Bear with me on this one, it's going somewhere I promise you.
There’s a lot of stories doing the rounds of the Interweb
about diesel cars that are fitted with particulate filters suffering with
premature failure of this expensive part.
What's a particulate filter? Briefly, if you’re as old as I am you will associate diesel
engines with lots of black smoke. Over the years, the manufacturers have
cleaned up the exhaust emissions, and although you see the odd vehicle (often a black cab) belching out soot, they are generally a lot cleaner than they used
to be. This is in part due to the fitting of a Diesel Particulate Filter (DPF).
What the DPF does is trap the soot, thus cleaning up the exhaust. When the
filter reaches a high enough temperature, the soot will simply burn off, like a chimney fire, thus cleaning
the filter. However, if the vehicle is used for a lot of short urban journeys,
the filter may never reach the required temperature to burn off the trapped
soot. The engine management computer can detect the soot build-up, and can
force the filter up to temperature by injecting extra fuel into the engine, or by various other
methods, but this doesn’t always work, and if the driver ignores the warning
lights indicating excessive soot build-up, the vehicle may end up needing a
very expensive new filter, or worse.
Over 50% of new cars sold in the UK these days are diesel.
No surprise there – with escalating fuel costs, buyers are tempted by the
superior efficiency of diesel, plus there’s usually a cost advantage in the
form of lower vehicle excise duty. But, being the car-dependent nation that we
are, a significant number of those cars will be used for exactly the type of
short urban journeys that are the enemy of the DPF. But for a lot of people,
the car is the default mode of transport, and they expect to just be able to
jump in their car and go without having to worry about dashboard warning
lights. As a result, car manufacturers have taken to warning potentialcustomers of this issue, and steering them towards petrol cars. This is a shame
in environmental terms, because although they emit lower amounts of certain
pollutants than diesel vehicles, petrol-fuelled cars have significantly higher
In the quest for lower emissions, manufacturers have been
coming up with more and more technological solutions, and the result is cars
that are becoming more and more complex and less reliable. If people used a
bike for their short urban journeys, that would reduce emissions, fuel bills, and reduce
the probability of their DPF failing. (It would also reduce the probability of
their heart failing, as an additional bonus.) Maybe manufacturers should
include a free bicycle with every diesel car. Even a decent bike is cheaper
than a DPF, and a bike will last a lifetime.