Going ‘Green’ doesn’t have to be boring…..


A while back, I was over at the Lotus Engineering Centre in Hethel, giving an IMechE sponsored talk on

Integrating Technologies for Low Carbon Vehicles

Lotus had laid on a display of a selection of their ‘Future Technologies’ vehicles, all of which concentrate on aspects of the green automotive agenda.

Lotus Exige Biofuel

The Lotus Exige Biofuel pictured runs on E85 biofuel which is an 85% Ethanol blend derived from bio-crops. Although Brazil has traditionally been the world-leader in this approach, it has recently been overtaken by the US. The approach does have some drawbacks however. In a by-volume comparison, E85 has 30% less energy potential than conventional gasoline. Critics have proposed that a net energy loss may result when the entire supply chain from starchy plant to vehicle is taken into account.

The 265E pictured here started its life as a standard Exige, but with the addition of larger fuel injectors and modifications to the supercharger, the vehicles engine management system has been adapted so that it can switch between conventional gasoline and E85.


Lotus ECO Elise

Also on show was the ECO Elise project, which concentrates on green technologies applied to the whole vehicle. The body panels are composites manufactured from sustainable materials such as Hemp. The dark brown stripe on the bonnet has been left unpainted and merely lacquered, to show off the bio-material making up the body panels. This approach extends to water-based body paint and minimisation of energy expended in manufacture.

A nice touch is the solar panels embedded into the hemp composite of the roof material.

Future Thinking

More information about these and more innovative projects can be found at


Lotus and Lincoln

Lincoln’s School of Engineering has a long history of performing collaborative research projects with Lotus Engineering, from novel powertrain design for hybrid vehicles, to providing consultancy services to organisations such as the Carbon Trust and ITI Energy.

Working the Bank Holiday

Thrifty Hire's biggest van parked up in Norwich

Staying over in Norwich tonight before the big event tomorrow, picking up the Free Piston Engine from Lotus Cars after its most recent modifications, fitting the new linear motor/generator.

I’m also meeting a representative from Toyota in Japan with Jamie Turner, Chief Engineer from Lotus, to discuss our free piston work.

I’m going to take the engine over to the ThinkTank in Lincoln tomorrow, where it will be stored in the interim until the move into an engine test cell in August.

Control Techniques, who supplied the electrical drives, will be re-commissioning the experimental rig.

DeVere Dunston Hall Norwich

The Lotus Free Piston Engine project story – people2

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

Youtube Free-Piston Video

The Lotus Free Piston Engine project story – people

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

The Lotus Free Piston Engine project story part I

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.