Pembakaran

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Pembakaran adalah satu is a proses kimia, satu tindakbalas eksotermik di antara satu bahan (bahan api) dan satu gas (pengoksidan), biasanya O2, untuk membebaskan haba. Dalam satu tindakbalas pembakaran yang sempurna, satu sebatian akan bertindakbalas dengan satu unsur yang beroksigen, dan hasilnya adalah sebatian dari setiap unsur bergabung di dalam bahanapi dengan unsur yang beroksigen. Sbagai contoh:

Pembakaran hutan.
Fail:Gas burner on stove.JPG
Pembakaran gas di dapur.

CH4 + 2 O2CO2 + 2 H2O + haba

CH2S + 6 F2CF4 + 2 HF + SF6 + haba

Jenis Pembakaran[sunting | sunting sumber]

Terdapat beberapa jenis pembakaran: -

Pembakaran Marak/Cepat[sunting | sunting sumber]

Pembakaran Marak/Cepat adalah merupakan satu bentuk pembakaran yang mana banyak tenaga haba dan cahaya dibebaskan. Pembakaran sebegini biasanya wujud sebagai api. Biasanya pembakaran ini digunakan dalam bentuk mekanisme, seperti enjin pembakaran dalaman, dan dalam senjata termobarik.

Pembakaran Perlahan[sunting | sunting sumber]

Pembakaran perlahan adalah satu bentuk pembakaran yang berlaku pada suhu rendah. Respirasi adalah satu contoh pembakaran perlahan.

Pembakaran Sempurna[sunting | sunting sumber]

Dalam pembakaran lengkap, zat tindakbalas akan terbakar di dalam oksigen, menghasilkan beberapa jenis produk. Apabila hidrokarbon terbakar di dalam oksigen, kesan tindakbalas akan hanya menghasilkan karbon dioksida dan air. Apabila elemen seperti karbon, nitrogen, sulfur dan besi terbakar, elemen tersebut akan menghasilkan oksida yang paling umum. Karbon akan menghasilkan karbon dioksida. Nitrogen akan menghasilkan nitrogen dioksida. Sulfur akan menghasilkan sulfur dioksida. Besi akan menghasilkan besi(III) dioksida. Pembakaran lengkap pada amnya adalah mustahil untuk dicapai kecuali tindakbalas yang berlaku dikawal secara berhati-hati (e.g. di dalam persekitaran makmal).

Pembakaran Turbulasi[sunting | sunting sumber]

Turbulent combustion is a combustion characterized by turbulent flows. It is the most used for industrial application (e.g. gas turbines, diesel engines, etc.) because the turbulence helps the mixing process between the fuel and oxidizer.

Pembakaran Tidak Sempurna[sunting | sunting sumber]

In incomplete combustion there is an inadequate supply of oxygen for the combustion to occur completely. The reactant will burn in oxygen, but will produce numerous products. When a hydrocarbon burns in oxygen, the reaction will yield carbon dioxide, water, carbon monoxide, and various other compounds such as nitrogen oxides. Incomplete combustion is much more common and will produce large amounts of byproducts, and in the case of burning fuel in automobiles, these byproducts can be quite lethal and damaging to the environment.

Pembakaran Pendam[sunting | sunting sumber]

Smouldering combustion is a flameless form of combustion, deriving its heat from heterogeneous reactions occurring on the surface of a solid fuel when heated in an oxidizing environment. The fundamental difference between smouldering and flaming combustion is that in smouldering, the oxidation of the reactant species occurs on the surface of the solid rather than in the gas phase. The characteristic temperature and heat released during smouldering are low compared to those in the flaming combustion of a solid. Typical values in smouldering are around 600 °C for the peak temperature and 5 kJ/g-O2 for the heat released; typical values during flaming are around 1500 °C and 13 kJ/g-O2 respectively. These characteristics make smolder to propagate at low velocities, typically around 0.1 mm/s, which is about two orders of magnitude lower than the velocity of flame spread over a solid. In spite of its weak-combustion characteristics, smouldering is a significant fire hazard.

Persamaan Kimia[sunting | sunting sumber]

Secara umumnya, persamaan kimia untuk pembakaran sempurna hidrokarbon (contohnyaoktana) dalam oksigen adalah seperti berikut:

CxHy + (x + y/4)O2xCO2 + (y/2)H2O

Contoh pembakaran propana adalah:

C3H8 + 5O2 → 3CO2 + 4H2O

Persamaan kimia mudah bagi pembakaran hidrokarbon adalah:

bahan pembakaran + Oksigenhaba + air + karbon dioxida.

Pembakaran bahan api cecair[sunting | sunting sumber]

Pembakaran bahan api cecair dalam atmosfera pengoksidaan sebenarnya berlaku di dalam fasa gas, iaitu wap yang terbakar bukannya cecair. Oleh itu, cecair biasanya akan menyala hanya di atas satu suhu tertentu yang dikenali sebagai takat kilat. Sekiranya suhu cecair berada di bawah suhu ini, ia tidak akan menyejat dengan cukup pantas untuk membentuk wap yang akan akan menyokong proses pembakaran.

Pembakaran Bahanapi Pepejal[sunting | sunting sumber]

The act of combustion consists of three relatively distinct but overlapping phases:

  • Preheating phase, when the unburned fuel is heated up to its flash point and then fire point. Flammable gases start being evolved in a process similar to dry distillation.
  • Distillation phase or gaseous phase, when the mix of evolved flammable gases with oxygen is ignited. Energy is produced in the form of heat and light, flame is often visible.
  • Charcoal phase or solid phase, when the output of flammable gases from the material is too low for persistent presence of flame and the charred fuel does not burn rapidly anymore but just glows and later only smoulders.

Suhu Pembakaran[sunting | sunting sumber]

Assuming perfect combustion conditions, such as an adiabatic (no heat loss) and complete combustion, the adiabatic combustion temperature can be determined. The formula that yields this temperature is based on the first law of thermodynamics and takes note of the fact that the heat of combustion (calculated from the fuel's heating value) is used entirely for warming up fuel and gas (e.g. oxygen or air).

In the case of fossil fuels burnt in air, the combustion temperature depends on

The adiabatic combustion temperature increases for higher heating values and inlet temperatures and stoiciometric ratios towards one.

Typically, the adiabatic combustion temperatures for coals are around 1500 °C (for inlet temperatures of room temperatures and {\lambda = 1.0}), around 2000 °C for oil and 2200 °C for natural gas.

Analisis Pembakaran[sunting | sunting sumber]

Combustion analysis is a process used to determine the composition of organic compounds.

Pautan Luar[sunting | sunting sumber]

Lihat Juga[sunting | sunting sumber]