Development and testing of paraffin-based hybrid rocket fuels

Hybrid motors have regain attention for future applications in aerospace science. Because standard hybrid fuels have limited combustion velocities, such engines are not use commercially for space application. The use of hybrids rockets, though, may increase operational safety, decrease on site emissions was well as reduce costs over current solid fuels. The propulsion team from the Energy and Environment Laboratory – University of Brasília, has been investigating a promising solid fuel for hybrid rockets, based on paraffin. A large number of tests indicated reliable ignition and stable combustion over a large operational envelop. This paper show the measured solid fuel regression rates obtained for paraffin-based solid fuel and nitrous oxide. In a 500 N motor with 75 mm inside diameter, we were able to get regression rates as high as 4.5 mm/. An effort to present a mathematical correlation for the combustion velocity as a function of oxidizer mass flux and pressure fail due to lack ...

Low regression rates limit application of hybrid rocket engines (HREs). In this paper, combustion of HTPB-and solid para©n wax-based fuels is investigated in a lab-scale burner by a time-resolved optical technique. The e¨ects of pressure are explored over the range 7 to 16 bar. Nanosized (ALEX TM , 100 nm, uncoated) and micronsized (MgB composite, 5 µm) metal additives are tested. For all runs, the instantaneous regression rate is not constant but higher at the beginning of tests. Overall, MgB performance and relatively ease of manufacturing enable to consider this additive as an interesting novel candidate to enhance hybrid rocket engines performance. NOMENCLATURE A space-averaged value (of parameter A) A time-averaged value (of parameter A) 2D two-dimensional a multiplicative factor [Eqs. (1) and (5)] a s mean surface particle diameter, nm ALEX TM ALuminum EXploded AP Ammonium Perchlorate BET BrunauerEmmetTeller CCP Condensed Combustion Product D port diameter, mm D i ith sampled port diameter, mm DMA Dynamic Mechanical Analysis

Progress in Propulsion Physics, 2013

Hybrid motors are considered an alternative for space launchers due to their safety and high energetic performance. Nevertheless, classical hybrid combustors employing polymeric fuels are characterized by a low fuel regression rate resulting in low thrust levels that may not be adequate. This research presents experimental investigation and theoretical model of liquefying (para©n-based) fuels, featuring high regression rates. The model developed includes an additional feature and mass loss mechanism, i. e., the liquid melt §owing along the grain. The test results exhibit a good correlation with the model predictions.

2014

We propose a conceptual study of prototype strained hydrocarbon molecules as high energy density additives for hybrid rocket fuels to boost the performance of these rockets without compromising safety and reliability. Use of these additives could extend the range of applications for which hybrid rockets become an attractive alternative to conventional solid or liquid fuel rockets. The objectives of the study were to confirm and quantify the high enthalpy of these strained molecules and to assess improvement in rocket performance that would be expected if these additives were blended with conventional fuels. We confirmed the chemical properties (including enthalpy) of these additives. However, the predicted improvement in rocket performance was too small to make this a useful strategy for boosting hybrid rocket performance. Detailed Description Hybrid rockets use a solid fuel with a liquid or gaseous oxidizer. They have advantages over solid fuel rockets for certain space applications because the solid fuel component is more stable than a combined solid fuel and oxidizer, and have advantages over liquid fuel rockets because the fuel does not require cryogenic storage or pumping and the burn rate can be controlled by regulating the flow of oxidizer. Ideal fuels should exhibit a fast regression rate, high density and good mechanical stability (so it will not break apart during burning). A current project at ARC is to evaluate hybrid rockets comprised of solid paraffin fuel and cryogenic nitrous oxide and LOX oxidizer and has shown that higher regression rates are needed. Strained cyclic hydrocarbons have positive enthalpy and can be blended with paraffins to make fuels for hybrid rockets, but to be effective the resulting solid must have physical and mechanical characteristics at least comparable to the pure paraffin fuels. The stable hydrocarbon molecules with the highest strain energy are comprised of triangular rings of carbon atoms (cyclopropane), but these are gases at normal temperatures and pressures. Recently, chemists have synthesized molecules (called ivyanes, shown in Figure 1) containing multiple cyclopropane rings bonded together. We propose investigating blends of ivyanes and paraffins to determine their Chem. 2010, 75, 4387) demonstrated thermochemical properties can be determined to an accuracy of 2 kJ/mol for hydrocarbon molecules containing 10-20 carbon atoms. In the second phase, the density, melting temperature and heat of sublimation of solid ivyanes and the blends will be determined from molecular dynamics simulations. Capabilities provided: Use of hydrocarbon additives could solve problems of fuel pellet break up encountered with aluminum or lithium additives without sacrificing higher regression rates (burn rates), and lead to enhanced safety and lower cost compared to solid and liquid rocket propulsion systems.

One of the objectives of the HYPROB program is the development of tools, design and manufacturing methodologies applicable to hybrid systems and the verification of these technological developments through the realization and test of a 30 kN rocket engine. The technological demonstrator is based on nitrous oxide (N 2 O) as oxidizer and paraffin as propellant and will have most attractive capabilities of hybrid systems compared to solid or liquid engines, as throttability and re-ignition. The project targets to achieve a TRL of enabling technologies for hybrid propulsion equal to 5. The paper reports the study logic defined to achieve the goals of the project and the status of the technical activities related to the preliminary design of the demonstrator, based on a design tool developed ad-hoc.

Progress in Propulsion Physics, 2011

2017

A series of fuels for hybrid rocket engine of our design were developed and tested. Poly(methylene oxide), paraffin wax and epoxy-based compositions were made, characterized by means of measured thrust, c*, Isp, thermal stability (DSC, TG) and chemical composition (FTIR). Various techniques of fuel casting which enabled us to obtain free of cracks and defects grains of paraffin wax and homogenous emulsion of paraffin in epoxy resin have been proposed.

Propellants, Explosives, Pyrotechnics, 2002

Cryogenic Solid Propellant (CSP)-technology is a new approach to develop more powerful rocket motors. CSPs include the advantages of classical solid propellants to save weight as well as those of a high energy content and safety of modern liquid propellants. The charges consist of liquid and/or gaseous fuels and oxidizers, both frozen. Two main versions of CSP-technology can be realised: 1. Mono-CSPs show the burning behavior of solid propellants. Experiments with mono-CSPs have been carried out under inert pressure conditions in a window bomb. Mono-CSPs have a stable burning behavior with a constant regression rate which follows the Vieille×s law under varying pressure conditions. 2. The advantage of high safety is obtained by assembling oxidizer and fuel in sandwich configurations. The grain geometry governs the burning behavior. Such systems can be externally controlled, e.g. by the heat from a gas generator or they can work selfsustained. A Rod-in-Matrix burner shows self-sustained combustion in an inert pressure atmosphere with overall burning rates in a similar range as solid rocket propellants which obey also a Vieille-like pressure law. Disc stack burners have also been investigated, the combustion of which is strongly dependent on the disc thickness. For a short time Mach×s nodes have been observed in the exhaust plume of a disc stack burner. Currently, the temperature ranges are limited to the boiling temperature of liquid nitrogen. Therefore, liquid oxidizers like H 2 O 2 have been used. However, for the first time a propellant strand of polymer rods embedded in solid oxygen was prepared and burnt. The experiments with CSPs end in the combustion of a small rocket motor showing no serious technical obstacles. Simplified models based on the heat flow equation can simulate the burning characteristics of the frozen energetic materials including phase transitions.

2019

The current project aims at the understanding of the propulsive parameters of hybrid rocket motors. Computational simulations using the software CEA-NASA were carried out. The fuels paraffin wax, hydroxyl-terminated polybutadiene (HTPB) and polymethyl methacrylate (PMMA) were combined with three oxidizers: liquid oxygen (LOX), nitrous oxide (N2O) and hydrogen peroxide (H2O2). The propulsive parameters examined were the characteristic velocity, specific impulse and adiabatic flame temperature. The propellant pair paraffin-LOX provided the highest performance for all parameters studied. This work was shown effective as a basis for the design of a static test bench and a hybrid propulsion system.

This paper shows the current status on hybrid propulsion technology carried by the Laboratory of Energy and Environment from University of Brasilia. Specifically we describe the development of a new hybrid motor, based on paraffin as the solid fuel and N 2 O as the oxidizer. In order to demonstrate the technology, a twelve months project was conceived to design, build and test a hybrid rocket capable of reaching 2600 meters altitude. The project was divided in three main phases: (i) static tests of the 500 N hybrid motor, (ii) design and construction of a hybrid rocket and (iii) launching of a model hybrid rocket. The regression rate tests confirmed that paraffin is a promising fuel for hybrid rockets. We were able to get reliable ignition and operation in the majority of the firings. Two rockets were then built and launch. The rockets flight and operation was considered a great success. To our knowledge, this was the first hybrid rocket ever built and launch by a research group in Brazil. The group is now leading a project sponsored by the Brazilian Space Agency (AEB) to design, integrate and test a hybrid sounding rocket capable of reaching 20000 m with avionics and recovery system.