The Wiebe function provides an approximation of

$($a$)$ the instantaneous heat transfer as a function of the crank angle $($units of measurement. J$).$

$($b$)$ the mass bumed of fuel as a function of the crank angle funits of measurement: $kg).$

$($c$)$ the heat release rate as a function of the crank angle $($units of measurement: J$/$CA$).$

$($d$)$ the adimensional mass fraction bumed of fuel as a function of the crank angle $($no units of measurement$).$