Sunday 13 December 2015

Delphi presses to widen Skip Fire use

Diesel equipment specialist Delphi is working with Tula Technology Inc. to widen the appeal of Dynamic Skip Fire, a system of cylinder deactivation. A 1.8-litre gasoline engine will run in 2016.
John Fuerst, vice president of engineering, powertrain systems at Delphi, interviewed for the latest issue of Ricardo’s RQ Magazine, Fuerst declares: “Delph recently invested in Tula Technology which has developed Dynamic Skip Fire (DSF), a new method to implement and control cylinder deactivation.”

According to Fuerst: “Instead of deactivating the same limited number of cylinders each time, DSF can deactivate any number of cylinders each engine cycle.”

Torque demand primarily determines the average number of cylinders to fire and so by choosing which specific cylinders to fire during each cycle it is possible to avoid firing frequencies that cause noise, vibration and harshness (NVH) problems.

“With DSF, any fractional  number of cylinders can be fired on average, so for example, a four-cylinder  engine could fire 0 cylinders on deceleration, 0.2 on average at 20 percent load, 1.2 cylinders at 30 per cent load, 2.8 cylinders at 70 per cent load, all the way up to all four cylinders when maximum torque is required,” claims Fuerst.

“Modulating average cylinder firing fraction like this unthrottles the engine to reduce pumping losses and improves in-cylinder thermodynamics for substantial CO2/fuel consumption benefits,” he adds.

According to Fuerst, Tula Technology (founded in 2008) has a large SUV demonstration (GMC Yukon) vehicle powered by a V8 engine that can deliver a 17 per cent fuel improvement (on the EPA combined cycle).

                                            Huge fuel savings

“We are currently working with Tula Technology to implement DSF in a turbocharged 1.8-litre GDI engine for which we are targeting 8 to 10 per cent fuel consumption improvement. Results from this four-cylinder engine will be available in the second half of 2016.”

Tula Technology Inc., based in Silicon Valley – San Jose, California – also has a base in Five Mile Road, Plymouth, Michigan. In 2012, GM Ventures has declared itself optimistic that its equity investment of that year would result in “revolutionary new fuel economy technology that could be deployed in future gasoline-powered GM vehicles”.

Fuerst, who works at Delphi Technical Centre, Luxembourg (which serves also as the headquarters of Delphi Powertrain Systems) believes DSF can be expected to improve diesel performance too. His comments will be good news for those who might consider the future of the diesel engine damaged by recent events at Volkswagen AG.

“Throttling losses are not an issue with diesels,” said Fuerst, “but DSF can still offer benefits through improved thermodynamic efficiency and after-treatment optimization.”

As to the future of the diesel, Fuerst of course has firm views.

“The diesel engine has a strong future in the light duty vehicle sector,” said Fuerst. “It offers low fuel consumption and CO2, along with excellent performance and driveability that many customers favour.”

Delphi specialises in diesel fuel injection systems having many years ago acquired the diesel fuel injection activities of UK company Lucas Industries.

“Emissions legislation around the world is increasing in stringency through tighter standards and through expanded test cycles to prove compliance over a broad range of operating conditions,” he adds.

“While the diesel is one prerequisite for meeting ambitious CO2 emissions targets, innovations in both gasoline and diesel powertrains will continue to improve efficiency and reduce emissions while providing the performance that customers expect.”

Fuerst notes that sensing systems will become increasing important in fuelling systems as the list of parameters that can be sensed and controlled continues to grow.

In this regard, Delphi has developed a simple single-wire circuit that engineers build in to Delphi’s diesel fuel injectors to measure precisely the injector opening and closing events.

“We do this by determining when the needle touches the injector lift stop or seat,” explained Fuerst. “This offers closed-loop control of all injection events, especially important as combustion schemes continue to implement more multiple injections. It also allows compensation over injector lifetime, and allows for corrections to account for part-to-part variation.”

                                          Vital role of sensors

Sensors are likely to play an increasingly important role in the control of lean NOx traps (LNT), Selective Catalytic Conversion (SCR) systems, and combined LNT and SCR.

“Control schemes are available for all three options, but control of LNT is more complex to implement as it requires specific engine operating modes for the NOx regeneration (to restore the storage capacity) and for the desulphation (to remove Sulphur contamination on the LNT). In contrast, the SCR system control does not directly affect engine control strategy,” notes Fuerst.

“Urea dosing level is determined to provide the appropriate reduction concentration for NOx conversion without producing ammonia breakthrough caused by overdosing,” explained Fuerst.

“System modelling is an essential factor for SCR system control and Delphi offers a unique ammonia sensor that enables closed-loop control of urea dosing based on direct ammonia measurement,” he said.

“Combining both LNT and SCR is an option available in order to meet increasing stringent standards for some larger engines producing higher NOx. Of course, this the most complex scheme in terms of both mechanization and control.”

As to diesel fuel injection pressure, Fuerst notes that engines continue to have an appetite for increased fuel pressures to enable efficient combustion with low emissions.

 “Increasing overall system configuration complexity through more sophisticated boost and EGR delivery continues to show benefit from higher fuel pressure,” said Fuerst. “Of course, pressure is only one aspect. Delivery of multiple, small injection pulses with high resolution and close spacing capability is also important.”

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