HOW TO DIAGNOSE BLACK SMOKE IN AN ENGINE

We have all seen clouds of black smoke emanating from the exhaust stacks of heavy-duty diesel engines especially it is under high load or hard acceleration. The black smoke is composed primarily of elemental carbon from incomplete combustion of diesel fuel and traces of engine lubricant. The exhaust of a typical diesel engine contains elemental carbon (soot), semi-volatile organic hydrocarbons, sulfates (primarily sulfuric acid), and water vapor. Elemental carbon which is black is formed for a wide range of reasons when the diesel fuel charge in the combustion cylinder is incompletely combusted. Incomplete combustion occurs and soot is formed when there is an overabundance of fuel (both diesel fuel and lube oil), the insufficient residence time in the combustion zone, and/or non-availability of sufficient oxidants.

When having challenges with black smoke the following should be considered:

1. Leaking fuel injector

2. Turbocharger

3. Incorrect calibration of poppet valve and injector or nozzle

3. Exhaust restriction

4. Air shutoff or emergency shutdown

5. Poor fuel supply

6. Air inlet restriction

LEAKING FUEL INJECTOR

In an engine principle, the ideal air to fuel ratio is expected to be 14.5:1 for diesel engines, this is to help maintain a good and perfect working condition. But if the ratio of air is higher than that of the fuel the result will be seen in an exhaust pipe of the engine. And once this is notice, take off the injector or nozzle for proper cleaning, with a technician with good technical knowledge, your injectors or nozzles can be restored to function like new ones.

TURBOCHARGER

A supercharger driven by exhaust gases and power by the turbine is known as a turbocharger. Turbocharger performance influences all-important engine parameters, this includes power emissions and fuel economy.

EXHAUST RESTRICTION

This simply means the process where the engine is not allowed to breathe properly and it can be caused by exhaust blockage or leakage.

INCORRECT CALIBRATION OF ENGINE POPPET VALVE AND INJECTOR OR NOZZLE

All marine and industrial engines have specific calibration in valves and injectors based on the manufacturer’s manual. Therefore, due processes or steps are to be followed when calibrating or recalibrating an engine poppet valve or injector.

Special attention is needed when it comes to this area because if valves are calibrated wrongly it might result in valve drop that may lead to damage of top cylinder head or piston etc. And this would lead to downtime in operation therefore special attention is needed in valves clearance. Like in Detroit diesel engine (GM) the standard valve filler gauge for valve clearance is 0.40mm or 0.16inches and the clearance must be accurate.

In the case of injectors, if it is not properly timed, the needle would atomize excess fuel into the combustion chambers which will increase the time taken for combustion.

Simple steps for remedies include the following:

1. Recalibrate the injector

2. Check for dripping by pressurizing it with a require testing machine

3. Recalibrate valves with the required number of filler gauge

4. Check out for a worn tapped or rocker arm bracket.

AIR SHUTOFF OR EMERGENCY SHUTDOWN

Basically, the air shutoff or emergency shutdown of an engine serves as a respiratory system to the engine system. In humans' bodies, once your nose is choked up, one will find it difficult to breathe; so also it is in the case of a mechanical engine. If the system is choked up, the amount of air required for proper combustion will not be admitted, causing limited air during the power stroke and the outcome of this would be seen in exhaust pipe as "black smoke".

REMEDY:

Check and ensure that the air shutoff valve or solenoid is OK.

Replace solenoid if they are bad.

POOR FUEL SUPPLY

When troubleshooting fuel supply in an engine, the movement of fuel should come first for easy step by step findings.

Fuel movement is described as follows:

The fuel pump receives fuel from the service tank and sends the same to the water separator. From water separator, the fuel goes to primary and secondary filters, then, to injectors (two-stroke) or from filters to injection pump (four-stroke) then injection pump atomizes the amount of fuel given to nozzle to spray in combustion chambers with a compressed charge air in it. Finally, a power stroke takes place.

HOW WOULD POOR FUEL SUPPLY CAUSE BLACK SMOKE?

The ideal (theoretical) ratio of air to fuel for diesel engines is said to be 14.5:1; but, if the ratio of air is higher than that of fuel, the burning will not balance. Then the system will be experiencing black smoke as a result of poor fuel supply.

NOTE:

If your fuel filters are clogged with impurities, injectors or nozzle will not deliver the expected amount of fuel needed for proper burning. Leaking or dripping injectors or nozzles are other key elements leaving an exhaust pipe of an engine with black smoke because if leaking or dripping, excessive fuel would be delivered to combustion chambers.

STEPS FOR REMEDIES:

1. Check fuel line for restrictions or leakages

2. Change fuel filters

3. Recalibrate injectors

4. Recalibrate nozzles and injection

5. Reset injector control tube.

AIR INLET RESTRICTION

1. Turbine wheel to be inspected to ensure free movement

2. Check the aftercooler for air restrictions

3. Replace air filters

4. Check air manifold for leakage

We hope this article helped you greatly? To discuss how we can assist you further in everything on General Maintenance, Repairs and Installation of Diesel engines, gearbox, pneumatic systems, navigation equipment, Technical Retainership, Offshore Vessel Chartering, Marine Consultancy, Instrument/Panel Control, please call us on : (+234)706 247 6068 or visit www.ugpeotechnique.com