Valve Actuation System Research Articles

Experimental investigations of gasoline partially premixed combustion with an exhaust rebreathing valve strategy at low loads

This paper investigates the combustion and emission characteristics using a commercial gasoline with Research Octane Number (RON) of 93 on a Partially Premixed Combustion (PPC) engine equipped with a Variable Valve Actuator (VVA) system. The effects of injection timing, internal exhaust gas recirculation (i-EGR) rate and intake pressure on combustion and emissions are studied. The i-EGR was achieved by an extra opening of the exhaust valve during the intake process. The study was conducted at an engine speed of 1500 r/min with cyclic fuel mass from 11.6 to 22.2mg. The operating region for high-efficient, clean and stable gasoline PPC (i.e., COVimep<5%, NOx<0.4g/kWh, Smoke<0.1 FSN, CO and HC as low as possible) was explored and discussed. The results illustrate that proper i-EGR rates with a fixed injection timing of −24°CA ATDC could maintain optimal thermal efficiency while minimizing CO and HC emissions as the engine load decreased from 3.9 to 2.1bar gross indicated mean effective pressure (IMEPg). However, high NOx at higher load was observed and the adoption of earlier injection timing with lower i-EGR rate has the potential to suppress the sharp Smoke increase at lower NOx levels. Improved combustion process can be obtained with later SOI timings as well as higher i-EGR rates as the intake pressure increased. It has been found that the low-load limit of stable gasoline PPC can be extended to 1.5bar IMEPg through the optimization of VVA, injection strategy and intake boosting.

Potential of internal EGR and throttled operation for low load extension of ethanol–diesel dual-fuel reactivity controlled compression ignition combustion on a heavy-duty engine

High levels of carbon monoxide (CO) and unburnt hydrocarbon (HC) emissions are some of the main limitations of ethanol–diesel dual-fuel reactivity controlled compression ignition (RCCI) combustion at light engine loads. In addition, low exhaust gas temperatures reduce the effectiveness of the oxidation catalyst, necessary to meet stringent emissions standards. Elevation of in-cylinder gas temperature and increased fuel/air equivalence ratio are desirable to reduce the CO and HC emissions and hence improve combustion efficiency and fuel conversion efficiency. In this work, experimental studies and engine modelling have been carried out to investigate the potential of internal exhaust gas recirculation (iEGR) and throttled operation for low load extension of ethanol–diesel dual-fuel RCCI combustion. The experiments were performed on a single cylinder heavy-duty (HD) diesel engine equipped with a variable valve actuation system capable of intake valve re-opening during the exhaust stroke. The engine model was built in a one-dimensional computational fluid dynamics software. The utilisation of higher residual gas fractions and higher global equivalence ratios increased the mean in-cylinder gas temperatures during combustion. The hotter combustion processes resulted in lower CO and unburnt HC emissions, and higher exhaust gas temperatures. The lower oxygen concentration and higher heat capacity of the in-cylinder charge using iEGR curbed nitrogen oxides (NOx) formation. Net indicated efficiency was improved with the use of iEGR and remained nearly constant while throttling the engine when compared to the dual-fuel combustion baseline at 0.32MPa net indicated mean effective pressure (IMEPnet). Compared with conventional diesel combustion, ethanol–diesel dual-fuel RCCI combustion minimised NOx and soot emissions from 0.3 to 0.6MPa IMEPnet and increased efficiency at loads above 0.5MPa IMEPnet.

A study of regulated and green house gas emissions from a prototype heavy-duty compressed natural gas engine under transient and real life conditions

A newly designed Compressed Natural Gas prototype engine was benchmarked against its parent Euro V compliant engine in terms of gaseous emissions and with particular view on regulated and Green House Gas emissions. The main technological innovation included a new cylinder head equipped with a Variable Valve Actuator system designed to increase the efficiency compared to the reference throttled engine. The objective of the study was to examine the effect of this system on the operation of the prototype engine. Engine stand-alone tests represented the first step of this analysis. Afterwards, both engines were installed on the same truck and tested under different operating conditions. Vehicle tests included measurements on a chassis dynamometer as well as on-road with the aim of verifying real-world emissions. CO2 emissions and Brake Specific Fuel Consumption of the prototype were lower compared to the reference engine, with this phenomenon being more pronounced on-road. Furthermore, reduced NOx and CO emissions were observed under all operating conditions. On the other hand, the introduction of the prototype engine had a negative effect on CH4 emissions. Despite that the prototype was initially designed to fulfill the EURO V standards, no pollutant exceeded the EURO VI limits over homologation cycles.

Precise lift control in a new variable valve actuation system using discrete-time sliding mode control

Precise engine valve lift control is essential in improving the efficiency of internal combustion engines and avoiding unwanted engine valve closure or mechanical interference between the valve and engine piston at different operating conditions. In this paper, a recently proposed hydraulic variable valve actuation (VVA) system [1] is equipped with a novel lift control architecture. In this technique, the hydraulic supply pressure is controlled using a proportional bleed valve. A discrete sliding mode controller is designed using the average model of the system on the basis of a discrete Lyapunov function. The stability of the designed controller is proven and sufficient conditions of the controller gains to stabilize the system are given. The experimental results show an excellent tracking performance of the proposed lift controller during sudden changes in the reference final valve lift. The results also show that using the proposed valve lift controller, the maximum lift deviation from its reference value does not exceed 0.4mm during transient operating condition.

Throttleless control of SI engine load by fully flexible inlet valve actuation system

A system with independent, early inlet valve closure (EIVC) has been analysed. The open, theoretical cycle has been assumed as a model of processes proceeding in the engine with variable inlet valve actuation. The system has been analysed individually and comparatively with open Seiliger-Sabathe cycle which is theoretical cycle for the classic throttle governing of engine load. The influence of EIVC on fuel economy, cycle work, relative charge exchange work and cycle efficiency has been theoretically investigated. The use of the analysed system to governing of an engine load will enable to eliminate a throttling valve from inlet system and reduce the charge exchange work, especially within the range of partial load. The decrease of the charge exchange work leads to an increase of the internal and effective works, which results in an increase of the effective efficiency of the spark ignition engine.

Effect of Variable Valve Timing to Reduce Specific Fuel Consump tion in HD Diesel Engine

Applying variable valve Actuation systems is one of the most effective ways to improve specific fuel consumption in an engine, which largely affect the pumping work. In this article determination of optimum valve timing angels, using approximation of discrete data and nonlinear regression analysis is investigated for a HD diesel engine to minimize SFC. In the first part of this study a model of compression ignition engine (OM457) in GT-SUITE software are applied for optimization. Then the indicated best angels for EVO, IVO, EVC and IVC were added to the model as lookup tables to shape the VVT system. Eventually, results indicated that using VVT angles the SFC parameter decreases more than 2% in average. Furthermore, to compare differences in emissions rate, the European stationary cycle (ESC) was applied and generated NOx pollutant was reduced 7.4%.

Performance Optimization of a Turbocharged Spark-Ignition VVA Engine at Part Load

Nowadays, modern internal combustion engines show more and more complex architectures in order to improve their performance. Referring to the spark-ignition (SI) engines, downsizing philosophy and Variable Valve Actuation (VVA) systems allow to reduce the Brake Specific Fuel Consumption (BSFC) at low and medium load, while maintaining the required performance at high load. On the other hand, the above solutions introduce additional degrees of freedom for the engine control, requiring longer calibration time and experimental effort. In the present work, a twin-cylinder turbocharged VVA SI engine is numerically investigated by a one-dimensional (1D) model (GT-PowerTM). The considered engine is equipped with a fully flexible VVA actuation system, realizing an Early Intake Valve Closure (EIVC) strategy. Proper "user routines" are implemented in the code to simulate turbulence and combustion processes. In a first stage, 1D engine model is validated against the experimental data under part load condition, both in terms of overall performance and combustion evolution. The validated 1D engine model is then integrated in a multipurpose commercial optimizer (mode FRONTIERTM) with the aim to identify the engine calibrations that simultaneously minimize BSFC and Brake Mean Effective Pressure (BMEP) under part load operation at a specified engine speed of 3000rpm. In particular, the decision parameters of the optimization process are the EIVC angle, the throttle valve opening and the waste-gate valve opening and combustion phasing. Proper constraints are assigned for the pressure in the intake plenum in order to limit the gas-dynamic noise radiated by the intake mouth. The adopted optimization approach shows the capability to reproduce with a very good accuracy the experimentally advised optimal calibration, corresponding to the numerically derived Pareto frontier in the Brake Mean Effective Pressure (BMEP)-BSFC tradeoff. The optimization also underlines the advantages of an engine calibration based on a combination of EIVC strategy and intake throttling, rather than a purely throttle-based calibration. The developed automatic procedure allows for a "virtual" calibration of the considered engine on completely theoretical basis and proves to be very helpful in reducing the experimental costs and the engine time-to-market.

Modeling and Control of an Electromagnetic Variable Valve Actuation System

A novel electromechanical valve actuation system comprised of a linear actuator, valve, and energy storing cam/spring mechanism is presented. The system dynamics are modeled using Lagrangian mechanics, and a minimum-energy point-to-point optimal control problem is solved to find an optimal trajectory and input. The optimal input is used as a feedforward component in a transition controller to move the valve between the open and closed positions. Between transitions, a simple linear controller stabilizes the valve in the open and closed positions. A high-order model capturing the distributed nature of valve springs is used to validate state constraints related to positive cam/follower forces and a nonslip condition on the cam/follower. Finally, a prototype system is fabricated and tested with promising results.

Comparison between Internal and External EGR Performance on a Heavy Duty Diesel Engine by Means of a Refined 1D Fluid-Dynamic Engine Model

The potential of internal EGR (iEGR) and external EGR (eEGR) in reducing the engine-out NOx emissions in a heavy-duty diesel engine has been investigated by means of a refined 1D fluid-dynamic engine model developed in the GT-Power environment. The engine is equipped with Variable Valve Actuation (VVA) and Variable Geometry Turbocharger (VGT) systems. The activity was carried out in the frame of the CORE Collaborative Project of the European Community, VII FP. The engine model integrates an innovative 0D predictive combustion algorithm for the simulation of the HRR (heat release rate) based on the accumulated fuel mass approach and a multi-zone thermodynamic model for the simulation of the in-cylinder temperatures. NOx emissions are calculated by means of the Zeldovich thermal and prompt mechanisms. As a first step, the model has been calibrated and assessed on the basis of experimental tests carried out on four characteristic operating conditions within the WHSC (World Harmonized Stationary Cycle). The considered engine points have been used to identify the optimal engine parameters on the basis of a DoE approach. As a second step, sweeps simulations centered on the previously considered operating points have been run for iEGR and eEGR in order to study the effects of these latter on combustion and NOx formation processes at steady-state conditions. Finally, a ramp from the WHTC (World Harmonized Transient Cycle) has been reproduced with both iEGR and eEGR modes and the engine performance have been compared in terms of fuel consumption, combustion and NOx emissions

Study of a new mechanical variable valve actuation system: Part II—estimation of the actual fuel consumption improvement through one-dimensional fluid dynamic analysis and valve train friction estimation

It is commonly recognized that one of the most effective ways to improve Brake-Specific Fuel Consumption (BSFC) in a spark-ignition engine at partial load is the adoption of VVA strategies, which largely affect the pumping work. Many different solutions have been proposed, characterized by different levels of complexity, effectiveness and costs. VVA systems currently available on the market allow for variable valve timing and/or lift (VVA). The design of a new mechanical VVA system has been discussed in Part I of this article. That study led to the development of a four-element VVA mechanism. Now, to estimate the potential advantages of the studied system on engine performances, one-dimensional thermo-fluid dynamic analyses were conducted, considering both full load and partial load operating conditions. For this reason, this article addresses the definition of the one-dimensional model of a 638-cm3 single-cylinder engine under development, which will be equipped with the four-element VVA system. The findings from the one-dimensional study will be discussed in detail. In particular, the parametric analyses, which concern the engine power at wide open throttle and the SFC at partial load, will be presented. These results, however, are only theoretical results because the one-dimensional simulation is not able to take into account the increased friction losses due to the complexity of the VVA system. Therefore, to correctly quantify the actual fuel consumption allowed by the studied system (net of the generally increased power dissipated by friction when compared to a conventional valve train), a specific methodology, discussed in Part I, has been adopted.

Investigation on the development and the controllability of a compact multi-functional, fully variable-valve-actuation system

A compact multi-functional, fully variable valve actuation system for six-cylinder engines was proposed. The system can run in both the drive mode and the brake mode of internal-combustion engines. With the help of a distributor, fully variable valve events were achieved with two oil-supply sets, two solenoid valves and one drain valve. The operational parameters of the valve can be adjusted independently for individual cylinders. A numerical study on the controllability of the system was carried out with AVL Hydsim. The calculation results revealed that the timing of the valve opening, the maximum lift, the duration and the time–area value can be adjusted independently or synchronously by controlling the solenoid valves and/or the drain valve. Further correlation analysis results revealed that all the operational parameters of the valve had approximately linear relationships with the corresponding control parameters, and all the correlation coefficients were larger than 0.95, indicating good controllability of the system.

Preliminary design and validation of a Real Time model for hardware in the loop testing of bypass valve actuation system

During the start-up and shut-down phases of steam power plants many components are subjected to pressure and temperature transients that have to be carefully regulated both for safety and reliability reasons. For this reason, there is a growing interest in the optimization of turbine bypass controllers and actuators which are mainly used to regulate the plant during this kind of operations. In this work, a numerically efficient model for Real Time (RT) simulation of a steam plant is presented. In particular, a modular Simulink™ library of components such as valves, turbines and heaters has been developed. In this way it is possible to easily assemble and customize models able to simulate different plants and operating scenarios. The code, which is implemented for a fixed, discrete step solver, can be easily compiled for a RT target (such as a Texas Instrument DSP) in order to be executed in Real Time on a low cost industrial hardware. The proposed model has been used for quite innovative applications such as the development of a Hardware In the Loop (HIL) test rig of turbine bypass controllers and valve positioners. Preliminary experimental activities and results of the proposed test rig developed for Velan ABV are introduced and discussed.

Experimental Validation of a Cogging Torque Assisted Valve Actuation System for Internal Combustion Engines

Electromechanical valve actuation (EVA) is an emerging technology that aims to optimize valve trains, allowing for significant improvements to engine performance, efficiency, and emissions. Recently, a simulation study introduced a novel cogging-torque-assisted motor-driven (CTAMD) valve actuation system. The actuator design emphasized a large output cogging torque that removed the need for conventional valve springs. The cogging torque developed by this actuator allows for highly efficient energy recovery that is superior to comparable systems that make use of mechanical springs. This paper experimentally validates the simulation study with a prototype actuator constructed using the specifications suggested in the previous simulation. The characterization procedure of the prototype is discussed and close agreement is found between the simulated and experimental motor parameters. Furthermore, this paper details a control system that minimizes Ohmic loss while providing fast transition times and low seating velocities. Finally, experimental results are displayed and compared to the simulated results as well as other EVA systems to validate the conjectured speed and efficiency of the CTAMD system.

Design and analysis of an electromechanical actuator for the valve train of a camless internal combustion engine

The conventional mechanical driven valve train for the internal combustion engines has difficulty to handle the various valve events. In this paper, an electromechanical actuated valve train system is developed to provide a more efficient option for valve timing management. The details of the mechanical design of the valve have been discussed, as well as the control system. A prototype of the valve actuation system has been built to verify the design. The testing has shown that the prototype system can actuate the valves to any desired timing at a maximum reliable speed of 3,000 RPM without soft seating, and achieve a partial soft seating at an engine speed of 500 RPM.

Analysis of cyclic variations during mode switching between spark ignition and controlled auto-ignition combustion operations

Controlled auto-ignition, also known as homogeneous charge compression ignition, has been the subject of extensive research because of their ability to provide simultaneous reductions in fuel consumption and NOx emissions from a gasoline engine. However, due to its limited operation range, switching between controlled auto-ignition and spark ignition combustion is needed to cover the complete operating range of a gasoline engine for passenger car applications. Previous research has shown that the spark ignition –controlled auto-ignition hybrid combustion (SCHC) has the potential to control the ignition timing and heat release process during the mode transition operations. However, it was found that the SCHC is often characterized with large cycle-to-cycle variations. The cyclic variations in the in-cylinder pressure are particularly noticeable in terms of both their peak values and timings while the coefficient of variation in the indicated mean effective pressure is much less. In this work, the cyclic variations in SCHC operations were analyzed by means of in-cylinder pressure and heat release analysis in a single-cylinder gasoline engine equipped with Variable Valve Actuation (VVA) systems. First, characteristics of the in-cylinder pressure traces during the spark ignition–controlled auto-ignition hybrid combustion operation are presented and their heat release processes analyzed. In order to clarify the contribution to heat release and cyclic variation in SCHC, a new method is introduced to identify the occurrence of auto-ignition combustion and its subsequent heat release process. Based on the new method developed, the characteristics of cyclic variations in the maximum rate of pressure rise and different stages of heat release process have been analyzed and discussed.

Study of a new mechanical variable valve actuation system: Part I—valve train design and friction modeling

This article addresses the design of a new mechanical Variable Valve Actuation (VVA) system. The basic scheme consists of three main elements, which enable valve lift variation. Although VVA systems could reduce the specific fuel consumption due to an important de-throttling of the intake system, the systems can lead to higher friction losses due to the increased number of components. For this reason, a specific numerical algorithm was implemented to determine either the cam profile or the kinematic and dynamic characteristics of the entire system. In this way, it was possible to estimate the instantaneous and average power dissipated by the frictions for the actuation of each valve. These evaluated frictions will be used in Part II for the estimation of the actual improvement in terms of specific fuel consumption at part load net of the increased mechanical power dissipated when compared to a conventional valve train. A preliminary thermo-fluid dynamic analysis revealed that the proposed variable valve actuation system is unable to significantly reduce the specific fuel consumption because of the inability to carry out valve actuation strategies that reduce the pumping work. A more flexible mechanical VVA system has been thus developed, which is able to allow intake valve deactivation, as well as variation in valve lift, timing and duration. Finally, in Appendix 1, an analytical procedure aimed at the determination of the geometry of the conjugate profiles of a generic mechanism has been described with the aim of obtaining a general methodology for the design of a mechanical VVA system.

자동차 엔진용 2단 가변밸브 기구의 스위칭 시스템 동적 거동에 관한 연구

Abstract : Variable valve actuation system is one of the widely used techniques to improve the fuel efficiency and power of automotive engines. 2-step variable valve actuation systems are also paid attention for the application to direct acting type valve train systems. Besides its advantages in size, weight, relatively simple structure, ets, however, 2-step variable valve actuation system has inherent disadvantages in dynamic instability of switching system to alter discontinuous lift modes. In this study, both experimental and analytical studies are performed to understand the dynamic behavior of a switching mechanism of a 2-step variable valve actuation system, and present a design method to improve its dynamic instability. Key words : 2-step variable valve(2 단 가변밸브), Automotive engine( 자동차 엔진), Latching system( 전환 시스템), Switching system(스위칭 시스템) Nomenclature 1) M SP : mass of switching pin, kgM LP : mass of lock pin, kgM RS : mass of return spring, kgk RS : stiffness of return spring, N/mc

Time-Varying Internal Model-Based Control of a Camless Engine Valve Actuation System

This paper focuses on the motion control of a camless engine valve actuation system during both steady state and transient engine operation. The precise tracking performance obtained using controllers based on the internal model principle for the constant speed case motivates the investigation under engine speed transients. The cyclic but aperiodic reference signal to be tracked is modeled using two different methods, i.e., as a combination of frequency varying sinusoids in the time domain or as a repetitive (periodic) signal in the rotational angle domain. The recently developed time-varying internal model-based controller is ideally suited for both the approaches. The details associated with the design of the controller for each of the approaches are first documented. A quantitative analysis comparing various performance metrics for both the approaches helps to highlight the relative advantages of each method. The experimental results from a prototype camless engine valve actuation system are then presented to help in validating the overall effectiveness of the proposed control method.

New mechanical variable valve actuation systems for motorcycle engines

This paper summarizes the results of the design of new mechanical variable valve actuation systems, developed for high-performance motorcycle engines, at University of Napoli Federico II, Department of Industrial Engineering – Section Mechanics and Energy. After a synthetic recapitulation of the main variable valve-actuation methods and of the main beneficial effects on performance, emissions, and consumptions of the modern automotive engines on which they are currently employed, the paper presents the results of our mechanical variable valve actuation systems, born to be applied on a MotoMorini engine, as required by the company. The paper starts with the description of a first study concerning a very simple system, used just to set up a model to be used for further and more complex activities. The study has been conducted implementing a numerical procedure specifically designed to determine cam profile and kinematic and dynamic characteristics of the whole system, starting from some input data (as described later). The model has been validated against the conventional timing system using kinematic simulations. The work has evolved through three main steps leading to three types of variable valve actuation systems, all mechanical systems (as defined in literature and described later). Results of the numerical procedure verify the validity of the variable valve actuation systems, and particularly, the last one shows a complete performance in terms of lift, duration, and timing variation of valve-lift law. This paper reports results reachable with these simple systems that give good perspectives of use for a new two-wheel vehicle engine.

Pre-lift Valve Actuation Strategy for the Performance Improvement of a DISI VVA Turbocharged Engine

Modern internal combustion engines (ICEs) are becoming more and more complex in order to achieve not only better power and torque performance, but also to respect the pollutant emissions and the fuel consumption (CO2) limits.The turbocharger, advanced valve actuation systems (VVA) and the EGR circuit allow the ICE's load control together with the traditional throttle valve and spark advance. Thus, an higher number of operating parameters are available for the calibration engineer to achieve the required performance target (minimum fuel consumption at part load, maximum power and torque at full load, etc.). On the other hand, the increased degrees of freedom may frustrate the potentialities of so complex systems because of the effort needed to identify the optimal engine control strategies. The development of proper numerical models may assist and direct the experimental activity in order to reduce the related times and costs.Although VVA solutions could bring a reduction in the specific fuel consumption thanks to an important de-throttling of the intake system, unfortunately they can simultaneously lead to higher noise levels radiated by the intake mouth. In fact, in this case, the pressure waves travelling through the intake ducts are not properly damped by the throttle valve.In this paper a numerical methodology is developed to define the engine calibration and the intake valve lift profile that simultaneously minimize the BSFC and the noise at part load. The engine object of the study is a turbocharged Spark-Ignition Direct Injection (SIDI) ICE equipped by a lost motion valve actuation system for the intake valves. In this study, the commercial 1D thermo fluid-dynamic code GT-PowerTM is provided with user routines for the description of the combustion process and the handing of variable valve lift profiles. The engine model is thus integrated with a commercial optimization code (modeFRONTIERTM) to identify the optimized load control strategies to achieve the set objectives. The proposed methodology is also used for the definition of unconventional valve lift profiles. Particularly, the advantages related to the use of a small pre-lift before the main valve lift profile are estimated compared to a conventional EIVC strategy.