MOT Diesel Emissions test numbers

Webley1991 · Aug 13, 2019

Can anyone here explain exactly what the MOT diesel emissions test is measuring?

I have asked an MOT tester before and they admitted they had no idea what the numbers or units really meant. They only knew it was a fail if the machine read above the upper limit.

For example, according to the official government website, a turbo diesel engine first used before July 2008 should have an upper limit of 3.0m-1. The page does not explain what the m-1 unit actually means.

Thanks for any replies.

Pappasmurf · Aug 13, 2019

Theres a sticker on the inside of the engine bay with the number on isn't there?

Al2O3 · Aug 13, 2019

Webley1991 said:
Can anyone here explain exactly what the MOT diesel emissions test is measuring?

I have asked an MOT tester before and they admitted they had no idea what the numbers or units really meant. They only knew it was a fail if the machine read above the upper limit.

For example, according to the official government website, a turbo diesel engine first used before July 2008 should have an upper limit of 3.0m-1. The page does not explain what the m-1 unit actually means.

Thanks for any replies.

A diesel vehicle is allowed to emit a certain 'amount' of soot particles. The 3.0m-1 refers the the number of moles (m) of soot, you are allowed to emit. A mole is a more pure scientific way of describing a volume of 'stuff'. It is equal to the molar mass divided by the molar density, which is why the negative exponent (-1) is there.

Webley1991 · Aug 15, 2019

Thanks for the reply. I vaguely remember moles being mentioned in secondary school science.

MOT Diesel Emissions test numbers

Webley1991

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Pappasmurf

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Al2O3

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Webley1991

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