Thermodynamic and dynamic modeling of a single cylinder four stroke diesel engine

Abstract

In this study the conjugate thermodynamic and dynamic modeling of a single cylinder four-stroke diesel engine was conducted. The gas pressure in cylinder was calculated with the first law of the thermodynamic and the general state equation of the perfect gases. The variation of the heat, given to the working fluid during the heating process of the thermodynamic cycle, was modeled with the Gaussian function. The dynamic model of the engine consists of the motion equations of piston, conrod and crankshaft. Conrod motion was modeled by 2 translational and 1 angular motion equations. In the derivation of the motion equations, the Newton method was used. Motion equations involve hydrodynamic and asperity frictions as well as gas forces. By preparing a heat release rate profile consistent with ones given in the literature, thermal efficiency, knocking, vibration, torque and emission characteristics of the engine were investigated. The counterweight mass and its radial distance were optimized. At full load, if the heat release period is initiated soon after the piston passed the top dead center, the pressure rise rate becomes critical from the knocking point of view however, a couple of degree of retarding of the heat release period avoids the knocking without causing significant loss in thermal efficiency. If the throttling is more than 70%, the temperature of the combustion gas is high enough for NOx formation. At full load the vibrational torque exerting on the crankshaft was determined as about 17 times the engine torque.