Acetylene-Hydrogen Rockets from Titan to Earth – Performance

Previously we looked at the Acetylene-Hydrogen rocket, but didn’t examine the performance in great detail. Glassman’s patent assumed a combustion chamber pressure of 20 atmospheres, exhausting to ambient of 1 atmosphere. The 1:8 ratio had a combustion temperature of just 1140 K and average molecular mass of 6.00 in the exhaust, reaching 275 seconds Isp. Using these figures we can compute a Titan surface performance of 261.5 seconds (1.448 atm pressure) and a vacuum performance (with a vacuum optimised engine bell) of 4,140 m/s. That’s an impressive figure for in-space maneuvers, beating the ~3,800 m/s that SpaceX’s hoping for its Raptor engines.

TABLE I  
Physical Properties
LIQUID ACETYLENE AND LIQUID HYDROGEN
Acetylene (B.P. -84? C.) :
dHf? (25? C.) (gas)54.19kcal/mole
dHvap (-84? C., atm.)1.52kcal/mole
dHf? (25? C.) (liq.) 52.67 kcal/mole
dHe (25? C.) (net) (liq.)47,900kJ/kg
Hydrogen (B.P. -252.8? C.):
dHf? (25? C.) (gas)0kcal/mole
dHvap (-252.8? C., 1 atm.)0.216kcal/mole
Cp (liq.) = 2.5 cal./gm. K.2.5cal./gm. K.
dH c = -2.5 (298.1-20.3)1.388kcal/mole
dHf (-253? C.) (liq.)-1.6kcal/mole
dHe (25? C.) (net)115,400kJ/kg
TABLE II       
ReactantsT (K)Mol. Mass (g)Isp (sec)
Products in Moles
CH2CH4dHo, MJ/kg
C2H2+1.0 H22,1501426022052.68
C2H2+1.5 H21,90011.626122.5054.89
C2H2+2.0 H21,7501026723056.99
C2H2+3.0 H21,5008.42681.83.60.260.71
C2H2+4.0 H21,3507.472701.554.10.4562.80
C2H2+5.0 H21,2756.852710.264.520.7466.76
C2H2+6.0 H21,2256.532730.834.661.1769.31
C2H2+7.0 H21,17562780.685.361.3271.64
C2H2+8.0 H21,140627505273.50
C2H2+9.0 H21,0505.527206275.36
TABLE III       
ReactantsT (K)Mol. MassIsp (sec)Products in Moles
CH2CH4dHo, MJ/kg
Isopropenyl-Acetylene1,380221664832.660.1743.8
Methyl-Acetylene1,680201913002045.8
C2H2-----3,10025.523620.980.0447.9
1-Hexyne1,09021.2484.762.522443.2
Isobutenyl-Acetylene1,25023.21475.442.880.5644.2
1-Butyne1,33014.91713.722.440.2845.1
1,7-Octadiyne1,45021.217485043.5
16-Heptadiyne1,67022.517974043.1
1,5-Hexadiyne2,0602619063044.2
C2H2+8.0 H21,140627505273.5
C2H2+O2---------3,5902660.0
1,5-Hexadiyne+17H21,1007.46242110565.8