Question

what are primary and secondary fuels

Answer 1

Primary fuels are the fuels that are found in nature and can be extracted, cleaned or graded, without any sort of energy conversion or transformation process. Ex. Coal, crude oil.

Secondary fuels are the fuels that are derived from some primary fuels through chemical or physical process. Ex. Kerosene, methane.
Hope it helps you

Answer 2

$\Huge{\underline{\underline{\underline{\overline{\overline{\overline{\fcolorbox{red}{yellow}{Primary fuels }}}}}}}}$

$\footnotesize\sf \blue{Primary \: fuels \: are \: fuels \: that \: are \: found \: in} \\ \footnotesize\sf\blue{nature \: and \: can \: be \: extracted, \: captured, } \\ \footnotesize\sf\blue{cleaned, \: or \: graded \: without \: any \: sort \: of \: energy } \\\footnotesize\sf \blue{ conversion \: or \: transformation \: process. \: This } \: \\ \footnotesize\sf\blue{ means \: that \: all \: processing \: and \: collecting \: of \: the }\: \\ \footnotesize\sf \blue{fuel \: is \: done \: before \: the \: fuel \: is \: converted \: into \: } \\\footnotesize\sf \blue{ heat \: or \: mechanical \: work.}$

$\huge{\underline{\underline{\underline{\overline{\overline{\overline{\fcolorbox{red}{grey}{Secondry fuels ⇣⇣⇣}}}}}}}}$

$\footnotesize\sf \green{Secondary \: fuels  \: are fuels  \: that \: are \: derived} \\ \footnotesize\sf \green{from \: some \: primary \:  fuel  \: or  \: fuels  \: through} \\ \footnotesize\sf \green{chemical \: or \: physical \: processes. \: These \: are \:  fuels} \\  \footnotesize\sf \green{that \: are \: not \: found \: as \: a \: natural} \\ \footnotesize\sf \green{ resource. \: The \: energy \: for \: these \:  secondary \: fuels } \\\footnotesize\sf \green{ comes \: initially \: from \: primary \: energy \: sources.}$