Editing Diesel engine (section)

==Fuel and fluid characteristics==
{{Main|Diesel fuel}}

Diesel engines can combust a huge variety of fuels, including several fuel oils that have advantages over fuels such as petrol. These advantages include:
* Low fuel costs, as fuel oils are relatively cheap
* Good lubrication properties
* High energy density
* Low risk of catching fire, as they do not form a flammable vapour
* [[Biodiesel]] is an easily synthesised, non-petroleum-based fuel (through [[transesterification]]) which can run directly in many diesel engines, while gasoline engines either need adaptation to run [[synthetic fuel]]s or else use them as an additive to gasoline (e.g., [[ethanol]] added to [[gasohol]]).
In diesel engines, a mechanical injector system atomizes the fuel directly into the combustion chamber (as opposed to a [[Aspirator (pump)|Venturi jet]] in a carburetor, or a [[Fuel injection|fuel injector]] in a manifold injection system atomizing fuel into the intake manifold or intake runners as in a petrol engine). Because only air is inducted into the cylinder in a diesel engine, the compression ratio can be much higher as there is no risk of pre-ignition provided the injection process is accurately timed.<ref name="Reif_2017_16" /> This means that cylinder temperatures are much higher in a diesel engine than a petrol engine, allowing less volatile fuels to be used.

[[File:MAN 630 L2A 03.jpg|thumb|The MAN 630's [[M-System]] diesel engine is a petrol engine (designed to run on NATO F 46/F 50 petrol), but it also runs on jet fuel, (NATO F 40/F 44), kerosene, (NATO F 58), and diesel engine fuel (NATO F 54/F 75)]]

Therefore, diesel engines can operate on a huge variety of different fuels. In general, fuel for diesel engines should have a proper [[viscosity]], so that the [[injection pump]] can pump the fuel to the injection nozzles without causing damage to itself or corrosion of the fuel line. At injection, the fuel should form a good fuel spray, and it should not have a coking effect upon the injection nozzles. To ensure proper engine starting and smooth operation, the fuel should be willing to ignite and hence not cause a high ignition delay, (this means that the fuel should have a high [[cetane number]]). Diesel fuel should also have a high [[lower heating value]].<ref name="vPhilippovich_1939_41" />

Inline mechanical injector pumps generally tolerate poor-quality or bio-fuels better than distributor-type pumps. Also, indirect injection engines generally run more satisfactorily on fuels with a high ignition delay (for instance, petrol) than direct injection engines.<ref name="vPhilippovich_1939_45" /> This is partly because an indirect injection engine has a much greater 'swirl' effect, improving vaporisation and combustion of fuel, and because (in the case of vegetable oil-type fuels) [[lipid]] depositions can condense on the cylinder walls of a direct-injection engine if combustion temperatures are too low (such as starting the engine from cold). Direct-injected engines with an [[M-System|MAN centre sphere combustion chamber]] rely on fuel condensing on the combustion chamber walls. The fuel starts vaporising only after ignition sets in, and it burns relatively smoothly. Therefore, such engines also tolerate fuels with poor ignition delay characteristics, and, in general, they can operate on petrol rated 86 [[Octane rating#Research Octane Number (RON)|RON]].<ref name="MAN_438" />

===Fuel types===
In his 1893 work ''[[Theory and Construction of a Rational Heat Motor]]'', Rudolf Diesel considers using [[coal dust]] as fuel for the diesel engine. However, Diesel just ''considered'' using coal dust (as well as liquid fuels and gas); his actual engine was designed to operate on [[petroleum]], which was soon replaced with regular [[petrol]] and kerosene for further testing purposes, as petroleum proved to be too viscous.<ref name="Diesel_1913_107" /> In addition to kerosene and petrol, Diesel's engine could also operate on [[ligroin]].<ref name="Diesel_1913_110" />

Before diesel engine fuel was standardised, fuels such as [[petrol]], [[kerosene]], [[gas oil]], [[vegetable oil]] and [[Lubricant#Mineral oil|mineral oil]], as well as mixtures of these fuels, were used.<ref name="MAN_436" /> Typical fuels specifically intended to be used for diesel engines were [[petroleum distillate]]s and [[creosote|coal-tar distillates]] such as the following; these fuels have specific lower heating values of:
* Diesel oil: 10,200&nbsp;kcal·kg<sup>−1</sup> (42.7&nbsp;MJ·kg<sup>−1</sup>) up to 10,250&nbsp;kcal·kg<sup>−1</sup> (42.9&nbsp;MJ·kg<sup>−1</sup>)
* Heating oil: 10,000&nbsp;kcal·kg<sup>−1</sup> (41.8&nbsp;MJ·kg<sup>−1</sup>) up to 10,200&nbsp;kcal·kg<sup>−1</sup> (42.7&nbsp;MJ·kg<sup>−1</sup>)
* Coal-tar [[creosote]]: 9,150&nbsp;kcal·kg<sup>−1</sup> (38.3&nbsp;MJ·kg<sup>−1</sup>) up to 9,250&nbsp;kcal·kg<sup>−1</sup> (38.7&nbsp;MJ·kg<sup>−1</sup>)
* [[Kerosene]]: up to 10,400&nbsp;kcal·kg<sup>−1</sup> (43.5&nbsp;MJ·kg<sup>−1</sup>)

''Source:''<ref name="vPhilippovich_1939_43" />

The first diesel fuel standards were the [[DIN 51601]], [[VTL 9140-001]], and [[NATO F 54]], which appeared after World War II.<ref name="MAN_436" /> The modern European [[EN 590]] [[diesel fuel]] standard was established in May 1993; the modern version of the NATO F 54 standard is mostly identical with it. The DIN 51628 biodiesel standard was rendered obsolete by the 2009 version of the EN 590; FAME biodiesel conforms to the [[EN 14214]] standard. Watercraft diesel engines usually operate on diesel engine fuel that conforms to the [[ISO 8217]] standard ([[Bunker C]]). Also, some diesel engines can operate on [[Fuel gas|gas]]ses (such as [[LNG]]).<ref name="Schwarz_2012_102" />

===Modern diesel fuel properties===
{|class="wikitable"
|+Modern diesel fuel properties<ref name="Reif_2014_53" />
|-
|
!EN 590 (as of 2009)
!EN 14214 (as of 2010)
|-
!Ignition performance
| ≥ 51 [[Cetane number|CN]]
| ≥ 51 CN
|-
!Density at 15&nbsp;°C
| 820...845&nbsp;kg·m<sup>−3</sup>
| 860...900&nbsp;kg·m<sup>−3</sup>
|-
!Sulfur content
| ≤10&nbsp;mg·kg<sup>−1</sup>
| ≤10&nbsp;mg·kg<sup>−1</sup>
|-
!Water content
| ≤200&nbsp;mg·kg<sup>−1</sup>
| ≤500&nbsp;mg·kg<sup>−1</sup>
|-
!Lubricity
| 460&nbsp;μm
| 460&nbsp;μm
|-
!Viscosity at 40&nbsp;°C
| 2.0...4.5&nbsp;mm<sup>2</sup>·s<sup>−1</sup>
| 3.5...5.0&nbsp;mm<sup>2</sup>·s<sup>−1</sup>
|-
![[Fatty acid methyl ester|FAME]] content
| ≤7.0%
| ≥96.5%
|-
!Molar H/C ratio
| –
| 1.69
|-
!Lower heating value
| –
| 37.1&nbsp;MJ·kg<sup>−1</sup>
|}

===Gelling===
DIN 51601 diesel fuel was prone to ''waxing'' or ''gelling'' in cold weather; both are terms for the solidification of diesel oil into a partially crystalline state. The crystals build up in the fuel system (especially in fuel filters), eventually starving the engine of fuel and causing it to stop running.<ref name="vB_2017_1018" /> Low-output electric heaters in [[fuel tank]]s and around fuel lines were used to solve this problem. Also, most engines have a ''spill return'' system, by which any excess fuel from the injector pump and injectors is returned to the fuel tank. Once the engine has warmed, returning warm fuel prevents waxing in the tank. Before direct injection diesel engines, some manufacturers, such as BMW, recommended mixing up to 30% petrol in with the diesel by fuelling diesel cars with petrol to prevent the fuel from gelling when the temperatures dropped below −15&nbsp;°C.<ref name="BMW_1985" />