Institution of Mechanical Engineers IMechE

Downsizing for Fuel Efficiency - A replacement for displacement?

04 October 2012

There's no replacement for displacement has been a catchphrase for big engine lovers for decades. In the modern era of fuel efficiency and CO2 concerns there needs to be a better way. The engine power installed in modern passenger cars engines is higher than ever in order to meet the increasingly demanding desires of the customer for heavier (more luxurious, larger and safer) vehicles with exciting driving performance. Delivering this power using a large engine means that almost all of the time the engine is operating at a tiny fraction of its maximum power and is therefore very inefficient.

Downsizing is the term given to installing a small engine in a vehicle but meeting the performance aspirations of the driver by designing the engine to operate at extremely high powers when needed. The most common approach to achieving this is through turbocharging and/or supercharging the engine. Both techniques compress the air entering the engine, allowing more fuel to be burnt and therefore more power to be generated. Most of the time though, the engine behaves as a normal small engine and therefore delivers improved fuel economy.

Downsizing is now an established trend, with all vehicle manufacturers offering some degree of downsized engine or working to deliver them. It is a very important development since it can be employed on all vehicles to deliver impressive fuel savings at modest additional cost using established manufacturing techniques and abundant materials.

The logical question to ask is "how far can we downsize?" This in turn leads to many questions - what are the practical problems that arise as we make the engine work harder and how can we overcome them? What are the challenges in compressing the inlet air to over three times atmospheric pressure? How can we burn fuel at these extreme conditions without damaging the engine through abnormal combustion? What are the expected fuel consumption benefits if we push to extreme levels downsizing? How can we maintain the driving feel of such vehicles and will they be exciting to drive?

This illustrated lecture seeks to answer these important questions. First through exploring the background to the pressure charging of engines and the development to date of downsized engines. It will then give details of current research at the University of Bath in a partnership including Jaguar LandRover, Lotus and Shell to deliver the performance of a 5l V8 from an extreme downsized four cylinder, 2l engine. It also looks ahead to future applications of downsizing including the forthcoming Formula 1 engine regulations.

Presented by Dr Chris Brace, Senior Lecturer In Automotive Engineering, Bath University

Dr Chris Brace is a senior lecturer in automotive engineering at the University of Bath. Chris was a student apprentice at Massey Ferguson Tractors in Coventry and studied for a thin sandwich degree at the University of Bath, graduating in 1990. Following a short spell designing transmissions at Massey Ferguson Chris returned to the University to work on an integrated Diesel CVT powertrain. Following the award of his PhD in 1996 Chris remained at the University progressing to Senior Lecturer in 2006. He leads a wide portfolio of powertrain based research projects with a common theme around the intensive measurement, analysis and control of multi-cylinder engine systems running under dynamic operating conditions. All of the research is in collaboration with industry, most notably Ford Motor Company and Jaguar LandRover.


Downsizing for Fuel Efficiency

: Presented by Dr Chris Brace, Senior Lecturer In Automotive Engineering, Bath University

Duration: 1h 15