Deisel

[edit] Petroleum diesel

A modern diesel pumpPetroleum diesel, or petrodiesel[1] is produced from petroleum and is a hydrocarbon mixture, obtained in the fractional distillation of crude oil between 200 Ð'oC and 350 Ð'oC at atmospheric pressure.

The density of petroleum diesel is about 850 grams per litre whereas petrol (gasoline) has a density of about 720 g/L, about 15% less. When burnt, diesel typically releases about 40.9 megajoules (MJ) per litre, whereas gasoline releases 34.8 MJ/L, about 15% less.[citation needed] Diesel is generally simpler to refine from petroleum than gasoline. The price of diesel traditionally rises during colder months as demand for heating oil rises, which is refined in much the same way. Due to its higher level of pollutants, diesel must undergo additional filtration[citation needed] which contributes to a sometimes higher cost. In many parts of the United States and throughout the UK, diesel may be higher priced than petrol.[2] Reasons for higher priced diesel include the shutdown of some refineries in the Gulf of Mexico, diversion of mass refining capacity to gasoline production, and a recent transfer to ultra-low sulfur diesel (ULSD), which causes infrastructural complications.[3]

Diesel-powered cars generally have a better fuel economy than equivalent gasoline engines and produce less greenhouse gas pollution. Their greater economy is due to the higher energy per-litre content of diesel fuel and the intrinsic efficiency of the diesel engine. While petrodiesel's 15% higher density results in 15% higher greenhouse gas emissions per litre compared to gasoline,[4] the 20вЂ"40% better fuel economy achieved by modern diesel-engined automobiles offsets the higher-per-liter emissions of greenhouse gases, and produces 10-20 percent less GHG emissions than comparable gasoline vehicles.[5][6][7] However, the EPA carbon footprint estimates do not include the carbon cost of vehicle manufacture, nor the carbon cost of filtering particulates, sulfates, and nitrates emissions. Biodiesel-powered diesel engines offer substantially improved emission reductions compared to petro-diesel or gasoline-powered engines, while retaining most of the fuel economy advantages over conventional gasoline-powered automobiles.

In the past, diesel fuel contained higher quantities of sulfur. European emission standards and preferential taxation have forced oil refineries to dramatically reduce the level of sulfur in diesel fuels. In the United States, more stringent emission standards have been adopted with the transition to ULSD starting in 2006 and becoming mandatory on June 1, 2010 (see also diesel exhaust). U.S. diesel fuel typically also has a lower cetane number (a measure of ignition quality) than European diesel, resulting in worse cold weather performance and some increase in emissions.[8] This is one reason why U.S. drivers of large trucks have increasingly turned to biodiesel fuels with their generally higher cetane ratings.

High levels of sulfur in diesel are harmful for the environment because they prevent the use of catalytic diesel particulate filters to control diesel particulate emissions, as well as more advanced technologies, such as nitrogen oxide (NOx) adsorbers (still under development), to reduce emissions. However, the process for lowering sulfur also reduces the lubricity of the fuel, meaning that additives must be put into the fuel to help lubricate engines. Biodiesel and biodiesel/petrodiesel blends, with their higher lubricity levels, are increasingly being utilized as an alternative.

The U.S. annual consumption of diesel fuel in 2006 was about 190 billion litres (42 billion imperial gallons or 50 billion US gallons). [1]

[edit] Chemical composition

Diesel is immiscible with waterPetroleum-derived diesel is composed of about 75% saturated hydrocarbons (primarily paraffins including n, iso, and cycloparaffins), and 25% aromatic hydrocarbons (including naphthalenes and alkylbenzenes).[9] The average chemical formula for common diesel fuel is C12H23, ranging from approx. C10H20 to C15H28

[edit] Algae, microbes, and water

There has been much discussion and misinformation about algae in diesel fuel[citation needed]. Algae require sunlight to live and grow. As there is no sunlight in a closed fuel tank, no algae can survive there. However, some microbes can survive there, and can feed on the diesel fuel.

These microbes form a colony that lives at the fuel/water interface. They grow quite rapidly in warmer temperatures. They can even grow in cold weather when fuel tank heaters are installed. Parts of the colony can break off and clog the fuel lines and fuel filters.

It is possible to either kill this growth with a biocide treatment, or eliminate the water, a necessary component of microbial life. There are a number of biocides on the market, which must be handled very carefully. If a biocide is used, it must be added every time a tank is refilled until the problem is fully resolved.

Biocides attack the cell wall of microbes resulting in lysis, the death of a cell by bursting. The dead cells then gather on the bottom of the fuel tanks and form a sludge, filter clogging will continue after biocide treatment until the sludge has abated.

Given the right conditions microbes will repopulate the tanks and re-treatment with biocides will then be necessary. With repetitive biocide treatments microbes can then form resistance to a particular brand.[citation needed] Trying another brand may resolve this.

Petrodiesel spilled on a road will stay there until washed away by sufficiently heavy rain, whereas gasoline will quickly evaporate. Diesel spills severely reduce tire grip and have been implicated in many accidents. They are especially dangerous for two-wheeled vehicles.

[edit] Synthetic diesel

Wood, hemp, straw, corn, garbage, food scraps, and sewage-sludge may be dried and gasified to synthesis gas. After purification the Fischer-Tropsch process is used to produce synthetic diesel.[10] This means that synthetic