Evaluation of Fuel Additives for Hybrid Rockets and SFRJ Systems

Abstract

A comprehensive assessment of fuel additives that are expected to improve the performance of hybrid rockets and solid fuel ramjet (SFRJ) systems is reported in this paper. A ranking of the selected fuel additives and binders have been made based on performance and other practical considerations including cost, availability and handling properties. One of the important conclusions of this study is that incorporating fuel additives into a binder is not an effective method to enhance the regression rate of hybrid rocket or SFRJ fuels. The key driver should be specific impulse and density impulse improvement. For low energy oxidizers such as nitrous oxide, aluminum turns out to be an excellent additive that strikes a good balance between the performance gain and key practical considerations such as availability/cost. Aluminum or other metals included in this study are not effective in improving Isp when they are used with oxygen. For hybrid rockets, AlH3 delivers the best performance benefit among all of the additives considered in this study. However its poor availability in the Western world diminishes its usefulness. Boron as an additive did not have a major performance impact for hybrid systems. It is believed that at the current energy and unit cost levels of the performance additives, they are not expected to generate an economical benefit (i.e. cost/payload mass) even for applications demanding high Isp's such as orbital launch vehicles. For SFRJ systems, boron and its compounds deliver significant performance improvement. Paraffin ranks as the best binder for both hybrids and also SFRJ's due to its high regression rate, good availability, hydrophobic nature, easy handling and low cost. NomenclatureAB = Ammonia Borane ADN = Ammonium dinitramide AMROC = American Rocket Company DCPD = Dicyclopentadiene GOX = Gaseous oxygen HTPB = Hydroxyl Terminated Polybutadiene LOX = Liquid oxygen NTO = Dinitrogen Tetraoxide (N2O4) pDCPD = Polydicyclopentadiene PE = Polyethylene polymer PMM = Polymethylmethacrylate SFRJ = Solid Fuel Ramjet Tf = Flame temperature, K

Hybrid Propulsion System: Novel Propellant Design for Mars Ascent Vehicles

“…Metallic powders serve as excellent fuel additives due to their significant volumetric and gravimetric heat release during the combustion process [8]. Purity, size and shape of metallic powders directly affect the combustion performance as they control the ignition delay and the formation of the condensed combustion product (CCP).…”

Metal–organic frameworks as hypergolic additives for hybrid rockets

“…This can be achieved with energy-dense additives in fuel grains made of solid hydrocarbons, including metal or organic hydrides and crystalline metals. 32,33 As an example, the incorporation of aluminum particles has been shown to improve the specific impulse of hybrid propellants relying on relatively weak oxidizers such as hydrogen peroxide or nitrous oxide. 32 Another way of making hybrid rockets more interesting is by inducing the hypergolic ignition of its fuel.…”

Experimental Observation and Characterization of B−HTPB‐based Solid Fuel with Addition of Iron Particles for Hybrid Gas Generator in Ducted Rocket Applications

“…Ramjet engine is superior among the various types of airbreathing engines. It is superior than equivalent rocket engine when compared in terms of specific impulse (I sp ), thrust, and simpler design [1][2]. In recent times, capability of solid fuel ramjet (SFRJ) engine is further augmented through improved internal design and use of energetic fuel/propellant.…”

“…Primary combustor is a fuel rich solid propellant gas generator. Combustion products from primary combustor with reminiscent unburnt fuel reach the secondary combustor where it is mixed with atmospheric air available from the duct and finally combusted [1]. Ducted air is bypassed from the atmosphere and its thermodynamic properties get modified before reaching the secondary combustor, because it depends on strength of the shock wave present at the inlet of the duct.…”

“…The new system has been evaluated theoretically as well as experimentally which exhibits potential advantages on cost, performance and, safety issues [3]. [1] Further amendment in SFRJ design has been accomplished through boron-based fuel/propellant which has been implemented by many researchers so far [5][6][7][8][9][10][11]. However, full-fledged boron-based fuel has not been incorporated in any existing propulsive system [12], though, boron has potential to produce high energy density.…”