August 21, 2009 - MDCA has been installed into the Combustion Integrated Rack (CIR) on the ISS and has completed its calibration testing.  Science burns were initiated in April 2009 for the FLEX set of experiments.  As of August 2009, a set of approximately 20 burns have been performed.  Science operations were suspended while reinstall of boot parameters were required for the MDCA Avionics Box.  Science operations (burns) will resume following STS-128.

Overview

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 2008.

MDCA On-Orbit Checkout photos.

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.  

As a result of the concurrent design process of MDCA and CIR, the MDCA team continues to work closely with the CIR team, developing Integration Agreements and an Interface Control Document during preliminary integration activities.  Integrated testing of hardware and software systems will occur at the Engineering Model and Flight Model phases.  Because the engineering model is a high fidelity unit, it will be upgraded to a flight equivalent Ground Integration Unit (GIU) when the engineering model phase is completed.  The GIU will be available on the ground for troubleshooting of any on-orbit problems.  Integrated verification testing will be conducted with the MDCA flight unit and the CIR flight unit.  Upon successful testing, the MDCA will be shipped to the Kennedy Space Center for a post-shipment checkout and final turn-over to CIR for final processing and launch to the International Space Station.  

Once on-orbit, the MDCA is managed from the GRC Telescience Support Center (TSC).  The MDCA operations team resides at the TSC.  Data is transmitted to the PI’s at their home sites by means of TREK workstations, allowing direct interaction between the PI and operations staff to maximum science.  Upon completion of a PI’s experiment, the MDCA is reconfigured for the next of the three follow-on experiments or ultimately removed from the CIR, placed into stowage, and returned to Earth.

Experiments Using the MDCA

FLEX

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.

FLEX-2

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.

FLEX-ICE-GA

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 intent of ICE-GA is to investigate the ignition and combustion of a single droplet of a surrogate bio-fuel in a quiescent microgravity environment.  The research will dispense, deploy and ignite single droplets and study the droplet and flame regression histories, in a well-controlled (and variable) ambient environment.  The results of the research will provide benchmark data that will assist in the development and validation of models of bio-fuel combustion.  Phenomena such as finite-rate gas-phase chemistry, multicomponent-species gas- and liquid-phase transport processes, production of soot and other pollutants, phase-change processes, liquid-phase species separation and fluid motion, and radiation and conductive energy transfer, are all present in microgravity droplet combustion.  These examples determine, to varying degrees, the performance of a practical combustor.  The metrics, for comparison, include burning rate, burning time, soot aggregate size, extinction diameter, flame diameter, and flame luminosity.

FLEX-2J

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.

MDCA/CIR Testing and Integration

Integrated testing between the MDCA hardware and CIR carrier will be performed on the engineering units of both pieces of hardware.  Both units are hi-fidelity, flight-like units.  Testing, planned for December 2002 will include a full array of sub-package testing, leading to a full end-to-end functional test.  Upon completion, the MDCA Engineering Model (EM) will undergo vibration & microgravity testing, EMI/EMC, and acoustical testing.  In parallel with EM environmental testing, the MDCA flight hardware will be procured and assembled.  Testing will be conducted on the flight unit in early summer 2005 in preparation for a turn-over of the hardware to CIR for flight integrated testing in August 2005.