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Some very long stroke engines have a maximum speed of around 80 rpm. The largest, most powerful engines in the world are slow speed, two stroke, crosshead diesels. Medium speed: any engine with a maximum operating speed in the range 300–1000 rpm. Many modern four-stroke medium speed diesel engines have a maximum operating speed of around 500 rpm.
The power output of medium-speed diesel engines can be as high as 21,870 kW, [169] with the effective efficiency being around 47-48% (1982). [170] Most larger medium-speed engines are started with compressed air direct on pistons, using an air distributor, as opposed to a pneumatic starting motor acting on the flywheel, which tends to be used ...
A typical turbocharged V8 diesel engine might have an engine power of 250 kW (340 hp) and a mass of 380 kg (840 lb), [1] giving it a power-to-weight ratio of 0.65 kW/kg (0.40 hp/lb). Examples of high power-to-weight ratios can often be found in turbines. This is because of their ability to operate at very high speeds.
While engines and motors have a large range of operating speeds, the power band is usually a much smaller range of engine speed, only half or less of the total engine speed range [1] (electric motors are an exception—see the section on electric motors below). Specifically, power band is the range of RPM around peak power output.
Such a propulsion system has a smaller footprint than a diesel-only power plant with the same maximal power output, since smaller engines can be used and the gas turbine and gearbox don't need that much additional space. Still, it retains the high fuel efficiency of diesel engines when cruising, allowing greater range and lower fuel costs than ...
The C32B is the most power-dense high-speed diesel engine [note 1] of Caterpillar. The engine can produce up to 2433 marine horsepower at 2300 rpm. [5] The peak torque of 5532 lb-ft occurs at an engine speed of 1300 to 1800 RPM. The engine has an iron block, painted in grey. The engine weighs over three tons at 7500 pounds. The C32B is used in ...
Diesel engines are typically well suited to turbocharging due to two factors: A "lean" air–fuel ratio, caused when the turbocharger supplies excess air into the engine, is not a problem for diesel engines, because the torque control is dependent on the mass of fuel that is injected into the combustion chamber (i.e. air-fuel ratio), rather than the quantity of the air-fuel mixture.
This made these medium-sized diesels a very popular choice for use in generator sets, replacing the hot bulb engine as the engine of choice for small-scale power generation. The development of small-capacity, high-speed diesel engines in the 1930s and 1940s, led to hot bulb engines falling dramatically out of favour.