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A Study of the Ignition Lag of Spontaneous Rocket Propellants


Clarke, Fredric B. and Sappington, Merrill Homer (1947) A Study of the Ignition Lag of Spontaneous Rocket Propellants. Engineer's thesis, California Institute of Technology. doi:10.7907/GV68-3M37.


For this investigation, ignition lag, as previously defined, is a time required for a reaction to build up an arbitrary pressure of the order of two inches of water. This definition is of particular interest in the study of liquid rockets since the rate of pressure build-up from the spontaneous reaction propellant components is important in the performance of the rocket motor. It makes possible a comparison of propellant combinations to determine which would be better so far as the time lag in reaching the critical pressure ratio is concerned.

It was found that under any one set of conditions it was possible to reproduce data consistently within ten percent. These consequently resulted in very smooth relationships which are of a nature that was generally expected in each case.

In the investigation it was found that at temperatures near the freezing point of aniline, ignition lags were of the order of 12 to 16 milliseconds. On reaching ordinary room temperatures the lag was reduced by a factor of three or four. Beyond this range the effect of temperature change was not so pronounced, and the curve tends to straighten out (see Figure 3). A temperature increase of 80 degrees beyond 100 degrees F produces a decrease of only 14 percent in ignition lag.

For the effect of dilution of the BPNA with water, two relationships were obtained--one by dropping acid into aniline, the other by reversing the two components. These relationships are plotted in Figure 2 and show that a small percentage of water as an impurity in acid will produce little noticeable effect on ignition. This should be of interest to those working with acid-aniline motors in the field. It is believed that the correct values of ignition lag for mixture ratios of a motor lie between the two curves plotted. For relatively pure acid and commercial grade aniline, 3 to 5 milliseconds were required to build up a pressure of two inches of water in a chamber of 2.655 liters volume.

By using several burettes of different tip sizes, it was shown that drops having volumes of more than about 0.0475 milliliters produced approximately the same ignition lags. Two curves, one for acid into aniline and the other for aniline into acid, are plotted in Figure 1 and give the relationship between drop volume and ignition lag. There is an almost constant difference of about two milliseconds between these two curves, which seems to be characteristic of which component is dropped into the other.

Item Type:Thesis (Engineer's thesis)
Subject Keywords:Aeronautical Engineering
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aeronautics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Altman, David
Thesis Committee:
  • Unknown, Unknown
Defense Date:1 June 1947
Record Number:CaltechETD:etd-12082008-080723
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4872
Deposited By: Imported from ETD-db
Deposited On:22 Dec 2008
Last Modified:16 Mar 2023 18:28

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