Simon Wilson setting up the motor control system in the engine test cells
Simon Wilson was in one of my 4th year MEng project groups at Sheffield Uni, and stayed on to read for a PhD with me on Temperature Estimation for Permanent Magnet AC Motors. Simon received an Industrial CASE award from Rolls-Royce Derby for the duration of his study. He can be seen here setting up the DSpace controller which supervises data acquisition and control for the engine.
Simon has subsequently joined EA Technology at Capenhurst as a consultant on new renewables technology.
Ed Winward setting up the control desk Labview front end
Next up is Ed Winward, who was working for Professor Rui Chen at Loughborough University. Ed designed and implemented the entire front-end for the free piston project in Labview (see picture left) which allowed us to start experimentation in earnest.
The best tribute to his part in this project is a YouTube video he made which documents an early run of the Free-Piston Engine
Close up of the Free-Piston Engine, showing timing belt, cam boxes, cylinder head and combustion chamber
After delivery to the engine test cells at Loughborough University AAE dept., it took a significant amount of time to put together the control system instrumentation, and the control architectures necessary to run the engine under Labview, and DSpace.
This part of the story is the people behind developing this part of the project.
First up is Dr Ben Taylor, who at the time was one of my Post-Doctoral researchers at the University of Sheffield Department of Electronic and Electrical Engineering, and is currently a Research Fellow there in the Department of Automatic Control and Systems Engineering. Ben designed and built the 100kW four-quadrant power converter which in the early stages of the project drove the permanent magnet servo-motor attached to the end of the tethering crankshaft. This arrangement allowed us to make the initial development happen relatively safely, without the danger of losing control and blowing up the engine. Later developments are untethered from the crankshaft and truly ‘Free-Piston’
Dr Ben Taylor connecting the 3-phase cables from the power converter to the PMAC servo-motor
Ben also designed the control system for the servo-motor, based around a TI Digital Signal Processor (DSP) which allowed accurate, real-time control of the motor currents, and position/velocity control of the motor, interfaced to a DSpace real-time controller.
Ben subsequently moved on to work for myself and Prof Chris Bingham on a RDA funded project on intelligent heating controls and methods for domestic houses.
The power converter which Ben designed and built is now in use driving the linear electrical machine embedded in the engine, whilst the drive of the crankshaft servo-motor has been take over by a custom designed four-quadrant inverter designed and installed by Control Techniques
Stage 1 development of the free-piston engine: engine and power converter.
Dr Ben Taylor with the control/data acquisition system
Graham Smith, Technician in Aeronautical and Automotive Engineering at the University of Loughborough brings in the new engine
The idea to develop a free piston engine has a long history, mainly focusing on two-stroke designs with a combustion chamber at each end of a linear motor generator. the main idea is to remove the physical constraints imposed by conventional crankshaft based engines, reduce the mechanical losses to improve the engine efficiency, and to introduce elements of piston trajectory control to allow advanced combustion control.
As if that wasn’t challenging enough, Jamie Turner of Lotus Engineering and I had the idea of pushing the envelope even further, to create a single combustion chamber, four-stroke design. This developed from the fact that two-ended designs are generally constrained to operate via an oscillating principle akin to simple harmonic motion for increase efficiency. In our view, we wanted to push the technology of the possible even further, and design what was originally called the Lotus Active Crank Train (ACT) and eventually became the Zero Constraint Free Piston Energy Converter.
We originally applied to the EPSRC ‘Adventure Fund’, but the application was rejected on the grounds that the proposal was ‘too adventurous’! The EPSRC however invited us to re-submit, and the project became…
EPSRC Grant: GR/S97507/01 ‘Zero Constraint Free Piston Energy Converter‘
PI: Paul Stewart. Co-Investigator: D. Howe. (University of Sheffield) Collaborating University: Dr Rui Chen, Dept. Aeronautical and Automotive Engineering, University of Loughborough UK. Collaborating Company: Lotus Engineering, Consortium Project Manager: Paul Stewart.
P. Stewart: £326,00, R. Chen £260,000, Lotus Engineering Contribution: £330,000
Rui Chen wondering what he has got himself involved with!
I was a Junior Lecturer at the time in the Electrical Machines and Drives Group at Sheffield University. I needed an engines/combustion collaborator, and since I had worked at Loughborough as a Post-doc, searched their web-site and approached Dr Rui Chen who was then also a Junior Lecturer (now Professor of Low Carbon Power Engineering) in the Department of Aeronautical and Automotive Engineering at the University of Loughborough. This was the start of a research relationship and friendship which lasts to this day.
In order to ‘de-risk’ the project, the free-piston was originally tethered to the crankshaft of a General Motors 1.8l engine so that we could conduct our initial development in relative safety. The engine as delivered from lotus is pictured above, the free-piston part (nick named the ‘rocket launcher’) is the tube and cylinder head sticking up from the GM crankcase. In the next part of the story, we get it running, and discover we can look at some hitherto unattainable fundamental aspects of combustion.
The free-piston engine at Lotus waiting for collection
Our free piston engine has had it’s major modifications completed by Lotus and is now ready for one of us to go over to Norwich and pick it up. The engine has had a new 25kW linear motor/generator fitted. When we get it back to our labs in Lincoln, Control Techniques will be coming over to re-commission the electrical system and load dynamometer. After this we will be continuing our research into novel combustion strategies and power plants for hybrid electric vehicles.
