FEM analysis of the opposed-piston aircraft engine block

An important aspect of aircraft engine design is weight minimization. However, excessive weight reduction may reduce mechanical strength of the engine. This is especially important for aero-engines due to consequences of engine failure in flight. The article presents the results of the FEM opposed-piston diesel engine block model tests. The tested engine is a PZL-100 two-stroke three-cylinder aircraft engine with two crankshafts and six pistons. Air is supplied via a mechanical compressor and a turbocharger. Stress in the engine block is induced by the operating process of the engine block. The pressure in the combustion chamber of the analyzed engine is 13 MPa. The pistons in one of the cylinders are then near their TDC, the deflection angle of the connecting rods is small so almost the entire piston force is transferred to the crankshafts and then to the main bearing supports. This results in the occurence of a tensile force for the engine block applied in the bolt holes of the shaft supports. The calculation results are presented as stress and displacement distributions on the surface and selected block sections. The maximum values on the outer surfaces of the block occurred in the area of the compressor attached to the block and reached 39 MPa. Maximum stresses were, however, observed inside the block on the air and exhaust flow separators between the cylinder liners. The stress value on the outlet side reached 44 MPa.

A Study on Anti-Shock Performance of Marine Diesel Engine Based on Multi-Body Dynamics and Elastohydrodynamic Lubrication

Diesel engine anti-shock performance is important for navy ships. The calculation method is a fast and economic way compared to underwater explosion trial in this field. Researchers of diesel engine anti-shock performance mainly use the spring damping model to simulate the main bearings of a diesel engine. The elastohydrodynamic lubrication method has been continuously used in the main bearings of diesel engines in normal working conditions. This research aims at using the elastohydrodynamic lubrication method in the main bearings of the diesel engine in external shock conditions. The main bearing elastohydrodynamic lubrication and diesel engine multi-body dynamics analysis is based on AVL EXCITE Power Unite software. The external shock is equivalent to the interference on the elastohydrodynamic lubrication calculation. Whether the elastohydrodynamic lubrication algorithm can complete the calculation under interference is the key to the study. By adopting a very small calculation step size, a high number of iterations, and increasing the stiffness of the thrust bearing, the elastohydrodynamic lubrication algorithm can be successfully completed under the external impact environment. The calculation results of the accelerations on engine block feet have a similar trend as the experiment results. Diesel engines with and without shock absorbers in external shock conditions are calculated. This calculation model can also be used for diesel engine dynamics calculations and main bearing lubrication calculations under normal working conditions.

Theoretical Disquisition on the Static and Dynamic Characteristics of an Adaptive Stepped Hydrostatic Thrust Bearing with a Displacement Compensator

Stepped hydrostatic thrust bearings used in metal-cutting machines are characterized by high load capacity and damping, which ensure the stable operation of structures. However, in comparison with throttle thrust bearings, they have a high compliance. It is preferable that, in addition to the main bearing function, a modern hydrostatic bearing has the ability to provide low (including negative) compliance for the implementation of an adaptive function in order to actively compensate for the deformation of the machine resilient system, thereby increasing the accuracy of metalworking. This paper considers the design of a stepped hydrostatic thrust bearing, which, in order to reduce the compliance to negative values, features a technical improvement consisting of the use of an active displacement compensator on an elastic suspension. In this paper, the results of mathematical modeling and theoretical research of stationary and non-stationary modes of operation of the adaptive thrust bearing are presented. The possibility of a significant reduction in the static compliance of the structure, including the negative compliance values, is shown. It was found that negative compliance is provided in a wide range of loads, which can be up to 80% of the range of permissible bearing loads. The study of the dynamic characteristics showed that with a targeted selection of parameters that ensure optimal performance, the adaptive thrust bearing is able to operate stably in the entire range of permissible loads. It has been established that an adaptive stepped hydrostatic thrust bearing with a displacement compensator has a high stability margin, sufficient to ensure its operability when implementing the adaptive function.

Optimized Extreme Learning Machine-Based Main Bearing Temperature Monitoring Considering Ambient Conditions’ Effects

Wind Turbines (WTs) are exposed to harsh conditions and can experience extreme weather, such as blizzards and cold waves, which can directly affect temperature monitoring. This paper analyzes the effects of ambient conditions on WT monitoring. To reduce these effects, a novel WT monitoring method is also proposed in this paper. Compared with existing methods, the proposed method has two advantages: (1) the changes in ambient conditions are added to the input of the WT model; (2) an Extreme Learning Machine (ELM) optimized by Genetic Algorithm (GA) is applied to construct the WT model. Using Supervisory Control and Data Acquisition (SCADA), compared with the method that does not consider the changes in ambient conditions, the proposed method can reduce the number of false alarms and provide an earlier alarm when a failure does occur.

Stiffness Evaluation and fast matching method of mechanical composite structure

Stiffness evaluation can improve the reliability and safety of combined machinery, which is often used to evaluate the performance of combined machinery. In order to study the stiffness evaluation method and rapid matching of mechanical composite structure, the composite machinery composed of high-power diesel is taken as the research object. The results show that the error between test mode and calculation mode is no more than 10%, indicating the reliability of finite element simulation model; two characterization methods of static stiffness and dynamic stiffness are determined, and the analysis methods of two characterization methods of combined machinery are discussed one by one. Taking the combined machinery of body, main bearing cap and oil pan as the research object, the overall stiffness characterization data of three parts are obtained one by one; finally, the principles of mechanical combination Stiffness Evaluation and rapid matching are summarized. This study provides a reference for Stiffness Evaluation and rapid matching of combined mechanical structures.

Property requirements of vibration measurements in wind turbine drivetrain bearing condition monitoring

Wind turbine drivetrain bearing failures continue to lead to high costs resulting from turbine downtime and maintenance. As the standardised tool to best avoid downtime is online vibration condition monitoring, a lot of research into improving the signal analysis tools of the vibration measurements is currently being performed. However, failures in the main bearing and planetary gears are still going undetected in large numbers. The available field data is limited when it comes to the properties of the stored measurements. Generally, the measurement time and the covered frequency range of the stored measurements are limited compared to the data used in real-time monitoring. Therefore, it is not possible to either reproduce the monitoring or to evaluate new tools developed through research for signal analysis and diagnosis using the readily available field data. This study utilises 12 bearing failures from wind turbine condition monitoring systems to evaluate and make recommendations concerning the optimal properties in terms of measurement time and frequency range the stored measurements should have. The results show that the regularly stored vibration measurements that are available today are, throughout most of the drivetrain, not optimal for research-driven postfailure investigations. Therefore, the storage of longer measurements covering a wider frequency range needs to begin, while researchers need to demand this kind of data.

Experimental Investigation of the Influence of Engine Operating and Lubricant Oil Parameters on Sliding Bearing and Friction Behavior in a Heavy-Duty Diesel Engine

In order to rise to global challenges such as climate change, environmental pollution and conservation of resources, internal combustion engine manufacturers must meet the requirements of substantially reduced emissions of CO2 and other greenhouse gases, zero pollutant emissions and increased durability. This publication addresses approaches that can help improve engine efficiency and durability through the engine crankshaft bearing and lubricant system. An understanding of the operating behavior of key engine components such as crankshaft main bearings in fired engine operation allows the development of appropriate tools for bearing condition monitoring and condition-based maintenance so as to avoid critical engine operation and engine failure as well as unnecessary engine downtime. Such tools are especially important when newly developed low viscosity oils are employed. Though these oils have the potential to reduce friction and to increase engine efficiency, their use comes with a higher risk of accelerated bearing wear and ultimately bearing failure. The specific target of this paper is therefore to obtain detailed knowledge of the influence of engine operating parameters and oil parameters on crankshaft main bearing temperature behavior and engine friction behavior in fired operation as a starting point for condition monitoring and condition-based maintenance approaches and as a basis for improving the bearing and lubricant system as a whole. To achieve this target, experimental investigations were carried out on an engine test bed employing an in-line six-cylinder heavy-duty diesel engine with a displacement of approximately 12.4 dm3. Defined and accurately reproducible engine operating conditions were ensured by comprehensive external conditioning systems for the coolant, lubricating oil, fuel, charge air and ambient air. Since the focus was on investigating the bearing and friction behavior by means of the base engine, several auxiliary systems were removed; these included the lubricating oil and coolant pumps, the front-end accessory drive and the generator. Each crankshaft main bearing was instrumented with a thermocouple on the back of its bottom bearing shell to measure the bearing temperature. Piezoelectric pressure transducers were applied to all six cylinders in order to facilitate the accurate determination of the friction mean effective pressure (FMEP) based on indicated and brake mean effective pressures. The variations in engine operating parameters (engine speed and torque) mainly serve as a reference for the variations in oil parameters. They confirm the existing knowledge that engine speed has a significant impact on FMEP and bearing temperature while the impact of engine torque is comparatively low. The variations in oil parameters reveal that lowering the viscosity grade from SAE 10W-40 to 5W-20 leads to a decrease in both bearing temperature and FMEP, which can be explained by the lower fluid friction in the bearing system and the increased mass flow and convective heat transport with the lower viscosity oil. An increase in the lubricating oil temperature at the engine inlet leads to a significant increase in bearing temperature and a decrease in FMEP; the former is explained by the increased heat influx from the lubricant oil, and the latter is caused mainly by the temperature dependency of the lubricant oil viscosity and its impact on fluid friction. The impact of engine oil inlet pressure on bearing temperature and FMEP is generally found to be low. The results will serve as the basis for future research that includes approaches to condition monitoring and evaluating improved engine operating strategies with regard to oil parameters.

Updatable Probabilistic Evaluation of Failure Rates of Mechanical Components in Power Take-Off Systems of Tidal Stream Turbines

This paper presents a method for the probabilistic evaluation of the failure rates of mechanical components in a typical power take-off (PTO) system of a horizontal-axis tidal stream turbine (HATT). The method is based on a modification of the method of the influence factors, when base failure rates, relevant influence factors and, subsequently, resulting failure rates are treated as random variables. The prior (i.e., initial) probabilistic distribution of the failure rates of a HATT component is generated using data for similar components from other industries, while taking into account actual characteristics of the component and site-specific operating and environmental conditions of the HATT. A posterior distribution of the failure rate is estimated numerically based on a Bayesian approach as new information about the component performance in an operating HATT becomes available. The posterior distribution is then employed to obtain the updated mean and lower and upper confidence limits of the failure rate. The proposed method is illustrated by applying it to the evaluation of the failure rates of two key components of the PTO system of a typical HATT—main seal and main bearing. In particular, it is shown that uncertainty associated with the method itself has a major influence on the failure rate evaluation. The proposed method is useful for the reliability assessment of both PTO designs of new HATTs and PTO systems of operating HATTs.