Internal Combustion Engines as Fluidized Bed Reactors

An internal combustion engine which is primarily designed for producing power can be utilized as a chemical reactor for a range of chemical processes given its inherent advantages including high throughput, high chemical conversion efficiency, and reactant/product handling benefits. For gas-phase processes requiring a catalyst, the ability to develop a fluidized bed reactor within the engine cylinder would greatly enhance gas/solid mixing, reducing mass transfer barriers and allowing the reactor to efficiently process large volumes of fluid. In addition, use of an engine could facilitate vibration and pulsed flow which may enhance fluidization quality. This work examines the fluidization behavior of particles within a cylinder of an internal combustion engine at various engine speeds using analytical and experimental methods. First, calculations were carried out to determine the maximum fluidization velocity and the corresponding engine speeds below which fluidization of a particle bed is possible given the properties of the particles and engine dimensions. Fluidization depends on particle properties as well as the engine used. For 40–63 micron diameter silica gel particles placed inside a modified Megatech Mark III transparent combustion engine (with a bore of 4.1 cm, stroke length of 5.1 cm and compression ratio of 2.4), calculations indicate that engine speeds of approximately 1.1 to 60.8 RPM would result in fluidization of the particles. For higher engine speeds, the fluidization behavior is expected to deteriorate as the maximum fluidization velocity is surpassed. Next, experiments were conducted using the transparent engine and video recording to obtain qualitative confirmation of the analytical predictions. Simulations were then performed using ANSYS Fluent to investigate pressure drop across the bed. Consistent with the calculations, for an engine speed of 48 RPM, fluidized behavior was observed. In contrast for an engine speed of 171 RPM, the fluidization was observed to deteriorate and result in a “cake” of particles that moved in a lumped manner. Overall, the investigation shows that a fluidized bed can be obtained within the cylinder of a reciprocating piston engine if the engine speed is within the range predicted by the maximum fluidization velocity.