# Operational Optimisation of a Non-Recuperative 1-kWe Organic Rankine Cycle (ORC) Engine Prototype
###### Abstract
[25] presented a techno-economic model to investigate the potential of a solar-powered ORC system using R245 fa as the working fluid, reporting a total electrical power of 776 kWh/year and 86% hot water supply capacity with a total system cost as low as \(E\)2700. The system performance was further improved by more than 50% (for a maximum annual power output of 1070 kWh) through optimising the working fluid and the solar collector configurations [12]. [PERSON] and [PERSON] [26] also conducted a thermo-economic analysis of a domestic solar combined cooling-heating-power system based on an ORC engine, where thermodynamic and economic models were adopted for multi-objective optimisation using genetic algorithms. [PERSON] et al. [27] investigated solar-powered ORC systems for residential applications and demonstrated a payback period of about 4 years after considering different uses (corresponding to system operation mode) and different locations in Spain (corresponding to various solar irradiance). ORC engines in ICE-WHR applications can be used to harness two main streams of waste heat, the high-temperature exhaust gases (200-600 \({}^{\circ}\)C) and the low-temperature jacket cooling water (80-100 \({}^{\circ}\)C). [PERSON] et al. [28] investigated a basic ORC system for WHR from a diesel engine and compared 20 working fluids, identifying specific optimal fluids in terms of different performance indexes, while [PERSON] et al. [29] and [PERSON] et al. [30] conducted similar analyses using dual-loop ORC systems. Novel ORC architectures have been explored as summarised in References [31; 32]. These innovative solutions include using zeotropic mixtures as working fluids and adopting multiple evaporation pressures in cascade cycles. Working-fluid selection is also critical in these scenarios. Beyond traditional working fluid pre-selection methods [PERSON] et al. [22; 33] proposed computer-aided molecular design (CAMD) of ORC working fluids. The resulting CAMD-ORC framework allows simultaneous optimisation of working fluid, thermodynamic and thermo-economic performance of ORC systems. As a leading company, Cummins [34] demonstrated a 3.6% improvement of the engine thermal efficiency over a road test through recovering waste heat with an ORC system operated with R245 fa. [PERSON] et al. [35] simulated an integrated ORC-ICE engine and stated that the ORC system brings an increase of 3.6% in engine thermal efficiency and a reduction of 10 g/kWh in engine brake specific fuel consumption at the engine rated condition, although the findings need to be experimentally verified. [PERSON] et al. [19] carefully calibrated an integrated model of the engine and an ORC-based system against experimental data and demonstrated a 2.3% improvement in engine brake thermal efficiency over a cruise driving cycle, which could be further improved to 4.2% through component optimisation. Small-scale ORC systems are a promising heat-to-power conversion technology in many applications, at least from a theoretical perspective, as reported in the open literature. However, experimental studies on small-scale ORC systems are still limited. For ORC engines operating with low-temperature heat sources, [PERSON] et al. [36] tested a small-scale ORC engine that exhibits up to 5% thermal efficiency using a 2-kW scroll expander and operated with R134a as a working fluid. [PERSON] et al. [37] tested a basic ORC system using thermal oil at 135-160 \({}^{\circ}\)C as the heat source and R245 fa as the working fluid. The expander isentropic efficiency was found to be less than 35%. [PERSON] et al. [38] reported preliminary dynamic testing results of a 3.75-kWe ORC system with R123. Turbine efficiency of 65% and ORC thermal efficiency of 7% were obtained. [PERSON] et al. [39] experimentally compared recuperative and non-recuperative ORC systems with R123 using a 10-kWe axial-flow single-stage turbine. [PERSON] et al.