BACKGROUND OF THE INVENTION This invention relates to burner igniters and more particularly to oil fired igniters designed to maintain a stable continuous pilot flame. In some applications, particularly those subject to volatile conditions, as may occur in boiler applications, transient conditions in the boiler or other application may cause the igniter flame to go out. The reliability of the igniter in being able to maintain a continuous pilot flame is the function of the environment in which the igniter is used. There is a need for igniters and, in particular, oil fired igniters, that maintain a stable, continuous pilot flame under adverse transient environmental conditions.

Summary of the Invention The igniter of the present invention implements a two-step ignition process with two combustion zones being defined by the igniter. The primary combustion zone is located at the tip of the igniter and a secondary combustion zone is situated in a protected location within the igniter. A spark ignites combustion at the secondary combustion zone in the protected location and flame is propagated from the protected location to the primary combustion zone at the igniter tip to maintain a continuous flame at the tip. Because the secondary combustion zone is protected within the igniter, it is not affected by transient conditions external to the igniter and, thus, combustion in this zone will be maintained. As a result, a principal advantage of the

invention is achieved as the burner is not susceptible to flame out due to external transient conditions around the igniter.

In a preferred embodiment of the invention, the fuel oil is atomized at the proximal end of the igniter and is carried to the tip of the igniter in atomized form. At the igniter tip, a portion of the atomized mixture is projected backwardly into the igniter to the secondary combustion zone where it is ignited by an electric spark. At the tip of the igniter, the atomized oil and fuel mixture is also projected outwardly from the nozzle of the igniter in the primary combustion zone in which the continuous pilot flame is generated. The igniter is not subject to flame out because the secondary combustion zone is protected from transient conditions and combustion in the secondary combustion zone will maintain a flame at the primary combustion zone in the tip of the igniter.

Description of the Drawings Fig. 1 is an axial sectional view of an igniter of the present invention; Fig. 2 is an exploded isometric view of the igniter of Fig. 1; Fig. 3 is an enlarged a side view in elevation of the assembly of the fuel tube and baffle of the igniter of Fig. 1; Fig. 4 is an end view in elevation of the assembly of the fuel tube and baffle of Fig. 3; Fig. 5 is an enlarged axial sectional view of the nozzle at the tip of the fuel tube; Figs. 6 and 7 are isometric views of the proximal end of the igniter where atomization takes place; Fig. 8 is an axial sectional view through the proximal end of the igniter, showing the atomization chamber for atomizing the fuel oil for the igniter; Fig. 9 is an enlarged side view in elevation of the spark rod tip used in the igniter; and Fig. 10 is an end view in elevation of the spark rod tip of Fig. 9.

Brief Description of the Preferred Embodiments As shown in the Figs. 1 and 2, the igniter comprises an outer casing 11 along the central axis of which is mounted a fuel tube 13 which extends from the proximal end 15 of the igniter to the distal end 17 of the igniter at which the pilot flame is generated for igniting a burner. As seen in Figs. 1 and 8, fuel oil is introduced radially into an atomization chamber 19 at the proximal end of the igniter. Atomizing air under pressure is introduced axially into the chamber and is redirected to flow transversely to the inflowing fuel oil. The velocity of the atomizing air and its transverse direction to the inflowing fuel oil creates a shearing action which generates tiny droplets of fuel that are suspended in the air flow. The mixture of air and fuel as droplets flows down the fuel tube 13 to the nozzle 21 near the distal end 17 of the fuel tube 13. The atomizing of the fuel oil into tiny droplets increases the surface area of the fuel oil facilitating complete combustion of the fuel oil when it is ignited. The atomized fuel oil droplets remain in suspension while traveling throughout the length of the fuel tube 13.

As shown in Fig. 5, upon reaching the nozzle 21, some of the atomized fuel oil and air mixture is projected forwardly out of the tip end of the igniter through passageways 23. One of the passageways 23 is oriented axially in the tip and additional passageways 23 are oriented at various angles with respect to the axis. A small part of the atomized fuel mixture is directed backwardly from the nozzle 21 through passageways 25 to the secondary combustion zone spaced inwardly from the distal end 17 of the casing 11. The atomized oil and fuel mixture is ignited by a spark produced by the spark rod 27 at the secondary combustion zone.

The spark is produced by a high voltage at the tip of the spark rod 27 across the gap between the center core 28 and the outer core 29 of the spark tip, as shown in Fig. 10. The spark rod 27, as shown in Fig. 2, is positioned near to the inner surface of the cylindrical casing 11.

When the atomized fuel mixture is ignited by the spark generated at the tip of the spark rod, the

flame will propagate to the fuel mixture being projected outwardly through the passageways 23 and thus provide the pilot flame projecting from the tip of the igniter in the primary combustion zone.

Just upstream of the secondary combustion zone is a baffle plate 31 shown in Figs. 3 and 4. The fuel tube 13 passes axially through the center of the baffle plate 31, and the baffle plate 31, which is shown as a generally circular shape, is centered within the casing 11 by means of tabs 33, which provide having an annular gap between the baffle plate 31 and the outer casing 11. The tip of the spark tube is situated in one of two U-shaped openings 35 in the periphery of the baffle plate 31. Cooling air is introduced under low pressure through inlet 37 (Fig. 1) into the space between the fuel tube 13 and the outer casing 11. The cooling air flows around the edge of the baffle plate 31 to the secondary combustion zone.

As indicated above, one of the U-shaped openings 35 in the periphery of the baffle plate 31 receives the tip of the spark rod 27. The other U-shaped opening 35 receives a viewing tube, not shown, which extends from the proximal end 15 of the igniter to the secondary combustion zone and enables an observer to view of the presence of a flame being generated by the igniter.

The location of the secondary combustion zone, spaced inwardly from the distal end 17 of the igniter within the cylindrical casing 11, enables combustion to be maintained in this protected secondary combustion zone in the presence of adverse transient conditions at the tip of the igniter. The maintenance of this combustion in the secondary combustion zone will continuously reignite and maintain combustion at the primary combustion zone by propagation of the flame from the secondary combustion zone to the primary combustion zone within the distal end 17 of the casing 11. In this manner, a continuous pilot flame is maintained in the presence of adverse transient conditions.

The invention has been described in detail with respect to a preferred embodiment. It will be apparent to those skilled in the art from the foregoing that changes and modifications may be made without departing from the invention in its broader aspects. The invention, therefore, as defined in the claims is intended to cover all such changes and modifications as fall within the true spirit of the invention.