• Energy Research
• 2016-2025close

Abstract Emission-free aerial propulsion can be achieved with a proton-exchange membrane fuel cell (PEM-FC). In the present investigation, this potential is addressed by designing a hybrid electric power system with fuel cells for an ultralight aerial vehicle to be retrofitted from a conventional fossil-fuelled piston engine configuration. The proposed power system includes a fuel cell, a lithium battery, and a compressed hydrogen vessel. A procedure is proposed to find the size of these components that minimizes the total mass and satisfies the target of a size below 200L and uses performance data of commercially available components. A comparison of different energy management approaches, with and without on-board charge of the battery, is performed. The results underline that the optimal solution is to select the size of the fuel cell to meet the cruise electric request and point out that the maximum discharge current of the battery must be regarded as a key issue in sizing this component, because of the very high take-off power.

Abstract The paper proposes a simulation approach to evaluate the power required by a rotorcraft in standard flight missions and in emergency landing maneuvers, and the corresponding fuel consumption, in order to compare the feasibility and potential fuel savings for different hybrid power systems. More in detail, three options are analyzed, namely electrification of the tail rotor, fully hybrid electric propulsion and electric emergency landing. Weight penalty and potential fuel saving for the proposed hybridization schemes are evaluated for an Agusta-Westland A109 twin engine helicopter model. Nonetheless the discussed methods of analysis have general validity for single main rotor helicopter configurations. Two different scenarios are considered in this investigation: current technologies for batteries and motors and improved electrical components, with performance projections as of 2040. According to this analysis, electrification of the tail rotor and parallel hybridization are feasible with available technology, whereas a fully electrical power system for emergency landing could be developed only in the future. Finally, a parallel hybrid electric power system is sized according to the analysis of power request over four different missions. Fuel savings are evaluated for different energy management strategies. According to the results of this investigation, the parallel hybrid electric power system with present-day and future technologies can save fuel up to 5% and 12%, respectively, with an appropriate energy management strategy.

Abstract This paper deals with hybrid electric fuel cell-powered drones energy management while targeting hydrogen saving and power supply system efficiency improvement. In this context, a commercially available quadcopter powered by the Intelligent Energy 650 W power module is adopted as a case study. Its power supply system is based on fuel cell and battery, and the power is conventionally managed using a basic rule-based strategy. To improve power management, a frequency separation rule-based approach is first proposed, and then an equivalent consumption minimization strategy is implemented for fuel economy seeking. An experimental flight test is carried out using a battery-powered hexacopter to extract a real power profile for load requirement modeling. The obtained load profile is repeated several times replicating the hovering phase to obtain a larger mission lifetime. Extensive simulation results clearly show that the proposed power management strategies enables power sources operating in their nominal area, extending their lifetimes, and inducing 3% minimization in hydrogen consumption. This optimization extends the drone endurance as much as the carried fuel amount, and it can increase the world endurance record by 21.81 min . It has also an economical benefit, which consists in the operating cost gain reaching 853.2€ per fuel cell module lifecycle. In fleet missions, this gain may further be increased.

In recent years, there has been a growing interest in utilizing hydrogen as an energy carrier across various transportation sectors, including aerospace applications. This interest stems from its unique capability to yield energy without generating direct carbon dioxide emissions. The conversion process is particularly efficient when performed in a fuel cell system. In aerospace applications, two crucial factors come into play: power-to-weight ratio and the simplicity of the powerplant. In fact, the transient behavior and control of the fuel cell are complicated by the continuously changing values of load and altitude during the flight. To meet these criteria, air-cooled open-cathode Proton Exchange Membrane (PEM) fuel cells should be the preferred choice. However, they have limitations regarding the amount of thermal power they can dissipate. Moreover, the performances of fuel cell systems are significantly worsened at high altitude operating conditions because of the lower air density. Consequently, they find suitability primarily in applications such as Unmanned Aerial Vehicles (UAVs) and Urban Air Mobility (UAM). In the case of ultralight and light aviation, liquid-cooled solutions with a separate circuit for compressed air supply are adopted. The goal of this investigation is to identify the correct simulation approach to predict the behavior of such systems under dynamic conditions, typical of their application in aerial vehicles. To this aim, a detailed review of the scientific literature has been performed, with specific reference to semi-empirical and control-oriented models of the whole fuel cell systems including not only the stack but also the complete balance of plant.

The electrification of aircraft is a well-established trend in recent years in order to achieve economic and environmental sustainability. In this framework, an application particularly interesting for hybrid electric power system is represented by urban air-mobility. For this application, the authors presented a parallel hybrid electric power system including a turboshaft engine and two electric motors and proposed a quasi-stationary simulation tool. As a further step, this paper deals with the dynamic modelling of the same turboshaft engine within the framework of a hybrid electric system where the pilot command is interpreted as a power request to be satisfied by the engine and the electric machine according to the selected energy management strategy. In this work, the dynamic behaviour of the turboshaft engine is analysed with and without the help of the electric motors to satisfy the power demand.

A rising number of aerospace manufacturers are working on the development of new solutions in the field of Urban Air Mobility with increasing attention addressing electric and hybrid electric propulsive systems. Hybrid electric propulsive systems potentially offer performance improvements during transient maneuvers, as well as sustaining the engine during flight phases characterized by high power demands. Among the challenges of hybridization in rotorcraft, there is the necessity to predict the dynamic behavior and its effect on the control of rotor shaft speed. In the present study, the dynamic behavior of a parallel hybrid electric propulsive system for a coaxial-rotor air taxi is analyzed in response to a typical sequence of pilot commands that encompasses the range of operations from hover to forward flight. The system is modeled with a dynamic approach and includes sub-models for the coaxial rotors, the turboshaft engine, the electric machine, and the battery. The results of the investigation show a better performance during transients of the hybrid system than a conventional turboshaft configuration, especially if the electric contribution to the power request is coordinated to account for the lag due to slower engine dynamic response.

Abstract The EU6d Emission Regulation requires Real Driving Emissions as an additional type approval requirement within the 2017 - 2020 timeframe in order to take into account the influence of the road profile, the ambient conditions and the traffic situation as well as the behavior of the driver. The new test uses Portable Emissions Monitoring System (PEMS) to measure on-board emissions. The trip sequence shall consist of a urban, a rural and a motorway sections with specific requirements in terms of distance and average speed for each section. For example, the overall trip duration shall be between 90 and 120 minutes. Due to these strong requirements, the execution of RDE measurements has to be preceded by an accurate planning of the route to reduce test failure risk and, consequently, experimental costs. The aim of the present investigation is to present a procedure to build a cycle for real driving emissions that minimizes the distance, is robust with respect to the uncertainties of traffic conditions and satisfy the requirements of the regulations. The procedure has been applied to routes from and to the Department of Engineering for Innovation. Moreover, a preliminary analysis of the effect of instantaneous speed and acceleration on real drive emissions is presented.