JLR pushes downsizing to the limit

Ultraboost project investigated the replacement of a 5-litre, naturally aspirated V8 with a forced-induction 2-litre four-cylinder

The Ultraboost project shows how fuel can be made to stretch further

Squeezing even more air into combustion chambers will enable next-generation petrol engines to squeeze more miles out of every gallon but boosting technology must improve first – that’s the conclusion of the Technology Strategy Board-funded Ultraboost project.

Jaguar Land Rover (JLR) was the lead partner on the project, which investigated the replacement of a 5-litre, naturally aspirated V8 with a forced-induction 2-litre four-cylinder. This downsizing delivered a 15% improvement in fuel efficiency with almost no difference in performance, but Ultraboost showed that further potential could be exploited using better turbos and superchargers.

JLR’s principal powertrain engineer, Dr James Turner, said: “Just by optimising what we have would theoretically give us another 6% fuel economy improvement from the engine alone. There’s still more to come from downsizing.”

For a given rating, smaller engines run at higher load and are therefore more efficient but have a greater tendency to knock. Despite the Ultraboost engine running at more than 35bar BMEP, pre-ignition was rarely a problem during development, Turner said, adding that the limit to extreme downsizing appeared to be boosting technology, not the combustion system itself.

The Ultraboost engine features a Honeywell turbo and an Eaton supercharger in series. These enabled a peak output of 550Nm, but there were problems in matching the V8’s torque output at 1,500rpm. Improved devices would enhance transient response and further downsizing.

JLR’s partners on the project included Lotus, Bath University, CD-adapco and Shell.