| 12
years ago, I read an article in Autocar regarding the revolution of
diesel engines. It foresaw the increasing popularity of diesel and the
fast improvement of performance, refinement and emission. Autocar
picked the contemporary BMW 325td engine as an example - the
turbocharged 6-cylinder displaced 2.5 litres and produced 115
horsepower, matching the output of a low-end 3-series petrol. Today, we
might not understand why that was regarded as a revolution, because the
progress of diesel technology during these 12 years was even bigger.
Now we are starting to compare the output of diesel and petrol engines
of the SAME displacement, not just in terms of the usually-acclaimed
torque but also horsepower. Ford Focus TDCi needs just 1.8 litres and
four cylinders to produce the same 115hp as the old 325td. BMW itself
is even more impressive - the new 320d generates 150hp out of 2 litres,
making it more efficient than its own Valvetronic-and-Bi-Vanos 2-litre
petrol. Volkswagen's pump injection even achieves 150hp from 1.9
litres, although it has drawback on turbo lag and noise.
Common-rail
injection technology is leading us into the Diesel Era, an era in which
most family cars, executive sedans, MPVs, on/offroaders are powered by
diesel. Right now, one-third of new cars sold in Europe are already
diesel cars. If the trend is to continue, if not accelerate, 10 to 20
years later petrol engines will be reserved for sports cars only. We
might even see a M-badged BMW diesel, just like what AMG is doing in
Stuttgart. Undoubtedly, the trend is going to be accelerated by the
introduction of "second-generation" common-rail diesel, which has been
serving the aforementioned Focus TDCi and 320d. By increasing injection
pressure from 1350 to 1600 bar, the new system enables finer fuel spray
hence more efficient combustion. It also applies "multi-jet" to cool
cylinder head, hence avoiding knock and reducing noise. It seems that
under the competition of second-generation common-rail VW's pump
injection technology will be eventually phased out. In fact, no one
else goes the pump-injection route. If not Volkswagen group's
substantial buying power, I'm afraid Bosch will no longer produce pump
injection system for it.
Admittedly,
diesel engines will never match petrol for power efficiency, as
measured by power-to-weight ratio. While a 150hp petrol 2-litre engine
is normally aspirated, BMW 320d needs a variable geometry turbocharger,
an intercooler and a sophisticated injection system. Therefore I said
sports cars will still favor petrol engines for their weight and weight
distribution advantage. Also because of their instantaneous response.
However, the advantage is reducing quickly as common-rail diesel is
gaining efficiency much faster than petrol. 12 years ago, a 2-litre 16V
engine produced about 140hp, virtually unchanged until today (though
gained a little bit more torque). During the same period, turbo diesel
gained about 50% power. Now I am predicting within this decade we can
see some good diesel engines breaking the 100hp/litre barrier. Can you
believe ?
Mark Wan
|