US3377219A - Nitrated organic liquid propellant composition having improved spark ignition - Google Patents

Description

United States Patent Oh 3,377,219 NITRATEI) ORGANIC LIQUID PROPELLANT COh ZPOSITIUN HAVING IMPROVED SPARK IGNITKON Ludwig Stiefel, Philadelphia,

Levittown, Pa, assignors to the United States of America as represented by the Secretary of the Army No Drawing. Filed Sept. 28, 1964, Ser. No. 399,943 4 Claims. (Cl. 149*88) ABSTRACT OF THE DISCLOSURE Liquid propellants capable of ready ignition by a submerged spark therewithin, the spark requiring but little energy to cause its formation due to the composition of said propellant which includes either a quaternary ammonium salt or colloidal graphite.

and Howard A. Kirshuer,

The invention described herein may be manufactured and used by or for the Government poses without the payment to us of any royalty thereon.

This invention relates to spark ignition of liquid propellants and particularly, to submerged spark ignition of non-conductive organic liquids used as propellants.

Many organic liquids propane, alkyl nitrates, and nitrate ester compounds are commonly employed as liquid propellants. Certain applications of these propellants require that they be ignited by electrical spark discharge generated across electrodes submerged in the propellants. However, efforts to conveniently ignite the propellants by this electrical spark discharge method have resulted in virtual failure. At the root of the problem is the very high order of electrical energy required for generating the ignition spark. The size and extent of the equipment necessary to provide this energy has been such as to render the method impractical. A principal reason advanced for the high electrical energy required for spark ignition is the poor electrical conduction properties of the propellants.

It is, therefore, an object of this invention to provide organic liquid propellants characterized by improved electrical conduction properties.

A further object is to provide a method for enhancing the electrical properties of organic liquid propellants to permit practical submerged spark ignition thereof.

The above and other objects are attained by adding into organic liquid propellants or blends thereof small amounts of either low molecular weight quaternary ammonium salts or colloidal graphite. For example, igniting 2. for governmental purincluding nitromethane, nitro- 3,377,219 Patented Apr. 9, 1968 ice trate propellant having increased electrical conductivity characteristics is obtained. Accordingly, the electrical energy required to generate the ignition spark is considerably diminished.

The improved propellants of this invention comprise any non-conductive, organic liquid propellants to which have been added between 0.5% and 3.0% by weight of an additive selected from the group consisting of a quaternary ammonium salt and colloidal graphite. In the case of the former, dissolution occurs in the propellant while in the case of the latter the graphite remains in suspension. However, the results in any of the'above mixtures are the same, that is, in comparison with non-conductive, organic liquid propellants not having the additives mentioned, substantially lower electrical energies are necessary for generating ignition spark-s across electrodes submerged in the propellants.

The following examples further illustrate the invention, which is not to be construed as limited thereby. Various quaternary ammonium salts as well as colloidal graphite were mixed under ambient conditions with base propellants. The examples are shown in. thefollowing table.

TABLE I Ex. No. Base Propellant Additive and Quantity Thereof 1 Ethyl Nitrate, 40% 1.5% b weight colloidal Propyl N itrate. graphite. 2 60% Ethyl Nitrate, 40% 1.5% by weight tetra ethyl Propyl Nitrate. ammonium chloride. 3 60% Ethyl Nitrate, 40% 0.5% by weight tetra n- Propyl Nitrare. propyl ammonium nitrate. 4 100% Propyl Nitrate 3.0% by weight tetra npropyl ammonium nitrate.

To illustrate the improved spark ignition characteristics of the propellants of this invention, spherical tipped stainless steel electrodes having a V inch diameter were submerged into an open cup of propellants of compositions set forth in the above examples. Two sets of electrodes having spark gaps of 0.042 and 0.050 inch respectively were used, both being connected to a 5000 volt, 6.0 microfrared variable capacitance electrical system. Electrical energy was applied until a spark was generated across the electrodes and the propellant ignited. The total energy required for ignition of the propellants was computed from the formula, W== /2CV where W is total energy in joules, C is capacitance in farads, and V is voltage applied in volts. The above procedure was applied to testing propellants without the additive of this invention. Results of the foregoing tests are given in the following table.

TABLE II.EFFECT OF ADDI'IIVES UPON SPARK IGNITION ENERGY Electrode Voltage System Energy Example No. Composition Gap, inches Applied, volts Capacitance, Applied, Results Inicrofarads joules Base propellant: 60% Ethyl Nitrate, 40% Propyl 0.042 5, 000 6.0 No ignition.

Nitrate, no additive. 1 Base propellant: 60% Ethyl Nitrate, 40% Propyl 0. 042 2,100 4.0 8.8 Ignition.

Nitrate, 1.5% by weight colloidal graphite added. 2 Base propellant: 60% Ethyl Nitrate, 40% Propyl 0.042 2,100 3.0 6. 6 Do.

Nitrate, 1.5% by weight tetra ethyl ammonium chloride added. 3 Base propellant: 60% Ethyl Nitrate, 40% Propyl 0.050 3,000 1.0 4.5 Do.

Nitrate, 0.5% by weight tetra n-propyl ammonium nitrate added. Base propellant: 60% Ethyl Nitrate, 40% Propyl 0.050 5,000 1.0 13 Noigmtion.

Nitrate, no additive. 4 Base propellant: propylnitrate,3.0% by weight 0.050 2,700 2.0 7.0 Ignition. tetra n-propyl ammonium nitrate added. Base propellant: 100% propyl nitrate, no additive 0. 050 5, 000 6. 0 75 N o ignition. an ethyl-propyl nitrate propellant without these additives The data in the foregoing table demonstrate the sigby means of a spark generated between electrodes submerged in the propellant requires a relatively high electrical energy. This is attributed to the low electrical conductivity of the propellant. By adding a quaternary ammonium salt or colloidal graphite, an ethyl-propyl ninificant improvement in spark ignition of non-conductive, organic liquid propellants as a result of the addition there- 0 to of quaternary ammonium salts or colloidal graphite.

The data show that with the inventive additives the energy required to generate an ignition spark is decreased by a Tetramethyl ammonium bromide Tetraethyl ammonium bromide Tetraethyl ammonium chloride Tetra-n-propyl ammonium nitrate Tetra-n-propyl ammonium iodide Tetra-n-butyl ammonium iodide Tetra-n-butyl ammonium picrate Since many examples of the foregoing compositions may be made without departing from the scope of the invention, the foregoing is to be interpreted as illustrative only, and not as defining or limiting the scope of the invention.

We claim:

1. An improved liquid propellant consisting essentially of an electrically non-conductive, nitrated organic liquid propellant and an additive selected from the group consisting of quaternary ammonium salts and colloidal graphite, said additive being present in an amount effective to permit practical spark ignition of said electrically nonconductive nitrated organic liquid propellant.

2. An improved liquid propellant consisting essentially of a member selected from the group consisting of ethyl nitrate, propyl nitrate, and mixtures thereof, and an additive selected from the group consisting of quaternary ammonium salts and colloidal graphite in an amount of 0.1% to 3.0% by weight.

3. A method for improving the spark ignition of an electrically non-conductive nitrated organic liquid propellant, said method comprising adding to said liquid propellant an additive selected from the group consisting of quaternary ammonium salts and colloidal graphite in an amount efiective to permit practical spark ignition of said electrically non-conductive nitrated organic liquid propellant.

4. A method for improving the spark ignition of a liquid propellant selected from the group consisting of ethyl nitrate, propyl nitrate, and mixtures thereof, said method comprising adding to said liquid propellant an additive selected from the group consisting of quaternary ammonium salts and colloidal graphite in an amount of 0.1% to 3.0% by weight.

References Cited UNITED STATES PATENTS 2,433,943 1/1948 Zwicky et al. l49-89 X 2,993,768 7/1961 Holzl 14989 X 3,116,187 12/1963 Scanlon et al. 14989 X 3,148,214 9/1964 Smith 149-88 X 3,208,891 9/1965 Eschrich et al. 149-89 X CARL D. QUARFORTH, Primary Examiner. S. J. LECHERT, 1a., Assistant Examiner.