NO20200463A1 - Design of combustion chambers in reciprocating engines that use highly flammable fuels - Google Patents

Description

The invention relates to the design of combustion chambers in piston engines that use highly flammable fuels.

Known technique:

Today's internal combustion engines are mainly designed to burn liquid or gaseous bio or fossil fuels that have good ignition and combustion properties. The problem with the transition to low- and zero-emission solutions is that internal combustion engines must be designed to also run on such fuels. Including, among other things, ammonia. The problem with several of these fuels is that they are both difficult to ignite, not flammable and have a low combustion rate. Ammonia is a typical case of this.

The current invention relates to the design of a combustion chamber with an antechamber in order to be able to use low-flammable fuels such as ammonia as fuel in internal combustion engines.

From known technology there are:

Traditional operation of diesel engines with prechamber/swirl chamber.

Use of coal as fuel, either in powder/dust form or mixed with water "coal slurry".

Honda's CVCC technology.

Mahle's Jet Ignition technology, PCT application WO2012061397A2, which describes the use of a pilot ignition system.

And Norwegian patent 343554, (PCT – WO/2019/035718)

"Zero emission propulsion system and generator system with ammonia as fuel" which describes the ignition of ammonia with the help of a pilot ignition.

Brief description of the invention:

The advantage of this invention is how the combustion chamber and pre-chamber are designed to optimize the ignition and combustion process of highly flammable fuels. This can be, among other things, ammonia, pure lignin or the lignin leaf in a liquid fuel such as ethanol or diesel. The combustion chamber can either be designed as part of the cylinder head or as a chamber in the piston. In order to achieve good ignition and combustion, in connection with the combustion chamber there will be a pre-chamber for igniting a pilot fuel which will ignite the mixture of air/main fuel in the combustion chamber.

In order to optimize pilot combustion in a separate antechamber, an additional intake valve can be used for the main combustion chamber to ensure either air or the air/pilot fuel mixture to the antechamber.

Description of figures:

Figure 1) is a sketch of an embodiment of a 4-stroke piston engine with a combustion chamber for burning an air/ammonia (NH3) mixture which is ignited with a pilot ignition from a pre-chamber. Ammonia is injected directly into the combustion chamber, and diesel into the antechamber. The diesel is ignited in the pre-chamber and is a pilot ignition of the air/ammonia mixture in the combustion chamber. The numbering follows Figure 4 in Norwegian patent 343554.

Figure 2) is a sketch of an embodiment of a two-part cylinder head.

Detailed description of the invention:

The system is for both 2-stroke and 4-stroke piston engines that follow Otto, Diesel, Atkinson or other principles for piston engines.

The same principle as described for piston engines can also be used for Wankel engines/rotary engines.

9-1) The piston engine's intake.

Here, air or an air/main fuel mixture will be sucked or pressed with a turbocharger or compressor into the cylinder. If the main fuel is supplied to the air in the intake, this can be done with a carburettor or injection nozzles for liquid fuels, or with a gas mixer or injection nozzles for gaseous fuels. For fuels in solid form, these will normally be fed directly into the combustion chamber (9-10).

9-2) Intake valve control.

For 4-stroke piston engines, this is a traditional valve control, alternatively with variable opening times and lift. The valve can also be electromechanically controlled with a solenoid valve, hydraulically or pneumatically controlled.

9-3) Piston engine exhaust outlet.

Engine exhaust outlet. The exhaust can optionally be led on to fully or partially drive other power-producing units such as a Stirling engine, or operation of a turbocharger. The exhaust heat can also be used for other purposes, such as water production on ships and other vessels. For generator systems, the exhaust heat can also be used to produce steam for the operation of a steam turbine.

9-4) Exhaust valve control.

For 4-stroke piston engines, this is traditional valve control. Also for 2-stroke piston engines with an exhaust valve, this will be a traditional valve control. Alternatively, it can have variable opening times and lifts. The valve can also be electromechanically controlled with a solenoid valve, hydraulically or pneumatically controlled.

9-5) The combustion chamber's intake.

Depending on whether the engines have an electric ignition system / foreign ignition or compression ignition, this intake will either supply the combustion chamber (9-10) and pre-chamber (9-6) with clean air or an air/pilot fuel mixture.

9-6) The anterior chamber.

This is the pre-chamber for igniting the pilot fuel. For engines with foreign ignition, the pilot fuel will be ignited by a spark plug (9-7), while for engines with compression ignition, there will be an injection nozzle and a glow plug (9-7) for the pilot fuel. The ratio between the volume of the pre-chamber and the volume of the combustion chamber (9-10) will normally be the same as the ratio between the stroke volume of the cylinder and the compression volume. The compression volume of the cylinder will consist of the volume between the piston (9-12) and the cylinder head (9-13) when the piston (9-12) is at top dead center, together with the volume of the combustion chamber (9-10) in addition to the volume of the pre-chamber. The reason for this is to ensure that as much as possible of the air or air/pilot fuel mixture that is in the combustion chamber (9-10) and the pre-chamber (9-6) at the beginning of the compression stroke is compressed into the combustion chamber (9-6). This is to ensure that an air or air/pilot fuel mixture in the antechamber has as little admixture of main fuel as possible. This is particularly important when using ammonia as the main fuel, as it is not desirable to have a combustion with both organic fuel and a

This is because it can lead to cyanide compounds [:C<=>mm

N:]<–>oniak together. Other ratios between the volumes of the cylinder, combustion chamber and the antechamber are also possible, and may be relevant especially when using lignin as the main fuel. Then, for example, a lean mixture (�>2) of air and petrol can be sucked in through the cylinder's intake (9-1) to improve combustion. Lignin is fed into the combustion chamber (9-10) via an injection device (9-11), and extra petrol and ignition of the pilot combustion takes place by the fact that there is both an extra injection nozzle for petrol and a spark plug which make up the pilot fuel's ignition device (9-7). An extra quantity of petrol will then be injected into the pre-chamber (9-6) so that the air/petrol mixture becomes stoichiometric in the pre-chamber (9-6). This is to ensure ignition of the pilot combustion with the spark plug (9-7).

9-7) The pilot fuel ignition device.

For engines with foreign ignition, this will be a spark plug. For engines with compression ignition, this will be an injection nozzle and a glow plug. For diesel engines, the diesel plant will be large enough so that the engine can be operated as a traditional diesel engine if the main fuel is not available as fuel.

9-8) The combustion chamber's intake valve.

Will normally be a normal intake valve. Due to the large heat load and low cooling effect that is normally in this part of the piston engine, it is important to design the valve control (9-9) so that sufficient cooling of this valve and the valve seat is ensured. Sodium (Na) filled valve stem may be required. Alternatively, another construction that provides sufficient cooling of this valve.

9-9) The combustion chamber's intake valve control.

This can be a traditional valve control with a camshaft, but to optimize operation and/or combustion, this can also be an electromechanically operated valve control with an electromagnet. Alternatively, there can be a hydraulic or pneumatic control of the combustion chamber's intake valve (9-8).

9-10) The combustion chamber.

For highly flammable fuels, and not least fuels with a low flame speed, it is important to have a combustion chamber designed to ensure that the energy turnover from combustion takes place as quickly as possible. Typically, this will mean a spherical, or nearly spherical, combustion chamber. The compression volume of the cylinder will consist of the volume between the piston (9-12) and the cylinder head (9-13) when the piston (9-12) is at top dead center together with the volume of the combustion chamber in addition to the volume of the pre-chamber (9-6). The combustion chamber can either be a chamber in the cylinder head (9-13) or in the top of the piston (9-12). Alternatively, divided by space in both the cylinder head (9-13) and the piston (9-12). If the combustion chamber is at the top of the piston (9-12) the pre-chamber (9-6) must have a connection with the combustion chamber to ensure that the pilot combustion provides a good ignition of the main fuel. If the combustion chamber is in the cylinder head (9-13), it is important that the outlet from the combustion chamber to the cylinder is sufficiently large so that there is no pressure loss for the burned and unburned gases.

9-11) Injection nozzle for the main fuel.

If the air/main fuel mixture is not mixed outside the engine in a carburettor, gas mixer or via fuel nozzles mounted on or in the intake (9-1), these will be injection nozzles for direct injection of fuel into the combustion chamber (9-10). These can be of all conventional nozzle designs for both liquid and gaseous fuels. For solid fuels, other dosing principles can be used. For pure lignin, a pump device of heated lignin will be used. Lignin, which is an amorphous material, will normally have a Tg (glass-transition temperature) of between 250<o>C to 500<o>C. This means that when heated, a viscous material can be obtained which can be pumped into the combustion chamber (9-10) with the help of a "pump nozzle" device or other pump device. A pump or injection systems for solid fuels will normally also have to be able to pump liquid fuels in order to be able to empty the system for solid fuels before a possible shutdown. This could be the case when using lignin. A hydraulically operated system would be an advantage if the fuel must reach a certain temperature before it can be used. This may be the case for lignin. When using solid fuels such as lignin or coal/biochar, the injection nozzle(s) for the main fuel should be positioned so that the main fuel is pumped or sprayed directly in front of, or directly in the outlet of the pre-chamber (9-6) to the combustion chamber (9-10) to use gas the flow from the pre-chamber (9-6) burnt gases to disperse and mix this main fuel with the air in the pre-chamber (9-10) and the cylinder.

9-12) Piston

The piston in the cylinder of the piston engine. All or part of the combustion chamber (9-10) can be a chamber at the top of the piston, as it is in many cases for direct injection diesel engines. In the case where the combustion chamber (9-10) is part of the piston, the outlet of the pre-chamber (9-6) must be directed directly towards this combustion chamber (9-10).

9-13) Cylinder head

The cylinder head can be two- or multi-part. Both because it can be simpler from a production-technical standpoint in the manufacture of the cylinder heads, but also to facilitate service and maintenance. When using marine fuel oils as pilot fuel, and/or when using solid main fuels such as lignin, a split cylinder head can be particularly important to facilitate cleaning of the combustion chamber (9-10) and pre-chamber (9-6) of soot and other deposits.

For direct injection diesel engines, the principle of a pilot ignition can also be used. The advantage is to reduce the pressure in the compression stroke, ensure better combustion of the diesel and burn a larger proportion of the fuel at top dead center to improve the efficiency of the engine. The injection nozzle(s) (9-11) for the main fuel are positioned so that the main fuel (diesel) is pumped or sprayed directly in front of the pre-chamber (9-6) outlet to the combustion chamber (9-10) in order to use the gas flow from the pre-chamber (9- 6) burnt gases to both ignite diesel from the main injection nozzle (9-11) and to ensure good atomization of the diesel and mixing with the air in the combustion chamber (9-10).

Configuration of the invention for three typical areas of use based on the design example in Figure 1:

A) 4-stroke "dual fuel" engine with ammonia as main fuel and with diesel as pilot fuel.

The system here will be as illustrated schematically in Figure 1, with the exception of mixing air and ammonia. Ammonia is used as the main fuel, which is mixed in a gas mixer in the intake (9-1) of the engine. This is to ensure a good mixture of air and ammonia. Diesel oil will be used as pilot fuel. To ensure good combustion of the diesel oil, it will be burned with an excess of air. Therefore, the air/ammonia mixture that is sucked/pressed in via the engine's intake (9-1) will be a "fat" mixture so that after combustion the excess air for the pilot combustion will compensate for the "fat" air/ammonia mixture, so that overall be a stoichiometric combustion of both ammonia and diesel in the engine.

Clean air will be sucked/pressed in via the combustion chamber's intake valve (9-8) so that during the intake this amount of air will correspond to the volume of the antechamber (9-6) and combustion chamber (9-10). The combustion chamber's valve control (9-9) is electromechanically controlled so that an optimal filling of air is ensured in the antechamber (9-6) and the combustion chamber (9-10). During compression, most of this air will then be pressed into and compressed in the antechamber (9-6), and only a smaller amount of an air/ammonia mixture will mix with the air in the antechamber (9-6). A pilot injection of diesel will take place at an injection nozzle (9-7) and possibly ignited using a glow plug (9-7). This combustion will ignite the main mixture of air and ammonia in the combustion chamber (9-10). One possibility to reduce NOx emissions is to burn a "fat" mixture in the engine, and control the valves so that at the end of the exhaust stroke and the start of the intake stroke, the exhaust valve(s) and the combustion chamber's intake valve (9-8) will be open to be able to supply extra air to the exhaust. Thus, the extra ammonia together with the now added air will contribute to an SCR cleaning of the exhaust. Alternatively, extra air and/or ammonia must be pumped or injected into the exhaust.

B) 2-stroke "dual fuel" engine with ammonia as main fuel and with diesel as pilot fuel.

For this type of engine, it will not be necessary to have a separate pilot intake system (9-5, 9-8 and 9-9) as here air will only be sucked/compressed via the intake (9-1) in the intake stroke. Ammonia will here be injected into the combustion chamber (9-10) with an injection nozzle (9-11), while diesel as pilot fuel is injected and ignited (9-7) in the antechamber (9-6). This is because it is not desirable to mix combustion of organic substances with ammonia because this can form cyanide compounds [:C<=>N:]<– >.

For 2-stroke engines, it would be desirable to have exhaust valve(s) in the cylinder head (9-13) to obtain optimal "flushing" of the cylinder. This (these) exhaust valve(s) can be electromechanically operated to achieve the desired degree of scavenging.

It would be desirable to have a "fat" mixture of air/ammonia to reduce the formation of nitrogen oxides (NOx).

The exhaust valve(s) will be able to be controlled to regulate the amount of air that is pressed/pumped out into the exhaust before the exhaust valve closes. This is for possible exhaust cleaning. C) 2-stroke "dual fuel" engine with lignin as main fuel and with diesel as pilot fuel.

The operation of such engines will be similar to the operation of a 2-stroke "dual fuel" engine with ammonia as described in point B, with the exception of the supply of the main fuel lignin. The lignin will first be heated to a temperature above Tg to become viscous, before it is pumped/injected with the injection device for the main fuel (9-11) into the outlet of the pre-chamber (9-6). Here, a hydraulically operated injection device (9-11) would be preferred in order to be able to regulate the supply of lignin so that this only happens when the lignin is viscous.

Diesel as pilot fuel will start to be injected into the antechamber with the injection nozzle (9-7) before the lignin is pumped/injected into the outlet of the antechamber (9-6) so that the combustion of diesel and thereby the pressure rise in the antechamber has started so that the lignin is blown out in the combustion chamber (9-10). There is one (or more) exhaust valve(s) in the cylinder head (9-13) to get optimal "flushing" of the cylinder. This (these) exhaust valves can be electromechanically operated to achieve the desired degree of scavenging. The exhaust valve(s) will be able to be controlled to regulate the amount of air that is pressed/pumped out into the exhaust before the exhaust valve closes. This is important in order to "flush" the cylinder of unburnt lignin (ash), as well as ensure that deposits do not settle on the exhaust valve(s).

Claims (1)

Patent claim: Requirement 1) Design of combustion chambers in reciprocating engines that use highly flammable fuels, c h a r a c t e r i s e s w e d to use a pre-chamber (9-6) for igniting a pilot fuel which will be used as an ignition source for a mixture of heavy flammable fuel and air in a combustion chamber (9-10). Requirement 2) Design of combustion chambers in reciprocating engines that use highly flammable fuels according to claim 1, c a r a c t e r i s e r s e that the engine's compression volume will consist of both: - volume between cylinder head (9-13) and piston (9-12) when the piston (9-12) is at top dead center, in addition to - volume of combustion chamber (9-10), as well - anterior chamber (9-6). Requirement 3) Design of combustion chambers in reciprocating engines that use highly flammable fuels according to claim 1, c a r a c t e r i s e r s e that for engines where air and the main fuel are mixed in the engine's intake (9-1), the size in volume between the combustion chamber (9-10) and the pre-chamber (9-6) will correspond to the engine's compression ratio. Requirement 4) Design of combustion chambers in reciprocating engines that use highly flammable fuels according to claim 1, c a r a c t e r i s e r s e that for 4-stroke engines where air and the main fuel are mixed in the engine's intake (9-1), the combustion chamber (9-10) will have its own intake system consisting of an intake (9-5), an intake valve (9-8) with intake valve control (9-9) for air or an air/pilot fuel mixture. Requirement 5) Design of combustion chambers in reciprocating engines that use highly flammable fuels according to claim 1, c a r a c t e r i s e r s e that where the combustion chamber (9-10) is part of the cylinder head (9-13) the outlet of the pre-chamber (9-6) will be located at the other end of the combustion chamber (9-10) than the outlet of the combustion chamber (9-10) to the cylinder. Requirement 6) Design of combustion chambers in reciprocating engines that use highly flammable fuels according to claim 1, c a r a c t e r i s e r s e that where the combustion chamber (9-10) is part of the piston (9-12) the outlet of the pre-chamber (9-6) will be positioned so that it is aimed directly at the combustion chamber (9-10) to ensure good ignition of the main fuel.