Program computes combustion delays, gas residence time, characteristic velocity, and other steady-state parameters required for solution of the characteristic equation. Equation is solved for critical values of injector pressure drops and chugging frequency

Szuch, J. R.

English

NASA Technical Reports Server

July 1971	 Brief 71-10215 
NASA TECH BRIEF 
Lewis Research Center 	
_4V 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the. Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Digital Computer Program for Analyzing Chugging Instabilities 
The problem: 
To devise a means for analyzing chugging, a com-
mon problem encountered in the development of 
liquid propellant rocket engines. Chugging is a low 
frequency instability caused by a coupling of the pro-
pellant feed system with the combustion dynamics in 
such a way as to reinforce any disturbance in pressure 
or propellant flow. 
The solution: 
A digital computer program designed to analyze 
chugging instabilities and generate stability limits for 
a bipropellant rocket engine. The program computes 
combustion delays, gas residence time, characteristic 
velocity, and other steady-state parameters required 
for the solution of the characteristic equation. The 
characteristic equation is solved for critical values of 
the injector pressure drops and the chugging fre-
quency. 
How it's done: 
A double-dead-time model, which requires the 
application of the respective time delay to each pro-
pellant and results in significantly different stability 
characteristics, was used in the analysis. Experimental 
data have been matched using this model. 
Linearized feed-system impedances are evaluated 
at each frequency of interest. In addition to chamber 
and injector flow dynamics, the program can handle 
combinations of pumps, valves, manifolds, and lines.
For any selected engine configuration, the program 
computes the required steady-state engine parameters 
for the solution of the characteristic equation. Avail-
able vaporization and drop-size correlations are used 
to calculate combustion time delays. 
Stability limits were generated for a specific 
flox-methane engine system. An expander cycle with a 
turbine-bypass throttle was assumed. Results were 
obtained for two candidate injector types. For each 
injector configuration, the limits for throttling at a 
constant mixture ratio and the effects that varying the 
fuel injection area had on stability were determined. 
Notes: 
1. This program is written in FORTRAN IV for use 
on the IBM-7094 computer. 
2. Requests for further information may be directed 
to:
COSMIC 
Barrow Hall 
University of Georgia 
Athens, Georgia 30601 
Reference: B71-10215 
Patent status: 
No patent action is contemplated by NASA. 
Source: J. R. Szuch
Lewis Research Center

(LEW-1 1294) 
Category 09 
in 
MW
This docume6t was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned.rights.
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Digital computer program for analyzing chugging instabilities

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