# Operational Optimisation of a Non-Recuperative 1-kWe Organic Rankine Cycle (ORC) Engine Prototype
###### Abstract
[40] experimentally tested a rolling-piston expander for a solar ORC system using R245 fa, which exhibits an expander isentropic efficiency of 45% and an overall thermal efficiency of 4%. For ORC engines operating with medium- or high-temperature heat sources, [PERSON] et al. [41] constructed a cascade Rankine cycle-ORC test rig for diesel engine waste-heat recovery and measured the system performance at different heat-source conditions. The net power output was estimated to 12 kWe at an assumed expander efficiency of 85%. [PERSON] et al. [42] tested ORC systems with different working fluids and recommended R123 for long-haul trucks and R245 fa for city buses. [PERSON] et al. [43] proposed ORC-based WHR systems operated with CO\({}_{2}\) and a 4.5-kW test bench was developed, using an expansion valve in lieu of a positive-displacement or turbo-expander. [PERSON] et al. focused on the effects of system layouts [44] and external perturbations [45] on the system dynamic responses of ORC-based waste-heat recovery systems. More information about the current state-of-the-art of ORC systems can be found in Reference [46]. Several studies propose heuristic physics-based models for optimal system design. After identifying the main losses (i.e., leakage losses, mechanical losses and the supply pressure drop) that affect the expander performance, [PERSON] et al. [47] proposed a semi-empirical model of an open-drive oil-free scroll expander using R123. [PERSON] et al. [48] developed physics-based dynamic modelling tools in Dymola, which has been verified against steady-state and transient experimental results from an 11-kWe stationary ORC engine, providing convenience for transient performance examination and control strategy development as reported in Reference [49] for comparison of adaptive model predictive control and gain-scheduled switching proportional-integral-derivative (PID) controller. [PERSON] et al. [16] developed semi-empirical models of ORC diaphragm pumps considering energetic performance, volumetric efficiency and cavitation limits. [PERSON] et al. [19] developed physics-based models for ORC systems adopting CO\({}_{2}\) as the working fluid in GT-SUITE software and predicted the actual performance under a driving cycle. Simultaneous working-fluid and component optimisation is key for the design and development of efficient and economically viable micro- and small-scale ORC engines [23], which can be achieved with integrated computer-aided molecular design (CAMD) tools and ORC optimisation algorithms, such as those proposed by [PERSON] et al. [22; 33; 50]. The confidence in the predicted techno-economic potential of the designed systems depends strongly on the capability of the thermodynamic model to capture engine performance in design and off-design conditions. In order to fully explore the market potential and examine the economical viability of small-scale ORC engines, high-fidelity experimental data must be provided, both from laboratory-scale experiments and real-life systems, for performance assessment and simulation model development. This paper presents data from an experimental investigation of a 1-kWe ORC testing facility under various heat-source conditions. The optimal operating conditions, that is, pump speed and expander load, are determined at each heat-source condition. The thermal efficiency of the system and the effects of the expander load on its power are fully examined, with part-load (or off-design) performance maps provided. The dynamic characteristics of the engine are also explored through a series of tests, whereby the transient step response of the engine is recorded with time-varying pump power. These data and the associated results are intended to inform physics-based model development and real-time control strategies.