$13.$ Why is heat balance calculation critical in assessing the performance of a combustion system?

$14.$ Discuss the environmental implications of sulfur content in fuels and the refining processes used to reduce it$.$

$15.$ What is isomerization in the context of petroleum refining, and what benefits does it offer to fuel quality?

$16.$ What determines the classification of a coal as either bituminous or anthracite?