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Hybrid Engines
• Conventional hybrid vs. “reverse” hybrid
• 4 Main Components of Hybrid Engine
• Ignition system
• Fuel chamber
www.aspirespace.org.uk
PMMA or HTPB?
• PMMA (Poly-Methyl Methacrylate) or plexiglass
• HTPB (Hydroxyl Terminated Poly-Butadiene) or rubber
• Properties:
• Pros and Cons of HTPB vs. PMMA
Properties HTPB PMMA
Specific Impulse (cp) (J/Kg-K) 2385.93 1466
Density (ρ) (kg/m3) 930 1190Thermal conductivity (Ks) (W/m-K) 0.217 0.17-0.19
Cost Evaluation
• PMMA is sold as either extruded or cast – Do = 0.05 m, Di =0.044 m, L = 0.5 m, t = 0.03
m is $202.00
– Do = 0.03 m, Di = 0.024 m, L = 0.5 m, t = 0.03 m is $234.00
• HTPB is a two part mix ($56)– one part thermoset elastomer– one part diisocyanate