QUESTION $4$: Combustion $(25$ Marks$)$

A sample of biogas from a renewable energy project is $80\%$ methane $(C{H}_4)$ by mass, but has other element present, given by mass below:

$\backslash$table$[[,$C$,$H$,$O$,$N$,$S$,$Ash,Moisture$],[,(\%),(\%),(\%),(\%),(\%),(\%),(\%)],[$Fuel$,??,??,6,5,4,3,2]]$

The atomic masses are: $C=12$;$H=1$;$O=16$;$N=14$;$S=32$; take Air as $23\%$ Oxygen and $77\%$ Nitrogen by mass. For excess air $($by mass$)$ of $100\%$ :

$($i$)$ Find the missing percentages for Carbon and Hydrogen given they are solely due to the methane $(C{H}_4).$

$(5$ Marks$)$

$($ii$)$ Calculate the stoichiometric air for complete combustion. $($Use sensible values for Carbon and hydrogen percentages if part $($i$)$ not answered.$)$

$(10$ Marks$)$

$($ii$)$ Calculate the percentages by mass of the dry exhaust products if $40\%$ excess air is used.

$(10$ Marks$)$