Important topics in Combustion and flame notes:
- What is Combustion?
- Ignition temperature
- Inflammable substance
- How Do We Control Fire?
- Types of Combustion
- Flame
- Structure of a Flame
- What is a Fuel?
- Fuel Efficiency
- Global warming
- Ideal Fuel
What is combustion?
- Burning of a substance is said to be combustion.
- Or simply, the chemical process in which a substance reacts with oxygen to give off heat and light is known to be combustion.
- Oxygen is necessary for combustion.
- Combustible substance: Those substances which undergo combustion are said to be combustible substance.
- Non-combustible substances: Those substances which do not burn in air are said to be non-combustible substances.
Ignition temperature
- The lowest temperature at which a substance catches fire is said to be ignition temperature.
- If the temperature of the substances is below the ignition temperature then that substance will not burn.
- Have you ever seen the oil kept in pan catches fire when kept for long on a burning stove? You can conclude that the temperature of oil reaches the ignition temperature then catches fire.
Inflammable substances:
- Those substances which catch fire easily are said to be inflammable substances.
- These have a low ignition temperature.
- LPG, Petrol are some of its examples.
Essential condition for burning:
- Presence of combustible substances or fuel
- Presence of air containing oxygen
- A temperature above ignition temperature is required.
How Do We Control Fire?
- Generally, we use water to extinguish fire.
- For fires that are caused by petrol, diesel or highly inflammable substance we don’t use water.
- In these cases we use carbon dioxide, sand etc. to extinguish fire.
- When a person catches with fire he should use blankets to escape or save themselves.
- Forest fires are uncontrollable as they spread rapidly.
Types of combustion
Different types of combustion are:
Rapid combustion:
- The combustion which occurs rapidly yielding large amount of heat and light.
- External heat source is required for rapid combustion.
- Burning of gas stove when a burning matchstick is taken near it is an example of rapid combustion.
Spontaneous combustion:
- The combustion which occurs without any application of external source of heat and burst out into flames.
- No external heat sources are required.
- Forest fires are spontaneous combustion.
Explosion:
- The combustion in which sudden reaction results in a large amount of heat, light and sound.
- A heavy amount of gases are also gets released.
- Firecracker after combustion releases a large amount of heat and light.
Flame:
- Flames are the region of burning of gases.
- The combustible substances vaporize during burning produces flame.
Structure of flame:
- There are different zones of flame of candle.
- Blue zone: It is near the base of the flame. Carbon monoxide burns completely with a blue flame in this zone.
- Luminous zone: The region of the flame in which hydrogen burns with a bright yellow luminous flame. The soot of the flame rises due to some unburnt carbon particles which are left in it.
- Dark Zone which is the middle layer of flame.
- Non-luminous zone which is the outermost zone of the flame. As here complete oxidation takes place, it is the hottest part of the flame.
What is fuel?
- Fuel is another name for combustible substances.
- The fuel should be cost-effective, easily available, and less amount of it must be capable of producing a large amount of heat.
- They should produce less undesired material after burning.
- Petrol, kerosene, hydrogen etc. are some examples of fuel.
Global warming:
Most fuels on combustion release carbon dioxide in the environment. Increase in concentration of carbon dioxide in the air is believed to cause global warming.
The efficiency of fuel:
- The efficiency of fuel is the amount of energy it releases during burning.
- We can determine the efficiency of fuel by its calorific value.
Calorific value:
- The calorific value is the measure of efficiency of fuel.
- The unit of calorific value is expressed in Kilojoule per kg.
Ideal Fuel:
- Those fuel which can meet most of the requirements for a particular use can be said as ideal fuel.
- For instance, probably no fuel is there that could be considered as an ideal fuel.
Characteristics of a good fuel
- Cheap and readily available.
- Burn at a quiet slow rate and its combustion should be controllable.
- Easy to store.
- Low ignition temperature.
- Produce a very small amount of residues such as ash.
- Should possess high calorific value.
- Do not produce gases which pollute the air.
- Easily transportable.
Harmful impacts of burning fuel:
The increase in burning of fuel on this earth affects environment in many ways.
- The unburnt particle of carbon fuels are dangerous pollutants and causes respiratory diseases, such as asthma.
- Incomplete combustion some fuels gives carbon monoxide gas which is a very poisonous gas. It can kill persons sleeping in a room containing carbon dioxide.
- Must fuel on oxidation releases carbon dioxide which is the major cause of global warming.
- Burning of coal and diesel in vehicles releases sulphur dioxide gas which is responsible for acid rain.