The Chemistry and Mechanics of Combustion with Applications to Rocket Engine Systems

Abstract

PREFACETask 1, as outlined in the original proposal, was to be a study of gas-gas mixing at the boLndary between two fast-moving gas streams. Work. on this task was postponed for the first year of the project in order to permit intensified effort -n other tasks.A review r the project as a whole, in the light of an opportunity afforded by changes in the sponsorship of related combustion oroJects, now leads us to propose replacing the task on mixing with one on polyirer decomposition rechanisms. We look upon this change as a means to strengthen the project by initiating the investigation of molecular mechaniszns of combustion, later expanding to the studty of molecular mechanisms of thermo-mechanical and chemico-mechanical behavior of propellant materials,The investigators have already reported some work on polym7%er decomposition (ArOSR Final Report 67-)901), and this work is still ir progress under other sponsorship. It has been concerned almost exclusively with measuremr!_,ts of the thermal effects attending the rapid heating of polymnes and propellant-lik. materials, very limited work having been done on the chemical aspects. The therml approach under other sponsorship should -be completed ir September 1968 anrd combined thermal and chemica-approach will be initiated as Task I under THF-MIS at that tim-e. The seve,-ai coriention.i .et --, eveloped for the study of the erma] decmposition C' polymeric and composite materials (DTA, TGA, "C) suffev from the defect that. at the sinall heating rates employed, ;e high-temperatore d.cn-.pooio: mechanisns probably active in combustion ",ocesses are not observed; thc virgin mtaterial is consumed or altered by w-.temperature mech~e 'ms before the decomicsition temperatures associated th combustion processes ;re readhe: TL: w)rk alrcady performed at this tcil.ty has employed heatii, , rates 50 to 100 times as great as those ed in conventional studies.Briefly, the studies with PBAA polymer havie revealed that, if heati;ng %es place in an inert, evircnnt, a pressure-dependent endother'm is served well before a significant amount of gaseous product is evolveJ.heating takes place in the presence of hot oxygen, or even in nitrogen en the polymer contains twenty percent or more of ammonium perchlorate, e first significant ewvnt iq an exotherm; and it is observed well before visible flame signals ignition. The dependence of the temperatures at Ich these even.s o,-rr o-heating rate, pressure, and oxygen tem-erature trits some !nfe-,rces LOcerning mechenism but serves mainly to identifyI I partial1y -to cnarac.terlze everts whse chemistry must be studitd before 3.ful result can be published, Studc2s now in progress define the problems which will be investigated Task I. The current study has yielded data concerning the polymeriger reaction which can be used to discriminate between proposed mechanisms the reaction. However, since these data were ob.tained under transient iditiris, Lneir vchanistic interpretation must account for time-dependent rder,ýture and concentration variations...