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The use of nontoxic propellants in future exploration vehicles would enable safer, more cost-effective mission scenarios. One promising green alternative to existing hypergols is liquid methane (LCH4) with liquid oxygen (LO2). A 100 lbf LO2/LCH4 engine was developed under the NASA Propulsion and Cryogenic Advanced Development project and tested at the NASA Glenn Research Center Altitude Combustion Stand in a low pressure environment. High ignition energy is a perceived drawback of this propellant combination; so this ignition margin test program examined ignition performance versus delivered spark energy. Sensitivity of ignition to spark timing and repetition rate was also explored. Three different exciter units were used with the engine s augmented (torch) igniter. Captured waveforms indicated spark behavior in hot fire conditions was inconsistent compared to the well-behaved dry sparks. This suggests that rising pressure and flow rate increase spark impedance and may at some point compromise an exciter s ability to complete each spark. The reduced spark energies of such quenched deliveries resulted in more erratic ignitions, decreasing ignition probability. The timing of the sparks relative to the pressure/flow conditions also impacted the probability of ignition. Sparks occurring early in the flow could trigger ignition with energies as low as 1 to 6 mJ, though multiple, similarly timed sparks of 55 to 75 mJ were required for reliable ignition. Delayed spark application and reduced spark repetition rate both correlated with late and occasional failed ignitions. An optimum time interval for spark application and ignition therefore coincides with propellant introduction to the igniter. Kleinhenz, Julie and Sarmiento, Charles and Marshall, William Glenn Research Center LIQUEFIED GASES; LIQUID OXYGEN; METHANE; SPARK IGNITION; REACTION CONTROL; SPARK PLUGS; AUGMENTATION; ALTITUDE; LOW PRESSURE; DATA REDUCTION; ENGINE DESIGN; WAVEFORMS; ELECTRICAL MEASUREMENT; ENERGY REQUIREMENTS; IGNITERS; OSCILLOSCOPES
The use of nontoxic propellants in future exploration vehicles would enable safer, more cost-effective mission scenarios. One promising green alternative to existing hypergols is liquid methane (LCH4) with liquid oxygen (LO2). A 100 lbf LO2/LCH4 engine was developed under the NASA Propulsion and Cryogenic Advanced Development project and tested at the NASA Glenn Research Center Altitude Combustion Stand in a low pressure environment. High ignition energy is a perceived drawback of this propellant combination; so this ignition margin test program examined ignition performance versus delivered spark energy. Sensitivity of ignition to spark timing and repetition rate was also explored. Three different exciter units were used with the engine s augmented (torch) igniter. Captured waveforms indicated spark behavior in hot fire conditions was inconsistent compared to the well-behaved dry sparks. This suggests that rising pressure and flow rate increase spark impedance and may at some point compromise an exciter s ability to complete each spark. The reduced spark energies of such quenched deliveries resulted in more erratic ignitions, decreasing ignition probability. The timing of the sparks relative to the pressure/flow conditions also impacted the probability of ignition. Sparks occurring early in the flow could trigger ignition with energies as low as 1 to 6 mJ, though multiple, similarly timed sparks of 55 to 75 mJ were required for reliable ignition. Delayed spark application and reduced spark repetition rate both correlated with late and occasional failed ignitions. An optimum time interval for spark application and ignition therefore coincides with propellant introduction to the igniter.
The use of non-toxic propellants in future exploration vehicles would enable safer, more cost effective mission scenarios. One promising "green" alternative to existing hypergols is liquid methane/liquid oxygen. To demonstrate performance and prove feasibility of this propellant combination, a 100lbf LO2/LCH4 engine was developed and tested under the NASA Propulsion and Cryogenic Advanced Development (PCAD) project. Since high ignition energy is a perceived drawback of this propellant combination, a test program was performed to explore ignition performance and reliability versus delivered spark energy. The sensitivity of ignition to spark timing and repetition rate was also examined. Three different exciter units were used with the engine's augmented (torch) igniter. Propellant temperature was also varied within the liquid range. Captured waveforms indicated spark behavior in hot fire conditions was inconsistent compared to the well-behaved dry sparks (in quiescent, room air). The escalating pressure and flow environment increases spark impedance and may at some point compromise an exciter.s ability to deliver a spark. Reduced spark energies of these sparks result in more erratic ignitions and adversely affect ignition probability. The timing of the sparks relative to the pressure/flow conditions also impacted the probability of ignition. Sparks occurring early in the flow could trigger ignition with energies as low as 1-6mJ, though multiple, similarly timed sparks of 55-75mJ were required for reliable ignition. An optimum time interval for spark application and ignition coincided with propellant introduction to the igniter and engine. Shifts of ignition timing were manifested by changes in the characteristics of the resulting ignition.
This book is intended for students and engineers who design and develop liquid-propellant rocket engines, offering them a guide to the theory and practice alike. It first presents the fundamental concepts (the generation of thrust, the gas flow through the combustion chamber and the nozzle, the liquid propellants used, and the combustion process) and then qualitatively and quantitatively describes the principal components involved (the combustion chamber, nozzle, feed systems, control systems, valves, propellant tanks, and interconnecting elements). The book includes extensive data on existing engines, typical values for design parameters, and worked-out examples of how the concepts discussed can be applied, helping readers integrate them in their own work. Detailed bibliographical references (including books, articles, and items from the “gray literature”) are provided at the end of each chapter, together with information on valuable resources that can be found online. Given its scope, the book will be of particular interest to undergraduate and graduate students of aerospace engineering.
A workhorse liquid oxygen-liquid methane (LOX/LCH4) rocket igniter was recently tested at NASA Glenn Research Center s (GRC) Research Combustion Laboratory (RCL). These tests were conducted in support of the Reaction Control Engine (RCE) development task of the Propulsion and Cryogenics Advanced Development (PCAD) project. The igniter was a GRC in-house design used to evaluate the ignition processes for LOX/LCH4. The test matrix was developed to examine the flammability of LOX/LCH4 over a range of oxidizer-to-fuel mixture ratios, both in the core fuel flow and total flow. In addition, testing also examined the durability of the hardware by accumulating ignition pulses. Over the course of testing, a total of 1402 individual ignition pulses were successfully demonstrated over the range of mixture ratios. Testing was halted after the failure of the ceramic in the igniter spark plug.
Doctoral Thesis / Dissertation from the year 2006 in the subject Electrotechnology, grade: 1, mit Ausgezeichnung bestanden, Vienna University of Technology (Insitut für Photonik), language: English, abstract: In this PhD thesis different fundamental aspects and the practical usability of a laser ignition system as a new, innovative and alternative ignition approach for internal combustion engines were investigated in great detail mainly experimentally. Ignition experiments in combustion chambers under high pressures and elevated temperatures have been conducted. Different fuels were investigated. Also the minimum breakdown energy in dependence of the initial temperature and pressure with the help of an aspheric lens with a high numerical aperture was studied. High-speed Schlieren diagnostics have been conducted in the combustion chamber. The different stages like the ignition plasma within the first nanoseconds via the shock wave generation to the expanding flame kernel were investigated. With the help of multi-point ignition the combustion duration could be reduced significantly. The controlled start of auto-ignition of n-heptane-air mixtures by resonant absorption of Er, Cr: YSGG laser radiation at 2.78 μm by additionally introduced water has been proven in combustion chamber experiments as a completely new idea. Beside experiments in the combustion chambers and long term tests under atmospheric conditions, various tests in SI engines up to 200 h, have been made. Different sources of contamination of the window surface have been identified. First experiments with a longitudinally diode-pumped, fiber-coupled and passively Q-switched solid-state laser α-prototype system with maximum pulse energy of 1.5 mJ at about 1.5 ns pulse duration were performed which allowed to ignite the engine successfully over a test period of 100 h. In cooperation with Lund University in Sweden, experiments have been performed on another engine test bed running in HCCI mode revealing the las