Emissions: Did you know?

With all engines, what goes in must come out. If you put in 1kg of fuel and 25kg of air, the end result will be 26kg of exhaust emissions.

All the atoms that enter the engine will also come out, but not necessarily as part of the same compounds they were in before.

The toxic substances contained in exhaust gas as it leaves the engine are known as 'primary pollutants', but once they have left the engine some of these may react with each other or with other compounds present in the atmosphere to create what are known as 'secondary pollutants'.

Examples of secondary pollutants include;

  • Ozone
  • Acid Rain
  • Photochemical smog
Blue Smoke
  • Blue smoke is caused by engine lubricating oil burning
  • The oil can enter the combustion chamber from several sources
  • Worn valve guides, or seals
  • Cylinder or piston ring wear
  • Cylinder glaze
  • Piston ring sticking
  • Incorrect grade of oil - too thin and getting past rings, or valve guides
  • Fuel dilution of the oil, making it too thin
  • Blue smoke is often evident at cold start, which can reflect reduced oil control due to carbon fouling deposits around the piston rings and/ or cylinder glaze. Blue smoke should not be evident at any stage
  • An engine may burn oil without the evidence of blue smoke, because good compression burns oil quite cleanly. However, it is not acceptable for any new engine or engine in good internal condition to burn large amounts of lubricating oil
White Smoke

White smoke is caused by raw, un-burnt fuel passing into the exhaust stream. Common causes include;

  • Incorrect fuel injection timing
  • Defective fuel injectors
  • Low cylinder compression
  • Low cylinder compression may be caused by leaking valves, sticking piston rings, ring wear, cylinder wear, or cylinder glaze. When white smoke occurs at cold start and then disappears as the engine warms up, the most common causes are fouling deposits around piston rings and/ or cylinder glazing
  • Continuous evidence of white smoke indicates a mechanical defect, or incorrect fuel timing
Part 2: Black Smoke
Black smoke is the most commonly emitted from diesel engines and indicates incomplete combustion of the fuel. Black Smoke causes can vary widely and include;
  • Incorrect fuel injection timing
  • Dirty or worn fuel injectors
  • Over fuelling
  • Faulty turbocharger or turbo lag
  • Faulty or dirty exhaust gas recycling (EGR) System
  • Incorrect valve clearance/ incorrect fuel to air ratio
Part 1: Black Smoke
  • Dirty or restricted air cleaner systems
  • Dirty Loading the engine
  • Poor fuel quality
  • Cool operating temperatures
  • Excessive carbon build-up in combustion and exhaust spaces
Black smoke can occur across the entire operating range, but is usually worse under full power, or during the lag before the turbocharger boosts air supply to match the fuel usage such as in the early stages of acceleration and during gear changes. Moderate turbo lag smoke is acceptable; otherwise black smoke should be hardly visible in a correctly running engine.