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Synergistic hypergolic ignition of blends of dienes and dienophiles with red fuming nitric acid as oxidizer
COMBUSTION
A N D F L A M E 76: 107-110 (1989)
107
BRIEF COMMUNICATION Synergistic Hypergolic Ignition of Blends of Dienes and Dienophiles with Red Fuming Nitric Acid as Oxidizer S. P. PANDA, S. G. KULKARNI, and C. PRABHAKARAN Faculty of Explosives and Applied Chemistry, Institute of Armament Technology, Girinagar, Pune 411 025, India
Synergistic hypergolic ignition of several fuel blends [1--4] and mixtures [5] with red fuming nitric acid (RFNA) as oxidizer has been reported by Panda and Kulkarni et al. The liquid fuels (Fig. 1) consisted of blends of 3-carene [1-2], cyclopentadiene [3], or norbornadiene [4] with cardanol in the weight ratio 70:30 for the first two and 85:15 for norbornadiene. In all these cases, synergism in ignition was believed to be due to the fast and exothermic oligomerization of 3-carene, cyclopentadiene, and norbornadiene in the presence of acid. The exothermicity of the systems was enhanced by the addition of cardanol to the unsaturation of oligomers, leading to the formation of highly oxidizable phenolic ethers [6-7]. Two more important reactions at the preignition stage were nitration and oxidation of the ethers leading to the production of gaseous combustibles and heat. In this case, an attempt has been made to extend the range of possible preignition reactions by introducing diene-dienophile Diels-Alder cycloaddition with a low activation energy by replacing cardanol with furfuryl alcohol or furfurylideneacetone having a furan ring to behave as acid polymerizable [8, 9] dienes in the above systems. In addition to 3carene, cyclopentadiene, and norbornadiene, dipentene, ot-pinene, and/5-pinene have been used as dienophiles. The choices are based on a low highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap between the diene and the dienophile essential Copyright © 1989by The CombustionInstitute Publishedby ElsevierSciencePublishing Co., Inc. 655 Avenueof the Americas,New York, NY I0010
for a fast 4 + 2 Diels-Alder cycloaddition [10, 111. Norbornadiene (Fluka AG), 3-carene, a-pinene, and ~-pinene (Camphor and Allied Products, India), furfuryl alcohol (BDH, England), and dipentene (Hulzen N.H., Holland) were obtained from the trade in extrapure form and were used without further purification. Cyclopentadiene was prepared by thermal cracking of dicyclopentadiene [12, p. 870]. Furfurylideneacetone was synthesized after Vogel [12, p. 795]. Red fuming nitric acid--specific gravity, 1.56 g/ml with HNO3, 77%; N204, 21%; and H20, 2%--was obtained from the High Explosives Factory, Kirkee, India. The ignition delay was measured by using a modified Pino's ignition delay apparatus as described by Kulkarni and Panda [13]. Measurements were carried out at different oxidizer to fuel (O/F) ratios to find out the optimum O/F ratio giving the lowest ignition delay. For each ratio, a minimum of five readings were taken, and their average value is given in Table 1. The standard deviation varied from 0.4 to 8.0 ms. However, the values below 50 ms were more consistent and had very low scatter. Figure 2 gives the ignition delay for a blend of norbornadiene and furfuryl alcohol with RFNA as oxidizer at the optimum O/F ratios. It can be seen that synergistic ignition occurs when the proportion of furfuryl alcohol is between 10% and 80% by weight. The highest synergism is realized when 0010-2180/89/$03.50
108
S.P. PANDA ET AL. OH
II
~-CH20H
Iv
Ill
~--CH=CH-CO-CH3 ~ ~
v
X
Vl
,, ~ Vll
Xl
, viii
ix
XII
Fig. 1. Structures of fuel molecules. I, 3-carene; If, cyclopentadiene; HI, norbomadiene; IV, cardanal; V, furfuryl alcohol; VI, furfurylideneacetone; VII, dipentene; VIII, c~-pinene;IX, /3-pinene;X, tetrahydrofurfuryl alcohol; XI, endodicyclopentadiene; XII, acrylonitrile.
the two components of the fuel blend are equally mixed (in 50:50 ratio). Interestingly, concentrated sulphuric acid, which decreases the ignition delay of hypergolic systems when cationic polymerization is an important preignition reaction, fails to do
so for the norbornadiene-furfuryl alcohol-RFNA system. On the contrary, when mixed with RFNA at 5% by weight, it dilutes the oxidizer and increases the ignition delay of the system. It was therefore suspected that diene-dienophile reaction
TABLE 1
Ignition Delay of Different Dienes, Dienophiles, and Their 50:50 Mixtures (by weight) with Furfuryl Alcohol and Furfurylideneacetone with RFNA as Oxidizer
Srl. No.
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Fuel/Fuel mixture
O/F by volume (optimum)
14. 15. 16. 17.
Fuffuryl alcohol Furfurylideneacetone Norbomadiene Norbomadiene-furfuryl alcohol Norbornadiene-furfurylideneacetone Cyclopentadiene Cyclopentadiene-furfuryi alcohol Cyclopentadiene-furfurylideneacetone 3-Carene 3-Carene-furfurylideneacetone Dipcntene Dipentene-furfuryl alcohol Dipentene-furfurylideneacetone o~-Pinene a-Pincne-furfuryl alcohol ~-Pinene-furfiuTlideneacetone /3-Pinene
2.0 2.0 2.0 2.4 2.4 2.0 2.0 2.0 3.5 2.2 -2.8 2.1 -2.1 2.3 --
18. 19.
/~-lainene-furfurylalcohol ~-Pinene-furfurylideneacetone
2.2 2.3
11.
12. 13.
Average Ignition Delay, ms 109.0 23.0 45.3 16.6 22.2 31.3 27.3 26.2 377.0 35.7 Nonhypergolic 79.3 36.0 Nonhypergolic 162.0 153.0 Weakly hypergolic (ID = 3000 millisec) 112.3 52.3
Standard Deviation, ms 4.10 0.50 0.57 0.50 0.40 2.09 1.13 0.50 8.30 2.00 -2.83 2.70 -5.00 1.00 -0.94 1.15
SYNERGISTIC HYPERGOLIC IGNITION
109
120 110 I 100 9O
~
d
70
"~ z
5(1
~ 7
40
30 20 'IO 0 0
I 10
I 20
loo
90
ao
I 30
I 40
I 50
I 60
I 70
I 80
I 90
FVRFURYLALCOHOL(WEIGHI'%) •
7o
6o
so
~o
3o 2o
I 100 *-
lo
o
:~ORBmNmEN~(WEK;HT~)
Fig. 2. Ignition delay for a blend of norbornadiene and furfuryl alcohol with RFNA as oxidizer at the optimum O/F ratios.
in 1:1 molar proportion might be a significant preignition reaction. To prove this point, norbornadiene was replaced by dienophiles like cyclopentadiene, dipentene, oz-pinene, and /3-pinene, and the maximum synergism in ignition was obtained for the 50:50 fuel blends with RFNA as oxidizer (Table 1). 3-Carene is not miscible in large proportions with furfuryl alcohol, whereas it dissolves furfurylideneacetone easily. Other fuels like norbornadiene, cyclopentadiene, dipentene, ot-pinene, and/~-pinene also dissolve furfurylideneacetone. Therefore, experiments were repeated with these fuels mixed with furfurylideneacetone in various quantities, and in each case the 50:50 (by weight) solution gave the highest synergism in ignition with RFNA. The results are reported in Table 1. This eliminates the doubt that the alcoholic group of furfuryl alcohol may add to the double bond of the dienophiles forming highly oxidizable ethers, which may be more critical than the diene-dienophile addition at the preignition
stage. Further, tetrahydrofurfuryl alcohol is nonhypergolic with RFNA. Mixed with all the fuels (dienophile) described above in 50:50 weight proportion, it fails to produce any synergistic ignition using RFNA as oxidizer. The dienophiles and the diene chosen are highly polymerizable in acid condition. Replacement of such dienophiles with less polymerizable unsaturated molecules like endodicyclopentadiene or acrylonitrile does not lead to synergism in ignition. This highlights the role of proton-initiated polymerization of the dienophile as one of the important preignition reactions in addition to Diels-Alder cycloaddition.
The authors are thankful to Dr. E. Bhagirathrao, Director and Dean, IA T, f or his kind interest in the work and permission to publish the paper.
110
S.P. PANDA ET AL.
REFERENCES 9. 1. Panda, S. P. and Kulkarni, S. G., J. Armt. Studies 17(2):26 (1981). 2. Kulkami, S. G. and Panda, S. P., Combust. Flame 56:241-244 (1984). 3. Kakade, Seema D., Kulkarni, S. G., and Panda, S. P., J. Armt. Studies 20:1-6 (1984). 4. Panda, S. P., Kulkarni, S. G., and Prabhakaran, C., J. Armt. Studies 22(1):52-57 (1986). 5. Kakade, Seema D., Kulkarni, S. G., and Panda, S. P., Combust. Flame 61:189-193 (1985). 6. Panda, S. P. and Kulkarni, S. G., J. Polym. Sci. (Polymer Letters Edition) 21:649-656 (1983). 7. Panda, S. P. and Kakade, Seema D., J. Polym. Sci. (Polymer Letters Edition) 24:403-.412 (1986). 8. Gandini, A. cited in Advances in Polymer Science
10.
11. 12.
13.
25:49-93 (1977). Lamb, B. S. and Kovacis, P., J. Polym. Sci. Polym. Chem. Ed. 18(8):2423-2435 (1980). Norman. R. O. C., Principles of Organic Synthesis, 2nd Ed., Chapman and Hall Ltd., London, 1981, pp. 291-295. Fleming, I., Frontier Orbitals and Organic Chemical Reactions, John Wiley & Sons, London, 1982, p. 22. Furniss, B. S., Hannaford, A. J., Rogers, V., Smith, P. W. C., and Tatchell, A. R., Vogel's Textbook of Practical Organic Chemistry, ELBS, Longman Group Ltd., London, 1978. Kulkarni, S. G. and Panda, S. P., Combust. Flame 40(1):29-36 (1981).
Received 17 December 1987; revised 18 April 1988
A N D F L A M E 76: 107-110 (1989)
107
BRIEF COMMUNICATION Synergistic Hypergolic Ignition of Blends of Dienes and Dienophiles with Red Fuming Nitric Acid as Oxidizer S. P. PANDA, S. G. KULKARNI, and C. PRABHAKARAN Faculty of Explosives and Applied Chemistry, Institute of Armament Technology, Girinagar, Pune 411 025, India
Synergistic hypergolic ignition of several fuel blends [1--4] and mixtures [5] with red fuming nitric acid (RFNA) as oxidizer has been reported by Panda and Kulkarni et al. The liquid fuels (Fig. 1) consisted of blends of 3-carene [1-2], cyclopentadiene [3], or norbornadiene [4] with cardanol in the weight ratio 70:30 for the first two and 85:15 for norbornadiene. In all these cases, synergism in ignition was believed to be due to the fast and exothermic oligomerization of 3-carene, cyclopentadiene, and norbornadiene in the presence of acid. The exothermicity of the systems was enhanced by the addition of cardanol to the unsaturation of oligomers, leading to the formation of highly oxidizable phenolic ethers [6-7]. Two more important reactions at the preignition stage were nitration and oxidation of the ethers leading to the production of gaseous combustibles and heat. In this case, an attempt has been made to extend the range of possible preignition reactions by introducing diene-dienophile Diels-Alder cycloaddition with a low activation energy by replacing cardanol with furfuryl alcohol or furfurylideneacetone having a furan ring to behave as acid polymerizable [8, 9] dienes in the above systems. In addition to 3carene, cyclopentadiene, and norbornadiene, dipentene, ot-pinene, and/5-pinene have been used as dienophiles. The choices are based on a low highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap between the diene and the dienophile essential Copyright © 1989by The CombustionInstitute Publishedby ElsevierSciencePublishing Co., Inc. 655 Avenueof the Americas,New York, NY I0010
for a fast 4 + 2 Diels-Alder cycloaddition [10, 111. Norbornadiene (Fluka AG), 3-carene, a-pinene, and ~-pinene (Camphor and Allied Products, India), furfuryl alcohol (BDH, England), and dipentene (Hulzen N.H., Holland) were obtained from the trade in extrapure form and were used without further purification. Cyclopentadiene was prepared by thermal cracking of dicyclopentadiene [12, p. 870]. Furfurylideneacetone was synthesized after Vogel [12, p. 795]. Red fuming nitric acid--specific gravity, 1.56 g/ml with HNO3, 77%; N204, 21%; and H20, 2%--was obtained from the High Explosives Factory, Kirkee, India. The ignition delay was measured by using a modified Pino's ignition delay apparatus as described by Kulkarni and Panda [13]. Measurements were carried out at different oxidizer to fuel (O/F) ratios to find out the optimum O/F ratio giving the lowest ignition delay. For each ratio, a minimum of five readings were taken, and their average value is given in Table 1. The standard deviation varied from 0.4 to 8.0 ms. However, the values below 50 ms were more consistent and had very low scatter. Figure 2 gives the ignition delay for a blend of norbornadiene and furfuryl alcohol with RFNA as oxidizer at the optimum O/F ratios. It can be seen that synergistic ignition occurs when the proportion of furfuryl alcohol is between 10% and 80% by weight. The highest synergism is realized when 0010-2180/89/$03.50
108
S.P. PANDA ET AL. OH
II
~-CH20H
Iv
Ill
~--CH=CH-CO-CH3 ~ ~
v
X
Vl
,, ~ Vll
Xl
, viii
ix
XII
Fig. 1. Structures of fuel molecules. I, 3-carene; If, cyclopentadiene; HI, norbomadiene; IV, cardanal; V, furfuryl alcohol; VI, furfurylideneacetone; VII, dipentene; VIII, c~-pinene;IX, /3-pinene;X, tetrahydrofurfuryl alcohol; XI, endodicyclopentadiene; XII, acrylonitrile.
the two components of the fuel blend are equally mixed (in 50:50 ratio). Interestingly, concentrated sulphuric acid, which decreases the ignition delay of hypergolic systems when cationic polymerization is an important preignition reaction, fails to do
so for the norbornadiene-furfuryl alcohol-RFNA system. On the contrary, when mixed with RFNA at 5% by weight, it dilutes the oxidizer and increases the ignition delay of the system. It was therefore suspected that diene-dienophile reaction
TABLE 1
Ignition Delay of Different Dienes, Dienophiles, and Their 50:50 Mixtures (by weight) with Furfuryl Alcohol and Furfurylideneacetone with RFNA as Oxidizer
Srl. No.
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Fuel/Fuel mixture
O/F by volume (optimum)
14. 15. 16. 17.
Fuffuryl alcohol Furfurylideneacetone Norbomadiene Norbomadiene-furfuryl alcohol Norbornadiene-furfurylideneacetone Cyclopentadiene Cyclopentadiene-furfuryi alcohol Cyclopentadiene-furfurylideneacetone 3-Carene 3-Carene-furfurylideneacetone Dipcntene Dipentene-furfuryl alcohol Dipentene-furfurylideneacetone o~-Pinene a-Pincne-furfuryl alcohol ~-Pinene-furfiuTlideneacetone /3-Pinene
2.0 2.0 2.0 2.4 2.4 2.0 2.0 2.0 3.5 2.2 -2.8 2.1 -2.1 2.3 --
18. 19.
/~-lainene-furfurylalcohol ~-Pinene-furfurylideneacetone
2.2 2.3
11.
12. 13.
Average Ignition Delay, ms 109.0 23.0 45.3 16.6 22.2 31.3 27.3 26.2 377.0 35.7 Nonhypergolic 79.3 36.0 Nonhypergolic 162.0 153.0 Weakly hypergolic (ID = 3000 millisec) 112.3 52.3
Standard Deviation, ms 4.10 0.50 0.57 0.50 0.40 2.09 1.13 0.50 8.30 2.00 -2.83 2.70 -5.00 1.00 -0.94 1.15
SYNERGISTIC HYPERGOLIC IGNITION
109
120 110 I 100 9O
~
d
70
"~ z
5(1
~ 7
40
30 20 'IO 0 0
I 10
I 20
loo
90
ao
I 30
I 40
I 50
I 60
I 70
I 80
I 90
FVRFURYLALCOHOL(WEIGHI'%) •
7o
6o
so
~o
3o 2o
I 100 *-
lo
o
:~ORBmNmEN~(WEK;HT~)
Fig. 2. Ignition delay for a blend of norbornadiene and furfuryl alcohol with RFNA as oxidizer at the optimum O/F ratios.
in 1:1 molar proportion might be a significant preignition reaction. To prove this point, norbornadiene was replaced by dienophiles like cyclopentadiene, dipentene, oz-pinene, and /3-pinene, and the maximum synergism in ignition was obtained for the 50:50 fuel blends with RFNA as oxidizer (Table 1). 3-Carene is not miscible in large proportions with furfuryl alcohol, whereas it dissolves furfurylideneacetone easily. Other fuels like norbornadiene, cyclopentadiene, dipentene, ot-pinene, and/~-pinene also dissolve furfurylideneacetone. Therefore, experiments were repeated with these fuels mixed with furfurylideneacetone in various quantities, and in each case the 50:50 (by weight) solution gave the highest synergism in ignition with RFNA. The results are reported in Table 1. This eliminates the doubt that the alcoholic group of furfuryl alcohol may add to the double bond of the dienophiles forming highly oxidizable ethers, which may be more critical than the diene-dienophile addition at the preignition
stage. Further, tetrahydrofurfuryl alcohol is nonhypergolic with RFNA. Mixed with all the fuels (dienophile) described above in 50:50 weight proportion, it fails to produce any synergistic ignition using RFNA as oxidizer. The dienophiles and the diene chosen are highly polymerizable in acid condition. Replacement of such dienophiles with less polymerizable unsaturated molecules like endodicyclopentadiene or acrylonitrile does not lead to synergism in ignition. This highlights the role of proton-initiated polymerization of the dienophile as one of the important preignition reactions in addition to Diels-Alder cycloaddition.
The authors are thankful to Dr. E. Bhagirathrao, Director and Dean, IA T, f or his kind interest in the work and permission to publish the paper.
110
S.P. PANDA ET AL.
REFERENCES 9. 1. Panda, S. P. and Kulkarni, S. G., J. Armt. Studies 17(2):26 (1981). 2. Kulkami, S. G. and Panda, S. P., Combust. Flame 56:241-244 (1984). 3. Kakade, Seema D., Kulkarni, S. G., and Panda, S. P., J. Armt. Studies 20:1-6 (1984). 4. Panda, S. P., Kulkarni, S. G., and Prabhakaran, C., J. Armt. Studies 22(1):52-57 (1986). 5. Kakade, Seema D., Kulkarni, S. G., and Panda, S. P., Combust. Flame 61:189-193 (1985). 6. Panda, S. P. and Kulkarni, S. G., J. Polym. Sci. (Polymer Letters Edition) 21:649-656 (1983). 7. Panda, S. P. and Kakade, Seema D., J. Polym. Sci. (Polymer Letters Edition) 24:403-.412 (1986). 8. Gandini, A. cited in Advances in Polymer Science
10.
11. 12.
13.
25:49-93 (1977). Lamb, B. S. and Kovacis, P., J. Polym. Sci. Polym. Chem. Ed. 18(8):2423-2435 (1980). Norman. R. O. C., Principles of Organic Synthesis, 2nd Ed., Chapman and Hall Ltd., London, 1981, pp. 291-295. Fleming, I., Frontier Orbitals and Organic Chemical Reactions, John Wiley & Sons, London, 1982, p. 22. Furniss, B. S., Hannaford, A. J., Rogers, V., Smith, P. W. C., and Tatchell, A. R., Vogel's Textbook of Practical Organic Chemistry, ELBS, Longman Group Ltd., London, 1978. Kulkarni, S. G. and Panda, S. P., Combust. Flame 40(1):29-36 (1981).
Received 17 December 1987; revised 18 April 1988