Dynamic skip fire cylinder deactivation will make production in an unconfirmed model from a 'large, global' car maker

A new and advanced dynamic cylinder deactivation technology that can cut CO2 emissions in petrol engines by up to 15% will make production in 2018.

Developed by parts supplier Delphi and automotive tech company Tula, the cylinder shut-off technology has the biggest effect in larger capacity engines like V8s, but is also claimed to trim CO2 emissions by 8% in smaller turbocharged four-cylinder engines, making them as efficient as their diesel counterparts.

The dynamic skip fire cylinder (DSF) deactivation system works by deciding whether to fire or skip each cylinder before its firing. If a cylinder is skipped, the intake and exhaust valves are held closed by Delphi’s cylinder deactivation hardware. The system works by controlling the car’s spark ignition, so only petrol cars are compatible. It makes independent decisions up to 32,000 times a minute.

Scott Bailey, president and CEO of Tula said: "Every time a cylinder is ready to be fired, the system makes a dynamic decision – do we fire this cylinder or do we drive this cylinder for torque reasons?"

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Bailey explained that this process takes place independently for each cylinder, so each one can be managed to maximise efficiency when not running at full throttle. "We don’t look at running fixed patterns [like conventional cylinder deactivation systems], so we can run anywhere from zero cylinders to 100% of the available cylinders, with any firing density between them," he added.

John Kirwan, chief engineer of advanced R&D at Delphi Powertrain, said that the biggest savings can be made in larger capacity engines like V8s and V12s, but that it will also help four cylinder turbocharged units and could enable further downsizing. "We can't say what model it'll be fitted to first, but we can say that a large, global manufacturer will be the first to use it in a car from 2018," he revealed.

The system is being demonstrated on a Volkswagen Jetta with a 1.8-litre four-cylinder turbocharged engine. Later down the line, the two companies will showcase a 48v hybrid system combined with the dynamic skip fire tech; a CO2 and fuel consumption reduction of up to 20% is possible with the two technologies, Delphi claims.

A wide range of engine sizes can accommodate the system, including three-cylinder engines, in which the system has also been tested. Torque demand from the driver, the effect of the cylinder on refinement and noise are among the decision criteria of whether to shut down a cylinder before firing.

A Delphi spokesman said the system is aimed at making petrol engines as efficient as diesels, with high fuel economy and low CO2 emissions. This could, if the system enters the mainstream, eliminate one of diesel’s key selling points in certain driving scenarios.

Delphi claims the system’s cost to a car manufacturer equates to about £34 for every 1% of CO2 saved per engine. "This compares to other forms of emissions reduction technology which are closer to [£70]," said Kirwan.

The (DSF) technology will be presented in full at the Vienna Motor Symposium later this week, as an industry first: the first fully variable cylinder deactivation system.

All four-cylinder engines are targeted, including downsized turbocharged units. The company also expressed the potential of the system to improve cars’ refinement; in cars with more cylinders, the shut-off system causes vibration when the cylinders are switched off; this new system, said the spokesman, doesn't and is as refined as when all the cylinders are running.

The system is also viable for use in hybrid cars, in addition to purely fossil-fuelled cars. In hybrids, the CO2 saving would be even greater, at up to 3% on top of the previous reduction, so in excess of 11% can be saved.

Delphi claims that the system causes the engine to run at near-peak efficiency, and also allows an evolution of the current cylinder shut-off systems’ approaches to saving fuel while decelerating, shutting down all cylinders when the car is decelerating.

Read more: 

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Is it time to say goodbye to diesel?

Join the debate


26 April 2017
While this sounds great, the truth is cars are no more economical in the real world than they were in 2001.
Example, focus 1.5T claimed economy 50mpg- actual 34mpg. 1.6 focus from 2006 claimed 47mpg, actual 44mpg. - honest john real world economy uploaded by real drivers.

26 April 2017
Presumably the system doesn't just skip the spark, but also the injection, otherwise no fuel would be saved and HC + CO emissions would be horrendous on the next firing of that cylinder.
Taking this presumption to the next step - if injection can be stopped on a cylinder-by cylinder case for a petrol engine, it could also be stopped for a common-rail diesel engine. It just needs a business case, and I assume with the current anti-diesel sentiments, the cost of getting diesels to meet EU6 with RDE, and the lessor savings from applying the tech to an already more efficient engine the economics don't currently stack up.

26 April 2017
All the time money and energy that was spent polishing the turd that is the diesel engine in the small cars (no need for hysteria) had better been spent on improving the petrol engine. A well engineered petrol engine with or without hybrid power train is capable of meeting or beating the emissions regulations. But the last 15 years saw billions of pounds wasted in developing diesel that nobody wanted in the first place if the deal was not sweetened with tax breaks and subsidies.

27 April 2017
Diesel engines were gaining popularity long before tax breaks came along and not enough money was spent on diesel which is why we are where we are at with them - this is just the sort of tech that should have been applied to diesels years ago along with mandatory DPFs and SCR/NOx cats, after all, complex emissions systems have been mandatory on petrols for 25 years.

XXXX just went POP.

26 April 2017
at anything other than tick-over, how will this actually achieve anything "real world"? especially taking stop-start into account. if the engine is producing the required energy to maintain a constant speed, then shutting off cylinders will either slow it down or have the other cylinders run at higher load - which must surely negate what's trying to be achieved? also, why keep the valves closed? isn't that an idea too many?

26 April 2017
russ13b wrote:

at anything other than tick-over, how will this actually achieve anything "real world"? especially taking stop-start into account. if the engine is producing the required energy to maintain a constant speed, then shutting off cylinders will either slow it down or have the other cylinders run at higher load - which must surely negate what's trying to be achieved? also, why keep the valves closed? isn't that an idea too many?

It is a shame that Autocar's article lacked enough detail to understand what they are really doing. I'm sure that russ13b is right when he says that the shutting off cylinders can only take place when the engine is not under load. And if BOTH inlet and outlet valves are kept closed, you are surely just going to add more resistance.

26 April 2017
I am not convinced anyone should be trying to make petrol engines as clean (or dirty) as diesel!
I assume that phrase is used to be deliberately provocative!

27 April 2017
As I m sure you know both petrol and diesel are "dirty" depending on what pollutants youre talking about.

XXXX just went POP.

26 April 2017
that's pretty much it. they do say it isn't fully unveiled yet so i accept - in autocar's defence - details may be lacking. buuuuut... given that we already have off-throttle fuel shut off (so what difference does stopping the spark make?), really accurate fuel injection, and stop-start, what can this actually do? for it to keep the valves closed i'm expecting solenoid actuation instead of a cam, and that that is where the actual improvement comes from (as seen with the koenigsegg camless engine). i really don't see how keeping them closed is the right idea!

27 April 2017
The reasons the valves are kept closed is twofold.
Firstly, pumping air through the catalysts massively reduces their efficiency (cats only really work at lambda 1 or close to it) and can cause exotherms as any unburnt fuel can be ignited in the catalysts due to the temperatures.
Secondly, by keeping the valves closed the air in the piston acts as an air spring so the work you put in to compressing it you get back as work on the piston. OK - not all of it but you get some of it back which you wouldn't do if you opened the exhaust valve and shoved it all down the exhaust.

Basically cylinders working at low loads are very inefficient. Having less cylinders working harder moves the engine in to a more efficient region.


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