A single$-$cylinder, $4-$stroke cycle engines using compressed natural gas as fuel has a cylinder, $20\mathrm{.}3$cm bore by $30\mathrm{.}5$cm stroke and runs at $300$rpm$.$ If the volumetric efficiency of the engine based on conditions approaching the cylinder is $48\%$ and the air$/$fuel ratio is $4$: $1,$ determine the volume of gas used per minute.

$(5$ marks$)$

$($b$)$ Explain with the aid of a diagram the layout of battery ignition systems and state the functions of all the parts.

$($c$)$ What is firing order? explain the firing order of six cylinder engines.