7 TH EUROPEAN CONFERENCE FOR AERONAUTICS AND SPACE SCIENCES (EUCASS) Copyright  2017 by Suhang Chen and Yue Tang. Published by the EUCASS association with permission. Characterization of HTPB-based Fuel Containing Multi- wall Carbon Nanoturbes (MWCNTs) for Hybrid Propellant Suhang Chen *, Yue Tang *, Wei Zhang *, Ruiqi Shen *, Luigi T. DeLuca**and Yinghua Ye* * School of Chemical Engineering, Nanjing University of Science and Technology, 200 Xiaolingwei, Xuanwu District, Nanjing 210094, China ** (Ret) Space Propulsion Laboratory, Department of Aerospace Science and Technology, Politecnico di Milano 34 Via La Masa, Milan 20156, Italy Abstract In order to investigate the effects of MWCNTs on the combustion performance of HTPB-based fuel for hybrid propellant, based on high speed photography recording the radical regression process of fuel grain under oxygen flow. The regression rate of HTPB-based fuel containing different kind of MWCNTs respectively were analysed. The regression of HTPB-based fuel containing 1 wt% >50nm, 1 wt% 20-40nm MWCNTs, 1 wt% 50nm, 1 wt% 20-30nm, 1 wt% <8nm MWCNTs-OH and 1 wt% carbon black respectively are increased by 57.2%, 52.4%, 24.6%, -15.6%, -2.9%, -33.0% at Gox=375 kg/m 2 s while decreased by -29.5%, -35.0%, -16.0%, -22.8%, -17.3%, -12.7% at Gox=150 kg/m 2 s. HTPB-based fuel containing MWCNTs increases regression to some extent but shows more sensitive to oxygen flux. MWCNTs form a three-dimensional heat conducting network to increase thermal conductive and heat radiation. 1. Introduction Hybrid propulsion is becoming a promising emerging technology for suborbital space tourism like SpaceShipOne[1] and space exploration mission due to its inherent safety for non-explosive nature, potential low-cost, throttleability, less complex and environment friendly. However, hybrids fuel is subject to their low regression rate which is due in part to the decrease of the heat transfer from the flame zone to the fuel surface[2, 3], resulted in complicated fuel grain design like port geometries and multi-port limiting their application. This low-fuel regression rate is the inherent limitation of diffusion flames. Fuel consumption rate is expressed as ̇  =  ̇  ,   - burning area(m 2 ), ̇ - regression rate(mm/s),   -density of hybrids fuel(kg/m 3 ). One method is to increase combustion area. Armold D M[4] designs a series of multi-port grain such as cylindrical port ,double-D, cruciform wagon wheel of acrylonitrile–butadiene–styrene copolymer(ABS) hybrid fuel grains, it definitely improves fuel mass burning rate but bringed a lot of problems such as complex design/fabrication, excessive unburned mass, uneven burning. Porous hybrid grains increase combustion area with the limitation of control difficultly and low density. The other method is to increase regression rate. Adding the energetic materials such as micron-sized metal particles, nano-sized metal particles[5-7], metal hydride such as NaBH4[8] or self-decomposing oxidizer to fuel can enhance heat release near the regressing surface improving the heat feedback. Frederick [8] has done many work in the addition of self-decomposing oxidizer (ammonium perchlorate) and iron(III) oxide(Fe2O3) to the fuel. The regression rate of HTPB with mass fraction of 25% AP increases by 200 ％ compared to pure HTPB at Gox=160 kg/m 2 s , but reduced safety and increased pressure dependency. Using fuel with low effective heat of gasification such as paraffin[9-11], but the paraffin is poor of mechanical properties and is prone to brittle deformation.Using swirling oxidizer flow[4, 12] and insertion of mechanical devices to increase the turbulent intensity ,but subjected to complexity, scaling, axial uneven burning. However, none of these methods is free from shortcomings. Almost all propellants are bad conductors of heat , embedded metal wires, graphite fibers, and carbon black was added to increase heat conduction, but the effect is not very good. Carbon nanotubes (CNTs) are the ideal fillers for improving thermal conductive and heat radiation from flame zone to fuel surface. Theoretical calculation and practical measurement show that the thermal conductivity of multi-walled carbon nanotube (MWCNTs) is 3000W/mK. MWCNTs has disorganized distribution in HTPB-based fuel, formed a three-dimensional heat conducting network in space in statistical under ideal conditions compared to a granular heat conductive filler such as carbon black. High speed photography was used to evaluate HTPB-based fuel regression of radical burning surface in oxygen flow through a radical regression rate test stand based on SPlab 2D radical hybrid burner. DOI: 10.13009/EUCASS2017-245