Browse Topic: Hybrid electric vehicles
There is a continued and growing need for better analysis and simulation of complex transmission systems with the rise of hybrid electric powerplants coming to future aviation vehicles. In this paper we discuss how reduced order modeling can help to efficiently predict the thermal behavior of gearboxes during operations smartly reusing data from SPH based oil flow simulations. To solve the thermal problem, a dynamic non-linear Reduced Order Model (ROM) is generated to estimate the Gear-Oil heat transfer coefficient (HTC) based on variable gearbox RPM and Oil fill level.
Electrification could improve full-size rotorcraft performance by reducing peak turbine power demand, reducing transmission system weight and complexity, and reducing operating costs. Integrating electric machines with mechanical powertrains requires careful consideration of the system-level weight and efficiency impacts. This paper presents an optimization framework for evaluating parallel hybrid powertrain configurations using Geometric Programming (GP). Both retrofit and clean-sheet vehicle designs are considered. The results show that high-speed electric motors integrated into a parallel hybrid configuration using batteries can reduce the sized gas turbine power, enabling more efficient engine operation at lower power levels. For retrofit designs, with a fixed vehicle gross weight, adding batteries and motors reduces usable fuel, decreasing mission capability. Clean-sheet designs offer additional flexibility to re-size the vehicle and rotor, resulting in energy savings for an equivalent design mission.
A simulation framework is essential for the development of a hybrid-electric tilt-wing aircraft such as Dufour Aerospace's Aero2 drone. The tilt-wing design with its complex interaction effects between the propellers and the aerodynamic surfaces presents unique modeling challenges, especially during early stages of development when only limited data is available. Furthermore, a delicate balance between accuracy and performance must be found while keeping complexity low to allow for rapid development. This paper introduces a modular design approach for a simulation framework, details the aero-propulsive models and shows ways to validate them using flight data and a system identification approach. By implementing models that capture all relevant effects, the framework helps building a deeper understanding for the dynamics of individual systems, serves as a basis for the design of the flight controller and offers capabilities for pilot training and hardware testing.
A regulated hybrid-electric power sharing architecture was developed and tested for VTOL applications. In this architecture, there are two power supply branches and one load. The first branch draws power from an engine-generator, and it has additional components of an AC-DC rectifier, a DC-DC buck converter, and a power diode. The second branch draws power from a battery, and it has additional components of a solid-state relay, a DC-DC boost converter, and a power diode. Any specified ratio of battery-to-engine power can be achieved with this architecture. Testing on the full range of power share ratios was conducted at a low load power of 300W. The key conclusions are that: (1) regulated power sharing is feasible between an AC supply and a DC battery, including the extremes of all engine and no battery to all battery and no engine, (2) a specified power share ratio can be achieved both in steady-state and transient conditions, and (3) there is a delay in achieving a specified power share ratio, caused not by the power plant, but rather by the change in RPM of the rotor.
The purpose of the NATO Next Generation Rotorcraft Capability (NGRC) Support Partnership funded Novel Powerplant concept study was to identify, analyze, and compare novel powerplant concepts that could fulfill the NGRC need in a solution-agnostic approach. The outcome of the study provided NSPA and the NGRC participating nations with increased knowledge and understanding of the powerplant domain to inform assessment of future NGRC platforms. This study modeled four aircraft configurations to derive propulsion sizing requirements and compared propulsion configurations for each. The propulsion system configurations considered included three levels of conventional gas turbine technology (In-service GT, 2025 GT, and 2035 GT), hybrid electric (battery), hybrid hydrogen fuel cell, and hydrogen combustion. The results of the study considered both quantitative and qualitative evaluations. The quantitative analysis determined aircraft and propulsion system sizing to align with the expected NGRC need at different max cruise speeds, and compared performance along with recurring, non-recurring, and operational costs for each. The qualitative analysis investigated the impacts of wider technical, capability, and supportability considerations for each propulsion concept. Assuming a notional NGRC entry into service target date of 2035, this study shows that, when considering both quantitative analysis and a qualitative review, a modern gas turbine is the most reasonable solution space to deliver the performance and multi-mission capability expected.
Hybrid-electric propulsion could provide numerous benefits for full-size rotorcraft, including reduced peak turbine power demand, reduced transmission system weight and complexity, and reduced operating costs. Variable speed electric motors, furthermore, could be configured to enable continuously variable rotor speed. Achieving these benefits requires accounting for coupling between the hybrid-electric drivetrain and vehicle performance within a large, unexplored design space. This paper presents a framework for simultaneous optimization of vehicle and electrified powertrain conceptual design using Geometric Programming (GP) methods. Four hybrid-electric powertrain architectures are evaluated relative to a baseline non-electrified powertrain for single main rotor, compound coaxial-rotor, and tiltrotor configurations. For designs with an upper limit on turbine power, electrification increases the maximum cruise speed for the compound coaxial-rotor configuration. Variation of the rotor speed by 15% allows the vehicle to carry 8% more fuel, relative to the non-electrified baseline, and 1,246 lb of battery. Operating the rotor at optimal speeds across the mission results in increased off-design mission performance, most notably a 43% increase in transport radius relative to a baseline powertrain. The results demonstrate the utility of the design optimization framework for exploration of novel hybrid-electric concepts as well as the challenges associated with incorporating electrical components into the drivetrain.
In this paper, a comprehensive dynamic simulation of a parallel hybrid gas-electric single main rotor helicopter involving a motor/generator (MG) pair and a differential planetary gear transmission (PGT) arrangement forming an electronic continuously variable transmission (E-CVT) was performed. This notional hybrid electric helicopter was sized based on a retrofit of a dual engine, 10000 lb, 2500 Hp class helicopter. The total weight added by the electric components was 182 lbs which increased the propulsion system weight from 1184 to 1366 lbs. The simulation results found that at 110 kts cruise, the hybrid electric system enabled a 27% reduction in main rotor rpm which resulted in an 18% reduction in the fuel burn rate. It is concluded that use of an E-CVT parallel hybrid propulsion system offers potential for increased flight range and reduced fuel consumption in medium to large-scale helicopter applications.
Data from a 3.43 kW piston engine-generator is integrated with rotorcraft sizing analysis to assess its impact. First, the measured SFC map of the powerplant is modeled. Second, the sizing is validated with XV-15 flight test aircraft and NASA conceptual reference quadrotor. The power and platform models are then integrated to size a hypothetical quadrotor bi-plane unmanned air vehicle of 5 lb payload. Several cases for how the engine can be operated to meet the vehicle torque and speed are detailed. The key conculsion is that a detailed SFC model is as important as the aircraft model. Without it, errors in tip speed reduction, gross weight, and range would be quite dramatic from 50-100%. A tip speed reduction to 65% hover in cruise was found to strike the best balance between rotor performance and engine performance of the hypothetical aircraft, resulting in a gross weight of 50 lb and range of 120 nm at 60 kts cruise speed.
In the pursuit of High-Speed Vertical Takeoff and Landing (HSVTOL) platforms, VerdeGo Aero offers its VH-5 hybrid-electric turbofan as the answer to missions requiring high power, vertical lift, and jet-like speeds. To evaluate the possibility of designing a real HSVTOL aircraft around VerdeGo's VH-5 powerplant, this paper investigates the size and expected performance of a militarized spinoff of NASA's Class B, High-Efficiency Civil TiltRotor (HECTR) concept, which has been renamed the VerdeGo Hybrid-Electric Combative TiltRotor, or "VHECTR" for short. Through an in-depth conceptual weight buildup of four commonly proposed tiltrotor architectures, this paper suggests that an entirely new, turbofan-driven propulsion system is needed if modern day HSVTOL demands are to be met. Hence, a separate, yet more conventional "Modified HECTR" tiltrotor configuration is considered to contest the proposed, VH-5 powered VHECTR concept. However, the results of a full-scale aircraft comparison, aerodynamic analysis, and mission analysis alongside the V-22 Osprey indicate the VHECTR concept is more HSVTOL mission capable with greater time and fuel savings than any advanced tiltrotor system to date.
Electrical vertical takeoff and landing (eVTOL) vehicles for urban air mobility (UAM) are garnering increased attention from both the automotive and aerospace industries, with use cases ranging from individual transportation, public service, cargo delivery, and more. Distributed electric propulsion systems are their main technical feature; they determine vehicle size and propulsion efficiency and provide distributed thrust to achieve attitude control. Considering the intended role of eVTOL vehicles, ducted-fan systems are ideal choice for the propulsor, as the duct provides a physical barrier between the rotating blades and the human, especially during the take-off and landing phases. Key Technology Challenges of Electric Ducted Fan Propulsion Systems for eVTOL introduces the main bottlenecks and key enablers of ducted-fan propulsion systems for eVTOL applications. Based on the introduction and discussion of these important issues, this report will help eVTOL engineers understand the key technical issues and inspire them to develop the ideal solutions that will enable eVTOL vehicle deployment for UAM operations. Click here to access the full SAE EDGETM Research Report portfolio.
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Driving cycles are usually defined by vehicle speed as a function of time and they are typically used to estimate fuel consumption and pollutant emissions. Currently, certification driving cycles are mainly used for this purpose. Since they are artificially generated, the resulting estimates and analyzes can generally be biased. In order to address these shortcomings, recent research efforts have been directed towards development of statistically representative synthetic driving cycles derived from recorded real-world data. To this end, this paper focuses on synthesis of multidimensional driving cycles using the Markov chain-based method and particularly on their validation. The synthesis is based on Markov chain of fourth order, where the road slope is accounted, as well. The corresponding transition probability matrix is implemented in the form of a sparse matrix parameterized with a rich set of recorded city bus driving cycles. A wide collection of statistical features, including the frequency domain indicators, unique cross-correlation velocity-acceleration-slope indicators, and indicators related to bus stops at stations are considered for the purpose of driving cycle validation. To prove the synthesis method validity, a comparative statistical analysis of distributions of the nominated statistical features of synthetic and recorded driving cycles is carried out. Finally, a multi-criteria method of driving cycle validation based on lumped metrics is outlined and examined.
Aircraft development efforts are rapidly shifting toward the use of distributed electric propulsion. As the industry moves along a path to full electrification, hybrid propulsion systems will be increasingly employed where battery technology does not support a fully electric design. The fuel systems in new aircraft designs can be challenging, and the existing regulatory framework may not be capable of dealing with unique aircraft designs that do not neatly fit within existing categories. This presents a challenge to aircraft designers. Fuel remains essential to the propulsion system, and an optimal, yet simple fuel system will be necessary to leave room in the design trade space for more challenging and risky functions. Understanding the certification requirements and having a basic knowledge of the tradeoffs in fuel measurement accuracy are the key elements necessary to support a systems approach to optimizing a fuel measurement subsystem.
A phenomenological simulation for a variable-voltage hybrid-electric powertrain was developed and compared with test data acquired on a 4 hp powertrain to understand the fundamental characteristics of such a system. The powertrain was modeled component by component, and compared with over 500 experimental data points, from the engine alone to the engine generator, to the engine-generator with four distributed propulsors. The principal conclusion of the predictive simulation and the experimental data was that generator voltage is a key parameter that needs careful control relative to rotor speed. For any operating state -- defined by rotor torque and RPM -- the generator voltage should be minimized to minimize engine specific fuel consumption. In general the system is influenced more by the engine generator than electric motors. Hence greater rotor torque and lower rotor RPM is desired. It was found that steady state performance can be confidently predicted with the engine model, if the thermal efficiency is calibrated with engine data. The overall understanding gained from this work is that the optimal operation of hybrid-electric powertrains in VTOL is closely coupled with controls and rotor aeromechanics as well as engine gas dynamics and thermodynamics, but can be captured with relatively simple phenomenological models.
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