Campfire: Fuel & Flame Physics (2D)

Combustion Basics

A campfire is a classic example of combustion, the rapid oxidation of a fuel source in the presence of an oxidizer (typically oxygen) to produce heat and light. The process can be described by the chemical equation: fuel + O2 -> CO2 + H2O + energy. In our 2D model, we simplify this complex reaction into a dynamic system where the rate of fuel consumption determines flame height.

The relationship between flame height and remaining fuel is governed by the square root law, which states that the flame height (H) scales with the square root of the remaining fuel (F): H ∝ F^(1/2). This reflects the fact that as more fuel is consumed, the available fuel for combustion decreases, leading to a reduction in flame size.

Buoyancy and Drag

The behavior of embers in the 2D model can be attributed to buoyant forces. As hot gases rise from the fire, they carry embers with them due to their lower density compared to cooler air. The drag force acting on these embers opposes their motion and depends on their size, shape, and velocity relative to the surrounding fluid (air).

The model incorporates a simple drag equation: Fd = 0.5 * ρ * v^2 * Cd * A, where Fd is the drag force, ρ is the density of air, v is the velocity of the ember, Cd is the drag coefficient, and A is the cross-sectional area of the ember.

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Wind's Impact

In our 2D campfire model, wind plays a crucial role in shaping the flame plume. The wind not only affects the direction but also the height and spread of the flames by shearing the flame plume sideways. This phenomenon can be described using the concept of shear stress: τ = μ * (∂v/∂y), where τ is the shear stress, μ is the dynamic viscosity of air, and ∂v/∂y represents the velocity gradient in the y-direction (perpendicular to wind direction).

The model simulates this effect by adjusting the position and orientation of the flame plume based on the wind speed. Higher wind speeds result in greater shearing forces, causing the flame to spread more horizontally.

Real-World Applications

Understanding campfire physics has practical applications beyond mere curiosity. For instance, it aids in designing efficient burners for heating and cooking appliances, optimizing fuel usage in industrial processes, and even predicting the spread of forest fires under varying weather conditions.

Moreover, studying combustion dynamics can lead to advancements in clean energy technologies, such as improving the efficiency of gas turbines or developing new materials that resist high-temperature degradation.

Frequently asked questions

How does the square root law apply to real campfires?

In reality, the relationship between flame height and fuel consumption is more complex but can be approximated by a similar square root dependence. As fuel decreases, the available energy for combustion diminishes, leading to smaller flames.

Why do embers drift with buoyancy?

Embers are less dense than surrounding air and thus experience an upward buoyant force due to their lower density compared to the cooler air. This causes them to rise and be carried by the wind, spreading the fire.

How does changing the wind speed affect the model?

Increasing the wind speed in the model shears the flame plume sideways, causing it to spread more horizontally due to increased drag forces on the embers and altered buoyant flow patterns.

What factors influence the burn rate of a campfire?

The burn rate is influenced by several factors including fuel type, oxygen supply, temperature, humidity, and wind speed. In our model, these are simplified to focus on key dynamics like fuel consumption and buoyancy.

Try it live

Everything above runs in your browser — open Campfire: Fuel & Flame Physics (2D) and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.

▶ Open Campfire: Fuel & Flame Physics (2D) simulation