Control Techniques engineer working on the AC drive unit
The rotary electrical drive on the Lotus free-piston experimental engine has now been re-commissioned by an engineer from Control Techniques.
The rig is now ready to be transported from the ThinkTank to its new home in an engine test cell in the new building.
The engine is part of a long-term R&D programme into new engine technologies and combustion control techniques led by Prof Paul Stewart, in collaboration with Lotus Engineering in Norwich.
The programme is looking at advanced drive trains for Hybrid Electric vehicles.
Lotus experimental engine, with Control Techniques drive cabinet open in the background
The CT drive supplies the Emerson 15kW Permanent Magnet AC Motor (PMAC) which is coupled to the crankshaft and acts as a motor-generator to control piston trajectory when the linear free piston engine is tethered to the crankshaft.
Now that the Free-Piston engine is back at the ThinkTank, the electrical drive to the main crankshaft servo will be re-commissioned by Control Techniques Ltd.
The Engine has been away for a while having a new linear electrical motor-generator fitted, and is now ready for electrical re-comissioning before we move it into it’s test-cell in the new School of Engineering building.
The engine is unique, in that it allows piston trajectory control for experimentation on both conventional (with crankshaft) and free-piston (linear electrical machine, no crankshaft) operation.
After re-commissioning and installation in the new building, Prof Stewart will be continuing research into fundamental combustion, multi-fuel operation with variable compression ratios and free-piston operation in collaboration with Dr Jill Stewart, Reader in Thermofluids.
Free-Piston engine in the ThinkTank lab waiting for re-commissionng
After a successful meeting with Lotus Powertrain and a representative from Toyota Research Laboratories, I loaded the van up with the free piston engine, and brought it back to Lincoln, where it will be installed in one of the experimental test cells when we move into the new building.
The next stage in the development will be for Control Techniques to recommission the electrical drive and position controller for the rotary machine.
The free-piston engine in the laboratory ready for re-commissioning
This engine is absolutely unique, as it is able to function as a conventional single cylinder research engine, or as a free-piston engine by disconnecting the connecting rod from the crankshaft.
Presently the engine is set up in conventional operating mode, as a single cylinder research engine. It is novel in this operating mode, as the crankshaft is connected to a low inertia, high torque electrical servo-motor, which allows us to not only apply dynamic loads to the engine, but also control the shape and phase of piston trajectories, particularly through top-dead-centre.
This has allowed us to achieve the first dynamic examination of Quasi-Constant-Volume-Combustion, by reducing the piston velocity through the combustion phase of the cycle through top-dead-centre. This activity resulted in the paper
The next research steps over the forthcoming year will be the investigation of the thermodynamic cycle using advanced control techniques, none of which are achievable on any currently produced engine configurations. We will be reporting on the research outputs in due course.
Prof Stewart at Lotus Headquarters in Hethel, hoping they'll let him take the Evora around the test track
Many thanks must go to the Lotus team for fitting the new linear motor/generator which we designed and built. In particular to Jim Young, who has been responsible for most of the modifications to this engine, which have been in many cases outlandish and seemingly impossible. Well done Jim!
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.
