Calculate energy content of 1 m³ of stoichiometric mixture of methane with air at 1 atmosphere pressure (101 kPa) and 298 K. LHV of methane is 50 Mj/kg.

Solution:

Stoichiometric mixture composition of methane is given by

Total moles of fuel-air mixture = 1 + 2 x 4.76 = 10.52

Energy content of mixture consisting of 1 kmol of methane:
            = mol wt x LHV 
= 16 x 50 = 800 MJ
 Volume of stoichiometric mixture consisting 1 kmol of methane

Energy content per unit volume of stoichiometric mixture = 800/258.07 = 3.10 MJ/m³               

Ans.

Alcohols: Methanol and Ethanol

Methanol at present is produced mostly from natural gas although both methanol and ethanol can be produced from renewable sources.  Methanol may be produced near the natural gas field and it being liquid can be more easily handled and transported over long distances compared to natural gas. Ethanol is produced almost entirely from the renewable agriculture sources by fermentation of sugar, grains, tapioca etc.

Alcohols in engines may be used as:

• Low concentration ( 5 to 10% by volume) blends in gasoline
• Neat alcohol or high level ( 85% by volume) blends

Neat ethanol (95% ethanol + 5% water) and anhydrous ethanol blended up to 20% in gasoline have been widely used in Brazil during 1980’s. In the USA, use of ethanol was promoted due to agricultural surplus for blending in the reformulated gasoline as oxygenate. Use of 5 to 10% ethanol as a blending component in gasoline is permitted in Europe and India.    Now, ethanol is the preferred oxygenate replacing MTBE. As mentioned earlier, methanol due to its toxicity is not permitted any more for blending into gasoline. The 10 percent ethanol-gasoline blends used in the USA are commonly referred as ‘Gasohol’. Key features of alcohols as motor fuel are;