LN03 - Internal Combustion Engines ME422 Yeditepe...

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1 Internal Combustion Engines – ME422 Yeditepe Üniversitesi IC-Engine Fuels Prof.Dr. Cem Soru ş bay Internal Combustion Engines IC Engine Fuels ¾ Introduction ¾ Classification of fuels ¾ Manufacture of engine fuels ¾ Fuel specifications in general ¾ Specifications of SI-engine and CI-engine fuels
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2 IC Engine Fuels In IC engines, the chemical energy contained in the fuel is converted into mechanical power by burning (oxidizing) the fuel inside the combustion chamber of the engine. As a result of the chemical reactions which occur inside the cylinder, heat is released . The fuel-air mixture (the working fluid before combustion) must stay in the cylinder for a sufficient time so that the chemical reactions can be completed. Fuels suitable for fast chemical reaction have to be used in IC engines. Hydrocarbons in liquid form Alcohols (methanol, ethanol) LPG (propane and butane) Natural gas (methane) Hydrogen Classification of Engine Fuels Liquid hydrocarbons Fuels are mainly mixtures of hydrocarbons, with bonds between carbon atoms and between hydrogen and carbon atoms . During combustion these bonds are broken and new bonds are formed with oxygen atoms, accompanied by the release of chemical energy. Principal products are carbon dioxide and water vapour. Fuels also contain small amounts of m n H C O H S N O 2 2 2 , , ,
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3 Alkanes Alkanes or Paraffins can in general be represented by all the carbon bonds are single bonds – they are “ saturated high number of H atoms, high heat content and low density (620 – 770 kg/m 3 ) The carbon atoms can be arranged as, a straight chain or as branched chain compounds. Straight chain group (normal paraffins) shorter the chain, stronger the bond not suitable for SI engines – high tendancy for autoignition according to the value of “n” in the formula, they are in gaseous (1 to 4), liquid (5 to 15) or solid (>16) state. 2 2 + n n H C Alkanes Branched chain compounds (isoparaffins) when four or more C atoms are in a chain molecule it is possible to form isomers – they have the same chemical formula but different structures, which often leads to very different chemical properties. example : iso-octane 2. 2 .4 trimethyl pentane 18 8 H C
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4 Naphthenes Also called cycloparaffins saturated hydrocarbons which are arranged in a circle have stable structure and low tendancy to autoignite compared to alkanes (normal paraffins) can be used both in SI-engines and CI-engines low heat content and high density (740 – 790 kg / m 3 ) n n H C 2 Alkenes Also called olefins mono-olefins or dio-olefins have the same C-to-H ratio and the same general formula as naphthenes, their behavior and characteristics are entirely different they are straight or branch chain compounds with one or more double bond. The position of the double bond is indicated by the number of first C atom to which it is attached, ie, CH2=CH.CH2.CH2.CH3 called pentene-1 CH3.CH=CH3 called butene-2 olefinic compounds are easily oxidized, have poor oxidation stability
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This note was uploaded on 10/04/2011 for the course ME 422 taught by Professor Cemsoruşbay during the Spring '11 term at Yeditepe Üniversitesi.

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LN03 - Internal Combustion Engines ME422 Yeditepe...

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