The Multi-user Droplet Combustion Apparatus (MDCA) is a multi-user facility designed to accommodate different droplet combustion science experiments.  The MDCA will conduct experiments using the Combustion Integrated Rack (CIR) of the NASA Glenn Research Center’s Fluids and Combustion Facility (FCF).  The payload is planned for the International Space Station.  The MDCA, in conjunction with the CIR, will allow for cost effective extended access to the microgravity environment, not possible on previous space flights.  It is currently in the Engineering Model build phase with a planned flight launch with CIR in 2007.   

The MDCA contains the hardware and software required to conduct unique droplet combustion experiments in space.  It consists of a Chamber Insert Assembly (CIA), an Avionics Package, and a multiple array of diagnostics.  Its modular approach permits on-orbit changes for accommodating different fuels, fuel flow rates, soot sampling mechanisms, and varying droplet support and translation mechanisms to accommodate multiple investigations.  Unique diagnostic measurement capabilities for each investigation are also provided.  Additional hardware provided by the CIR facility includes the structural support, a combustion chamber, utilities for the avionics and diagnostic packages, and the fuel mixing capability for PI specific combustion chamber environments.  Common diagnostics provided by the CIR will also be utilized by the MDCA.  Single combustible fuel droplets of varying sizes, freely deployed or supported by a tether are planned for study using the MDCA.  Such research supports how liquid-fuel-droplets ignite, spread, and extinguish under quiescent microgravity conditions.  This understanding will help us develop more efficient energy production and propulsion systems on Earth and in space, deal better with combustion generated pollution, and address fire hazards associated with using liquid combustibles on Earth and inspace.

The FLEX experiment was designed to assess and quantify the effectiveness of inert-gas suppressants in microgravity and obtain the most conservative estimate of the limiting oxygen index for steady combustion.  FLEX is studying the behavior of near-limit diffusion flames examining in detail liquid- and gas-phase transport and chemical kinetics, and developed and is validating detailed and reduced-order transport and chemistry models that are the foundation for real engine simulations.

The second in the FLEX series of experiments, the FLEX-2 investigation uses fuels and environmental conditions that mimic real combustor conditions.  The investigation will extend and advance the research into droplet combustion, studying the influence of sub-buoyant convective flows on combustion rates, determining the influence of a second burning droplet on a linear array, and beginning the study of practical fuels by burning bi-component and surrogate fuels.  As the research extends into increasingly complex fuels, FLEX-2 data can help verify models of real fuels used in transportation and industry.  Results of the FLEX-2 experimental data will help to develop verified detailed and reduced-order models of droplet combustion, particularly with flow-field and droplet-droplet interactions.

The FLEX-2J experiment is a joint effort between NASA and the Japanese Space Agency, JAXA, as well as Nihon University and Yamaguchi University.  Derived from the JAXA Group Combustion Experiment science objectives, the FLEX-2J will complement those goals using the NASA FLEX-2 hardware and combustion facilities on ISS.  FLEX-2J will observe and measure fuel droplet motions during flame spreading along a one-dimensional droplet array.  Three droplets will be deployed to fixed positions upon ceramic beads on a silicon carbide fiber.  Then an additional three to ten movable droplets are positioned to the fiber at known locations.  The first fixed droplet is ignited and the flame is propagated down the array from droplet to droplet.  The subsequent burning and motions of the unpinned droplets are recorded; particularly the velocities of the free droplets before and after flame spread are measured.  In addition, the experiment will obtain the history of flame leading edge position, flame spread limit span, and the growth process of the group flame along the fuel droplet array.  Specifically, the experiment will measure burning rate, burning time, flame spread and droplet motion as a function of inter-droplet spacing, ambient pressure and gas composition.

The FLEX-Italian Combustion Experiment for Green Air will test surrogate fuels as defined by the Italian Space Agency (ASI) within the CIR in the FLEX-2 configuration.  A collaborative agreement between U.S. and Italian scientists from the Italian National Research Council–Istituto Motori will allow collaboration on research into biologically derived fuels (bio-fuels) in an investigation into new, green energy sources.  Researchers from the NRC–Istituto Motori have identified the fuels to be used as 50–50 mixtures of n-heptane/ethanol and 50–50 n-hexanol/n-decane.

The Light Microscopy Module (LMM) is planned as a remotely controllable on-orbit microscope subrack facility, allowing flexible scheduling and control of physical science and biological science experiments within the GRC Fluids Integrated Rack (FIR) on the International Space Station.

Within the FIR, an initial complement of four fluid physics experiments will utilize an instrument built around a lightmicroscope. These experiments are the "Constrained Vapor Bubble" experiment (Peter C. Wayner of Rensselaer Polytechnic Institute), the "Physics of Hard Spheres Experiment–2" (Paul M. Chaikin of Princeton University), the "Physics of Colloids in Space–2" experiment (David A. Weitz of Harvard University), and the "Low Volume Fraction Entropically Driven Colloidal Assembly" experiment (Arjun G. Yodh of the University of Pennsylvania). The first experiment investigates heat conductance in microgravity as a function of liquid volume and heat flow rate to determine, in detail, the transport process characteristics in a curved liquid film. The other three experiments investigate various complementary aspects of the nucleation, growth, structure, and properties of colloidal crystals in microgravity and theeffects of micromanipulation upon their properties. Key diagnostic capabilities include video microscopy to observe sample features including basic structures and dynamics, thin film interferometry, laser tweezers for colloidal particle manipulation and patterning, confocal microscopy to provide enhanced three-dimensional visualization of colloidal crystal structures, and spectrophotometry to measure colloidal crystal photonic properties. In addition to using the confocal system, biological experiments can conduct fluorescence imaging by using the fiber-coupled output of the Nd:YAG laser operating at 532-nm, the 437-nm line of a mercury arc, or appropriate narrow-band filtering of the FIR provided metal halide white light source.

The use of interfacial free energy gradients to control fluid flow naturally leads to simpler and lighter heat transfer systems because of the absence of mechanical pumps. Therefore, “passive” engineering systems based on this principle are ideal candidates for the space program. In this context, “passive” refers to the natural pressure field for fluid flow due to changes in the intermolecular force field under an imposed nonisothermal temperature field. This force field is a function of the shape, temperature, and composition of the system. For example, heat pipes which rely on these forces have been proposed frequently to optimize heat transfer under microgravity conditions. However, the basic thermophysical principles controlling these systems are not well understood and, as a result, they have under performed. In general, the full potential of interfacial forces has not been realized in transport phenomena.

Therefore, the basic experimental and theoretical studies of the constrained vapor bubble (CVB) under microgravity conditions to help remedy this undesirable situation. The proposed use of a transparent glass cell and related optical measurements will increase the understanding of transport systems controlled by interfacial phenomena because the system is viewed directly. Relatively large systems with high heat fluxes and small capillary pressure levels set in the condenser will be emphasized.