- Published in Focus.
Spark ignition engines are beginning to close the gap on diesels, thanks to turbocharging and gasoline direct injection (GDI). If OEMs can cut CO2 but keep costs below those of compression ignition units they’ll make a big difference to fleet average carbon dioxide emissions.
Ford is rolling out its 1.6- and 2-litre GDI turbos globally in applications such as the C-segment Focus and D-segment Mondeo. Now the OEM is turning its attention to the small-car segments. These are becoming increasingly popular as consumers downsize. These vehicles need more efficient engines too.
“The main thrust now is the 1-litre three-cylinder – that’s my team’s big programme for this year,” says Andrew Fraser, Ford’s manager for gasoline powertrain development and integration. “It’s the first time we’ve done a three-cylinder engine so there’s a lot of learning just from the fact that it’s got three cylinders instead of four.
“The combustion system is virtually the same as the 1.6 – centrally mounted direct injection, dual variable camshaft timing and turbocharging – but the base engine architecture is new. There’s no sharing.”
NVH is one of the biggest challenges – Fraser says that consumers don’t expect any loss in refinement. Meeting those demands will be tough.
Vibration is the main issue. Balancer shafts are the most effective way to mitigate it but add weight, friction and cost and take up valuable packaging space. Optimising the powertrain mounting system can be effective too – Ford is evaluating both of these measures.
The turbochargers Ford will use will be conventional. Nothing as radical as variable turbine geometry, Fraser says, just heavily optimised and making the most of the three cylinders’ widely spaced exhaust gas pulsations: “It’s good for the scavenging effect – you can use more valve overlap without pulse interference.”
A more complex valvetrain would help too, but the benefits must be balanced against cost. Fraser is a fan of Fiat’s Multiair variable valvelift system and says that Ford is looking at similar technology too but that, for now, the focus is on getting the most from dual cam phasing.
Integrated exhaust manifolds are another technology that could improve efficiency, response and warm-up times. Audi’s latest 1.8-litre engine has one. Other OEMs will follow.
“They’re definitely coming in the future,” says Fraser. “It’s a particularly good feature because you’ve got to bring the exhaust ports together in a short distance and link them to the turbocharger. And you recover a lot of heat in the coolant which cuts down the time for the engine to reach operating temperature.”
Ever more stringent emissions regulations mean that powertrain engineers will always have work to do but the main technical challenges ahead in gasoline development, says Fraser, come from downsizing.
Engines that can deliver the very high brake mean effective pressures – as much as 30bar – required for high torque ratings at low engine speeds will require a lot more R&D effort in managing the combustion process to avoid knock. And turbos which supply enough boost for that won’t be optimised for transient response. Ford is working on a project with development firm Ricardo to apply a 12V electric supercharger from supplier Controlled Power Technologies to a 1-litre turbocharged engine.
“You only need the bottom-end response for a couple of seconds so you don’t want to pay too much for it or lose much fuel efficiency to deliver it,” says Fraser. “You can recover the energy required to drive the supercharger through regenerative braking.”
The supercharger is only needed for a second or two after tip in, so energy consumption is relatively low. It recovers some of that through regenerative braking.
The technology won’t appear in Ford’s first-generation three-cylinders because its smaller, lighter vehicles won’t need it. If the technology worked successfully in the Focus the four-cylinder engine’s days could be numbered there too.
Three-cylinders could have a big future at Ford.