Pollutant emissions from aircraft in the vicinity of airports and at altitude are of great public concern due to their impact on environment and human health. The legislations aimed at limiting aircraft emissions have become more stringent over the past few decades. This has resulted in an urgent need to develop low emissions combustors in order to meet legislative requirements and reduce the impact of civil aviation on the environment. This article provides a comprehensive review of low emissions combustion technologies for modern aero gas turbines. The review considers current high Technologies Readiness Level (TRL) technologies including Rich-Burn Quick-quench Lean-burn (RQL), Double Annular Combustor (DAC), Twin Annular Premixing Swirler combustors (TAPS), Lean Direct Injection (LDI). It further reviews some of the advanced technologies at lower TRL. These include NASA multi-point LDI, Lean Premixed Prevaporised (LPP), Axially Staged Combustors (ASC) and Variable Geometry Combustors (VGC). The focus of review is placed on working principles, a review of the key technologies (includes the key technology features, methods of realising the technology, associated technology advantages and design challenges, progress in development), technology application and emissions mitigation potential. The article concludes the technology review by providing a technology evaluation matrix based on a number of combustion performance criteria including altitude relight auto-ignition flashback, combustion stability, combustion efficiency, pressure loss, size and weight, liner life and exit temperature distribution.

The performance benefits of boundary layer ingestion in aircraft with distributed propulsion have been extensively studied in the past. These studies have indicated that propulsion system integration issues such as distortion and intake pressure losses could mitigate the expected benefits. This paper introduces and develops a methodology that enables the assessment of different propulsion system designs, which are optimized to be less sensitive to the effects of the aforementioned issues. The study models the propulsor array and main engine performance at design point using a parametric approach, and further at component level, the study focuses on identifying optimum propulsor configurations, in terms of propulsor pressure ratio and BL capture sheet height. At a system level, the study assesses the effects of splitting the thrust between the propulsor array and main engines. The figure of merit used in the optimization is the TSFC. The suitability of the concepts is further assessed using performance predictions for HTS electrical motors. For the purpose of this study, the NASA N3-X aircraft concept is selected as baseline configuration, where the different propulsion designs are tested. As the study focuses on performance assessment of the propulsion system, sizing implication issues and aircraft performance installations effects have not been included in the analysis. The results from the parametric analysis corroborated previous studies regarding the high sensitivity of the propulsion system performance to intake losses and BL inlet conditions. As the study found low-power consumption configurations at these operating conditions, this may be considered as a major issue. The system analysis from the study indicated that splitting the thrust between propulsors and main engines results in improved system efficiency with beneficial effects in fuel savings. When a 2% increase in intake pressure losses and a similar reduction in fan efficiency were assumed due to boundary layer ingestion, the study found an optimum configuration with 65% of thrust delivered by the propulsor array. To summarize, the present work built on past research further contributes to the field through the inclusion of the thrust split as a key variable in the propulsion system design. The thrust split, when introduced, enabled reduction of the detrimental effects of intake losses on the overall system performance. Additionally, as it reduces the power required for the propulsor array, it is expected to reduce the operating power of HTS and cooling systems and therefore improve the effectiveness of the concept.

Boundary layer ingesting systems have been proposed as a concept with great potential for reducing the fuel consumption of conventional propulsion systems and the overall drag of an aircraft. These studies have indicated that if the aerodynamic and efficiency losses were minimised, the propulsion system demonstrated substantial power consumption benefits in comparison to equivalent propulsion systems operating in freestream flow. Previously assessed analytical methods for BLI simulation have been from an uninstalled perspective. This research will present the formulation of an rapid analytical method for preliminary design studies which evaluates the installed performance of a boundary layer ingesting system. The method uses boundary layer theory and one dimensional gas dynamics to assess the performance of an integrated system.The method was applied to a case study of the distributed propulsor array of a blended wing body aircraft. There was particular focus on assessment how local flow characteristics influence the performance of individual propulsors and the propulsion system as a whole. The application of the model show that the spanwise flow variation has a significant impact on the performance of the array as a whole. A clear optimum design point is identified which minimises the power consumption for an array with a fixed configuration and net propulsive force requirement. In addition, the sensitivity of the system to distortion related losses is determined and a point is identified where a conventional free-stream propulsor is the lower power option. Power saving coefficient for the configurations considered is estimated to lie in the region of 15%. NomenclatureAcronyms AR = Aspect ratio BL = Boundary layer BLC = Boundary layer control BLI = Boundary layer ingestion BWB = Blended wing Body FPR = Fan pressure ratio FS = Free-stream KE = Kinetic energy KEG = Kinetic energy non-dimensional group * PhD Researcher, Propulsion Engineering Centre, Cranfield University, Student Member. † Lecturer, Propulsion Engineering Centre, Cranfield University.

Life cycle emissions Engine/aircraft performance Thermodynamics Numerical modelling a b s t r a c t Biojet fuels have been claimed to be one of the most promising and strategic solutions to mitigate aviation emissions. This study examines the environmental competence of BioSynthetic Paraffinic Kerosene (Bio-SPKs) against conventional Jet-A, through development of a life cycle GHG model (ALCEmB e Assessment of Life Cycle Emissions of Biofuels) from "cradle-grave" perspective. This model precisely calculates the life cycle emissions of the advanced biofuels through a multi-disciplinary study entailing hydrocarbon chemistry, thermodynamic behaviour and fuel combustion from engine/aircraft performance, into the life cycle studies, unlike earlier studies. The aim of this study is predict the "cradle-grave" carbon intensity of Camelina SPK, Microalgae SPK and Jatropha SPK through careful estimation and inclusion of combustion based emissions, which contribute z70% of overall life cycle emissions (LCE). Numerical modelling and non-linear/dynamic simulation of a twin-shaft turbofan, with an appropriate airframe, was conducted to analyse the impact of alternative fuels on engine/aircraft performance. ALCEmB revealed that Camelina SPK, Microalgae SPK and Jatropha SPK delivered 70%, 58% and 64% LCE savings relative to the reference fuel, Jet-A1. The net energy ratio analysis indicates that current technology for the biofuel processing is energy efficient and technically feasible. An elaborate gas property analysis infers that the Bio-SPKs exhibit improved thermodynamic behaviour in an operational gas turbine engine. This thermodynamic effect has a positive impact on aircraft-level fuel consumption and emissions characteristics demonstrating fuel savings in the range of 3e3.8% and emission savings of 5.8e6.3% (CO 2 ) and 7.1e8.3% (LTO NOx), relative to that of Jet-A.

Wind energy is a mature renewable energy source that offers significant potential for near-term (2020) and long-term (2050) greenhouse gas (GHG) emissions reductions. Similar to all sectors of the transportation industry, the marine industry is also focused towards reduction of environmental emissions. A direct consequence of this being is a renewed interest in utilising wind as supplementary energy source for propulsion on cargo/merchant ships.This research utilises a techno economic and environmental analysis approach to assess the possibility and benefits of harnessing wind energy, with an aim to establish the potential role of wind energy in reducing GHG emissions during conventional operation of marine vessels. The employed approach enables consistent assessment of different competing traditional propulsion systems when operated in conjunction with a novel environmental friendly technology, in this instance being the Flettner rotor technology. The assessment specifically focuses on quantifying the potential and relative reduction in fuel consumption and pollutant emissions that may be accrued while operating on typical Sea Lines of Communication.The results obtained indicate that the implementation of Flettner towers on commercial vessels could result in potential savings of up to 20% in terms of fuel consumption, and similar reductions in environmental emissions.