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Fuel properties

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Fuel properties

Diesel – legislation and standards

Engine and after-treatment technology impose requirements for fuel quality. Basic fuel analyses were developed to screen general performance and operability of fuels in internal combustion engines. Fuel properties important in environmental contexts, such as compatibility of fuel with emission control devices, were defined subsequently. The functionality and general performance of diesel fuel can be defined, for example, in terms of ignition quality, distillation, viscosity, and additives. Environmental performance can be defined in terms of aromatics and sulfur content.

Fuel properties are controlled by legislation and by fuel standards. In Europe, Fuel Quality Directive 2009/30/EC defines the requirements for basic fuel properties for diesel fuel. European standard EN 590 includes more extensive requirements than Fuel Quality Directive to ensure proper functionality of diesel fuel on market. In Europe, CEN (European Committee for Standardization) develops standards.

In the US, ASTM D 975 is a specification for diesel fuel. ASTM standard includes several classes. There are also a number of other regional and national standards on fuels.

Automobile and engine manufacturers have defined recommendations for fuels in “World Wide Fuel Charter” (WWFC). Category 5 is the most stringent WWFC category for “markets with further advanced requirements for emission control to enable sophisticated NOx and particulate matter after-treatment technologies”.

Selected requirements and fuel properties are shown in Tables 1 and 2 below.

Table 1. Selected requirements as examples for diesel fuel properties in Europe and in the U.S., together with automanufacturer's recommendations (WWFC). Complete requirements and standards are available from respective organizations.

	Standard A 2022 ^a	Standard B 2014 ^a	WWFC:2019 Category 5 ^a
Cetane number	≥51.0	≥40	≥55.0
Cetane index	≥46.0	≥40 or aromatics ≤35 vol-%	depends on additive use
Density at 15 °C, kg/m³	820^b - 845		815^b - 840
Viscosity at 40 °C, mm²/s	2.0^b - 4.5	1.9 - 4.1	2.0^b - 4.0
CFFP, °C	^b	agreed by buyer and seller	equal or lower than the lowest expected ambient temperature
Flash point, °C	>55.0	≥52	>55
Evaporated, vol-%	E250: <65 E350: ≥85
Evaporated, °C	T95: ≤360	T90: 282 - 338	T90: ≤320 T95: ≤340
Final boiling point, °C			≤350
Dist. residue/loss, vol-%		≤2
Total aromatics, wt-%		Total ≤35 or Cl ≥40	≤15
Polycyclic aromatic hydrocarbons (PAH di+), wt-%	≤8.0		≤2.0
Sulfur content, mg/kg	≤10.0	≤15	≤10
FAME content, vol-%	≤7.0	≤5.0	Non-detectable
Other biofuels			HVO, BTL
Methanol/ethanol, wt-%			Non-detectable
Lubricity, wear scar diameter at 60 °C, µm	≤460	≤520	≤400
Copper strip corrosion (3h, 50 °C)	Class 1	≤3	Class 1
Ferrous corrosion			Max. light rust
Total acid number, mg KOH/g			≤0.08
Carbon residue (10% dist.), wt-%	≤0.3	≤0.35	≤0.20
Ash content, wt-%	≤0.01	≤0.01	≤0.001
Metal content, mg/kg	≤2.0 manganese		Non-detectable
Chlorine, mg/kg			Non-detectable
Oxidation stability 95 °C, g/m³	≤25		≤25
Oxidation stability, h/min	>20/>60 ^c		/>65 (PetroOxy)
Total contamination, mg/kg	≤24		<10
Particulate contamination, size distribution			18/16/13 per ISO 4406
Injector cleanliness/filter blocking tendency			limit vary with test method/ <1.6
Water and sediment, wt%	water ≤0.02	≤0.05	water ≤0.02
Foam volume, ml/vanishing time, sec.			≤100/≤15
Biological growth			Zero content
Conductivity, pS/m		≥25

^aOnly selected requirements presented here. ^bSeveral classes. Climate-dependent properties vary. ^cLimits depend on test methods. For diesel fuel containing above 2 vol-% FAME.

Table 2. Examples of some non-limited diesel fuel properties. ^a,b

Property	Example	Property	Example
Carbon number	C12 - C20	Nitrogen, mg/kg	~30
Molecular weight range, g/mol	~150 - 250	Total aromatics, wt-%	~20
Carbon/Hydrogen, wt-%	~86.5/13.5	Stoichiometric air to fuel ratio	14.7
Distillation, °C	200 - 360	Vapor density
LHV energy content, MJ/kg	43	Autoignition temperature, °C	230
LHV energy content, MJ/I	35	Flammability limits, vol-%	0.6 - 5.6/6.5
HHV energy content, MJ/kg	46	Electrical conductivity, µS/m*	10^-4
Heat of vaporization, kJ/kg	225 - 280

* Electrical conductivity depends on the concentration of metallic ions. Degaldo (2007) reported 200 µS/m for hydrous ethanol and 10 µS/m for Brazilian gasoline. ^aMurphy 1998 ^bMurtonen et al. 2009

Gasoline - legislation and standards

The engine and after-treatment technology impose requirements on fuel quality. Basic fuel analyses were developed to screen general performance and operability of fuels in internal combustion engines. Fuel properties important in environmental contexts, such as compatibility of fuel with emission control devices, were defined subsequently. The functionality and general performance of gasoline can be defined, for example, in terms of octane rating, volatility, olefin content, and additives. Environmental performance can be defined, for example, in terms of aromatics, olefins, benzene content, oxygenates, volatility, and sulfur (lead is not allowed in most countries). Fuel properties are controlled by legislation and by fuel standards. There are also a number of other regional and national standards on fuels.

In Europe the Fuel Quality Directive, 2009/30/EC, defines the requirements for basic fuel properties for gasoline. The European standard EN 228 includes more extensive requirements than Fuel Quality Directive to ensure proper functionality of gasoline on market. CEN (European Committee for Standardization) develops standards in Europe.

In the US, ASTM D 4814 is a specification for gasoline. The ASTM standard includes a number of classes, waivers, and exceptions taking into account climate, region and, for example, ethanol content of gasoline. In 2011 US EPA accepted waiver for usage of 15 vol-% ethanol blend for 2001 and newer cars. In the US gasoline-oxygenate blends are considered “substantially similar” if they contain hydrocarbons, aliphatic ethers, aliphatic alcohols other than methanol, up to 0.3 vol-% methanol, up to 2.75 vol-% methanol with an equal volume of butanol, or higher molecular weight alcohol. The fuel must contain no more than 2.0 wt-% oxygen except the fuels containing aliphatic ethers and/or alcohols (excluding methanol) that must not contain more than 2.7 wt-% oxygen. In the USA, so called P-Series fuel consisting of butane, pentanes, ethanol, and the biomass-derived co-solvent methyltetrahydrofuran (MTHF) is allowed for FFV cars.

Automobile and engine manufacturers have defined recommendations for fuels in “World Wide Fuel Charter” (WWFC). Category 6 is the most stringent WWFC category for “markets with further advanced requirements for emission control to enable sophisticated NOx and particulate matter after-treatment technologies”.

Selected requirements and fuel properties are shown in Tables 3 and 4 below.

Table 3. Selected requirements for gasoline properties in Europe and in the U.S., together with automanufacturer's recommendations (WWFC). Complete requirements and standards are available from respective organizations.

	Standard A 2012/2017 ^c	Standard B 2014 ^c,d	WWFC:2019 Category 6 ^{c, g}
RON	≥95.0		≥98^a
MON	≥85.0		≥88^a
Vapor pressure, kPa ^e	45 - 60^a	≤62^a	45 - 60^a
Density at 15 °C, kg/m³	720 - 775		720 - 775
Evaporated, vol-%	E70: 22 - 50^a E100: 46 - 72 E150: ≥75.0		E70: 20 - 45^a E100: 50 - 65^a E180: ≥90
Evaporated, °C		T10: ≤70^a T50: 77 - 121 T90: ≤190	T10: ≤65^a T50: 77 - 100^a T90: 130 - 175
Final boiling point, °C	≤210	≤225	≤205
Dist. residue, vol-%	≤2	≤2

Oxygen content, wt-%	≤3.7	^d	≤3.7
Methanol, vol-%	≤3.0^f	^d	Not permitted
Ethanol, vol-%	≤10.0^f	^d	≤10.0
Isopropyl alcohol, vol-%	≤12.0
tert-Butyl alcohol, vol-%	≤15.0
Isobutyl alcohol, vol-%	≤15.0
Ethers, C5+, vol-%	≤22.0		Preferred
Other oxygenates, vol-% ^b	≤15.0

Olefins, vol-%	≤18.0		≤10
Aromatics, vol-%	≤35.0		≤35
Benzene, vol-%	≤1.00		≤1.0
Sulfur content, mg/kg	≤10.0	≤80.0	≤10.0
Lead content, mg/l	≤5.0	≤13	see trace metals
Manganese content, mg/l	≤2.0		see trace metals
Trace metals, chlorine, organic contaminants, mg/kg			No intentional addition

Oxidation stability, min.	≥360	≥240	≥480
Sediment, mg/l			≤1
Existent gum (washed/unwashed), mg/100 ml	≤5/-	≤5/-	≤5/≤30
Copper strip corrosion	Class 1	≤1	Class 1
Silver strip corrosion		≤1	Class 1

^aSeveral classes. Vapor pressure limits depend on season. ^b Mono-alcohols and ethers with final boiling point max. 210 °C. ^c May include other requirements than presented here. ^d In 2011, US EPA accepted 15 vol-% ethanol blend for 2001 and newer cars. "Substantially similar" rule allows e.g. up to 2.75 vol-% methanol with an equal volume of butanol, or higher molecular weight alcohol; fuels containing aliphatic ethers and/or alcohols (excluding methanol) must contain no more than 2.7 wt-% oxygen. ^e The vapor pressure of gasoline is measured at 100 °F (37.8 °C). ^fStabilizing agents shall be added for methanol, and may be added for ethanol. Ethanol for blending shall conform to EN 15376. ^g RON 102, MON 88 quality also. Requirements for e.g. fuel injector cleanliness, combustion chamber, Particulate Matter Index (PMI).

Table 4. Examples of some non-limited gasoline properties.

Properties	Example	Properties	Example
Carbon number	C4 - C12	Nitrogen, mg/kg	~3
Molecular weight range, g/mol	~60 - 150^a	Flash point, °C	~40^a
Carbon/hydrogen, wt-%	~86.5/13.5	Stoichiometric air to fuel ratio	14.7^a
Viscosity at 15 °C, mm²/s	0.83^a	Autoignition temperature, °C	300^a
Cetane number	8 - 14^a	Flammability limits, vol-%	1.4 - 7.6^a
Distillation, °C	30 - 210	Vapor density	2 - 4^a
LHV energy content, MJ/kg	42.6^a	Surface tension of hexane and benzene at 20 °C, mN/m	18.4, 28.9^b
LHV energy content, MJ/I	32.9^a	Odor threshold	0.2^a
HHV energy content, MJ/kg	45.4^a	Electrical conductivity, µS/m*	10^c
Heat of vaporization, kJ/kg	275 - 365^a

* Electrical conductivity depends on the concentration of metallic ions. ^aMurphy 1998 ^bCRC handbook ^c Degaldo 2007