DIESEL cars that emit virtually no particles will go on sale in France next
year. The cars, made by Peugeot Citro毛n, have a filter that removes
particles from the exhaust gases.
PM10s, particles with a diameter of less than 10 micrometres, are thought to
kill 10 000 people each year in Britain alone. Although particle traps have been
fitted to trucks and buses, this is the first commercial system for cars.
The filters work by trapping particles and then using the heat of the exhaust
gases鈥攊n some cases aided by a catalyst鈥攖o periodically burn off the
accumulated soot, preventing it from clogging the filter. It is easier to make
the filters work on trucks and buses because they have hotter exhaust gases.
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The Peugeot system gets round this problem by adding a cerium catalyst to the
fuel. This lowers the temperature needed to burn off the soot from 550 掳C to
450 掳C.
The system is entirely automatic. Sensors monitor the build-up of dirt in the
filter. When necessary鈥攗sually every 500 kilometres or so鈥攖he engine
management computer injects extra fuel, which increases the exhaust temperature
from 150 掳C to 450 掳C and burns off the soot.
Sensors also monitor the fuel level, and when you top up the car at a filling
station the cerium is automatically added from a 5-litre tank next to the fuel
tank. Paul Lefebvre, Peugeot鈥檚 project director has high hopes for the system.
鈥淚t鈥檚 the greatest innovation since the invention of the engine by Rudolf
Diesel,鈥� he claims.