Torsional vibration is one of the major issues and very important calculation for the safe running of heavy-duty diesel engines, specifically crankshaft. Because of different applications of a heavy-duty diesel engine, different driven machine and different attaching systems are inevitable that affect the torsional system. The cranktrain contains the flywheel and torsional damper. The properties of these parts have significant effect on torsional vibration of the system as well as the crankshaft strength. Initial selection of these properties is usually specified based on engine designer experience and also the torsional vibration calculation of the cranktrain. In this paper, the focus is to find the optimum and reliable operating points for the elements in cranktrain using computer-aided engineering (CAE) tools. These are parameters like tuned mass inertia, flywheel inertia, damper stiffness, damper inertia, damper damping, coupling damping and coupling stiffness. The effect of these parameters on system design criteria, especially crankshaft life, was investigated. The results show high sensitivity of crankshaft safety factor to parameters like tuned mass inertia, damper damping coefficient and damper stiffness. Therefore, damper selection is the most important factor to increase the crankshaft life. The new contribution is that the parameters related to the whole cranktrain system that have the greatest effect were obtained and an optimisation was executed on these parameters to fulfil the vibration targets as well crankshaft life.

Wear and cavitation erosion are the common damages in engine bearing shells. In the case of cavitation damage, the generation and immediate collapse of small gas bubbles cause high pressure pulses and the bearing surface is being locally damaged. Cavitation damage is observed in heavy duty diesel engine due to highly dynamic loading, oscillation of pins, turbulence of oil flow and other factors. Wear damage induces adjustment in the bearing geometry and affects the oil film pressure and the durability of bearing shell. In this paper, wear and cavitation damages in connecting rod big end bearing have been studied. In order to compute the bearing lubrication characteristic such as minimum oil film thickness and maximum oil film pressure, Elasto-Hydrodynamic method that incorporates mass conserving algorithm has been utilized. Wear and cavitation damages in two different designs of connecting rod structure in a heavy duty diesel engine have been assessed and the results have been presented. Furthermore, the effect of connecting rod structure on wear damage has been investigated.

The breakup of a liquid sheet or jet is led to atomization phenomenon. The liquid sheet surface instability controls spray formation and determines the spray characteristics. Therefore, the instability study of the liquid jet has attracted a lot of attentions so that a lot of works have been carried out on this subject. The instability study of a swirling annular liquid sheet exposed to inner and outer gas streams is represented in the paper. A three-dimensional flow for the liquid sheet and a two-dimensional flow for inner and outer gas streams have been considered. In previous studies, a cylindrical liquid sheet has been considered, but in this study, the instability theory is implemented on a conical liquid sheet for different cone angles. The effects of swirl velocity of the liquid sheet and axial velocity of the gas streams on the sheet instability and breakup length have been investigated. Results show that liquid swirl Weber number has a destabilizing effect on a conical liquid jet. Study of the effect of ambient pressure shows that disturbance growth rate increases with increasing gas-to-liquid density ratio. The effect of spray angle on the instability of the liquid sheet is a very important issue in combustion chamber design especially when the available space and/or weight is limited. Higher spray angle enhances the instability of the liquid sheet, and it leads to a shorter breakup length and larger ligaments. Sheet thickness is another parameter that has been considered. Increasing sheet thickness enhances the sheet instability. These behaviors are consistent with the experimental observations.

The maximum entropy principle is one of the first methods, which have been used to predict droplet size and velocity distributions of liquid sprays. Due to some drawbacks in this model, the predicted results do not match well with the experimental data. This paper presents a different approach for improving the maximum entropy principle model. It is suggested to improve the available energy source in the maximum entropy principle model equation by numerical solution of flow inside the injector based on the computational fluid dynamics technique. This will enhance the calculation accuracy of the turbulent kinetic energy of the output spray. Application of this procedure enhances the model predictions. The liquid sheet properties resulted from the analysis are also applied for calculation of the momentum source in the maximum entropy principle model. The proposed model is applied to predict the droplet size distribution of a hollow-cone spray formed by a swirl injector. The results show a better agreement with the available experimental data than the results of prior models.

When two bearing shells are assembled in the bearing housing, it is possible that the edges of the two shells do not fit in the radial direction completely and have an offset relative to each other. This assembly error, which can have different causes, is called the bearing step in this paper. The bearing step can lead to wear damage in bearings. The effects of bearing step on the lubrication performance of main bearings and the probable wear damage have been investigated. To calculate the bearing lubrication characteristics such as maximum oil film pressure and minimum oil film thickness, elasto-hydrodynamic model, which includes the mass conservation algorithm, has been applied. The objective of this work is to investigate the effects of bearing steps on the lubrication performance of the main bearings and assess the probable wear damage of main bearings due to bearing step. The prediction of elasto-hydrodynamic model is very proximate to what really happened. The results show that for the under-study 12-cyl engine, main bearing No. 2 involved with medium wear damage. Wear damage in this main bearing No. 3 is not a concern, while main bearing No.4, 5 and 6 do not predict the probability of wear damage. For main bearing No.7, it is concluded that considering step and bore relief in simulation has high importance so that the solution without step and bore relief does not predict the wear, but with step and bore relief predicts medium wear damage.

In multi-cylinder diesel engines, hydrodynamic pressure distribution of main bearings has significant effect on the load distribution applied on engine crankcase, therefore, has an effect on the stress distribution and deflection of crankcase. Flexibility of crankshaft and crankcase assembly has significant effect on load distribution in engine main bearings. In this paper, the effect of elastic deformations of both crankshaft and crankcase on the load distribution in the main bearings is studied. Considering deformations of crankcase and crankshaft together with the elasto-hydrodynamic (EHD) analysis of main bearing is vital to obtain the realistic load distribution and accurate main bearing performance. At the beginning, the results of flexible body dynamic analysis of engine crank train with considering EHD joint for main bearings are presented and the main bearing force and moment are compared with rigid body dynamic analysis. Then, the effects of crankshaft and crankcase flexibilities on main bearing force and moment are studied. Several models with different flexibilities and stiffness of crankcase and crankshaft were prepared using Elasto-hydrodynamic simulation of diesel engine main bearings. According to the results, the load distribution on the engine main bearings and consequently the bearing shell deformation are affected by crankcase and crankshaft elasticities. A fast and time-saving method to obtain reasonably accurate results is proposed in the present paper.

Torsional vibration (TV) is one of the major issues and very important calculation for the safe running of internal combustion engines, specifically crankshaft. The properties of parts connected to the crankshaft have significant effect on vibration of the system as well as the crankshaft life. Initial selection of this part is usually specified based on engine designer experience and also the torsional vibration calculation of the crank train. In this paper, the focus is to find optimum tuned mass to connect to the crankshaft from the damper side using CAE tools. It is a mounting disk at the free end of the crankshaft named tuned mass. Therefore, the effect of tuned mass inertia on design criteria, especially crankshaft life, was investigated. The results show high sensitivity of high cycle fatigue safety factor of crankshaft to tuned mass. Therefore, adding a suitable tuned mass to the system can increase the crankshaft life, when needed. The results were presented in the paper in detail.

Torsional vibration (TV) is one of the major issues and very important calculation for the safe running of internal combustion engines, specifically crankshaft. The properties of parts connected to the crankshaft have significant effect on vibration of the system as well as the crankshaft life. Initial selection of this part is usually specified based on engine designer experience and also the torsional vibration calculation of the crank train. In this paper, the focus is to find optimum tuned mass to connect to the crankshaft from the damper side using CAE tools. It is a mounting disk at the free end of the crankshaft named tuned mass. Therefore, the effect of tuned mass inertia on design criteria, especially crankshaft life, was investigated. The results show high sensitivity of high cycle fatigue safety factor of crankshaft to tuned mass. Therefore, adding a suitable tuned mass to the system can increase the crankshaft life, when needed. The results were presented in the paper in detail.