IMPROVEMENT IN COMBUSTION PROCESS

GROUP MEMBERS

SAMER (2K13-MECH-27) TAYYAB SAJJID ZARGHAM Mehr Ali

COMBUSTION

Combustion is defined as the burning of a fuel and oxidant to produce heat and/or work. It is the major energy release mechanism in the Earth and key to humankind's existence. Combustion includes thermal, hydrodynamic, and chemical processes. It starts with the mixing of fuel and oxidant, and sometimes in the presence of other species or catalysts. The fuel can be gaseous, liquid, or solid and the mixture may be ignited with a heat source.

EFFECT OF COMBUSTION

The negative effects of combustion on the environment – particularly greenhouse gas (GHG) emissions released to the atmosphere that contribute to global warming – have received much attention in recent years. This issue is addressed in the Kyoto Protocol (1997). Canada, which signed the Protocol, aims to reduce emissions between 2008 and 2012 by six percent of 1990 levels. Climate change resulting from global warming is one of the greatest challenges facing not only Canada but also the world. Managing combustion processes better and improving the efficiency of energy generation and use are two of the key strategies for reducing atmospheric emissions.

EMISSION FROM COMBUSTION AND THEIR EFFECTS

EMISSION SOURCE EFFECT CO2 (carbon dioxide)

Complete combustion of carbon in fuel

Global warming

CO (carbon monoxide) Incomplete

combustion of carbon in fuel

Smog

SO2 (sulphur dioxide)

Combustion of sulphur in fuel

Smog, acid rain

NOx (nitrogen oxides)

By-product of most combustion processes

Acid rain

N2O (nitrous oxide)

By-product of some combustion processes

Global warming

CH4 (methane) Principal component of natural gas; leakage from gas wells, pipelines and distribution systems

Global warming

H2O (water vapour)

Combustion of hydrogen in fuel

Localized fog

ACID RAIN

Acid rain is a result of air pollution. When any type of fuel is burnt, lots of different chemicals are produced. The smoke that comes from a fire or the fumes that come out of a car exhaust don't just contain the sooty grey particles that you can see - they also contains lots of invisible gases that can be even more harmful to our environment.

Power stations, factories and cars all burn fuels and therefore they all produce polluting gases. Some of these gases (especially nitrogen oxides and sulphur dioxide) react with the tiny droplets of water in clouds to form sulphuric and nitric acids. The rain from these clouds then falls as very weak acid - which is why it is known as "acid rain".

GLOBAL WARMING

Global warming is the term used to describe a gradual increase in the average temperature of the Earth's atmosphere and its oceans, a change that is believed to be permanently changing the Earth’s climate. The increased volumes of carbon dioxide and other greenhouse gases released by the burning of fossil fuels, land clearing, agriculture, and other human activities, are believed to be the primary sources of the global warming that has occurred over the past 50 years. 

Tayyab Raza Shah2K13-Mech-37

Combustion process and its types

Complete vs Incomplete Smouldering Rapid Spontaneous Turbulent Microgravity Micro Combustion The degree of combustion can be measured and analysed with test

equipment. HVAC contractors, firemen and engineers use combustion analysers to test the efficiency of a burner during the combustion process.

Complete vs Incomplete CombustionIn complete combustion, the reactant burns in oxygen, producing a limited number of products. When a hydrocarbon burns in oxygen, the reaction will primarily yield carbon dioxide and water.

Incomplete combustion will occur when there is not enough oxygen to allow the fuel to react completely to produce carbon dioxide and water. It also happens when the combustion is quenched by a heat sink, such as a solid surface or flame trap.

Effects of In-complete Combustion

For most fuels, such as diesel oil, coal or wood, pyrolysis occurs before combustion. In incomplete combustion, products of pyrolysis remain unburnt and contaminate the smoke with noxious particulate matter and gases. Partially oxidized compounds are also a concern; partial oxidation of ethanol can produce harmful acetaldehyde, and carbon can produce toxic carbon monoxide.

Improvement In Combustion ProcessThe quality of combustion can be improved by the designs of combustion devices, such as burners and internal combustion engines. Further improvements are achievable by catalytic after-burning devices (such as catalytic converters) or by the simple partial return of the exhaust gases into the combustion process. Such devices are required by environmental legislation for cars in most countries, and may be necessary to enable large combustion devices, such as thermal power stations, to reach legal emission standards.

Chemical Equations

Zargham Khan 2K13-Mech-07

Smouldering Combustion

Smouldering is the slow, low-temperature, flameless form of combustion, sustained by the heat evolved when oxygen directly attacks the surface of a condensed-phase fuel. It is a typically incomplete combustion reaction. Solid materials that can sustain a smouldering reaction include coal, cellulose, wood, cotton, tobacco, peat, duff, humus, synthetic foams, charring polymers (including polyurethane foam) and dust.

Rapid Combustion

Rapid combustion is a form of combustion, otherwise known as a fire, in which large amounts of heat and light energy are released, which often results in a flame. This is used in a form of machinery such as internal combustion engines and in thermobaric weapons. Such a combustion is frequently called an explosion, though for an internal combustion engine this is inaccurate. An internal combustion engine nominally operates on a controlled rapid burn. When the fuel-air mixture in an internal combustion engine explodes, that is known as detonation.

Spontaneous Combustion

Spontaneous combustion is a type of combustion which occurs by self heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high temperatures) and finally, ignition. For example, phosphorus self-ignites at room temperature without the application of heat.

Mehr Ali2K13-Mech-35

Turbulent Combustion

Combustion resulting in a turbulent flame is the most used for industrial application (e.g. gas turbines, gasoline engines, etc.) because the turbulence helps the mixing process between the fuel and oxidizer.

Micro Combustion

Combustion processes which happen in very small volumes are considered micro-combustion. The high surface-to-volume ratio increases specific heat loss. Quenching distance plays a vital role in stabilizing the flame in such combustion chambers.