Control Techniques re-commission the Lotus experimental engine

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.

Recommissioning the Lotus Experimental Free-Piston Engine

Camshaft drive transfer box

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

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.

Setting up the engine laboratories in the New School of Engineering

Engine lab control room for the Free-Piston Engine

It’s only 12 weeks until we move into our new building. On the ground floor are some of our experimental laboratories, in particular our engine test cells. The cells each have an associated control centre separated by safety materials, from where experiments can be conducted remotely.

Pictured is the control centre for the Lotus Free-Piston Engine when it was under development in the Test Cells at the University of Loughborough, with the actual engine cell visible in the background through double safety glass.

The task I’ve got now is to move our experimental engines into the new build, and get them all running, commissioned and most challenging of all, correctly wired up into the data acquisition and control systems.

A fully working and commissioned Lotus Free-Piston Engine

The picture of the Lotus engine gives an indication of the amount of sensor and actuator cabling associated with each engine.

Engines are generally under computer control via either LabView, or running Matlab and Simulink developed control algorithms under DSpace. It’s quite rare for me to hand write code these days, DSpace compiles control structures from simulink into C, and downloads it onto ta converters.he host control microprocessor and associated A-D and D-A converters.

A lot of our engine laboratory equipment has been stored at the ThinkTank until the move, so we’re just starting the process of going through it all and allocating space.

A haulage company delivering some of our dynamometer equipment to the ThinkTank prior to our move.

Free-Piston experimental engine returns to Lincoln:Engineering labs

Free-Piston engine cambelt drive transfer box

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

Chen, Rui and Winward, Edward and Stewart, Paul and Taylor, Ben and Gladwin, Dan (2009) Quasi-constant volume (QCV) spark ignition combustion. In: 2009 SAE World Congress, 20-23 April, 2009, Cobo Centre, Detroit, MI, USA.

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!