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We present details of the design, implementation, test and operation with live mice of a closed-loop integrated ECLSS ground test apparatus for the Mars Gravity Biosatellite. The sealed system includes accommodations for two flight-design habitat modules, which can be deployed in either a rotational or a non-rotational configuration. Installed within the apparatus are scaled-down versions of a subset of flight-equivalent atmospheric reconditioning subassemblies together with sensors, actuators and a computer to perform autonomous feedback-driven supervisory control. We present data that validates an integrated closed-loop system which includes oxygen replenishment, carbon dioxide scrubbing via reaction with lithium hydroxide, ammonia removal using acid-treated activated charcoal, and humidity control with a custom-designed condensing heat exchanger.

We present results which verify the design parameters and suggest performance capabilities/limitations of the Mars Gravity Biosatellite's proposed atmospherics control subassembly. Using a combination of benchtop prototype testing and analytic techniques, we derive control requirements for ammonia. Further, we demonstrate the dehumidification performance of our proposed partial gravity condensing heat exchanger. Ammonia production is of particular concern in rodent habitats. The contaminant is released following chemical degradation of liquid waste products. The rate of production is linked to humidity levels and to the design of habitat modules in terms of bedding substrate, air flow rates, choice of structural materials, and other complex factors. Ammonia buildup can rapidly lead to rodent health concerns and can negatively impact scientific return.

A rotating spacecraft which encloses an atmospheric pressure vessel poses unique challenges for thermal control. In any given location, the artificial gravity vector is directed from the center to the periphery of the vehicle. Its local magnitude is determined by the mathematics of centripetal acceleration and is directly proportional to the radius at which the measurement is taken. Accordingly, we have a system with cylindrical symmetry, featuring microgravity at its core and increasingly strong gravity toward the periphery. The tendency for heat to move by convection toward the center of the craft is one consequence which must be addressed. In addition, fluid flow and thermal transfer is markedly different in this unique environment. Our strategy for thermal control represents a novel approach to address these constraints. We present data to theoretically and experimentally justify design decisions behind the Mars Gravity Biosatellite's proposed payload thermal control subassembly.

To model sprays from pressure-swirl atomizers, the connection between the injector and the downstream spray must be considered. A new model for pressure-swirl atomizers is presented which assumes little knowledge of the internal details of the injector, but instead uses available observations of external spray characteristics. First, a correlation for the exit velocity at the injector exit is used to define the liquid film thickness. Next, the film must be modeled as it becomes a thin, liquid sheet and breaks up, forming ligaments and droplets. A linearized instability analysis of the breakup of a viscous, liquid sheet is used as part of the spray boundary condition. The spray angle is estimated from spray photographs and patternator data. A mass averaged spray angle is calculated from the patternator data and used in some of the calculations.

Mass-related properties of four atomizers were estimated with the use of a mechanical transient patternator. The properties presented on a temporal and spatial basis are the axial liquid mass flux, liquid fuel to air ratio, and liquid axial velocity. The data are presented in two formats. The first format consists of the mass-related properties that occurred radially between two planes positioned 2.0 cm and 2.25 cm along the atomizer axis. A second format consists of interpolated contour plots of the axial liquid mass flux for all of the spray systems studied. The atomizers used in the study consisted of three liquid-only high-pressure systems and one air-assist system. Two of the liquid-only high-pressure systems and the air - assist system were operated with a volumetric delivery of 20 mm3 per injection while injecting into ambient conditions. A third liquid-only high-pressure system was operated with a delivery of 15 mm3 per injection.

Two distinct atomization strategies are contrasted through the measurement of time and spatially dependent mass flux. The two systems investigated include a pressure atomizer (6.9 MPa opening pressure) and an air-assist atomizer. Both systems have potential for use in direct injection spark ignition engines. The mass flux data presented were obtained using a spray patternator that was developed to allow phased sampling of the spray. The temporal mass related history of the spray was reconstructed as volume versus time plots and interpolated mass flux contour plots. Results indicate substantial differences in the distribution of both mass and mass flux in space and time for the two injection systems. For example, the pressure atomizer at high mass delivery rates produced a spray that collapsed into a dispersed cylindrical shape while at low rates, generated a hollow cone structure.

Previous experiments using an air-assisted spray in a two-stroke direct-injected engine demonstrated a significant improvement in combustion stability at part-load conditions when a wide injection spray was used. It was hypothesized that the decrease in variability was due to the spray following the combustion chamber wall, making it less affected by variations in the in-cylinder gas flows. For this study, experiments were conducted to investigate engine spray combustion for cases where engine performance was not dominated by cyclic variation. Combustion and emission performance data was collected for a wide range of injection timings at several speed/load conditions. Experimental data for combustion shows that combustion stability is relatively unaffected by injection timing changes over a 40 to 100 degree window, and tolerant to spark gap projections over a range of 0.7 to 5.2 mm, depending on operating conditions.

To help understand the fundamental processes involved in direct injection, a research project was conducted using a single-cylinder, two-stroke research engine at a mid-speed, boat load operating condition. A 24 statistical factorial experimental design was applied. Of the factors tested at this operating condition, spray type was the most important factor affecting hydrocarbon emissions, followed by in-cylinder flow-related factors. Injection spray was also most important for nitrogen oxide emissions, carbon monoxide emissions, and efficiency. The dominant mechanism influencing the results was misfire, with other mechanisms present for specific responses.