We propose to design, model, build, and test a novel flash cracking reactor to convert plastic waste, and potentially other unconventional hydrocarbon feedstocks, into tunable molecular weight fuels. The innovative reactor technology "flashes off" desired hydrocarbon products as they form, thus preventing the over-cracking of the polymers into more volatile hydrocarbons. This leads to improved selectivity for low vapor-pressure hydrocarbons, which are easier to store as fuel in large quantities at low pressures, as well as tunable molecular-weight products for multiple applications. Our design approach in Phase I will use a combination of heat/mass transfer modeling with pyrolytic kinetics modeling for PE and PP, which will be used as a model system for waste plastic pyrolysis. We will first demonstrate, using our pyrolytic model, that the hydrocarbon product distribution can be modified and tailored by varying the reactor and condenser temperatures, nitrogen gas flow rate, and system pressure. We will also build and test the reactor system based on our model results. Controlling the product distribution of a flash cracking reactor while minimizing parasitic losses will be the primary challenge during the Phase I effort.