José I. Tafoya

Experimental Validation of Gas Gun to Evaluate Components of Explosively Actuated Valves

This paper describes the development and validation of a new experimental tool used to study the operation of explosively actuated valves without the use of explosives. A gas gun is used to provide a high pressure pulse for valve actuation. The pressure pulse provides repeatable initial conditions not easily attainable using pyrotechnics. The system is modular and can be adapted to investigate various valve design parameters. The diagnostics system provides measurements such as pressure, velocity, and impact force. The gas gun system can be used to test current valve functional parameters as well as explore design variations for future valves. I. Introduction Explosively actuated valves are used extensively in aerospace, defense, and industrial applications for their high energy to weight ratio, small volume, long-term energy storage stability, and controllable initiation. These valves use a pyrotechnic or explosive to generate a pr essure wave which accelerates a plunger down a bore tube. The required energy to overcome friction and perform mechanical work, such as cable or tube cutting, is extracted from this pressure impulse. Plunger rigid body dynamics within a bore tube associated with valve applications have been studied by various researchers using plungers driven by electro -explosive actuators. However actuators utilizing explosives do not produce repeatable plunger driving energy. This leads to ambiguous parametric study results and difficulties determining parameters such as the threshold pressure impulse. This paper describes a new experimental tool designed and tested, at Los Alamos National Laboratory, to evaluate valve design and performance. Instead of explosives, a gas gun is used to generate a high pressure impulse to initiate plunger motion. The gas gun provides a repeatable plunger driving energy, which facilitates experimental study of valve performance characteristics. The gas gun allows for independent variation of plunger driving pressure, geometry, and materials of the plunger and bore tube. The diagnostics include a portable velocity interferometer system for any reflector (VISAR), ballistic and static pressure transducers, and an impact sensor. The diagnostics system is designed to simultaneously measure driving pressure, pressure at various points down the bore tube, plunger velocity, and impact force.

Pyrovalve Function Testing using Gas Gun Actuation

Utilizing a gas gun specifically designed to provide a repeatable impulse simulating a pyrotechnic actuator a study was conducted on a normally closed gas transfer valve to quantify the energy expenditure in performing the valve function; in this case tube shearing. The paper describes how the gas gun system was tuned to replicate pyrotechnic actuator output. The gas gun impulse curves were compared to data taken from the manufacturers actuator qualification tests. Velocity of the piston was monitored during valve actuation with and without shear tubes present; allowing for the extraction of energy expenditure involved in tube shearing. This energy expenditure was then compared to the integration of force with the respect to displacement of a quasi-static test, in which a Carver ® hydraulic press was used to perform the valve function. Additional diagnostics include utilizing a mass spectrometer to analyze a sample of transferred gas, providing valuable insight into dynamic blow-by around the piston. We describe the test protocol and hardware configuration. Finally, a results section provides a discussion of the observations, and future direction.

Evaluation of Explosively Actuated Valve Components Using a Gas Gun

*† ‡ § A gas gun system that provides a repeatable driving energy allows for independent variation of parameters in the study of components of explosively actuated valves. The gas gun was utilized in a series of closed volume and valve actuation tests. Piston velocity measurement and acoustic emission detection were added to the existing pressure and impact force diagnostics. Test procedure and configuration of the experimental apparatus for each category of tests is described. Closed volume tests revealed the gas gun can generate pressure waves similar in both magnitude and rise time to those generated by explosive actuators during first 350 μs. Piston velocity measured by VISAR (Velocity Interferometer System for Any Reflector) was integrated into the valve actuation tests. The resulting piston velocity measurements were confirmed with the average velocity calculated by dividing pressure port spacing by the temporal shift of the pressure response. I. Introduction HE study of explosively actuated valves is of importance given their extensive use in aerospace, defense, and industry. Valve actuation can be described by the following sequence of events; an electrical signal is sent to a pyrotechnic; deflagration of the pyrotechnic generates a pressure wave which accelerates a piston down a bore tube. The kinetic energy imparted to the piston overcomes friction and executes a function, such as cable cutting. The motion of a piston within a bore tube for valve operations has been studied extensively. In most of this work, the pistons were driven by electro-explosive actuators. However, the use of explosives to initiate piston motion does not provide a mechanism to control the amount of energy which is transferred to the piston. This makes the determination of the threshold energy required to perform cable cutting or other secondary operations experimentally difficult and parametric studies ambiguous. The gas gun eliminates the relative unpredictable initial conditions, high temperature gases, and high velocity particulate, associated with pyrotechnics from valve operation to facilitate parametric study. A gas gun system provides a repeatable (±2%) driving energy that allows for independent variation of parameters in the study of components of explosively actuated valves. Previous work related to this project, design of the gas gun, and preliminary testing of the system can be found in reference 1. In this work, we report on the application of the gas gun in a series of closed volume tests and on the integration of VISAR (Velocity Interferometer System for Any Reflector) to measure piston velocity in valve actuation tests. Acoustic emission detection also was added to the existing pressure and impact force diagnostics in the gas gun system. We describe test procedure and configuration of the experimental apparatus for each category of tests. A results section provides a summary of the observations, and future direction. In the series of closed volume tests, we compared the pressure pulse generated by the gas gun to measured pressure pulses from closed volume tests of pyrotechnic actuators. We also explored the effect of pressure transducer port orientation on these measurements. Traditional pyrotechnic tests use a pressure port located at 90° from the path of the pressure wave to prevent damage to the pressure transducer. The gas gun apparatus generates a similar pressure pulse to that of an actuator without the hostile environment; allowing us to measure the pressure impulse directly in its path. These tests also demonstrated the gas gun can generate a repeatable (±2%) pressure pulse similar to that of a pyrotechnic.

Regenerative fuel cell engineering - FY99

The authors report the work conducted by the ESA-EPE Fuel Cell Engineering Team at Los Alamos National Laboratory during FY99 on regenerative fuel cell system engineering. The work was focused on the evaluation of regenerative fuel cell system components obtained through the RAFCO program. These components included a 5 kW PEM electrolyzer, a two-cell regenerative fuel cell stack, and samples of the electrolyzer membrane, anode, and cathode. The samples of the electrolyzer membrane, anode, and cathode were analyzed to determine their structure and operating characteristics. Tests were conducted on the two-cell regenerative fuel cell stack to characterize its operation as an electrolyzer and as a fuel cell. The 5 kW PEM electrolyzer was tested in the Regenerative Fuel Cell System Test Facility. These tests served to characterize the operation of the electrolyzer and, also, to verify the operation of the newly completed test facility. Future directions for this work in regenerative fuel cell systems are discussed.