Editing Diesel engine (section)

==Diesel engine particularities==

===Mass===
The average diesel engine has a poorer power-to-mass ratio than an equivalent petrol engine. The lower engine speeds (RPM) of typical diesel engines results in a lower [[Power (physics)|power]] output.<ref name="Braess_2012_225" /> Also, the mass of a diesel engine is typically higher, since the higher operating pressure inside the combustion chamber increases the internal forces, which requires stronger (and therefore heavier) parts to withstand these forces.<ref name="Schreiner_2014_22" />

=== Noise ("diesel clatter") ===
[[File:AKD 112 Z.webm|thumb|Engine noise of a 1950s [[MWM AKD 112 Z]] two-cylinder diesel engine at idle]]
The distinctive noise of a diesel engine, particularly at idling speeds, is sometimes called "diesel clatter". This noise is largely caused by the sudden ignition of the diesel fuel when injected into the combustion chamber, which causes a pressure wave that sounds like knocking.

Engine designers can reduce diesel clatter through: indirect injection; pilot or pre-injection;<ref name="Böge_2017_1150" /> injection timing; injection rate; compression ratio; turbo boost; and [[exhaust gas recirculation]] (EGR).<ref name="EngTips" /> Common rail diesel injection systems permit multiple injection events as an aid to noise reduction. Through measures such as these, diesel clatter noise is greatly reduced in modern engines. Diesel fuels with a higher [[Cetane number|cetane rating]] are more likely to ignite and hence reduce diesel clatter.<ref name="Comb in IC" />

===Cold weather starting===
In warmer climates, diesel engines do not require any starting aid (aside from the [[Starter (engine)|starter motor]]). However, many diesel engines include some form of preheating for the combustion chamber, to assist starting in cold conditions. Engines with a displacement of less than 1&nbsp;litre per cylinder usually have [[Glow plug (diesel engine)|glowplugs]], whilst larger heavy-duty engines have [[flame-start system]]s.<ref name="Reif_2014_136" /> The minimum starting temperature that allows starting without pre-heating is 40&nbsp;°C (104&nbsp;°F) for precombustion chamber engines, 20&nbsp;°C (68&nbsp;°F) for swirl chamber engines, and 0&nbsp;°C (32&nbsp;°F) for direct injected engines.

In the past, a wider variety of cold-start methods were used. Some engines, such as [[Detroit Diesel]] engines used{{When|date=September 2010}} a system to introduce small amounts of [[Diethyl ether|ether]] into the inlet manifold to start combustion.<ref name="FreeLib_1995" /> Instead of glowplugs, some diesel engines are equipped with starting aid systems that change valve timing. The simplest way this can be done is with a decompression lever. Activating the decompression lever locks the outlet valves in a slight down position, resulting in the engine not having any compression and thus allowing for turning the [[crankshaft]] over with significantly less resistance. When the [[crankshaft]] reaches a higher speed, flipping the decompression lever back into its normal position will abruptly re-activate the outlet valves, resulting in compression − the flywheel's [[mass moment of inertia]] then starts the engine.<ref name="Hawks_73" /> Other diesel engines, such as the precombustion chamber engine XII Jv 170/240 made by Ganz & Co., have a valve timing changing system that is operated by adjusting the inlet valve camshaft, moving it into a slight "late" position. This will make the inlet valves open with a delay, forcing the inlet air to heat up when entering the combustion chamber.<ref name="Kremser_1942_190" />

=== Supercharging & turbocharging ===
[[File:BMW_E28_engine_2_16.09_JM.jpg|thumb|1980s [[BMW M21]] passenger car turbo-diesel engine]]
{{see also|Turbo-diesel}}
[[Forced induction]], especially turbocharging is commonly used on diesel engines because it greatly increases efficiency and torque output.<ref name="Reif_2014_41" /> Diesel engines are well suited for forced induction setups due to their operating principle which is characterised by wide ignition limits<ref name="Pischinger_2016_348" /> and the absence of fuel during the compression stroke. Therefore, knocking, pre-ignition or detonation cannot occur, and a lean mixture caused by excess supercharging air inside the combustion chamber does not negatively affect combustion.<ref name="Reif_2017_16" />