Electrical Machines and Drives Group

The Lotus Free Piston Engine project story part I

Paul Stewart
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.

Engineering : student as producer

Paul Stewart
The Sir Frederick Mappin Building at Sheffield University, which houses the Department of Electronic and Electrical Engineering. The Machines and Drives Group occupies the left wing of the building

Way back in another millennium, I was a hard up first year undergraduate in Control Engineering at Sheffield University, and overheard a conversation that a disabled PhD student in the Electrical Engineering Department had a grant to pay for a part-time lab technician to build rigs etc. for his research. I presented myself in the Mappin Building (pictured) the next morning at 9.00am, of course the PhD student in question didn’t roll up till mid-day! My first lesson about academia.

Keith Leonard was the PhD researcher in question, and he gave me the job. Now in addition to my degree, I was spending all my spare time building power electronics, data acquisition systems and learning how to programme in assembler and ‘C’ for real time control. I was also (although I didn’t know it then) about to embark on a 16 year association with the Department’s Electrical Machines and Drives Group (EMD). The group had a reputation for working and playing hard, and had risen to being one of the biggest and best of its kind in Europe. This was the turning point for me, I couldn’t believe how exciting research was, and fired me up to set goals to become a researcher.

Of course I still had the business of finishing my degree, and spent the final substantial part of it in one of the EMD labs completing my final year project in Real-Time Fuzzy Logic Control. The important thing here is that Engineering has been doing its own version of ‘student as producer’ for a long, long time. Lecturers tend to be research active, degrees are very ‘hands on’, projects are real-life problems, and funding has historically been there to encourage and retain students into research. I had no idea about the mechanics of research and publishing, so it wasn’t until much later that I realised the significance of my undergrad project and published on it:

Stewart P., Stone D.A. and Fleming P.J. “Design of robust fuzzy-logic control systems by multi-objective evolutionary methods with hardware in the loop” IFAC Journal of Engineering Applications of Artificial Intelligence, Vol.70, no.3, pp.275-284, May 2004.

Keith Leonard strikes a pose at the EMD Research Group fancy dress party in '97

I guess that really is ‘student as producer’. However the real story here is capturing people’s attention and firing their enthusiasm to become active researchers. My story started as an undergrad in Lab D137 in the Mappin Building, a lab which was always my home more than any office became. Chris Bingham (now here at Lincoln as Professor of Energy Conversion in the School of Engineering) joined the group in 1994 from Cranfield, and we started what has turned out to be a very long-standing research collaboration.

Keith never finished his PhD, but he was still an excellent researcher, shame he couldn’t have written his thesis on beer, kebabs and curry. He inspired me, and I wouldn’t be here doing what I do without Keith.

Keith died last week, and we will miss him.

Cheers Keith, RIP, thanks for everything.