Cost Effective Maintenance advise that visible smoke from a diesel engine indicates that something is not right. It should be taken as an indication that there is a problem existing that will potentially shorten the engine life or result in unnecessary costs. It should be regarded as an opportunity to take measures that will save money in both long and short terms. At the least, that smoke may be due to a simple problem, that is causing poor combustion efficiency and resulting in excessive fuel bills (carboned up engine from excessive idling, stop start operation or short run times). At the other end of the scale, it may be the last chance to act, before a catastrophic engine failure occurs ( piston seizure, valve or turbocharger failure).
A diesel engine in good condition should produce no visible smoke from the exhaust, under most operating conditions. A short puff of smoke when an engine is accelerated under load may be acceptable, due to the lag before the turbocharger speed and air flow is able to match the volume of diesel injected into the cylinders. This would only apply to older technology diesel engines, but with modern type diesels, no smoke should be evident.
The value in focusing on minimising smoke was demonstrated to a large bauxite mine, which as a result, consistently achieved better than 20,000 hours service life from their Caterpillar 3500 Series engines.
There are three basic types of smoke, as identifiable by their colour. Black smoke is the most common smoke emitted from diesel engines. It indicates poor and incomplete combustion of the diesel fuel.
Following are some of the causes for black smoke:
- Incorrect timing
- Dirty or worn injectors
- Over-fuelling
- Faulty turbocharger (not enough air to match the fuel)
- Incorrect valve clearance
- Incorrect air/fuel ratio
- Low cylinder compression (sticking piston rings or worn components)
- Dirty air cleaner
- Restricted induction system (system too small or kinked inlet piping)
- Other engine tune factors
- Poor quality fuel
- Excessive carbon build up in combustion and exhaust spaces
- Cool operating temperatures
Worn or damaged components must be replaced. Earlier identification fixes the problem and less damage will occur. Engine tune issues including valve adjustments, and regular servicing of air, fuel and oil filters should be checked. Individuals should also avoid buying fuel from suspect outlets. Dirty components, such as injectors can be easily restored to full cleanliness by using an effective and reliable fuel system cleaner. Cleanpower from Cost Effective Maintenance is a reliable fuel system cleaner.
Cleaning of internals of engines has usually been possible at overhaul; however, Cost Effective Maintenance provide two products to enable vehicle and equipment owners to quickly and safely restore full cleanliness to combustion and exhaust spaces (FTC Decarboniser) as well as piston rings, oil pumps, oil galleries, oil coolers, piston skirts and valve gear (Flushing Oil Concentrate).
Black smoke is high in carbon or soot, which is an undesirable product of diesel combustion. The combustion of diesel is a complicated process of breaking down of various hydrocarbon fuel molecules into progressively smaller molecules, by burning in the presence of oxygen. The main and ideal end products of combustion are CO2 and H2O (carbon dioxide, the greenhouse gas and water). It is believed that the last step in the process is carbon monoxide (the poisonous gas) to carbon dioxide. This is also the slowest step by far, and when combustion conditions deteriorate, some upstream bottle necking occurs in the chain of combustion reactions. This results in polymerisation of smaller partly burnt molecules into much larger ones, which become visible as soot or black smoke.
Blue smoke is an indication of oil being burnt. The oil can enter the combustion chamber for the following reasons.
- Worn valve guides or seals
- Wear in power assemblies (cylinders, piston rings, ring grooves)
- Cylinder glaze
- Piston ring sticking
- Incorrect grade of oil ( oil too thin and migrating past the rings)
- Fuel dilution in the oil (oil thinned out with diesel)
At cold start, blue smoke is often evident, and can reflect reduced oil control, due to fouling deposits around piston rings or cylinder glaze, which is actually carbon deposited in the machined cylinder crosshatching. These tiny grooves actually hold a film of oil, which in turn completes the seal between the combustion chamber and the oil wetted crankcase. Blue smoke should not be evident at any time, but it is worth noting, that engines with good sound compression can burn a lot of oil without evidence of blue smoke. Good compression allows oil to burn cleanly, as part of the fuel.
Restore physical cleanliness to all components and replace worn parts where necessary. In some situations, where the engines are worn, cleaning with the previously mentioned products, followed by effective additional anti-wear protection, will reduce internal stresses on all those tired components, providing extended service life. AW10 Antiwear, from Cost Effective Maintenance, achieves these criteria.
White smoke occurs when raw diesel comes through, the exhaust remains intact and unburned. Some causes for white smoke include:
- Faulty or damaged injectors
- Incorrect injection timing (could be a worn timing gear or damaged crankshaft keyway).
- Low cylinder compression (e.g. caused by leaking or broken valves, piston ring sticking, cylinder and/or ring 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. Use of Flushing Oil Concentrate and FTC Decarboniser from Cost Effective Maintenance address these respective problems.
Water entering combustion spaces will also create white smoke. Faulty head gaskets and cracked cylinder heads or blocks are a common cause of water entry.