READERS may have noted that some countries have plans to prohibit diesel vehicles from some of their cities because of pollution.

Not wishing to be wise after the event, I did often wonder if dirty diesel engines even with advanced technology in fuels and engines did emit extremely harmful particles into the atmosphere.

Petrol is a highly refined oil product and the engine uses a spark to ignite the vapour/ air mixture in the combustion chamber.

Diesel engines use a less refined oil, needs no spark, but uses a very high compression to burn the fuel.

Who can remember in the 1950s and 60s sitting in a static queue of vehicles choking on the evil smell of petrol engine exhaust fumes and the nauseating smell of the black clouds of smoke belching from diesel lorries?

Improvements in technology in fuel, engine design and platinum based catalytic converters have almost eliminated this.

Also certainly up until the late 1960s on extremely cold mornings the diesel in the fuel tank and pipeline would go thick and refuse to flow, meaning the engine would not work.

Again on cold mornings it was sometimes necessary to use an aerosol spray of volatile liquid to give a short burst into the air filter intake.

This spray was not recommended for stubborn petrol engines.

Derek Weeks, Martin Way, Andover