Fuels, Part 1

As mentioned in the previous lesson, fuels are substances that burn. In this context, it is important to remember that the term "fuel" is not limited only to what we generally imagine when someone says fuel, such as gasoline or liquified petroleum gas.

Matter generally exists in three physical states: solid, liquid, and gas. Solids dissolve to become liquids which can then vaporize into gases. Fundamentally, all fuels are converted to gas at high enough temperatures.

Each different physical state exhibits different physical and chemical properties that directly affect a fuel's combustibility. For example, gasoline as a liquid does not burn, but the vapors rising from it do.

Fuels can be sourced naturally or artificially. Examples of natural fuels are coal and natural gas. These were formed over millions of years from animal and plant remains and are now deposited underground. These are also called fossil fuels and account for about 90% of the world's energy sources. Synthetic fuels are those derived from fossil fuels. For instance, crude oil is converted to gasoline through refinement.

Most fuels release energy by burning with oxygen in the air. Others, such as chemical fuels utilized in rockets, need special oxidizers to burn. Nuclear fuels, on the other hand, release energy through fission or fusion of atoms.

Classifications of Combustible Materials

Class C and Class D fuels can be distinguished from each other by their action. Class C fuels are only potentially dangerous while electricity is running through them. Class D fuels can be explosive on their own.

General Categories of Combustible Materials

Solid Fuels

The most common solid fuels are wood, paper, and cloth. Their burning rates depend upon their configurations. For instance, a pile of crumpled pieces of paper will burn faster than a stack of neatly folded sheets.

Kinds of Flammable Solids

1. Pyrolyzable solid fuels are those materials that are commonly known as easy to burn, including wood and paper. The vapors released during their chemical decomposition aid in sustaining flaming combustion.

2. Non-pyrolyzable solid fuels are those that are hard to ignite. A typical example would be charcoal. Chemical decomposition does not occur during the combustion of these materials, so vapors are not released during the process.

Groups of Solid Fuels

Biomass are replaceable organic matters like wood, garbage, and animal fat which can be used to produce energy. They are frequently utilized in processing plants. In the country, rice hulls are a common waste product that is transformed into power.

Effects of various factors on the combustibility of wood and wood-based products:

• physical form - the smaller the pieces, the easier/faster they burn

• moisture/water content - as shown in a video in a previous lesson, dry wood burns faster than fresh wood

• heat conductivity - the higher the conductivity, the faster the material burns

• rate and period of heating - less-flammable materials do not readily ignite

• rate of combustion - fuel is consumed faster if the combustion is more intense

• ignition temperature - the lower the number, the faster it will be reached, thus the fire can start sooner

Fabrics and Textiles

Fibers are very delicate and thin strands of material. Fabrics are twisted or woven fibers. While textiles are machine-woven or knitted fabrics.

Classifications of Fabrics

• Natural Fibers come from animals (e.g. wool, silk), plants (e.g. abaca, pineapple, coconut), and minerals (e.g. asbestos).

• Synthetic or Artificial Fibers are manmade and synthesized from various chemicals. Examples include acetate, fiberglass, and steel.

Effect of various factors on the combustibility of fibers

• chemical composition - Natural and artificial fibers are generally highly combustible, especially when they're dry. Mineral and artificial inorganic fibers are usually fire-resistant.

• fiber finish or coating merged with organic fibers supports the continued burning of the fabric

• fabric weight - heavier fabrics resist ignition

• tightness of weave - tighter woven cloth take more time to ignite

• flame retardant treatment - as the name implies, treated cloth has higher ignition resistance

Fabric Ignition

Limiting Oxygen Index (LOI) is a measure of the tendency of a fabric to continue burning after the initial ignition source is removed. Fabrics with higher LOI and ignition temperature are safer for clothing and furniture because they are likely to cease burning once the initial flame is removed.

Plastics are categorized as Class A fuels except for cellulose nitrate or those that contain it. It is a chemical powder used in bombs and is also called pyroxylin.

Coal is a black, combustible, solid mineral that is produced when matter undergoes partial decomposition due to exposure to varying temperatures. It is generally used to heat buildings and energize machinery.

Coal comes in the following forms: lignite or brown coal, sub-bituminous coal, bituminous coal, and anthracite.

Bituminous coal contains more carbon and produces more heat than either lignite or sub-bituminous coal. Thus, it is considered the most important type of coal in industry. Bituminous coal also appears most abundantly in nature.

Anthracite, while it contains more carbon and produces more heat than the other types, is not used as much since it is the toughest type of coal making it difficult to ignite and slow-burning. Additionally, anthracite is rare compared to the others.