The use of heavy fuel in marine diesels

Currently, all two-stroke and a significant part of four-stroke marine diesel engines have been converted to heavy fuel of degraded quality. This required not only additional fuel treatment on the ship, but also the use of heat-resistant and corrosion-resistant materials, and the improvement of the thermal process of the engines.


Large fuel savings are provided by the waste heat recovery systems of exhaust gases (exhaust gas) and cooling water of diesel engines. Deep recycling systems with a turbocompound unit have the greatest effect. The system was developed by Mitsubishi. The system consists of a recycling boiler that supplies two pressures of steam to a steam turbine that drives an electric generator. Due to the high efficiency of the diesel turbocharger, part of the exhaust gas is sent to the power gas turbine, then to the halogen generator (VG). If the additional power is not completely absorbed by electric consumers, then part of it is spent on rotating the propeller. This system fully provides all consumers with electric and thermal energy due to the utilization of exhaust gas heat. The turbocompound unit generates up to 15.4% of the power of the main engine (HD), i.e. from 150 to 300 kW.


MBD uses similar installations for the MS/MSE series of mods, reducing fuel consumption by up to 4%. The power turbine is connected to a gear train, through which it gives power to the GD or VG. The latter is connected to a planetary gearbox, which provides an increase in the speed of rotation of the VG to the required level. MBD and others widely use the Renk RCF transmission for power take-off from GD to VG, which ensures the stability of the VG rotation speed regardless of the operating mode of the GD. The circuit uses a hydrostatic speed control. The high efficiency of this transmission (from 93 to 97%) makes it more efficient than the electrical control system. The combination of RCF with a turbocompound system ensures reliable operation of the recycling and power take-off system. During the period of operation of 15,000 hours, the system had two failures.


Along with the use of single-fuel main and auxiliary engines running on heavy fuel (TT), dual-fuel gas-liquid marine diesels have been developed, which is associated with the conditions of transportation of liquid cargo on gas carriers. The fact is that part of the liquefied gas (methanol, natural gas, propane, etc.) evaporates and is used as fuel, since it is economically impractical to have a gas re-liquefaction unit on the ship. The diesel engine operates on a gas-liquid cycle with injection of a small amount of liquid fuel in the load range from 25 to 100%. An example of such an engine is the RTA84 two-stroke diesel engine from Sulzer, manufactured under license from IHI and powered by diesel fuel or TT and methanol. Of the four-stroke dual-fuel engines, the Vasa 4R22 diesel from Vyartsilya Diesel can be named, which runs on a mixture of gas and a 5% diesel fuel additive supplied to the diesel engine at a pressure of 25 MPa through valves installed on each cylinder. https://1winind.in/1win-app/