Questions tagged [combustion]

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4answers
122 views

Does burning always produce a flame and if so why?

I have been looking at thermodynamics and I tried to find the answer on the internet but nothing of relevance came up and even this site did not have the answer so I ask this question to any physics ...
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1answer
47 views

Another Free Energy Question :P :)

Hello StackExchange users. Before you read my question I would like to thank you for taking the time to help me out :). So anyways, my question is about the formation of coal seeming to break the laws ...
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1answer
61 views

Water from air concept – is this plausible?

Here’s an idea I had: Consider how a rocket stove works.. There is an inlet where wood is fed into the stove and an outlet for which the exhaust can vent. Very simple but very effective. Now apply ...
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2answers
59 views

How much energy is needed to make fire?

I'm so curious about fire. So I searched a lot in the internet. And now, I knew that fire is some kind of chain reaction and combustion energy make the other molecule hot and the other molecule makes ...
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2answers
11k views

Why doesn't increasing the temperature of something like wood or paper set them on fire?

Imagine we have paper book. If we put this into a pan and increase its temperature, this book would not catch on fire. If on the other hand the book interacts with this heat source directly, it does ...
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3answers
80 views

Why use multiple cylinders in an internal combustion engine?

In an Internal Combustion Engine, why have eight cylinders in an engine? Why not have one big cylinder of same displacement of eight cylinders instead?
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1answer
49 views

When we burn a wood it burns with flame although it do not contain any gaseous substance [duplicate]

In books it is given that flame is only produced when gaseous substance burn but when dry wood is burnt it also burn with flame.why.
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1answer
78 views

Why does the flame of a gas stove not spread backwards?

On lighting a gas stove the flame is active only above the burner. However, the gas input from beneath the burner and all the way to the pipeline contains gas fuel. Why doesn't it all ignite up ? I am ...
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0answers
16 views

Breaking the Strain Rate into normal and tangential components

I was looking through a set of notes on combustion and I found this definition of the strain rate at a point on a flame surface: $K_s = -\mathbf n \cdot \mathbf E \cdot \mathbf n $ where $ \mathbf n$...
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3answers
459 views

Would blowing someone else's candle out make mine shine brighter?

Is the claim in this sign correct? Would a candle shine slightly brighter with slightly more oxygen in the room? And what do you mean "The candles aren't literal."?
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0answers
16 views

Why does Magnesium burn hotter than other Group 2 elements?

It seems apparent, when one performs the standard "flame tests" in a lab, for the Group II elements that Magnesium burns by far the hottest and brightest. Why is this true? I wouldn't expect this at ...
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1answer
75 views

When we burn a match stick it did not go at $c$ speed, why?

When we burn a match stick then mass is converting into energy then according to the relativity match stick particles should go at speed of light but it did not happen why
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Deconstructing harmonics

If I am firing a burner into a cylindrical chamber with a flat rear refractory wall, and we are experiencing constructive amplitude because of a coincidence of sound frequency and vessel length - can ...
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2answers
80 views

Is spark from spark plug in SI engine (IC engine) not counted as a hot reservoir in Heat Engine?

Are the Heat Engine (HE) and Internal Combustion Engine (ICE) not the same because ICE only exchanges the heat to the surrounding[only one reservoir]? And I have a question what if it's an SI engine ...
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1answer
17 views

Can fire create pressure if it released it energy as fast as an explosion [closed]

Since fire release energy, I wanna know if it can create a shockwave if it release it energy as fast as an explosion
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0answers
183 views

Why does the humidifier “really” make a stove's flame orange? [duplicate]

I answered this question- Why does the humidifier make a stove's flame orange? and earned 300 rep points for it as an "accepted" answer, but serious doubts have arisen about its correctness. ...
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6answers
13k views

Why does the humidifier make a stove's flame orange?

Just like this guy's, the color of my stove's flames were affected by the humidifier as well. Why does this happen? Is it a good thing or a bad thing ?
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0answers
58 views

Is flame temperature and the temperature above the flame about the same?

This is a practical question that looks not that academic. I'm trying to design an integrated forge that can do heating and forging together. Blacksmiths usually make a forge kiln like Figure 2, as ...
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1answer
97 views

Ideal gas law in combustion engine analysis

I'm studying this derivation of the Diesel engine theoretical efficiency: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/diesel.html Here the ideal gas law is used in many occasions. Why is it ...
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1answer
66 views

How much UV does a hydrogen flame emit?

A hydrogen flame is invisible but emits ultraviolet (and infrared) radiation. How much UV does a hydrogen flame emit for a given reactant flow or a given heating power? Could a hydrogen flame be used ...
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2answers
242 views

Does the depth that the accelerator pedal is depressed correspond more closely to the force or the power that the engine delivers to a car?

Consider a car that only moves directly forward without turning (so that we can model its trajectory as motion in one dimension), and assume we can neglect both air resistance and the frictional ...
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1answer
35 views

Does the presence of a flame affect the flow rate of gas out of a lighter or torch?

If I were to set a propane torch's valve to a fixed open position, would it run out of gas faster lit or unlit? Does the flame produce any kind of pressure change that affects the flow rate through ...
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2answers
96 views

If it was heated up enough, could water-soaked wood in a vacuum catch on fire? [closed]

Obviously you can set a damp piece of wood on fire- not exactly revolutionary. I specifically mean if the wood was in a perfect vacuum. It doesn't matter where the heat comes from-just say the amount ...
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2answers
397 views

Is a flame whistle, pipe organ or flute possible?

Could one arrange a simple candle or wick oil lamp in a way that it would make a sound while it is burning? A simple device without a Sterling engine etc. Does the rising hot air have enough energy ...
3
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0answers
28 views

Surface fluctuations in the combustion of ethanol in a woosh bottle

A whoosh bottle demonstration typically involves igniting ethanol vapor in a large bottle with a narrow opening. The rapidly expanding gas creates the whooshing noise as it vacates the container. This ...
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1answer
66 views

How does the lower-explosion-limit (LEL) of gasoline depend on O2 concentration?

The lower-explosion-limit (equal to lower-flameable-limit) of gasoline is 1.4 vol.-%. (https://en.wikipedia.org/wiki/Flammability_limit) I assume that this value derived for the mixture between ...
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1answer
35 views

What is the purpose of a combustion chamber in a jet engine? [duplicate]

I've learned that in combustion chamber fuel and air are mixed and burned but I dont understand the outcome. Ive heard that after combustion it is still very hot and I also seen that you loss heat as ...
2
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1answer
32 views

Are all spark types occurring for the same reason?

Are all sparks the same exact thing, merely created by different means? Or are some sparks actually different in some fundamental way? There are 3 types of sparks I notice that all look identical ...
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1answer
108 views

Fire behaviour in microgravity

The NASA has conducted an experiment in space (Flame Extinguishment Experiment (FLEX)) where they'd initiate a combustion in microgravity in order to test the effectiveness of different fire ...
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2answers
224 views

Does internal energy increase or decrease during a combustion reaction?

Combustion has negative enthalpy, and negative q. By dU = q + w (assume constant pressure), dU should be negative. However, U is a function of T, yet the gas gets hotter after combustion. Is dU ...
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1answer
41 views

Why can't you blow out a smouldering reaction?

It's possible to blow out a candle flame so how come once it's blown out, if the wick is still smouldering, blowing on it just makes it glow brighter instead of stopping the smouldering reaction.
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2answers
36 views

flame temperature and pollutant

When burning fossil fuel or wood, there would always be pollutant. But some technology claims that it could redece pollution by decreasing the burning temperature. Is that true? And can any one give ...
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1answer
389 views

Purpose of coil in liquid propane torch

Many liquid propane torches (including burners for hot-air balloons) have coils placed in the line of fire heating the liquid before it reaches the nozzle. I am very puzzled by the exact function of ...
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1answer
127 views

Why did these stalagmite-like structures form on the side of my candle?

Two slender, "stalagmite-like" structures -- separated from the main mass of melted now solidified wax -- have formed on the side of my candle, rising considerably above, and below, the level at ...
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1answer
66 views

How can one calculate brightness of a flame?

I imagine there must be many factors involved in order to do so, but what are they, and what mathematical formulas are useable? Perhaps a candle, for example is a better concrete circumstance, but I'...
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1answer
53 views

What form of energy creates heat during combustion?

We know that energy is released during oxidation but it is not clear what form it takes initially. I read the energy of chemical bonds of the fuel is not much different from that of the product, so it ...
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1answer
244 views

Equivalence between LHV and energy balance in combustion

I have seen in many textbooks the following equation for a combustion chamber $$ \eta \, m_{fuel} LHV = m_{out}h_{out}(T_{out}) - m_{in}h_{in}(T_{in}). \quad (1) $$ Consider now the stoichiometric ...
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3answers
1k views

Burning vs Melting - when applied to cooking chocolate

I'm aware melting is simply heat causing molecules to go from solid to liquid, and burning is a chemical reaction, normally with oxygen; but I don't understand how this applies to cooking chocolate. ...
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1answer
113 views

Would a homogeneous stoichiometric fuel/air mixture ignite?

I'm not sure if I'm reading the details on flammability limits and air/fuel ratios correctly, but it seems to me that it wouldn't ignite. For gasoline, the stoichiometric air/fuel (mass air/mass fuel) ...
2
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1answer
739 views

What is the role of a combustion chamber in a rocket engine?

The most important function that happens in a rocket engine is the conversion of high temp/pressure gases to high velocity gases. How does the combustion chamber help in this objective. Why cant the ...
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1answer
3k views

Combustion Chamber Pressure

I am going to calculate thrust for a theoretical solid propellant rocket engine I will be making. I have come across many equations for all sorts of aspects of the rocket engine. The measurements I ...
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1answer
959 views

What explains the 'stripy' pattern on a burning wood log?

I have noticed that when I burn a wood log in my fireplace, the log will soon take on a kind of 'alligator' pattern, with vertical stripes going up, spaced somewhere between half an inch to an inch ...
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1answer
80 views

Difference of density ratio in 1D detonation(C-J point) and 1D normal shockwave as p2/p1 goes infinite

1D detonation equations: $$ \rho_1u_1 = \rho_2u_2 $$ $$ p_1 + \rho_1u_1^2 = p_2+\rho_2u_2^2 $$ $$ c_pT_1 + \frac{1}{2}u_1^2 + Q = c_pT_2 + \frac{1}{2}u_2^2 $$ 1D normal shockwave equations: $$ \...
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0answers
242 views

Why is fire sticky? [closed]

I've always wondered why it is possible to pick things up with a burning ember if those things also catch fire. The simplest example I know of, or perhaps just common, is the "cherry" falling off a ...
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0answers
173 views

Physics behind a blue “firenado”

In the NYTimes video Harnessing the Firenado, a rotating yellow sooty flame is suddenly transformed into a clean blue rotating flame. What is the physics behind this transformation? What is it about ...
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2answers
865 views

Calculating internal energy of formation

I'm working on some code to simulate combustion at constant volume instead of constant pressure and I need to calculate the internal energy of formation for the species involved because I can only ...
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1answer
270 views

Adiabation Flame Temperature Overestimation (Hydrogen Gas)

I'm working on some code that computes adiabatic flame temperature given a balanced equation and the relevant thermodynamic properties and I'm starting with the simplest combustion reaction I can ...
4
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3answers
367 views

Flame shape and size (length) depending on gravity [duplicate]

How would the shape and size of a flame, e.g. from a simple candle depend on gravity? Suppose all the relevant information is known, including candle dimensions and chemical composition, atmosphere ...
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1answer
181 views

What's the minimum time scale for a candle to be lit in order for it to establish a steady state?

My Understanding When a candle is lit initially, it goes through a few stages (see, e.g. this explanation from the National Candle Association): Wick burns. Crusted wax on wick melts, evaporates ...
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1answer
309 views

Why do things catch fire from flame more easily than from a hot object?

I was just reading some chemistry article and among the list of materials there was: hotplate or other flameless heat source (to avoid igniting the ethanol) This made me wonder. It's ...