Penner, Stanford S.

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ropellants and Combustion 
um.NG the last year, several signifi-
cant publications dealing with pro~ 
pellants and combustion were pub~ 
lishec1. The most voluminous and 
extensive effort is represented by the 
proceedings of the Eighth Inf;errw.-
tional Com.bustion Symposium, w-hich 
was devoted to papers dealing with 
combustion research on rocket engines, 
ions in flames, and other basic topics 
such as laminar Rarne. theory, detona~ 
ti.ons, etc. The American B.ocket So-
ciety contributed Vol. 6 of the series 
on Progress in A"itl'Onautics and 
Rocketry, w-hich deals with. detona-
tions, two-phase flow in nozzles, and 
combustion .in liquid-fuel rockets. 
Since the writer served as chairman of 
the Papers Subcommittee of the Com-
bUStiOIt Symposium and as one of the 
editors of the AIlS publication, he is 
clearly in no position to offer ohjective 
comments on these two produ.ctions. 
However, at the risk of overstepping 
the bounds of propriety~ he will never-
theless assert that careful study of the 
papers published in these proceed-
ings, as wen as examination of original 
articles contributed to Combustion 
and Flame and the rather surprisingly 
srn.aU uuml)er of papers published in 
the ARS ]o-urnal,wiU Justify the con-
clusions fhat follow. 
L Significant progress has been 
made in our understanding of the es~ 
sential features of the steady com-
bustion processes in a ( one-dimen-
sional) liquid-fuel rocket engine. 
BY STANfORD S. PENNER 
INSTITUTE FOR DEFENSE ANALYSIS, WASHINGTON, D,C. 
CHAIRMAN, ARS PROPELLANTS AND COMBUSTION COMMITTEE 
2. The burning mechanislH and de-
composition rate of ammonium per-
chlorate are now well understood, ex·· 
cept for some details concerning the 
low-pressure deflagration limit, that is, 
the limiting pressure below which the 
propellant ceases to bum, 
3. The problem of two-phase nozzle 
How is well described insofar as the 
gross features of the physical processes 
are concerned. 
4. Shock and detonation phenom-
ena continue to be of fun.damental in-
terest and importance, Progress is 
being made in clarifying the micro-
scopic processes not only in gas mix-
tures but also in the condensed phases. 
There is growing evidence that the 
structure of the detonation waves may 
not be steady (on the microscopic 
scale) although the "vave front JS es-
sential1y Hat. 
5, The microscopic des·criptions of 
composite propellant burning mecho 
an ism and of resonance burning in 
solid rockets require further elucida~ 
tion, Nevertheless, in spite of sig-
nificant experimental and theoretical 
developments~ we regard it as un~ 
likely that a useful prediction can ulti-
mately be made of bu.ming rates on 
the basis of chemical composition and 
of stability behavior on the basis of 
chemical composition and geornetric 
considerations, 
6_ No real progress has been 
achieved in connecting liquid-rocket 
instabilities with microscopic proc-
(Reprinted/rom ASTHONAlfTJC8, Novemher, 19(;2) 
esses. But, i:l useful phenomenological 
methodology has been developed for 
correlating observational results. 
7> The important problenl of super-
sonic burning is receiving the atten·· 
bon which it deserves and preliminary 
results have encouraged some people 
to the point where they are willing to 
state tbat the design of the comhus~ 
tion chamber wiE not be a major 
stumbling block to the development of 
hypersonic xamjets. If this optimism 
is justified remains to be seen, 
8. Hybrid rockets promise bJ be-
come the next significant target for 
research on combustion processes moti-
vated by propulsion development, 
g, The combustion processes of 
metals have bee.n studied and some 
interesting suggestions :have been 
made concerning ()ombustion mechan-
isms. 
10. M neh remains to be learned 
about the nature of the elementary 
processes responsible for the produc-
tion of ions and electrons in HaInes. 
Some general observationB with re-
gard to advances ill propellant tech-
nology can also b·e made, Today, 
N20 4 with a mixture of UD:MH <'md 
hydrazine is an operational propellant 
system. Liquid hydrogen~Hquid oxy~ 
gen engines are currently under ex-
tensive development Composite solid 
propellants using high-weight frac-
tions of aluminum particles are Hnd-
ing daily use. It has 110\V become 
generally accepted that large perforrn-
C('pyright, lWi2, hy t!ll' Anwricall Hockt·t SCH·ldy, :Inc" and repriut-I-d by l)(~rnlission ofUw cnpyrigb! O\\IWl", 
ance increases in either storable liq-
uid or solids or even liquid hydrogen-
liquid oxygen can be obtained only 
through addition of the light metallic 
elements. Research in solid propel-
lants thus takes the direction of either 
removing partially the heterogeneous 
oxidizer by modification of the binder 
to contain oxidizer elements so that 
larger mass fractions of metals may be 
added or complete removal of the oxi-
dizer and reverting to hybrid tech-
nology. Similarly, metal addition in 
liquids can be obtained by suspension 
in gels. Thus the search for thixo-
tropic gelling agents for liquid propel-
lants that will permit suspension of 
reasonable quantities takes on some 
significance. 
The theoretical advantages of fluo-
rine-liquid hydrogen with respect to 
performance and of fluorine-hydrazine 
93 AstronauUcs / November 1962 
for extended early space missions per-
mits fluorine to keep its place in the 
propellant spectrum. In the opinion 
of some, the disadvantages of fluorine 
may overshadow the apparent gains 
and the efforts associated with this 
propellant are much smaller than those 
with other oxidizers, 
Four major symposiaciealing with 
propeHantsand combustion were held 
during 1962. These were the AGAHD 
Colloquium on "High-Temperature 
Phenomena" in Braunschweig, Ger-
many, during April; the Ninth Inter-
national Combustion Symposium at 
Cornell Univ. during August; an ARS-
sponsored specialist meeting on "Ions 
in Flames and Rocket Exhausts" at 
Palm Springs, Calif., during October; 
and a group of tutorial papers at the 
ARS Annual Meeting in Los Angeles 
during November. This heavy sched-
ule of combustion symposia attests to 
the vigor of eif01i in this field as weB 
as to the fact that com bustion research-
ers burn up a great denl of energy and 
time in attending meetings. The de-
tailed technical summary of the ac-
complishments of the 1962 symposia 
\"ill be left to the next Annual Review. 
However, the preliminary conclusion 
of one. indefatigable combustionist 
who attended nearly all four of the 
meetings is that the previously item-
izedconclusions remain invariant, that 
real progress is almost undetectably 
slow, and that serious consideration 
should be given to the definition of 
crudal studies by the stalwarts work-
ing on propeHants and combustion. 
Acknow.ledgment 
The author is indeb~ed toUro L Glassman £01" 
contributing the discussilm on propellant tech~ 
noloID'". . ~~ 


Propellants and Combustion

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Propellants and Combustion

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