Development and Testing of a Green Monopropellant Ignition System

Abstract

Green" propellants based on Ionic-liquids (ILs) like Ammonium DiNitramide and Hydroxyl Ammonium Nitrate have recently been developed as reduced-hazard replacements for hydrazine. Compared to hydrazine, ILs offer up to a 50% improvement in available density-specific impulse. These materials present minimal vapor hazard at room temperature, and this property makes IL's potentially advantageous for "ride-share" launch opportunities where hazards introduced by hydrazine servicing are cost-prohibitive. Even though ILs present a reduced hazard compared to hydrazine, in crystalline form they are potentially explosive and are mixed in aqueous solutions to buffer against explosion. Unfortunately, the high water content makes IL-propellants difficult to ignite and currently a reliable "cold-start" capability does not exist. For reliable ignition, IL-propellants catalyst beds must be pre-heated to greater than 350 C before firing. The required preheat power source is substantial and presents a significant disadvantage for SmallSats where power budgets are extremely limited. Design and development of a "micro-hybrid" ignitor designed to act as a "drop-in" replacement for existing IL catalyst beds is presented. The design requires significantly lower input energy and offers a smaller overall form factor. Unlike single-use "squib" pyrotechnic ignitors, the system allows the gas generation cycle to be terminated and reinitiated on demand. Nomenclature= ignitor nozzle exit area, cm 2 A surf = droplet surface area, cm 2 a = Van der Waal parameter, kPa-m 6 /kg-mol 2 B flux = HAN decomposition mass flux, g/s-cm 2 b = Van der Waal parameter, m 3 /kg-mol = ignitor discharge coefficient C p ign = ignitor exhaust products specific heat at constant pressure, J/kg-K = HAN-solution injector discharge area, cm 2 C pc = mean specific heat of gaseous products in chamber, J/kg-K C p HAN = specific heat of pure HAN, J/kg-K C p H2O = specific heat of pure water, J/kg-K = HAN-solution specific heat, J/kg-K D droplet = atomized HAN-solution droplet size, mm f = HAN mass fraction in solution 2 H c = total enthalpy of gaseous products in chamber, J = chamber enthalpy rate, W = enthalpy rate of injected HAN-solution, W = total output enthalpy rate of ignitor, W h ign = specific output enthalpy of ignitor, J/kg L chamber = HAN decomposition length, cm L vap H2O = latent heat of vaporization of water, J/g M HAN = moles of HAN in solution or collected in chamber M H2O = moles of water in solution or collectrd in chamber M ign = moles of ignotor exhaust products collected in chamber M w = generic m,olecular weight term, kg/kg-ml M W HAN = molecular weight of pure HAN, 96.04 kg/kg-mol M W H2O = molecular weight of pure water, 18.02 kg/kg-mol M W HAN/H2O = molecular weight of HAN-solution m c = total fluid mass collected in chamber, g m HAN = total HAN mass collected in chamber, g m ign = total ignitor product mass collected in chamber, g m H2O = total water mass collected in chamber or mass of water in atomozed solution droplet, g = vaporization mass flo...

Research on hierarchical combustion theory of high performance HAN thruster

“…In 2002, Courtéoux [20] used a batch reactor to study the thermal decomposition of binary HAN/aqueous solution, and found that 60% solution concentration required energy input up to 387W/(g/s). In 2013, Stephen [21] put forward a thermal decomposition ignition scheme called "micro mixing" igniter, and successfully ignited 60% HAN solution and achieved self-sustaining combustion in 2015 [22] . In 2018, Alan [23] et al…”

“…The main propellant will not be ignited instantaneously after being injected into the combustion chamber, so it is necessary to calculate the cumulative mass of the combustion chamber in this delay process. The mass balance of the combustion chamber adopts the uniform vapor model [21] , that is, it is assumed that the propellant solution entering is fully atomized by the injector, expressed as vapor, and fully mixed with the products of the ignition branch. With the accumulation of propellant in the combustion chamber, the pressure in the combustion chamber has a pressure building process.…”

Continuous‐Wave Laser Ignition of Non‐Solvent Ionic Liquids Based on High Energetic Salts with Carbon Additives

“…Green monopropellants (GmPs) [1] have been widely investigated as the next-generation candidates for high-performance and low-toxicity propellants. They could be used as alternatives to the conventional propellant hydrazine.…”

Additive Manufacturing of Ceramic Materials: a Performance Comparison of Catalysts for Monopropellant Thrusters

“…Over the past two decades, catalysts for HTP, ADN and HAN propellant blends have received a lot of attention due to an increased interest in possible replacements for hydrazine [4][5][6][7] . A particular difficulty with catalysts for ionic liquids is that a certain amount of preheating is required to initiate the decomposition process 8,9 . This has system disadvantages such as necessary heating power (typically ~10 W for a 10 N thruster) and the required time for preheating (typically 30 min), reducing the agility of the system.…”