Marine Revive | Keep Marine Engines Healthy

MARINE TURBOCHARGERS

Modern diesel engines rely on turbochargers to maximise performance. Whilst major internal engine breakdowns do occur, failure of water pump or fuel pumps are quite common, failures of turbochargers are a regular occurrence.

Turbochargers are prone to trouble, due to the high component speed, heat and vibration. It is therefore prudent to be aware of the symptoms of impending problems and to minimise the risk of failure. Understanding how a turbocharger works is a good step.

HOW IT WORKS

COMPRESSING ENERGY

A diesel engine compresses fuel and oxygen with enough pressure to create a controlled explosion. The more energy produced in this reaction, the more power that can be delivered to your propeller. The volume of fuel and oxygen is limited by the size of each cylinder, if more power is required the engine needs to squeeze more oxygen (and fuel) into each cylinder measure of air.

As fuel heats up, it expands. This expansion means a loss of energy. This principle also applies to air. A cubic foot of air that heats up and expands will contain less oxygen (and therefore less energy) than cooler air. Although if the air is compressed the air will contain more oxygen, improving combustion and therefore engine performance. This is the function of a turbocharger, by forcing air into the cylinders, compressing it to increase the combustion and power.

HOW A TURBO CHARGER WORKS

The cast housings of turbochargers contain the turbine wheel, the compressor wheel, connected by an axle. Bearings are lubricatedby oil from the engine, whilst engine coolant helps reduce heat.

The turbocharger is similar to a high-speed fan.The turbine blades accelerate the airflow, powered by the engine’s exhaust gas, the turbine on one end of the axle spins at a remarkably high rate. This high-speed rotation also spins the compressor wheel and this process forces compressed air into the engine.

Exhaust gas (red) enters the chamber and spins the turbine on the right before exiting into the exhaust system. At the other end of the axle a compressor wheel then turns, forcing air into the engine at the top-left (blue). The blue on the exhaust side (right) shows coolant circulation from the engine.
Courtesy: Borg Warner TurboSystems

COOLING THE AIR

Converting the energy from the exhaust gas into compressed air for the engine’s air intake generates heat, which in turn reduces efficiency. As compressed air heats up, there is less energy going to the engine.

To counter this there is usually some form of cooler system, or heat exchanger. These are often referred to as intercoolers. This heat exchanger is designed to reduce the temperature of the compressed air and increase its density before it enters the cylinders.

COMMON FAILURES

Poor lubrication of the rotating components is a common cause of failure. Due to the incredibly high rotation speeds of the turbines, a lack of lubrication can have a devastating effect. It is prudent to maintain the engine with good quality oil as this is likely to prolong both the life of the engine and the turbocharger.

Another common cause of turbocharger failure is foreign material entering the turbine or the compressor. This is often on the compressor side of the turbocharger, where it is designed to run on clean air. An appropriate, and well maintained air filter, will help protect the air intake side. Foreign material entering the exhaust side of the turbocharger, no matter how small, will cause serious damage to the thin, precise vanes on the turbine. The foreign material can be bits of internal metal components, degrading gaskets or hose. Given the velocity of rotation and the relatively fragile nature of the components, it doesn’t take much to cause damage that can put your turbo out of commission.

Marine turbochargers also have continual exposure to salt air. Over time this exposure corrodes turbocharger housing. This has the effect of gradually increasing the clearance between the turbine blades and the housing, leading to a loss of boost pressure. The engine will suffer from reduced performance and often excessive exhaust smoke.

Running an engine at low rpm can cause a buildup of carbon deposits on the turbine blades,also inside the housing. Due to the small tolerances of the turbocharger turbine wheels any carbon layers on the blades can cause an imbalance, creating vibration, excessive bearing wear, and a potential breakage of the blades. A common symptom is a large soot deposit at the exhaust discharge.