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Direct osmotic concentration (DOC) is an integrated membrane treatment process designed for the reclamation of spacecraft wastewater. The system includes forward osmosis (FO), membrane evaporation, reverse osmosis (RO) and an aqueous phase catalytic oxidation (APCO) post-treatment unit. This document describes progress in the third year of a four year project to advance hardware maturity of this technology to a level appropriate for human rated testing. The current status of construction and testing of the final deliverable is covered and preliminary calculations of equivalent system mass are funished.

The oxidation chemistry of paraffins, aromatics, olefins and MTBE were examined. Detailed chemical kinetics calculations were carried out for oxidation of these compounds in the engine cycle. The oxidation rates are very sensitive to temperature. At temperatures of over 1400 K (depending on the fuel), all the hydrocarbons are essentially oxidized for typical residence time in the engine. Based on the kinetics calculations, a threshold temperature is defined for the conversion of the fuel species to CO, CO2, H2O and partially oxidized products. The difference in the survival fraction between aromatics and non-aromatics is attributed to the higher threshold temperature of the aromatics.

The chemistry of unburned hydrocarbon oxidation in SI engine exhaust was modeled as a function of temperature and concentration of unburned gas for lean and rich mixtures. Detailed chemical kinetic mechanisms were used to model isothermal reactions of unburned fuel/air mixture in an environment of burned gases at atmospheric pressure. Simulations were performed using five pure fuels (methane, ethane, propane, n-butane and toluene) for which chemical kinetic mechanisms and steady state hydrocarbon (HC) emissions data were available. A correlation is seen between reaction rates and HC emissions for different fuels. Calculated relative amounts of intermediate oxidation products are shown to be consistent with experimental measurements.

A one-dimensional model has been developed for the species and energy transfer over a thin (0.1-0.5 mm) layer of liquid fuel present on the wall of a spark-ignition engine. Time-varying boundary conditions during compression and flame passage were used to determine the rate of methanol vaporization and oxidation over a mid-speed, mid-load cycle, as a function of wall temperature. The heat of vaporization and the boiling point of the fuel were varied about a baseline to determine the effect of these characteristics, at a fixed operating point and lean conditions (ϕ = 0.9). The calculations show that the evaporation of fuels from layers on cold walls starts during flame passage, peaking a few milliseconds later, and continuing through the exhaust phase.

The effect of engine operating parameters (speed, spark timing, and fuel-air equivalence ratio [Φ]) on hydrocarbon (HC) oxidation within the cylinder and exhaust system is examined using propane or isooctane fuel. Quench gas (CO2) is introduced at two locations in the exhaust system (exhaust valve or port exit) to stop the oxidation process. Increasing the speed from 1500 to 2500 RPM at MBT spark timing decreases the total, cylinder-exit HC emissions by ∼50% while oxidation in the exhaust system remains at 40% for both fuels. For propane fuel at 1500 rpm, increasing Φ from 0.9 (fuel lean) to 1.1 (fuel rich) reduces oxidation in the exhaust system from 42% to 26%; at 2500 RPM, exhaust system oxidation decreases from 40% to approximately 0% for Φ = 0.9 and 1.1, respectively. Retarded spark increases oxidation in the cylinder and exhaust system for both fuels. Decreases in total HC emissions are accompanied by increased olefinic content and atmospheric reactivity.

A one-dimensional model for crevice HC post-flame oxidation is used to calculate and understand the effect of operating parameters and fuel type (propane and isooctane) on the extent of crevice hydrocarbon and the product distribution in the post flame environment. The calculations show that the main parameters controlling oxidation are: bulk burned gas temperatures, wall temperatures, turbulent diffusivity, and fuel oxidation rates. Calculated extents of oxidation agree well with experimental values, and the sensitivities to operating conditions (wall temperatures, equivalence ratio, fuel type) are reasonably well captured. Whereas the bulk gas temperatures largely determine the extent of oxidation, the hydrocarbon product distribution is not very much affected by the burned gas temperatures, but mostly by diffusion rates. Uncertainties in both turbulent diffusion rates as well as in mechanisms are an important factor limiting the predictive capabilities of the model.

An experimental study was performed to develop a more fundamental understanding of the effects of secondary air injection (SAI) on exhaust gas emissions and catalyst light-off characteristics during cold start of a modern SI engine. The effects of engine operating parameters and various secondary air injection strategies such as spark retardation, fuel enrichment, secondary air injection location and air flow rate were investigated to understand the mixing, heat loss, and thermal and catalytic oxidation processes associated with SAI. Time-resolved HC, CO and CO₂ concentrations were tracked from the cylinder exit to the catalytic converter outlet and converted to time-resolved mass emissions by applying an instantaneous exhaust mass flow rate model. A phenomenological model of exhaust heat transfer combined with the gas composition analysis was also developed to define the thermal and chemical energy state of the exhaust gas with SAI.

The effects of several variables on pitting fatigue life of carburized steels were analyzed using a geared roller test machine (GRTM). The material variables that were primarily used to influence retained austenite include aim surface carbon concentration (0.8 % and 0.95 %), alloy (SAE 4320 and a modified SAE 4122), and cold treatment (performed on one material condition per alloy). Testing variables included contact stress in addition to a variation in lambda ratio (oil film thickness/surface roughness), arising from variation in roughness among the machined surfaces. Test results are presented, and differences in performance are considered in terms of material and testing variables. A primary observation from these results is an improvement in contact fatigue resistance apparently arising from cold-treatment and the associated reduction of retained austenite at the surface.

The extent of oxidation of hydrocarbons desorbing from the oil layer has been measured directly in a hydrogen-fueled, spark-ignited engine in which the lubricant oil was doped with a single component hydrocarbon. The amount of hydrocarbon desorbed and oxidized could be measured simultaneously as the dopant was only source of carbon-containing species. The fraction oxidized was strongly dependent on engine load, hydrogen fuel-air ratio and dopant chemical reactivity, but only modestly dependent on spark timing and nitrogen dilution levels below 20 percent. Fast FID measurements at the cylinder exit showed that the surviving hydrocarbons emerge late in the exhaust stroke.

Prediction of fatigue performance of large structures and components is generally done through the use of a fatigue analysis software, FEA stress/strain analysis, load spectra, and materials properties generated from laboratory tests with small specimens. Prior experience and test data has shown that a specimen size effect exists, i.e. the fatigue strength or endurance limit of large members is lower than that of small specimens made of same material. Obviously, the size effect is an important issue in fatigue design of large components. However a precise experimental study of the size effect is very difficult for several reasons. It is difficult to prepare geometrically similar specimens with increased volume which have the same microstructures and residual stress distributions throughout the entire material volume to be tested. Fatigue testing of large samples can also be a problem due to the limitation of load capacity of the test systems available.

The effectiveness of three different techniques, designed to improve the bending fatigue life in comparison to conventionally processed gas-carburized 8620 steel, were evaluated with modified Brugger bending fatigue specimens and actual ring and pinion gears. The bending fatigue samples were machined from forged gear blanks from the same lot of material used for the pinion gear tests, and all processing of laboratory samples and gears was done together. Fatigue data were obtained on standard as-carburized parts and after three special processing histories: shot-peening to increase surface residual stresses; double heat treating to refined austenite grain size; and vacuum carburizing to minimize intergranular oxidation. Standard room-temperature S-N curves and endurance limits were obtained with the laboratory samples. The pinions were run as part of a complete gear set on a laboratory dynamometer and data were obtained at two imposed torque levels.

The effects of austenite grain size on the bending fatigue crack initiation and fatigue performance of gas carburized, modified 4320 steels were studied. The steels were identical in composition except for phosphorus concentration which ranged between 0.005 and 0.031 wt%. Following the carburizing cycle, specimens were subjected to single and triple reheat treatments of 820°C for 30 minutes to refine the austenite grain structure, and oil quenched and tempered at 150°C. Specimens subjected to bending fatigue were characterized by light metallography to determine microstructure and grain size, X-ray analysis for retained austenite and residual stress measurements, and scanning electron microscopy for examination of fatigue crack initiation and propagation. The surface austenite grain size ranged from 15 μm in the as-carburized condition to 6 and 4 μm diameter grain size for the single and triple reheat conditions, respectively.