The design of aircraft brake systems, employing cooling to increase brake life

A research program was initiated to determine the feasibility of using cooling to increase brake life. An air cooling scheme was proposed, constructed and tested with various designs. Straight and curved slotting of the friction material was tested. A water cooling technique, similar to the air cooling procedure, was evaluated on a curved slotted rotor. Also investigated was the possibility of using a phase-change material within the rotor to absorb heat during braking. Various phase-changing materials were tabulated and a 50%, (by weight) LiF - BeF2 mixing was chosen. It was shown that corrosion was not a problem with this mixture. A preliminary design was evaluated on an actual brake. Results showed that significant improvements in lowering the surface temperature of the brake occurred when air or water cooling was used in conjunction with curved slotted rotors

Development of a Gravity-Insensitive Heat Pump for Lunar Applications

Mainstream Engineering Corporation is developing a gravity-insensitive system that will allow a vapor-compression-cycle heat pump to be used in both microgravity (10(exp -6)g) and lunar (10(exp -6)g) environments. System capacity is 5 kW to 15 kW at design refrigerant operating conditions of 4.44 C and 60 C evaporating and condensing temperatures, respectively. The current program, performed for NASA Johnson Space Center (JSC) and presented in this paper, includes compressor performance analysis, detailed system design, and thermal analysis. Future efforts, including prototype fabrication, integration of a solar power source and controls, ground-testing, and flight-testing support, are also discussed

Extension of the high load limit in the Homogeneous Charge Compression Ignition engine

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Includes bibliographical references (p. 120-121).The Homogeneous Charge Compression Ignition (HCCI) engine offers diesel-like efficiency with very low soot and NOx emissions. In a HCCI engine, a premixed charge of air, fuel and burned gas is compressed to achieve autoigntion. Combustion occurs throughout the chamber volume resulting in short overall burn duration. This short burn duration can cause excessively high pressure rise rates which lead to unacceptable engine noise and potentially reduced engine life. To combat this high pressure rise rate the engine must be operating with significant diluent, either excess air or burned exhaust gas. However this high level of dilution limits the specific output of the HCCI engine to levels far below spark ignition or diesel engines. The high load limit is a major challenge for the HCCI engine. This study utilized a single cylinder research to examine the high load limit and possible methods to extend it. The details of the high load limit were first explored across a range of intake temperatures, boost pressures, trapped residual fractions, equivalence ratios and external EGR ratios for a gasoline fueled HCCI engine. A significant finding was that the high load limit always occurs at the misfire limit and that for a given pressure rise rate constraint, the high load limit occurs at lowest possible intake pressure and trapped residual fraction needed to prevent misfire. A possible means to allow operation at higher boost pressures is to utilize cooled external EGR or to reduce the intake temperature. For a given burn fraction, increasing the EGR rate or reducing the intake temperature provided reduced MPRR.(cont.) However with these changes, the misfire limit also shifted such that the value of the maximum load does not materially change. Thus boosting coupled with EGR or intake temperature reduction can not be used to significantly extend the high load limit. A correlation was developed for the burn duration. Multi-zone combustion simulations were used to confirm the form of this correlation. The multi-zone based correlations were then used to quantitatively examine the potential of thermal stratification as a means to extend the high load limit. It was shown that for a doubling of the width of the in-cylinder temperature distribution, a 30% increase in the high load limit is possible.by Robert J. Scaringe.Ph.D

Effect of directed port air flow on liquid fuel transport in a port fuel injected spark ignition engine

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 65-67).With highly efficient modem catalysts, startup HC emissions have become a significant portion of the trip total. Liquid fuel is a major source of HC emissions during the cold start and fast idle period. Thus the control of liquid fuel, particularly during startup, is required for future engine designs. The effect of a turbulence plate, or charge motion control valve, on the port liquid fuel mass is examined. A purging process was used to examine the effect of a charge motion control plate on the port fuel film mass. It was found that the charge motion plate can provide substantial reductions in both the total and downstream intake fuel film mass. These reductions are the result of the increased intake turbulence that results from the charge motion plate. This increased turbulence provides enhanced fuel - air mixing and increases port film strip atomization due to the increased viscous shear. The effect of different film locations was postulated and backed experimentally. The downstream and valve films have the most immediate effect on the fuel delivery. Large upstream films, which can take thousands of cycles to develop, influence the fuel delivery on a much longer time scale.(cont.) In-cylinder hydrocarbon measurements were made. Despite the high level of scatter in the measurements, similar transient responses were observed for both CMCV open and closed. This similarity despite different film masses was attributed to different t and x values.by Robert J. Scaringe.S.M

{[Na1(μ-H2O)Na2]2[(C2O4)2Cr(μ-OH)2Cr(C2O4)2]·H2O}n, a novel hydrated form

The unit cell of the title compound, poly[[μ-aqua-μ-hydroxido-di-μ-oxalato-chromium(III)disodium] monohydrate], {[CrNa2(C2O4)2(OH)(H2O)]·H2O}n, contains four [Na1(μ-H2O)Na2][(C2O4)2Cr(μ-OH)·H2O] formula units, each of which consists of two crystallographically independent Na+ sites (bridged by one aqua ligand), one half of a centrosymmetric di-μ-hydroxido-bis­[cis-bis­(oxalato)chromate(III)] dimer, [(C2O4)2Cr(μ-OH)2Cr(C2O4)2]4−, and one uncoordin­ated water mol­ecule. The structure is best described as a coordination polymer in which the three-dimensional lattice framework is realized by the inter­connection of the metallic atoms via the O atoms of the aqua, hydroxide and oxalate ligands. One Na atom is hepta­coordinated by one water, one hydroxide and five oxalate O atoms, whilst the other is penta­coordinated by one water and four oxalate O atoms. The coordination around the Cr3+ sites is pseudo-octa­hedral, involving four aqua and two hydroxide O atoms. Adjacent Na atoms are separated by 3.593 (2) Å, whereas the intra­dimer Cr⋯Cr spacing is 2.978 (1) Å. The crystal structure is consolidated by extended relatively weak O—H⋯O hydrogen bonding with O⋯O distances ranging from 2.808 (4) to 3.276 (5) Å

2′-Methylseleno-modified oligoribonucleotides for X-ray crystallography synthesized by the ACE RNA solid-phase approach

Site-specifically modified 2′-methylseleno RNA represents a valuable derivative for phasing of X-ray crystallographic data. Several successful applications in three-dimensional structure determination of nucleic acids, such as the Diels–Alder ribozyme, have relied on this modification. Here, we introduce synthetic routes to 2′-methylseleno phosphoramidite building blocks of all four standard nucleosides, adenosine, cytidine, guanosine and uridine, that are tailored for 2′-O-bis(acetoxyethoxy)methyl (ACE) RNA solid-phase synthesis. We additionally report on their incorporation into oligoribonucleotides including deprotection and purification. The methodological expansion of 2′-methylseleno labeling via ACE RNA chemistry is a major step to make Se-RNA generally accessible and to receive broad dissemination of the Se-approach for crystallographic studies on RNA. Thus far, preparation of 2′-methylseleno-modified oligoribonucleotides has been restricted to the 2′-O-[(triisopropylsilyl)oxy]methyl (TOM) and 2′-O-tert-butyldimethylsilyl (TBDMS) RNA synthesis methods

Base-specific spin-labeling of RNA for structure determination

To facilitate the measurement of intramolecular distances in solvated RNA systems, a combination of spin-labeling, electron paramagnetic resonance (EPR), and molecular dynamics (MD) simulation is presented. The fairly rigid spin label 2,2,5,5-tetramethyl-pyrrolin-1-yloxyl-3-acetylene (TPA) was base and site specifically introduced into RNA through a Sonogashira palladium catalyzed crosscoupling on column. For this purpose 5-iodouridine, 5-iodo-cytidine and 2-iodo-adenosine phosphoramidites were synthesized and incorporated into RNA-sequences. Application of the recently developed ACE (R) chemistry presented the main advantage to limit the reduction of the nitroxide to an amine during the oligonucleotide automated synthesis and thus to increase substantially the reliability of the synthesis and the yield of labeled oligonucleotides. 4-Pulse Electron Double Resonance (PELDOR) was then successfully used to measure the intramolecular spin–spin distances in six doubly labeled RNA-duplexes. Comparison of these results with our previous work on DNA showed that A- and B-Form can be differentiated. Using an all-atom force field with explicit solvent, MD simulations gave results in good agreement with the measured distances and indicated that the RNA A-Form was conserved despite a local destabilization effect of the nitroxide label. The applicability of the method to more complex biological systems is discussed