What Is The Hottest Part Of A Candle?

A candle is a wax or tallow-based ignitable fuel source with an embedded wick. When lit, the candle provides light and in some cases fragrance (Candle Science; Wikipedia). In this article, we will identify the hottest part of a candle when lit and explain why that part reaches the highest temperature.

Wick

The wick’s main role is to deliver fuel (liquefied wax) to the flame so that the candle can keep burning (https://www.cathybaker.org/coming-to-our-summer-senses-shine-sister-shine/). Acting like a fuel pump, the wick draws the melted wax up into the flame to be burned (https://shopee.ph/%E2%99%9ENylon-Candle-Wick-%28Candle-Material%29-i.1000417055.24057928941). The wick is made from materials like cotton, nylon, or paper that will burn along with the wax. Without the wick constantly soaking up liquefied wax and bringing it into the flame, the candle would quickly stop burning.

Flame

The flame is the visible part of the combustion reaction of a candle burning. As the wax vaporizes, it mixes with oxygen in the air and ignites, resulting in an exothermic reaction that gives off heat and light energy. The high temperatures of the flame, reaching up to 1400°C, cause the wax vapors and oxygen to undergo combustion and release energy in the form of radiation that is visible to our eyes as brightness and color (1).

The primary chemical reaction taking place is:
Wax vapors (fuel) + Oxygen → Carbon dioxide + Water + Heat energy + Light energy
This exothermic reaction releases approximately 31 kJ/g of heat energy which heats up the surrounding air and provides the high temperatures needed to keep the wax vaporizing and the flame burning (2). The color and brightness of the flame depends on multiple factors like wax composition, wick material, and temperature gradient.

Sources:

(1) https://www.slideshare.net/JuliePen/ecgs-module-12

(2) https://www.scribd.com/presentation/640591562/Untitled

Middle of the Flame

The hottest part of a candle flame is usually found in the middle portion of the flame. This is because the middle of the flame is where complete combustion occurs (http://m.publicitet.al/ViewSwitcher?mobile=True&returnUrl=http%3A%2F%2Fsft460r43.%D1%82%D0%B3%D0%BF4.%D1%80%D1%84).

For complete combustion to happen, the candle wax needs to vaporize, mix with oxygen, and ignite. The middle of the flame provides the optimal conditions for this process. The wick brings liquefied wax to the flame. This wax vaporizes in the heat and mixes with oxygen from the surrounding air. With sufficient heat, oxygen, and fuel, the wax vapor and oxygen combine in chemical reactions that produce light, heat, carbon dioxide, and water vapor. The peak temperature is achieved when the combustion reactions occur rapidly and completely.

Toward the base of the flame, the wax vapor has not fully mixed with oxygen. At the tip of the flame, oxygen levels have diminished, slowing the reaction. But in the middle, the conditions are just right for the combustion reactions to occur quickly and completely. This maximizes the amount of energy released in the form of heat and light, making the middle of the candle flame the hottest part (https://adservice.google.bg/ddm/clk/425484003;227454619;f;;%3F//krBT2dE01-10li72.%D1%81%D0%BF%D0%B1%D0%B3%D0%B0%D1%83.%D1%80%D1%84).

Temperature Gradient

There is a temperature gradient within the candle flame, with the coolest temperatures at the base of the flame near the wick and the hottest temperatures in the middle of the flame. According to a study published in Nature, “The temperature distribution curve is then calculated and is shown to comprise three distinct flame zones that can be identified by the chemical processes occurring there: a primary combustion zone where the fuel pyrolyzes and subsequently oxidizes; an intermediate zone where oxidation continues; and an outer flame zone where oxidation is completed and where luminous combustion takes place” (Chen, 2019).

The lowest temperatures, around 250-300°C, are found at the very base of the flame next to the wick where the wax is vaporizing. As you move up through the flame, temperatures increase to around 1400-1600°C in the very middle of the flame where complete combustion is occurring with plenty of oxygen. The maximum temperature depends on the type of wax used. The hottest zone extends for only a small region in the center of the flame. Above this zone, temperatures cool down slightly again to around 1000°C at the tip of the visible part of the flame.

So in summary, the candle flame exhibits a clear temperature gradient with the hottest temperatures concentrated in the middle and upper middle part of the flame.

Melting Point

The melting point of candle wax varies depending on the type of wax. Paraffin wax, which is commonly used in candle making, has a melting point between 122-158°F. However, according to this Ebay listing, a specific paraffin wax called Candlewick 4144 has a melting point of 140°F.

As the candle burns, the flame heats up the wax immediately around the wick. This heat is conducted down the wick and melts the wax surrounding it. Once the wax reaches its melting point temperature, it liquefies and is drawn up the wick by capillary action to fuel the flame. The melting point of the wax determines the minimum temperature required for this melting and wicking process to occur.

Different waxes, like soy, beeswax and coconut wax have varying melting points, generally between 120-180°F as referenced from this article on melting points. The type of wax impacts how easily it melts from the heat of the flame. Higher melting point waxes require more heat to liquefy.

Flame Movement

The movement of the flame on a candle is caused by convection currents, which are the circular movement of hot air and gases (1). As the flame heats the air around it, the hot air becomes less dense and rises upward. This allows cooler, denser air to flow in and take its place at the base of the flame. This circular motion of hot air rising and cooler air sinking creates convection currents.

These convection currents cause the flame to flicker and move around. The hot gases rising from the flame pull the flame upward in the center. Meanwhile, the cooler air rushing in at the bottom pushes the flame outward at its base. This uneven heating makes the flame unstable, causing it to flicker (2).

Convection also transports hot melted wax upward, causing more rapid melting than would occur without convection currents. So convection is key to both the movement and the melting ability of candle flames (2).

Sources:

(1) https://www.youtube.com/watch?v=m_lqsyrOpvc

(2) https://www.nasa.gov/wp-content/uploads/2009/07/315952main_Microgravity_Candle_Flames.pdf

Factors Affecting Flame

Several factors can affect the temperature and behavior of a candle’s flame, including the size and material of the wick, the type of wax, and air currents.

The wick is the most important factor. Thicker wicks allow more wax to travel up to the flame, producing larger flames and more heat. According to the Harlem Candle Company, thick wicks can make the flame reach temperatures over 1400°C. Thinner wicks produce smaller, cooler flames. Wick materials like cotton generate hotter flames than materials like paper.

Wax composition also affects the flame. Harder waxes like paraffin burn slower and cooler than softer waxes like soy or beeswax. Softer waxes melt faster, allowing quicker fueling of the flame. Additives like fragrance oils and dyes can also influence temperature.

Air currents from fans, open windows, or ventilation cause the flame to flicker. More oxygen makes the flame burn hotter and faster, while drafts can bend the flame away from vertical.

According to CandleScience.org, all of these factors change how much fuel reaches the flame over time, altering its size, temperature, and shape.

Safety

When using candles, it’s important to keep some safety tips in mind to prevent fires and injuries. According to the National Fire Protection Association (NFPA), candles are an open flame that can easily ignite flammable materials if not used properly (NFPA). Here are some key candle safety guidelines:

• Keep candles at least 12 inches away from anything that can burn, like curtains, furniture, bedding, books, paper, etc. (PuroClean).
• Never leave a burning candle unattended. Extinguish candles before leaving a room.



• Do not burn candles near pets or small children who may knock them over.
• Keep wicks trimmed to 1⁄4 inch to avoid high flames.
• Always use candle holders specifically designed for candle use. Do not burn candles directly on surfaces.
• Avoid burning candles for more than 4 hours at a time.
• Do not burn too many candles in one area at the same time.
• Never use candles if oxygen is used in the home.

Following basic precautions like these can help prevent candle fires and keep your home safe.

Conclusion

In summary, the hottest part of a candle flame is the middle section, right above the wick. This is because the middle area has the most complete combustion occurring. The inner blue zone is the coolest, around 100°C, since this is where melted wax vaporizes. The middle yellow/orange section reaches up to 1300°C as the wax vapors ignite and burn. The outer zone drops off to around 800°C as oxygen depletes and combustion becomes incomplete. Factors like airflow, candle shape, and wick materials can all influence flame temperature. But in general, the peak heat is concentrated in the bright yellow/orange center of the flame, right above the wick. This explains why it’s best to keep flammable objects away from this part of a candle to prevent ignition. So when lighting candles, remember that the tiny middle section packs the most heat!