Production of anteiso-branched fatty acids in Escherichia coli; next generation biofuels with improved cold-flow properties
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Haushalter, Robert W.↗
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Superior performance biodiesel from biomass-derived fusel alcohols and low grade oils: Fatty acid fusel esters (FAFE)
We demonstrated production of a superior performance biodiesel referred to here as fatty acid fusel alcohol esters (FAFE) – by reacting fusel alcohols (isobutanol, 3-methyl-1-butanol, and (S)-(-)-2-methyl-1-butanol) with oil (glyceryl trioleate) using lipase from Aspergillus oryzae. Reaction conditions corresponding to a molar ratio of 5:1 (fusel alcohols to oil), enzyme loading of 2% w/w, reaction temperature of 35 °C, shaking speed of 250 rpm, and reaction time of 24 h achieved >97% conversion to FAFE. Further, FAFE obtained from reacting a fusel alcohol mixture with corn oil were evaluated for use as a fuel for diesel engines. FAFE mixtures showed superior combustion and cold-flow properties, with the derived cetane numbers up to 4.8 points higher, cloud points up to -6 °C lower, and the heat of combustion up to 2.1% higher than the corresponding FAME samples, depending on the fusel mixture used. This represents a significant improvement for all three metrics, which are typically anti-correlated. Finally, FAFE provides a new opportunity for expanded usage of biodiesel by addressing feedstock limitations, fuel performance, and low temperature tolerance.
09 BIOMASS FUELS↗
Biodiesel Basics [Fact Sheet]
This fact sheet provides a brief introduction to biodiesel, including a discussion of biodiesel blends, which blends are best for which vehicles, where to buy biodiesel, how biodiesel compares to diesel fuel in terms of performance, how biodiesel performs in cold weather, whether biodiesel use will plug vehicle filters, how long-term biodiesel use may affect engines, biodiesel fuel standards, and whether biodiesel burns cleaner than diesel fuel. The fact sheet also dismisses the use of vegetable oil as a motor fuel.
09 BIOMASS FUELS↗
Biodiesel Basics (Spanish Version); Clean Cities, Energy Efficiency & Renewable Energy (EERE)
This Spanish-language fact sheet provides a brief introduction to biodiesel, including a discussion of biodiesel blends, which blends are best for which vehicles, where to buy biodiesel, how biodiesel compares to diesel fuel in terms of performance, how biodiesel performs in cold weather, whether biodiesel use will plug vehicle filters, how long-term biodiesel use may affect engines, biodiesel fuel standards, and whether biodiesel burns cleaner than diesel fuel. The fact sheet also dismisses the use of vegetable oil as a motor fuel.
33 ADVANCED PROPULSION SYSTEMS↗
Biodiesel Basics (Spanish Version)
This Spanish-language fact sheet provides a brief introduction to biodiesel, including a discussion of biodiesel blends, which blends are best for which vehicles, where to buy biodiesel, how biodiesel compares to diesel fuel in terms of performance, how biodiesel performs in cold weather, whether biodiesel use will plug vehicle filters, how long-term biodiesel use may affect engines, biodiesel fuel standards, and whether biodiesel burns cleaner than diesel fuel. The fact sheet also dismisses the use of vegetable oil as a motor fuel.
33 ADVANCED PROPULSION SYSTEMS↗
Fuel/oxidizer-rich high-pressure preburners
The analyses, designs, fabrication, and cold-flow acceptance testing of LOX/RP-1 preburner components required for a high-pressure staged-combustion rocket engine are discussed. Separate designs of injectors, combustion chambers, turbine simulators, and hot-gas mixing devices are provided for fuel-rich and oxidizer-rich operation. The fuel-rich design addresses the problem of non-equilibrium LOX/RP-1 combustion. The development and use of a pseudo-kinetic combustion model for predicting operating efficiency, physical properties of the combustion products, and the potential for generating solid carbon is presented. The oxygen-rich design addresses the design criteria for the prevention of metal ignition. This is accomplished by the selection of materials and the generation of well-mixed gases. The combining of unique propellant injector element designs with secondary mixing devices is predicted to be the best approach.
Schoenman, L.↗
Temperature Measurements in Hypersonic Wind Tunnels via Femtosecond Coherent Anti-Stokes Raman Scattering
A femtosecond coherent anti-Stokes Raman scattering (fs CARS) instrument is developed to perform gas-phase thermometry in cold-flow hypersonic wind tunnels. Measurements are reported for Mach 8 and 14 pure-nitrogen flows. The fs CARS instrument includes a 100 fs pump/Stokes pulse and a spectrally narrow probe pulse from a second harmonic bandwidth compressor. Important experimental considerations such as limits on the pump/Stokes pulse energy are discussed. The fs CARS focusing and collimating optics are mounted on a two-axis translation stage system to scan the measurement location during a 30 second wind tunnel run. Single-laser-shot rotational CARS spectra are recorded at the laser repetition rate of 1 kHz in the wind tunnel freestream and near simple cone models. Spectral fitting is used to determine quantitative gas temperatures. Freestream temperatures at Mach 8 and 14 spanned ranges of 40–75 and 35–50 K, respectively, depending on tunnel operating conditions. Temperature variations across the central 100 mm span of the wind tunnel were quantified. Measured temperature jumps across conical bow shocks from various models varied by less than 1% from predicted values. Hypersonic boundary layer measurements were demonstrated. In conclusion, these measurements illustrate the utility and robustness of this instrument for the study of complex fluid flow phenomena in challenging ground test facilities.
Aerodynamics↗
Cycle-to-Cycle Variations in Multi-Cycle Engine RANS Simulations
Reynolds-averaged Navier-Stokes (RANS) modeling is expected to deliver an ensemble-averaged result for the majority of turbulent flows. This could lead to the conclusion that multi-cycle internal combustion engine (ICE) simulations performed using RANS must exhibit a converging numerical solution after a certain number of consecutive cycles. However, for some engine configurations unsteady RANS simulations are not guaranteed to deliver an ensemble-averaged result. In this paper it is shown that, when using RANS modeling to simulate multiple engine cycles, the cycle-to-cycle variations (CCV) generated from different initial conditions at each cycle are not damped out even after a large number of cycles. A single-cylinder GDI research engine is simulated using RANS modeling and the numerical results for 20 consecutive engine cycles are evaluated for two specific operating conditions. One condition is characterized by stoichiometric operation and stable combustion (COVIMEP < 2%) and the other features dilute combustion resulting in misfire events and much higher COVIMEP. In both cases, multi-cycle RANS simulation results show cyclic variability. An in-depth analysis of the most significant physical and chemical quantities highlights that CCV are caused primarily by the variability of the in-cylinder flow. For stoichiometric combustion this does not greatly affect flame propagation, and the resulting fluctuations of the pressure traces are narrow. However, in the event of dilute combustion, the variability of the flow gains more importance, therefore delivering large cyclic fluctuations of in-cylinder pressure. Even though unsteady RANS simulations are not expected to predict as much variability in engine flows as LES, in particular for stable cases, they can still be used to capture typical combustion stability features in an internal combustion engine. This paper shows that the occurrence of CCV when using multi-cycle RANS modeling is not a numerical artifact or the effect of changes in the computational grid from cycle to cycle. Cold-flow analysis reveals that the variability of the simulated flow is intrinsic for the unsteady RANS approach and can only be damped out by increasing numerical viscosity, either by increasing the cell size or by adding up-winding. This is proved in a simplified non-ICE case such as the simulation of the vortex shredding from a cylinder in cross flow. Also, the effect of numerical viscosity on CCV is shown for multi-cycle engine simulations by using a simplified combustion model. Finally, it is shown that multi-cycle RANS can successfully predict the effect of changing specific engine parameters, such as the properties of the ignition system, on cyclic variability and combustion stability.
Scarcelli, Riccardo↗
An Analog Computer Study of the Low-Frequency Flow Dynamics of Two Nuclear-Rocket Cold-Flow Engine Systems
An analog computer study is made of the low-frequency flow dynamics observed with liquid hydrogen flowing in two different nuclear-rocket cold-flow (unfueled) engine systems. The prediction of the low-frequency response depends largely upon the generation of the proper mass-flow storage in the system. This is achieved by relating, in the model lumping, the average values of fluid enthalpy and a certain thermodynamic fluid property. A two-phase state equation is derived for thermodynamic equilibrium between the gas and liquid phases. Parametric studies are made which demonstrate the effect of the pump characteristics on the flow damping.
Fox, Harry W., Jr.↗
Design and aerodynamic performance evaluation of a high-work mixed flow turbine stage
As axial and radial turbine designs have been pushed to their aerothermodynamic and mechanical limits, the mixed-flow turbine (MFT) concept has been projected to offer performance and durability improvements, especially when ceramic materials are considered. The objective of this NASA/U.S. Army sponsored mixed-flow turbine (AMFT) program was to determine the level of performance attainable with MFT technology within the mechanical constraints of 1997 projected ceramic material properties. The MFT geometry is similar to a radial turbine, exhibiting a large radius change from inlet to exit, but differing in that the inlet flowpath is not purely radial, nor axial, but mixed; it is the inlet geometry that gives rise to the name 'mixed-flow'. The 'mixed' orientation of the turbine inlet offers several advantages over radial designs by allowing a nonzero inlet blade angle yet maintaining radial-element blades. The oblique inlet not only improves the particle-impact survivability of the design, but improves the aerodynamic performance by reducing the incidence at the blade inlet. The difficulty, however, of using mixed-flow geometry lies in the scarcity of detailed data and documented design experience. This paper reports the design of a MFT stage designed with the intent to maximize aerodynamic performance by optimizing design parameters such as stage reaction, rotor incidence, flowpath shape, blade shape, vane geometry, and airfoil counts using 2-D, 3-D inviscid, and 3-D viscous computational fluid dynamics code. The aerodynamic optimization was accomplished while maintaining mechanical integrity with respect to vibration and stress levels in the rotor. A full-scale cold-flow rig test was performed with metallic hardware fabricated to the specifications of the hot ceramic geometry to evaluate the stage performance.
Neri, Remo N.↗
The Properties of Flowing Sheets Formed by Impingement of Liquid Jets on Curved Surfaces
An applied research program was conducted to determine the properties of flat sheets of propellants formed by directing jets of liquid tangentially against concave, cylindrical deflector surfaces. The dimensions and spatial orientation of the resultant sheets were found to depend only on the orifice diameter and deflector geometry for three propellant simulants of widely-varying physical properties, over the range of injection velocities encountered in liquid rocket engines. Correlating equations, suitable for use in injector design, are presented for free-sheet width and spreading angle. Distribution of mass and velocity across the free-flowing sheets is also reported. Conditions were discovered under which true sheets do not form, or at best malformed or pulsating sheets result. An envelope of geometrical constraints for deflector design is tentatively defined in order to avoid these undesirable operating regions. The results of the present cold-flow tests are compared with firing test data for impinging-sheet injectors and combustion performance is related to single sheet behavior.
Riebling, Robert W.↗