Spectroscopy Diagnosis Study On The Spatial Location And Intensity Of Hydroxyl Radical(OH) In Solid Propellant

We report on the application of laser-induced fluorescence (LIF)spectroscopy technique for the detection of OH vertical concentrationdistribution in the alcohol burner, premixed methane/oxygen and solidpropellant flames. For explain phenomena, we add correlative theories to thedissertation. It will make reasoning be precise and content be abundant. At thesame time, the dissertation show many kinds of the characteristics andapplications of spectroscopy diagnosis, and build the basis for this experimentand the intending work.The first part is the academic analysis. According to the developmentalprocess in organic chemistry, we know that, the conception of radical is notstrict. We use the definition for reference physical chemistry scientists andchemic physics scientists. The radical is any transient species (molecule, ion andatom). So we confirm our researching object. We expel from the steady molecule likeO₂, NO, et al. We include C₂, CH₂, CHF and the ion of the molecule and the atom. In basic conception of combustion, we explain the scientific combustiondefinition and the basic characteristic. We analyse the differ of premixed flame anddiffused flame, and connection between two flames and the solid propellantcombustion. It provide a nicer gist for building the solid propellant model.The combustion of premixed methane/oxygen is the most common model ofcombustion in lab. And it is a preconditioning method of analysis combustion of thesolid propellant. But this model has a complicated dynamics process too.The most ordinary that can explain the result of methane oxidation in lowtemperature is:According to analyzing the reaction chain in the combustion, we knowwhat role radical play. For instance, we use CO to estimate the question of thelow temperature oxidation, find more concentration of O and H radical in high temperature reaction, find OH and H radical to be a dominant position andreveal plenitude capability, find HO2 radical to be inexistent in hightemperature reaction.The different premixed proportion of methane and oxygen will come intobeing different combustion and velocity of flow, and influence the product andtemperature of the combustion. Compare to the solid propellant's owncharacteristic, we make it be a basic method that simulate how deficient andadequate in the solid propellant.In the last part of academic analysis, we discuss basic theory aboutmolecular spectroscopy. As illustrated in Fig. 1, it can strength understand themolecular spectroscopy, the origin of expressions, the design of energy levelsand the rule of radical transition. Thereout, it help us to research spectroscopydiagnosis applications in detecting the radical, and expediently build the basisfor the innovative experiment in the future. The second part is experiment discussion. We introduce and analysismany spectroscopy methods in the combustion diagnosis. We discuss their ownelements, characteristic and application. This summarize is a research condensein this field, and Laid the groundwork for lab work in the future.We special analyse and discuss the elements and method of LIF. It is basicin this experiment. LIF spectroscopy technology is a method of detecting on thefluorescence spectra by laser induced fluorescence. According to the LIF theory,fluorescence intensity from the media can be theoretically expressed:where the summation is over all transition. The fluorescence quantum yield isdetermined by A/(A+Q); and Copt is transmission efficiency of the collection optics.Thus, it can be seen that LIF signal intensity is a function of temperature, pressure,mole-fraction and a number of other known experimental parameters. Usually, Q >> Aand Q is approximately P/KT in the flame. The fluorescence signal is basicallyindependent of the pressure. On the other hand, the factors that relate to thetemperature are included inEvaluating the derivative of fJ (T)with respect to temperature and equating itto zero leads to:where T is an average flame temperature, J* is the rotational level whosepopulation is most insensitive to temperature changes and Bv is rotational constant. So by appropriately selecting the initial level for excitation, namely J*, the measurementsbecome quite insensitive to temperature.By the theoretical equation above and the LIFBASE program, excitation wasmade in the Q-branch of the (1,0) band of the OH A–X system near 282.7 nm, and thefluorescence from the A–X (0,0) band around 309.1 nm was collected in the presentexperiment. Moreover, using the homemade mechanical system which canautomatically lift, we could change the spacial location of the combustion medium.The hardware required to implement PLIF can be divided into three subsystems,the excitation system, experience building, detection system, and mechanical systemwhich can automatically lift the burning medium.As illustrated in Fig. 2, excitation and detection systems are described. Afrequency-tripled Nd:YAG (Continuum, Model GCR-230-10R) (temporal width 10 ns,repetition rate 10 Hz) pumped a dye laser (Sirah, Model CSTR-GA-24) operated withRhodamine 590. The dye laser output light at 565.4 nm, which was frequency-doubled,produced UV light at 282.7 nm. Each pulse of the laser usually produced about 0.2 mJof energy. This light excited Q1 transition in the A²Î£+-X²Î (1, 0) band of OH at 282.7nm, and nonresonance fluorescence around 309.1 nm was detected. After passing aPellin-Broca prism, the second harmonic radiation was sent into the flame, when theresidual of the fundamental beam after the prism was sent to trigger diode. The LIF signal from the flame was focused onto the entrance slit of a monochromator (ActonResearch Corporation, Model 500i) by a lens (f = 150 mm), and in the exit slit aphotomultiplier tube (PMT) connected to a Boxcar Integrator (PARC model 4402)which was used as the detector for the monochromator. The monochromator, PMTand Boxcar Integrator were used to record the laser-induced fluorescence spectra.A schematic set-up of the homemade mechanical system which can automaticallylift the burning medium is shown in Fig. 3. Utilizing automatically lift platform of thestep motor, the vertical location of the combustion medium could be changed.Furthermore, the diameter of the probed volume in the flame is 1 mm, and the probedvolume kept the same position when the flame was shifted.In this experiment, regarding alcohol burner, premixed methane/oxygen and solidpropellants as the combustion mediums, OH radical vertical concentrationdistributions in three flames were measured.First, regard the measurement of the alcohol burner flame as the calibration of theentire optical route. The LIF signal of OH vertical concentration distribution inatmospheric pressure flame of alcohol burner is presented in Fig. 4. The abscissa is thevertical height above the bottom of the probe flame; the ordinate is the simplifiedsignal intensity. The height of the flame was 9.5 cm. The shift velocity in vertical orientation of the flame was 1 mm/s. Shown in Fig. 4 is that, in outer flame region,OH concentration showed a maximum because the air provided sufficient oxygen forthe combustion. Dots are experimental data; the solid line is a fit according toexperimental data.With the same experimental set-up used in the alcohol burner flame measurement,varying oxygen proportion in premixed methane/oxygen system, the OH radicalvertical concentration distributions were measured in different atmospheric pressureflames. The maximal height of the four flames was 14, 13, 14 and 15 cm, respectively.Other experimental parameters were the same as the ones in the measurement of thealcohol burner flame. Fig. 5(a-d) provides experimental data (dots) and the fittings toexperimental data (solid lines). As illustrated in those fits, the OH radicalconcentration changes dramatically with different proportions of oxygen.With above measurement approach, the flames of the three different solidpropellant samples provided by Modern Chemistry Research Institute of Xi'an, wereprobed. The three solid propellants were labeled with 4th, 10th and 17th, of which oxidizer proportions were different. OH radical vertical concentration distributions areshown in Fig. 6(a-c). All the heights of the solid propellants were 8 cm. The maximalheight of the flames during the burning process was 12, 17 and 14 cm, and the burningtime was 16, 21, 14 s, respectively. So we can obtain the burning velocities of 0.51, 0.38 and 0.57 cm/s. Moreover, owing to the burning velocity of the solid propellant,the excitation light could cover the entire flame height in the burning process.Consequently, the additional shift velocity in vertical orientation of the solidpropellant flame was not needed.So, we analyse that it is shown that the variation ofoxygen proportion in the mixtures makes a big difference in the spacial location andintensity of sufficient combustion in the flames. With the increase of oxygenproportion, the spacial location where the OH concentration shows a peak shiftstoward the bottom of the flame, and appropriate oxygen proportion results in thelargest peak of OH concentration. Obviously, it indicates that in the bottom of flame,the premixed oxygen has already started to work in oxidation processes of methane.When the oxygen proportion is suitable, the OH concentration will reach its maximumand the combustion will be most sufficient.However, shown in Fig. 6 is that, the spacial location, where the OH maximumconcentration is located, shifts toward top of flame with the increase of the samplenumber of the solid propellant. The 4th solid propellant sample burned sufficiently inthe middle part of the flame, while this process of the 10th and the 17th propellantoccurred in the top of the flame. It could be due to that the burning velocity of thesolid propellant was faster than that of the premixed methane/oxygen, and it is too fastto burn sufficiently in the bottom of the flame. As can be seen from the peak relativeintensity of Fig. 5, the peak of the 1st propellant reaches a maximum. Furthermore, inorder to obtain OH fluorescence relative power, firstly, the measurement points shownin Fig. 5 are integrated in the vertical position. Then, the integral value is divided bythe burning time of the propellant. The acquired final values are the OH fluorescencerelative power which all the three propellants produced in the burning process, whichis 0.191, 0.138 and 0.141, respectively. As a consequence, according to the peak intensity and relative power of OHfluorescence in the burning process as illustrated in Fig. 5, if only considering therelation between the oxidizer proportion in the solid propellant and the sufficientburning process, oxidizer proportion of the 1st propellant is most suitable.As a consequence of the above,measure of Radical that is produced incombustion process is contributed to understand the particularity case of combustionand the process of dynamics. Laser spectroscopy diagnosis that has its advantagedpredominance play a important role in the combustion diagnosis. With this experiment,we use LIF that is mature and effective to measure the spatial location and intensity ofOH radical in the solid propellant flame。LIF can evaluate oxidant that isproportioning quantity and rationality. The result of this study is helpful to understandthe sufficient burning process of the solid propellant flame, and is valuable to thesynthesis of solid propellant material.