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Which is dirtier, petrol or diesel?

2013-11-07 08:26

TESTING TIME: Dirty exhaust gases cause 25% of vehicles in the UK to fail their annual Ministry of Transport test - but which is worse, petrol or diesel? Image: AP

LONDON, England - The most recent test data in the UK shows that excess exhaust emissions account for more than a 25% of all failures in annual vehicle licence tests.

What was surprising, perhaps, was that petrol-fuelled cars were twice as polluting as diesels (10% against 4%). Which should give the lie to general belief that diesel engines "are dirty".

The figures have been released by fuel-additive provider Redex which produces additives that minimise engine emissions by breaking down engine carbon deposits that prevent the efficient, clean running of vehicle fuel systems. The company analysed data from transport ministry testing stations across Britain.


The most recent data (2010 and the first nine months of 2011) shows that about 48-million MOT tests were done over that period and that 14.5-million vehicles failed the test, 3.8-million were refused a certificate because their exhaust emissions exceeded permitted levels.

Bruce Ellis, research and development manager at Redex, said: "There are a number of possible explanations for the marked difference in MOT emissions failure rates between petrol and diesel cars - among them their varying driving cycles. Petrol cars are more likely than diesels to be chosen for frequent short urban trips; diesels for longer freeway journeys.

"Also, diesels operate at lower engine speeds and so are a little less stressed than higher-revving petrol engines.

“The most obvious explanation is likely to be the test itself. Petrol cars are assessed for a high number of gases and hydrocarbons in the exhaust emissions, diesels are tested only for smoke levels, so relatively speaking diesels probably have an easier emissions test than petrol cars.”

So, the diesel/petrol debate continues...

Ellis added: "For modern as well as older cars – petrol or diesel – regular use of a quality fuel system additive reduces carbonaceous deposits that can restrict the fuel flow through the engine’s injectors. Blocked injectors can reduce the efficiency of combustion, leading to increased exhaust emissions.

"Obstructed fuel systems can also increase fuel consumption.”

Read more on:    britain  |  pollution

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