Shortly before officials announced the January deadline for smoke emitting vehicles to comply with the laid down regulations or risk being rendered not –roadworthy, a good friend of mine had for several occasions, rather silently, complained about the issue of pollution on our roads.

There is this day; a misty  morning  traveling from the Northern Province to the capital rushing with the allowed maximum speed probably not to be late for the meeting.

He narrated to me how he was unable to overtake a truck because he could not see the road properly and any object in front of him.

The potato truck had turned the road and the atmosphere around into a thick miasma of black sooty mass. It even forced my friend to turn on the light, which also could not help as the miasma remained impervious.

So he had to accept the check offered by the truck.

This phenomenon is an experience that many a motorist and road users in general have gone through and the regulations to curb the omen is welcome and good news to both the truck owners and other road users like my friend.

What are the factors that make a truck to emit black thick smoke from its exhaust pipe?

An answer from an engineering point of view will not only excite you but also thrill many motorists bearing in mind that if the causal factors are rectified, then truck owners will save much fuel and increase their mileage to fuel ratio consumed.

When you study diesel engines closely, the black smoke is caused by an imbalance in the air to fuel ratio. It means there is a lot of fuel injected with less air for combustion.

Basically much fuel is used for the burning process yet little oxygen is supplied to ensure complete burning of the fuel. The result is incomplete combustion, less energy and the production of smoke residue is magnified.

During such incomplete combustion large diesel particles remain yet they should have been burnt and so they are emitted as waste through the exhaust pipe resulting in the black thick smoke.

Therefore a truck that emits such smoke will use much fuel in covering a small distance making the vehicle to be less profitable fuel wise hence a need for immediate corrective measures to achieve optimal fuel mileage ratio.

The common cause for the insufficient supply of oxygen to burn the fuel completely may be attributed to the following factors: faulty injectors, a faulty injector pump, bad air filter blocking the supply of oxygen, a bad EGR valve making the valve to clog or even a bad turbocharger.

Other reasons may be faulty cold start or a faulty advance/retard mechanisms, incorrect air/fuel ratio setting, low pressure turbocharger or leaks, dirty or worn fuel injectors having carbon deposits affecting spray patterns.

Carbon deposits in combustion chambers in lightly loaded engines may also trigger emissions of black smoke not forgetting sticking pistons, incorrect valve clearances, faulty valve stem seals, engine overload and high altitude as other probable causes.

A good number of the reasons stated above can be solved mechanically by replacing worn out or damaged components, keeping close engine checks including valve adjustments, regular servicing of air/fuel and oil filters is necessary.

Cleaning of the fuel injectors using effective and reliable fuel system cleaners can reduce effectively the emissions when done regularly.

There are other causes that may lead to persistent emission of black smoke even when the mechanical problems have been corrected. Factors such as engine overload and operations in high altitude may still lead to the emissions despite correcting the mechanical bottlenecks.

When a truck with a normal load climbs a hill, there are high chances it will produce the smoke. Why? Because always in high altitude areas, the supply of oxygen is low and the force to be overcome when climbing increases creating engine overload hence heavy emission.

With these factors in consideration, I think the enforcers of the black smoke ban should be considerate in this respect.  Remembering high altitudes affect the oxygen supply into the engine for complete combustion of the fuel and increase in engine load due to the height.

Protecting our environment from smoke pollution is the duty of all truck owners. The regulator should ensure the rules are followed and the mechanics should provide excellent maintenance on the engine since without excellent expertise, vehicle owners may be penalized for reasons emanating from poor mechanical work done by the mechanics.

Other external factors such as engine overload and altitude should also be put into consideration so that trucks plying high altitude areas can be shielded from heavy penalties.

The writer is an industrial engineer based in Kigali