Assessment of Thermo-Electric Power Plants for Rotorcraft Application

Abstract

This paper assesses a parallel electric hybrid propulsion system utilizing simple and recuperated cycle gas turbine configurations. An adapted engine model capable to reproduce a turboshaft engine steady state and transient operation is built in Simcenter Amesim and used as a baseline for a recuperated engine. The transient operation of the recuperated engine is assessed for different values of heat exchanger effectiveness, quantifying the engine lag and the surge margin reduction which are results of the heat exchanger addition. An oil and gas (OAG) mission of a twin engine medium helicopter has been used for assessing the parallel hybrid configuration. The thermoelectric system brings a certain level of flexibility allowing for better engine utilization, thus first a hybrid configuration based on simple cycle gas turbine scaled down from the baseline engine is assessed in terms of performance and weight. Following the recuperated engine, thermoelectric power plant is assessed and the performance enhancement is compared against the simple cycle conventional and hybrid configurations. The results indicate that a recuperated gas turbine based thermo-electric power plant may provide significant fuel economy despite the increased weight. At the same time, the electric power train can be used to compensate for the reduced specific power and potentially for the throttle response change due to the heat exchanger addition.

Performance and Emission Assessment of Thermo-Electric Power Plant for Rotorcraft Propulsion

“…It consists of a five-stage axial and a single-stage centrifugal flow compressor mounted on the same shaft; a low-fuel-pressure, annular combustion chamber; a two-stage axial flow gas generator turbine; and a two-stage uncooled independent power turbine [18]. A model capable to represent with very good accuracy the steady state and transient operation of the engine has been developed by the authors [5] and validated against data reported by Ballin [19].…”

“…These calculations have been added to the ATLAS framework. For batteries and inverter, the simplified approach of energy and power density is used, as discussed in [5]. For the motor and generator, the method suggested in [25] is used (Figure 10) using data reported in [30].…”

“…For this PMS the electric motor should be capable to provide the MCR of the baseline engine during T/O and climb which is 987kW [5]. The baseline gas turbine is part of the configuration and is idling during these flight phases for redundancy.…”

“…The gas turbine is scaled down to 90%, 80% and 70% of nominal MCR. This PMS allows the utilization of the gas turbine at high specific power-high efficiency operating points, hence it may offer performance benefits, as discussed in [5] for an Oil and Gas mission. The engine power is scaled down by scaling down the engine mass flow, reducing the engine size.…”

“…Electrical technology can enable variable rotor speed, by decoupling the gas turbine rotational speed from the rotor one, which may reduce the main rotor power requirement up to 14% across different flight phases as discussed by Mistry and Gandhi [4]. Additionally, electrification can enable better throttle response, given the almost instant high torque capability of electric components [5], it may enhance energy harvesting and reduce the need for heavy gearboxes [3]. These advantages come with increased weight and complexity of the whole propulsion system, thus for assessing the performance of a hybrid propulsion system the increased weight of the helicopter should be considered.…”