Solid fuel gas generator for ducted rocket engine

Abstract

In the development of new minimum signature ducted rocket technology, the U.S. Army MICOM Propulsion Directorate has conducted studies for the development of fuel-rich gas generators for ducted rockets. The propellant formulation goals of this study include increasing burning rate, pressure exponent, and combustion efficiency without significantly decreasing fuel value. Formulations described in this application contain an energetic nitramine-prepolymer, a range of curing agents, and zirconium hydride (ZrH2) fuel element and carbon (C) as an optional fuel element.

Description

BACKGROUND OF THE INVENTION

The U.S. Army MICOM has conducted investigations in the development of fuel-rich gas generator formulations for minimum signature and smokey ducted rockets. The majority of work has primarily involved the incorporation of carbon as a fuel in a binder system based on glycidyl azide polymer (GAP). Goals of the ducted rocket engine formulations include high delivered volumetric heating values, tailorable burning rates and exponents, low temperature sensitivity, good mechanical properties, low combustion chamber temperatures, and good ignitability over a wide temperature range.

SUMMARY OF THE INVENTION

In studies conducted by MICOM, nitramine-containing prepolymers such as ORP-2 and 9-D, T-NIDA were evaluated as alternatives to GAP. These studies show ORP-2 and 9-D, T-NIDA to have superior compatibility and mechanical properties to GAP while still offering the low combustion temperatures which made GAP of interest initially. These formulations also contain zirconium hydride, ZrH 2 , as a fuel additive. ZrH 2 has been demonstrated to improve ignitability relative to standard carbon-containing formulations. Based on the results of initial tests with these ingredients, a formulation range (TABLE 3) has been developed. Examples of formulations derived from this formulation range are outlined below in TABLE 1. These examples demonstrate the theoretical performance [specific impulse, (Isp), impulse density, (IspD), chamber temperature, (Tcham), and exhaust temperature, (Texit)] available with combinations of these ingredients and the resulting theoretical concentration of exhaust products.

DESCRIPTION OF THE PREFERRED EMBODIMENT(s)

Examples of formulations derived from the formulation ranges of Table 3 are shown in Table 1 along with the combustion products and some relative performance characteristics. Table 2 lists additional performance characteristics. The ingredients with abbreviations shown in Table 1, Table2, and Table 3 are identified hereinbelow under “Table: Ingredients Defined” prior to the listing of ingredients set forth in Tables 1-3.

TABLE
Ingredients Defined
ORP-2                            a nitramine-containing prepolymer based on
                                 undecanedioc acid as detailed in U.S. Pat. No.
                                 4,916,206 issued to Day and Hani.
CARBON                           carbon black
HMDI                             hexamethylene diisocyanate
IPDI                             Isophorone diisocyanate
N100                             a polyfunctional isocyanate which is the reaction product
                                 of hexamethylene diisocyanate and water
ZrH                                                                        2 zirconium hydride as fuel additive
DBTDL                            dibutyl tin dilaurate, curing catalyst
9-D, T-NIDA                      nitramine-containing prepolymer based on
                                 nitraminodiacetic acid, diethylene glycol,
                                 and triethylene glycol.

	TABLE 1
	INGREDIENT	%	%	%
	ORP-2	82.65	78.30	82.65
	N100	12.34	11.69	12.34
	C	5	0	3
	ZrH 2	0	10	2
	DBTDL	0.01	0.01	0.01
	PERFORMANCE
	VALUE
	Isp(sec)	140.2	149.8	143.2
	IspD	6.7	7.6	6.9
	Tcham(K)	999	1105	1024
	Texit(K)	664	760	687
	EXHAUST	WEIGHT	WEIGHT	WEIGHT
	PRODUCT	%	%	%
	C	33.31	27.28	31.35
	CH 4	0.19	8.54	10.05
	CO	0.23	1.56	0.38
	CO 2	18.78	17.08	18.83
	H 2	0.65	1.57	0.83
	H 2 O	22.54	17.21	21.63
	N 2	14.29	13.53	14.29
	ZrO 2	0	13.	2.64

The theoretical values shown are within the acceptable ranges for the application of these formulations to solid fuel gas generators.

Solid fuel gas generator formulations are also characterized by their theoretical volumetric and gravimetric heating values. Theoretical heating values for the formulations described above in TABLE 1 are outlined in TABLE 2.

	TABLE 2
	INGREDIENT	%	%	%
	ORP-2	82.65	78.3	82.65
	N100	12.34	11.69	12.34
	C	5	0	3
	ZrH 2	0	10	2
	DBTDL	0.01	0.01	0.01
	PERFORMANCE
	VALUE
	VHV,	441	425	431
	BTU/in3
	GHV,	9188	8598	9018
	BTU/lb

	TABLE 2
	INGREDIENT	%	%	%
	ORP-2	82.65	78.3	82.65
	N100	12.34	11.69	12.34
	C	5	0	3
	ZrH 2	0	10	2
	DBTDL	0.01	0.01	0.01
	PERFORMANCE
	VALUE
	VHV,	441	425	431
	BTU/in3
	GHV,	9188	8598	9018
	BTU/lb

In a comparison with other binder systems (prepolymer with curing agents), it has been determined that energetic nitramine containing binders offer advantages over current ducted rocket engine fuel gas generator formulations and lead to improved overall performance. These advantages include superior compatibility and mechanical properties without adversely affecting low temperature combustion. Because of these advantages and the initial test results which show that combinations of ORP-2 with ZrH 2 , in solid fuel gas generators display improved ignitability relative to standard carbon containing formulations, we claim this combination as unique and more suitable for solid fuel gas generators.

While the present invention is outlined by specifications listed in TABLE 3, it is not intended to be limited specifically to this range. There are many variations possible within the scope of the claims.

EXAMPLE 1

Ingredients                      Weight Percents
Nitramine-containing prepolymer based 82.65
on undecanedioc acid
Polyfunctional isocyanate (reaction product of 12.34
Hexamethylene diisocyanate and water)
Carbon black                     3
Zirconium hydride as fuel additive 2
Dibutyl tin dilaurate curing catalyst 0.01

EXAMPLE 2

Ingredients                      Weight Percents
Nitramine-containing prepolymer based 78.30
on undecanedioc acid
Polyfunctional isocyanate (reaction product of 11.69
Hexamethylene diisocyanate and water)
Zirconium hydride as fuel additive 10
Dibutyl tin dilaurate curing catalyst 0.01

Claims

1. A solid fuel gas generator for ducted rocket engine comprising a range in weight percent of the following ingredients:i. an energetic nitramine prepolymer binder in the amount from 60-85 weight percent of the gas generator composition; ii. a curing and crosslinking agent selected from the group of curing and crosslinking agents consisting of hexamethylene diisocyanate, a polyfunctional isocyanate which is the reaction product of hexamethylene and water, and isophorone diisocyanate 5-15 weight percent of the gas Generator composition; iii. ZrH2 fuel additive and ignition aid of about, 0.5-10 weight percent of the gas generator composition; iv. carbon black fuel element of about 0-30 weight percent of the gas generator composition; and, v. a curing catalyst of dibutyl tin dilaurate 0.01 weight percent of the gas generator composition.

2. The solid fuel gas generator for ducted rocket engine as defined in claim 1 wherein said energetic nitramine prepolymer binder is present in weight percent amount of about 82.65; wherein said curing and crosslinking agent is said polyfunctional isocyanate which is present in weight percent amount of 12.34; wherein said carbon black is present in weight percent amount of 3; wherein said ZrH2 is present is present in weight percent amount of 2; and wherein said curing catalyst dibutyl tin dilaurate is present in weight percent amount of 0.01.

3. The solid fuel gas generator for ducted rocket engine as defined in claim 1 wherein said energetic nitramine prepolymer binder is present in weight percent amount of about 78.30; wherein said curing and crosslinking agent is said polyfunctional isocyanate which is present in weight percent amount of 11.69; wherein said ZrH2 is present in weight percent amount of 10; and wherein said curing catalyst dibutyl tin dilaurate is present in weight percent amount of 0.01.