Variable CR con rod
switches compression
ratio from 13:1 to 17:1S
HOULDthe diesel engine be
tossed onto the scrapheap?
Headline writers shouldn’ t
forget that all combustion
engines produce nitr ogen oxides. While
diesel NOx is higher than petrol (Euro6
NOx limits allow 80mg/ℓ for diesel and
60mg/ℓ for gasoline), the ro llout of new
NOx after-treatment systems will allow
diesel to match gasoline. Chris Brace,
automotive propulsion professor at Bath
university, believes today’s ‘after-
treatments will fixemissions and air
qualityissues. Whenreal dr iving
emission tests are enforc ing Euro 6.2 in
2017, the air qualityissue will be largelybeaten. Then it’s back to CO2 business
as usual.’ Of course, that’s where denser
diesel fuel has the edge, containing
about 15% moreener gythan petrol, plus
diesel engines are ab out 20% more
efficient. The downside is that diesel
produces 2.65kg of CO2 per kilo burnt,
compared to 2.3kg for petrol. However,
since diesel consumes 25% less fuel than
a gasoline engine, it emits 15% less CO2.
And that’ll be vital to help car makers
avoid a €95 (approx. R1500) fine for
every gram emitted over 95g/km– PER
car sold – from 2021. Reason enough for
the bean-counters to sanction these
NOx-beating technologies...Don’t letVW’swoesfoolyou intothinkingdieselisdead.
It’smore efficientthanpetrol,and willget cleanerstill5 technologies
to save the diesel
Depending on the engine and vehicle
size, different exhaus t gas treatment
(EGT) systems will be empl oyed.
Bosch has developed modular
systems that incor porate a NOx
Storage Convertor ahead of a double
selectiv e catalyst reduction (SCR).
The NOx trap appears to be tailor-
madefor many urban traffic situa tionsdue to the lower te mper ature limit
of its oper ating range. The first
SCR, with AdBlue urea inje ction,
combined with a diesel pa rticulate
filter (DPF) reduces low te mper ature
urban exhaus t emissions; a second,
optional, SCR further cleans the
high temper ature exhaus t gase s, if
necessary.1
Exhaust after-treatments
Today’ s Golf al ready has cylinder
deactivation – but onits 1.4
petrol (above). But for diesel?
Tula Technology’s Dynami c
Skip Fire (DSF) uses audio
electronics-derived digi tal signal
processing to continu ously vary
the number of cylinders firing
at any one time, controlling
diesel exhaus t te mper ature
independent of engine load.
Dies el after-treatment devi ces
have a relatively narrow window
of temper atures in which they
are effectiv e. A common
problem with NOx
traps and SCRcatalysts is that, at low loads,
the exhaus t is actually too cold
for the after-treatment devi ces
to work at peakeffectiv eness.
Running DSF allows control of
the exhaus t te mper ature so the
systems operate more effectiv ely.
As a separate but related
advantage, wit h DSF it is easier
to achi eve the te mper atures and
equivalence ratios requir ed to
regenerate a particula te filter.3
Cylinder deactivation
Variable CR con rod
switches compression
ratio from 13:1 to 17:1Because compression ratio (CR) is
fixed across all oper ating boundaries
it is a compromise. A high CR is
used for cold ambient star t and
engine warm-up – improving star ting,
hydrocarbon/carbonmonoxide (HC/
CO) reduction and increased thermal
efficiency. With increased in-cylinder
temper ature at the star t of inje ction
the rate of igniti on is improved and
stab ilised, resulting in more completecombustion and reduced HC/CO
emissions. It is also used for part load
in warm engine conditio ns to increase
the combustion’s therma l efficiency,
decr ease CO 2 emission and fuel
consumption. A reduction in CR is
neededas the engine load increases
to protect components. For high er
loadsthe amount of fuel and cylinder
charge isincreased along with cylinder
peakpressure.2
Variablecompression ratio
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96 TOPCAR.CO.ZA|January 20 16The innovations transforming our driving world
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