Editing Diesel engine (section)

=== RPM operating range ===
Günter Mau categorises diesel engines by their rotational speeds into three groups:<ref name="Mau_1984_15" />
* High-speed engines (> 1,000 rpm),
* Medium-speed engines (300–1,000 rpm), and
* Slow-speed engines (< 300 rpm).

; High-speed diesel engines
High-speed engines are used to power [[truck]]s (lorries), [[bus]]es, [[tractor]]s, [[automobile|cars]], [[yacht]]s, [[Gas compressor|compressors]], [[pump]]s and small [[electrical generator]]s.<ref name="Reif_2014_11" /> As of 2018, most high-speed engines have [[Direct fuel injection|direct injection]]. Many modern engines, particularly in on-highway applications, have [[common rail]] [[Direct fuel injection|direct injection]].<ref name="Tschöke_2018_295" /> On bigger ships, high-speed diesel engines are often used for powering electric generators.<ref name="Mau_1984_42" /> The highest power output of high-speed diesel engines is approximately 5&nbsp;MW.<ref name="Mau_1984_43" />

; Medium-speed diesel engines
[[File:12 Cylinder Diesel Engine.jpg|thumb|right|Stationary 12 cylinder turbo-diesel engine coupled to a generator set for auxiliary power]]
Medium-speed engines are used in large electrical generators, railway [[diesel locomotive]]s, ship propulsion and mechanical drive applications such as large compressors or pumps. Medium speed diesel engines operate on either diesel fuel or heavy fuel oil by direct injection in the same manner as low-speed engines. Usually, they are four-stroke engines with trunk pistons;<ref name="Mau_1984_33" /> a notable exception being the [[EMD 567]], [[EMD 645|645]], and [[EMD 710|710]] engines, which are all two-stroke.<ref>{{Cite conference |last=Kettering, E.W. |date=29 November 1951 |title=History and Development of the 567 Series General Motors Locomotive Engine |url=https://books.google.com/books?id=QuUiAQAAMAAJ |conference=ASME 1951 Annual Meeting |location=Atlantic City, New Jersey |publisher=Electro-Motive Division, General Motors Corporation}}</ref>

The power output of medium-speed diesel engines can be as high as 21,870&nbsp;kW,<ref name="Mau_1984_136" /> with the effective efficiency being around 47-48% (1982).<ref name="Mau_1984_121" /> 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 for smaller engines.<ref name="Merker_2014_280" />

Medium-speed engines intended for marine applications are usually used to power ([[Roll-on/roll-off|ro-ro]]) ferries, passenger ships or small freight ships. Using medium-speed engines reduces the cost of smaller ships and increases their transport capacity. In addition to that, a single ship can use two smaller engines instead of one big engine, which increases the ship's safety.<ref name="Mau_1984_33" />

; Low-speed diesel engines
[[File:5S50MC.jpg|thumb|right|The MAN B&W 5S50MC, a two-stroke, low-speed, [[straight-five engine|inline five-cylinder]] marine diesel engine on board a 29,000 tonne chemical carrier]]

Low-speed diesel engines are usually very large in size and mostly used to power [[ship]]s. There are two different types of low-speed engines that are commonly used: Two-stroke engines with a crosshead, and four-stroke engines with a regular trunk-piston. Two-stroke engines have a limited rotational frequency and their charge exchange is more difficult, which means that they are usually bigger than four-stroke engines and used to directly power a ship's propeller.

Four-stroke engines on ships are usually used to power an electric generator. An electric motor powers the propeller.<ref name="Mau_1984_15" /> Both types are usually very [[Stroke ratio#Undersquare or long-stroke engine|undersquare]], meaning the bore is smaller than the stroke.<ref name="Mau_1984_129" /> Low-speed diesel engines (as used in ships and other applications where overall engine weight is relatively unimportant) often have an effective efficiency of up to 55%.<ref name="Reif_2014_13" /> Like medium-speed engines, low-speed engines are started with compressed air, and they use heavy oil as their primary fuel.<ref name="Merker_2014_280" />