Lightweight fossil fuels — gas-state fuels — have high counts of unsaturated hydrocarbon. Heavy, stable fossil fuels like diesel, bunker fuel, and fuel oil have far fewer unsaturated hydrocarbons. Gasoline is a medium weight fuel that falls somewhere in the middle.
Diesel and fuel oil have, essentially, the same hydrocarbon makeup. Both are composed primarily of saturated hydrocarbons. Saturated versus unsaturated hydrocarbons is one difference between light and heavy fossil fuels. But, there are also differences between fossil fuels because of the difference between hydrocarbons in those two categories.
There is a total of four classes of hydrocarbons: paraffins, naphthenes, aromatics, and olefins. Paraffins and naphthenes are the two classes of saturated hydrocarbons. Aromatics and olefins are the two classes of unsaturated hydrocarbons.
Paraffins are also known as alkanes. Alkanes are single-chain hydrocarbons. The backbone of an alkane consists of carbon atoms. Alkanes are one of the two saturated hydrocarbon classes. The other class of saturated hydrocarbons is cycloalkanes, a. The difference between paraffins and naphthenes is that naphthenes have branches. And sometimes naphthenes loop. Naphthene carbon atoms often have more than just the two carbon atom bonds along the spine of the molecule.
The carbon atoms in a naphthene can have two, three, four or five bonds with other carbon atoms. A notable trait of naphthenes is that they are the most energy dense hydrocarbon class in either category of hydrocarbons. The two classes of unsaturated hydrocarbons are aromatics and olefins. Aromatics occur naturally in crude oil. Olefins are a byproduct of crude oil refinement and do not occur naturally in crude oil.
Unstable and volatile, aromatics and olefins produce the most toxic emissions. Additionally, aromatics and olefins also produce emissions with the greenhouse gases with the greatest global warming potential.
Another difference between light and heavy fossil fuels is the size of the hydrocarbons they contain. The molecules and molecule chains in light fossil fuels are short and small. Those in heavy fossil fuels are long and large. Lightweight fossil fuels, as one might expect, consist of smaller molecules and molecule chains than heavy fossil fuels.
And, again, unsaturated hydrocarbons comprise a larger portion of the hydrocarbons in light fuels. Heavy fossil fuels have a greater percentage of saturated, large and long hydrocarbon molecule chains. The larger and longer the hydrocarbon molecule chains in a fuel, the greater the density of the fuel. However, the longer and larger the hydrocarbon molecule chains in a fossil fuel, the more difficult achieving combustion efficiency is. So, while there is more energy in heavy, dense fossil fuels, the more energy is wasted.
The problem with diesel, fuel oil, and bunker fuel is that a high percentage of their hydrocarbons go unburned. Achieving the same combustion efficiency typical of lightweight fuels when combusting heavy fuels requires higher heat and more advanced technologies.
The combustion efficiencies of diesel, fuel oil and bunker fuel are one of the biggest differences. And, combustion efficiency is a property of the hydrocarbons.
The biggest difference between diesel and fuel oil are the hydrocarbon sizes within each, not the hydrocarbon classes. Unlike the hydrocarbons in gasoline vs diesel, the hydrocarbons in diesel and fuel oil are very similar.
In fact, they are almost the same in several cases. Health and Human Services Department. Diesel and fuel oils consist of mixtures of aliphatic and aromatic hydrocarbons. If preheating is necessary, check if the tracing is sufficient. Be careful that the tracing does not heat the fuel more than necessary. Make sure that the new fuel is not preheated in an unintended way. The fuel change-over affects the three common burner types normally supplied for marine boiler installations in various ways.
It is recommended a post-purge of the furnace whenever MGO has been used. It should be observed that the lower viscosity for fuel pumps in systems supplied by most manufacturers is normally 4. This means that if a fuel with a lower viscosity is used, the fuel pumps must be changed or modified. A lower viscosity may also cause an increase in the fuel input through the nozzle, and the risk of increasing smoke emission arises.
For larger burners, there is a risk of coke deposit creation in the burner cup, if the installation is not fitted with a suitable heat shield. This happens because the heat radiation into the rotary cup generates a too high temperature of the fuel in the rotary cup causing the fuel to start coking. It is therefore recommended having the rotary cup installation checked and if necessary modified. As the viscosity of the fuel burned in the steam atomizing burner is commonly in the range 15—30 cSt, the lower viscosity of a lighter fuel may cause over-firing if the pressure alone controls the oil amount to the burner.
For continuous operation with lighter fuels, it is recommended to use, either compressed air as the atomizing medium, or changing the lance to a type that does not heat the fuel in the same way as the traditional lance. The lance is constructed so the steam piping is insulated from the fuel piping in the burner lance thus avoiding preheating.
On burner plants, usually only one flame scanner is installed main flame supervision from the outset. It is recommended to have two flame scanners for the main flame supervision and in addition one separate flame scanner to detect the operation of the ignition burner. The lowest viscosity suitable for two-stroke diesel engines is 2 cSt at engine inlet. However, this viscosity limit cannot necessarily be used as a fuel specification for purchasing the fuel, as the viscosity in a purchase specification is tied to a reference temperature.
This is due to the fact that the external fuel systems have an individual effect on the heating of the fuel and, thereby, the viscosity of the fuel when it reaches the engine inlet. The external fuel oil systems on board today have been designed to keep a high temperature for HFO operation.
This can make it difficult to keep the fuel system temperature as low as possible, and thereby as high a viscosity as possible, when changing to DO and GO operation.
Many other factors influence viscosity and its influence on the engine, such as engine condition and maintenance, fuel pump wear, engine adjustment, actual fuel temperature in the fuel system, human factors, etc.
Which bunker fuel is used by ocean-going vessels for the high seas? Which bunker fuel do recreational vessels use? Red diesel for marine use According to the UK Government , recreational boaters can purchase red diesel for travelling within UK waters, however, they must pay the full rate of tax as they would for regular diesel fuel.
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To unsubscribe to marketing tick here. For these reasons, a number of standards emerged and were developed regarding diesel bunker for ships. The impact of low-grade bunker on equipment became doubly important for the technical departments of shipping companies and they became more selective in their choice of bunker for their ships.
Gradually the shipping sector came to realize that when ordering bunker, viscosity is not a sufficient criteria and that other characteristics of bunker must be taken into consideration. In , the last revision of ISO was published and today many bunker buyers place their orders in accordance with the ISO standards.
These bunkers have high viscosity and are sold around the world at cheaper prices. Medium Fuel Oil Sometimes bunkers with lower viscosity than the cheap bunker is available.
Light fuel oils are characterized by a maximum viscosity of 50 degrees Celsius.
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