US3501050A - Autogenous ignition suppressor - Google Patents

Description

March 17, 1970 v s w ETAL AUTOGENOUS IGNITION SUPPRESSOR Filed Feb. 29, 1968 3 Sheets-Sheet 1 2 O ls 4 4 FIG.| 55

I J n u. 500 [TEMPERATURE O 15 .05 PSI PRESSURE 2 T f 1 l I l l l TIME MINUTES FIG. 5

INVENTORS EDWARD F. VERSAW 8| WALTER W. SPOECKER ATTORNEY March 17, 1970 Filed Feb. 29, 1968 FIG.6

E. F. VERSAW ETAL 3,501,050

AUTOGENOUS IGNITION SUPPRESSOR Sheets-Sheet 2 PSI .75 PSI PRESSURE o l l I l l l l l l I l 0 IO 3O E0 BO I00 TIME- SECONDS |.5 mcu CORRUGATED GAP so a o S r; 32 2.5 mcu coanusmzo GAP l g 40 g 2o FIG 50 2.5 mcn CORRUGATED GAP |.5 men GORRUGATED'GAP o u l l TEMPERATURE F FIG."

INVENTORS EDWARD F. VERSAW a WALTER W. SPOECKER MJM ATTORNEY -March 17, 1970 E. F. VERSAW ErAL 3,501,054)

AUTOGENOUS IGNITION SUPPRESSOR Filed Feb. 29, 1968 3 Sheets-Sheet 5 7.62 men FLAT WALL GAP 7 I I I/ I" I so I, l 36 a 0.5 NO REACTION UP *ro 150 2i /I g 4.0 mcu FLAT WALL GAP g I 7 a 34 5 30 l 2.5 mm: FLAT wALL GAP I 7.62 men FLAT WALL GAP 1o o l l l l l TEMPERATURE- "F |"ao.5" NO REACTION UP TO 150 f/ 70 h l ll 36 T I g 40 men FLAT 5 \IMLLGAP a2 40 5 345 l 20 7.62 men FLAT WALL GAP 1o TEMPERATURE- F I I I Goo A00 500 600 700 no 2.5 men CORRUGATED GAP .41 I, F|G.9 8'50 O c I I A 3.40 l 32 l g I .5 men CORRUGATED GAP 2, l INVENTORS w" I, EDWARD F. VERSAW 8: .20 WALTER W. SPOECKER l 2.: man connuenso GAP 47 47/ TEMPERATURE-"F I I 7 4 300 400 soo e00 ATFORNEY United States Patent 3,501,050 AUTOGENOUS IGNITION SUPPRESSOR Edward F. Versaw, La Canada, and Walter W. Spoecker,

Van Nuys, Calif., assignors to the United States of America as represented by the Secretary of the Army and/ or the Administrator of the Federal Aviation Administration Filed Feb. 29, 1968, Ser. No. 709,619 Int. Cl. B65d 25/00 U.S. Cl. 220--88 4 Claims ABSTRACT OF THE DISCLOSURE The disclosure describes a confining passageway for removing leaked fuel vapors, whereby the ignition temperature of the vapors in the structure is raised considerably from the temperature that would exist Without the presence of the removal passageway, and autogenous ignition due to high structural temperatures is prevented.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to an autogenous ignition suppressor used to prevent leaked fuel vapor from spontaneously igniting due to contact with surfaces having a temperature in excess of the ignition temperature of the vapor. More specifically, it relates to a discovery that a re moval passageway of more than minute dimensions bordering the fuel storage raises the ignition temperatures of the fuel to a safe level.

Description of the prior art A number of safety fuel tanks have been designed in the past, utilizing an auxiliary tank adjacent to the main tank. However, these designs have been concerned only with the collection, storage, and gradual consumption of leaked fuel liquid, rather than the vapor, and as such have not dealt with the problem which arises when the struc ture forming the auxiliary tank itself reaches a temperature in excess of the ignition temperature of the fuel. Examples of these are the fuel tanks disclosed in the U.S. Patent No. 2,464,827 issued to H. Noyes on Mar. 22, 1949, and the U.S. Patent No. 2,404,418 issued to B. Walker on July 23, 1946. Unless the problem of the vapors is solved, autogenous ignition leading to fire and/or explosion is likely. The problem becomes acute when supersonic aircraft are involved, as the structure in the neighborhood of the tanks becomes aerodynamically heated in many cases to a temperature in excess of 500 F.

In addition, there was some suggestion in the prior art that to be effective a passageway would have to be so narrow as to make the manufacture of it unfeasible. Specifically, in the August 1956 issue of the National Advisory Committee for Aeronautics Technical Note 3276, on page 32, appears an article by H. C. Barnett and R. R. Hibbard which states that the equation for determining the maximum quenching distance, QD, where P=absolute pressure in atmospheres and T=temperature R., is:

At sea level, T=520 R. and P l, so QD becomes 0.1 inch. Utilizing the temperature of ram air and the standard atmospheric pressure as provided on page 3372 of the 40th edition of the Handbook of Chemistry and Phys- 3,501,050 Patented Mar. 17, 1970 ics, quenching distances at other altitudes can be calculated to be as follows:

Altitude (1000 it) T. R.) lfP (Atmos- QD (inches) 10 514. 69 l. 45 0. 14 20 492. 69 2. 2 0. 21 30 475. 69 3. 38 0. 31 40 451. 69 5. 4 0. 48 50 553. 69 8.8 0. 69 655. 69 14. 2 0. 97 70 959. 69 About 22 About 1.19

SUMMARY OF THE INVENTION This invention provides a safe fuel system by suppressing autogenous ignition of leaked fuel vapors through the raising of the ignition temperature of these vapors. We have discovered that this can be done by using in conjunction with a fuel container, means for continuously removing the vapors from the neighborhood of the fuel container, the means including a passageway adjacent to at least one side of the fuel container having a flow width between one-half inch and about seven inches and means for continuously replacing the volume of gas occupying that passageway at the rate of three volume changes per minute. The result is that the ignition temperature of the vapors is substantially raised above the temperature of the structure confining the fuel vapors.

Accordingly, it is an object of this invention to provide a fuel system which prevents fire or explosion due to escaped fuel vapor by raising the ignition temperature of those vapors to a safe level.

It is a further object to provide a fuel system of the above character by utilizing structural dimensions which are economically practical in the construction of large systems.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary section in perspective of a fuel system constructed according to the invention;

FIG. 2 is a cross-section of the fuel ssytem of FIG. 1 taken generally along a plane through line 22 in FIG. 1, perpendicular to the walls 20;

FIG. 3 is a fragmentary cross-section similar to that of FIG. 2, but illustrating an alternative embodiment;

FIG. 4 is a section of the passageway confining the vapor and illustrates still another embodiment of the invention;

FIGS. 5 and 6 are graphs illustrating typical temperature and pressure recordings for mild and explosive reactions, respectively, obtained in tests made on the invention;

FIGS. 7 through 10 are graphs illustarting the results of the tests;

FIG. 11 is a fragmentary cross-section of a drain utilized in the invention, taken along the line 1111 in FIG.

2; and

FIG. 12 is a fragmentary cross-section taken along the ne 1212 in FIG. 11;

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention is utilized in conjunction with a fuel conainer defined by the walls 11, 12 and 13, and containig fuel 14. The container can be a fuel tank or a conduit nd can be supported in a fixed housing or in a vehicle. IS illustrated, the container is a fuel tank in an airplane ling 16 having a forward edge 17, the walls 11 correponding to the wing surfaces themselves. The space 18 epresents the dry bay area normally found adjacent a uel tank in an aircraft.

In accordance with our invention, to confine vapor :aking from the container a smooth-walled vapor barrier 0 is spaced away from the container Wall by a prescribed istance so as to define a passageway 21. The barrier conists of thin sheet pure titanium, and is hermetically sealed 3 the walls 11. As shown in FIG. 2, the container walls re flat and substantially parallel to the barrier, and the assageway extends around all four vertical walls 12 and 3 of the fuel container with no inlet provided from the :ading edge 17. In this embodiment of the invention, the Ildth of the passageway as determined by our tests infra my be as little as one-half inch but should be less than our inches for supersonic aircraft designed to exceed lach 2.7. For aircraft designed to fly at speeds of Mach .7 or lower, a width of up to 7.62 inches has been found y the tests to adequately increase the autogenous ignition :rnperature of escaped fuel vapors to a temperature at :ast 50 F. above the temperature which the structure eaches. This 50 differential is considered essential to the iaintenance of safety in any aircraft utilizing our inention.

To remove the vapor occupying the passageway, a numer of drains 22 are spaced at the back of the passageway xiting to the atmosphere at a low pressure area, namely arough the trailing edge of the wing. As illustrated in IG. 11, the drain consists of a short tube 23 penetrating hrough the trailing edge of the wall or wing skin 11. "0 provide what is essentially an open vent to the atmoshere, it has been found that the tube must have a dimeter of at least 1%. inches for passageways having the .bove-stated widths. To prevent a flame which has been gnited outside the tube from traveling into the passage;

ectional area of the tube, so that open vent flow is mainained.

In accordance with an alternate embodiment of the nvention, the volume of gas, including the vapors, can e forcibly replaced at a prescribed rate. To do so, the )revious embodiment of FIG. 2 is modified so as to in- :lude in the leading edge 17 of the wing ram air inlets 26 consisting of tubes and drilled holes 28 as shown in IG. 3. The sizes of the holes 28 and of the drains 22 ire adjusted so that the rate of change of the gas in the )assageway is three volume changes per minute.

In accordance with still another embodiment of the nvention, the passageway may have obstructions such as he wall reinforcements 30 on the container wall 12, FIG. L and still achieve the desired result provided that the limension (BA) does not exceed 1.5 inches.

TESTS The above dimensions of the passageway and the rate |f volume change used in the alternative embodiment vere discovered by experiment. A test specimen was constructed utilizing a rectangular shell which housed a fixed, simulated fuel tank wall and a barrier which together defined a passageway for trapping fuel vapors. Both the tank wall and the vapor barrier hermetically sealed thereto were fabricated from 0.063 inch pure titanium sheet, and the barrier was adjustable so as to vary the effective flow width of the passageway. The fixed dimensions of the passageway were: length, 68 inches and height, 24 inches. The entire shell was inserted in an altitude chamber wherein the pressure was adjusted to simulate various altitudes, and the outside of the walls of the passageway were heated up to 750 F. by quartz lamps to the desired test temperatures, thus simulating the heating of the passageway structure under operating conditions. In the illustrated example, the lamps simulated aerodynamic heating. In the ends of the fixed portions of the passageway cutouts and exterior manifolds were provided to pro vide for an open vent to the simulated atmosphere, to provide purge air at the end of each test, and to supply ram air for some of the experiments. The temperature of the ram air used in the tests was adjusted to represent the temperature under actual high-speed flying conditions. That is, the temperature was set as determined by the following equation where T =temperature in degrees absolute of the air after it has been rammed into the passageway; T =temperature in degrees absolute of the static atmosphere at the desired altitude; and M=the speed expressed as a Mach number:

Variable area flowmeters (rotameters) were used to insure a constant flow rate in those experiments utilizing ventilation. Fuel vapor from three fuels meeting the ASTM D1655 Jet A1 kerosene fuel specification was introduced utilizing fuel/air ratios varying from 1.2 to 2.5 times stoichiometric. The fuel was intrOduced four different ways: spray, solid flow, drops and mist. Ignition was detected by thermocouples, differential pressure probes and by observation through viewing ports provided in the shell. Reactions were defined as follows:

(a) No reaction: no rise in pressure or temperature from equilibrium conditions, no visible flame.

(b) Mild reaction: any small, slow rise in equilibrium pressure or temperature or faint blue flame (see FIG. 5).

(c) Explosive reaction: large rapid rise in equilibrium pressure and temperature with visible yellow flame (see FIG. 6).

As a control, the same tests were run on a 500 gallon unvented tank several feet in width to determine the effect of vapor leaking into an essentially unlimited volume. This would be the effect if no vapor barrier were used to trap the vapor.

Graphs (FIGS. 7-10) were made of the mild reactions, with the temperature of the onset of the reaction plotted versus the corresponding simulated altitude, as determined by the absolute pressure prior to the reaction. Included on the graphs were the temperatures which the heavy structure of a supersonic aircraft has been found to undergo at the various altitudes and under an emergency descent. The dashed lines 32 represent the emergency descent of a Mach 2.7 airplane while the dashed lines 34 represent the emergency descent of a Mach 3.0 airplane. The circled lines 35 represent the safety margin of 50 F. above the temperature of the structure of the Mach 3.0 airplane. The broken lines 36 represent the mild reaction in the case of the 500 gallon unvented tank; that is, of the effect of having no vent and no vapor barrier. The temperature difference between the circled lines 35 and any of the test results of the passageway at any given altitude represents an additional margin of safety over and above the minimum temperature margin of safety of 50 F. which is required.

EXAMPLE NO. 1

A passageway consisting of substantially smooth parallel walls was tested utilizing an open vent and no ram air inlet. The vapor barrier was positioned at five different distances from the container wall so as to define five different effective flow widths for the passageway. The results appear in FIG. 7. All of the configurations are satis factory when used in a Mach 2.7 airplane. A Mach 3.0 aircraft, however, would require a passageway less than four inches wide.

EXAMPLE NO. 2

The same passageway was used as in Example No. 1, except that the gas in the passageway was ventilated during the test at the rate of three volumes per minute, to simulate ventilation by ram air. The results appear in FIG. 8, and all configurations are satisfactory when used in a Mach 2.7 or 3.0 airplane. Comparison with the results of FIG. 7 indicates a marked improvement is obtained by using ram air ventilation.

EXAMPLE NO. 3

The same test was run as in Example No. 1, except that the passageway was modified by having obstructions attached to the container wall to simulate structure needed for other functions, such as structural support. As shown in FIG. 4, the obstructions in the test consisted of trapezoidal sections 30 attached to the container wall 12. The A dimension was fixed at 1 inch, but the B dimension was set at both 1.5 inches and 2.5 inches in separate tests. The results appear in FIG. 9 and indicate the eifect the obstructions create by disturbing the flow of the vapor towards the open vent. Comparison with the results obtained in FIG. 7 indicates that the presence of the obstructions does lower the ignition temperature, but not so much as to make the tested configuration unsafe for use with a Mach 2.7 or 3.0 airplane.

EXAMPLE NO. 4

The same test was run as in Example No. 3, except that as in Example No. 2, the gas in the passageway was ventilated at the rate of three volumes per minute. The results appear in FIG. 10, and indicate that the tested configurations are satisfactory in all respects when used in a Mach 2.7 or 3.0 airplane. As in the case of Example No. 2, marked improvement is obtained by ventilation.

It is apparent from these tests that the passageway does not have to be as narrow as the quenching distance of between 0.1 inch and 1.2 inches, as taught by the prior art,

to obtain significant results. Accordingly, the tests indicate that the use of a passageway is practical because constnlction utilizing such small dimensions can be avoided.

While the invention has been described in connection with a preferred embodiment, it will be understood that we do not intend to limit the invention to that described. For example, the invention is applicable to ground structure or a vehicle in which the heat effect comes from the presence of an engine located in the space 18.

We claim:

1. An autogenous ignition suppressor for use in conjunction with a fuel container and fuel vapor escaped therefrom, said ignition suppressor and said fuel container being mounted within a structure having an outer wall, said suppressor comprising means for continuously removing escaped fuel vapor from the neighborhood of the fuel container, said means including a passageway formed by a vapor barrier wall adjacent to the side walls of said container, said passageway having an effective flow width between one-half and about seven inches, and drains connected between said vapor barrier wall and said outer wall.

2. An autogenous ignition suppressor as defined in claim 1 wherein said drains include a flame arrestor therein.

3. An autogenous ignition suppressor as defined in claim 1 wherein said passageway is defined by smooth parallel walls.

4. An autogenous ignition suppressor as defined in claim 1 in which said removing means also include air inlets connected between said vapor barrier wall and said outer wall.

References Cited UNITED STATES PATENTS 1,705,928 3/ 1929 Lambert. 1,783,701 12/1930 Cooke et al. 2,439,603 4/1948 Heritage 220-9 X 2,719,583 10/1955 Malick 137- 576 X FOREIGN PATENTS 28,496 1913 Great Britain. 150,053 8/ 1920 Great Britain. 367,579 2/1932 Great Britain.

RAPHAEL H. SCHWARTZ, Primary Examiner

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