A validated finite element model for predicting dynamic responses of cylinder liners in an IC engine*

Vibration of cylinder liners affects not only engine combustion performances but also tribological behaviour and noise radiations. However, it is difficult to characterize it experimentally due to multiple sources, strong background noise, and nonlinear transfer paths. Therefore, a finite element model is established in this study to predict the dynamic responses of cylinder liners under respective sources. The model takes into account both the characteristics of structural modes and nonlinearities of assembly constraints when selecting adequate elements for efficient computation of the responses under both the highly nonlinear combustion pressure excitations and subsequent piston slap impacts. The predictions are then evaluated against experimental results under different engine operating conditions. In addition, continuous wavelet analysis is employed to process the complicated responses for key response events and their frequency ranges. The results show agreeable correspondences between the numerical predictions and measured vibration signals, paving the way for investigating its effect on combustion and lubrication processes

Investigation into the dynamic response of cylinder liners in an IC engine based on a validated finite-element model

To understand the effects of vibration of cylinder liners on engine combustion performance, tribological behaviour and vibro-acoustic radiations, this study investigates the dynamic responses of cylinder liners by finite-element modelling and experimental validation. The finite-element model is established in this study to predict the dynamic responses of cylinder liners to two significant sources: combustion shock and piston side thrust. It takes into account both the characteristics of structural modes and nonlinearities of assembly constraints when selecting adequate elements for efficient computation of the responses under both the highly nonlinear combustion pressure excitations and subsequent piston slap impacts. The predictions are then evaluated against experimental results under different engine operating conditions. To suppressing noise in measured signals, continuous wavelet analysis is employed to process the complicated responses for characterizing key response events and their frequency ranges. The results show agreeable correspondences between the numerical predictions and measured vibration signals, paving the way for investigating its effect on the combustion and lubrication processes

A Dynamic Deformation based Lubrication Model between the Piston Rings and Cylinder Liner

The piston ring-cylinder liner friction pair is one of the most important friction pair in IC engines. In previous modelling studies, most researches were carried out based on a hypothesis that the inner surface of liner is an ideal cylindrical shell without considering the effects of dynamic deformation on oil film distribution. To investigate the potential influences of structural deformations on tribological behaviors of cylinder assemblies, the dynamic deformation of liner surface was obtained by FEM-based dynamic simulation, and then introduced into the lubrication model. Different from the traditional lubrication model where the pressure stress factor and shear stress factor are regarded as constant, this paper calculated these factors in real time by numerical integration to achieve more realistic simulation results. This study shows that the friction force obtained from the improved model manifests obvious fluctuations, and shows a significant reduction compared to original model

Investigation into the Vibrational Responses of Cylinder Liners in an IC Engine Fueled with Biodiesel

The paper presents a study of the relationship between the combustion behavior and vibration response of internal combustion (IC) engines fueled with biodiesel based on finite element modelling along with experimental evaluation. An improved finite element (FE) model is established and validated to predict the dynamic responses of cylinder liners with respect to two main sources: combustion shock and piston side thrust. Based on the validated FE model, the response characteristics of the cylinder liner in an IC engine fueled with biodiesel and its causal relationship with excitation sources have been predicted. Due to the lower calorific value of biodiesel, a greater amount of fuel is injected into the combustion chamber to maintain power outputs, which results in a prolonged combustion duration and subsequent higher overall vibration levels, compared with that of diesel. The advanced ignition of biodiesel is the main cause to the compound effect on the coupling of piston side-thrust force, thereby resulting in a nonlinear increase in the root mean square (RMS) of local vibration response close to the combustion top dead center (TDC). These key findings provides insight understandings for not only biodiesel combustion diagnostics but also more accurate diagnostics of fossil diesel based on nonintrusive vibrations

Investigation into the dynamic responses and tribological characteristics of cylinder liners in a IC engine with alternative fuels

Promoted by the realisation of dwindling fossil fuel supplies and their adverse environmental impacts, there more and more types of alternative fuels to fossil diesel have been used and investigated in compression ignition engines. However, the majority of researches on alternative fuels mainly focus on their power performance, efficiency and emission performance, without fully investigating the potential effects on the vibro-acoustic emissions and tribological characteristics of engines caused by their significant differences in physical and chemical properties. Consequently, the impacts of long-term use of alternative fuels on structural failure, lubrication degradation, friction aggravation, overall service life spans and associated maintenance activities of internal combustion (IC) engines have not yet been fully understood. To reduce this gap this thesis focuses on the investigation into the vibration responses of cylinder liners in a diesel engine to accurately characterises the tribological behaviour between the piston rings and cylinders which is one of the most decisive sub-processes that determine engine performance and yet is correlated with the combustion of different fuels. In particular, the investigation was carried out by coupling the hydrodynamic lubrication model with structural vibration effects through a series of extensive numerical simulations and systematic experimental evaluations in order to establish a vibration based technique to monitoring tribological behaviour and thereby accurately assess the influence. Based on the dynamic coupling mechanisms between the combustion characteristics of alternative fuels and the tribological behaviours of cylinder liners, the most significant influences from the fuel burning on tribological behaviour of cylinder liners concerned in this study is a direct and physical approach such as the effect of liner vibrations on cylinder friction process, even though an indirect and chemical but very slow approach such as the deterioration of oil properties by combustion products can happen. To characterise the direct influence a finite element dynamic model was developed and validated for predicting the dynamic responses of cylinder liners to respective excitation sources including the highly nonlinear combustion pressure shocks and subsequent piston slap impacts. The realistic consideration of both the characteristics of structural modes up to 15kHz and nonlinearities of elastic assembly constraints allows obtaining accurate prediction that the combustion shocks cause vibrations in a frequency range around 10kHz with an amplitude order of 0.01μm, whereas the piston slaps in frequency range from 1k to 5kHz with an amplitude order 0.2μm, which gives a clear and quantitative indication of the nonlinear phenomena of liner vibration due to combusting alternative fuels and varying lubrication conditions. In addition, a decomposition analysis of piston side-thrust forces provides more insight of the localized response characteristics corresponding to coupling interactions of combustion force with inertia force of piston assembly. To further investigate the potential influences of structural deformations to tribological behaviours of cylinder assemblies, a new dynamic deformation based lubrication model was developed based on an employment of improved shearing factors in which the effect of inevitable liner vibrations is included to obtain a more realistic lubricating film formation, distribution and tribological behaviours. The simulation studies show that this advancement in modelling oil films predicts that the biodiesel with more intense vibration emissions is able to reduce the friction loss between pistons and liners, whereas the methanol-diesel blend with weakened liner dynamic response may exacerbate the friction loss of IC engines. This finding confirms further that the vibration responses allow a straightforward and in-depth indication of the effect generated by using different fuels. In addition, a further experimental investigation was carried out based on a motoring engine test, in which high frequency sinusoidal vibrations at 25 kHz, 30 kHz and 40 kHz are added to the external surface of the linear. The observable changes in motoring torque verify that proper external vibrations can affect the tribological behaviours between the pistons and liners, including both asperity friction and viscous friction, and resulting in the friction reduction of IC engines. Particularly the 40 kHz vibration at the maximal driving power of the test device can achieve a reduction of 1.79% in the motoring torque. This has demonstrated more on the effectiveness of this vibration based diagnostic method in assessing the influences of alternative fuels upon tribological behaviours of piston ring and cylinder liners. Finally, further researches on the subjects is also proposed in order to complete the vibration based diagnostics in achieving more accurate assessment of engine lubrication conditions and effective friction reduction

Turbine Engine Hot Section Technology (HOST)

Research and plans concerning aircraft gas turbine engine hot section durability problems were discussed. Under the topics of structural analysis, fatigue and fracture, surface protective coatings, combustion, turbine heat transfer, and instrumentation specific points addressed were the thermal and fluid environment around liners, blades, and vanes, material coatings, constitutive behavior, stress-strain response, and life prediction methods for the three components

Aeropropulsion 1987. Session 5: Subsonic Propulsion Technology

NASA is conducting aeropropulsion research over a broad range of Mach numbers. In addition to the high-speed propulsion research described, major progress was recorded in research aimed at the subsonic flight regimes of interest to many commercial and military users. Recent progress and future directions in such areas as small engine technology, rotorcraft transmissions, icing, Hot Section Technology (HOST) and the Advanced Turboprop Program (ATP) are covered

Loads and aeroelasticity division research and technology accomplishments for FY 1985 and plans for FY 1986

The Langley Research Center Loads and Aeroelasticity Division's research accomplishments for FY85 and research plans for FY86 are presented. The rk under each branch (technical area) will be described in terms of highlights of accomplishments during the past year and highlights of plans for the current year as they relate to five year plans for each technical area. This information will be useful in program coordination with other government organizations and industry in areas of mutual interest

Research and technology highlights of the Lewis Research Center

Highlights of research accomplishments of the Lewis Research Center for fiscal year 1984 are presented. The report is divided into four major sections covering aeronautics, space communications, space technology, and materials and structures. Six articles on energy are included in the space technology section

Aeronautical Engineering: A special bibliography with indexes, supplement 72, July 1976

This bibliography lists 184 reports, articles, and other documents introduced into the NASA scientific and technical information system in June 1976