Engine Exhaust Valves Research Articles

Diagnostic-Oriented Vibroacoustic Model of the Reciprocating Engine

The method of modelling the signal of vibrations of the internal combustion engine based on the discrete wavelet transform (DWT), is presented in the paper. This method is suitable for the representation of transient processes, which occur in the vibroacoustic signal (VA) generated by the engine. The model is identified on the basis of the vibration signal recorded during the car driving at a constant speed. The base model and its measures are created for the new engine and the control measurements, performed either at the determined time periods or car mileage, are compared to them. This base model must be actualised after each engine overhaul and as its wear and tear progresses, due to changes of the vibration characteristics. On account of a random character of vibration responses the envelope of the modelled signal is utilised for diagnostic purposes. The model based diagnostic method was verified in the paper on the example of the engine exhaust valve defect.

Mineral-Metal, Multiphase Coatings to Protect Combustion Chamber Components Against Hot-Gas Corrosion and Thermal Loading

Many marine and stationary engines operate on fuels that contain corrosive elements, with the result that some highly loaded combustion chamber components must be replaced frequently. Märkisches Werk, GmbH (MWH) has pioneered the development of mineral-metal, multiphase coatings to protect valves and other highly loaded engine components against hot-gas corrosion. Mineral-metal, multiphase coatings are a unique and innovative approach to improving hot-gas corrosion resistance in a cost-effective manner. In general, these coatings combine the beneficial chemical and thermal attributes of ceramic coatings with the mechanical properties and substrate adhesion characteristics of a metal. Extensive laboratory and field trials have proven that MWH CrystalCoat protects heavy fuel oil (HFO) engine exhaust valves against hot-gas corrosion. It is projected that the newest coating formulation (CrystalCoat HT) will protect four-stroke HFO exhaust valves against hot-gas corrosion over their entire service life.

Influence of cutting tool geometry, feed rate and cutting fluid on the machinability of Inconel 751

Inconel represents a family of nickel-based super alloys with a wide range of application including components that work at high temperatures. Despite of this, nickel-based super alloys are generally known to be one of the most difficult materials to machine. In this paper, attention is focused on the machinability of Inconel 751 which is a nickel-based super alloy normally used to manufacture exhaust valves of internal-combustion engines. In this case, an experimental investigation where a series of dry and wet rapid facing trials (turning) using coated carbide tools were performed. Metal removing process was carried out for two different feed rates and two different tool geometries. For indirectly quantifying the tool wear, the machined surface profile has been measured using a centesimal dial gauge. Moreover, cutting tools have been analysed with a scanning electronic microscope. The results provide important practical information about the machinability of Inconel 751.

A Dynamic Model of an Electropneumatic Valve Actuator for Internal Combustion Engines

This paper presents a detailed model of a novel electropneumatic valve actuator for both engine intake and exhaust valves. The valve actuator’s main function is to provide variable valve timing and variable lift capabilities in an internal combustion engine. The pneumatic actuation is used to open the valve and the hydraulic latch mechanism is used to hold the valve open and to reduce valve seating velocity. This combination of pneumatic and hydraulic mechanisms allows the system to operate under low pressure with an energy saving mode. It extracts the full pneumatic energy to open the valve and use the hydraulic latch that consumes almost no energy to hold the valve open. A system dynamics analysis is provided and followed by mathematical modeling. This dynamic model is based on Newton’s law, mass conservation, and thermodynamic principles. The air compressibility and liquid compressibility in the hydraulic latch are modeled, and the discontinuous nonlinearity of the compressible flow due to choking is carefully considered. Provision is made for the nonlinear motion of the mechanical components due to the physical constraints. Validation experiments were performed on a Ford 4.6 l four-valve V8 engine head with different air supply pressures and different solenoid pulse inputs. The simulation responses agreed with the experimental results at different engine speeds and supply air pressures.

Inorganic Polymer Matrix Composite Strength Related to Interface Condition

Resin transfer molding of an inorganic polymer binder was successfully demonstrated in the preparation of ceramic fiber reinforced engine exhaust valves. Unfortunately, in the preliminary processing trials, the resulting composite valves were too brittle for in-engine evaluation. To address this limited toughness, the effectiveness of a modified fiber-matrix interface is investigated through the use of carbon as a model material fiber coating. After sequential heat treatments composites molded from uncoated and carbon-coated fibers are compared using room temperature 3-point bend testing. Carbon-coated Nextel fiber reinforced geopolymer composites demonstrated a 50% improvement in strength, versus that of the uncoated fiber reinforced composites, after the 250 °C postcure.

High-Temperature Oxide Regrowth on Mechanically Damaged Surfaces

X-ray elemental maps are used with single-point abrasion tests of a nickel-based superalloy, exposed to air at 850 °C, to demonstrate how high-temperature oxidation products form differently on damaged and non-damaged tribosurfaces. These findings complement previous work on the nature of sliding combined with oxidation. Results have implications for modeling the wear processes of exhaust valves in internal combustion engines.

Modeling and simulation of a dual-mode electrohydraulic fully variable valve train for four-stroke engines

In modern four-stroke automotive engine technology, variable valve timing and lift control offer potential benefits for making a high-performance engine. In this paper, a novel design named dual-mode electrohydraulic fully variable valve train (EHFVVT) for both engine intake and exhaust valves is introduced. The system is mainly controlled by either proportional flow control valves or proportional pressure relief valves, and hence two different families of valve displacement patterns can be achieved. The construction of the mathematical model of the valve train system and its dynamic analysis are also presented in this paper. Experimental and simulation results show that the dual-mode electrohydraulic variable valve train can achieve fully variable valve timing and lift control, and has the potential to eliminate the traditional throttle valve in the gasoline engines. With the proposed system, the engine performance at various speeds and loads will be significantly improved.

Flatness-Based Tracking of an Electromechanical Variable Valve Timing Actuator With Disturbance Observer Feedforward Compensation

A comprehensive control strategy for an automotive solenoid variable valve timing actuator is presented that addresses the issues of feedback sensors, soft seating or landing control, disturbance rejection and feedforward design. In particular, the motion control of the engine exhaust valve actuator subject to large cycle-to-cycle gas force variations is successfully demonstrated in simulation and on an experimental test-bench. Also provided is a method of characterization and online cycle-to-cycle identification of combustion gas force disturbances. The identified gas forces are used in energy-based feedforward and flatness-based landing algorithms. Simulated and experimental results indicate the proposed control methodology is capable of compensating for the combustion gas force disturbances experienced by exhaust valve solenoid actuators.

Computational Visualization and Simulation of Diesel Engines Valve Lift Performance Using CFD

The paper visualized and simulated the intake and exhaust valve lift in the single-cylinder four-stroke direct injection diesel engine. The visualization and simulation computational development were using the commercial Computational Fluid Dynamics of STAR-CD 3.15A software and GT-SUITE 6.2 software. The one dimensional of valve lift modeling was developed using GT-POWER software and the visualization the model using STAR-CD. The model simulation covers the full engine cycle consisting of intake, compression, power and exhaust. The visualization and simulation shown the diesel engine intake and exhaust valve lifting and moving based on the crank angle degree parameters. The result of this visualization and simulation shows the intake and exhaust valve lift moving and air fluid flow of the diesel engine model.

Processing-structure-property aspects of particulate- and whisker-reinforced titanium matrix composites

The demand for lightweight, high performance and high temperature materials for advanced structural applications is increasing in many industrial sectors. Cost-effective discontinuously reinforced titanium matrix composites (TMCs) exhibit high strength, high stiffness, excellent wear resistance and high temperature durability. Hence, TiC p/Ti–6Al–4V and TiB w/Ti composites have been used commercially as structural materials for exhaust valves in automotive engines. They are also attractive materials for usage in aerospace, advanced military, biomedical engineering sectors and sporting goods. Titanium boride whisker (TiB w) is considered an effective ceramic reinforcement for titanium since it can be synthesized in situ in titanium matrix during composite fabrication. The TiB whiskers strengthen the composites remarkably via a load-transfer mechanism. Moreover, in situ TiB whiskers also enhance creep and high-cycle fatigue resistances of Ti-based composites when compared to un-reinforced Ti alloys. In this review, state-of-the-art developments on processing, microstructural characterization and mechanical properties of particulate and whisker reinforced TMCs are discussed. Particular attention is given to the structural–mechanical property relationships of high performance TMCs. This review provides useful guidance to those working on the development of novel Ti-based composites for advanced structural applications.

Influences of microstructure on service properties of 5Cr21Mn9Ni4N heat resistant alloy

The plates of four diesel engine exhaust valves used in a truck failed when servicing for 2000 h, which are made of 5Cr21Mn9Ni4N (21-4N) heat resistant alloy. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction were performed on the plate material of the failed valves and a new valve. The results show that the plate material before service is composed of first carbides (Cr23C6) and γ austenite matrix. However, appearance of the lamellar structure and plate-like precipitates within the grain is the general metallurgical features of the plate material of the failed valves, which indicates that the austenite matrix decomposed in service. XRD and electron diffraction results demonstrate that the lamellar structure is mainly composed of Cr23C6 and γ austenite, coexisting CrN phase, which formed by the discontinuous precipitation mechanism. Electron diffraction shows that the convex lens-like CrN phases precipitate within the grain, which formed by the continuous precipitation mechanism. Fractographic studies indicate that the fatigue is the dominant failure mechanism of the three valves and burning-through occurred on the plate of another failed valve. Formation of the lamellar structure and plate-like precipitations within the grain is mainly responsible for the failure of the valves. Isothermal aging tests were conducted on the plate material from the new valve to study the material stability at high temperatures. The microstructure development during aging was observed by SEM and optical microscopy. The influence of the microstructure on the service properties was discussed and possible failure causes of the valves were assessed.

Impact of different configurations of a Diesel oxidation catalyst on the CO and HC tail-pipe emissions of a Euro4 passenger car

Different configurations were used to study the impact of a Diesel oxidation catalyst position on the HC and CO oxidation efficiency of a Euro4 Diesel passenger car. An oxidation catalyst of 0.8 L downstream EGR port is the original configuration. Another two configurations are studied in this work: the same catalytic volume put upstream EGR port and four small close-coupled catalysts of 0.06 L each put in the exhaust manifold very close to the engine exhaust valve. The results show that the configuration upstream EGR port leads to a significant increase on HC conversion efficiency; however, CO tail-pipe emissions remain practically unchanged. The four small close-coupled catalysts put in the exhaust manifold, despite the higher exhaust temperature, show lower oxidation efficiency due to the high space velocity, however, they can be used in the case of little available space for a bigger catalyst. In all configurations studied, there is a significant difference on CO and HC conversion efficiency and thus on tail-pipe emissions in the case of aged oxidation catalysts compared to fresh ones.

Strength retention of silicon nitride after long-term oil immersion exposure

Two commercial grade silicon nitride ceramics (Honeywell GS44 and Kyocera SN235) were exposed to an oil ash to evaluate the long-term corrosion/oxidation resistance in a simulated diesel engine environment. The exposure condition was at 850 °C for 1000 h in air. Subsequently, the exposed specimens were tested in flexure for strength degradation at room temperature and 850 °C at stressing rates of 30 MPa/s and 0.003 MPa/s in air, respectively. A similar set of specimens not exposed to the oil ash was also tested in flexure for purpose of comparison. Little change in strength was measured after 1000 h exposure in the oil ash environment. Also, the values of Weibull modulus obtained for all of the exposed silicon nitride materials were similar to those with the unexposed specimens whose strength were obtained under the same conditions. However, both exposed and unexposed GS44 specimens exhibited a low fatigue exponent, suggesting a susceptibility to slow crack growth at test temperature. In addition, detailed SEM/EDAX analyses indicated that no oil ash elements (e.g., Zn, Ca, P, Na, and S) were detected beneath a thin layer in the surface; thus, there were no changes in the chemistry of the secondary phase(s) within the bulk. These elements were detected only in a region about 1–3 μm below the exposed surface, but no apparent changes in microstructure observed. Results of mechanical properties and microstructural characterizations indicated that these candidate silicon nitride materials exhibited excellent corrosion/oxidation resistance in the simulated diesel engine environment and, based on their excellent mechanical strengths, would be ideal candidates for diesel engine exhaust valve applications.

Simulation of Electric Upsetting and Forging Process for Large Marine Diesel Engine Exhaust Valves

The manufacturing process of the exhaust valve in large marine diesel engines consists of an upset forging and final forming process. In the past, the exhaust valves in large marine diesel engines have been made through free forging by using the stretch forming method. This method has used the ingot and the billet as a preliminary forming process. Nimonic 80A, a superalloy, is presently used for the material of the exhaust valve. For the forming method of the valve, the electric upset method is used. Solid bar is raised up to the forming temperature by using electric energy and is continually deformed by upset pressure. The electric upsetting processing is a useful method for the high quality of exhaust valves in large marine diesel engines. It can keep the continuous grain flow, excellent mechanical property, and corrosion resistance because of the elaborate macrostructure of the valve face. The purpose of this paper is to predict the optimum process condition through simulation of the exhaust valve with a diameter of 73mm. The experimental result of an exhaust valve with a diameter of 19mm is in good agreement with the simulation result using the “QForm” that can solve electric upsetting problems. Finally, the optimal manufacturing process of the electric current and the upset load are surveyed.

Tribological properties of laser clad Stellite 6 coatings on steel substrates

The laser cladding of diesel engine exhaust valves is an emerging technology that provides excellent results in terms of the wear and corrosion resistance of the repaired materials. This work focuses on the deposition by laser cladding of Stellite 6 alloy coatings on two different base materials: an AISI 1045 carbon steel and an AISI 304 stainless steel. Following a process optimisation criterion, several of the fundamental laser treatment parameters were varied in order to obtain defect-free coatings with good adherence and minimal dilution. The metallographic structure of the clad material, irrespective of the substrate used, consists of a typical dendritic microstructure in a solid solution of Co. The mechanical strength of the layers was analysed by measuring HV0·1 microhardness and sliding wear behaviour. Laser coatings achieved hardness greater than 500 HV0·1, and presented excellent dry sliding wear behaviour, with a dimensional wear coefficient k one and a half orders of magnitude lower than that of the substrates. A combined oxidation and abrasion mechanism dominated the wear of the Stellite 6 layers, while in the case of AISI 1045 steel substrate, the wear was caused mainly by a surface oxidation mechanism. For the AISI 304 steel, the wear resulted from a combined adhesion, abrasion and plastic deformation mechanism.

Optimización del recorrido y de la potencia de un haz láser de CO<sub>2</sub> en el tratamiento térmico de válvulas de motores diesel

In this article, a model for the process of CO 2 laser treatment of diesel engine exhaust valves is presented. The treatment consists on the remelting of a nickel based alloy which has been previously plasma sprayed on the valve seat. Such process can be well described by means of a transient heat transfer equation, even if some numerical method must be applied when both temperature dependent thermophysical properties and realistic geometry description of the workpiece are taken into account. For this work the Finite Element Method, within the framework of ANSYS®, was chosen, to solve that equation and this was done in the framework of ANSYS®. The use of the process parameters previously assessed during a the theoretical and experimental study of box shaped workpieces requires a fine tuning based on simulation in order to be sure that the treatment of the valve seat gets comparable results to that of the flat workpieces. Among the important conditions to be satisfied stands the need for the temperature map to be parallel to the valve seat surface and so have the same treated depth. Besides, as the beam describes a circular path, coming back to the starting position, the initial temperature at that point will be higher than for rest of the workpiece. Therefore the beam power has to be optimized in order to get adapted to this new situation. Phase transition is included in the model by using the right thermophysical properties and a correct estimation of the effective absorption coefficients in both phases. This work shows the advantages of the process modelling to support the optimization of laser surface treatment of complex geometry workpieces using the model validation performed in simpler workpieces.

Technology of plasma-powder surfacing exhaust valves of engines of VAZ cars

Technology of plasma-powder surfacing exhaust valves of engines of VAZ cars

Failure analysis and metallurgical investigation of diesel engine exhaust valves

This paper presents a failure analysis of three diesel engine exhaust valves used in a truck which failed in service. The failure had taken place at the plates of the exhaust valves. The plate material is made from 5Cr21Mn9Ni4N steel. The fracture surfaces were investigated by SEM and visual observation. The results show that the cracks initiated from the interface of the tapered plane and the transitional region of the plate and propagated toward the bottom of the valve for two failed exhaust valves. Fractographic studies indicate fatigue as the dominant mechanism of the failure of the two exhaust valves. Burning-through occurred on the plate of another failed exhaust valve. The microstructure and phases of the plates of the failed valves were investigated by SEM and XRD, and compared with those of a new valve. The austenitic matrix decomposed to form the lamellar structure consisting of γ + Cr 23C 6 at the boundary and within the grains in service, which is the general metallurgical character of plate material for the three failed valves. The lamellar structure separates the matrix to decrease strength, toughness, the loading ability of the matrix, and gas corrosion resistance. Formation of the lamellar structure is mainly responsible for the failure of the exhaust valves. The appearance of the lamellar structure in the plate material of the failed valves in service is related to the original metallurgical structure, and depends on the solution-aging treatment.

The Pulsating Flow Field in a Mixed Flow Turbocharger Turbine: An Experimental and Computational Study

The turbine stage of an automotive pulse system turbocharger is subjected to an unsteady pulsating flow field due to the rapid opening and closing of the reciprocating engine exhaust valves. This leads to a complex and highly disturbed flow field within the delivery volute and turbine passages, which results in an unusual “hysteresis” type performance characteristic. The aim of this paper is to investigate the flow field within the turbine stage under these representative conditions, using a computational method validated against experimental data. This paper is separated into two sections. The first deals with the validation of the numerical code and modeling approach. A mesh dependency study is undertaken with cell discretization ranging 200,000, 850,000, and 1,750,000 cells, where the accuracy is assessed through comparison with experimental performance and flow field measurements. The second part presents an investigation of the flow field under pulse conditions. Time accurate spectra of turbine performance and flow properties at various locations in the turbine stage are presented, as well as contour plots of velocity within a turbine passage at two critical positions during the pulse period.

Recubrimiento de <i>Stellite 6</i> sobre acero inoxidable realizado con láser de CO<sub>2</sub> para válvulas de escape de motores diesel

To reduce the recovery or the replacement costs of diesel engine exhaust valves, they are manufactured with an economic base material, and a coating which is deposited on the seat valve in order to reach high hardness and good impact, corrosion and high temperature wear resistance (>550 °C) and without lubrication. In this work, appropriate laser cladding parameters have been determined to obtain Stellite 6 coatings over AISI 304 steel (as plane test specimens) and SAE EV8 steel (as valves) substrates. One and two superimposed tracks were deposited on the seat valves, and modifying the laser power as a function of the rotated angle at the beginning and the end of the circular tracks, pores and cracks have been minimized and the thickness of the track were made uniform. Hardness, dilution and final microstructure of the different coatings have been analysed. A 10 % dilution and 550 HV in the tracks over plane test specimens was observed, while valves with one track showed 25 % and 430 HV respectively. With two superimposed tracks the hardness was up to 470 HV in the upper track.