Theoretical Analysis of Specific Impulse at Lower Geo-Potential Altitude Range for a Paraffin-Fueled Hybrid Rocket Motor

Abstract: This paper presents a theoretical performance of paraffin-based hybrid rocket motors, focusing on the ideal specific impulse performance (Isp) at lower geo-potential atmospheric altitudes. The study considers n-docosane (C22H46) as fuel with oxidizer as nitrous oxide (NO). Simplified mathematical modelling is employed to perform the analysis. The input thermodynamic parameters are calculated for exhaust gas mixture under balanced stoichiometric chemical reaction based on fixing a standardized exhaust temperature of 1000oK in relevance with material considerations. The analysis underscores the influence of specific heat capacity and specific heat ratio on thrust coefficients. The nozzle area ratio is fixed as 2.5 and accordingly the design exit Mach number (Me) is calculated using Chebyshev iterative method by formulating a transcendental non-linear function and accordingly theoretical computations are performed based on the methodology followed. The inference reveals that the ideal specific impulse ranges from 218 to 246 seconds across lower atmospheric geo-potential altitudes. This also highlights the influence of chamber pressure on altitude as a performance assessment for propulsion system. The findings are theoretical and delivers valuable insight into application of hybrid propulsion systems for altitude operations in future.