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How Does Firewood Burn? (Heat, Light, Chemistry)

When wood burns, there are two major constituents that decompose to provide the light and heat energy.

Both cellulose (C14H26O11) and lignin (C81H92O28) are composed of hydrogen and carbon atoms; as a result, they possess properties similar to hydrocarbons. In fact, lignin is considered a unique hydrocarbon, despite the presence of oxygen, but both of these materials lend themselves to the generation of more sophisticated synthetic hydrocarbons.

Those can be used a biofuel, or as the base stock for building or developing polymers such as bioplastic without necessitating the use of fossil-sourced petroleum materials.

Burning process

  1. Drying: As the wood is heated, the moisture in the wood evaporates. The heat causes the water molecules to transition from liquid to vapor, which then escape from the wood.
  2. Pyrolysis: As the temperature increases, the wood begins to break down through a process called pyrolysis. This process involves the thermal decomposition of the wood’s organic compounds into smaller molecules such as gases, liquids, and solid char. The gases and liquids released during pyrolysis include water vapor, carbon dioxide, carbon monoxide, methane, and various volatile organic compounds (VOCs). These gases and vapors are collectively known as wood smoke.
  3. Ignition: When the temperature of the wood and released gases reaches a certain point, known as the ignition temperature, the gases ignite and produce a visible flame. This is the stage of combustion that most people associate with burning wood.
  4. Combustion: During the combustion stage, the ignited gases react with oxygen in the air. The primary reactions involve the oxidation of carbon, hydrogen, and other elements in the wood, producing water vapor, carbon dioxide, and other gases. These exothermic reactions release heat and light, which sustain the combustion process.
  5. Char burning and ash formation: After the volatile gases have been burned off, the remaining solid char, which is mostly composed of carbon, continues to burn slowly in the presence of oxygen. This process is called char burning, and it results in the formation of ash, which is the residue of inorganic compounds that do not burn, such as minerals and metals.

 

The chemical equation for the combustion of wood:
C_xH_yO_z + O2 → CO2 + H2O + heat

Usually lignin and cellulose are tightly bound together and make wood very strong and resilient. Many trees can resist hurricane force winds without breaking or toppling.

When wood gets hot, however, in the vicinity of 260º Celsius (500º Fahrenheit), the cellulose and lignin molecules disintegrate and separate. This allows the carbon to mix with oxygen in the air to make carbon dioxide, and for the hydrogen to mix with the oxygen to make water.

These energetic reactions are what we call “burning”. Flames generally consist primarily of CO2, H2O, oxygen, and nitrogen.

When heated sufficiently, the gases may become ionized and move into the fourth state of matter, plasma. A candle flame is not hot enough to have any plasma aspect to it. Something must be very hot indeed to disassociate electrons from the nucleus of an atom so that the two swim around independently.

Both CO2 and H2O vapor are gases that are invisible to our eyes. What has happened is that the solid wood has simply altered its state to become heat, light, and two types of gas. That vapor is carried away by the air, explaining where the mass seemingly disappears to…

As Antoine Lavoisier observed in 1785, “matter is neither created nor destroyed”, which applies equally to energy, too, since matter and energy are simply two states of the same thing. His Law of the Conservation of Mass thus became the Law of the Conservation of Mass-Energy that we know today, aka: the First Law of Thermodynamics.

Campfire smoke follows people around a campfire because we create low-pressure areas to flow because we disrupt the vacuum around the fire automatically. Your clothing will also start to absorb heat, causing the hot air from the fire to bring smoke towards you.

 

What Affects the Direction of Smoke from A Campfire?

To properly stop yourself from getting smoked out of your campsite, you need to understand all the things that will affect the smoke from the fire. You need to consider several things when trying to control the direction of the smoke, especially if you are making a fire on the ground.

Each of these will have different effects on how the smoke travels and how the heat permeates throughout your campfire. We recommend that you ensure that everything is considered when you first choose the location of your campfire, as your tent might be the victim of the smoke.

 

Air Temperature

The colder the surrounding air is, the less likely it is that the smoke will be attracted to you, like the heat from the fire rises more rapidly. However, if it is relatively warm, the heat spreads out more, taking the smoke with it; this is why it’s recommended to have a smaller, hotter fire in summer.

When it is cold, the heat from the fire rises almost straight into the air, causing a stronger vacuum to be formed around it, naturally taking all smoke with it. During winter, it’s always best to consider this, as the fire will keep you warm and smoke will be less of a problem thanks to this effect.

 

Air Pressure

The air pressure of the altitude you are camping at and the air pressure around the fire will need to be considered when you create the fire. If you are low-pressure, the rising heat is more likely to settle down, while higher pressure areas will have hot air rising to low-pressure areas.

Your tent, chair, other people, and equipment around the fire also affect the fire’s total air pressure levels. You must ensure that the pressure stays the same, which is usually why smoke travels towards the person that has just joined the fire circle.

 

What You Wear

The chances are that if you are wearing an oversized jacket when you start the fire, this jacket absorbs the heat from the fire, attracting the smoke. This is why people who only have a t-shirt and shorts attract the smoke less often than those who are wearing more clothes.

You should be wearing a jacket, even when sitting next to a campfire, which is why it’s better to sit when you are next to a campfire. This lowers your total mass and means that you are absorbing heat from the side of the fire, away from the direction that the smoke is most likely traveling.

How Close You Are

This is most often the cause of smoke suddenly overtaking you, as you want to be closer to absorb as much heat from the fire as possible. However, this creates a fluctuation in air pressure and the heat to be absorbed, attracting the smoke towards you all at once.

Moving away, either standing a bit further away or moving your chair backward, will naturally allow the smoke to move away from you. As the pressure changes and the heat is not absorbed, the fire will correct itself, and the air will take all the smoke into the air.

 

What Can You Do To Reduce Campfire Smoke?

Now that you know what can cause it, you need to be aware of how you can force the smoke from happening. This is the trick that many veteran campers use when they create their fires, as a good campfire should not have any smoke to deal with at all.

Timing

The wood you are using will heavily determine how much smoke you have from your campfire, with a large number of people thinking that wet wood will dry out in the fire. However, if you are using wood that is still a bit wet, there will be constant smoke, even with the hottest fire.

To ensure that you are not getting constant smoke, you must use the driest wood you can find, ignite instantly instead of smoldering. Wet wood smolders for quite a while before actually burning, taking away heat from your fire and making large plumes of smoke.

Force Airflow

This is the way that few people think about having their smoke controller and their fire burning hot. Building a funnel out of rocks around the fire and ensuring that it is not an entirely closed circle; the fire will move the air and smoke away from you.

Having fresh airflow over the fire will ensure that it does not respond poorly to new people joining the fire circle. Further, the smoke moves in how the air is flowing; if there is a constant flow of air away from people, the smoke will follow this.

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Best types of wood for minimal smoke production in campfires.

  1. Hardwoods

Hardwoods, such as oak, maple, hickory, and ash, are excellent choices for campfires. I found hey burn longer and produce less smoke than softwoods, 6 logs last me 3 hours. I usually bring 2 bundles of 6 each.

  1. Fruitwoods

Fruitwoods, such as apple, cherry, and peach, are another great option for campfires. They have a sweet smell and burn cleanly, with very little smoke production.

  1. Nutwoods

Nutwoods, such as pecan and almond, also burn cleanly and produce very little smoke. They are a great choice for campfires if you can find them.

  1. Cedar

Cedar is a popular choice for outdoor fires, as it has a pleasant aroma and burns cleanly. However, it should be used sparingly, as it can produce a lot of smoke if burned in large quantities.

  1. Pinion Pine

Pinion Pine is a great choice for campfires, as it produces very little smoke and has a pleasant aroma. It is commonly found in the western United States at reasonable expense.

  1. Beech

Beech is another hardwood that is a good choice for campfires. It burns hot and produces very little smoke, making it a great option for cooking over an open fire.

  1. Ash

Ash is a hardwood that produces very little smoke and burns hot. It is also easy to split and is a popular choice for firewood.

  1. Birch

Birch is a hardwood that produces very little smoke and burns hot. It is also easy to split and is a popular choice for kindling.

  1. Maple

Maple is a hardwood that burns hot and produces very little smoke. It is also a popular choice for cooking over an open fire.

  1. Oak

Oak is a hardwood that burns hot and produces very little smoke. It is a popular choice for firewood, as it is easy to split and burns for a long time.

How Do You Avoid the Smoke from A Campfire?

Moving a few steps away from the fire will cause the vacuum around the fire to work correctly, pulling the smoke in the direction of the wind. A constant draft of wind sitting or standing away from it will cause the smoke to follow that draft and not get near anyone.

A standard solution found with permanent campfire locations is to raise the campfire slightly higher simply. Doing so means that you are sitting equal with the fire, with most chair legs coming up to the bottom of the fire, creating a natural way for the smoke to rise above you.

I have noticed firelogs give off more smoke than firewood. I get the fire started using one per 3 regular logs so I do not have to use small sticks and kindling. This way I have a full fire going in about 15min.

The most simple rule of thumb is that the smoke will never travel down; it will always rise, even when it is going sideways first. If the fire is too hot or is on an equal level when sitting, the smoke will always travel away from you as you are not disrupting airflow.

 

I can still recall that autumn weekend when I ventured into the heart of the Shenandoah Valley for a camping retreat. The air was crisp, carrying the scent of fallen leaves and pine, and the forest was alive with the vibrant colors of the season. Setting up my campsite was like a ritual, each step deliberate, from pitching my tent to gathering wood for the campfire.

As dusk approached, I carefully built a campfire, mindful of the safety measures I’d learned over years of outdoor adventures. The fire pit, a circular stone enclosure about 3 feet in diameter, was the centerpiece of my site. I arranged the kindling and logs in a classic teepee structure, leaving enough space to allow the fire to breathe. Striking a match, I watched the flames come to life, their warm glow a stark contrast against the encroaching night.

But as the fire grew, so did an unexpected annoyance: the smoke seemed to have developed a fondness for me. No matter where I moved, it followed, as if I were a magnet for the gray, swirling tendrils. I shifted my foldable camping chair—a lightweight, aluminum-framed seat with a durable polyester fabric—from one side of the fire to the other, but the smoke pursued me relentlessly.

I tried the old trick of saying, “I hate rabbits,” a silly superstition that’s supposed to ward off campfire smoke, but to no avail. The smoke clung to me, seeping into my clothes and hair. It was as though the smoke had a mischievous spirit, playing a game only it knew the rules to.

I couldn’t help but laugh at the situation, remembering childhood camping trips where my cousins and I would compete to see who could evade the smoke the longest. Those memories brought a smile to my face, even as my eyes watered from the pungent sting.

Eventually, I resigned myself to the smoke’s presence and focused on the hypnotic dance of the flames. They flickered in shades of orange, red, and blue, casting a warm, flickering light that illuminated the surrounding trees. The fire crackled and popped, sending sparks up to join the stars that had begun to pepper the night sky.

Despite the smoke’s persistence, I felt a deep sense of peace sitting there by the fire. The hardships of daily life seemed to melt away, replaced by the simple joys of being one with nature.

Alternatives to campfires:

  1. Propane or gas stoves: These are popular among campers who prefer a flameless heat source.
  2. Solar-powered lights: These are a great option for those who want to create a cozy atmosphere without the heat of a fire.
  3. Battery-powered heaters: These heaters are ideal for camping in colder months.
  4. Natural materials: You can also use natural materials such as leaves, branches, and pine cones to create a small fire without producing a lot of smoke.
  5. Cook stoves: A cook stove can be used to prepare meals while camping. They are portable, easy to use, and come in various sizes and styles.
  6. Charcoal grills: Charcoal grills are another option for campers who want to cook food without the use of a campfire. They are portable and easy to use, making them perfect for camping trips.

 

Environmental Concerns

  1. Air quality: The smoke from campfires contributes to air pollution, particularly in popular camping areas where multiple fires may be burning simultaneously.
  2. Greenhouse gas emissions: Burning wood releases carbon dioxide, a greenhouse gas that contributes to climate change. Although wood is considered a carbon-neutral fuel source, burning it inefficiently can still release excessive amounts of carbon dioxide into the atmosphere.
  3. Wildlife disturbance: Smoke from campfires can disrupt local wildlife by displacing animals from their natural habitats and affecting their behavior. Not good.

What smoke is made of:

  1. Carbon monoxide
  2. Carbon dioxide
  3. Methane
  4. Nitrogen oxides
  5. Sulfur dioxide
  6. Formaldehyde
  7. Benzene
  8. Polycyclic aromatic hydrocarbons
  9. Fine particulate matter (PM2.5)
  10. Volatile organic compounds
  11. Ammonia
  12. Hydrogen chloride
  13. Hydrogen sulfide

 

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