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Electrification of the propulsion system has opened the door to a new paradigm of propulsion system configurations and novel aircraft designs, which was never envisioned before. Despite lofty promises, the concept must overcome the design and sizing challenges to make it realizable. A suitable modeling framework is desired in order to explore the design space at the conceptual level. A greater investment in enabling technologies, and infrastructural developments, is expected to facilitate its successful application in the market. In this review paper, several scholarly articles were surveyed to get an insight into the current landscape of research endeavors and the formulated derivations related to electric aircraft developments. The barriers and the needed future technological development paths are discussed. The paper also includes detailed assessments of the implications and other needs pertaining to future technology, regulation, certification, and infrastructure developments, in order to make the next generation electric aircraft operation commercially worthy.

This paper presents the development and application of a modelling approach of variable geometry conceptsfor low pressure ratio fans; namely Variable Area Nozzle and Variable Pitch Fan. An enhanced approachfor Outlet Guide Vane pressure loss predictions and an aerothermodynamic analysis of variable pitchconcept are developed and integrated into a multi-disciplinary conceptual engine design framework. Astreamline curvature algorithm is deployed for the derivation of the off-design fan performance map,alleviating scaling issues from higher pressure ratio fan designs. Correction deltas are derived through thevariable pitch analysis for calculating the re-shaped off-design fan performance map. The aforementionedvariable geometry concepts are evaluated in terms of surge margin at engine and aircraft level for a lowpressure ratio aft-fan of a hybrid-electric configuration. Performance assessments carried out suggest thata +8° closing of fan blade cascades leads to a 33% surge margin improvement (with reference being thesurge margin without variable geometry) compared to a 25% improvement achieved by +20% opening thenozzle area at end of runway take-off conditions. Although weight and complexity implications of variablegeometry are not considered, the integrated modelling approach is shown to be able to assess and comparesuch novel engine technologies for low pressure ratio fans in terms of operability.

A conceptual design of a hybrid Gas Turbine - Solid Oxide Fuel Cell (SOFC) system is presented for civil aviation applications. The system operates using hydrogen as fuel, for the aircraft’s propulsion, while at the same time produces electrical energy in the fuel cell. Hydrogen is produced during flight by reformation of methane. The motivation of the study is to investigate hydrogen’s use for aviation purposes, so the hybrid system’s operation characteristics need to be examined. A configuration is designed, where a SOFC and the burner is modeled as one and simulated, in a modern multidisciplinary programming environment, in order to analyze the thermodynamic characteristics of the hybrid system. The fuel cell sets into motion when the aircraft reaches top of climb. During operation, liquefied natural gas is converted to hydrogen in the fuel cell and part of it is used to produce electrical energy while the rest for combustion. To determine the efficiency of the system, its performance was simulated using two scenarios, one for longhaul flights and one for short-haul flights. Comparing the results, for long-haul flights, the hybrid system presents a reduction in fuel consumption and an increase in thermal efficiency. For flights of a short range, the existing conditions in the fuel cell inlet were found to be prohibitive for it’s operation and the use of the hybrid system ineffective. For the system’s efficiency, the larger the pressure in the SOFC’s inlet the better. However, SOFC’s pressure limits restrict the pressure range and the cell’s use only during flight. Concluding, according to the study’s results, the hybrid system can operate in flight conditions, making the use of hydrogen in civil aviation possible. As a result, a 12% and 35% benefit is achieved, in fuel saving and thermal efficiency respectively.

A mixer may be damaged either by cracks or mechanical deformation causing a change in geometry. Only the latter case is, in some cases, possible to detect by shifts in physical measurements such as pressures and temperatures. In general, deformations of the geometry of a mixer due to damage is very hard to identify and quantify with the onboard measurements available, especially for turbofans with high bypass ratio (BPR) where a damaged mixer may cause a slight loss in thrust rather than shifts in measurable quantities. A special case of mixer damage that may be detected is burn-through of the afterburner liner in low bypass afterburning turbofans. The liner is used to protect the outer casing of the gas turbine to the high temperatures during afterburner operation. For this, the liner need to be continuously cooled by bypass air to withstand the temperatures. A burn-through is generally caused by a local blockage of the cooling path, leading to temperatures the liner cannot withstand. In severe cases it may cause a burn-through of the gas turbine outer casing as well where it may cause a fire in the engine bay. In this paper, two diagnostic routines are developed to identify a burn-through of an afterburner liner. The diagnostics is intended to be performed as a part of the startup check of the gas turbine to increase the confidence that no burn-through has occurred during the last operation. For these methods a mixer model of high enough fidelity is required, which is described in the paper. The main conclusion is that with enough data it is possible to detect a burn-through but the data collection time is so long that the methods need to be further enhanced to be of any practical use. DIAGNOSIS

In this paper, a turbo‐electric propulsion system was analyzed, and its performance was assessed. The aircraft considered here was a single‐aisle, medium‐range configuration targeting a capacity of 150 Pax. The propulsion concept comprised two boosted geared turbofan engines mounted under‐wing. Those main engines were supported by an electrically driven aft‐propulsor contributing to the thrust generation and by taking advantage of ingesting the boundary layer of the fuselage for potentially higher levels of propulsive efficiency and allowing for the improved operation of the main engines. The performance assessment as carried out in the context of this paper involved different levels: Firstly, based on the reference aircraft and the detailed description of its major components, the engine performance model for both main engines, as well as for the electrically driven aft‐propulsor was set up. The methodology, as introduced, has already been applied in the context of hybrid‐electric propulsion and allowed for the aforementioned aircraft sizing, as well as the subsequent gas turbine multi‐point synthesis (simulation). A geared turbofan architecture with 2035 technology assumptions was considered for the main engine configuration. The present trade study focused on the design and performance analysis of the aft‐propulsor and how it affected the performance of the main engines, due to the electric power generation. In order to allow for a more accurate description of the performance of this particular module, the enhanced streamline curvature method with an underlying and pre‐optimized profile database was used to design a propulsor tailored to meet the requirements of the aft propulsor as derived from the cycle synthesis and overall aircraft specification; existing design expertise for novel and highly integrated propulsors could be taken advantage of herein. The resulting performance characteristics from the streamline curvature method were then fed back to the engine performance model in a closely coupled approach in order to have a more accurate description of the module behavior. This direct coupling allowed for enhanced sensitivity studies, monitoring different top‐level parameters, such as the thrust/power split between the main engines and the aft propulsor. As a result, different propulsor specifications and fan designs with optimal performance characteristics were achieved, which in return affected the performance of all subsystems considered.

Real-time engine condition monitoring and fault diagnostics results in reduced operating and maintenance costs and increased component and engine life. Prediction of faults can change the maintenance model of a system from a fixed maintenance interval to a condition based maintenance interval, further decreasing the total cost of ownership of a system. Technologies developed for engine health monitoring and advanced diagnostic capabilities are generally developed for larger gas turbines, and generally focus on a single system; no solutions are publicly available for engine fleets. This paper presents a concept for fleet monitoring finely tuned to the specific needs of micro gas turbines. The proposed framework includes a physics-based model and a data-driven model with machine learning capabilities for predicting system behaviour, combined with a diagnostic tool for anomaly detection and classification. The integrated system will develop advanced diagnostics and condition monitoring for gas turbines with a power output under 100 kW.

Various aspects of a multi-disciplinary aero engine conceptual design approach and computational framework are presented. The approach closely integrates different disciplines and is capable of homing in on the best designs in the presence of techno-economic and environmental risk. The framework can assist in the transition from the traditional, human-centered design procedure that involves complex manual iterations, to a more automated process. It considers the following disciplines: engine performance, engine aerodynamic and mechanical design, aircraft design and aerodynamic performance, emissions prediction and environmental impact, engine and airframe noise, and production, maintenance and direct operating costs. The proposed explicit conceptual design algorithm reduces system complexity, improves computational speed and can make design space exploration and optimisation results easier to interpret. Through a good set of constraints, it will also give an optimal aero engine conceptual design that may prove feasible in terms of major engine certification and customer requirements. The power of the proposed conceptual design approach has been demonstrated through a variety of unique case studies. These range from technology assessment and design sensitivity analysis to design space exploration and optimization. Overall, the work sets the necessary base for an assessment methodology that can quantify risks and assess the impact of gas turbine design on the environment, by comparing and helping to rank future technologies and design concepts for civil aviation on a formal and consistent basis.

In this work, a design for a new turbofan engine intended for a conceptual supersonic business jet expected to enter service in 2025 is presented. Due to the increasing competition in the aircraft industry and the more stringent environmental legislations, the new engine is expected to provide a low fuel burn to increase the chances of commercial success. The objective is to perform a preliminary design of a jet engine, complying with a set of specifications. The conceptual design has mainly been focused on the thermodynamic and aerodynamic design phases. The thermodynamic analysis and optimization have been carried out using the Numerical Propulsion System Simulation (NPSS) code, where the cycle parameters such as fan pressure ratio, overall pressure ratio, turbine inlet temperature and bypass ratio have been optimized for overall efficiency. With the cycle selected, and the fluid properties at the different flow stations known, the component aerodynamic design, sizing and efficiency calculations were performed using MATLAB. Several aspects of the turbomachinery components have been evaluated to assure satisfactory performance. The result is a two spool low bypass axial flow engine of similar dimensions as the reference engine but with increased efficiency. A weighted fuel flow comparison of the two engines at the key operating conditions shows a fuel burn improvement of 11.8 % for the optimized design.

NEWAC researches new engine core concepts and lean-burn combustion. This paper describes whole engine and technology assessments undertaken, including preliminary design studies to set specifications and technology targets, and use of ‘TERA2020’ models for sensitivity and optimization studies including economic and environmental assessment of intercooling, recuperation, aspiration and active control technologies.

Within the European research project EnVIronmenTALly Friendly Aero Engines, VITAL, a number of low pressure system component technologies are being investigated. The emerging progress will allow the design of new power plants capable of providing a step change in engine fuel burn and noise. As part of the VITAL project a Technoeconomic, Environmental and Risk Assessment tool, the TERA2020, is being developed. Within this tool, means to assess the impact of component technology progress on the engine/aircraft system level has been implemented. Sensitivities relating parameters traditionally used to describe component performance, such as allowable shaft torque, low pressure turbine stage loading, fan blade weight and system level parameters have previously been published. The current paper makes an assessment of the impact of failing to deliver specific technology advancements, as researched under the VITAL project. The impact has been quantified, in terms of power plant noise and CO2 emissions.

This paper presents a methodology for Technoeconomical, Environmental and Risk Analysis (TERA) of multidisciplinary systems. Work in Cranfield University on the development and adaptation of TERA models for complex mechanical systems can be traced back to the early 90’s. Tools implementing the “TERA approach” can be used for radically exploring the design space available in novel aero engine configurations during the conceptual design phase. The methodology can be used for assessing advanced power generation schemes and for technology risk analysis. Details of the application of the method in aero engine design and industrial power generation systems are given together with sample results. TERA can rank and make a selection among different power generation cycles, for various objectives, so that investments can be allocated efficiently. The capability of the tool to identify those gaseous pollutants and flight phases that contribute the most to global warming is illustrated.