Design of trapezoidal piston motion using an innovative connecting rod for improving the performance of single cylinder diesel engines

Abstract

A new technique of altering reciprocating motion of the piston in an IC engine is developed and proposed in this study. This new technique creates a trapezoidal motion that has significant advantages over the standard sinusoidal motion. Theoretical, experimental and numerical methodologies are utilized in the arrival of an optimal trapezoidal motion from different trials. In conventional IC Engine, velocity profile of piston motion is Sinusoidal. The existing Slider-crank mechanism develops and uses this sinusoidal motion for histories and it has lot of advantages. The aero-thermal and emission characteristics for the sinusoidal profile are almost ideal. In spite of many advantages, the sinusoidal piston motion has substantial drawbacks such as high mean velocity that leads to high inertial force, frictional losses, wear and high rate of heat leakages. Nearly 20% of the total power produced by the engine is dissipated into heat because of friction. Of this 20% about 75% is due to friction of piston rings on the cylinder walls. This is an irreversible loss and can be seen as a consequence of high mean piston velocity associated with the existing Sinusoidal Piston Velocity Profile. In addition, constantly varying velocity associated with sinusoidal profile can cause rapid acceleration and finally jerks which lead to objectionable mechanical vibration and noise. As a result, the mechanical strength of engine material will be high to withstand the inertial force, friction and wear. To overcome these difficulties, an extensive attempt is made to improve the piston movement by restructuring the piston velocity profile and the connecting rod mechanism. A proposed connecting rod configuration with internal gear and pinion arrangement is designed to achieve four differenttrapezoidal piston motion Profiles. Different gear combinations with different module values are used to form these four distinct Trapezoidal Profiles. The mathematical expressions for these Trapezoidal Profiles as a function of internal gear, pinion teeth values and module are also found. The piston velocity profile is arrived for combinations of pinion and gear teeth values (18-26, 18-28, 20-28 and 20-30) with compression ratio (14, 17.5 and 21). A comparative investigation on four different trapezoidal is done against the conventional Sinusoidal Profile for Kirloskar (water cooled, single cylinder and 661cc capacity) Diesel Engine to find out the optimum trapezoidal model whose performance is analogous to Sinusoidal model using Computational Fluid Dynamics (CFD). newline