Alex graduated from the University of Bath in 2019 with an MEng (hons) in Integrated Mechanical & Electrical Engineering. Throughout the degree, his passion for internal combustion engines was perpetuated by various courses and projects, especially during his final two years with Team Bath Racing (TBR) - Bath’s ICE Formula Student Team. During his penultimate year, he worked on Engine Simulation and Intake System Design, which he used to optimise the boosting system used on the car. In his final year, he assisted in Engine Mapping whilst designing and manufacturing the wiring harnesses and PCBs for the various control systems on the car. Whilst at competition, he gained valuable insight to the demands of running a race team as he continued to tune the engine and control system set-ups for each event. He hopes to use his passion for ICEs to deliver ground-breaking research as part of the AAPS CDT into futuristic hybrid powertrain systems.
The opposed-piston 2-stroke (OP2S) engine has historically been applied to aircraft propulsion as well as engines for power generation and rail traction with great success. More recently, Achates Power have shown the potential of the OP2S engine for automotive applications. The low surface area to volume ratio of the combustion chamber in OP2S engines, combined with its lack of a cylinder head, results in lower heat losses yielding high exhaust gas energy, making it an ideal candidate for turbocharging, as well as increased brake thermal efficiency. However, due to the requirement for a positive delta pressure across the cylinder at all operating points (intake manifold pressure must be higher than exhaust manifold pressure) to ensure the scavenging performance of 2-stroke engines, crankcase scavenging is typically used instead as, unlike a turbocharger-driven charging system, it guarantees a positive delta pressure gradient at all operating points. Nevertheless, other scavenging systems, such as a supercharger in conjunction with a turbocharger, have been shown to provide effective scavenging performance whilst utilising the otherwise wasted exhaust gas energy. Moreover, the use of a combined supercharger/turbocharger charging system with an OP2S architecture provides greater flexibility in the air-fuel-ratio control and exhaust temperature management, whereas conventional 4-stroke engines are expected to require the use of cylinder deactivation or other thermal management strategies to meet the low emissions standards. Furthermore, the use of electrically assisted turbochargers not only increases this flexibility but also provides a means of extracting excess work from the turbine by turbocompounding, whilst simplifying the intake air path.
The purpose of this work is to investigate a novel pressure-balanced free-piston engine concept. An OP2S engine model will first be adapted from prior work with a view to understanding the effects of crank phasing and port geometries on gas dynamics. A Libertine free-piston engine will then be used to inform and verify a linear generator engine model constructed using a similar geometrical arrangement as the Libertine engine. Having completed this work, a verified free-piston OP2S engine model can be developed using learnings from the prior work. This model will yield a greater understanding of the capabilities of the conceptual engine arrangement whilst also providing insight into the intrinsically linked relationships between the mechanical and electrical subsystems. The model could also be used to assist in the design of a prototype of the concept engine, the manufacture of which would be dependant on time and funding.
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