Power plants – Combustion products used as motive fluid
Reexamination Certificate
1998-07-09
2001-02-06
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S039821, C060S039826, C431S261000
Reexamination Certificate
active
06182436
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ignition system, and more particularly, to an injector for such ignition systems.
2. Description of the Prior Art
It has been found that dependable ignition using conventional aircraft engine ignition systems is not possible under certain situations. Of particular difficulty is to attempt to ignite a small engine at very low speed using large flow number or air blast fuel injectors. Small engines cannot produce a significant combustor pressure drop during cranking conditions and, therefore, atomization of fuel by the main fuel injector is poor.
Large flow number injectors are sized for optimum performance at full power. Fuel flows during the starting mode are not sufficient to pressurize the injectors at the starting mode flow rates and thus atomization of the fuel is inadequate, resulting in difficulty.
So-called hot starts can result if the fuel flow rate is increased at such low speed conditions. In order to solve the above problem, very small pressure atomizers, known as primary injectors, are used in association with larger secondary injectors. The small size of these primary injectors produces a greater fuel pressure at low speed, allowing for better atomization of the fuel.
The disadvantage with these small primary injectors is their tendency to become contaminated owing to the very small orifice sizes. This requires increased maintenance in the field. In addition, a second fuel manifold and fuel flow divider valves add to the complexity of the system and to the cost. At high altitude and in conditions where flame-out of the combustor might be more prevalent, requires that the primary injectors be continuously operating to inject fuel into the combustion chamber which, in fact, diverts fuel from the secondary fuel injectors to thereby hamper the cooling of the secondary injectors.
So-called torch igniters utilize a small primary injector in close proximity to the igniter, thus eliminating the requirement for a large number of small injectors. However, these primary injectors still have the problem of contamination in view of their very small orifice sizes. In order to keep the injector cool, it must be operated throughout the entire engine cycle.
Although torch igniters can solve some problems, particularly of ignition during low speed cranking conditions, their performance can still suffer at high altitudes when it is required to reignite after a flame-out, because the air flow rates and the combustor pressure drops are much greater.
SUMMARY OF THE INVENTION
It is an aim of the present invention to provide an igniter system that can ignite injectors at low speeds during a cranking mode or at high altitude conditions when fuel flow rates are low.
It is a further aim of the present invention to eliminate the need for small orifice injectors.
It is a still further aim of the present invention to provide a continuous controllable source in order that burning may occur as soon as a flammable mixture of air and fuel is supplied.
It is a yet further aim of the present invention to provide an improved fuel distribution system for an igniter that reduces the occurrence of carbon buildup and coking since small orifices or small dead spots in the conduits are not present.
A construction in accordance with the present invention comprises a fuel and air distribution means for use with an igniter in a combustor. The distribution means includes a tubular member having a bore with a first end near the igniter such that the igniter tip is within the bore at the first end and the second end projects into the combustor characterized in that the tubular member is porous material chosen from a material having high thermal tolerance whereby liquid fuel and air are fed to the tubular porous device such that the liquid fuel is retained and distributed by capillary action toward the bore of the device where the liquid fuel will vaporize and form an atomized mixture with the air.
In a more specific embodiment of the present invention, the igniter is a plasma igniter of the type described in U.S. Pat. No. 5,587,630, Dooley, issued Dec. 24, 1996.
In a still further embodiment of the present invention, the conduits supplying fuel to the porous tubular member are relatively large bore conduits, thus reducing the risks of coking.
It is a still further embodiment of the present invention whereby the tubular porous member is a circular cylinder, and the porosity of the cylinder ranges between 60 pores per inch and 200 pores per inch.
It is also contemplated that the tubular device might be spherical or frusto-conical.
A method for distributing atomized fuel to an igniter in a combustion chamber in accordance with the present invention comprises the steps of placing a tubular member having a bore with a first end near the igniter such that the igniter tip is within the bore at the first end and the second end projects into the combustor characterized in the steps of choosing the tubular member from a porous material having high thermal resistance, feeding liquid fuel to the tubular porous member such that the liquid fuel is retained and distributed by capillary action toward the bore of the device, passing air through the tubular porous member to carry the liquid fuel and vaporize the fuel and form an atomized mixture with the air.
Thus, as might be contemplated, the tubular porous member is installed to the combustor with the igniter tip just within the bore of the tubular device, and the liquid fuel is supplied to the porous tubular device where, by capillary action, the fuel will soak the porous member, but the pressurized air, also being fed to the porous tubular member, will atomize the fuel as it carries the fuel into the bore portion of the tubular device.
An advantage of the present invention is the ability to use pure air blast injectors in the combustor at low cranking speeds and high altitude conditions.
Another advantage of the present invention is the formation of a combustion cavity fed by controlled fuel and air flow rates independent of the conditions in the combustor.
Furthermore, the plasma igniter may be cooled by the air flow through the porous tube.
Flow number is defined as the fuel mass flow divided by the square of the pressure drop across the nozzle to drive that flow. The smaller the flow number, the greater the pressure drop required to flow a certain rate of fuel. It is a measure of the orifice size of the nozzle. Small flow numbers are anywhere from 0.5 to 1.5 while large flow numbers are greater than 10.
REFERENCES:
patent: 1401404 (1921-12-01), Hoffman
patent: 3531229 (1970-09-01), Berglund
patent: 3937007 (1976-02-01), Kappler
patent: 4141213 (1979-02-01), Ross
patent: 4789331 (1988-12-01), Kawamura
patent: 5587630 (1996-12-01), Dooley
patent: 5673554 (1997-10-01), DeFreitas et al.
patent: 2821160 (1979-11-01), None
patent: 1262225 (1972-02-01), None
patent: 1377648 (1974-12-01), None
patent: 1498135 (1978-01-01), None
Acolacol Rolando Buenafe
Prociw Lev Alexander
Astle Jeffrey W.
Freay Charles G.
Pratt & Whitney Canada Corp.
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