Medium and Low-Speed Engines

D High-viscosity fuel for use in medium- and low-speed engines utilized in sustained load, constant-speed applications... 

A further differentiation is the fuel. Most high-speed engines are using high-quality standard diesel fuel like trucks or passenger cars. However, heavy fuel oil (HFO), which can contain a significant amount of sulfur (up to 5 %) [1], is the preferred fuel for medium- and low-speed engines. 

The diesel engine, being a reciprocating machine, is mechanically complex, and in arduous environments its wear rate can be high. Major overhauls on high-speed engines are usually stipulated at 15,000 running hours, which extends to 20,000 and 30,000 on medium- and low-speed machines, respectively. 

Fuels used in marine applications are quite diverse in their properties. Low-viscosity distillate fuels and high-viscosity residual fuels can both be considered marine fuels. The applications, though, would differ and could include use in direct injected diesel engines, boilers, and gas turbines. Also, high-speed, medium-speed, and slow-speed engines can be found in marine applications. 

These are fuels for low and medium speed engines or as a feedstock for catalytic cracker refining... 

An important difference between high-speed and low- or medium-speed engines with respect to the exhaust system is the fuel. 

Winter grade diesel fuel oil is recommended for use in ambient temperature environments as low as -25.6°F (-32°C). It is intended for use in high-speed automotive-type diesel engines and nonaircraft-type turbine engines. This fuel may be used for medium-speed stationary engine applications. 

Systems for low- or medium-speed diesel engines used as gendrive or for propulsion of ships with fixed propellers often work with look-up tables or a characteristic curve as input for an open-loop reductant dosing control (Fig. 2.31). As the engines only use a small band within the engine map (Fig. 2.32) the NOx-emission and thus the reductant dosing rate has a fixed correlation to either engine speed or load. 

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