While this question often serves as a classic riddle, when considering physical materials, specific types of fuel are known for burning with minimal to no visible smoke. Based on the provided reference, the answer points to several examples of smokeless fuels.
Understanding Smokeless Fuels
Smokeless fuels are solid fuels that produce little to no smoke during combustion. This characteristic is highly desirable, especially in urban areas or for indoor heating, as it contributes to better air quality compared to traditional coal or wood fires. These fuels typically have a high carbon content and low levels of volatile compounds, which are the primary source of smoke in combustion.
Key Examples from the Reference
The reference specifically lists several materials known for burning without smoke. These examples include:
- Anthracite: A hard, compact variety of coal that has a high luster. It has the highest carbon content and the fewest impurities of all types of coal, making it the cleanest burning.
- Coke: A fuel made by heating coal in the absence of air. This process drives off volatile impurities, resulting in a porous, high-carbon material that burns with little smoke.
- Charcoal: Produced by heating wood in the absence of oxygen. Similar to coke, this removes volatile compounds, leaving behind mostly carbon that burns cleanly.
- Hexamine fuel tablets: A solid fuel often used for heating cooking utensils or camp stoves. They are made from hexamine and burn with a smokeless flame.
For domestic use, these smoke-free carbonaceous fuels are commonly prepared in convenient forms. The reference notes they are "usually supplied in the form of standard pillow-shaped briquettes." Briquettes are compacted blocks of fuel that offer consistent size and burn characteristics.
These specific substances are recognized for their property of burning cleanly, making them key examples when considering materials that burn without producing smoke.
