Penner, S. S.

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THE ROLE OF COMBUSTION RESEARCH IN ROCKET PROPULSION 
By 
S. S. Penner! 
Summary 
In spite of significant progress on the development of advanced propulsion tech-
niques (i.e., of nucle~thermal propulsion, nuclear-electric propulsion, and large 
air-breathing boosters), it appears quite certain that chemical rockets will remain 
the most widely used vehicles for missile and space exploration for some years to 
come and, furthermore, will continue to playa vital role for special missions in fu-
ture years. For this reason, it is not inappropriate to discuss the extent to which 
basic research on combustion has contributed in the past to powerplant development 
and to what extent current and future studies are likely to facilitate new develop-
ments of chemical rockets. 
The chemical rocket provides an almost classical example of a device that is 
too complex for detailed, quantitative description. Nevertheless, significant prog-
ress has been made in understanding the essential features of many of the steps in-
volved in the utilization of propellant energy. 
Reasonably simple models and descriptions are available for spray formation, 
droplet ignition, flame propagation, spray burning, and chemical changes in the noz-
zles of liquid-fuel rocket engines. Important aspects of the elusive processes re-
sponsible for unstable combustion are now understood and it is not inconceivable 
that proper utilization of these findings will ultimately lead to useful methods for 
engine scaling. 
The development of solid-fuel rockets, like that of liquid-fuel engines, ha~ been 
the result of intelligent empirical evolution, sometimes guided in qualitative terms 
by the findings and theories derived from basic studies. Although we do not yet 
know how to predict theoretically the burning rates of propellants from first princi-
ples, or to estimate the stability behavior of specified propellant formulations in 
particular engine configurations, it is nevertheless true that development of a quan-
titative theory of burning of ammonium perchlorate monopropellant, or of conceptu-
ally appealing pictures for the combustion of double-base and of composite propel-
lants, has aided in the construction of useful models of resonance burning and has 
*This paper has been prepared for presentation at the Xllth Congress of the Intema- . 
tional Astronautical Federation, Washington, D. C., October 1961. Combustion research at 
the California Institute of Technology has been supported by the U. S. Army Research Of-
fice-Durham under Contract DA 04-495-0rd-1634. 
IDaniel and Florence Guggenheim Jet Propulsion Center, California Institute of Tech-
nology, Pasadena, California, U. S. A. 
474 
THE ROLE OF COMBUSTION RESEARCH IN ROCKET PROPULSION 475 
led to useful specifications of experiments which should, ultimately, help to define 
propellant and motor characteristics for completely stable engines. 
It is not generally feasible to perform a demonstration of the close connection 
between basic combustion research and powerplant construction. For this reason, 
we shall content ourselves with a summary of representative basic studies in com-
bustion that are motivated by engine development, which are of basic interest in 
their own right, and which may lead to useful pictures for the engine designer in the 
sense that they may help to clarify a significant approach for curing specific ills. 
These examples are illustrative of the work that is being done. They are not meant 
to be the "best" or "most pertinent" illustrations since they were selected primar-
ily because the author has been involved in at least some aspects of the work dis-
cussed and because their use lessens materially the onerous task of writing a "sur-
vey." We choose the following combustion studies for further elaboration: 
1. Burning of propellant droplets; flame propagation in arrays of liquid droplets; 
one-dimensional theory of combustion in liquid-fuel rocket engines. 
2. The burning mechanism of pure ammonium perchlorate; combustion of solid com-
posite propellants. 
3. Correlation of mass burning rates of cylindrical plexiglass tubes in oxygen. 
It is apparent that the specified studies have some bearing on combustion proc-
esses in liquid-fuel, solid fuel, and hybrid rockets, respectively. 


The role of combustion research in rocket propulsion

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The role of combustion research in rocket propulsion

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