Showing papers in "SAE transactions in 1991"

The Autoignition Chemistry of Paraffinic Fuels and Pro-Knock and Anti-Knock Additives: A Detailed Chemical Kinetic Study

Abstract: A numerical model is used to examine the chemical kinetic processes which lead to knocking in spark-ignition internal combustion engines. The construction and validation of the model is described in detail, including the low temperature reaction paths involving alkylperoxy radical isomerization. The numerical model is then applied to C{sub 1} to C{sub 7} paraffinic hydrocarbon fuels, and a correlation is developed between the Research Octane Number (RON) and the computed time of ignition for each fuel. Octane number is shown to depend on the rates of OH radical production through isomerization reactions, and factors influencing the rate of isomerization such as fuel molecule size and structure are interpreted in terms of the kinetic model. The knock behavior of fuel mixtures is examined, and the manner in which pro-knock and anti-knock additives influence ignition is studied numerically. The kinetics of methyl tert-butyl ether (MTBE) is discussed in particular detail. 28 refs., 5 figs., 5 tabs.

Designing Design Processes in Decision-Based Concurrent Engineering

Abstract: We believe that the efficiency and effectiveness of human designers can be improved by making available tools that can be used to help negotiate solutions to open or unstructured parts of the process of designing. We assert that the efficiency and effectiveness of a designer can be increased by increasing the speed with which the design iteration is accomplished and reducing of the number of iterations. An increment in the iteration speed can be achieved if at least some parts of a design process are known and can be modelled on a computer. One way of reducing the number of iterations in design is by avoiding this corrective redesign. This provides the stimulus for developing approaches to design that include Concurrent Engineering considerations. Thus, in our opinion, a necessary ingredient in increasing efficiency and effectiveness of human designers is the modeling of design processes in a manner that they can be analyzed, manipulated and implemented. This is the central theme of our paper. OUR FRAME OF REFERENCE PROBLEM IDENTIFICATION Often flaws in the solution of a design problem are detected during manufacture and even maintenance. The corrective redesign effort is usually extremely expensive and ideally should be have been “designed out” prior to manufacture. The effort to reduce such costly iterations has provided the stimulus for developing approaches to design that include life cycle considerations (that is, design, manufacture and support). Approaches to design that incorporate life cycle considerations include Concurrent Engineering [13]*, simultaneous engineering, Unified Life Cycle Engineering (ULCE) [4-7], producibility engineering [8]. Companies that have made use of some of these approaches have reported impressive benefits [3]. Our primary interest is in developing the capabilities for a team of human designers to design concurrently in the early stages of project initiation. Why? Dierolf and Richter in the conclusion of a recent study for the Institute of Defense Analysis state [6]: “The importance of early design decisions is widely recognized. It is often stated that roughly 70 percent of the total life cycle cost of the system is determined during the conceptual phase. Due to the lack of hard data, very few traditional CAD tools are available to support the early stages of design. Considering the high leverage of the decisions made during these stages, this is an undesirable situation.” * Numbers in parentheses designate references at end of paper. * Numbers in parentheses designate references at end of paper.

Hybrid III Sternal Deflection Associated with Thoracic Injury Severities of Occupants Restrained with Force-Limiting Shoulder Belts

Abstract: A relationship between the risk of significant thoracic injury (AIS is greater than or equal to 3) and Hybrid III dummy sternal deflection for shoulder belt loading is developed. This relationship is based on an analysis of the Association Peugeot-Renault accident data of 386 occupants who were restrained by three-point belt systems that used a shoulder belt with a force-limiting element. For 342 of these occupants, the magnitude of the shoulder belt force could be estimated with various degrees of certainty from the amount of force-limiting band ripping. Hyge sled tests were conducted with a Hybrid III dummy to reproduce the various degrees of band rearing. The resulting Hybrid III sternal deflections were correlated to the frequencies of AIS greater than or equal to 3 thoracic injury observed for similar and tearing in the field accident data. This analysis indicates that for shoulder belt loading a Hybrid III sternal deflection of 50 mm corresponds to a 40 to 50 percent risk of an AIS greater than or equal to 3 thoracic injury.