ASTM_D_2389_-_83_1994.pdf

Designation:D 2389 83(Reapproved 1994)Standard Test Method forMinimum Pressure for Vapor Phase Ignition ofMonopropellents1This standard is issued under the fixed designation D 2389;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method2covers the determination of theminimum pressure at which a monopropellant ignites in thevapor phase.1.2 This standard should be used to measure and describethe properties of materials,products,or assemblies in responseto heat and flame under controlled laboratory conditions andshould not be used to describe or appraise the fire hazard orfire risk of materials,products,or assemblies under actual fireconditions.However,results of this test may be used aselements of a fire risk assessment which takes into account allof the factors which are pertinent to an assessment of the firehazard of a particular end use.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Summary of Test Method2.1 The minimum pressure for vapor-phase ignition is alimiting measure of what is conceived to be a fundamentalmonopropellant property,the minimum ignition energy.Theminimum pressure for vapor-phase ignition is that pressurebelow which it is impossible to ignite a monopropellant vaporwith a fixed quantity of energy applied in a well-definedmanner.It is expected that,by employing greater quantities ofenergy or applying them in somewhat different fashions,ignition may be obtained at lower pressures.However,thequantity obtained using the procedure described in Section 5gives useful relative values which are for most practicalpurposes a minimum pressure for vapor-phase ignition.Theprincipal advantage of this test is the small quantity(only a fewmillilitres)of sample required,the simple apparatus in whichthe experiment can be performed,and the versatility of theapparatus.(However,it is important to realize the limitationsset on interpreting such information.)3.Significance and Use3.1 In vapor-air mixtures the minimum spark-ignition en-ergy has been very helpful in evaluating fuels,both forperformance and for handling characteristics.The techniquereported herein is useful for evaluating a similar characteristicfor monopropellants in the vapor phase.For monopropellantsthat ignite easily at normal pressure,that is,very close to 1 atm,the usual minimum spark-ignition energy techniques can beemployed.It has been found,however,that most usefulmonopropellants will not ignite in the vapor phase at a pressureof 1 atm.At the higher pressures necessary to obtain ignition,experimental difficulties are experienced with electric spark.For example,the high voltages required to jump the spark gapare difficult to handle in this type of system.3.2 A technique has,therefore,been partially developed todetermine the minimum pressure for vapor-phase ignition.Thistechnique involves the electrical fusion of small wires.Inpractice the experimental evaluation of energy is somewhatdifficult;however,a useful quantity,the minimum pressure atwhich ignition can be obtained with a fixed energy,can bereadily determined.The significance of this quantity can bebetter understood by reference to Fig.1 where the minimumspark-ignition energy for n-pentane-air is plotted as a functionof the total pressure.This curve,which is representative of allthe air-fuel mixtures studied,is employed because no compa-rable data are available for monopropellants.The monopropel-lants already studied behave in the same manner.For acetyleneat 100C and 0.07 J,a minimum pressure of 3.5 atm wasobtained in a small 38-mm diameter cylindrical bomb,and 2.2atm in a larger 76-mm diameter spherical bomb.Instead ofobtaining a curve similar to that shown in Fig.1,which wouldbe desirable,only one point was obtained,namely the pressureat a fixed ignition energy.The temperature is always a variableand must be specified.4.Apparatus4.1 Fig.2 shows a schematic drawing of the apparatus usedfor determining the ignition pressure limits of vapors by fusedwires(Note 1)at any temperature from 25 to 260 C.Theapparatus shall consist of:(1)a thermostat-equipped stainless-steel bomb into which the monopropellant vapor is placed,(2)1This test method is under the jurisdiction of ASTM Committee F-7 onAerospace Industry Methods and is the direct responsibility of SubcommitteeF07.02 on Propellant Technology.Current edition approved April 29,1983.Published August 1983.Originallypublished as D 2389 65T.Last previous edition D 2389 70(1980).2This method is identical in substance with the JAANAF method“MinimumP