Biodiesel is a diesel fuel substitute produced from renewable sources such as vegetable oils, animal fats, and recycled cooking oils. Chemically, it is defined as the mono alkyl esters derived from renewable sources. Biodiesel is typically produced through the reaction of a vegetable oil or animal fat with methanol or ethanol in the presence of a catalyst to yield glycerin and biodiesel (chemically called methyl or ethyl esters). Biodiesel can be used in neat form, or blended with petroleum diesel for use in (the) diesel engines. Biodiesel has similar physical and chemical properties to petroleum diesel with reference to the operation of a diesel motor.. Its physical and chemical properties as it relates to operation of diesel engines are similar to petroleum based diesel fuels.

Advantages of using biodiesel
Biodiesel can be used alone or mixed in any ratio with petroleum diesel fuel, when it is burned, CO2 is released into the atmosphere which is then recycled and absorbed by growing plants which can later be processed into fuel. It produces 80% less carbon dioxide, 100% less sulfur dioxide (major component of acid rain) and up to 75% less exhaust smoke emissions. The flash point of biodiesel is ± 150°C as opposed to petroleum diesel at ± 70°C. It degrades about 4 times faster after spillage and provides significant lubricity improvement over petroleum diesel fuel.

Biodiesel's attributes
Across the globe environmental concerns and energy security issues have prompted legislation and regulatory actions spurring demand for alternative fuels such as biodiesel. However, the greatest driving force for the use of biodiesel and biodiesel blends is the need to have a fuel that fulfills all of the environmental and energy needs. One of the largest roadblocks to the use of alternative fuels is the change of performance noticed by users. Biodiesel has many positive attributes associated with its use, but by far the most noted attribute highlighted by consumers is the similar operating performance to conventional diesel fuel and the lack of changes required in facilities and maintenance procedures.

Biodegradability
Biodiesel has desirable degradation attributes which make it the fuel of choice by environmentally conscious users. Studies at the University of Idaho, USA, compared the biodegradation of biodiesel in an acqueous solution to diesel fuel and dextrose (sugar). Biodiesel samples degraded more rapidly than dextrose, and were 95% degraded at the end of 28 days. The diesel fuel was approximately 40% degraded after 28 days.

It should also be noted that blending biodiesel with diesel fuel accelarates its biodegradability. For example, blends of 20% biodiesel and 80% diesel fuel degraded twice as fast as petroleum diesel. Thus, biodiesel use has demonstrated biodegradability benefits at levels lower than 100%. Simply stated, neat biodiesel degrades as fast as sugar and a 20% blend will degrade twice as fast as petroleum based diesel fuel.

Flash Point
The flash point of a fuel is defined as the temperature at which the fuel becomes a mixture that will ignite when exposed to a spark or flame. The flash point of biodiesel has been tested and reported by various sources. Specific testing concludes that the flash point of biodiesel blends increases as the percentage of biodiesel increases. Therefore pure biodiesel and blends of biodiesel with petroleum diesel are safer to store, handle, and use than conventional diesel fuel. Neat biodiesel has a flash point (150°C) well above the flash point of petroleum based diesel fuel (± 70°C).

Emissions reductions
The use of biodiesel in a conventional diesel engine results in substantial reduction of unburned hydrocarbons, carbon monoxide, and particulate matter. Emissions of nitrogen oxides are either slightly reduced or slightly increased depending on the duty cycle of the engine and testing methods employed.

Particulate emissions from conventional diesel engines are generally divided into three components. Each component is present in varying degrees depending on fuel properties, engine design and operating parameters. The first component, and the one most closely related to the visible smoke often associated with diesel exhaust, is the carbonanceous material. This material is composed of sub-micron sized carbon particles which are formed during the diesel combustion process. It is especially prevalent under conditions when the fuel-air ratio is overly rich. The second component is hydrocarbon material which is absorbed on the carbon particles, commonly referred to as the soluble fration. A portion of this material results from incomplete combustion of the fuel. The remainder is derived from engine lube oil that passes by the piston oil rings. The third particulate component is comprised of sulfates and bound water. The amount of this material is directly related to the fuel sulfur content.

The use of biodiesel decreases the solid carbon fraction of particulate matter (since the oxygen in biodiesel enables more complete combustion to CO 2 ), eliminates the sulfate fraction (as there is no sulfur in the fuel).

In addition to reducing the overall levels of pollutants and carbon, the compounds that are prevalent in biodiesel and diesel fuel exhaust are different. Research conducted by Southwest Research Institue (USA) on a Cummins N14 engine indicates that the biodiesel exhaust has a less harmful impact on human health than petrodiesel. Biodiesel emissions have decreased the levels of all targest polycyclic aromatic hydrocarbons (PAH) and nitrited PAH compounds were reduced by 75-85%.

Lubricity
In the United States the sulfur level of diesel fuel that is used for on-road purposes is limited to 0.05% by weight. This limit was mandated in October 1993 as a method to decrease particulate matter emitted from diesel powered vehicles. With the introduction of mandated Environmental Protection Agency (EPA) low-sulphur diesel fuel, fleet operators began to encounter premature wear and/or failure of injector pumps in increasing numbers. Pump manufacturers such as Bosch began recommending the use of lubricity additives to alleviate the serious damage that the reduced sulphur content of low sulphur diesel was causing to their injection pumps.

Testing at labs such as Southwest Research Institute, Standyne Automotive and Engineering Testing Services have demonstrated that biodiesel provides significant lubricity improvement over petroleum diesel fuel. Lubricity results of biodiesel and petroleum diesel using the High Frequency Reciprocating Rig test indicate that there is a marked improvement in lubricity when biodiesel is added to conventional diesel fuel, even at blend levels below 1%.

Infrastructure
In general, the standard storage and handling procedures used for petroleum diesel can be used for biodiesel. The fuel should be stored in a clean, dry, dark environment. Temperature extremes should be avoided. Acceptable storage tank materials include stainless steel, fluorinated polyethylene and fluorinated polypropylene. Biodiesel has a solvent effect which may release deposits accumulated on tank walls and pipes from previous fuel storage. The release of deposits may clog filters initially and precautions should be taken.

Materials compatability
Biodiesel over time, will soften and degrade certain types of elastomers and natural rubber compounds. Precautions are needed when using high percent blends to ensure that the existing fueling system, primarily fuel hoses and fuel pump seals, does not contain elastomer compounds incompatible with biodiesel. Manufacturers recommend that natural or butyl rubbers not be allowed to come in contact with neat biodiesel.

---