Abstract: A laboratory scale fluid catalytic cracking apparatus and method of use thereof, which provides cracking performance that emulates commercial riser cracking. The apparatus includes a reactor having a removable feed injector to quickly facilitate changing hydrocarbon contact time without varying the feed rate or diluent rates, or catalyst charge, and also without the expense of a new reactor. The feed injector is a tube within a tube design. The feed injector allows hydrocarbon feed as well as fluidization gas to be delivered to a prescribed axial position within a catalyst bed in the reactor to directly affect hydrocarbon contact time. The reactor also includes a conical bottom head having a conical section and a lower fluidization gas nozzle connected at its apex. The total included angle of the conical section may vary between 10.degree. and 1700.degree.