Cleaning the fuel carried on board by cleaning the fuel separator, filtration and sedimentation. Advocated in the slop oil tanks. The process of sedimentation is deposited on the bottom of the vessel under the influence gravitational forces of mechanical impurities and water. At the same time, from dirt to mud and fall partly Asphaltic-resinous compounds. The speed of deposition of various impurities depends on their weight, size and shape, as well as the viscosity of the fuel. The greater the difference in specific weights and fuel impurities and less fuel viscosity, the higher deposition rate.

Therefore the process of settling of diesel fuel, which has in comparison with Heavy fuel less dense proceeds more rapidly. To reduce the viscosity of heavy fuel oil (heavy oil) in the slop tanks are usually heated to 60-70 C by steam heating elements with thermostats, automatically maintaining the correct temperature. Marine fuel is filtered based on the separation of impurities contaminating its size due to the difference-through cells or slits filter and filter out particles. Fuel is filtered out in stages en route from the stock tank to fuel pump motors. In toplivoperekachivayuschih and receiving marine pump separators are placed coarse filters.

Ship separator cleans the fuel from water and small particles. After the fuel separator, it enters the supply tanks. From there goes to the engines. Before the fuel pump filters are usually applied with a finer mesh or slotted. Before engine installed fine filters. Coarse filters, the main purpose of which is the detention of large mechanical parts, are meshed with the filter elements from metal grids and slotted with filter elements drawn from separate plates (disks). In one case equipped with two filter elements, one of which can be cleaned while the other will work. Pressure drop before and after the filter typically amounts to 0.2 kgf/cm2, increasing the pressure drop over 0.4 kgf/cm2 indicates contamination, and the lack of difference – the fault filter (break the grid). Filtering materials of fine filters are special paper, felt, felt, porous bronze, ceramics, etc. In contrast to the pre-filter wash their filtering ability is not fully recovered, so these elements are periodically replaced. In recent time the work is automated pre-filter, cleaning is carried out by washing the reverse flow of fuel, which then together with the dirt down into the mud tank. For smooth, reliable operation of the fuel system sizes remaining in the fuel filter after the mechanical parts must be smaller than the gap in high-precision pairs of pumps and nozzles, and therefore should not exceed 3-5 nm.

Distinguish steady and unsteady modes of ship power plant. As mentioned, the steady state is characterized by the constancy of the thermal state of the diesel engine parts. For transient modes of the diesel is characterized by instability of its technical and economic characteristics. In accordance with state standards distinguish the following basic modes of operation of diesel engines: nominal (full), maximum and minimum capacity, as well as treatment of minimally stable engine speed. Nominal mode (full) characterizes the effective power of long-term operation of diesel in rated crankshaft speed set by the manufacturer.

The value of the maximum allowable effective performance of diesel engines, which he can develop a limited time set manufacturer determines the maximum power mode. For marine diesel engines are not allowed to work more than 1 h with an overload of the power by 10%, and engine speeds – 3% above nominal. Long-term operation diesel at the lowest effective power, guaranteed by the manufacturer, describes the minimum power mode. The minimum effective capacity of 10-20% of the nominal, is determined to reduce the limit ship's speed. Mode of minimally stable engine speed marine diesel engine determines the maneuverability of the vessel. In this mode, the energy resources of diesel used by 3-4% rated power and 30% of the nominal speed of the crankshaft. The duration of the diesel in this mode should not exceed 2-3 h. In addition to the standard modes, marine diesel engines can also work on modes of operating power and idling.

By operating power include high power diesel engine for the planned load and speed of the vessel. For cargo ships, it is 85 – 90% of rated capacity for towing – 90-95%. In determining the targets of the ship on the operational performance of diesel fuel consumption is normalized. Plants that are shipping the device for separation of the propeller shaft diesel engines can operate and at idle speed. Diesel operation in this mode is accompanied by significant non-uniformity of the fuel, and sometimes pass outbreaks in the cylinders, leading to carbon formation on the pistons, seals rings, valves, spray nozzles, and therefore the duration of idling must not exceed 0.25-0.5 hours in exceptional cases, related to the preservation of people or cargo, the watch chief may decide to inclusion in the work and faulty diesel engines. This mode of operation is called EMS emergency. Sometimes in an emergency mode of operation of diesel engines is provided if necessary for the craft to the point of repair. In this case, the watch chief (mechanic) must be organized under constant watch in the engine room to closely monitor the technical condition of the diesel engine.