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Biodiesel – Technical Standards

The common international standard for biodiesel is EN 14214, while ASTM D6751 is the most common standard referenced in the United States and Canada (Table B-6). In Germany, the requirements for biodiesel are fixed in the DIN EN 14214 standard, and in the UK, the requirements for biodiesel is fixed in the BS EN 14214 standard, although these last two standards are essentially the same as EN 14214 and are just prefixed with the respective national standards institution codes.

Table B-6 Specifications for diesel and biodiesel (ASTM).

Property	Diesel	Biodiesel
Standard	ASTM D975	ASTM D6751
Composition	HC* (C10–C21)	FAME** (C12–C22)
Specific gravity (g/mL)	0.85	0.88
Flash point (^oC)	60–80	100 - 170
Cloud point (^oC)	-15 to 5	-3 to 12
Pour point (^oC)	-35 to -15	-15 to 16
Water, % v/v	0.05	0.05
Carbon, wt%	87	77
Hydrogen, wt%	13	12
Oxygen, wt%	0	11
Sulfur, wt%	0.05	0.05
Cetane number	40–55	48 - 60
HC: hydrocarbon derivatives *FAME: fatty acid methyl esters

There are standards for three different varieties of biodiesel, which are made of different oils: (i) rapeseed methyl ester, DIN E51606, (ii) vegetable methyl ester, purely vegetable products, DIN E51606, and (iii) fat methyl ester, vegetable and animal products, according to DIN V51606. The standards ensure that the following important factors in the fuel production process are satisfied; there needs to be (i) complete reaction, (ii) removal of glycerin, (iii) removal of catalyst, (iv) removal of alcohol, (v) absence of free fatty acids, and (vi) low sulfur content.

Basic industrial tests to determine whether the products conform to the standards typically include gas chromatography, a test that verifies only the more important of the variables above. Fuel meeting the quality standards is very non-toxic, with a toxicity rating (LD50) of greater than 50 mL/kg.

Biodiesel has promising lubricating properties and cetane ratings compared to low sulfur diesel fuels. Fuels with higher lubricity may increase the usable life of high-pressure fuel injection equipment that relies on the fuel for its lubrication. Depending on the engine, this might include high pressure injection pumps, pump injectors (also called unit injectors), and fuel injectors.

Generally, the heat content (calorific value) of biodiesel is lower than that of the regular crude oil-derived diesel, and variations in biodiesel energy density are more dependent on the feedstock used than the production process. Biodiesel can provide better lubricity and more complete combustion, thus increasing the engine energy output and partially compensating for the higher energy density of petrodiesel. The color of biodiesel ranges from golden to dark brown, depending on the production method. It is slightly miscible with water, has a high boiling point, and, consequently, a low vapor pressure. The flash point of biodiesel exceeds 130°C (266°F), which is significantly higher than that of crude oil-derived diesel which may be as low as 52°C (126°F). Biodiesel has a density of on the order of 0.88 g/cm³, higher than petrodiesel (which is approximately 0.85 g/cm³). Typically, biodiesel does not contain sulfur, and it is often used as an additive to ULSD fuel to aid with lubrication, as the sulfur compounds in petrodiesel provide much of the lubricity.

ASTM International (ASTM), formally known as the American Society for testing materials, is an international organization which develops and publishes information on the technical standards of various products, materials, systems, and services. It is one of the largest and most highly regarded standards development organizations in the world. The available literature on the performance of biofuels when compared with traditional fossil fuels normally uses ASTM and ISO (International Standards Organization) specifications and parameters. The specifications provide details on requirements for fuel characteristics as well as the relevant standard test methods to use for each.

Because of the focus on alternate fuel standards (particularly the standards for biodiesel) over the past two decades, the development of biodiesel standards started in the 1990s in order to support the increasing use of alkyl esters-based biodiesel and its blends as automotive fuels. The first ASTM standard (ASTM D6751) was adopted in 2002 while in Europe; EN 14214 biodiesel standard (based on former DIN 51606) was finalized in October 2003. The US and EU standards have international significance; they are usually the starting point for biodiesel specifications developed in other countries. However, in the United States, the standard (ASTM D6751) establishes specifications for a biodiesel blend stock for middle distillate fuels and, while the specification was written for B100, it is not intended for neat biodiesel used as automotive fuel. Rather, it is for the biodiesel component that is to be blended to produce biodiesel/diesel fuel blends. Since 2012, the ASTM D6751 standard has defined two grades of biodiesel (i) grade 2-B, which is identical to biodiesel defined by earlier versions of the standard, and (ii) grade 1-B, which has more strict controls on monoglycerides and cold soak filterability. In addition, the ASTM Standard Specification for Diesel Oil (ASTM D975) was modified in 2008 to allow up to 5% biodiesel to be blended into the fuel while a standard for biodiesel blends (ASTM D7467) is a specification for biodiesel blends from B6 to B20.

Most countries of the world uses a system known as the “B” factor to state the amount of biodiesel in any fuel mix, in contrast to the “BA” or “E” system used for bioalcohol. Pure biodiesel is referred to as B100, while fuel containing 20% biodiesel is labeled “B20.” The common international standard for biodiesel is EN 14214, while ASTM 6751 is most referenced in the U.S. In Germany, the requirements for biodiesel are fixed in the DIN EN 14214 standard.

One of the most important fuel properties of biodiesel and conventional diesel fuel derived from crude oil is viscosity, which is also an important property of lubricants. Ranges of acceptable kinematic viscosity are specified in various biodiesel and crude oil standards. Reducing viscosity is one of the main reasons why vegetable oils or fats are transesterified to biodiesel because the high viscosity of neat vegetable oils or fats ultimately leads to operational problems such as engine deposits.

The viscosity of biodiesel is slightly greater than that of petrodiesel but approximately an order of magnitude less than that of the parent starting material (vegetable oil or fat). Biodiesel and its blends with petrodiesel display temperature-dependent viscosity similar to that of neat petrodiesel. Influencing factors are chain length, position, number, and nature of double bonds as well as the nature of the oxygenated moieties.

Generally, biodiesel has a higher cloud point (temperature at which a fuel becomes hazy or cloudy and starts to gel) than petrodiesel. This makes its use impractical in cooler climates and limits its potential market. Other important chemical and physical properties described in ASTM standards for biodiesel are acid number (TAN – total acid number, indicates the presence of free fatty acids and carboxylic acids present), corrosion (describes the potential for copper corrosion, measured using ASTM method D130), low temperature performance [describes pour points (PP), and cloud points (CP) using ASTM D5949 and ASTM D5773 methods], and oxidation stability (normally evaluated using Differential Scanning Calorimetry and Oxidation Stability Index). In addition, according to the EMA (Engine Manufacturers Association), a blend of crude oil diesel fuel meeting ASTM D975 and 100% (neat) biodiesel fuel meeting either ASTM 6751 or EN 14214, where the biodiesel content of the blended fuel is no more than 20% biodiesel by volume (B20), shall meet the requirements identified in at the point of delivery of the fuel to the end user.

In terms of the effects of biodiesel on fuel filters, use of biodiesel blends which do not meet up to the designated specifications, have shown to drastically reduce filter life. Blends greater then B20 may have enough of a solvent to break down the varnish deposits on the walls of existing fuel storage tanks or fuel systems. The breakdown of these varnish deposits will contaminate the fuel with particulate, which can cause fuel filters to plug rapidly.

Another disadvantage of biodiesel is that it tends to reduce fuel economy. Energy efficiency is the percentage of the thermal energy of the fuel that is delivered as engine output, and biodiesel has shown no significant effect on the energy efficiency of any test engine. Volumetric efficiency, a measure that is more familiar to most vehicle users, is usually expressed as miles traveled per gallon of fuel (or kilometers per liter of fuel). The energy content per gallon of biodiesel is approximately 11% lower than that of crude oil diesel. Vehicles running on B20 are therefore expected to achieve 2.2% (20 % x 11 %) fewer miles per gallon of fuel.

Areas of concern and interest are for the biofuels industry to have in place a good quality control protocol for the measurement of bioalcohols, to avoid metal corrosion from water and acid corrosion (due to weak and strong acids and inorganic chlorides in solution). Also of importance are the limits set on phosphorous content (less than 5.0 mg/L in ethanol) to prevent engine catalyst deterioration, and copper content (less than 0.1 mg/kg), along with a sulfur content less than 10 mg/kg.

Up to a 10% blend level, the performance of bioethanol-blended gasoline is similar to ordinary gasoline. At higher levels, however, some engines may begin to exhibit problems, for example, stumbling under slight acceleration. The fuel also has more aggressive properties at higher concentrations of bioethanol which increases the possibility of deterioration of some components. Gasoline must be volatile enough to move from the carburetor or injectors into the cylinders and to vaporize prior to combustion. However, gasoline cannot have such a volatility that allows it to vaporize and boil in the injectors, carburetor, fuel lines, or fuel pump, which could prevent it from being metered correctly. Also, if the gasoline is too volatile, more evaporates into the air adding to environmental problems. There are a number of volatility specifications to ensure suppliers get this balancing act right. Adding bioethanol to gasoline as low-level blends increases the volatility of the blended fuel.

The Engine Fuel Specifications Regulations specify volatility measures for bioethanol-blended petrol. The limits for blends are similar to those for gasoline so as to ensure no changes in vehicles are required. Bioethanol introduces more oxygen into the fuel. In vehicles with simple fuel metering systems such as carburetors, this causes the mixture to become a little leaner. Leaning is good for fuel economy and is generally good for lowering some types of exhaust emissions. However, it may cause some engines to stumble if they are already tuned reasonably lean. If a vehicle stumbles on bioethanol-blended gasoline, re-tuning should solve the problem. A vehicle tuned correctly for use on ordinary gasoline would normally not exhibit problems when using bioethanol blends.