What is Combustion: Definition and 357 Discussions

Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion does not always result in fire, because a flame is only visible when substances undergoing combustion vapourise, but when it does, a flame is a characteristic indicator of the reaction. While the activation energy must be overcome to initiate combustion (e.g., using a lit match to light a fire), the heat from a flame may provide enough energy to make the reaction self-sustaining. Combustion is often a complicated sequence of elementary radical reactions. Solid fuels, such as wood and coal, first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them. Combustion is often hot enough that incandescent light in the form of either glowing or a flame is produced. A simple example can be seen in the combustion of hydrogen and oxygen into water vapor, a reaction commonly used to fuel rocket engines. This reaction releases 242 kJ/mol of heat and reduces the enthalpy accordingly (at constant temperature and pressure):

2H2(g) + O2(g) → 2H2O(g)Combustion of an organic fuel in air is always exothermic because the double bond in O2 is much weaker than other double bonds or pairs of single bonds, and therefore the formation of the stronger bonds in the combustion products CO2 and H2O results in the release of energy. The bond energies in the fuel play only a minor role, since they are similar to those in the combustion products; e.g., the sum of the bond energies of CH4 is nearly the same as that of CO2. The heat of combustion is approximately −418 kJ per mole of O2 used up in the combustion reaction, and can be estimated from the elemental composition of the fuel.Uncatalyzed combustion in air requires relatively high temperatures. Complete combustion is stoichiometric concerning the fuel, where there is no remaining fuel, and ideally, no residual oxidant. Thermodynamically, the chemical equilibrium of combustion in air is overwhelmingly on the side of the products. However, complete combustion is almost impossible to achieve, since the chemical equilibrium is not necessarily reached, or may contain unburnt products such as carbon monoxide, hydrogen and even carbon (soot or ash). Thus, the produced smoke is usually toxic and contains unburned or partially oxidized products. Any combustion at high temperatures in atmospheric air, which is 78 percent nitrogen, will also create small amounts of several nitrogen oxides, commonly referred to as NOx, since the combustion of nitrogen is thermodynamically favored at high, but not low temperatures. Since burning is rarely clean, fuel gas cleaning or catalytic converters may be required by law.
Fires occur naturally, ignited by lightning strikes or by volcanic products. Combustion (fire) was the first controlled chemical reaction discovered by humans, in the form of campfires and bonfires, and continues to be the main method to produce energy for humanity. Usually, the fuel is carbon, hydrocarbons, or more complicated mixtures such as wood that contains partially oxidized hydrocarbons. The thermal energy produced from combustion of either fossil fuels such as coal or oil, or from renewable fuels such as firewood, is harvested for diverse uses such as cooking, production of electricity or industrial or domestic heating. Combustion is also currently the only reaction used to power rockets. Combustion is also used to destroy (incinerate) waste, both nonhazardous and hazardous.
Oxidants for combustion have high oxidation potential and include atmospheric or pure oxygen, chlorine, fluorine, chlorine trifluoride, nitrous oxide and nitric acid. For instance, hydrogen burns in chlorine to form hydrogen chloride with the liberation of heat and light characteristic of combustion. Although usually not catalyzed, combustion can be catalyzed by platinum or vanadium, as in the contact process.

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  1. A

    I How is combustion energy released?

    Is it possible that in combustion, the chemical energy of reaction is released wholly through photon emission. Say as in simple burning of wood.
  2. Astronuc

    Hydrogen-fueled Internal Combustion Engine (ICE)

    https://www.msn.com/en-us/autos/news/toyota-s-upcoming-hydrogen-powered-5-0-v-8-engine-has-the-potential-to-bury-evs/ar-AA15Q9mq See also an old thread - https://www.physicsforums.com/threads/hydrogen-combustion-engines.70653/ But what material. I know that Nippon Steel & Sumitomo Metals...
  3. A

    B Deuterium combustion within inertial fusion schemes

    Hydrogen as well as Deuterium are both flammable chemically, I read that both hydrogen as well as deuterium can ignite/combust upon compression even in ordinary ICE engines. Hydrogen has been investigated and used as fuel for internal combustion engines. Now in a inertial fusion approach the...
  4. agm

    Finding the Equivalence Ratio of Combustion (Methane + Air)

    I'd like to do some experiments with flames at different Equivalence Ratios - but I'm confused as to how I can find the Equivalence Ratio for different conditions. Wiki-article So the stoichiometric balance for Methane + Air is CH4 + 2(O2 + 3.76N2) -> CO2 + 2H2O + 7.52N2 Referencing equations...
  5. J3J33J333

    I Can you put out a fuse (fire) with a laser?

    I was wondering you if you could use a laser to put out a fuse or to stop combustion? Could you use some form of laser/laser cooling to put out an explosion mid-explosion?
  6. J3J33J333

    Why don't cars use something like a rail gun instead of combustion?

    Why don't cars use something like a rail gun instead of combustion to drive pistons?
  7. R

    How does a 4-piston, 4 stroke internal combustion engine work?

    Hi, This post is about a 4-piston, 4 stroke internal combustion engine(ICE).Here is an youtube animation for such an engine. I actually have 2 questions. Q1: We have seen in demos and videos that in a 4-piston (ICE) engine, the pistons P1 ,P4 (pair 1) and P2, P3 (pair 2) are in phase when...
  8. M

    Internal Combustion Engines: Liquid Gasoline or Vapor?

    In an Internal Combustion Engine, does liquid gasoline itself burn/combust, or is it the gasoline VAPOR emitted from the liquid gasoline by evaporation that burns/ combusts? (assuming that Oxygen is present in the Air and Fuel mixture)
  9. duchuy

    Maximum flame temperature during Combustion of CH4

    Hi, I have to calculate the maximum flame temperature of the reaction above. The answer is 4805K but I didn't manage to obtain that answer. Please help me find my error, thank you so much! The values of C are below the solution attempt.
  10. voltech444

    Automotive Ozone Enhanced Combustion of Water/Diesel Emulsion in CI Engines

    I have a single cylinder 5kW diesel generator to use for fuel efficiency and emissions reductions improvement experiments. I built an emulsifier out of an old drill press and paint cans. It's basically just a spinning cylinder inside another cylinder to get a lot of shearing force. The...
  11. L

    Biomass gasification unit vs biomass combustion unit

    Good morning to all of you. For my diploma thesis I have to compare the combined production of electricity and heat from a biomass gasification unit and from a biomass combustion unit. So I would like to ask you if you know data or refer me to papers so that I can compare these 2 technologies...
  12. ZdMh

    Automotive Can I convert a combustion engine car to a hybrid car?

    Hello all, I'm thinking of converting my car to Electricity. I know that some internal systems have to change. Can that work? and how?
  13. seandepagnier

    Hydrogen combustion catalyst

    I am interested in build a hydrogen stove for cooking and wish to use a catalytic stove. I cannot find much information about this anywhere, but only that nickel can be used for hydrogen rather than platinum. 1) Can I just use stainless scotch brite scrub pad as catalyst assuming it...
  14. D

    Chemistry Thermochemistry and the heat of complete combustion

    The balanced reaction wil be : ##2C_6H_{6(l)}+15O_{2(g)}->12CO_{2(g)}+6H_2O_(l)## in order to compute the the standard enthalpy of reaction : ##\Delta H°_{f} H_2O_(l)= -285,8 \frac {KJ}{mol}##; ##\Delta H°_{f} CO_{2(g)}= -393,5 \frac {KJ}{mol}##; ##\Delta H°_{f} C_6H_{6(l)}=49,04 \frac...
  15. Seibtsantos

    Pressure in a bomb calorimeter at the moment of combustion

    First, I calculated the number of moles of glucose. n = m / M n = 1.8 / 180 n = 0.01 moles of glucose So I checked the combustion reaction. 1 C6H12O6 + 6 O2 -> 6 CO2 + 6 H20 1 + 6 -> 6 + 6 0.01 + 0.06 -> 0.06 + 0.06 I considered the number of moles at the end of the reaction. I subtracted...
  16. iVenky

    B Mass Reduction in Combustion: Real or Myth?

    I have studied in high school that all chemical reactions obey conservation of mass, as the atoms are merely re-arranged, but when I read through special relativity, I was reading that you can show an infinitesimal change in mass (based on E=mc2) in combustion that's not noticeable that's being...
  17. bobbyg

    Relative volume of combusted hydrogen

    Hi, If I had a volume of Brown's gas at 20°C / 1atm, what would the expected volume [of the resultant steam] be immediately after it was ignited? Thanks! Bob
  18. L

    Chemistry Find the formula of a hydrocarbon using combustion data

    number of moles of CO2 =0.089moles (using 2/22.4) number of moles of water = 0.067 (using 1.205/18) I know that all the carbon from the hydrocarbon is in the CO2 and all the hydrogen from the hydrocarbon is in the water and water creates x2 hydrogens so number of moles of C : H = 0.089 ...
  19. S

    Pressure/force calculation for combustion in a cylinder

    Hi. How do i calculate the dynamic combustion pressure, force and piston velocity for different fuels in a cylinder? Assuming perfect combustion and no thermal loss trough the walls and piston. I am thinking about an application similar to for example a fuel driven nail gun that runs on a...
  20. M

    Automotive Exploring Combustion Engines for Cars & Planes: Student Research Ideas

    Hi All, I am helping a student (9th grader) develop a research topic related to his interests in physics for an independent study program he is applying for at our school. My background is Geology, so I am not too knowledgeable regarding topics in physics. This student is interested in...
  21. J

    Enthelpy of combustion of acetylene and fluorine

    Hi Folks, I have been trying to find data on the enthalpy of combustion of acetylene and fluorine. I have found the data for oxygen but am curious about the use of pure fluorine in stochiometric conditions and the resulting upper heating value when the oxidant is acetylene. I am happy to...
  22. btk87

    CO Combustion Reaction: What's the Chemical Reaction?

    First time poster and also chemistry layman. I am starting on a new job building a carbon monoxide boiler in an oil refinery. As the construction contractor, we don't get into the operation/process of the equipment we build. I have found online that CO becomes combustible at around 1400F...
  23. A

    Chemistry Constant Volume Heat of Combustion from heat capacity of calorimeter

    Q=heat capacity calorimeter*(-)change in T*moles =0.009089mol*-6.8C*4.38kj/C =-0.2707kj/mol This answer is wrong but it was the only one I could come up with right now. I just noticed units in the answer would be wrong too. Any suggestions?
  24. P

    HVAC Accessible metal product for a combustion chamber

    So I'm still playing with my waste oil heating system, and as I figured the oil spraying out of the burner doesn't burn 100% clean without a combustion chamber. I set it up outside with the burner pointing into a 12" section of 6" steel stove pipe with an elbow on the end, and it works perfect...
  25. Majorana

    Smokeless (sootless) combustion of vegetable oil

    Hello :oldsmile: I need to design a little burner, fed with vegetable oils like olive, soybean, sunflower and corn (alone or as a mixture). The fundamental requisite of the burner is that it must not generate any soot (smoke): since "zero" is something hardly attainable in technology, "very...
  26. Mbenj

    How do I calculate the torque of an Internal Combustion Engine?

    Hello all, This is my first post on here so sorry if its not the greatest. I am starting to make a car based video game for the ios in which you are able to customise cars and race them. One feature i wanted to include in this game was the ability to create unique engines. I don't want it...
  27. J

    What is the heat of combustion of 1 kg carbon dioxide w/ magnesium?

    I am trying to find out the heat of combustion of one kilogram of carbon dioxide with magnesium. I am looking for results for stochiometric conditions of these two reactants. I have found the following equation online 2 Mg(s) + CO2 ---> 2 MgO(s) + C(s) yields a standard enthalpy of --810.1...
  28. DarkSkinDude

    Combustion of an explosive liquid bubble

    Problem Statement: An explosive liquid at temperature 300 K contains a spherical bubble of radius 5 mm, full of its vapour. When a mechanical shock to the liquid causes adiabatic compression of the bubble, what radius of the bubble is required for combustion of the vapour, given that the vapour...
  29. P

    Would a charged lithium battery combust more energetically?

    Conceptually this question makes sense to me I know a overcharged lithium battery will became unstable however with identical batteries except a different level of charge what would the properties of their combustion be? In depth conceptual, and mechanical explanations are always appreciated as...
  30. C

    Automotive Can anybody suggest some forum about internal combustion engines?

    Could anybody suggest some forums(or bbs(s)) of internal combustion engine? Hello guys, I'm a physics fan, recently I was doing some research of internal combustion engines, could anybody who could suggest some forums or bbs(s) of internal combustion engine? i need somewhere to find some...
  31. Delta Force

    Using Fuel as a Combustion Engine Coolant?

    Some jet and rocket engines use their own fuel as coolant. Hydrocarbons have even been used to cool electronics and nuclear reactors. Would it be viable for a combustion engine to use its own fuel as coolant instead of water or another liquid?
  32. A

    Higher and Lower heat value of combustion of Coal?

    hello my friends , i have two question about calorific value of coal why Lower heating value decrease with increase oxygen content but increase with increasing hydrogen , sulfur and carbon content ? Do this elements influence the higher heating value or not ?
  33. D

    Why is enthelpy of combustion 0Kjmol-1 for oxygen

    Homework Statement Why is enthalpy of combustion 0KJmol-1 for oxygen? I need to know this for my exam coming up soon. Homework Equations The enthalpy change when 1 mole of a substance is burnt in excess oxygen under standard states under standard conditions. The Attempt at a Solution Oxygen...
  34. Dustyneo

    Chemistry Combustion Analysis- Empirical and molecular formula

    Homework Statement Menthol, the substance we can smell in mentholated cough drops, is composed of C, H, and O. A 0.1005-g sample of menthol is combusted, producing 0.2829 g of CO2 and 0.1159 g of H2O. What is the empirical formula for menthol? If menthol has a molar mass of 156 g/mol, what is...
  35. S

    Work done by Octane Combustion Engine

    Homework Statement There is an insulated internal combustion engine fueled by one mole of octane. It operates at a constant pressure of 5.0 bar. The initial temperature is 200°C. Calculate the heat exchanged with the surroundings, the Δh for the gas, the final temperature, the work performed...
  36. José Ricardo

    About the efficiency of engines

    if we had an entire car made of Starlite (a material that was created resistant to 18032 °F). Would the efficiency of the combustion engine be close to that of the electric and that of the electric would be almost 100% efficient? https://en.wikipedia.org/wiki/Starlite
  37. C

    Heat released during combustion at constant pressure vs volume

    Greetings! I've been brushing up on some thermodynamics recently and came across a perplexing sentence in my notes and text from undergrad. It says that for a combustion reaction, such as the combustion of heptane: C7H16 (l) + 11O2 (g) ---> 7CO2 (g) + 8H2O (l) That this process carried out at...
  38. G

    Chemistry 35yo combustion chemistry PhD, free time and still no plan

    Hi there, TL/DR - I have a community college job with a sufficient salary. Should I be happy with that + freetime or should I try to get a job which really uses my PhD? If I go with happy freetime option, are any of the projects I propose interesting AND feasible? If I am too lazy to follow...
  39. C

    What is the combustion efficiency of liquid fuel rockets?

    How efficiently is the fuel burned in a typical liquid fuel rocket engine? I've heard numbers ranging from 95% to below 50%.
  40. T

    Heat Transfer and Combustion -- A furnace wall consists of three layers of material

    Homework Statement A furnace wall consists of three layers of material as shown below. The thermal conductivities are: Firebrick = 1.15 W m–1 K–1 Insulating brick = 0.17 W m–1 K–1 Ordinary brick = 0.62 W m–1 K–1 Calculate: (i) the thermal resistance of each layer (ii) the heat...
  41. T

    Heat Transfer and Combustion -- reheating furnace wall consists of 200 mm of firebrick

    Homework Statement A small reheating furnace wall consists of 200 mm of firebrick. The inner surface of the wall is at a temperature of 320 °C and the outside temperature is 35 °C. Calculate the rate at which heat is transferred, by conduction, through unit area of the wall. The thermal...
  42. Hydrous Caperilla

    Enthalpy of Combustion: Definition & Reactions

    I got two definitions for this enthalpy: I)Heat change when 1 mole of a substance is completely burned or oxidised(My textbook) 2) Heat change when 1 mole of compound is completely burnt or oxidized in oxygen(From a site) So if I had this reaction: H2(g)+1/2 O2(g)---->H20...
  43. T

    Heat Transfer & Combustion: Estimate Pipe Heat Loss/m

    << Mentor Note -- poster reminded to use the standard Template >> Question Three A pipe of outside diameter 200 mm is lagged with an insulating material of thermal conductivity 0.06 W m-1 K-1 and thickness 75 mm. The pipe carries a process fluid at a temperature of 300 °C and the average...
  44. T

    Heat Transfer and Combustion

    Question: A pipe of outside diameter 200 mm is lagged with an insulating material of thermal conductivity 0.06 W m–1 K–1 and thickness 75 mm. The pipe carries a process fluid at a temperature of 300 °C and the average temperature of the outer surface of the lagging is 45 °C. (a) Estimate the...
  45. B

    Combustion Emit Light: Reasons & Benefits

    Why does combustion emit light? For heat, for excited electrons or for other reasons?
  46. Franz Rojas Ayala

    Maximum pressure for a combustion chamber

    Greetings All! I am not sure if this is the correct place to post this, but I think that since rocket fuel is considered a chemical reaction, this sections seems appropriate. Right, to the topic. Me and my team from the spaceflight society are looking forward to building a hybrid rocket fuelled...
  47. hilbert2

    Flame in a background atmosphere of fuel

    In combustion science, typical flames that are studied are premixed or diffusion flames, where a stream of methane, propane or some other fuel is released to an atmosphere of air or oxygen and ignited. Another scenario is a "pool fire", where a puddle of volatile solvent is burning in air and...
  48. S

    Calculate the molar heat of combustion of anthracene

    Homework Statement A 2.56g sample of anthracene, C14H10, was burned to heat an aluminum calorimeter (mass=945 g). The calorimeter contained 1.50 L of water with an initial temperature of 20.5 C and a final temperature of 34.3 C. a) Calculate the molar heat of combustion of anthracene...
  49. mishima

    Butane Combustion Analysis Demo for a High School Chemistry Class

    Hi, I'm a high school chemistry teacher trying to develop a lab experience demonstrating combustion analysis. This is usually something we go through theoretically during discussion of percent composition and empirical formula. I'd like to actually perform one. I was wondering if this could...
  50. MCTachyon

    Net calorific value (CV) per kmol of an fuel/air mix

    Homework Statement [/B] A fuel gas consists of 75% butane (C4H10), 10% propane (C3H8) and 15% butene (C4H8) by volume. It is to be fed to the combustion chamber in 10% excess air at 25°C, where it is completely burnt to carbon dioxide and water. The flue gases produced are to be used to...