FUEL SYSTEM

Description

PRIORITY CLAIM

This patent application claims priority to and the benefit of European Patent Application No. 24315491.1, filed Oct. 23, 2024, and European Patent Application No. 25207304.4, filed Oct. 7, 2025, the entire contents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a combustion tool. In particular, the present disclosure relates to a combustion tool fuel delivery system.

SUMMARY

According to a first aspect, the present disclosure relates to a combustion tool fuel delivery system comprising a reservoir connection mechanism for connecting, for example releasably connecting, to a reservoir containing combustible gas; a chamber connection mechanism for connecting to a combustion chamber of the combustion tool; and a metering system located between the reservoir connection mechanism and the chamber connection mechanism, the metering system for variably controlling an amount, for example a volume, of combustible gas provided from the reservoir connection mechanism to the chamber connection mechanism.

According to embodiments, the reservoir connection mechanism is for connecting to a reservoir containing combustible gas at a pressure of greater than 2 bar, for example greater than 5 bar, 10 bar, 14 bar, 20 bar, 25 bar, 50 bar, 100 bar, 150 bar, 200 bar, 250 bar 300 bar, 350 bar, 400 bar, 450 bar, 500 bar, 550 bar, 600 bar, or 650 bar, for example at 20° C.

According to embodiments, the metering system comprises an injection valve with a variable opening time, the combustion tool fuel delivery system optionally comprising a pressure gauge for measuring pressure upstream of the injection valve, the combustion tool fuel delivery system optionally comprising a controller configured to open the injector valve and to then close the injector valve, for example when a threshold pressure is reached upstream of the injector valve, or optionally the injector valve being configured to receive a control signal to open the injector valve and to then close the injector valve, for example when a threshold pressure is reached upstream of the injector valve.

According to embodiments, the metering system comprises a pressure reducing valve and/or pressure regulator located between the reservoir connection mechanism and the injection valve.

According to embodiments, the metering system comprises a variable volume dosing chamber, for example comprising an adjustable wall partially defining a variable gas volume, and optionally comprising an outlet valve, for example the outlet valve being in fluidic communication with the chamber connection mechanism and located between the chamber connection mechanism and the variable gas volume, the combustion tool fuel delivery system optionally comprising a controller for controlling the volume of the variable gas volume by adjusting the adjustable wall.

According to embodiments, the metering system comprises a pressure reducing valve and/or a pressure regulator located between the reservoir connection mechanism and the variable volume dosing chamber.

According to embodiments, the metering system comprises a variable pressure regulator downstream of the reservoir connection mechanism, and a dosing chamber upstream of the variable pressure regulator, the combustion tool fuel delivery system optionally comprising a valve, for example an on/off valve, being in fluidic communication with the chamber connection mechanism and located between the chamber connection mechanism and a gas volume of the dosing chamber, the combustion tool fuel delivery system optionally comprising a controller for controlling the pressure at an outlet of the variable pressure regulator and for optionally controlling the valve, or optionally the variable pressure regulator and/or the valve being configured to receive a control signal to control the pressure at the outlet of the variable pressure regulator or to control the valve, respectively.

According to embodiments, the combustion tool fuel delivery system comprises a first valve, for example a solenoid valve, with a variable opening time, and a dosing chamber, the fist valve being located between the reservoir connection mechanism and the dosing chamber, the combustion tool fuel delivery system optionally comprising a second valve, for example an on/off valve, being in fluidic communication with the chamber connection mechanism and located between the chamber connection mechanism and a gas volume of the dosing chamber, the combustion tool fuel delivery system optionally comprising a controller for controlling the opening time of the first valve and optionally controlling operation of the second valve.

According to embodiments, the metering system comprises a fuel delivery assistance system, the fuel delivery assistance system comprising: a chamber, for example a cylinder; a piston slidably located within the chamber; a first inlet at an inlet end of the chamber facing a first side, for example an inlet side, of the piston wherever the piston is located in the chamber, the first inlet being in fluidic communication with the reservoir connection mechanism; a second inlet in fluidic communication with the reservoir connection mechanism and located at a position along the chamber, and being spaced from the first inlet by a distance greater than a thickness of the piston; an outlet proximal or at the outlet end of the chamber; wherein, either the second inlet is located closer to the inlet end of the chamber than the outlet end of the chamber, or a valve, for example an on/off valve is located downstream of the second inlet to selectively allow or prevent pressurised gas flowing to the second inlet.

According to embodiments, the chamber connecting mechanism comprises a plurality of inlet conduits for transferring combustible gas to the combustion chamber.

According to embodiments, the reservoir connection mechanism is for connecting to a reservoir containing hydrogen gas.

According to a second aspect, the present disclosure relates to a combustion tool comprising a combustion tool fuel delivery system according to the first aspect, optionally comprising a combustion chamber, the chamber connection mechanism being connected to the combustion chamber.

According to embodiments, the combustion tool comprises a combustion pre-chamber located between the combustion chamber and the chamber connection mechanism, and optionally an ignition source located in the pre-chamber, wherein, optionally the pre-chamber has a smaller cross-sectional area and/or a smaller volume than the combustion chamber.

According to embodiments, the combustion tool is a combustion nailer or a combustion stapler.

According to a third aspect, the present disclosure relates to a combustion nailer comprising the combustion tool fuel delivery system according to the first aspect.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE FIGURES

Example embodiments of the present disclosure are illustrated in the accompanying drawings.

FIG. 1 is a schematic of a combustion tool fuel system according to a first example embodiment of the present disclosure.

FIG. 2 is a schematic of a combustion tool fuel system according to a second example embodiment of the present disclosure.

FIG. 3 is a schematic of a combustion tool fuel system according to a third example embodiment of the present disclosure.

FIG. 4 is a schematic of a combustion tool fuel system according to a fourth example embodiment of the present disclosure.

FIG. 5 is a schematic of a combustion tool fuel system according to a fifth example embodiment of the present disclosure.

FIGS. 6A, 6B, 6C, and 6D are schematics of a fuel delivery assistance system according to a first example embodiment of the present disclosure.

FIG. 7 is a schematic of fuel delivery assistance system according to a second example embodiment of the present disclosure.

FIG. 8 is a schematic of a two-chamber combustion chamber of one embodiment of the present disclosure.

FIG. 9 is a schematic of a two-inlet conduit combustion chamber of one embodiment of the present disclosure.

DETAILED DESCRIPTION

While the systems, devices, and methods described herein may be embodied in various forms, the drawings show, and the specification describes certain exemplary and non-limiting embodiments. Not all components shown in the drawings and described in the specification may be required, and certain implementations may include additional, different, or fewer components. Variations in the arrangement and type of the components; the shapes, sizes, and materials of the components; and the manners of connections of the components may be made without departing from the spirit or scope of the claims. Unless otherwise indicated, any directions referred to in the specification reflect the orientations of the components shown in the corresponding drawings and do not limit the scope of the present disclosure. Further, terms that refer to mounting methods, such as mounted, connected, etc., are not intended to be limited to direct mounting methods but should be interpreted broadly to include indirect and operably mounted, connected, and like mounting methods. This specification is intended to be taken as a whole and interpreted in accordance with the principles of the present disclosure and as understood by one of ordinary skill in the art.

The illustrated example embodiments relate to combustion tool fuel systems. A combustion tool is a tool which is powered by combustion of a gas and may otherwise be referred to as a gas tool.

In these embodiments the amount of combustible fuel or combustible gas provided to a combustion chamber determines how rich or lean combustion is within the combustion chamber, and so can be used to determine an amount of power delivered by the combustion tool. For example, in a combustion nailer or stapler the leanness of combustion in a combustion chamber determines how much energy is delivered to a nail to drive the nail into a substrate. These embodiments are especially suitable for combustion tools where the combustible gas is stored at high pressure, for example 300 to 700 bar at 20° C., for example where the combustible gas is hydrogen. By way of an example, traditional hydrocarbon fuels are typically stored at less than 20 bar at 20° C. in a combustion tool reservoir, for example at 2 bar at 20° C. The combustible has referred to herein and in the appended claims may be either in a vapour phase or may be liquified combustible gas.

FIG. 1 illustrates a schematic of a combustion tool fuel system 10. The combustion tool fuel system 10 has a reservoir 11 and a combustion chamber 19 at either end of a fluid flow path, the fluid flow path indicated by arrows in FIG. 1. When in use in a combustion tool (not shown), the reservoir 11 may be removable for refilling and/or replacement. A combustion tool fuel delivery system is defined as the parts shown in FIG. 1 without the reservoir 11 and combustion chamber 19. The combustion tool fuel delivery system has a reservoir connection mechanism 111 for connecting, for example releasably connecting, to the reservoir 11 containing combustible gas, for example hydrogen gas. The combustion tool fuel delivery system has a chamber connection mechanism 191 for connecting to the combustion chamber 19. A metering system is located between the reservoir connection mechanism 111 and the chamber connection mechanism 191. The metering system is for variably controlling an amount, for example a volume, of combustible gas provided from the reservoir 11 via the reservoir connection mechanism 111 to the combustion chamber 19 via the chamber connection mechanism 191.

In the example of FIG. 1 the metering system comprises an injection valve 13 with a variable opening time. By varying the opening time of the injection valve 13 a variable volume of combustible gas may be provided to the combustion chamber 19 to control a leanness of the fuel and air mixture. The combustion tool or the combustion tool fuel delivery system may also have a pressure gauge (not shown) for measuring pressure upstream of the injection valve 13. The pressure gauge may measure pressure in a conduit between the injection valve 13 and the chamber connection mechanism 191, at the chamber connection mechanism 191, or in the combustion chamber 19. The combustion tool fuel delivery system or the combustion tool may have a controller (not shown). The controller may be configured to open the injector valve and to then close the injector valve. The controller may be configured to open the injector valve and to then close the injector valve when a threshold pressure is reached upstream of the injector valve 13. The injector valve 13 may additionally or alternatively be configured to receive a control signal to open the injector valve and to then close the injector valve, for example when a threshold pressure is reached upstream of the injector valve. The control signal may be provided by the controller comprised in the combustion tool or combustion tool fuel delivery system, or may be provided by an external device (not shown) such as an external controller.

Referring now to FIG. 2, there is shown another example of a combustion tool fuel system 20. Features of the combustion tool fuel system 20 of this example which are similar to features of the combustion tool fuel system 10 of the example of FIG. 1, are denoted with reference numerals starting with ‘2’ instead of a ‘1’.

The combustion tool fuel delivery system of this example differs from that shown in FIG. 1 in that the metering system comprises a pressure reducing valve and pressure regulator 22 located between the reservoir connection mechanism 211 and the injection valve 23. The pressure reducing valve and pressure regulator 22 reduces and regulates the pressure of fuel from the reservoir 21 for delivery to the injection valve 23. This may be beneficial because the pressure in the reservoir 21 reduces as combustible gas is consumed, and so use of the pressure reducing valve and pressure regulator 22 mechanism that the pressure delivered to the injection valve 23 is constant. In other examples, either one of the pressure reducing valve or the pressure regulator may be omitted such that the remaining pressure reducing valve or pressure regulator reduces the pressure of gas delivered to the injection valve 23. Operation of the injection valve 23 may be by the same mechanism as described with reference to FIG. 1.

Referring now to FIG. 3, there is shown another example of a combustion tool fuel system 30. Features of the combustion tool fuel system 30 of this example which are similar to features of the combustion tool fuel system 20 of the example of FIG. 2, are denoted with reference numerals starting with ‘3’ instead of a ‘2’.

The combustion tool fuel delivery system 30 of this example differs from that shown in FIG. 2 in that the metering system comprises a variable volume dosing chamber 34 instead of an injection valve. The variable volume dosing chamber 34 has an adjustable wall (not shown) partially defining a variable gas volume (not shown), and may have an outlet valve (not shown). If present, the outlet valve is in fluidic communication with the chamber connection mechanism 391 and is located between the chamber connection mechanism 391 and the variable gas volume. The outlet valve may instead be an on/off valve located downstream of the variable volume dosing chamber 34.

The adjustable wall may be adjusted via a control signal from a controller comprised in the combustion tool or the combustion tool fuel delivery system, or from an external device. In this example the metering system comprises a pressure reducing valve and/or pressure regulator 32 located between the reservoir connection mechanism 311 and the variable volume dosing chamber 34. However, one of the pressure reducing valve or pressure regulator 32 may be omitted. The amount of combustible gas delivered to the combustion chamber 39 of this example is controlled by controlling the volume of the variable volume dosing chamber 34, because gas is delivered to the variable volume dosing chamber at a constant pressure, as controlled by the pressure regulator and/or pressure reducing valve 32. Any of the pressure regulator, outlet valve and on/off valve, if present, may also be controlled by a control signal.

Referring now to FIG. 4, there is shown another example of a combustion tool fuel system 40. Features of the combustion tool fuel system 40 of this example which are similar to features of the combustion tool fuel system 30 of the example of FIG. 3, are denoted with reference numerals starting with ‘4’ instead of a ‘3’.

The combustion tool fuel delivery system of this example differs from that shown in FIG. 3 in that the metering system comprises an optional pressure reducer 42, a variable pressure regulator 45, a dosing chamber 46 and a valve, for example an on/off valve 47. In this example the dosing chamber 46 has a fixed volume. The variable pressure regulator 45 is downstream of the reservoir connection mechanism 411. The dosing chamber 46 is upstream of the variable pressure regulator 45. The on/off valve 47 is in fluidic communication with the chamber connection mechanism 491 and located between the chamber connection mechanism 491 and a gas volume of the dosing chamber 46.

In this example, the pressure reducer 42 reduces the pressure of gas delivered from the reservoir 41 via the reservoir connection mechanism 411. The variable pressure regulator 45 regulates the pressure to a desired amount, and the gas, at the desired pressure, is delivered to the dosing chamber 46. The on/off valve 47 is then opened to deliver the combustible gas from the dosing chamber 46 to the combustion chamber 49. The leanness of combustible gas delivered to the combustion chamber 49 is controlled by controlling the variable pressure regulator 45, as more gas particles will be provided to the dosing chamber 46 if a greater pressure is used. The variable pressure regulator 45 and the on/off valve 47 may be controlled via a control signal from a controller comprised in the combustion tool or the combustion tool delivery system, or from an external device.

Referring now to FIG. 5, there is shown another example of a combustion tool fuel system 50. Features of the combustion tool fuel system 50 of this example which are similar to features of the combustion tool fuel system 40 of the example of FIG. 4, are denoted with reference numerals starting with ‘5’ instead of a ‘4’.

The combustion tool fuel delivery system of this example differs from that shown in FIG. 4 in that the metering system comprises a first valve, for example a solenoid valve 58, a dosing chamber 56 and a second valve, for example an on/off valve 57. In this example, there is also a pressure gauge 561 associated with the dosing chamber 56, for example in the dosing chamber or at an inlet to the dosing chamber 56. The pressure gauge 561 measures pressure within the dosing chamber 56. The solenoid valve 58 is located between the reservoir connection mechanism 511 and the dosing chamber 56. The on/off valve 57 is in fluidic communication with the chamber connection mechanism 591 and is located between the chamber connection mechanism 591 and a gas volume of the dosing chamber 56. In use, the solenoid valve 58 is opened until a threshold pressure is achieved in the dosing chamber 56, as measured by the pressure gauge 561. A pressure reading from the pressure gauge 561 may be measured by a controller comprised in the combustion tool or the combustion tool fuel delivery system, or by an external device. The controller or external device may control the opening time of the solenoid valve 58 and may control operation of the on/off valve 57.

Referring now to FIG. 6, there is shown a fuel delivery assistance system 60. In this example, the fuel delivery assistance system 60 is connected to a reservoir at one end, via reservoir connection mechanism 611, and connected to a combustion chamber 69 at another end, via chamber connection mechanism 691. The fuel delivery assistance system 60 has a chamber, for example a cylinder 601, which provides a dosing chamber. A piston 602 is slidably located in the cylinder 601, and, when a gas pressure inside the cylinder 601 is ambient, a resilient biasing mechanism, for example a spring 603, urges the piston 602 to an inlet end of the cylinder 602. The cylinder 601 has a first inlet 604 at the inlet end of the cylinder 601, facing a first side, or inlet side, of the piston 602 wherever the piston 602 is located in the cylinder 601. The first inlet 604 is in fluidic communication with the reservoir connection mechanism 611. The cylinder 601 has a second inlet 605 located partway along the cylinder 601, closer to the inlet end of the cylinder 601 than an outlet end of the cylinder 601, and spaced from the first inlet 604 by a distance greater than a thickness of the piston 602. The second inlet 605 is in fluidic communication with the reservoir connection mechanism 611. There is a valve, for example an on/off valve 606, located in fluidic communication with, and between, the first and second inlets 604, 605 and the reservoir connection mechanism 611.

The cylinder 601 has an outlet 607 at the outlet end of the cylinder 601. The outlet 607 is in fluidic communication with the chamber connection mechanism 691. In some examples there may be an outlet valve (not shown) located at the outlet of the cylinder 601, or between the outlet of the cylinder 601 and the chamber connection mechanism 691.

In this example the fuel delivery assistance system 60 comprises a stop conduit 608 located nearer to the outlet end of the cylinder 601 than the inlet end. The stop conduit 608 is open to the cylinder at two locations spaced apart along the length of the cylinder, by a distance greater than the thickness of the piston 602.

In some examples a pressure reducer and/or pressure regulator may be provided between the reservoir connection mechanism 611 and the valve 606. In some examples a variable pressure regulator may be provided between the reservoir connection mechanism 611 and the valve 606. In some examples the valve 606 may be a solenoid valve.

Operation of the fuel delivery assistance system 60 is now described.

As shown in FIG. 6A, before the valve 606 is opened, a force from the spring 603 urges the piston 602 to the inlet end of the cylinder 601 such that the first inlet 604 is located on a side of the piston 602 facing the inlet side of the piston 602 and the second inlet 605 is located on a side of the piston 602 facing a second side, or outlet side, of the piston 602.

As shown in FIG. 6B, when the valve 606 is opened such that pressurised gas is able to flow from the reservoir to the first and second inlets 604, 605, pressurised gas enters the cylinder 601 on the inlet side of the piston 602 and on the outlet side of the piston 602. However, because an outlet volume inside the cylinder 601, which is the volume on the outlet side of the piston 602, is greater than an inlet volume inside the cylinder 601, which is on the inlet side of the piston 602, the piston 602 moves towards the outlet end of the cylinder 601. When no outlet valve is present, combustible gas also starts to flow into the combustion chamber 69 through the outlet of the cylinder 601. The piston 602 passes the second inlet 605, thereby preventing any more combustible gas from entering the outlet volume of the cylinder 601.

This effect is still realised if an outlet valve is present, but combustible gas does not begin to flow into the combustion chamber 69 yet.

Because the valve 606 is still open, pressurised gas continues to be delivered to the inlet volume of the cylinder 601 through both the first and second inlets 604, 605, and so this pressurised gas drives the piston 602 to the outlet end of the cylinder 601. In this way, most or all of the combustible gas which was delivered to the outlet volume of the cylinder 601 can be delivered to the combustion chamber 69.

As shown in FIG. 6C, when the stop conduit 608 is present, and when the piston passes the first opening of the stop conduit 608, combustible gas is able to flow from the inlet volume to the outlet volume, which causes the pressure in the outlet volume to increase and so stop the movement of the piston 602.

In FIG. 6D, combustion takes place in the combustion chamber 69, valve 606 is closed, and an exhaust valve 609 is opened, the exhaust valve 609 being in fluidic communication with the inlet volume. The expansion of gas from the combustion chamber causes the piston 602 to return to the inlet end of the cylinder 601, and any combustible gas in the inlet volume is expelled through the exhaust valve 609.

It will be appreciated that the cylinder 601 of the fuel delivery assistance system 60 operates similarly to a dosing chamber with a fixed volume, because supply of combustible gas to the inlet volume is stopped when the piston 602 passes the second inlet 605. Therefore, the amount of combustible gas supplied to the combustion chamber can be controlled by changing an opening time of the valve 606, when the valve 606 is a solenoid valve, or by varying the inlet pressure via a regulator. In this way, a dosing chamber is provided which can be used in place of the dosing chambers 46, 56 in the combustion tool fuel systems 40, 50 shown in FIGS. 4 and 5.

Referring now to FIG. 7 there is shown a second example of a fuel delivery assistance system 70. Features of this fuel delivery assistance system 70 which are similar to those of the fuel delivery assistance system 60 of the previous example are denoted with the same reference number starting with ‘7’ instead of ‘6’.

This example fuel delivery assistance system 70 differs from the example shown in FIG. 6 in that an inlet end of the chamber 701 has a smaller cross-sectional area than the outlet end. The piston 702 has a correspondingly larger cross-sectional area on the outlet side than the inlet side.

In this example, an inlet valve 706 is located between the reservoir 71 and the first inlet 704 of the chamber 701. This example differs in that the second inlet 705 is in fluidic communication with a first outlet 7010, the first outlet 7010 being located in the inlet volume of the chamber 701. A second valve 7011 is located in a fluid conduit between the first outlet 7010 and the second inlet 705.

As in the previous example, the combustion chamber 79 is in fluidic communication with a second outlet 707 of the chamber 701, located in the outlet volume of the chamber 701. In this example, a third valve 7012 is located between the second outlet 707 and the chamber connection mechanism 791.

Operation of this fuel delivery assistance system 70 is now described.

Firstly, when all valves are closed and the chamber 701 is not pressurised, the spring 703 urges the piston 702 all the way to the inlet end of the chamber 701.

When the inlet valve 706 is opened, but other valves remain closed, the piston 702 moves all the way to the outlet end of the chamber 701 due to pressurised gas entering the inlet volume of the chamber 701, on the inlet side of the piston 702.

The inlet valve 706 is then closed and the second valve 7011 is opened, such that pressurised gas flows from the inlet volume of the chamber 701 to the outlet volume of the chamber 701. Due to the larger cross-sectional area of the piston 702 at the outlet side than the inlet side, the piston 702 is forced all the way to the inlet end of the chamber 701. The second valve 7011 is then closed. In examples, the second valve 7011 can be opened for less time so that less combustible gas travels from the inlet volume to the outlet volume. In this case, the piston 702 would not move all of the way to the inlet end of the chamber 701 and so a variable volume dosing chamber is provided.

The third valve 7012 is then opened, such that pressurised gas in the outlet volume is able to travel into the combustion chamber 79 via the chamber connection mechanism 791. The inlet valve 706 is also opened, whilst the second valve 7011 remains closed, such that pressurised gas from the reservoir 71 is provided to the inlet volume of the chamber 701. This forces the piston 702 to move to the outlet end of the chamber 70, and so expels all, or most of, of the combustible gas from the outlet volume of the chamber 701 and into the combustion chamber 79.

Exhaust valve 709 may be opened to expel any pressurised gas from the outlet volume of the chamber 701, before or after combustion. If the exhaust valve 709 and the second valve 7011 are both opened, then combustible gas can also be expelled from the inlet volume of the chamber 701.

Similarly to the example of FIG. 6, the fuel delivery assistance system 70 of this example may have a pressure reducer and/or pressure regulator located between the inlet valve 706 and the reservoir 71. The pressure regulator may a variable pressure regulator and may be used to vary the pressure of gas supplied to the chamber 701, to adjust the leanness of combustion, as described previously. Additionally, or alternatively, the inlet valve 706 may be a solenoid valve, which may be opened for a specific amount of time to control the leanness of the combustion, for example by measuring pressure in the chamber 701 and controlling the solenoid valve 706 to be open until a threshold pressure is reached. In this way, a dosing chamber is provided which can be used in place of the dosing chambers 46, 56 in the combustion tool fuel systems 40, 50 shown in FIGS. 4 and 5. By varying the amount that the piston 702 moves to the inlet end of the chamber 701, a variable volume dosing chamber can be provided as described previously, to be used in the combustion tool fuel system 30 shown in FIG. 3.

Referring now to FIG. 8, there is shown a combustion tool fuel system 80 which is similar to the combustion tool fuel system 50 shown schematically in FIG. 5. Features of the combustion tool fuel system 80 of this example which are similar to features of the combustion tool fuel system 50 of the example of FIG. 5 are denoted with reference numerals starting with ‘8’ instead of ‘5’. In this example, the metering system comprises a first valve, for example a solenoid valve 88, a dosing chamber 86 and a second valve, for example an on/off valve 87. In this example, there is also a pressure gauge 861 associated with the dosing chamber 86, for example in the dosing chamber 86 or at an inlet to the dosing chamber 86. The pressure gauge 861 measures pressure within the dosing chamber 86. The solenoid valve 88 is located between the reservoir connection mechanism 811 and the dosing chamber 86.

The combustion tool fuel system 80 of this example differs from the combustion tool fuel system 50 of FIG. 5 in that there is a there is a combustion prechamber 8013 located between the on/off valve 87 and the combustion chamber 89. The chamber connection mechanism 891 may be considered to be provided by a connection between the combustion prechamber 8013 and the on/off valve 87. The combustion chamber may be considered to be provided by a main combustion chamber 89 and the combustion prechamber 8013. In this example, the combustion prechamber 8013 has a smaller cross-sectional area than the main combustion chamber 89.

The combustion tool fuel system 80 of this example works in the same way as the combustion tool fuel system 50 of FIG. 5, except that ignition is started in the combustion prechamber 8013. This causes a flame front and a compressing front to propagate from the combustion prechamber 8013 to the main chamber 89, which enhances turbulence and combustion in the main chamber 89.

In other examples, the combustion chamber may have a separator, or baffle, dividing an internal volume of the combustion chamber into a main combustion chamber and a combustion prechamber. In such an example, a volume of the combustion prechamber is lower than a volume of the main combustion chamber, and the separator, or baffle, has apertures therethrough to allow combustible gas and a flame front to pass through. Operation of the combustion tool fuel delivery system of such examples is the same as described with reference to FIG. 8.

Referring now to FIG. 9, there is shown a combustion tool fuel system 90 which is similar to the combustion tool fuel system 30 shown schematically in FIG. 3. Features of the combustion tool fuel system 90 of this example which are similar to features of the combustion tool fuel system 30 of the example of FIG. 3 are denoted with reference numerals starting with ‘9’ instead of ‘3’.

Similarly to the example of FIG. 3, the metering system of this example comprises a variable volume dosing chamber 94, which has an adjustable wall 941 partially defining a variable gas volume 942, and may have an outlet valve (not shown). If present, the outlet valve is in fluidic communication with the chamber connection mechanism 391 and is located between the chamber connection mechanism 391 and the variable gas volume. The outlet valve may be replaced by an on/off valve located downstream of the variable volume dosing chamber 94.

The adjustable wall 941 may be adjusted via a control signal from a controller comprised in the combustion tool or the combustion tool fuel delivery system, or from an external device. In this example the metering system comprises a pressure reducing valve and/or pressure regulator 92 located between the reservoir connection mechanism 911 and the variable volume dosing chamber 94. However, one of the pressure reducing valve or pressure regulator 92 may be omitted. The amount of combustible gas delivered to the combustion chamber 99 of this example is controlled by controlling the volume of the variable volume dosing chamber 94 because gas is delivered to the variable volume dosing chamber at a constant pressure, because it is controlled by the pressure regulator and/or pressure reducing valve 92. Any of the pressure regulator, outlet valve and on/off valve, if present, may also be controlled by a control signal.

The combustion tool fuel system 90 of this example differs from that of FIG. 3 in that the chamber connection mechanism comprises two inlet conduits 991a, 991b. This allows combustible gas to be delivered into the combustion chamber 99 at different locations to improve the distribution of the gas and so improve combustion. It will be appreciated that although two inlet conduits 991a, 991b are shown in FIG. 9, any number could be used to improve the distribution of combustible gas provided into the combustion chamber 99.

It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the present disclosure described herein. For example, the plurality of inlet conduits 991a, 991b of FIG. 9 could be used with any other of the combustion tool fuel systems. Furthermore, a combustion tool may comprise more than one of the combustion tool fuel systems described here in, and may use any which is appropriate for the particular intended use. It will also be appreciated that the combustion tool may be provided without the reservoir, because this may be removable to be replaced or refilled.