Fundamental Analysis of a Linear Two-Cylinder Internal Combustion Engine

Linear, crankless, internal combustion engines may find application in the generation of electrical power without the need to convert linear to rotary motion. The elimination of the connecting rod and crankshaft would significantly improve the efficiency of the engine and the reduced weight and cost is an added advantage. The case of two opposed cylinders, with two pistons linked by a solid rod, was considered for idealized modeling. The piston/rod assembly was considered to oscillate with only constant frictional drag. The Otto cycle was used to model efficiency, and this in turn determined compression ratio. Dimensionless groups governing the engine working were identified and used in formulating a description of the engine behavior. Two-stroke operation was assumed. Velocity and position can be related analytically to yield a phase plot. The heat input, midpoint pressures, frictional force encountered and the ratio of instantaneous piston position to the maximum theoretical half stroke of the piston led to a closed loop solution for instantaneous piston velocity versus instantaneous piston position in dimensionless parameters. Compression ratio was found to be highly sensitive to the idealized engine operating condition. The fundamental analysis proves useful in the study of effects of load changes, timing variations, changes in compression ratio and basic understanding of a linear two-cylinder internal combustion engine