WO2012098348A2

WO2012098348A2 - Glow plug

Info

Publication number: WO2012098348A2
Application number: PCT/GB2012/000034
Authority: WO
Inventors: Nicholas Julian MOSS; Peter Alan HALMAN
Original assignee: Ripmax Ltd
Priority date: 2011-01-17
Filing date: 2012-01-13
Publication date: 2012-07-26
Also published as: WO2012098348A3; GB201100764D0

Abstract

A glow plug 1 is described for use in an engine 20. The glow plug 1 includes a body 2 having a cavity or recess 12 in which a platinum coil 10 is installed. An additional coil 11 is provided across the end face 14 of the plug 1. The coil 10 is connected between electrical contacts so that it can be heated when an electrical current is passed through it. In use the glow plug can facilitate ignition of gasoline in the engine 20.

Description

GLOW PLUG

The present invention relates to a glow plug and an internal combustion engine that includes a glow plug.

A glow plug (sometimes spelled "g!owplug" or "glow-plug") is a device that is used to ignite fuel in an internal combustion engine. In contrast to spark plugs, glow plugs do not cause ignition with a spark. Instead a compressed and heated fuel air mixture is ignited because of a catalytic reaction involving the fuel and a catalyst in the glow plug. Platinum is the primary material used as a catalyst in this type of glow plug.

The conventional fuel in a glow plug engine is methanol, although nitromethane and other additives may also be present in some instances. Generally methanol fuel also includes around 20% oil by volume. In operation the fuel air mixture is compressed in a combustion chamber (usually with a piston) and a platinum filament in the plug is heated to a high temperature. The fuel air mixture is heated as it is compressed, and it is ignited with the assistance of the hot, platinum filament.

The platinum filament in the glow plug is arranged to be heated with an electrical current because ignition is achieved more easily with a pre-heated filament. The electrical heating to the filament is typically withdrawn after the fuel air mixture is first ignited because the filament can be maintained at a high temperature by the combustion process.

The document US 5,537,973 is an example of the use of glow plugs in a rotary engine.

The document US 4,345,555 describes a self-heating ignition plug in which a resistive coil is embedded within a catalyst. The resistive coil can be energised in order to heat the catalyst and stimulate ignition of injected fuel.

The document GB 2 256 989 describes an ignition system for an engine in which a glow plug is installed in an ignition chamber. The position of the glow plug within the ignition chamber can be adjusted to control the performance of the engine.

Figure 1 is a cross-sectional view of an example of a conventional glow plug 1 , and Figure 2 is an end view of the same device. The conventional glow plug 1 includes a body 2 having a main axis 4. The body 2 includes a threaded section 6 and an electrical connector 8. The threaded section 6 has a cavity or recess 12 in which a coil 10 is installed. The coil 10 is installed in the cavity 12 so that it is wound around the main axis 4 of the body 2.

The threaded section 6 is designed to be installed in the wall of a combustion chamber (not shown). The glow plug 1 is screwed into the wall so that the cavity 12 and the coil 10 can communicate with fuel air mixture in the combustion chamber.

The coil 10 includes two ends, one of which is connected to an electrical connector 8 in the cavity 12 and one of which is connected to an electrical contact on an end face 14 of the threaded section 6. A potential difference can be applied between the electrical contacts so that the resistive coil can be heated.

Figure 3 is a cross-sectional view of another known glow plug 1 , and Figure 4 is an end view of the same device. There is no cavity in this glow plug 1, and the coil 10 is wound flat on the end face 14 of the threaded section 6. One end of the coil 10 is connected to the electrical connector 8 on a central stem of the body 2, and the other end is connected to an electrical contact on the edge of the end face 14. In this arrangement the coil 10 spirals outwards from a central point, with the spiral arranged around the main axis 4 of the body 2.

Spark plugs are an alternative to glow plugs, and these can be used to ignite a fuel air mixture that includes gasoline (petrol). A disadvantage of spark plugs is that they require high voltage electricity in order to produce a spark. Typically the high voltage is produced by a magneto or an ignition coil, both of which are heavy and bulky.

Glow plug engines are typically used in environments where conventional gasoline engines would be too bulky and/or heavy. Examples include model aircraft and model cars where the weight of a gasoline engine renders it impractical. Glow plug engines are generally effective, but methanol fuel has limitations. In particular, the calorific value (energy release per unit mass) of methanol is low which means that regular refuelling is required in situations where a large fuel tank is impractical. An object of the present invention is to provide a device that permits the use of gasoline in an engine with reduced weight. Another object of the invention is to provide a device that permits the use of alternative fuels in a glow plug engine. According to an aspect of the present invention there is provided a glow plug for a gasoline engine comprising: a body suitable for assembly in a wall of an engine combustion chamber, the body having a main axis; and at least two catalytic components connected to the main body, wherein the body includes a recess that communicates with the engine combustion chamber, in use, and wherein a first catalytic component is situated within the recess; wherein a second catalytic component projects from the main body and extends at least in part in a direction that coincides with the orientation of the main axis of the body, so that, in use, the second catalytic component projects from the body into the combustion chamber to enable or facilitate the ignition of gasoline fuel, wherein at least one of the first and second catalytic components is a resistive wire that is configured to be heated by an electrical current.

In this way a greater surface area of the catalytic component can be presented to fuel in the engine combustion chamber. This can improve the rate of burning of a compressed fuel air mixture in the combustion chamber. Significantly, the inventors have found that this arrangement can result in successful ignition of gasoline in a glow plug engine. Surprisingly, the inventors have found that the catalyst in a glow plug can assist the burning of gasoline. However, the catalytic effect is far smaller for gasoline than it is for methanol, which is traditionally used in a glow plug engine. In order to ignite gasoline successfully the inventors have determined that it is necessary for a catalytic component in a glow plug to project from the body into the engine combustion chamber. This increases the surface area of the catalytic component that is in contact with fuel in the fuel air mixture,

Gasoline in the combustion chamber can be burnt in part due to a catalytic reaction and heat retention involving the first catalytic component in the recess, and in part due to a catalytic reaction and heat retention involving the second catalytic component that projects from the main body. The second catalytic component can also generate turbulence in order to increase the interaction between the first catalytic component and the fuel air mixture.

It is desirable to pre-heat the first or second catalytic component because a heated catalyst has been found to be more effective at stimulating ignition than a cold catalyst. In some embodiments electrical heating may be applied initially but withdrawn after the first ignition. In other embodiments electrical heating may be maintained even after the first ignition in order to boost the heat of the catalyst.

The resistive wire may extend between electrical connections so that it can be heated rapidly by applying an electrical current. It may be most convenient to heat the first catalytic component, situated in the body recess, by applying an electrical current. This can be achieved by providing electrical contacts at spaced positions in the recess. In some embodiments it may be possible to heat the second catalytic component that projects from the body into the combustion chamber. Respective electrical connections may be provided at positions on the main body such as its end face so that the catalytic component can extend between them. In one arrangement the first catalytic component may be heated electrically to stimulate the first ignition and the second catalytic component may extend beyond the body in order to present a large surface area to the fuel air mixture and maintain subsequent ignitions. Any number of separate catalytic components may be provided in the recess and/or projecting from the body in any desirable configuration. However, a preferred configuration may be for a single catalytic component in the recess.

The second catalytic component may take a variety of forms that can project from the main body and extend at least in part in a direction that coincides with, or is substantially parallel to, the main axis of the body. For example the second catalytic component may be formed in a coil and the axis of the coil may extend in a direction that is substantially parallel or substantially perpendicular to the main axis of the body. In other examples the second catalytic component may be in the form of a zigzag, mesh, or a forest of spikes, all of which include components that project along the main axis of the body. In one specific example the mesh could rest on legs with components that extend from the body in a direction that is parallel to the main axis.

The main axis of the body may be substantially perpendicular to the wall of the engine combustion chamber when it is assembled; thus, the main axis of the body may be aligned with the direction in which the glow plug is assembled in the wall. In some embodiments the main axis of the body can be aligned with the main axis of a piston. In other embodiments the main axis of the body can be at an angle to the main axis of the piston; in a chainsaw, for example, the main axis of the body may be at an angle of around 45° relative to the main axis of the piston.

Preferably the second catalytic component is arranged about an axis that, at least in part, is non-parallel with the main axis of the body. This may be a particularly convenient way to increase the surface area of the catalyst in the combustion chamber. A zig-zag or coil of wire may be arranged about an axis that extends away from the main axis of the body so that the catalytic component does not interfere with a movable member in the combustion chamber.

In one embodiment the second catalytic component may be formed in a coil, wound around an axis that, at least in part, is non-parallel with the main axis of the body. In this way it is possible to increase the surface area of catalyst significantly without projecting the catalytic component too far beyond the body. This helps to avoid any undesirable physical interaction between the catalytic component and a moveable member such as a piston in the engine combustion chamber. In some arrangements the clearance between a piston and the main body may be as little as 2mm which means that a limit can be placed on the maximum extent of the catalytic projection. As mentioned, a plurality of catalytic components may be provided with one component in the recess and a separate component projecting from the main body. In other configurations a single catalytic component may be provided with a portion in the recess and a portion projecting from the body. In these embodiments the portion projecting from the body may be wound round an axis that at least partially extends along the wall of the combustion chamber and/or away from the main axis of a coil in the recess; in this way a large surface area can be presented to the fuel air mixture without causing interference with a moveable piston.

Preferably the first catalytic component is formed in a coil and is wound around an axis that, at least in part, is parallel with the main axis of the body. The recess may have a longitudinal axis that is parallel with and coincides with the main axis of the body so that the coil therein can communicate with the fuel air mixture in the combustion chamber. In this configuration the coil can fit easily in the recess while presenting a large surface area to assist with fuel ignition. In addition, the filament- like coil can be heated rapidly with an electrical current; this can be compared to the rapid heating of a filament in an electrical light bulb. The body may include an end face, and the second catalytic component that projects from the body may extend at least in part across and/or along the end face. In this way a large surface area of the second catalytic component may be presented to fuel air mixture in the combustion chamber. The second catalytic component may have a main axis that subtends any of a variety of angles with respect to the main axis of the body. For example, the catalyst may be formed in a coil having a sinuous or circuitous axis so that it subtends a different angle to the main axis of the body at different positions along the coil. The second catalytic component may be arranged about an axis that is substantially perpendicular to the main axis of the body. This configuration may present the maximum surface area of catalyst to the fuel air mixture, while minimizing the extent to which the catalyst projects into the combustion chamber. This is advantageous because it maximises the catalytic effect of the glowplug without projecting any component too far into the combustion chamber such that it would interfere with a movable member such as a piston.

According to another aspect of the present invention there is provided a glow plug for a gasoline engine comprising: a main body suitable for assembly in a wall of an engine combustion chamber; at least one catalytic component connected to the main body; and a turbulence generator configured to create turbulence in an airflow in order to increase the interaction between the catalytic component and a gasoline air mixture to enable or facilitate the ignition of the gasoline fuel air mixture. As mentioned, the present inventors have found that the catalytic effect is far smaller for gasoline than it is for methanol, which is traditionally used in a glow plug engine. One option for increasing the rate of reaction in order to ignite gasoline involves creating turbulence in the airflow to the catalytic component. The turbulence generator can increase the interaction between the catalytic component and the gasoline/air mixture in order to enhance the catalytic effect. The effect of this feature may be comparable to increasing the surface area of the catalytic component that is in contact with the fuel air mixture.

Preferably the catalytic component is provided in a recess of the main body. Thus, the turbulence generator may be configured to increase the air turbulence in the recess. The turbulence generator may take a variety of different forms. In one example the turbulence generator may include a coil across the end of the recess. The coil may be of any material, including catalytic and non-catalytic materials, and it may have the effect of creating turbulence as the air flows into the recess thereby increasing the interaction between the catalytic component and the air gasoline mixture. In other examples the turbulence generator may include apertures in the sides of the main body and/or a sinuous path that leads towards the recess in order to increase the air turbulence around the catalytic component.

According to another aspect of the present invention there is provided a gasoline engine comprising: a combustion chamber having a wall in which the glow plug as previously defined is assembled; and a movable member that is movable from a first position to a second position when gasoline is ignited at the glow plug and burnt in the combustion chamber.

According to another aspect of the present invention there is provided a gasoline engine comprising, a combustion chamber having a wall in which a glow plug is assembled; and a movable member that is movable from a first position to a second position when gasoline is ignited by the glow plug and burnt in the combustion chamber, wherein the glow plug and the wall are arranged such that they can only be assembled together when the glow plug has a particular orientation with respect to the wall.

In this way the end face of the glow plug can always be presented to the combustion chamber in the same orientation. This may be desirable for achieving optimal performance of the engine.

Some glow plugs may be arranged with features that are not rotationally symmetrical about the end face of the glow plug. This may include a projection that extends into the combustion chamber. In these glow plugs it may be desirable for the nonsymmetrical projection, which may be a catalytic component, to be situated towards one side of the end face of the glow plug. In use, the projection may have a specific position and/or orientation, and this may enhance performance of the engine.

The projection may be arranged about an axis that is generally perpendicular to the path in which fuel is expelled from the fuel transfer port. Preferably the projection is a coil that includes catalytic material. By arranging the glow plug and wall so that they can only be assembled with a particular respective orientation, the projection on the end face can be locked in position during use. In one arrangement the projection may be positioned toward a fuel transfer port. By contrast, in a traditional threaded plug the end face of the glow plug can have an unpredictable orientation when assembled in the wall, depending on a variety of factors including how tightly the plug is assembled. This issue has not previously been viewed as significant because most conventional glow plugs are rotationally symmetrical, and glow plug orientation has not been thought to have any influence on the operation of the engine.

Preferably the glow plug comprises a shaped component that complements a shaped component in the wall of the combustion chamber. In a specific example the glow plug may include a D-shaped component that can fit together with a D-shaped recess in the wail. A variety of other complementary shapes may be provided in the glow plug and wall to ensure that the glow plug can only be assembled in a single orientation.

According to yet another aspect of the present invention there is provided a method of operating the engine as previously defined comprising the steps of: supplying gasoline to the combustion chamber; and igniting the gasoline in a reaction involving the glow plug so that the movable member can move from a first position to a second position.

Preferably the movable member is a piston. However, a rotary engine configuration would also be possible in which the movable member is rotational. The engine may be operable in two-stroke or four-stroke cycles, as applicable.

The present engine allows the ignition of gasoline with a glow plug, instead of methanol as is conventional. Gasoline refers to a variety of substances that are used as fuel in internal combustion engines. Gasoline often includes a mixture of substances but the main ingredient is generally a hydrocarbon with between around four and twelve carbon atoms per molecule; a typical chemical formula for the main ingredient in gasoline may be C₈H₁₈. Gasoline has a greater calorific value than methanol, and therefore the present engine can run for longer on gasoline, without increasing fuel tank volume.

The present engine enables the ignition of gasoline without a spark plug, and its associated electrical components which include an ignition coil or magneto. This permits a significant weight saving. It also permits a cost saving because a glow plug is significantly cheaper to manufacture than a spark plug plus an ignition coil / magneto.

The engine may be used in a variety of diverse applications including, but not limited to. model vehicles, chainsaws, and lawn mowers. In all of these applications a standard gasoline engine can be operated with less weight because a spark plug and ignition coil can be replaced by a low-weight glow plug.

From another perspective, a standard glow plug engine can be improved because methanol fuel can be replaced by gasoline or other fuel which has a higher calorific value which means that less fuel is required for the same energy output.

Accordingly a glow plug engine running with gasoline may carry less fuel which advantageously reduces weight. In addition, the pollution and cost of a standard glow plug engine can be reduced because less oil is burned when methanol fuel is replaced by gasoline.

Preferably the gasoline engine has a higher compression ratio than would normally be expected for a glow plug engine fuelled with methanol. The compression ratio may be defined as the ratio of the volume of the combustion chamber with the movable member in the second position to the volume of the combustion chamber with the movable member in the first position. In one embodiment the trapped compression ratio for the engine may be in the range of 9: 1 to 11:1, whereas a corresponding glow plug engine fuelled with methanol may have a compression ratio in the range of 7: 1 to 10.5: 1.

Preferably the engine includes a crank casing; a head portion; and cooling fins provided on the crank casing and head portion. The cooling fins on the crank casing may be larger than the fins on the head portion, and the total area of cooling fins in the engine may be larger than those in a conventional glow plug engine running on methanol. The cooling fins in a methanol fuelled engine can be relatively small because methanol engines typically run at a fairly low temperature. A low operational temperature is achieved in part because methanol fuel itself acts as a coolant while it is drawn through the engine. The cooling fins in the gasoline engine may be larger than for a methanol fuelled glow plug engine. It is believed that two effects lead to the requirement for larger cooling fins. First, gasoline is believed to be a less effective coolant than methanol. Second, the flow rate of gasoline through the engine is lower because less gasoline is required per unit time for the same energy output.

The gasoline engine may comprise a roller bearing for connecting a piston to a drive shaft instead of a simple bush, as is often used in a methanol fuelled glow plug engine. A roller bearing is preferred in the present engine because the frictional effect of a bush may be too high, given that gasoline fuel is run with low oil content.

The engine may include a connection to a fuel tank comprising gasoline fuel so that gasoline can be supplied to the combustion chamber. Any apparatus features may be provided as method features and vice-versa.

Preferred features of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a conventional glow plug;

Figure 2 is an end view of the glow plug shown in Figure 1 ;

Figure 3 is a cross-sectional view of another known glow plug;

Figure 4 is an end view of the glow plug shown in Figure 3;

Figures 5 to 12 are end views of glow plugs in embodiments of the present invention; Figure 13 is a cross-sectional view of an engine in an embodiment of the present invention;

Figure 14 is a perspective view of the engine shown in Figure 13; Figure 15 is a right side view of the engine shown in Figure 13; Figure 16 is a left side view of the engine shown in Figure 13; Figure 17 is a front view of the engine shown in Figure 13; and

Figure 18 is a rear view of the engine shown in Figure 13.

Figure 19A is a front view of a glow plug in an embodiment of the present invention;

Figure 19B is a cross-sectional view of the glow plug of Figure 19A taken through the line A-A;

Figure 19C is a side view of the glow plug of Figure 19A;

Figure 19D is an end view of the glow plug of Figure 19A; Figure 20A is a front view of another glow plug in an embodiment of the present invention;

Figure 20B is a cross-sectional view of the glow plug of Figure 20A taken through the line A-A;

Figure 20C is a side view of the glow plug of Figure 20A;

Figure 20D is an end view of the glow plug of Figure 20A; Figure 21 is an exploded view of a glow plug, a cylinder head and a clamp nut in another embodiment of the invention;

Figure 22 is an end view of the glow plug shown in Figure 21; and Figure 23 is a perspective view of the glow plug shown in Figures 21 and 22.

Detailed Description of Embodiments of the Invention

Figure 13 shows a cross-sectional view of an engine 20 in an embodiment of the invention. The engine 20 is intended to be operated in two-stroke cycles. The engine 20 includes a head 22 that is assembled to a crank case 24. A piston 26 is moveable within the crank case 24, and a combustion chamber 34 is defined between the piston and the head 22. The piston 26 is connected to a drive shaft 28 with a needle roller bearing 30. Fuel/air mixture transfer windows 36 are provided in side walls of the combustion cylinder 32. The engine includes a connection to a fuel tank (not shown) including gasoline. Gasoline fuel is mixed with oil and delivered to the combustion chamber 34 for burning. The oil content in the gasoline/oil mixture is around 3%, which is significantly lower than a conventional glow plug engine where oil represents around 20% of the methanol/oil mixture.

Oil is incompressible and therefore the combustion chamber 34 is designed differently for a gasoline fuel rather than a methanol fuel. In particular, the trapped compression ratio (TCR) is generally higher when gasoline is used as a fuel. Cooling fins 38, 40 are provided respectively on the head 22 and on the crank case 24. The total area of cooling fins 38, 40 is larger in the engine 20 than for a corresponding glow plug engine fuelled with methanol.

A glow piug 1 is assembled in a wall of the combustion chamber 34. The glow plug 1 includes a cavity 12 and a coil 10 situated within the cavity 12. An additional coil 11 is provided on an end face 14 of the glow plug 1 , projecting therefrom into the combustion chamber 34. The additional coil 11 is wound round an axis that is substantially perpendicular to the main axis 4 of the glow plug 1 and the main axis of the piston 26. Both of the coils 10, 11 include platinum because it is believed that this can act as a catalyst in the burning of gasoline. In addition the thermal inertia of platinum means that it can retain heat transferred by combustion.

In the preferred embodiment the coil 10 within the cavity extends between electrical contacts so that it can be heated. The additional coil 11 on the end face 14 of the glow plug is not connected to any electrical contacts.

In operation, an electrical current is applied to the coil 10 so that it is heated and glows in the cavity 12. A mixture of gasoline and oil is then injected into the combustion chamber 34 through the fuel/air mixture transfer windows 36. The fuel/oil/air mixture is compressed in the combustion chamber 34 by the piston 26. Turbulence in the airflow to the cavity 12 is created by the coil 11 on the end face 14 of the glow plug. Ignition of the gasoline occurs near the pre-heated coil 10. Ignition of the gasoline creates an expansion in the combustion chamber 34 that drives the piston 26. The piston is connected to the drive shaft 28 via the needle roller bearing 30. After the first ignition has occurred the electrical current to the coil 10 can be withdrawn because both coils 10, 11 are maintained at a high temperature due to a catalytic reaction involving the coils and heat from combustion in the combustion chamber 34. Subsequent fuel ignitions can occur due to reactions at either of the hot coils 10, 11.

In the engine shown in Figure 13 there are two coils 10, 11. The first coil 10 is situated within a cavity 12 and is heated electrically. The second coil 11 is situated outside the cavity and is wound in a direction that is perpendicular to the main axis 4 of the glow plug 1. Figures 19A to 19D show more detail of a glow plug 1 that could be used in the engine 20. The glow plug 1 includes a body 2 having a cavity or recess 12 in which a coil 10 is installed. The coil 10 is installed in the cavity 12 so that it is wound around the main axis 4 of the body 2. One end of the coil 10 is connected directly to a centre post 8 which is configured to be connected to an electrical connector, and the other end of the coil is connected to the end face 14 of the plug 1. An insulator 13 is provided between the centre post 8 and the end face 14 so that a potential difference can be applied between the two and across the coil 10. Thus, the resistive coil 10 can be heated electrically in the cavity 12.

The glow plug 1 includes an additional coil 11 that extends diametrically across the end face 14 of the plug 1. The additional coil 11 is wound around an axis that is perpendicular to the main axis 4 of the plug 1. As mentioned, the additional coil 11 is arranged to create turbulence in the flow of air towards the coil 10 in the recess 12. Although the preferred configuration is for the additional coil to be of catalytic material, it can also be manufactured of non-catalytic material such as copper. A copper coil can still create air turbulence and thereby increase interaction between the fuel and the catalytic coil 10.

A seal 19 is also provided at the join between the centre post 8 and the remainder of the glow plug 1. This is important because the combustion chamber 34 can experience high pressures, and it is desirable for there to be no gas escape route through the glow plug 1.

Figures 20A to 20D show an alternative design for a glow plug 1 in which two additional coils 11 are provided across the end face 14. In this arrangement the coils 11 extend across the end face 14 and are wound around an axis that is

perpendicular to the main axis 4 of the plug 1.

Figures 5 to 12 are end views of a variety of alternative glow plugs 1. In particular, Figures 5 to 12 show a non-exhaustive set of possible configurations for catalytic coils 11 that are attached to the end face 14 of a glow plug 1 and extend therefrom into a combustion chamber 34. In all of these embodiments a further coil (not shown) is desirably situated in a cavity 12 in the glow plug 1.

In Figure 5 a single coil 11 extends diametrically across the end face 14 of a glow plug 1. Figures 7 and 9 show configurations in which multiple coils 11 extend across the end face 14 of the glow plug 1 from one edge to another. Figures 8 and 10 to 12 illustrate configurations in which multiple coils 11 extend from a central stem 15 to the edge of an end face 14 of a glow plug; the multiple coils 11 could be separate entities or a single entity connected via the stem 15. Finally, Figure 6 illustrates an arrangement in which multiple coils 11 extend between points on the edge of an end face 14.

A variety of other configurations for coils 11 could be used as would occur to a person skilled in the art. In addition, while a coil may be the most convenient form of a catalyst projecting from the body 2, a variety of alternatives exist. For example, the coil 11 may be replaced by a zig-zag, mesh, or a forest of spikes. In all of these examples the catalytic projection includes at least one component that extends along the main axis of the plug 1 and extends from its end face 14. Also, in all of these examples the coil 11 or its alternatives may create turbulence in the flow of air towards the further coil 10 in the cavity 12.

In some arrangements the coil 10 in the cavity 12 can be omitted. This can reduce the complexity of the glow plug design. In these arrangements it may be desirable to heat one of the coils 11 in order to facilitate the first ignition of gasoline. In the embodiments shown in Figures 8 and 10 to 12 a potential difference could be applied between the stem 15 and the edge of the end face 14; thus, the coils 11 may be provided as parallel resistors that glow red-hot on application of a voltage. In the embodiments shown in Figures 5, 7 and 9 a potential difference may be provided between opposing edges of the end face 14 so that the coils 11 can be heated electrically.

Another embodiment of the invention is explained with reference to Figures 21-23. Figure 21 shows an exploded view of a glow plug 100, a portion of a cylinder head 122, and a clamp nut 150. The glow plug 100 includes a D-shaped portion 152 that is arranged to fit together with a D-shaped recess 154 in the wall of the combustion chamber.

The glow plug includes a catalytic coil 110 in a cavity 112 and an additional coil 111 that extends across the end face 114. The additional coil 111 may be catalytic or non-catalytic, and it extends in a chord between two points on the circumference of the end face 114. In this way, the additional coil 111 is arranged towards one side of the end face 114.

In use, the glow plug 100 is inserted into an open aperture in the cylinder head 122 in such a way that the D-shaped portion 152 meshes with the D-shaped recess 154. Thus, the glow plug 100 can only be inserted into the cylinder head 122 in one orientation. When the D-shaped portion 152 is received in the D-shaped recess 154, the clamp nut 150 can be fitted by threaded engagement to clamp the glow plug 100 in place. The glow plug 100 is designed so that the additional coil 111 can assume a predictable position and orientation when assembled in the combustion chamber. It has been found that this arrangement can improve the performance of the engine. In the particular arrangement shown the additional coil 111 is positioned at the side of the glow plug 100 that is closest to the fuel transfer port (not shown) in the combustion chamber, however, different positions and orientations for the additional coil 111 may provide optimal engine performance in other configurations.

Claims

Claims 1. A glow plug for a gasoline engine comprising:

a body suitable for assembly in a wall of an engine combustion chamber, the 5 body having a main axis; and

at least two catalytic components connected to the main body,

wherein the body includes a recess that communicates with the engine combustion chamber, in use, and wherein a first catalytic component is situated within the recess;

i 0 wherein a second catalytic component projects from the main body and extends at least in part in a direction that coincides with the orientation of the main axis of the body, so that, in use, the second catalytic component projects from the body into the combustion chamber to enable the ignition of gasoline fuel;

wherein at least one of the first and second catalytic components is a resistive 15 wire that is configured to be heated by an electrical current.

2. The glow plug of claim 1 wherein the at least one catalytic component is arranged about an axis that, at least in part, is non-parallel with the main axis of the body. 0

3. The glow plug of claim 1 or claim 2 wherein the at least one catalytic component is formed in a coil, wound around an axis that, at least in part, is non-parallel with the main axis of the body.

4. The glow plug of any of the preceding claims wherein the first catalytic

5 component is a resistive wire configured to be heated by an electrical current. 5. The glow plug of any of the preceding claims wherein the second catalytic component is a resistive wire configured to be heated by an electrical current. 0

6. The glow plug of any of the preceding claims wherein the body includes an end face and wherein the at least one catalytic component that projects from the body extends at least in part across the end face.

7. The glow plug of any of the preceding claims wherein the at least one catalytic component that projects from the main body is arranged about an axis that is at least in part substantially perpendicular to the main axis of the body.

8. The glow plug of claim 7 wherein the at least one catalytic component is wound around the axis that is substantially perpendicular to the main axis of the body.

9. The glow plug of any of the preceding claims comprising a turbulence generator configured to create turbulence around the catalytic component.

10. A glow plug for a gasoline engine comprising:

a main body suitable for assembly in a wall of an engine combustion chamber; at least one catalytic component connected to the main body; and

a turbulence generator configured to create turbulence in an airflow in order to increase the interaction between the catalytic component and a gasoline/air mixture to enable or facilitate the ignition of gasoline fuel;

wherein the main body includes a recess that communicates with the engine combustion chamber, in use, and wherein the catalytic component is situated within the recess.

11. The glow plug of claim 10 wherein the turbulence generator comprises a sinuous path to create a turbulent airflow around the catalytic component.

12. A gasoline engine comprising:

a combustion chamber having a wall in which a glow plug as defined in any of the preceding claims is assembled; and

a movable member that is movable from a first position to a second position when gasoline is ignited by the glow plug and burnt in the combustion chamber.

13. The gasoline engine of claim 12 further comprising a roller bearing

14. The gasoline engine of any of claim 12 or claim 13 further comprising a connection to a fuel tank that includes gasoline so that gasoline can be supplied to the combustion chamber.

15. A gasoline engine comprising:

a combustion chamber;

a glow plug assembled in a wall of the combustion chamber, the glow plug having a body with a main axis, and at least two catalytic components connected to the main body, wherein the body includes a recess that communicates with the engine combustion chamber, in use, and wherein a first catalytic component is situated within the recess, and wherein a second catalytic component projects from the main body, and at least in part along the main axis of the body, into the combustion chamber to enable the ignition of gasoline fuel in the combustion chamber, wherein at least one of the first and second catalytic components is configured to be heated by an electrical current; and a movable member that is movable from a first position to a second position when fuel is ignited by the glow plug and burnt in the combustion chamber.

16. A gasoline engine comprising:

a combustion chamber having a wall in which a glow plug is assembled; and a movable member that is movable from a first position to a second position when gasoline is ignited by the glow plug and burnt in the combustion chamber, wherein the glow plug and the wall are arranged such that they can on/y be assembled together when the glow plug has a particular orientation with respect to the wall.

17. The gasoline engine of claim 16 wherein the glow plug comprises a projection that extends from the body into the combustion chamber.

18. The gasoline engine of claim 17 wherein the projection is arranged towards one side of an end face of the glow plug.

19. The gasoline engine of any of claims 16 to 18 wherein the glow plug is defined in any of claims 1 to 11.

20. The gasoline engine of any of claims 16 to 19 wherein the glow plug comprises a shaped component that complements a shaped component of the wall of the combustion chamber.

21. The gasoline engine of claim 20 wherein the glow plug includes a D-shaped component that can fit together with a D-shaped feature in the wall.

22. A method of operating the gasoline engine as defined in any of claims 12 to 21 comprising the steps of:

supplying gasoline to the combustion chamber; and

igniting the gasoline by virtue of a reaction involving the glow plug in order to move the movable member from a first position to a second position.