Assessing selected technologies and operational strategies for improving the environmental performance of future aircraft

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006.Includes bibliographical references (p. 87-89).The aviation industry is expected to grow at a rate of 4-5% in the next 20 years. Such a growth rate may have important impacts on local air quality, climate change and community noise. This work assesses selected technologies and operational procedures aimed at improving the environmental performance of future airplanes. Two different studies are presented: estimating turbine durability benefits from jet engine water injection and evaluating improvements in fuel burn and operating costs from using advanced technology, high bypass ratio engines and varying the design cruise speed. Water injection in commercial airplane engine combustors lowers operating temperatures and can lead to significant reductions in NO, and soot emissions, potentially improving engine hot section life. With increasing fuel prices and possible introduction of emissions trading in the future, fuel burn may become a more critical aircraft design driver. Increasing engine bypass ratio and lowering cruise speed can lead to reduced fuel consumption. The dominant mechanisms of failure in turbine blades are low cycle fatigue, creep and oxidation. The Universal Slopes method is used to evaluate possible fatigue life benefits from water injection for three representative blade materials.(cont.) For a 67K change in turbine inlet temperature, metal temperature changes up to 47K are expected. Life improvement with a 47K change in metal temperature is possible up to a factor of 1.90 for Inconel 625, up to 1.46 for Inconel 706 and up to 2.85 for Ren 80 depending on the strains imposed. Blade life effects of creep and oxidation for varying temperatures are presented based on a literature review. The absolute value of possible benefits strongly depend on material properties, metal and gas temperatures (internal and external to the blade) and stress levels. In addition, a maintenance cost analysis is performed to evaluate and compare benefits resulting from engine de-rate and water injection using an engine cycle program (GasTurb) and airline data for a typical 1970's technology mixed flow turbofan engine. A 67K change in Tt4 from water injection corresponds to an average de-rate value of 8.4%. Material maintenance costs in 2004 dollars are reduced by 16.52% to 2.86% for a 1-hour and 12-hour flight length respectively. Results show that shorter range flights, with more takeoffs per day, experience larger benefits.(cont.) Engine durability analysis capabilities of a numerical simulation design tool - the Environmental Design Space (EDS) are examined. EDS currently does not have the capability for durability analyses and given the inherent difficulty in finding reliable physics-based models for part life prediction that do not require proprietary data, it seems unlikely that EDS will be able to develop such a capability. The engine bypass-ratio and cruise speed trade study is conducted for a 737-sized future airplane using Boeing internal tools and data. At higher cruise speeds a clear optimum bypass ratio value for minimizing fuel burn is found; for the UEET engines this optimum BPR is about 14. As cruise speed is lowered, fuel burn continually decreases with increasing bypass ratio for the engines examined. At a fixed bypass ratio, flying slower seems most beneficial for very high fuel prices for minimizing both fuel burn and operating costs.by Anuja Mahashabde.S.M

Assessing environmental benefits and economic costs of aviation environmental policy measures

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 157-169).Despite the recent global economic downturn, longer term growth is anticipated for aviation with an increasing environmental impact, specifically in the areas of noise, air quality, and climate change. To ensure sustainable growth for aviation, decision-makers and stake-holders need to be armed with information on balancing environmental and economic interests. The main objective of this thesis is to address key shortcomings in current decision-making practices for aviation environmental policies. This work demonstrates how the inclusion of environmental impact assessment and quantification of modeling uncertainties can enable a more comprehensive evaluation of aviation environmental policy measures. A comparison is presented between the conventional cost-effectiveness analysis and an illustrative cost-benefit analysis focused on assessing a subset of the engine NO, emissions certification stringency options under consideration for the upcoming eighth meeting of the International Civil Aviation Organization's Committee on Aviation Environmental Protection. The Aviation environmental Portfolio Management Tool (APMT) is employed to conduct the aforementioned policy assessments. Monte Carlo methods are adopted to explicitly quantify uncertainties in the modeling process. To enable the aviation climate impact assessment required by the policy analysis, a separate component of this work focuses on advancing the climate impact modeling capabilities within APMT. Major contributions towards assessing aviation climate impacts in APMT include: improved characterization of uncertainty for NO1-related effects and for aviation climate damages, introduction of a reduced-order methodology for assessing climate impacts of methane emissions from the processing of alternative jet fuels, and comparison and validation of APMT results with external sources. This work also discusses the importance of uncertainty assessment for understanding the sensitivity of policy analysis outcomes to input and model parameter variability and identifying areas of future work. An uncertainty analysis for the APMT Climate Module is presented. Radiative forcing from short-lived effects, climate sensitivity, damage function, and discount rate are identified to be the model parameters with the greatest contribution to output variability for the Climate Module for any given aviation scenario. Key contributors to uncertainty in the difference between policy and baseline scenarios are determined by the nature of the policy. For the NO, stringency analysis, the NO. radiative forcing and associated efficacies are significant contributors to uncertainty in analysis outcomes. Information based on model uncertainty assessment is also used for distilling and communicating key analysis results to the relevant stake-holders and policy-makers through the development of the lens concept. The lens, defined as a combination of inputs and model parameters representing a particular perspective for conducting policy analysis, is applied in conducting the engine NO, stringency policy assessment.by Anuja Mahashabde.Ph.D