The ultimate analysis provides weight percentages of C, H, O, N, and S. The carbon content of softwood species is 50-53%, and that of hardwood species 47-50% due to varying lignin and extractives content. All wood species contain about 6% H. At high temperatures, char contains little hydrogen.

Wood is mainly constituted by elements of carbon (C, 50%), oxygen (O, 44%), and hydrogen (H, 6%).

For most fuels, chars, and volatiles, the heat of combustion correlates roughly with its carbon content. This correlation is due to the cancellation of effects from hydrogen atoms in some fuels and oxygen in others.

Overall, wood has an elemental composition of about **50% carbon, 6% hydrogen, 44% oxygen**, and trace amounts of several metal ions (Rowell, 2013).

There are two major chemical components in wood: **lignin (18–35%) and carbohydrate (65–75%)**. ... Overall, wood has an elemental composition of about **50% carbon, 6% hydrogen, 44% oxygen**, and trace amounts of several metal ions.

Average chemical contents of wood fuels – share, % of dry matter weight: Carbon 45–50%, Hydrogen 6.0–6.5%, Oxygen 38–42%, Nitrogen 0.1–0.5%, Sulphur max 0.05%. For complete combustion, C + O2 → CO2 + 32.8 MJ/kg (carbon) and 2H2 + O2 → 2H2O + 142.1 MJ/kg (hydrogen).

In short, wood undergoes thermal degradation as it heats up, giving rise to volatile, flammable gases which burn when they contact a source of ignition. Cellulose, hemicellulose, and lignin, the principal components of wood, decompose over different temperature ranges, producing a complex mixture of gases, vapors, and char.

This study affirms that the fire behaviour of wood is highly dependent on several factors including the species, moisture content, experimental conditions, density, heat exposure time, etc. However, it is quite clear that, wood flammability is a very complex process due to the fact that three main constituents, cellulose, hemicellulose and lignin, ‘degrade’ at different temperatures. Cellulose pyrolysis determines the combustion rate of wood since it releases a major part of the flammable volatiles.

All of these compounds consist of roughly 50% carbon (C), 44% oxygen (O), and 6% hydrogen (H). The combustive heat values of the deciduous specimens ranged from 18.88 to 21.98 MJ/kg, with an overall average combustive heat of 20.25 MJ/kg. The similar elemental composition explains the relatively narrow range in heat of combustion among species.

For an organic fuel of composition C_c H_h O_o N_n, the (higher) heat of combustion is 418 kJ/mol × (c + 0.3 h − 0.5 o) usually to a good approximation (±3% for more than 500 organic compounds). The heating value can be calculated using Dulong's formula, which treats carbon, hydrogen, sulfur as combustible elements: HHV [kJ/g] = 33.87 m_C + 122.3 (m_H − m_O/8) + 9.4 m_S, where m_C, m_H, m_O and m_S are the mass fractions of carbon, hydrogen, oxygen, and sulfur. A typical wood fuel has a higher heating value around 16–21 MJ/kg, reflecting its carbon and hydrogen content partly offset by bound oxygen.

The major chemical elements found in natural wood products are carbon, hydrogen, and oxygen. When thermally decomposed, these elements primarily produce carbon monoxide, carbon dioxide, and water.

Once the wood gets to about 150°C, the cellulose in it starts to decompose (pyrolysis) and releases volatile organic compounds. The burning of the volatiles provides most of the flames you see.

The chemical composition of wood varies from species to species, but is approximately **50% carbon, 42% oxygen, 6% hydrogen, 1% nitrogen, and 1% other elements** (mainly calcium, potassium, sodium, magnesium, iron, and manganese) by weight. Wood also contains sulfur, chlorine, silicon, phosphorus, and other elements in small quantity. It consists of cells, and the cell walls are composed of micro-fibrils of **cellulose (40–50%) and hemicellulose (15–25%)** impregnated with **lignin (15–30%)**.

Medium dry wood contains **49 to 50% carbon, 6% hydrogen, 43 to 44% oxygen** and only slightly 0.12% nitrogen. Wood consists of organic substances, which contain the following chemical elements: **carbon (C), hydrogen (H), oxygen (O) and nitrogen (N)**.

The average chemical composition of wood used in this study was 49.5% of carbon, 6.3% of hydrogen and 44.2% of oxygen. Material with higher density uses more energy to ignite and burn, however the tree species with higher hemicellulose content are more flammable even in case that they have higher density.

The net heat of combustion for cellulosic materials was found to be 13.23 kJ/g times the ratio of stoichiometric oxygen mass to fuel mass, r_o, regardless of the material composition. The stoichiometric oxygen consumption to fuel ratio can be derived from elemental contents and correlated to wood structural contents as r_o = 1.19(fraction holocellulose) + 1.91(fraction lignin). This shows how elemental composition, particularly carbon and hydrogen bound in holocellulose and lignin, controls combustion heat release.

The vapors are called volatiles and the char is composed of carbon and ash. The volatiles are what actually begin to burn, producing a flame. The carbon-rich char produces glowing embers or coals, which are needed to keep the fire sustained.

Vegetal biomass mainly consists of carbon (C), oxygen (O) and hydrogen (H). Through oxidation of carbon the fuel energy content is released. The higher heating value of wood fuels is primarily related to their carbon content, while chemically bound oxygen reduces the energy available from combustion.

Summing these heats of combustion weighted by their composition element mass fractions obtains the overall heat of combustion. The net and gross heat of combustion via the oxygen consumption correlation (Dietenberger 2002) for each composition element j (lipid, glucose, fructose, protein, pectin, hemicellulose, cellulose, starch, phenolic, lignin, minerals, and silicates) demonstrate that the combustible organic components rich in carbon and hydrogen dominate the heat of combustion of plant materials, whereas mineral and ash components do not contribute.

The materials in wood mostly consist of organic molecules made of only hydrogen, carbon and oxygen. Cellulose has lots of chemical energy stored in its C–C and C–H bonds. When the wood temperature increases to over 250°C, the cellulose inside begins to break down. The smaller pieces of cellulose are still organic molecules, so they can combine with O2 to form CO2 and H2O.

Elemental makeup of the dry wood (typical): C ~50%, H ~6%, O ~44%. The lower heating value (LHV) of dry wood is about ≈ 15 MJ/kg (this varies with species and moisture), and the net heat of combustion for seasoned wood (wet) is about 15 MJ/kg as well. These values are based on typical elemental composition and demonstrate that roughly half the wood’s mass as carbon and a small fraction as hydrogen account for its energy content when burned.

The chemical composition of wood varies from species to species, but is approximately **50% carbon, 42% oxygen, 6% hydrogen, 1% nitrogen, and 1% other elements** (mainly calcium, potassium, sodium, magnesium, iron, and manganese) by weight. Lignin is the third component at around **27% in coniferous wood vs. 23% in deciduous trees**. Cellulose makes up **41–43%** and is a crystalline polymer derived from glucose.

Combustion of biomass: C and H oxidize in an exothermic reaction. The carbon content in biomass is considerably higher (~45%) than the hydrogen content (~6.5%). The main combustible chemical elements of solid fuels are carbon and hydrogen.

Average chemical contents of wood (elements, % of dry matter weight): **Carbon 45-50%, Hydrogen 6.0-6.5%, Oxygen 38-42%, Nitrogen 0.1-0.5%, Sulphur max 0.05**. Wood is mainly composed of **cellulose, hemicellulose, lignin and extractives**. The table shows cellulose about 39.5–45%, hemicellulose 19.2–32.4%, and lignin 22.0–31.3% depending on species.

Dry wood is primarily composed of **cellulose, lignin, hemicelluloses**, and minor amounts (5% to 10%) of extraneous materials. Cellulose, the major component, constitutes approximately **50% of wood substance by weight**. Lignin constitutes **23% to 33%** of the wood substance in softwoods and **16% to 25%** in hardwoods.

For lignin samples that do not contain carbohydrates the value of HHV_daf can reach 29.2 MJ kg−1 with the elemental composition C_daf = 70.0 wt%, H_daf = 6.5 wt%, O_daf = 23.5 wt%. In comparison, fuel elemental composition for typical biomass shows C_daf ≈ 44.4 wt%, H_daf ≈ 6.2 wt%, O_daf ≈ 49.4 wt%. These data illustrate that higher carbon content (with similar hydrogen) in lignin correlates with higher heating value, supporting the role of carbon and hydrogen in fuel energy but also showing that oxygen lowers HHV.

All common wood is made up of roughly 50 ±3% carbon, 6 ±1% hydrogen and 44 ±3% oxygen with the rest inorganic ash. Softwoods tend toward higher carbon and lower oxygen content than hardwoods.

The flammability of the pyrolytic gases from wood therefore comes largely from the mist of tar carried with them. At higher temperatures, wood pyrolysis produces gases and tars that drive the flame.

Wood is a mixture of three natural polymers -- **cellulose, lignin and hemicelluloses -- in an approximate ratio of 50:25:25**, depending on species, biological variations such as genetic differences within species, and growing conditions. Cellulose is a long-chain polymer of glucose. Lignin and hemicelluloses are the other major constituents of wood.

When carbonising fir wood to 777 °C, the resulting char residue is 91.2% carbon, 1.5% hydrogen, 4.0% oxygen, 0.1% nitrogen, and 3.1% ash; at 877 °C it is 92.1% carbon, 1.2% hydrogen, 3.3% oxygen, 0.1% nitrogen, and 3.3% ash. The calorific value depends on the amount of carbon, hydrogen and oxygen in the material.

Wood is approximately **60-75% cellulose, 20-30% lignin, 1-10% extractives and 0-4.5% ash** (Marra, 1992). Three elements, namely **carbon, hydrogen, and oxygen**, are organized into β-D-glucose units and linked together to form long linear chains that are arranged in one plane (describing cellulose). Generally, softwoods have a larger percentage of lignin than hardwoods, accounting for **23-33% in softwoods and 16-25% in hardwoods**.

Science Spotlight: The combustion of wood – wood is made up of a bunch of different compounds that contain mostly carbon, hydrogen and oxygen atoms and these compounds are held together by bonds. When wood is heated, some of the bonds break and different chemical compounds are released as vapor into the air. When these vapors mix under high heat with oxygen from the air, they burn and release more heat and also produce carbon dioxide and water.

The element composition of dry wood is about **50% carbon, 6% hydrogen, 44% oxygen**, and less than 0.1% nitrogen. The chapter further breaks down proportions of lignin and cellulose in different wood species, confirming the dominance of carbon-rich biopolymers such as cellulose and lignin in wood.

Combustion, the process through which firewood burns, involves the reaction of the wood's main components—cellulose, hemicellulose, and lignin—with oxygen from the air. When ignited, these components undergo rapid oxidation. Oxygen molecules collide with the carbon and hydrogen atoms in the wood, breaking and reforming bonds in a cascade of reactions that release energy and produce carbon dioxide and water as primary combustion products.