Lecture 8: Combustion Flashcards by Clodagh cultra

What is the combustion reaction in words

Fuel + Oxygen —–> Gases + Heat + Light

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What is the chemical combustion reaction

CH4 + 2O2 ——> 2H20 + Heat + Light

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What are the 3 sources of fuel for combustion

Solid (woods)
Liquids (accelerants)
Gas (propane, butane etc.)

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What does heat do in a combustion reaction

Breaks the bonds of the reactants

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Why is combustion an exothermic reaction

Releases energy

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Why is combustion a continuous reaction

Combustion will continue until the fuel or oxygen runs out

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What are the factors affecting the rate of combustion

Physical state of the fuel (solid, liquid or gas)
The temperature of the flammable liquids

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What are the different rates of a combustion reaction

Detonation
Deflagration

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What is detonation

The speed of combustion is faster than the speed of sound (sonic), Produces a devastating shockwave which destroys everything

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*What is deflagration

The speed of the combustion reaction is slower than the speed of sound (subsonic), produces a wave of flame front.

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What are the combustible solids

Pyrolyzable (Woods)
Non-pyrolyzable (Charcoal, Cigarettes)

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What are pyrolyzable solids

Can undergo combustion at high temperatures, without the presence of oxygen.

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When wood undergoes pyrolysis what does it produce

gaseous products

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Gaseous products + Oxygen =

Flaming fire + heat

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How long does combustion of pyrolyzable solids last

Until all solids within the wood have been consumed

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What remains following the combustion of pyrolyzable solids

a carbon based residue which undergoes glowing combustion, smoldering

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What are non pyrolyzable solids

Undergoes glowing combustion

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What is charcoal

Pure carbon

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What happens when carbon is heated

Doesn’t break down or produce vapours, instead the surface oxidises and undergoes glowing combustion

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How does the oxidation of carbon occur

Oxidation starts at the outer surface, consumes it and moves onto the next surface and continues until there is nothing left.

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What are the constituents of inorganic gun shot residue?

-Lead
-Antimony
-Barium

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What is required for definitive identification of gun shot residue?

Identification of all 3 elements
*As they can be found individually in legal things

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What technique is used to analyse inorganic gunshot residue?

SEM-EDX

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What does SEM-EDX stand for?

Scanning electron microscopy - energy dispersive X-Rays

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How does SEM-EDX work?

-The microscope produces the image of the particle -X-ray determines the elemental composition

What happens when a bullet is ejected from a gun barrel?

-Firing pin strikes the primer, detonating it producing flames -The flames ignite the propellant which produces gas causing the bullet to travel down the barrel of the gun

What are the combustion reactions causing the ejection of a bullet from a gun?

1. Firing pin strikes the primer, detonating it 2. Fire ignites the propellant

What are the series of combustion reaction causing the ejection of a bullet from a gun called?

A low explosive train

What are the changes in energy causing the ejection of a bullet from a gun?

1.Fire pin strikes primer: Mechanical energy 2.Detonation of primer produces heat: Mechanical to heat energy 3.Heat causes the production of gas: Heat to chemical energy 4.Movement of bullet: Chemical to kinetic energy

What are the 3 factors affecting the acceleration of a bullet?

-Rate of gas production -Burn rate -Burn pattern

How does the rate of gas production affect the acceleration of a bullet?

Steady state production of gas is required to ensure smooth movement of the bullet down the barrel

What will happen to the acceleration of the bullet if the rate of gas production is too fast?

The initial momentum won't be maintained and the bullet will slow down as it exits the gun

What will happen to the acceleration of the bullet if the rate of gas production is too slow?

The bullet will have exited the barrel before all gases have been produced

What is a progressive burn pattern?

burns from end to the other

What is a degressive burn pattern?

Burns from the outside in

What is a neutral burn pattern

Burns in a neutral pattern produces pores, increasing surface area

Why must burn rate be controlled for the acceleration of a bullet?

To ensure maximum kinetic energy is imparted to the bullet

What shape of propellant particle does a shotgun require?

Disc shape

What shape of propellant particle does a revolver require?

tubular shape

What can propellant particles be coated with that inhibits combustion?

A detterant

What does the detonation speed of an explosive depend on?

The density of the explosive

How does the density of an explosive impact the detonation speed?

Greater density = Faster detonation

What are the shockwaves produced by a bullet?

1. Mach cone 2. Canneluer 3. Wake

What is the shockwave produced at the front of a bullet?

Mach cone

What is the shockwave produced from the middle of the bullet?

Canneleur

What is the shockwave produced from the base of the cone?

Wake

What is a molecular explosive?

-Detonate easily -Explosives in their purest form -Difficult to handle safely -Highly unstable

What is are examples of a molecular explosive?

-Nitroglycerin -Nitrocellulose

What are low explosives?

-Deflagration explosives -Won't detonate in normal conditions -Will detonate when confined, producing a throwing action -Decomposed by a flame front moving sub-sonically through the object

What are examples of low explosives?

-Nitrocellulose -Gun powder/ black powder

What are the uses of low explosives?

-Gun powders -Flares -Propellants

What are high explosives?

-Detonating explosives -Decomposed by high pressure shock waves which move sonically

What are primary explosives?

-A high explosive -Sensitive to shock and impact -Detonated by shock, impact, friction etc. -Produces a powerful shock wave that will detonate 2nd explosives and propellants

What are examples of primary explosives?

-Lead azide -Lead styphnate -Mercury fulminate

What are uses of primary explosives?

-Blasting caps -Military fuses -Primers in cartridges

What are secondary explosives?

-Main explosives -Will burn under normal circumstances -not sensitive to shock or impact -Only detonates due to primary explosive shock waves

What examples of secondary explosives?

-TNT -Dynamite (Nitroglycerine) -HMX

What is the full name for TNT?

2,4,6-Trinitrotolune

What is the full name for HMX?

1,3,5,7-tetranitro,1,3,5,7-tetracycloctane

What are propellants?

-Used to accelerate a projectile to high speed -Don't detonate only ignite

What is a single base propellant?

Nitrocellulose

What is a double base propellant?

Nitrocellulose + Nitroglycerin

What is a triple base propellant?

Nitrocellulose + Nitroglycerin + Nitroguanidine

Lecture 8: Combustion Flashcards

(63 cards)