Latest Developments in Turbocharger Applications in Marine Diesel Engines

A Power Turbine Generator (PTG) is a system that utilizes the energy of exhaust gases from the main engine to drive an auxiliary turbine, which in turn drives a generator to produce electrical power. The turbine is usually connected downstream of the main turbocharger’s turbine. This setup offers several benefits:

• Enhances energy recovery by converting otherwise wasted exhaust gas energy into usable electricity.
• Assists in reducing fuel consumption by supplementing the ship’s electrical power demand.
• Improves overall plant efficiency and contributes to meeting emission control requirements.
• The generated power can be used for propulsion (as in electric propulsion ships) or to support auxiliary systems.

Hybrid Turbochargers (T/C) are designed to recover exhaust gas energy not only to turn the compressor, which supplies scavenge air to the main engine, but also to generate electricity. This is achieved through an alternator attachment integrated into the turbocharger, known as a Marine Energy Recovery Turbocharger (MET HYBRID T/C).

The core principle involves the turbine and compressor performing heat energy recovery, while the alternator generates electrical power without consuming additional fuel, as it is driven by the turbocharger's blower.

For a Hybrid T/C, three basic requirements are:

1. A conventional T/C with an extended shaft to accommodate an alternator at the blower end.
2. A specially designed, compact alternator capable of running at very high RPMs, around 9000 rpm.
3. A dedicated cooling system for the alternator, as its compact size and high RPM operation generate significant heat.

Working Principle:

The speed of the power mover directly governs the voltage and frequency of the electrical output. An initial DC power supply is provided to achieve the required output voltage and frequency. A hybrid system, when operating at 950 kW, can generate approximately 756 kW, which is sufficient to meet the full sea load of a normal-sized vessel.

The alternator and compressor are connected by a specially designed flexible coupling. Compared to a conventional system, a Hybrid T/C has an increased length of 313 mm and an additional weight of 4600 kg.

Construction:

The hybrid turbocharger features a two-part shell made from cast steel, fitted to the blower side. This shell is built with higher rigidity to support the alternator within the T/C silencer. The lower half of the shell is attached first and designed to act as a sump, collecting lubricating oil discharged from the alternator.

The intake filter and silencer are mounted above the alternator assembly, with sufficient gap to allow air to pass over the shell into the compressor blades. An oil/water jacket made of aluminum is provided around the rotor winding, and cooling air is supplied to both the extreme ends and the center of the windings.

An Electrically-Assist Turbocharger (EAT) incorporates an electric motor to assist in powering the compressor, particularly when exhaust gas flow is insufficient to produce the desired load.

A high-speed permanent magnet motor is directly mounted to the T/C in an overhung configuration, eliminating the need for additional bearings. This motor applies torque to accelerate the T/C's rotor at low engine exhaust flow rates (i.e., at low loads), ensuring sufficient charge air supply to enhance engine performance. This negates the requirement for a separate auxiliary power source.

EATs optimize performance during slow steaming, improving the main engine's fuel combustion efficiency and enabling comparable or better performance than traditional auxiliary blowers while consuming minimal power. An electro-assist T/C can save approximately 30% of electric power consumption compared to conventional auxiliary blowers.

Advantages:

• Ideal for slow steaming, providing improved engine performance at under-part and low loads.
• Compact design and enhanced reliability.
• Eliminates the need for a separate auxiliary blower.