Tiki torch fuel does evaporate, but the process is significantly slower than with common liquids like water or alcohol. The fuel is primarily composed of petroleum-based liquids, such as highly refined lamp oil or paraffin, sometimes infused with citronella for insect repellent properties. The chemical structure of these oils dictates a low rate of loss under normal conditions. This slow evaporation rate explains why a torch can sit unused for weeks without completely drying out.
The Chemistry of Fuel Evaporation
Tiki torch fuel is a petroleum distillate made up of long-chain hydrocarbon molecules. The length of these chains results in a high molecular weight, which influences its low volatility. In contrast, highly volatile liquids like gasoline or rubbing alcohol consist of much lighter molecules that escape easily into the air.
The low volatility of torch fuel is quantified by its low vapor pressure, typically less than 1 millimeter of mercury (mmHg) at room temperature. Vapor pressure measures a liquid’s tendency to change into a gaseous state. A low vapor pressure means only a small fraction of the fuel’s molecules possess enough energy to break free from the liquid surface and become airborne vapor.
The fuel is technically evaporating, but the process is slow enough that it is often considered negligible. This slow release of molecules allows you to smell the faint petroleum or citronella scent even when the torch is not lit. This chemical resistance is why lamp oil is non-drying and maintains its quality for years when stored correctly.
External Factors Influencing Fuel Loss
While the fuel’s chemistry resists evaporation, external conditions can accelerate the rate of loss. Ambient temperature is the most important environmental factor. Higher temperatures increase the kinetic energy of the fuel molecules, making it easier for them to overcome the cohesive forces holding them in the liquid state.
Increased airflow, or wind, contributes to fuel loss by sweeping away the vapor molecules hovering above the liquid surface. This maintains a steep concentration gradient, encouraging more liquid molecules to turn into vapor. Oil evaporation is a “diffusion-regulated” process, meaning the rate is less affected by wind than the evaporation of water.
The exposed surface area of the liquid is another significant factor. A wider torch reservoir opening or a high wick setting exposes more liquid surface to the air, providing more escape routes. High humidity has a less pronounced effect on oil evaporation compared to water, but it can slightly slow the rate by reducing the air’s capacity to hold the oil vapor.
Practical Steps for Minimizing Evaporation
Users can take several steps to counteract the environmental factors that promote fuel loss. The most effective action is to always use the protective cap or snuffer that comes with the torch when it is not actively burning. Covering the reservoir immediately minimizes the exposed surface area of the fuel, which is the direct point of vapor escape.
Storing the fuel container and the torches in a cool, shaded location helps reduce the molecular energy that drives evaporation. Since heat accelerates the process, moving the torches out of direct sunlight or a hot shed conserves the fuel supply. Fuel containers should always have their caps tightly sealed to prevent vapor escape.
It is also beneficial to lower the wick into the torch body when the flame is extinguished. A high wick acts as an extension of the liquid surface, drawing fuel up through capillary action and exposing it to the open air. Retracting the wick reduces this exposed area, limiting the potential for both evaporation and accidental ignition.