As human beings, owing to instinct we tend to panic on sighting smoke. Often times, we are sure that this is as a result of something burning (i.e. fire) for people in the safety industry, the color of the smoke is an indication of the properties of the burning material.
However, it is very unfortunate that little/no attention is paid when an internal combustion engine begins to give off smoke. Every engine works right with little emission and no visible smoke at first, but, overtime as wear and tear takes place and the internal components wilt away, the efficacy of the machine begins to reduce and emission become higher to the point of visible smoke coming out through the tail pipe or other vents of the machine. In some cases, a faulty sensor or component on the engine, alters its workings and performance also leading to higher emissions. Various countries have been able to set emission standard for automobiles and are enforcing the laws by refusing to re-validate the vehicles papers when found wanting.
Recently in Nigeria, some states have begun conducting emission test for vehicles, generators and equipment that run on internal combustion engines. As laudable as this is, the effect has not gone beyond revenue generation.
Vehicles, especially commercial transport operators bellowing with smoke (white, blue and black) have been seen carrying emission compliance stickers. While these stickers are supposed to show that the vehicle is environmentally friendly, reverse has been the case.
Now let us examine the causes of these smoke:
BLACK SMOKE: The engine is designed to generate power, to do this; it requires fuel as well as proper lubrication. A certain amount of fuel proportional to the load it has to carry is expected to be burnt. In this process, a certain ratio of air/fuel mixture is ideal. A tip in the balance of either results in poor performance of the vehicle as well as higher emission.
A vehicle is said to be experiencing rich air/fuel mixture when, the quantity of fuel is not proportional to the amount of air available. Either the fuel being dumped in the combustion chamber is too much or the flow of air is obstructed. In some cases the sensor that is responsible for the fuel air metering and others that regulate the performance of the engine could be faulty leading to alteration of the combustion process. The result of these is emission of black smoke from the tail pipe of the vehicle. When unchecked, the oil breaks down faster owing to huge carbon build-up due to incomplete combustion. Ultimately, the engine is ruined.
Fuel Injectors: A leaking or dripping fuel injector will cause a rich fuel condition.
Fuel Pressure Regulator: A stuck closed fuel pressure regulator will cause a rich fuel condition.
Fuel Return: A restricted fuel return line will cause a rich fuel condition.
Oxygen (Air/Fuel) Sensors: These are attached to the exhaust line to monitor the gases going through and sending signals to the Engine Control Unit for proper adjustment of the fuel trim. Faulty oxygen sensors will keep the system in an open loop (fuel guzzling) state
BLUE/GREY SMOKE: Moving parts in the engine need to do so without hindrance caused by friction. To ensure this, lubricants are used in engines. However, this lubricant is confined to a chamber to prevent it from being burnt in the combustion process. Rubber seals and rings are used to keep it in the lubrication chamber.
These are possible symptoms and causes:
Valve Seals: Leaking valve seals will cause blue/Grey smoke at startup because oil leaks past the seals into the cylinder after the engine shut down.
Valve Guides: Excessive clearance between the valve stem and the valve guide allows oil to leak past the gap into the cylinder.
Piston Rings: Worn or damaged piston rings will cause blow-by resulting in blue/Grey smoke.
Worn Cylinder Walls: Worn cylinder walls cause blow-by resulting in blue/Grey smoke.
PCV System: A stuck closed PCV (Positive Crankcase Ventiliation) valve will cause excessive crankcase pressure resulting in blue/Grey smoke.
WHITE SMOKE: The engine is doing so much of work and in the process generating so much heat. This needs to be properly dissipated to prevent overheating. The coolant also needs to stay within its designated enclosure to ensure effectiveness.
White exhaust smoke is an indication that coolant is burning in the combustion chamber.
These are possible causes:
Cylinder Head: A crack in the cylinder head (around the coolant jacket) will cause coolant to enter the combustion chamber.
Engine Block: A crack in the deck of an engine block near the coolant jacket will cause coolant to enter the combustion chamber.
Head Gasket: A damaged or blown head gasket will cause coolant to enter the combustion chamber resulting in white/Grey smoke coming from the tailpipe.
Going through all of the above mentioned, it is obvious that something has to be burning for a vehicle to emit any color of smoke and in most cases it is as good as burning MONEY!