The push toward the miniaturization of electro-mechanical devices and the resulting need for micro-power generation (milli-watts to watts) with low-weight, long-life devices has led to the recent development of the field of micro-scale combustion. The concept behind this new field is that since batteries have low specific energy, and liquid hydrocarbon fuels have a very high specific energy, a miniaturized power generating device, even with a relatively inefficient conversion of hydrocarbon fuels to power would result in increased lifetime and/or reduced weight of an electronic or mechanical system that currently requires batteries for power. In addition to the interest in miniaturization, the field is also driven by the potential fabrication of the devices using Micro Electro Mechanical Systems (MEMS) or rapid prototyping techniques, with their favorable characteristics for mass production and low cost. The micro-power generation field is very young, and still is in most cases in the feasibility stage. However, considering that it is a new frontier of technological development, and that only a few projects have been funded, it can be said that significant progress has been made to date. Currently there is consensus, at least among those working in the field, that combustion in the micro-scale is possible with proper thermal and chemical management. Several meso-scale and micro-scale combustors have been developed that appear to operate with good combustion efficiency. Some of these combustors have been applied to energize thermoelectric systems to produce electrical power, although with low overall efficiency. Several turbines/engines have also been, or are being, developed, some of them currently producing positive power, also with low efficiency to date. Micro-rockets using solid or liquid fuels have been built and shown to produce thrust. Hydrogen-based micro size fuel cells have been successfully developed, and there is a need to develop reliable reformers (or direct-conversion fuel cells) for liquid hydrocarbons so that the fuel cells become competitive with batteries. In this work, some of the technological issues related to meso and micro-scale combustion and the operation of thermochemical devices for power generation will be discussed. Some of the systems currently being developed will be presented and described.

/pdf/micropower-generation-using-combustion-issues-and-approaches-297ywwh8t7.pdf

Micropower generation using combustion: Issues and approaches

New energetic materials (EMs) are the key to great advances in microscale energy-demanding systems as actuation part, igniter, propulsion unit, and power. Nanoscale EMs (nEMs) particularly offer the promise of much higher energy densities, faster rate of energy release, greater stability, and more security (sensitivity to unwanted initiation). nEMs could therefore give response to microenergetics challenges. This paper provides a comprehensive review of current research activities in nEMs for microenergetics application. While thermodynamic calculations of flame temperature and reaction enthalpies are tools to choose desirable EMs, they are not sufficient for the choice of good material for microscale application where thermal losses are very penalizing. A strategy to select nEM is therefore proposed based on an analysis of the material diffusivity and heat of reaction. Finally, after a description of the different nEMs synthesis approaches, some guidelines for future investigations are provided.

https://homepages.laas.fr/rossi/Publi/Nanoenergetics-Review-JMEMS-2.pdf

Nanoenergetic Materials for MEMS: A Review

This paper studied the large amplitude vibration and the nonlinear bending of a sandwich plate with carbon nanotube-reinforced composite (CNTRC) face sheets resting on an elastic foundation in thermal environments. The material properties of CNTRC face sheets are assumed to be graded in the thickness direction, and are estimated through a micromechanical model. The governing equation of the plate that includes plate-foundation interaction is solved by a two-step perturbation technique. The thermal effects are also included and the material properties of both CNTRC face sheets and homogeneous core layer are assumed to be temperature-dependent. A detailed parametric study is conducted to study the effects of nanotube volume fraction, core-to-face sheet thickness ratio, temperature change, foundation stiffness and in-plane boundary conditions on the nonlinear vibration characteristics and nonlinear bending behaviors of sandwich plates with functionally graded CNTRC face sheets. The results for the same plate with uniformly distributed CNTRC face sheets are also provided for comparison.

Nonlinear vibration and bending of sandwich plates with nanotube-reinforced composite face sheets

https://www.mne.psu.edu/sfnm/Publications1_files/UMD/1-s2.0-S0010218014000492-main.pdf

Assembly and reactive properties of Al/CuO based nanothermite microparticles

: Microscale combustion is of interest in small-volume energy-demanding systems, such as power supplies, actuation, ignition, and propulsion Energetic materials can have high burning rates that make these materials advantageous, especially for microscale applications in which the rate of energy release is important or in which air is not available as an oxidizer In this study we examine the combustion of mixtures of nanoscale aluminum with molybdenum trioxide in microscale channels Nanoscale composites can have very high burning rates that are much higher than typical materials Quartz and acrylic tubes are used Rectangular steel microchannels are also considered We find that the optimum mixture ratio for the maximum propagation rate is aluminum rich We use equilibrium calculations to argue that the propagation rate is dominated by a convective process where hot liquids and gases are propelled forward heating the reactants This is the first study to report the dependence of the propagation rate with a tube diameter for this class of materialsWefind that the propagation rate decreases linearly with 1=d The propagation rate remains high in tubes or channels with dimensions down to the scale of 100 m, which makes these materials applicable to microcombustion applications

Combustion of Nanoscale Al/MoO3 Thermite in Microchannels

The integration of propellant within a silicon micromachined systems enables the realization of a new class of MEMS devices called microscale rocket. These new devices seem to respond to a real need in the field of high energetic microscale actuation. Their main originality is the use of only one solid propellant loaded in a small tank micromachined in a ceramic or silicon substrate. The structure consists of a sandwich of three micromachined silicon substrates: nozzles, igniters and propellant chambers. The thrust force issued from the combustion of the solid propellant ranges from 1 mN to a few mN. Just by geometrical and dimensional considerations, it is possible to adapt the thrust impulse depending on the application requirements. One identified application of microrockets is space with the realization of microscale thrusters for the control of the attitude or/and the station keeping of very small satellite. In a first part of the paper, we present the process of fabrication and the assembling of microthrusters as well as the specific equipment developed to load the solid propellant into microcavities. On a second part, we present briefly the modeling tools developed to predict the thruster performances.

Design, fabrication and modeling of solid propellant microrocket-application to micropropulsion

With the development of microspacecraft technology micropropulsion concepts are introduced for course correction and orbit insertion as well as attitude control of the microspacecraft. In this context, we have introduced a new concept of MEMS-based technology microthruster responding to the spatial constraints (volume constraints, high level of integration) and MEMS characteristics (miniaturization, low cost, mass production). The originality of these new thrusters is the use of only one solid propellant loaded in a small tank micromachined in a ceramic, glass or silicon substrate and the fabrication of arrays of N independent microthrusters in the same chip. The structure consists of a sandwich of three micromachined silicon substrates: nozzles, igniters and propellant chambers. The thrust force generated can be set from a few hundred µN to a few tens of mN by geometrical and dimensional considerations. In this paper we present the fabrication and assembly of one prototype: it is an array of 36 microthrusters that proved the technological feasibility of this new concept of small-scale thrusters. We also investigate the influence of nozzle geometry on the performances of our thruster.

https://iopscience.iop.org/article/10.1088/0964-1726/10/6/304/pdf

Design, fabrication and modelling of MEMS-based microthrusters for space application

Within an European project, 1 MEMS-based pyrotechnical devices have been developed. The operational concept is simply based on the combustion of a solid energetic material stored in a micromachined chamber. One possible application is the micropropulsion for nanosatellite but other applications can be addressed as microrocket for military needs. Arrays built to validate the concept contain 16 O1.5 mm × 1.5 mm rockets on 200 mm 2 . After a brief overview of the design and dimension, this paper presents the final experimentations that permitted to validate the pyrotechnical thrusters concept. At the millimetre scale, having a successful and reproducible ignition as well as a sustained propellant’s combustion is a critical point of this technology. That is why, ignition, combustion and thrust has been experimented with great attention to fully validate the concept and results are reported in this paper. © 2005 Elsevier B.V. All rights reserved.

https://homepages.laas.fr/rossi/Publi/Characterization%20thruster.pdf

Final characterizations of MEMS-based pyrotechnical microthrusters

On presente le developpement de matrices de micro propulseurs a propergol solide sur silicium. Le concept est base sur la combustion d'un materiau pyrotechnique de type propergol stocke dans un reservoir en silicium ou en Foturan micro usine. Chaque propulseur est constitue de trois parties : un initiateur thermique, un reservoir et une tuyere. Du fait de leur caracteristique mono coup, les propulseurs sont disposes en matrice. Une application essentielle est la realisation de module de micro propulsion pour les nano satellites. Les matrices de micro propulseurs presentes dans cet article contiennent 16 propulseurs unitaires sur une surface de 64 mm 2 . Chacun des propulseurs a une section de combustion de 2.25 mm 2 avec des diametres de col.de tuyere de 105μm et 150 μm. Les procedes de fabrication sont detailles et des resultats sur l'initiation et les vitesses de combustion sont donnes

Micropropulseur à propergol solide pour des applications spatiales

Solid propellant micro-thruster is an alternative option to cold gas and field emission electric propulsion systems for space. It can also be used for autonomous Micro-Air-Vehicles (MAV) micro-propulsion in complement to electrical motor. It is simple, cheap and requires low power to ignite the micro-combustion of a few milli-grammes of a solid propellant. This paper presents two concepts of solid propellant micro-thruster. The first one is a sandwich of three parts: a combustion chamber (with one or several wafers), an igniter and a convergent-divergent nozzle. They produce force thrust between 0.28mN and 14mN making them good candidates for station keeping or orbit maneuvers for micro-spacecraft. The second one is a planar structure, more powerful in comparison with the first structure. It is designed to deliver thrusts between 10mN and 50mN for civil and military applications, like the stabilization of MAV during stationary fly. It is made of three layers : (i) a combustion chamber and a micro-nozzle are micromachined on the same silicon wafer; (ii) a ceramic reservoir is reported on the top; (iii) a Pyrex glass seals the back side of the structure. The design, the micro-fabrication and the characterization of both structures are reported.

Main directions of solid propellant micro-propulsion activity at LAAS

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