Green shipping: Saving fuel with precise torque measurements

The marine industry is in a state of transformation around the world. Mandatory step-by-step reduction of pollutant emissions produced by shipping traffic has been regulated by the international MARPOL Convention. This has led to an advance in engines that are able to burn different types of fuel such as Liquefied Natural Gas (LNG). The gas supply to the engine can be controlled using a precise load signal from the drive shaft. This makes it possible to achieve the required reduction in pollutant emissions. HBM has developed a torque transducer specially designed for to adhere to these regulations in the marine industry, theT40MAR. Within a few years, emission levels in shipping will have to be drastically reduced, according to the requirements of the MARPOL Convention. To comply with these requirements, the marine industry is following two different approaches:

After-treatment of exhaust gases for conventional drives
Development of new, cleaner drives

Alternative drives on the rise

After-treatment of exhaust gases for conventional drives refers to exhaust gas recirculation, particle filters and catalytic converters. Expensive components must also be installed for this purpose. The challenge is to achieve the lowest possible fuel consumption to operate them. The development of new, clean drives is led by engines that are able to burn different types of fuel, such as all conventional marine fuels plus LNG. The advantage of this type of drive is that it burns very cleanly, making it possible to achieve the required lower exhaust gas levels easily. LNG is also more costeffective than oil and will be available for longer in the future as a resource. Engines that can burn different types of fuel must be able to switch quickly from one fuel to another – without any loss of power. When the engine is running in LNG mode, critical operating states must also be reliably prevented. This is achieved by a sensitive controller whose most important element is a load signal with very low tolerances. This ensures that depending on the navigating situation, the engine is always in an optimum operating state. Additionally, this offers considerable fuel savings.

Load signal generated by torque measurement

The rotational speed and torque must be measured to generate the load signal. Until now the torque of large marine engines has been determined indirectly, by measuring auxiliary quantities and then calculating torque. The disadvantage of this is that the measurement uncertainty is very high and very difficult to verify. Installing a measurement flange calibrated to the torque as a measurement directly onto the drive train enables direct and very precise measurements with measurement uncertainty that can be clearly demonstrated. An overall measurement uncertainty of well under 1 % can be achieved, as the accuracy class of the torque transducer itself is 0.1. The very short signal run times also make it possible to implement control commands quickly. HBM offers a torque sensor for use with the T40MAR, specially developed for the drive systems of ships. The transducer has analog and digital signal outputs and allows for direct torque measurements up to 400 kNm. T40MAR is easy to install and parameterize. Measurement signals are also transferred without contact.