GB2590952A

GB2590952A - Selective cylinder deactivation, particularly in turbocharged diesel engines with high power density

Info

Publication number: GB2590952A
Application number: GB2000261.4A
Authority: GB
Inventors: Derrick Turnock Adam; Singh Gill Simaranjit; Edward Richard Pardoe James; Paul Timmins Nicholas
Original assignee: Perkins Engines Co Ltd
Current assignee: Perkins Engines Co Ltd
Priority date: 2020-01-09
Filing date: 2020-01-09
Publication date: 2021-07-14
Anticipated expiration: 2040-01-09
Also published as: CN113107686B; GB2590952B; GB202000261D0; CN113107686A

Abstract

Disclosed is a method and apparatus for running an internal combustion engine at low load or during start-up by deactivating cylinders 4 at opposite ends of a row of cylinders in an engine block 12 while running all of the remaining cylinders 3 located in the middle of the row in continuous or skip-fire mode. Also disclosed is a method and apparatus for controlling exhaust emissions from a turbocharged diesel engine 1 with a mean break effective pressure, BMEP, in excess of 30 bar by deactivating selected cylinders 3, 4 at low load or start-up, even where the compression ratio is 13.5:1 or less.

Description

Selective cylinder deactivation, particularly in turbocharged diesel engines with high power density

Technical Field

100011 This disclosure relates to control systems for selectively de-activating individual cylinders of a turbocharged diesel engine or other internal combustion piston engine, e.g. in a so-called -skip-fire" pattern, to reduce emissions on startup or when running at low load.

[0002] In particular, although not exclusively, the disclosure is directed to large diesel engines with a high power density.

Background

100031 Power density is an important parameter of internal combustion engines, and in piston engines is commonly expressed as brake mean effective pressure or BM EP. Ceteris paribus, an engine with higher power density can do more work.

100041 In a piston engine, cylinder pressure increases through the cycle from an initial charge pressure before compression, to a peak cylinder pressure generated by combustion of the fuel. The initial charge pressure can be increased by arranging a turbocharger to force more air into the cylinder during each cycle. By also proportionately increasing the amount of fuel supplied to the cylinder during each cycle, the power density of the engine can be increased. However, it is necessary to ensure that the peak cylinder pressure remains within the design limit of the engine.

[00051 The cylinder pressure at the moment of ignition is a function of the initial charge pressure and the compression ratio of the cylinder. Thus, for a given initial charge pressure, reducing the compression ratio will reduce the cylinder pressure at the moment of ignition.

[0006] Since the peak cylinder pressure is a function of the cylinder pressure at the moment of ignition, and the energy released during combustion, reducing the compression ratio will also reduce the peak cylinder pressure for a given initial charge pressure and quantum of fuel energy.

100071 Accordingly, by reducing the compression ratio in a turbocharged engine, it is possible to increase the initial charge pressure and quantum of fuel energy on each stroke, and so to increase the power density, without exceeding the maximum permissible peak cylinder pressure.

[0008] It is known to employ this technique to increase the power density of large diesel engines, for example, engines with a total capacity (maximum total combustion chamber volume for all cylinders) of 201 or more for use in fixed speed generating sets.

[0009] However, when the compression ratio drops below 14:1, poor combustion resulting in uneven running and white smoke output is observed when the engine is started from cold, or operated at no or low load, or in a cold climate. For this reason such engines generally have a compression ratio of at least 13.6: 1, more commonly 14:1 or more.

[0010] A piston engine running at full load will typically have better combustion characteristics than when running at low load or idling.

[0011] Accordingly, one approach to reducing emissions in diesel and other types of piston engines is to selectively deactivate one or more cylinders of the engine, for example, in a so-called "skip firing" pattern wherein combustion alternates between different ones of the cylinders on successive cycles of the engine. This reduces the power output of the engine to better match the load while increasing the load on the active cylinders and so helps to reduce emissions.

[0012] For example, US8651091 B2 teaches to deactivate selected cylinders of an internal combustion engine while operating the remaining cylinders at optimal efficiency, e.g. at or near a full throttle position, with the amount of fuel injected being optimized based on a lookup table according to the operational state of the engine.

Summary of the Disclosure

100131 In a first aspect., the present disclosure provides an internal combustion piston engine including a control system and a plurality of cylinders. Each cylinder defines a combustion chamber and has a piston reciprocable in the cylinder. At least some of the cylinders are controllable by the control system in normal operation of the engine to define, alternatively: an active mode in which combustion occurs in the respective cylinder, and an inactive mode in which combustion does not occur in the respective cylinder.

100141 The engine is arranged to operate alternatively: in a Ml power mode, wherein in the full power mode the control system is arranged to control all of the cylinders in the active mode, and in a reduced power mode, wherein in the reduced power mode the control system is arranged to control one or more of the cylinders in the inactive mode.

[0015] The cylinders are arranged in at least one row, and include end cylinders arranged at opposite ends of the at least one row, and intermediate cylinders arranged between the opposite ends of the at least one row.

[0016] In the reduced power mode of the engine, the control system is arranged to control the end cylinders in the inactive mode, and to control at least some of the intermediate cylinders in the active mode, until operation of the engine in the reduced power mode is terminated.

100171 In a related aspect, the disclosure provides a method of operating the engine, including: operating the engine in the reduced power mode, and controlling, by the control system, the end cylinders in the inactive mode, and at least some of the intermediate cylinders in the active mode, until operation of the engine in the reduced power mode is terminated.

[00181 In another aspect, the disclosure provides a turbocharged, diesel fuelled, compression ignition, internal combustion piston engine including a control system and a plurality of cylinders. Each cylinder defines a combustion chamber and has a piston rceiprocable in the cylinder to vary a volume of the combustion chamber from a maximum volume to a minimum volume, wherein a compression ratio of the cylinder is defined as a ratio of the maximum volume to the minimum volume.

100191 At least some of the cylinders are controllable by the control system in normal operation of the engine to define alternatively: an active mode in which combustion occurs in the respective cylinder, and an inactive mode in which combustion does not occur in the respective cylinder.

[0020] The engine is arranged to operate alternatively: in a full power mode, wherein in the full power mode the control system is arranged to control all of the cylinders in the active mode, and in a reduced power mode, wherein in the reduced power mode the control system is arranged to control one or more of the cylinders in the inactive mode.

[0021] In the fill] power mode the engine has a maximum brake mean effective pressure BMEP in excess of 30 bar.

[00221 The compression ratio is not more than 13.5: I.

Brief Description of the Drawings

[0023] Further features and advantages will be apparent from the illustrative embodiment which will now be described, purely by way of example and without limitation to the scope of the claims, and with reference to the accompanying drawings, in which: [00241 Fig. 1 shows an 8-cylinder, in-line turbocharged diesel engine with a control system in accordance with a first embodiment; 100251 Fig. 2 shows the downward movement of the piston in one cylinder of the engine during the power stroke after ignition of the mixture; and [0026] Fig. 3 is a graph showing the measured hydrocarbon emissions from the engine during startup from cold.

Detailed Description

[0027] Fig. 1 shows a turbocharged, diesel fuelled, compression ignition, internal combustion piston engine 1 including a control system 2 and an engine block 12 defining a plurality of cylinders 3, 4 which are supplied with air A from the compressor wheel of a turbocharger 11, which could be any turbocharger assembly as known in the art, e.g. a single stage turbocharger as shown, or a multiple stage turbocharger assembly. Exhaust gases F. from the cylinders flow back through the turbine wheel of the turbocharger to the exhaust system (not shown).

[00281 Each cylinder 3, 4 defines a combustion chamber 5 and has a piston 6 which is reciprocable in the cylinder to drive a crankshaft 7 in rotation. As the piston 6 reciprocates in the cylinder 3, 4 through distance D it varies the volume of the combustion chamber 5 (which is to say, the entire volume containing the Fuel/air mixture) from a maximum volume (Vmax) to a minimum volume (Vmin). The compression ratio of the cylinder 3, 4 is defined as a ratio of the maximum volume Vmax to the minimum volume Vmin.

10029] At least some of the cylinders 3, 4 are controllable by the control system 2 in normal operation of the engine (i.e. while the engine is producing power to rotate the crankshaft 7) to define, alternatively: an active mode in which combustion occurs in the respective cylinder, and an inactive mode in which combustion does not occur in the respective cylinder. In particular, at least the end cylinders 4 may be controllable in this way. Preferably, each of the cylinders 3, 4 is controllable in this way.

[0030] The control system 2 may be embodied in software stored in memory and running on a controller, i.e. a processor, to form part of an engine control unit ECU as well known in the art, and may control the cylinder 3, 4 by controlling the volume of diesel fuel 8 admitted to the cylinder, e.g. by controlling the operation of a fuel injector 9 through which the fuel is injected into the cylinder.

100311 In order to control a cylinder in the inactive mode, the control system 2 could prevent fuel from entering the cylinder 3, 4, e.g. by maintaining the fuel injector 9 in an inactive condition, or by preventing fuel from entering the injector 9. The air inlet and exhaust valves 10 may continue to operate normally or could operate differently in inactive mode compared with active mode, as known in the art.

100321 The control system 2 is arranged to operate the engine 1 alternatively in a full power mode, and in a reduced power mode -which is to say, the engine can be operated selectively in either mode. Reduced power mode may be selected for example when starting the engine, or when the engine is idling, or when the sensed load is below a threshold value.

100331 The control system 2 may control various operating parameter values of the engine I, e.g. the fuel injection volume and/or timing and the rotational speed of the turbocharger assembly (e.g. by means of a vvastegate, adjustable vanes controlling the flow of exhaust gas into the turbine, an exhaust gas bypass valve or otherwise as well known in the art).

100341 The control system 2 may receive sensed operating parameter values via sensors (not shown), e.g. intake manifold air pressure, cylinder pressure, crankshaft angle and rotational speed, NOx or other exhaust emissions, user control inputs, etc. [0035] The control system 2 may store in memory a map of reference or target values and may be configured to control the controllable operating parameters responsive to the sensed values by reference to the stored values, as well known in the art. In a similar way, the control system 2 may be configured to select the operating mode of the engine 1 to minimise emissions and optimise efficiency, responsive to the sensed values and/or user control inputs, and by reference to the stored values.

[0036] In the full power mode the control system 2 is arranged to control all of the cylinders 3, 4 in the active mode. Thus, it will be understood that in this specification, "full power mode" does not imply that the engine is producing its maximum power output; rather, it means that combustion occurs in all cylinders. Under such conditions the engine could be running at full load or less than full load.

[0037] In the reduced power mode, the control system 2 is arranged to control one or more of the cylinders 3, 4 in the inactive mode. Under such conditions, the engine I will be running at less than full load. The active cylinders could be producing their maximum power output, or less than their maximum power output.

[0038] The cylinders 3, 4 are arranged in at least one row. and include end cylinders 4 arranged at opposite ends of the at least one row, and intermediate cylinders 3 arranged between the opposite ends of the at least one row.

[0039] As illustrated, the engine may be an in-line engine, which is to say, all of the cylinders 3, 4 may be arranged in-line in a single row. For example, the engine could be a 6-cylinder or 8-cylinder in-line engine. Alternatively the cylinders could be arranged in two rows in a V configuration, typically with the cylinders axes angled alternately on opposite sides of a central plane along the length of the block. For example, the engine could be a V-8 or V-12 engine.

[0040] In accordance with a first aspect of the disclosure, the engine has a maximum brake mean effective pressure BMEP in the full power mode in excess of 30 bar (3 MPa), while the compression ratio is not more than 13.5: 1.

[0041] Advantageously, the compression ratio may be not more than 13: 1, for example, as low as 12.7: 1 or 12.8: 1.

100421 Advantageously, the BMEP in full power mode may be in excess of 32 bar. For example, the BMEP in frill power mode may be at least 33 bar.

[0043] The engine may be a direct injection engine (as shown), or an indirect injection engine.

100441 The diesel fuelled engine may be a dual fuelled engine configured to run on diesel fuel only but operable alternatively or additionally on a gas fuel.

[0045] The combustion chambers of the cylinders may have a total combined maximum volume of at least 20 1 (twenty litres). For example, the total combined volume could he 23 I or more.

[0046] The control system 2 may be arranged to run the engine 1 at a substantially invariable speed in normal use of the engine. For example, the rotational speed of the engine I may be arranged to vary by not more than about 5% when running stably in normal operation. A very low compression ratio of about 13:1 or less may be particularly useful in maximising output from a large diesel engine with high power density which runs at a constant speed, for example, as the prime mover in an electrical generator. For such applications the engine could run, for example, at a fixed crankshaft speed of 1500 or 1800 RPM.

[0047] Brake mean effective pressure (BMEP) is calculated conventionally as (T.2-11) / (Vci / nc), wherein BMEP is expressed in pascal; tic is the number of revolutions of the crankshaft per power stroke; T is engine output torque in newton-metre as measured by a dynamometer connected to the crankshaft; and Vd is the total displacement volume, which is to say, the total of (Vmax -Vmin) for all of the cylinders, in cubic metre.

[0048] Additionally, or alternatively and in accordance with a second aspect of the disclosure (which may be implemented also in other types of piston engine), when the engine 1 is operating in the reduced power mode, the control system 2 may be arranged to control the end cylinders 4 in the inactive mode, and to control at least some of the intermediate cylinders 3 in the active mode, until operation of the engine 1 in the reduced power mode is terminated (for example, by turning off the engine, or by commencing or resuming operation in full power mode responsive to increasing load on the engine).

[0049] In the reduced power mode of the engine 1, the control system 2 may be arranged to control each of the intermediate cylinders 3 alternately in the active mode and the inactive mode (i.e. in a skip-fire mode), such that on each cycle of the engine, different ones of the intermediate cylinders 3 are respectively in the active mode and the inactive mode. Thus, an intermediate cylinder 3 that is active during one cycle of the engine will be inactive during the next cycle. Different skip-fire patterns are possible as known in the art. For example, when operating in skip-fire mode, a cylinder could be operated alternately in active and inactive mode for a defined time period in each mode, e.g. 5 seconds in active mode followed by 5 seconds in inactive mode.

100501 Alternatively, the control system 2 may operate all of the intermediate cylinders 3 in the active mode.

100511 Alternatively, the control system 2 may operate some of the intermediate cylinders 3 in the active mode and the rest in a skip-fire mode.

100521 Alternatively, the control system 2 may operate some of the intermediate cylinders 3 in the inactive mode, and the rest in the active mode or the skip-fire mode.

Industrial Applicability

[0053] In tests, where turbochargers and fuel supply are set to deliver a maximum BMEP of at least 30 bar in normal operation on all cylinders, a strategy of selectively deactivating respective ones of the cylinders, e.g. during low load or cold start, is found to be surprisingly effective in controlling emissions from a turbocharged diesel engine below acceptable limits even when the compression ratio is reduced below what was previously regarded as the practical limit, e.g. to a value as low as 12.7: 1 or 12.8: 1. This advantageous effect is particularly observed in fixed speed engines, e.g. for use in generating sets, which may reflect the more constant combustion conditions in such engines.

[0054] In turbocharged diesel engines and other piston engines more generally, improved emissions control on part load or cold start can be achieved by selectively deactivating the end cylinders in the row while operating the remaining cylinders in active mode.

[0055] In accordance with the method of operation, the engine 1 is operated in the reduced power mode while the control system 2 controls the end cylinders 4 in the inactive mode, and at least some of the intermediate cylinders 3 in the active mode, until operation of the engine 1 in the reduced power mode is terminated.

[0056] In tests it is found that the end cylinders 4 tend to have a less effective combustion, hence a worse emissions profile, than the intermediate cylinders 3 when running cold or at low load. This may reflect that the end cylinders 4 tend to receive less heat by direct thermal conduction from the adjacent cylinders 3 while losing more heat to the exposed outer surface of the engine block 12, so that they heat up relatively more slowly, and lose heat relatively more quickly than the intermediate cylinders 3. By maintaining the end cylinders 4 in the inactive mode while some or all of the remaining cylinders 3 are operated in the active mode, the engine 1 as a whole is observed to operate with better combustion and reduced emissions compared with prior art selective deactivation strategies which do not distinguish between cylinders based on their position in the engine.

[0057] The advantageous effect may be observed particularly in an in-line engine, which is to say, an engine wherein all of the cylinders are arranged in-line in a single row.

[0058] Although the various aspects of the present disclosure can be applied independently of one another, they may be combined together to minimise emissions in a. turbocharged diesel engine.

[0059] By way of example, Fig. 3 shows the measured values of total hydro-carbons (HC) in parts per million by volume in the exhaust emissions of an in-line, 8 cylinder, direct injection, turbocharged, compression ignition diesel piston engine 1 with a total displacement volume in excess of 201, a maximum brake mean effective pressure (BMEP) of 33 bar, and a compression ratio below 13: I, as shown in Fig. 1.

[0060] The hydrocarbon emissions (HC) from the engine exhaust were measured in parts per million by volume (ppm) during a time interval (T) of about 400 seconds (s) after starting the engine from cold.

[0061] Trace A shows the engine I started from cold and run at idle speed in full power mode (i.e. with all of the cylinders 3, 4 in active mode, which is to say, with normal combustion in all cylinders 3, 4).

100621 Trace B shows the engine 1 started from cold and run al idle speed under the same conditions, in reduced power mode, i.e. with normal combustion in only some of the cylinders. In the test of Trace B, the two end cylinders 4 at the opposite ends of the engine block 12 were maintained in the inactive mode throughout the test, while the six remaining cylinders 3 in-between the end cylinders 4 were controlled in a skip-fire pattern -which is to say, each of those six remaining, intermediate cylinders 3 was controlled alternately in the active mode and the inactive mode, so that only some of those six remaining cylinders 3 were active on any cycle of the engine.

100631 In each trace, the small spike at about 180 seconds shows a small amount of load applied to the engine 1 and then removed again.

100641 Despite the unusually low compression ratio it can be seen that, following the initial spike in emissions at start-up (30 seconds), the strategy applied during startup (trace B) of maintaining the two end cylinders 4 in inactive mode while skip-firing the remaining six cylinders 3 reduces hydrocarbon emissions to an acceptable level of less than I 000ppm at the 120 seconds time point. This strategy resulted in a substantial reduction in emissions over the first four minutes compared with the emissions profile obtained by running on all cylinders 3, 4 (trace A).

100651 In summary, piston engine exhaust emissions may be reduced at low load or start-up by deactivating the cylinders 4 at opposite ends of the engine block 12 while running some or all of the remaining cylinders 3 in continuous or skip-fire mode. In another aspect, exhaust emissions from a turbocharged diesel engine 1 with a BMEP in excess of 30 bar may be controlled within acceptable limits by deactivating selected cylinders 3, 4 at low load or start-up, even where the compression ratio is 13.5: 1 or less.

[0066] Many further adaptations are possible within the scope of the claims.

100671 In the claims, reference numerals and characters are provided in parentheses, purely for ease of reference, and are not to he construed as limiting features.

LIST OF ELEMENTS

TITLE: Selective cylinder deactivation, particularly in turbocharged diesel engines with high power density FILE: 19-0985-73643 1 Engine 2 Control system 3 Intermediate cylinder 4 End cylinder Combustion chamber 6 Piston 7 Crankshaft 8 Diesel fuel 9 Fuel injector Air inlet and exhaust valves 11 Turbocharger 12 Engine block A Air Piston stroke distance Exhaust gas HC (ppm) Total hydro-carbons in parts per million by volume -1 5-T (s) Time in seconds Vmax Maximum volume of combustion chamber Vm n Minimum volume of combustion chamber

Claims

CLAIMSWhat is claimed is: 1. An internal combustion piston engine (1) including a control system (2) and a plurality of cylinders (3, 4), each cylinder (3, 4) defining a combustion chamber (5) and having a piston (6) reciprocable in the cylinder; at least some of the cylinders (3, 4) being controllable by the control system (2) in normal operation of the engine (1) to define alternatively: an active mode in which combustion occurs in the respective cylinder (3, 4), and an inactive mode in which combustion does not occur in the respective cylinder (3, 4); the engine (1) being arranged to operate alternatively: in a full power mode, wherein in the full power mode the control system (2) is arranged to control all of the cylinders (3, 4) in the active mode, and in a reduced power mode, wherein in the reduced power mode the control system (2) is arranged to control one or more of the cylinders (3, 4) in the inactive mode; the cylinders (3, 4) being arranged in at least one row, and including end cylinders (4) arranged at opposite ends of the at least one row, and intermediate cylinders (3) arranged between the opposite ends of the at least one row; wherein in the reduced power mode of the engine (1), the control system (2) is arranged to control the end cylinders (4) in the inactive mode, and to control at least some of the intermediate cylinders (3) in the active mode, until operation of the engine (1) in the reduced power mode is terminated.
2. An engine (1) according to claim 1, wherein in the reduced power mode of the engine, the control system (2) is arranged to control each of the intermediate cylinders (3) alternately in the active mode and the inactive mode, such that on each cycle of the engine, different ones of the intermediate cylinders (3) are respectively in the active mode and the inactive mode.
3. An engine (1) according to claim 1, wherein all of the cylinders (3, 4) are arranged in-line in a single row.
4. A method of operating an engine (1) as defined in claim I, including: operating the engine (1) in the reduced power mode, and controlling, by the control system (2), the end cylinders (4) in the inactive mode, and at least some of the intei mediate cylinders (3) in the active mode, until operation of the engine (1) in the reduced power mode is terminated.
5. A turbocharged, diesel filched, compression ignition, internal combustion piston engine (1) including a control system (2) and a plurality of cylinders (3, 4), each cylinder (3, 4) defining a combustion chamber (5) and having a piston (6) reciprocable in the cylinder (3, 4) to vary a volume of the combustion chamber (5) from a maximum volume (Vmax) to a minimum volume (Vmin), wherein a compression ratio of the cylinder (3, 4) is defined as a ratio of the maximum volume (Vmax) to the minimum volume (Vmin); at least some of the cylinders (3, 4) being controllable by the control system (2) in normal operation of the engine to define alternatively: an active mode in which combustion occurs in the respective cylinder (3, 4), and an inactive mode in which combustion does not occur in the respective cylinder (3, 4); the engine (1) being arranged to operate alternatively: in a full power mode, wherein in the full power mode the control system (2) is arranged to control all of the cylinders (3, 4) in the active mode, and in a reduced power mode, wherein in the reduced power mode the control system (2) is arranged to control one or more of the cylinders (3, 4) in the inactive mode; wherein in the full power mode the engine (1) has a maximum brake mean effective pressure BMEP in excess of 30 bar; and the compression ratio is not more than 13.5: 1.
6. An engine (1) according to claim 5, wherein the compression ratio is not more than 13: 1.
7. An engine (1) according to claim 5, wherein in the full power mode the engine (1) has a maximum brake mean effective pressure BMEP in excess of 32 bar.
8. An engine (1) according to claim 5, wherein in the full power mode the engine (I) has a maximum brake mean effective pressure BM EP of at least 33 bar.
9. An engine (1) according to claim 5, wherein the engine (1) is a direct injection engine.
10. An engine (1) according to claim 5, wherein the control system (2) is arranged to run the engine (1) at a substantially invariable speed in normal use of the engine.
11. An engine (1) according to claim 5, wherein the combustion chambers (5) of said cylinders (3,4) have a total combined maximum volume of at least 201.
12. An engine (1) according to claim 5, wherein the cylinders (3, 4) are arranged in at least one row, and include end cylinders (4) arranged at opposite ends of the at least one row, and intermediate cylinders (3) arranged between the opposite ends of the at least one row; and in the reduced power mode of the engine (1), the control system (2) is arranged to control the end cylinders (4) in the inactive mode, and at least some of the intermediate cylinders (3) in the active mode, until operation of thc engine (1) in thc reduced power mode is terminated.
13. An engine (l) according to claim 12, wherein in the reduced power mode of the engine (I), the control system (2) is arranged to control each of the intermediate cylinders (3) alternately in the active mode and the inactive mode, such that on each cycle of the engine (1), different ones of the intermediate cylinders (3) are respectively in the active mode and the inactive mode.
14. An engine (1) according to claim 12 herein all of the cylinders (3, 4) are arranged in-line in a single row.