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So what’s the difference between N2 & NO2?

October 16, 2014

As published in Truck and Track magazine:

Bob Turnock of RWT Commercial Services gets straight to the point

A diesel engine in its raw state produces diesel particulate matter and the gas N2. Diesel particulate matter comprises the fine particles of soot that you find on the inlet side of the exhaust. The gas emitted in its raw state is N2 (nitrogen) and, were we not to put any restraints on the exhaust, the cancer-forming particulate matter (PM) and the N2 would be discharged into the atmosphere.

PM is a definite contributory factor to lung cancer and needs to be restrained. N2 is a gas lighter than air and so will discharge into the atmosphere. When a filter is fitted that incorporates a diesel oxidation catalyst (DOC), the N2 gas is converted into NO2 (nitrous oxide).

Unfortunately there is a risk that this filter will allow nitrous oxide to slip out and discharge into the atmosphere. This gas is heavier than air and will linger at pavement level. So the question is: what can we do to eliminate this gas from our urban environment?

The most favoured solution is to inject urea, commonly known as AdBlue, into the exhaust: this vaporises into ammonia. There are several other systems that use an ammonia base. So can we offer a retrofit NOX abatement system at a competitive price? The answer is “yes”.

A number of devices have been designed and developed by exhaust manufacturers to try to eliminate the problem – in many cases with success but also at a high cost, sometimes running to five figures per vehicle.

So the question then arises: is it viable to fit such devices to all commercial vehicles? Their residual value always needs to be taken into consideration, as does their model and uses. If we are talking about a straight flatbed tractor unit or curtainsider, then the cost of the retrofit may not be economically justifiable. However, for vehicles custom-built for special purposes, the cost is probably fully warranted.

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