Browse Topic: Liquid propellants

Items (49)
Activation and Control of Autoignition in HCCI Engines Using Volumetrically-Distributed Ignition of As-Produced Single-Walled Carbon Nanotubes2012-01-16919/10/2012
The discovery that nanostructured materials exhibit properties different than their bulk materials provided many exciting opportunities with technological applications. One such opportunity is the observed ignition of the single-walled carbon nanotubes (SWCNTs) with an ordinary camera flash. In this paper, light-activated ignition characteristics of the as-produced SWCNTs (50 wt% iron nanoparticle content) with a camera flash are presented. The primary objective of this work is to use nanostructured materials as means for distributed (or volumetric) ignition and improved combustion in propulsion systems. Important examples are homogeneous-charged compression ignition (HCCI) engines, liquid rocket fuel sprays, and enhanced flame stabilization in gas turbine engines. The idea was originally proposed by the author in April 2003 and the first patent filed in July 2004 following a series of initial investigations. Based on these and additional tests, this new ignition method is now considered as a potential enabling technology for volumetric and distributed ignition of liquid fuel sprays or gaseous fuel-air mixtures with the lowest incident power intensity possible. This means remote and spatial ignition within any desired and adjustable region defined by the shape of the light from a pulsed light source. Average intensities in between 10 to 150 W/cm₂ are required for ignition of SWCNTs. This is a factor of 80 less than cases where lasers (pulsed and continuous wave (cw)) are used in coal particles. Results acquired in a premixed gaseous fuel-air mixture in a cylindrical combustion chamber, comparing a spark plug with the light-activated distributed ignition of SWCNTs, confirmed the patented concept and showed a truly on-demand activation of the autoignition process for HCCI engine applications. Faster fuel-air mixture burn rate reaching up to a factor of 3 has been demonstrated for distributed ignition under lean mixture as compared with a conventional spark ignition system.
Chehroudi, Bruce
Design of a High Effectiveness Micro Exchanger for Mars Applications2000-01-362010/31/2000
NASA is extending human exploration of space beyond the low earth orbit and moon to Mars. To save cost, it has been determined that In Situ Propellant Production (ISPP) is a key enabling technology in Mission to Mars. A cryocooler is needed to liquefy and store oxygen and methane on the Mars surface. In an earlier study by the authors, a single-stage reverse Brayton cycle cryocooler was proposed with neon as the working fluid. The cryocooler operates between 80K and 310K. It was shown that a highly effective recuperative heat exchanger is vital to the overall efficiency of the cryogenic system. To achieve a COP of 0.2 or better, the heat exchanger should have an effectiveness of 0.97 or better while the percentage pressure drop should be less than 3%. In this paper, the design and analysis of a highly effective micro heat exchanger is presented. The heat exchanger is a multi-layer pile of parallel square ducts. The cold and hot fluids flow in a counter flow manner. One-dimensional and three-dimensional numerical models were used to aid in the design. It was determined that in order to achieve an overall pressure drop of 3% or less, the system pressure should be at 4 bars or higher. The need to reduce axial wall conduction to an acceptable level suggests that the heat exchanger should utilize thin wall ducts (20 microns thick) and be constructed with materials with low thermal conductivity (silicon dioxide). The optimal dimensions of the duct are 100 microns for the duct width and 83 mm for the length of the duct.
Zhou, LeiKapat, J. S.Chow, L. C.Li, Xiaoyi
Long-Term Storage of Liquid Rocket Propellant Tankage and Components7008002/1/1970
Air Force weapons systems require long-term maintenance-free storage, preferably under uncontrolled environmental conditions. Liquid propulsion system components must be capable of satisfactory operation after years of exposure to highly reactive propellants while retaining the propellant without leakage under severe ambient conditions of temperature and relative humidity. Oxidizer leakage caused by improper component design and severe ambient storage conditions has presented serious operational problems. The Air Force Rocket Propulsion Laboratory (AFRPL) has initiated a program to investigate the storability of liquid system components and tankage under extreme conditions of relative humidity and temperature. A variety of system components and tankage materials are being evaluated for long-term storability with storable liquid rocket fuels and oxidizers. Storage conditions are 85 F temperature and 85% RH for oxidizer systems and +65 to +165 F temperature for fuel systems. The propellants under test are N2O4, C1F5, N2H4, and MHF-5. Tankage materials under test are various alloys of aluminum, steel, and titanium. The results of almost 3 years of testing on a representative number of tankage materials have indicated that leakage of propellant can occur as a result of improper weld joint design, inadequate quality control in fabrication and inadequate acceptance leakage testing. Factors which can contribute to the development of oxidizer leakage are a high ambient relative humidity (30%) and stress-corrosion cracking susceptibility of the tank material in combination with the propellant and trace quantities of foreign compounds/elements in the propellant.
Branigan, John E.
Space Shuttle Reaction Control System7008022/1/1970
The reaction-control-system requirements for the space shuttle include long life, high reliability, reusability, minimal easy system maintenance, and refurbishment in addition to the usual requirements of reasonable system performance, minimum system weight, and flexibility to operate over a wide range of environmental and operational conditions. The use of gaseous-oxygen/hydrogen propellants potentially provides this capability. Identifiable space-shuttle reaction-control-system requirements are presented, and the two most promising system concepts described and compared. These concepts are the low-chamber-pressure concept, in which the main injection tanks are used as accumulators and heat exchangers to provide the reaction-control engines with the gaseous propellants; and the high-chamber-pressure concept, in which a gas generator/turbopump/heat exchanger is used to provide the propellants to the engines. The overall performances of the two systems are compared and results of sensitivity studies presented. Results of the Manned Spacecraft Center in-house oxygen/hydrogen reaction-control-system-engine technology program are examined, including performance evaluation (combustion efficiency, heating rates, etc.) of three basic injector concepts. Significant factors that influence the engine design relative to application to the space shuttle are discussed.
Pohl, Henry O.Vaughan, Chester A.Kendrick, Darrell
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