| On-board diagnostics (OBD) is
exploding the complexity of future emissions control systems. Advanced
powertrain technologies are drastically increasing the amount of software
in engine ECUs.
The situation is worst in the US and will affect engineers working on
diesels for North America.
Regulations there are aligned with California’s OBD II limits –
the world’s most stringent. In OBD II, the engine must detect when
one or more of its cylinders is misfiring and generate and log fault codes.
GM Powertrain’s executive director of advanced engineering Dr Uwe
Grebe said: “A system for North America is like a stack of text
books up to your head. The top three contain the code to run the engines;
the rest is OBD. Everything we add to the engine has to be diagnosed.”
From 2010, vehicles must log any misfiring causing harmful emissions exceeding
1.5 times the legal limits. This will affect the growing number of diesels
with in-cylinder pressure sensors and gasoline engines with ion-current
measurement.
OBD monitors everything influencing operation – from coolant thermostats
to exhaust catalysts. Adding cylinder pressure sensors means yet more
OBD work.
Homogeneous charge compression ignition (HCCI) will face an even greater
challenge. The engines need, at a minimum, the addition of cylinder pressure
monitoring, fast-acting variable valve timing and advanced exhaust gas
recirculation systems.
“Because our HCCI system is designed to mitigate NOx, we need to
diagnose all the elements. This takes a lot of work,” said Grebe.
HCCI ignites the mixture at idle and part-load using compression ignition.
Combustion is efficient but at the limits of stable operation. Control
is the greatest challenge and any misfiring or miscombustion events cause
emission spikes.
Extending HCCI operation into higher speed and load ranges is desirable
because it maximises fuel economy benefits. HCCI gasoline engines are
more fuel efficient.
© Automotive Engineer, 2007 |
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