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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