A High Efficiency SACI 1 kW Generator System with Integrated Waste Energy Recovery

We propose a novel high efficiency (≈40%) generator system capable of providing 1 kWe along with hot water on-demand. The integration of two novel concepts: 1) an internal combustion engine (ICE) operating on Spark-Assisted Compression Ignition (SACI) combustion of natural gas (NG), and 2) a bottoming Organic Rankine Cycle (ORC) with waste energy recovery (WER) from ICE exhaust enables the overall power generation efficiency (PGE) to exceed the 40% target. The proposed concept improves the overall system PGE over state-of-the-art SI gensets due to (1) SACI combustion of NG with limited flame propagation at high compression ratios (CR), increased specific heat ratios due to dilution with exhaust gas recirculation (EGR), reduced cylinder heat transfer losses by ensuring lower combustion temperatures and by avoiding flame quenching in the cylinder walls, ICE downspeeding (also increases component life) to operate at higher torques for a given power, (2) WER from the ICE exhaust using an ORC with a positive-displacement scroll expander (SE), specially designed for a thermodynamically optimal working fluid (WF), and (3) an induction generator with >95% efficiency. A liquid-cooled Spark Ignition (SI) ICE modified for SACI operation will be the first-choice prime mover for this concept. Salient features include: high CR~12-14, dilution and thermal stratification with EGR, optimized intake passages and piston geometry from CFD studies. The proposed ORC WER system utilizes a regenerator for preheating the WF before superheating it in an ICE exhaust heat exchanger to maximize ORC system efficiency and to increase SE power output. With this surplus power compounded to the ICE crankshaft, the overall fuel conversion efficiency (FCE) to mechanical power can be dramatically improved even with NG operation to produce a robust 1 kWe electric power generation system. The proposed system utilizes the excess energy of the coolant exiting the engine cylinder block/head to provide hot water on demand. The target efficiency will be achieved by simultaneous optimization of the SACI combustion process (ANL and MSU) and the ORC system for WER (Purdue and Air Squared (ASI)).