MIL-STD-202H.pdf - 第59页

MI L - S TD - 202 - 10 9 M E TH O D 1 0 9 EX PL O SI O N 1. SCOPE 1. 1 P urpose . T he pur po s e o f t hi s m et hod i s t o d et er m i ne i f a par t , w hi l e oper at i n g, w i l l i gn ite an a mbient ex plosive a…

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MIL-STD-202-109
CONTENTS
PARAGRAPH PAGE
FOREWORD…………………………………………………………. ii
1. SCOPE 1
1.1 Purpose………………………………………….……..…………. 1
2. APPLICABLE DOCUMENTS 1
3. DEFINTIONS 1
4. GENERAL REQUIREMENTS 1
4.1 Apparatus ……………………………………………..…………. 1
4.1.1 Test facility……………………………………………………….. 1
4.1.1.1 Test facility performance requirements. …………………….. 1
4.1.1.1.1 Chamber design pressure…………………………………..….. 1
4.1.1.1.2 Pressure altitude. ………………………………..…………..….. 1
4.1.1.1.3 Chamber air temperature. …………………………………..….. 1
4.1.2 Fuel…..…………………………..….…………….………………. 2
4.1.3 Fuel vapor mixture. …………..….…………….……………….. 2
4.1.3.1 Effect of humidity on flammable atmosphere………………… 2
4.1.4 Altitude simulation. ……..….…………….…………….……….. 2
4.2. Procedure……..………………..….…………….………………. 3
4.2.1 Test preparation ………………………..……………………..… 3
4.2.1.1 Controls..……………………..………………………….……..… 3
4.2.1.1.2 Mounting..…………………..……………………..…….……..… 3
4.2.1.2 Loading. …………………..………..……………..…….……..… 3
4.2.2 Test execution..…………..………..……………..…….……..… 4
4.2.3 Test altitudes….…………..………..……………..…….……..… 4
5. DETAILED REQUIREMENTS 4
5.1 Summary……………..…………………………..………………. 4
6. NOTES 5
6.1 Supersession data………………………………………………. 5
FIGURE PAGE
1 Specific gravity of n-hexane…………………………………………..…… 3
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北测（上海）电子科技有限公司
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MIL-STD-202-109
METHOD 109
EXPLOSION
1. SCOPE
1.1 Purpose. The purpose of this method is to determine if a part, while operating, will ignite an ambient explosive
atmosphere. This environment is prevalent in aircraft; therefore, the test is conducted at ground level and various
reduced barometric pressures. The parts subjected to this type of test are not enclosed in casings designed to
prevent flame or explosion propagation.
2. APPLICABLE DOCUMENTS
This section not applicable to this standard.
3. DEFINTIONS
This section not applicable to this standard.
4. GENERAL REQUIREMENTS
4.1. Apparatus.
4.1.1 Test facility. The test apparatus consists of a test chamber or cabinet together with associated equipment,
safety provisions, and auxiliary instrumentation necessary to establish, maintain, and monitor the specified test
conditions. The chamber should be equipped with a system for mixing and circulation of the explosive air-fuel
mixture, a means to ignite the air-fuel mixture such as a spark-gap device, as well as a means to collect and
determine the explosiveness of a sample of the mixture such as a spark gap or glow plug ignition source with
sufficient energy to ignite a 3.82 percent hexane mixture. An alternative method of determining the explosive
characteristics of the vapor is use of a calibrated explosive gas meter that verifies the degree of explosiveness and
the concentration of the air-fuel mixture. The chamber or cabinet should include provisions for the electrical and
mechanical operation of the specimen under test.
4.1.1.1 Test facility performance requirements.
4.1.1.1.1 Chamber design pressure. The test chamber shall be capable of withstanding any explosion pressure up
to and including 300 pounds per square inch (2 megapascals).
4.1.1.1.2 Pressure altitude. The test chamber shall be capable of maintaining any desired pressure altitude from
sea level to 60,000 feet (18,250 meters) ± 2 percent.
4.1.1.1.3 Chamber air temperature. The air temperature within the test chamber shall be uniform and shall be
controllable between 20°C ± 3°C and 240°C ± 3°C.
1
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MIL-STD-202-109
4.1.2 Fuel. Unless otherwise specified, the fuel for explosive atmosphere testing shall be the single-component
hydrocarbon n-hexane, either reagent grade or 95% n-hexane with 5% other hexane isomers. This fuel is used since
its ignition properties for flammable atmosphere testing are equal to or more sensitive than the similar properties of
both 100/130 octane aviation gasoline, JP-4, and JP-8 jet engine fuel. Optimum mixtures of n-hexane and air will
ignite from hot-spot temperatures as low as 223°C (433°F) while optimum JP-4 jet engine fuel-air mixtures require a
minimum temperature of 230°C (445°F) for auto-ignition, and 100/130 octane aviation gasoline and air requires
441°C (825°F) for hot-spot ignition. Minimum spark energy inputs for ignition of optimum fuel vapor and air mixtures
are essentially the same for n-hexane and for 100/130 octane aviation gasoline. Much higher minimum spark energy
input is required to ignite JP-4 or JP-8 jet engine fuel and air mixtures. Use of fuels other than hexane is not
recommended. CAUTION: If the individual specification allows the use of an alternate fuel, the specification must
also provide all the specific details associated with the alternate fuel, such as safety precautions and fuel-air mixture
equation.
4.1.3 Fuel vapor mixture. Use a homogeneous fuel-air mixture in the correct fuel-air ratios for the explosive
atmosphere test. Fuel weight calculated to total 3.8 percent by volume of the test atmosphere represents 1.8
stoichiometric equivalents of n-hexane in air, giving a mixture needing only minimum energy for ignition. This yields an
air/vapor ratio (AVR) of 8.33 by weight.
a. Required information to determine fuel weight:
(1) Chamber air temperature during the test
(2) Fuel temperature
(3) Specific gravity of n-hexane (see figure 1)
(4) Test altitude: (e.g. 20,000 feet (6100 meters)). Atmospheric pressure in pascals: 46.6 kPa (6.76 psia)
(5) Net volume of the test chamber, free volume less test item displacement expressed in liters or cubic
feet.
b. Calculation of the volume of liquid n-hexane fuel for each test altitude:
(1) In metric units:
Volume of 95 percent n-hexane (ml) =
−
−
)hexanenof
gravityspecific(x)K(
tempchamber(
)
pascals(pressure
chamber(x
)liters(volchamber
net(
)x.
(
4
10
274
(2) In English units:
Volume of 95 percent n-hexane (ml) =
−
)hexanenofgravityspecific(x)R(tempchamber(
)psia(pressurechamber(
x))ft(volchambernet(
).(
3
41150
4.1.3.1 Effect of humidity on flammable atmosphere. Humidity is always present in an explosive atmosphere test.
The effect of humidity upon the fuel-air composition need not be considered in the test if the ambient air dewpoint
temperature is 10°C (50°F) or less because this concentration of water vapor only increases the n-hexane fuel
concentration from 3.82 percent to 3.85 percent of the test atmosphere. If the atmospheric pressure is cycled from
an equivalent of 5000 feet (1525 meters) above the test level to 5000 feet below (a 34 percent change in pressure),
the volume of n-hexane will decrease from 4.61 percent to 3.08 percent. This decrease will compensate for the fuel
enrichment effect that results from water vapor dilution of the test air supply.
4.1.4 Altitude simulation. The energy required to ignite a fuel-air mixture increases as pressure decreases.
Ignition energy does not drop significantly for test altitudes below sea level. This test is not appropriate for test
altitudes above approximately 52,000 feet (≈16,000 meters) where the lack of oxygen inhibits ignition.
2
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