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10 years of MaK VRT pressure charging: Variable turbine geometry optimises torque and reduces emissions
The capacity of marine diesel engines has increased steadily over the years. One of the methods chosen to achieve this was to continuously raise mean effective pressures. Unfortunately, the high-efficiency turbochargers used to do this cannot always sufficiently cover the air requirement of the engine in the part load range, which in turn results in torque losses and thermal overload.Torque weakness has a particularly negative effect on towage since tugs are often equipped with fixed-pitch propeller plants running at continually changing speeds.
MaK came up with a solution actually adjusting the engine's turbine during operation as early as the 1980s. Called Variable Multi Pulse (VMP) technology, it was used in the MaK M 332 C engine with axial turbine, particularly on tugs. When the new MaK long-stroke generation was launched from 1992, VMP technology was developed into VRT technology and adjusted to the KBB turbocharger models with radial turbine used for the M 20 and M 25 engine series.
The basic principle of VRT is as simple as it is convincing. The nozzle ring in the turbocharger consists of two parts with different cross sections (full load ring and part load ring). Depending on the engine load, either one or the other ring can be activated. The changeover between the two is fully automatic and affected by means of compressed air depending on engine speed and charging pressure. The nozzle ring simultaneously acts as an air cylinder, which eliminates the need for a complex adjusting mechanism.
After Michel became the first vessel to be equipped with this technology in 1998, many other tugs were provided with MaK engines types 8 M 20 and 8 M 25 that included the VRT technology. Daily use fully confirmed the expected improvements in torque characteristics and ramp-up behaviour. Further advantages are low thermal load on the engine, reduced exhaust emissions and low fuel consumption. The heavy fuel compatibility of VRT technology has also been proven in practice.
It only remains, then, to answer the question why Michel is no longer the toughest conventionally driven tug in Hamburg, despite her optimal MaK engine technology. It's because Michel got a bigger brother, "Peter", in September of last year. It goes without saying that this tug is also equipped with engines from Caterpillar Marine Power Systems (CMPS). Only this time, two high-speed engines Cat® 3516B were installed, each of 2,090 kW at 1,600 rpm.
Regardless of whether MaK or Cat marine engines are used, ship operators across the world swear by their power, reliability and longevity. Technical innovation is an integral part of the product philosophy as the market launch of MaK VRT technology confirmed in 1998 - at a time when competition was still looking for viable problem solutions to improve ramp-up behaviour, engine emissions and fuel consumption.
For more than 80 years, Caterpillar Inc. has been making progress possible and driving positive and sustainable change on every continent. With 2007 sales and revenues of $44.958 billion, Caterpillar is a technology leader and the world's leading manufacturer of construction and mining equipment, clean diesel and natural gas engines and industrial gas turbines.
More information is available at: www.Cat.com.
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