varying timing will affect engine efficiency and scavenging process. As scavenge process is changed, the resulting bulk temperature also changes. By opening the exhaust valve 4 very early there is no flow to the scavenge air receiver 2 when the piston 10 subsequently opens the scavenge ports 18. When the exhaust valve 4 is opened very late there is a large flow to the scavenge air receiver 2 when piston 10 subsequently opens the scavenge ports 18. These measures change the scavenging process, and therefore the fraction of ‘dirty hot’ gas from previous combustion which joins the next compression stroke. Thus, by opening the exhaust valve 4 very early there will be more "dirty hot” gas from the previous combustion and therefore the compression air excess ratio will decrease and the bulk compression temperature will increase. Opening the exhaust valve 4 very late there will be less "dirty hot gas

>; DK 180308 B1 from the previous combustion and therefore the compression alr excess ratio will increase at the bulk compression temperature will decrease.

When increasing compression by closing the exhaust valve 4 earlier, less gas escapes through the exhaust valve 4, and more gas is therefore captured in the combustion chamber.

This increases the air excess ratio.

Also, increasing compression leads to more compression work done by the piston 10 on the gas in the combustion chamber.

This leads to higher gas temperatures in the combustion chamber.

Increasing exhaust gas recirculation flow by activating the exhaust gas recirculation blower 43 or by increasing the speed of the exhaust gas recirculation blower 43 more exhaust gas flows from exhaust gas receiver 3 to turbocharger compressor outlet or scavenge air receiver 2) and this will reduce the compression air excess ratio, with some reduction on bulk compression temperatures in combustion chamber.

Increasing the speed of the auxiliary blower 16 will slightly the increase compression air excess ratio, and reduce bulk compression temperatures in combustion chamber.

For engines with water injection, injecting water into the combustion chamber during compression will decrease bulk compression temperature.

Scavenge Air Cooler Bypass (not shown): bypassing intercooler 14 will significantly increase bulk compression temperatures in combustion chamber, with minor effect on the compression air excess ratio.

Je DK 180308 B1 For engines provided with a variable geometry turbine 6, the effect of reducing the turbine flow area is a reduction in scavenge air pressure, and therefore in captured air mass in combustion chamber. As a consequence, this measure is suitable for reducing compression air excess ratio, with only minor impact on compression bulk temperature. For engines provided with a turbocharger assist, speeding up the turbocharger 5 by increasing the assist will increase compression air excess ratio, with minor effect on compression temperature.

Another measure is varying ratio between gaseous fuel and liquid fuel (e.g. marine diesel). Reducing the gas fuel fraction of the total injected fuel energy reduces the compression air excess ratio. The liquid fuel fraction is correspondingly increased, ensuring that crankshaft torque is maintained.

For engines in which a heat exchanger is installed in the exhaust gas receiver (or having a heat exchanger receiving a fraction of the exhaust gas), increasing the fraction of exhaust gas passed through the heat exchanger, i.e. extracting more heat from the exhaust gas causes reduction in scavenge air pressure, and therefore in captured air mass in combustion chamber. As a consequence, this measure is suitable for reducing compression air excess ratio, with only minor impact on compression bulk temperature. The heat exchanger can be used for steam production.

> DK 180308 B1 For engines with a hot scavenge bypass, opening a hot scavenge bypass control valve establishes or increases flow from compressor outlet to ambient or compressor inlet causes significant reduction in scavenge air pressure, and therefore in captured air mass in combustion chamber. As a consequence, this measure is suitable for reducing compression air excess ratio, with only minor impact on compression bulk temperature. In an embodiment, the lower compression air excess ratio threshold, the upper compression air excess ratio threshold, the lower bulk compression temperature threshold and the upper bulk compression temperature threshold are engine operating conditions dependent parameters. The engine operating conditions determined by parameters such as the engine load, the ambient temperature, the ambient humidity, the engine speed, etc. The values for these operating conditions dependent parameters are available for the controller 60, through e.g. lookup tables or algorithms or combinations thereof.

In an embodiment the controller 60 is configured: to perform further compression air excess ratio increasing measures (e.g. selected from the measures mentioned above) when the determined or measured average compression air excess ratio is below a minimum compression air excess ratio threshold that is lower than said lower compression air excess ratio threshold, to perform further compression air excess ratio decreasing measure when the determined or measured average compression air excess ratio is above said maximum compression alr excess ratio threshold that is

DK 180308 B1 higher than a maximum upper compression air excess ratio threshold, that is higher than said upper compression alr excess ratio threshold, to perform at least one further bulk compression temperature increasing measure when the determined or measured bulk compression temperature is below a minimum bulk compression temperature threshold that is lower than said lower bulk compression temperature threshold, and to perform at least one further bulk compression temperature decreasing measure when the determined or measured bulk compression temperature is above a maximum bulk compression temperature threshold that is higher than said upper bulk compression temperature threshold.

These further measures are taken when the conditions in the combustion chambers have moved out of the action zone 52 into the critical zone 53 that surrounds the action zone 52. Thus, the controller 60 is configured to take as many actions as is necessary to move the process back into the action zone 52 and further back into the normal running zone 51. The controller 60 is configured to minimize constraints, i.e. measures mentioned above in order to move the engine back to operating conditions within the normal zone 51. Thus, the controller is configured to and all of the above mentioned measures when the conditions in the combustion chambers have returned into the normal running zone.

51 DK 180308 B1 Fig. 8 is a flowchart showing the process of operating the engine in accordance with the configuration of the controller 60 described above.

After start of the process controller checks if compression alr excess ratio is below the lower threshold. If the answer is No, the controller moves to checking if the upper compression air excess ratio threshold is exceeded, and if the answer is Yes, the controller 60 takes a compression air excess ratio increasing measure from one of the measures mentioned above. Next, the controller 60 checks if compression alr excess ratio is below the minimum threshold. If the answer is No, the controller moves to checking if the upper compression excess ratio threshold is exceeded and if the answer is Yes, the controller 60 takes a further compression excess ratio increasing measure from the measures mentioned above and moves to the step of checking if the compression excess ratio is above the upper threshold.

The controller 60 checks if compression air excess ratio is above the upper threshold. If the answer is No, the controller moves to checking if the lower bulk compression temperature threshold is exceeded, and if this is Yes, the controller 60 takes a compression air excess ratio decreasing measure from one of the measures mentioned above. Next, the controller 60 checks if compression air excess ratio is above the maximum threshold. If the answer is No, the controller moves to checking if the lower bulk compression temperature threshold is exceeded, and if the answer is Yes, the controller 60 takes a further compression excess ratio decreasing measure from the measures mentioned above and thereafter moves to the step

> DK 180308 B1 of checking if the bulk compression temperature is below the lower threshold.

The controller 60 checks if the bulk compression temperature is below the lower threshold.

If the answer is No, the controller of 60 moves to the next step of checking if the bulk compression temperatures above the upper threshold and if the answer is Yes, the controller 60 takes a bulk compression temperature increasing measure.

Thereafter, the controller 60 checks if the bulk compression temperature is below the minimum threshold and if the answer is No the process of 60 moves to the step of checking if the bulk compression temperature is above the upper threshold and if the answer is Yes, the controller 60 takes a further bulk temperature increasing measure from the measures mentioned above and thereafter moves to step of checking if the bulk compression temperature threshold is exceeded.

The controller 60 checks if the bulk compression temperature threshold is exceeded and if the answer is No, the controller 60 moves back to the step of checking if the compression air excess ratio is below the lower threshold and if the answer is Yes, the controller 60 takes a bulk temperature decreasing measure from the of measures mentioned above.

Next the controller 60 checks if the book compression temperature is above the maximum threshold and if the answer is now the controller 60 moves back to the step of checking if the compression air excess ratio is below the lower threshold and if the answer is Yes the controller 60 takes a further bulk temperature decreasing measure from measures mentioned above

> DK 180308 B1 and thereafter moves to the step of checking 1ÅAf the compression air excess ratio is below the lower threshold. In embodiment, the controller is provided with an algorithm, a lookup table or other information to decide which of the available measures for increasing or decreasing the book compression temperatures is the most suitable measure for the present operating conditions of the engine. Likewise, the controller 60 is provided with an algorithm, lookup table or other information to decide which of the available measures for increasing or decreasing the compression air excess ratio is the most suitable measure in the present operating conditions of the engine.

The various aspects and implementations have been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed subject-matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor, controller or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. The reference signs used in the claims shall not be construed as limiting the scope.

Claims

. DK 180308 B1 PATENT REQUIREMENTS

A large, turbocharged long-stroke two-stroke internal combustion engine configured to run on a gaseous fuel as a main fuel in a gaseous mode of operation, the engine comprising: a plurality of combustion chambers, each defined by a cylinder liner (1), a piston ( 10) and a cylinder cover (22), purge ports (18) arranged in the cylinder liner (1) for supplying purge air in the combustion chamber, an exhaust gas outlet arranged in the cylinder cover (22) and controlled by an exhaust valve (4), an exhaust valve timing system with variable timing actuation one control unit (60) connected to the engine, the at least one control unit (60) being configured to determine and control the opening and closing timing of the exhaust valve (4), the at least one control unit (60) being configured to determine and control the amount; of gaseous fuel entering the combustion chambers, characterized in that:

, 180808 B1 the at least one control unit (60) is configured to determine or measure an average compression air excess ratio for the combustion chambers,

the at least one control unit (60) is configured to determine or measure a bulk compression temperature in the combustion chambers at the time of combustion start, the at least one control unit 60) is configured to perform at least one measure of increasing compression-air excess ratio when the determined or measured average compression air excess ratio is below a lower compression air excess ratio threshold,

the at least one control unit (60) is configured to perform at least one measure of reducing compression air excess ratio when the determined or measured average compression air excess ratio is above an upper compression air excess ratio threshold,

the at least one controller (60) is configured to perform at least one bulk compression temperature rise measure when the determined or measured bulk compression temperature is below a lower bulk compression temperature.

threshold, and the at least one controller (60) is configured to perform at least one bulk compression temperature drop measure when the determined or measured bulk compression temperature is above an upper bulk compression temperature threshold.

DK 180308 B1

The engine of claim 1, wherein the at least one control unit (60) comprises or is connected to a compression air excess ratio observer (46) for determining a momentary average compression air excess ratio in the combustion chambers.

An engine according to claim 1 or 2, wherein the at least one at least one control unit (60) comprises or is connected to a bulk compression temperature observer (47) for determining the average instantaneous bulk compression temperature 1 of the combustion chambers.

An engine according to any one of claims 1 to 3, wherein the at least one measure for increasing the compression-air excess ratio is selected from the group comprising: - timing of the closing of the exhaust valve (4) earlier, - for engines comprising a purge diversion (37): closing or increasing throttling of a purge diversion valve (38), - for engines with hot-cylinder diversion (29): opening or reducing throttling of a hot-cylinder diversion control valve (31), - for auxiliary fan motors (16): activation of the auxiliary fan (16), - for motors with a variable geometry turbine (6): reduction of the effective turbine flow range, - for motors with turbocharger assistance: increasing the speed of the turbocharger (5) .

An engine according to any one of claims 1 to 4, wherein the at least one measure for reducing compression-air excess conditions is selected from the group comprising: - timing of the closing of the exhaust valve (4) later, - for engines, comprising a cold flush bypass (37): opening or reducing throttling of the cold flush bypass control valve (38), - for engines comprising an exhaust gas bypass (39); opening or reducing throttling of the exhaust gas bypass control valve (40), - for engines comprising an exhaust gas recirculation duct (42): activating or increasing the speed of an exhaust gas recirculation fan (43) in the exhaust gas recirculation duct (42), - for engines 6) with variable geometry: increase of the effective turbine flow range, - for liquefied fuel ignition engines, reduction of the gaseous fuel fraction and increase of the liquid fuel fraction, - for engines with a heat exchanger between the exhaust valve and the turbocharger inlet: increase the amount of heat dissipated by the exhaust gas with the heat exchanger, - for engines with turbocharger assistance: reduction of turbocharger (5) assistance.

An engine according to any one of claims 1 to 5, wherein the at least one bulk compression temperature rise measure is selected from the group consisting of: - for engines comprising a cold-cylinder bypass (35): opening or reducing the throttle of a cold cylinder diversion control valve (36),

- GB 180308 B1 - for engines with hot-cylinder diversion (29): opening or reducing throttling of a hot-cylinder diversion control valve (31), - for engines with a purge air cooler diversion: opening the purge air cooler diversion control valve or reducing the throttle control flow of the purge valve , - advance of closing of the exhaust valve.

An engine according to any one of claims 1 to 6, wherein the at least one bulk compression temperature drop measure is selected from the group of: - temporarily preventing change in the timing of the exhaust valve closure (4), - timing of the exhaust valve closure (4) later, - for hot-cylinder diversion engines (29): closing or increasing the throttle of a hot-cylinder diversion control valve (31), - for auxiliary fan engines (16): activating the auxiliary fan (16) , - for engines with water injection, injection of water into the combustion chamber during compression.

An engine according to any one of claims 1 to 7, wherein the at least one control unit (60) is configured to perform further action to increase compression air excess ratio when the determined or measured average compression air excess ratio is below a minimum compression air excess ratio threshold. is lower than the lower compression air excess ratio threshold.

. DK 180308 B1

An engine according to any one of claims 1 to 8, wherein the at least one control unit (60) is configured to perform further action to reduce compression air excess ratio when the determined or measured average compression air excess ratio is above the maximum compression air excess ratio threshold. , which is higher than a maximum upper compression air excess ratio threshold higher than the upper compression air excess ratio threshold.

An engine according to any one of claims 1 to 9, wherein the at least one control unit (60) is configured to perform at least one additional measure of bulk compression temperature rise when the determined or measured bulk compression temperature is below a minimum bulk compression temperature. temperature threshold lower than the lower bulk compression temperature threshold.

An engine according to any one of claims 1 to 10, wherein the at least one control unit (60) is configured to perform at least one additional measure of bulk compression temperature drop when the determined or measured bulk compression temperature is above a maximum bulk compression temperature. temperature threshold higher than the upper bulk compression temperature threshold.

A method of controlling a large, turbocharged two-stroke internal combustion engine, which engine is configured to run on a gaseous fuel as the main fuel in a gaseous operating mode, and which engine comprises:

A plurality of combustion chambers, each delimited by a cylinder liner (1), a piston (10) and a cylinder cover (22),

flushing ports (18) arranged in the cylinder liner (1) for supplying flushing air into the combustion chamber, an exhaust gas outlet arranged in the cylinder cover (22) and controlled by an exhaust valve (4),

a variable timing exhaust valve actuation system, at least one control unit (60) connected to the engine, the at least one control unit (60): determining and controlling the opening and closing timing of the exhaust valve, determining and controlling the amount of gaseous fuel entering the combustion chambers, characterized in that the control unit (60): determines or measures an average compression air excess ratio for the combustion chambers, to determine or measure a bulk compression temperature in the combustion chambers at the time of combustion start,

2 DK 180308 B1 performs at least one measure to increase the compression air excess ratio when the determined or measured average compression air excess ratio is below a lower compression air excess ratio.

threshold, performs at least one measure to reduce compression air excess ratio when the determined or measured average compression air excess ratio is above an upper compression air excess ratio threshold, performs at least one measure of bulk compression temperature rise when the determined or measured bulk compression temperature is below performs at least one bulk compression temperature drop measure when the determined or measured bulk compression temperature is above an upper bulk compression temperature threshold.