4102 Diesel Engine Emissions

Whilst diesel fuel is derived from the distillation of the same crude oil as petrol, it has quite different properties in terms of volatility and viscosity. It has a similar composition to petrol, in terms of carbon and hydrogen content, but the method of mixing air and fuel in the combustion chamber and the high pressures required to produce spontaneous combustion cause there to be quite different conditions inside the combustion chamber. These different conditions cause smoke (soot) and NOx to be the main areas of concern with regard to diesel engine emissions.

NOx is reduced by exhaust gas recirculation and accurate control of fuelling. The test for compliance with the regulations requires the use of an analyser that measures the opacity (denseness) of the smoke and for test purposes the opacity is measured in units that are given the symbol K. When the tests were first introduced in the UK, two maximum readings were used: for naturally aspirated engines (no turbocharger) the level was K = 3.2; and for turbocharged engines the maximum permitted level was K = 3.7.

Difficult starting

Irregular Idle and Fast Idle

:ient Maximum

Erratic Running/Surging Excessive Smoke_

Excessive Noise Lack of Power ~

Excessive Fuel Consumption


Slow Engine Die-down

Engine cannot be Shut Off

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