Scaling of Performance in Liquid Propellant Rocket Engine Combustion Devices

This paper discusses scaling of combustion and combustion performance in liquid propellant rocket engine combustion devices. In development of new combustors, comparisons are often made between predicted performance in a new combustor and measured performance in another combustor with different geometric and thermodynamic characteristics. Without careful interpretation of some key features, the comparison can be misinterpreted and erroneous information used in the design of the new device. This paper provides a review of this performance comparison, including a brief review of the initial liquid rocket scaling research conducted during the 1950s and 1960s, a review of the typical performance losses encountered and how they scale, a description of the typical scaling procedures used in development programs today, and finally a review of several historical development programs to see what insight they can bring to the questions at hand

Dispelling the Myths of Modern Mediation

This note serves as an introductory analysis of mediation\u27s potential to resolve commercial disputes. It will briefly explain the conceptual framework of mediation and attempt to address any prejudice attorneys may have towards using mediation to settle commercial disputes

Liquid-Propellant Rocket Engine Throttling: A Comprehensive Review

Liquid-Propellant Rocket Engines (LREs) are capable of on-command variable thrust or thrust modulation, an operability advantage that has been studied intermittently since the late 1930s. Throttleable LREs can be used for planetary entry and descent, space rendezvous, orbital maneuvering including orientation and stabilization in space, and hovering and hazard avoidance during planetary landing. Other applications have included control of aircraft rocket engines, limiting of vehicle acceleration or velocity using retrograde rockets, and ballistic missile defense trajectory control. Throttleable LREs can also continuously follow the most economical thrust curve in a given situation, compared to discrete throttling changes over a few select operating points. The effects of variable thrust on the mechanics and dynamics of an LRE as well as difficulties and issues surrounding the throttling process are important aspects of throttling behavior. This review provides a detailed survey of LRE throttling centered around engines from the United States. Several LRE throttling methods are discussed, including high-pressure-drop systems, dual-injector manifolds, gas injection, multiple chambers, pulse modulation, throat throttling, movable injector components, and hydrodynamically dissipative injectors. Concerns and issues surrounding each method are examined, and the advantages and shortcomings compared

Performance and Stability Analyses of Rocket Thrust Chambers with Oxygen/Methane Propellants

Liquid rocket engines using oxygen and methane propellants are being considered by the National Aeronautics and Space Administration (NASA) for future in-space vehicles. This propellant combination has not been previously used in flight-qualified engine systems developed by NASA, so limited test data and analysis results are available at this stage of early development. As part of activities for the Propulsion and Cryogenic Advanced Development (PCAD) project funded under the Exploration Technology Development Program, the NASA Marshall Space Flight Center (MSFC) has been evaluating capability to model combustion performance and stability for oxygen and methane propellants. This activity has been proceeding for about two years and this paper is a summary of results to date. Hot-fire test results of oxygen/methane propellant rocket engine combustion devices for the modeling investigations have come from several sources, including multi-element injector tests with gaseous methane from the 1980s, single element tests with gaseous methane funded through the Constellation University Institutes Program, and multi-element injector tests with both gaseous and liquid methane conducted at the NASA MSFC funded by PCAD. For the latter, test results of both impinging and coaxial element injectors using liquid oxygen and liquid methane propellants are included. Configurations were modeled with two one-dimensional liquid rocket combustion analysis codes, the Rocket Combustor Interactive Design and Analysis code and the Coaxial Injector Combustion Model. Special effort was focused on how these codes can be used to model combustion and performance with oxygen/methane propellants a priori, and what anchoring or calibrating features need to be applied, improved or developed in the future. Low frequency combustion instability (chug) occurred, with frequencies ranging from 150 to 250 Hz, with several multi-element injectors with liquid/liquid propellants, and was modeled using techniques from Wenzel and Szuch. High-frequency combustion instability also occurred at the first tangential (1T) mode, at about 4500 Hz, with several multi-element injectors with liquid/liquid propellants. Analyses of the transverse mode instability were conducted by evaluating injector resonances and empirical methods developed by Hewitt

Hormones and breast and endometrial cancers: preventive strategies and future research.

A number of hormonal approaches for prevention of endometrial and breast cancers have been proposed. Because of the hormonal responsiveness of both tumors, much attention has focused on effects of exogenous hormone use. Although estrogens in hormone replacement therapy increase the risk of endometrial cancer, the disease is substantially reduced by long-term use of oral contraceptives. The issues with breast cancer are more complex, mainly because of a variety of unresolved effects. Long-term estrogen use is associated with some increase in breast cancer risk, and certain patterns of oral contraceptives appear to predispose to early-onset disease. With respect to estrogens, preventive approaches for both tumors would include use for as limited periods of time as possible. Addition of a progestin appears to lower estrogen-associated endometrial disease, but its effect on breast cancer risk remains less clear. Additional studies on effects of detailed usage parameters should provide useful insights into etiologic mechanisms. Other preventive approaches for endometrial cancer that may work through hormonal mechanisms include staying thin, being physically active, and maintaining a vegetarian diet. Breast cancer risk may possibly be reduced by extended periods of breastfeeding, restriction of intake of alcoholic beverages, remaining thin later in life, and being physically active. Additional research is needed to clarify the biologic mechanisms of these associations. The bridging of epidemiology with the biologic sciences should clarify many unresolved issues and lead to better preventive approaches

Review of Combustion Stability Characteristics of Swirl Coaxial Element Injectors

Liquid propellant rocket engine injectors using coaxial elements where the center liquid is swirled have become more common in the United States over the past several decades, although primarily for technology or advanced development programs. Currently, only one flight engine operates with this element type in the United States (the RL10 engine), while the element type is very common in Russian (and ex-Soviet) liquid propellant rocket engines. In the United States, the understanding of combustion stability characteristics of swirl coaxial element injectors is still very limited, despite the influx of experimental and theoretical information from Russia. The empirical and theoretical understanding is much less advanced than for the other prevalent liquid propellant rocket injector element types, the shear coaxial and like-on-like paired doublet. This paper compiles, compares and explores the combustion stability characteristics of swirl coaxial element injectors tested in the United States, dating back to J-2 and RL-10 development, and extending to very recent programs at the NASA MSFC using liquid oxygen and liquid methane and kerosene propellants. Included in this study are several other relatively recent design and test programs, including the Space Transportation Main Engine (STME), COBRA, J-2X, and the Common Extensible Cryogenic Engine (CECE). A presentation of the basic data characteristics is included, followed by an evaluation by several analysis techniques, including those included in Rocket Combustor Interactive Design and Analysis Computer Program (ROCCID), and methodologies described by Hewitt and Bazarov

Red-throated diver breeding ecology and nest survival on Shetland

The aim of this thesis is to identify and measure biological, environmental and behavioural factors relevant to red-throated diver breeding ecology and then to distinguish their relative importance in determining breeding success and nest survival. Migratory birds that breed at high latitudes are at particular risk from human mediated climate change because the time window available for breeding in these areas is short, and if peak abundance of key prey items alters in response to climatic cues (Shultz et al. 2009), it may not be possible for birds to adjust their breeding strategies to compensate. Moreover, large scale environmental cues that migratory birds use to time their migration and breeding may become less reliable (Both & Visser 2001; Frederiksen et al. 2007). For such species it is particularly important to understand and monitor breeding biology, particularly the factors that determine breeding performance and nest survival, as these are likely to respond to large scale ecosystem changes before population changes are detected, and additionally provide valuable information that can be used to establish conservation priorities for the species. Red- throated divers are migratory fish-eating seabirds with a predominantly arctic breeding distribution that have apparently declined in large areas of their breeding range in the recent past (Groves et al. 1996; Hagemeijer & Blair 1997). In addition to the demonstrated effects of food availability (Eriksson & Sundberg 1991; Ball 1994), disturbance (Pakarinen & Järvinen 1984) and vulnerability to pollutants (Eriksson & Lindberg 2005) on breeding performance, direct and indirect effects of climate change are predicted, in particular a contracting of the European breeding range (Huntley et al. 2006) and vulnerability to both onshore and offshore renewable energy developments (Garthe & Huppop 2004; Halley & Hopshaug 2007).This research tests the importance of proximate factors influencing red-throated diver breeding performance using modern nest survival analysis with the intention that the findings will provide clues about the larger mechanisms driving population processes. First I developed a number of linear regression models using nest temperature signatures and photographic measures of chick size that; allowed timing of breeding to be estimated from a single field visit; were of comparable accuracy to established methods such as egg flotation (Westerkov 1950); and extended the period during the breeding cycle when timing of breeding estimates could be made, to include the later stages of incubation and chick rearing. I used these techniques to obtain timing of breeding estimates for the study sample. This allowed me to use an information-theoretic modelling approach (Burnham & Anderson 2002) to determine the daily nest survival rate and evaluate the importance of a set of biological and environmental effects on red-throated diver nest survival patterns. I found support for models that suggested that nest survival increased with nest age and individual quality and decreased with laying date. I explored the effects of habitat characteristics at different spatial scales and found support for models that suggested that both environmental conditions and predator avoidance were important determinants of nest survival rate. Finally I examined nest attendance behaviour and variation in nest temperature during incubation and found patterns in attendance in relation to nest age and through the day but no strong evidence of trends in survival in relation to attendance patterns

Scaling of Performance in Liquid Propellant Rocket Engine Combustors

The objectives are: a) Re-introduce to you the concept of scaling; b) Describe the scaling research conducted in the 1950s and early 1960s, and present some of their conclusions; c) Narrow the focus to scaling for performance of combustion devices for liquid propellant rocket engines; and d) Present some results of subscale to full-scale performance from historical programs. Scaling is "The ability to develop new combustion devices with predictable performance on the basis of test experience with old devices." Scaling can be used to develop combustion devices of any thrust size from any thrust size. Scaling is applied mostly to increase thrust. Objective is to use scaling as a development tool. - Move injector design from an "art" to a "science

Local Heat Flux Measurements with Single and Small Multi-element Coaxial Element-Injectors

To support NASA's Vision for Space Exploration mission, the NASA Marshall Space Flight Center conducted a program in 2005 to improve the capability to predict local thermal compatibility and heat transfer in liquid propellant rocket engine combustion devices. The ultimate objective was to predict and hence reduce the local peak heat flux due to injector design, resulting in a significant improvement in overall engine reliability and durability. Such analyses are applicable to combustion devices in booster, upper stage, and in-space engines with regeneratively cooled chamber walls, as well as in small thrust chambers with few elements in the injector. In this program, single and three-element injectors were hot-fire tested with liquid oxygen and gaseous hydrogen propellants at The Pennsylvania State University Cryogenic Combustor Laboratory from May to August 2005. Local heat fluxes were measured in a 1-inch internal diameter heat sink combustion chamber using Medtherm coaxial thermocouples and Gardon heat flux gauges, Injector configurations were tested with both shear coaxial elements and swirl coaxial elements. Both a straight and a scarfed single element swirl injector were tested. This paper includes general descriptions of the experimental hardware, instrumentation, and results of the hot-fire testing for three coaxial shear and swirl elements. Detailed geometry and test results the for shear coax elements has already been published. Detailed test result for the remaining 6 swirl coax element for the will be published in a future JANNAF presentation to provide well-defined data sets for development and model validation