Mechanical & Fluid Systems

Hybrid Automotive Engine Using Ethanol-Burning Miller Cycle

This engine would operate with high fuel efficiency and generate little pollution.

A proposed hybrid (internal-combustion/ electric) automotive engine system would include as its internal-combustion subsystem, a modified Miller-cycle engine with regenerative air preheating and with autoignition like that of a Diesel engine. The fuel would be ethanol and would be burned lean to ensure complete combustion. Although the proposed engine would have a relatively low power-to-weight ratio compared to most present engines, this would not be the problem encountered if this engine were used in a non-hybrid system since hybrid systems require significantly lower power and thus smaller engines than purely internal-combustion-engine-driven vehicles. The disadvantage would be offset by the advantages of high fuel efficiency, low emission of nitrogen oxides and particulate pollutants, and the fact that ethanol is a renewable fuel.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Ethanol, Hybrid engines, Hybrid electric vehicles

Modular Rake of Pitot Probes

Individual probes can be replaced more easily than was possible before.

The figure presents selected views of a modular rake of 17 pitot probes for measuring both transient and steady-state pressures in a supersonic wind tunnel. In addition to pitot tubes visible in the figure, the probe modules contain (1) high-frequency dynamic-pressure transducers connected through wires to remote monitoring circuitry and (2) flow passages that lead to tubes that, in turn, lead to remote steady-state pressure transducers.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Pitot-static instruments, Test equipment and instrumentation, Wind tunnel tests

Innovative, High-Pressure, Cryogenic Control Valve: Short Face-to-Face, Reduced Cost

This design includes several improvements over prior designs.

A control valve that can throttle high-pressure cryogenic fluid embodies several design features that distinguish it over conventional valves designed for similar applications. Field and design engineers worked together to create a valve that would simplify installation, trim changes, and maintenance, thus reducing overall cost. The seals and plug stem packing were designed to perform optimally in cryogenic temperature ranges. Unlike conventional high-pressure cryogenic valves, the trim size can be changed independent of the body.

Posted in: Briefs, Mechanical Components, Mechanics, Design processes, Product development, Valves

Flight-Test Evaluation of Flutter-Prediction Methods

Experiments have demonstrated the accuracy of predictions of instability.

The flight-test community routinely spends considerable time and money to determine a range of flight conditions, called a flight envelope, within which an aircraft is safe to fly. The cost of determining a flight envelope could be greatly reduced if there were a method of safely and accurately predicting the speed associated with the onset of an instability called flutter.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Finite element analysis, Vibration, Airworthiness, Flight tests

Aerostructures Test Wing

Test data can be used to refine predictions of the onset of flutter.

The Aerostructures Test Wing (ATW) was an apparatus used in a flight experiment during a program of research on aeroelastic instabilities. The ATW experiment was performed to study a specific instability known as flutter. Flutter is a destructive phenomenon caused by adverse coupling of structural dynamics and aerodynamics. The process of determining a flight envelope within which an aircraft will not experience flutter, known as flight flutter testing, is very dangerous and expensive because predictions of the instability are often unreliable.

Posted in: Briefs, Mechanical Components, Mechanics, Wings, Finite element analysis, Vibration, Flight tests, Test equipment and instrumentation

Piezoelectrically Actuated Microvalve for Liquid Effluents

Power consumption and size would be reduced.

Modifications have been proposed to effect further improvement of the device described in “Improved Piezo- electrically Actuated Microvalve” (NPO-30158), NASA Tech Briefs, Vol. 26, No. 1 (January 2002), page 29. To recapitulate: What is being developed is a prototype of valves for microfluidic systems and other microelectromechanical systems (MEMS). The version of the valve reported in the cited previous article included a base (which contained a seat, an inlet, and an outlet), a diaphragm, and a linear actuator. With the exception of the actuator, the parts were micromachined from silicon. The linear actuator consisted of a stack of piezoelectric disks in a rigid housing. To make the diaphragm apply a large sealing force on the inlet and outlet, the piezoelectric stack was compressed into a slightly contracted condition during assembly of the valve. Application of a voltage across the stack caused the stack to contract into an even more compressed condition, lifting the diaphragm away from the seat, thereby creating a narrow channel between the inlet and outlet. The positions of the inlet and outlet, relative to the diaphragm and seat, were such that the inlet flow and pressure contributed to sealing and thus to a desired normallyclosed mode of operation.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Microelectromechanical devices, Product development, Parts, Seals and gaskets, Valves

Larger-Stroke Piezoelectrically Actuated Microvalve

Liquids carrying small particles could be handled.

A proposed normally-closed microvalve would contain a piezoelectric bending actuator instead of a piezoelectric linear actuator like that of the microvalve described in the preceding article. Whereas the stroke of the linear actuator of the preceding article would be limited to ≈6 μm, the stroke of the proposed bending actuator would lie in the approximate range of 10 to 15 μm — large enough to enable the microvalve to handle a variety of liquids containing suspended particles having sizes up to 10 μm. Such particulate-laden liquids occur in a variety of microfluidic systems, one example being a system that sorts cells or large biomolecules for analysis.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Sensors and actuators, Particulate matter (PM), Product development, Valves

Bearing-Seal System for Safe Motion Transfer in Deep Submersible Pressure Vessels

Elastomeric bearings permit leak-free transfer of rotary motion through the hull.

Designers of deep submersibles are reluctant to use conventional shafts and seals to penetrate the hulls of deep sub- mersible, pressure vessels fearing seal failure under extreme pressures. The unique design of this patented system, designated LAMIFLEX®, incorporates elastomeric bearings in order to achieve an absolute hermetic seal and permit leak-free transfer of rotary motion up to at least 15 degrees through the hull of these highly pressurized vessels. External functions, such as control surface deflection, can be driven internally with inherent safety and backup. There are no sliding surfaces (packings, lip, or face seals) that could fail. It also exhibits a smooth spring-like reaction and limited shaft movement without friction. The new designs have been implemented and tested at pressures of 10,000 psi for more than a million cycles at ±15 degrees with no leakage.

Posted in: Briefs, Mechanical Components, Mechanics, Elastomers, Bearings, Seals and gaskets, Performance tests, Marine vehicles and equipment

Safer Roadside Crash Walls Would Limit Deceleration

These walls would protect both vehicle occupants and bystanders.

The figure depicts the aspects of a proposed deceleration-limiting design for crash walls at the sides of racetracks and highways. The proposal is intended to overcome the dis- advantages of both rigid barriers and kinetic-energy-absorbing barriers of prior design. Rigid barriers can keep high-speed crashing motor vehicles from leaving roadways and thereby prevent injury to nearby persons and objects, but they can also subject the occupants of the vehicles to deceleration levels high enough to cause injury or death. Kinetic-energy-absorbing barriers of prior design reduce deceleration levels somewhat, but are not designed to soften impacts optimally; moreover, some of them allow debris to bounce back onto roadways or onto roadside areas, and, in cases of glancingly incident vehicles, some of them can trap the vehicles in such a manner as to cause more injury than would occur if the vehicles were allowed to skid along the rigid barriers. The proposed crash walls would (1) allow tangentially impacting vehicles to continue sliding along the racetrack without catching them, (2) catch directly impacting vehicles to prevent them from injuring nearby persons and objects, and (3) absorb kinetic energy in a more nearly optimum way to limit decelerations to levels that human occupants could survive.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Product development, Crashworthiness, Impact tests, Roads and highways

Quasi-Sun-Pointing of Spacecraft Using Radiation Pressure

A report proposes a method of utilizing solar-radiation pressure to keep the axis of rotation of a small spin-stabilized spacecraft pointed approximately (typically, within an angle of 10° to 20°) toward the Sun. Axisymmetry is not required. Simple tilted planar vanes would be attached to the outer surface of the body, so that the resulting spacecraft would vaguely resemble a rotary fan, windmill, or propeller. The vanes would be painted black for absorption of Solar radiation. A theoretical analysis based on principles of geometric optics and mechanics has shown that torques produced by Solar-radiation pressure would cause the axis of rotation to precess toward Sun-pointing. The required vane size would be a function of the angular momentum of the spacecraft and the maximum acceptable angular deviation from Sun-pointing. The analysis also shows that the torques produced by the vanes would slowly despin the spacecraft — an effect that could be counteracted by adding specularly reflecting "spin-up" vanes.
Posted in: Briefs, TSP, Mechanical Components, Mechanics, Propellers and rotors, Attitude control, Sun and solar, Radiation, Spacecraft

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