Internal Combustion Engines as Chemical Reactors: Issues and Challenges

摘要

An internal combustion (IC) engine is inherently a chemical reactor that produces high temperature and pressure conditions, while efficiently managing reactant delivery and product exhaust flows. There have been several examples of IC engines utilized as chemical reactors in previous work; these efforts include the partial oxidation of solid carbonaceous fuels to produce syngas and of methane to produce hydrogen. In the current work, we analyze key issues involved in utilizing a diesel engine as a chemical reactor to convert natural gas constituents into chemical industry feedstocks. Inflow and outflow processes determine the throughput of the reactor and the economic viability of the IC engine as an industrial reactor. We have modeled these engine flow processes using Matlab with engine specific input data taken from a commonly used Cummins 6.2 liter diesel engine. Key issues related to safe operation of an engine reactor; including the stoichiometry of the in-cylinder mixture and its relation to the possibility of an explosive mixture being generated, and the peak pressure generated upon ignition of an explosive mixture; were investigated using Chemkin routines and appropriate chemical kinetic models. A CONVERGE CFD code for the engine under consideration was used to obtain the in-cylinder fluid flow information required for designing a chamber volume with maximum reactor yield. In summary, we have conducted parametric studies to understand key issues related to the design and operation of an IC engine as a chemical reactor. These issues involve: 1) flow conditions including choked flow at the engine intake and exhaust, 2) explosive mixture formation and peak pressures that can be generated in the cylinder, and 3) in-cylinder gas flows during engine operation.