A Bunsen burner is a common piece of laboratory equipment designed to produce a single, controlled open flame for various tasks like heating, sterilization, and combustion experiments. This device operates by safely burning a continuous stream of flammable gas mixed with air. In most standard academic and industrial laboratory settings, the gas most frequently used to power a Bunsen burner is natural gas.
The Primary Fuel Source
Natural gas is the standard fuel choice for Bunsen burners due to its widespread availability through utility lines and its specific chemical properties. The primary component of natural gas is methane (CH4), a simple hydrocarbon molecule. This gas is favored because it burns cleanly and efficiently, producing a hot, stable flame with minimal soot or residue compared to other fuels.
The methane in natural gas provides a high energy output when combusted, making it effective for controlled laboratory heating. Its consistency and low cost further solidify its position as the preferred fuel source for burners connected to a central gas supply. For complete combustion to occur, approximately two moles of oxygen are required for every one mole of methane.
Alternative Fuel Options
In situations where a central natural gas line is unavailable, such as in mobile or remote field laboratories, Bunsen burners may be fueled by liquefied petroleum gas (LPG). The two most common components of LPG are propane (C3H8) and butane (C4H10), which are typically supplied via portable tanks or cartridges.
Propane and butane are heavier hydrocarbons than methane, meaning they have different energy densities and combustion requirements. Burners designed for natural gas cannot safely or efficiently use propane or butane without modification. Using an incorrect fuel type requires a different nozzle or jet size to ensure the proper air-to-fuel ratio is maintained for safe operation and optimal flame temperature.
How Bunsen Burners Utilize the Gas
The Bunsen burner is designed to premix the flammable gas with oxygen before ignition, a process that relies on the Venturi effect. The gas enters the base of the burner and flows upward through a small jet, which draws in surrounding air through adjustable holes in the barrel. This controlled mixing ensures that enough oxygen is present for the combustion reaction to be efficient and produce high heat.
Controlling the amount of air drawn into the barrel is accomplished by rotating an adjustable collar or sleeve at the bottom of the tube. When the air holes are completely or mostly closed, the gas only mixes with oxygen at the point of combustion, resulting in an incomplete reaction. This produces a cooler, luminous yellow flame, which is sometimes called a safety flame, due to the incandescence of unburned carbon particles.
Opening the air holes allows a greater volume of air to mix with the gas stream, leading to complete combustion. This results in a hotter, non-luminous blue flame that is preferred for most heating applications. The hottest part of this blue flame, which can reach temperatures of approximately 1,500°C (2,700°F), is located just above the tip of the inner blue cone.