Effects Of Valve Timing Research Articles

THE INFLUENCE OF VALVE TIMING ON IN-CYLINDER PRESSURE SPARK IGNITION ENGINES PERFORMANCE CHARACTERISTICS

The performance of the engine depends on many factors. One of the factors is valve timing known to be the timing of opening and closing of valves that has a significant effect on the in-cylinder performance. However, there is less information in the study about valve timing effect on single cylinder engine performances. In this study, the focus is to analyze in-cylinder pressure characteristics on a single piston fuel injection for a spark-ignition engine. This can be done by simulating the effects of valve timing on in-cylinder pressure. The methodology of this project will be simulation-based by using commercial one-dimensional software. The research results are engine performance parameters which are volumetric efficiency, brake torque, brake power, and cylinder pressure in 1000 to 5500 RPM engines. The results show a positive increment in engine performance from the baseline model (CTA240) which is 9.06% for brake power, 2.85% for brake torque, and 13.09% for volumetric efficiency. At low engine speed, it was also found improvement in cylinder pressure when advancing the intake valve timing opening (IVO) by 20 to 25 degrees bTDC. For high speed, the cylinder pressure was found to improve once the retardation of intake valve timing closing (IVC) was done between 40 to 45 degrees aBDC by comparing it with the baseline results. The result highlights the importance of intake valve timing setup by varying the opening and closing of the intake valve to give better output for engine performance.

Thermodynamic analysis of an engine with compression ignition according to the controlled Miller cycle

Introduction (problem statement and relevance). This article presents the thermal calculation results of an in-line six-cylinder highly accelerated engine with a displacement of 13 liters with compression ignition, according to the controlled Miller cycle. The result of the study is the main performance indicators that testify the potential for using the controlled Miller cycle with the intake valves early closing in a highly forced engine as one of the ways to improve energy efficiency.The purpose of the study was to evaluate the effect of valve timing and the intake and exhaust valves lift on the average specific fuel consumption of a highly forced automobile engine with compression ignition at the early stages of design.Methodology and research methods. Computational and theoretical studies were carried out using mathematical modeling of thermodynamic processes in a one-dimensional setting. The reliability of the calculations was verified by comparing the simulation data and the results of experimental studies of the internal combustion engine. To develop the laws of valve lift, the method of sequential nonlinear quadratic programming was used.Scientific novelty and results. The law of valve lift of a highly accelerated automobile engine with compression ignition according to the controlled Miller cycle has been developed, which made it possible to reduce the minimum specific fuel consumption by up to 7.8% in comparison with the basic version of the engine.Practical significance. The developed thermodynamic models make it possible to evaluate the qualitative and quantitative contribution to achieving fuel efficiency through the use of the controlled Miller cycle and obtain initial data in the form of a valve lift law for further work on the development of a valve timing mechanism.

Numerical and Experimental Investigation of Electrical Efficiency Improvement of a Micro Combined Heat and Power (m-CHP) System by Modifying Cam Curve of OHVG Engine

Background: The purpose of this research is to study the solutions for improving the efficiency of a micro combined heat and power (m-CHP) system based on OHVG (OverHead Valve Gas fueled) engine. Method: In this regard, the effects of valve timing and changing the camshaft on the power and fuel consumption of the engine have been numerically and experimentally investigated. The tests have been performed for engine speed range from 1000 rpm to 3500 rpm, while the engine's fuel was natural gas. The numerical results are found to be in good agreement with experimental ones. The effect of changing the valve timing and camshaft on the performance of the m-CHP has been investigated through the experiments in the test room. The engine speed was 1500 rpm; output hot water was fixed at 55oC; and output electrical power varies from 8 kW to 13 kW in the experiments. Results & Conclusion: The experimental results of the engine test indicate that, by changing the camshaft for full load operation and speed 1500 rpm, engine torque and volumetric efficiency improved by 7.2% and 6.0%, respectively, and fuel consumption decreased by 0.8%. According to the results, the best point for the performance of m-CHP is close to the full load of the electrical power because by increasing the electrical load, electrical efficiency increases from about 25.9% to 32.3%, while the thermal efficiency decreases from about 61.9% to 56.1%.

Numerical investigation on the effects of valve timing on in-cylinder flow, combustion and emission performance of a diesel ignition natural gas engine through computational fluid dynamics

In the present study, a diesel engine was modified to a diesel pilot ignited natural gas engine and the influences of intake valve closing timing on in-cylinder flow, combustion and emission performance of engine were investigated by three-dimensional computational fluid dynamics simulation. Based on the geometric model and basic parameters of this engine, the simulation model was built under three operating conditions and then validated by experimental data. On this basis, the validated model was applied to investigate the effects of the intake valve closing timing strategy. The simulation results indicated that, the volumetric efficiency decreases with the retarding of intake valve closing timing in three cases while it increases as the intake valve closing timing is advanced by 10°CA at 1200 rpm. The in-cylinder turbulence kinetic energy decreases with the retarding of intake valve closing timing. The peak in-cylinder pressure decreases when the intake valve closing timing is either advanced or retarded at 50% load. Nevertheless, the maximum peak in-cylinder pressure occurs at advancing 10°CA intake valve closing timing at 1200 rpm and 100% load, which rises by 4.5 bar compared with that at the original intake valve closing timing. Additionally, the maximum heat release rate appears at advancing 10°CA intake valve closing timing at 100% load, which is 26 J/deg higher than that at the original intake valve closing timing. Simultaneously, the shortest combustion duration occurs at advancing 10°CA intake valve closing timing at 1200 rpm and 100% load. For the emissions, the NOx emissions decrease with the retarding of intake valve closing timing but the variation becomes unobvious with the advancing of the intake valve closing timing. Besides, the intake valve closing timing strategy has little effect on HC and CO emissions.

Development and Experimental Investigations on Two Stage GM Type Pulse Tube Refrigerator for 20 K Applications

Because of the absence of any moving components at the cold region, low vibration and high reliability, two stage GM type pulse tube refrigerator (PTR) is nowadays preferred compared to conventional GM refrigerator for cooling of superconducting magnets, SQUIDs, and cryopumping applications. The second stage regenerative material plays an important role in achieving low temperature below 20 K. Leads balls with 0.2 mm to 0.4 mm average diameter was selected as second stage regenerator matrix material while 200 mesh of SS 304 material was filled in the first stage. A two stage GM type PTR was developed. A rotary valve was fabricated and the valve timing effects on cooling performance of PTR were also studied. The valve timings were varied by the different width of rotor slit forming the flow area with stator ports. The lowest no-load temperature of 18.52 K and cooling capacity of 7 W at 29.58 K were obtained with an optimum frequency of 1.6 Hz, charging pressure of 16.5 bar.

Effect of Valve Timing and Excess Air Ratio on Torque in Hydrogen-Fueled Internal Combustion Engine for UAV

In this study, in order to convert a 2.4 L reciprocating gasoline engine into a hydrogen engine an experimental device for supplying hydrogen fuel was installed. Additionally, an injector that is capable of supplying the hydrogen fuel was installed. The basic combustion characteristics, including torque, were investigated by driving the engine with a universal engine control unit. To achieve stable combustion and maximize output, the intake and exhaust valve opening times were changed and the excess air ratio of the mixture was controlled. The changes in the torque, excess air ratio, hydrogen fuel, and intake airflow rate, were compared under low engine speed and high load (wide open throttle) operating conditions without throttling. As the intake valve opening time advanced at a certain excess air ratio, the intake air amount and torque increased. When the opening time of the exhaust valve was retarded, the intake airflow rate and torque decreased. The torque and thermal efficiency decreased when the opening time of the intake and exhaust valve advanced excessively. The change of the mixture condition’s excess air ratio did not influence the tendency of the torque variation when the exhaust valve opening time and torque increased, and when the mixture became richer and the intake valve opening time was fixed. Under a condition that was more retarded than the 332 CAD condition, the torque decreased by about 2 Nm with the 5 CAD of intake valve opening time retards. The maximum torque of 138.1 Nm was obtained at an optimized intake and the exhaust valve opening time was 327 crank angle degree (CAD) and 161 CAD, respectively, when the excess air ratio was 1.14 and the backfire was suppressed. Backfire occurred because of the temperature increase in the combustion chamber rather than because of the change in the fuel distribution under the rich mixture condition, where the other combustion control factors were constantly fixed from a three-dimensional (3D) computational fluid dynamics (CFD) code simulation.

Characterization of Performance of Short Stroke Engines with Valve Timing for Blended Bioethanol Internal Combustion

The present study provides a feasible strategy for minimizing automotive CO2 emissions by coupling the principle of the Atkinson cycle with the use of bioethanol fuel. Motor cycles and scooters have a stroke to bore ratio of less than unity, which allows higher speeds. The expansion to compression ratio (ECR) of these engines can be altered by tuning the opening time of the intake and exhaust valves. The effect of ECR on fuel consumption and the feasibility of ethanol fuels are still not clear, especially for short stroke engines. Hence, in this study, the valve timing of a short stroke engine was tuned in order to explore potential bioethanol applications. The effect of valve timing on engine performance was theoretically and experimentally investigated. In addition, the application of ethanol/gasoline blended fuels, E3, E20, E50, and E85, were examined. The results show that consumption, as well as engine performance of short stroke motorcycle engines, can be improved by correctly setting the valve controls. In addition, ethanol/gasoline blended fuel can be used up to a composition of 20% without engine modification. The ignition time needs to be adjusted in fuel with higher compositions of blended ethanol. The fuel economy of a short stroke engine cannot be sharply improved using an Atkinson cycle, but CO2 emissions can be reduced using ethanol/gasoline blended fuel. The present study demonstrates the effect of ECR on the performance of short stroke engines, and explores the feasibility of applying ethanol/gasoline blended fuel to it.

Effects of valve timing, valve lift and exhaust backpressure on performance and gas exchanging of a two-stroke GDI engine with overhead valves

The current demand for fuel efficient and lightweight powertrains, particularly for application in downsized and hybrid electric vehicles, has renewed the interest in two-stroke engines. In this framework, an overhead four-valve spark-ignition gasoline engine was modified to run in the two-stroke cycle. The scavenging process took place during a long valve overlap period around bottom dead centre at each crankshaft revolution. Boosted intake air was externally supplied at a constant pressure and gasoline was directly injected into the cylinder after valve closure. Intake and exhaust valve timings and lifts were independently varied through an electrohydraulic valve train, so their effects on engine performance and gas exchanging were investigated at 800rpm and 2000rpm. Different exhaust backpressures were also evaluated by means of exhaust throttling. Air trapping efficiency, charging efficiency and scavenge ratio were calculated based on air and fuel flow rates, and exhaust oxygen concentration at fuel rich conditions. The results indicated that longer intake and exhaust valve opening durations increased the charge purity and hence torque at higher engine speeds. At lower speeds, although, shorter valve opening durations increased air trapping efficiency and reduced the estimated supercharger power consumption due to lower air short-circuiting. A strong correlation was found between torque and charging efficiency, while air trapping efficiency was more associated to exhaust valve opening duration. The application of exhaust backpressure, as well as lower intake/exhaust valve lifts, made it possible to increase air trapping efficiency at the expense of lower charging efficiency.

An HCCI Control Oriented Model that Includes Combustion Efficiency

A control oriented model that includes combustion timing, engine load and combustion efficiency for Homogeneous Charge Compression Ignition (HCCI) engines is developed. In HCCI engines, a lean homogeneous air-fuel mixture auto-ignites due to compression and combustion occurs at lower temperatures compared to spark ignition and diesel engines. The low HCCI combustion temperature results in low NOx level, however unburnt HC and CO levels are high. Higher thermal efficiencies are realized for higher combustion efficiencies when combustion timings is appropriate. First, the effects of valve timing and fueling rate on combustion efficiency are investigated experimentally. Then, the influence of combustion efficiency on HC and CO emissions is studied. A physics based control oriented model of HCCI engine combustion efficiency and emissions for future control design is developed. This model includes the effect of trapped residual gas and fueling rate on combustion timing and output power. The developed model has acceptable accuracy for combustion timing, load and combustion efficiency prediction when compared to experimental data. This model is useful for combustion timing and load control in HCCI engines while simultaneously considering the constraints of combustion efficiency and emission.

High load performance and combustion analysis of a four-valve direct injection gasoline engine running in the two-stroke cycle

With the introduction of CO2 emissions legislation or fuel economy standards in Europe and many countries, significant effort is being made to improve spark ignition gasoline engines because of their dominant market share in passenger cars and potential for better fuel economy. Amongst several approaches, the engine downsizing technology has been adopted by the automotive companies as one of the most effective methods to reduce fuel consumption of gasoline engines. However, aggressive engine downsizing is constrained by excessive thermal and mechanical loads as well as knocking combustion and low speed pre-ignition (also known as super-knock). In order to overcome such difficulties, a gasoline direct injection single cylinder engine was modified to run under the two-stroke cycle by operating the intake and exhaust valves around bottom dead centre (BDC) at every crankshaft revolution. The combustion products were scavenged by means of a reversed tumble flow of compressed air during the positive valve overlap period at BDC. The engine output was determined by the charging and trapping efficiencies, which were directly influenced by the intake and exhaust valve timings and boost pressures. In this research a valve timing optimisation study was performed using a fully flexible valve train unit, where the intake and exhaust valve timings were advanced and retarded independently at several speeds and loads. A supercharger was used to vary the load by increasing the intake pressure. The effects of valve timing and boost pressure in this two-stroke poppet valve engine were investigated by a detailed analysis of the gas exchange process and combustion heat release. Gaseous and smoke emissions were measured and analysed. The results confirmed that the two-stroke cycle operation enabled the indicated mean effective pressure to reach 1.2MPa (equivalent to 2.4MPa in a four-stroke cycle) with an in-cylinder pressure below 7MPa at an engine speed as low as 800rpm. The engine operation was limited by scavenging inefficiencies and short time available for proper air–fuel mixing at high speeds using the current fuel injector. The large amounts of hot residual gas trapped induced controlled auto-ignition combustion at high speeds, and thus the abrupt heat release limited higher loads.

Thermo-kinetic modelling of variable valve timing effects on HCCI engine combustion

In this study the effects of variable valve timing on the combustion of an Homogeneous Charge Compression Ignition (HCCI) engine have been analysed using a new modelling approach for HCCI engine cycle. A novel sequential modelling platform is developed using a combination of detailed multi-zone thermo-kinetic combustion model, 1D intake flow model and exhaust gas flow model. The new model utilizes CHEMKIN-PRO and GT-POWER software along with in-house exhaust gas flow model. Experimental data from a single-cylinder HCCI engine is used to validate the model. Validation results show that the model can predict combustion phasing and Indicated Mean Effective Pressure (IMEP) with average errors of 1.1 crank angle degrees (CAD) and 0.3 bar, respectively. The experimentally validated model is then used to investigate the effects of intake valve timing on HCCI auto-ignition radicals, zonal temperature, combustion phasing, IMEP, and exhaust emissions. Ozet: Bu calismada, HCCI motor cevrimi icin yeni bir model yaklasimi kullanilarak, homojen dolgulu sikistirma ateslemeli (HCCI) bir motordaki yanmaya degisken supap zamanlamasinin etkisi incelenmistir. Detayli bir cok-bolgeli termo-kinetik yanma modeli, 1D emme akis modeli ve egzoz gazi akis modeli kombinasyonu kullanilarak yeni bir ardisik modelleme platformu gelistirilmistir. Yeni model, yalnizca egzoz manifoldundaki gaz akis modeli ile CHEMKIN-PRO ve GT-POWER yazilimi kullanmaktadir. Modeli dogrulamak icin tek silindirli bir HCCI motordan elde edilen deneysel veriler kullanilmistir. Dogrulama sonuclari gostermistir ki model, 1.1 krank acisi derecesi ve 0.3 bar ortalama hatalar ile yanma fazini ve ortalama efektif basinci tahmin edebilmektedir. Deneysel olarak dogrulanan model daha sonra emme supabi zamaninin HCCI otomatik atesleme karakterine, bolgesel sicakliga, yanma fazina, ortalama efektif basinca ve egzoz emisyonlarina etkisini arastirmak icin kullanilmistir.

A Control-Oriented Two-Zone Charge Mixing Model for HCCI Engines With Experimental Validation Using an Optical Engine

A control-oriented two-zone charge mixing model is developed to simplify, but to describe mixing of fresh charge and residual gas during the intake stroke. Engine valve timing has a strong influence on the realization of stable homogeneous charge compression ignition (HCCI), since it affects turbulent flow that promotes mixing of fresh charge and residual gas. Controlled auto-ignition of a HCCI engine is achieved by good mixing of fresh charge and residual gas. Therefore, it is useful to develop a mixing model that can be executed in real-time to help extend the operational range of HCCI. For model derivation, the cylinder volume is artificially divided into two zones with a fictitious divider between them. First, the mixed zone consists of fresh charge induced by opening intake valves and some residual gas transferred from the unmixed zone. They are assumed to have been mixed homogeneously so that cold fresh charge gains thermal energy from hot residual gas. Second, the unmixed zone contains the rest of hot residual gas. Mass transfer between them which is forced by a fluid jet is directed from the unmixed zone to the mixed one. Based on the definitions of two zones and interaction between them, a two-zone charge mixing model is derived. To investigate phasing effects of valve timing on charge mixing, comparative simulation was carried out with different valve timings. For experimental validation and calibration of the proposed model, optical engine tests were performed with an infrared (IR) camera, together with GT-power simulation. From good agreement between the model temperature and the estimated temperature from IR images, the model turns out to be useful to describe mixing of fresh charge and residual gas.

Effect of Valve Timing and Residual Gas Dilution on Flame Development Characteristics in a Spark Ignition Engine

Effect of Valve Timing and Residual Gas Dilution on Flame Development Characteristics in a Spark Ignition Engine

Experimental and Numerical Analysis of the Valve Timing Effects on the Performances of a Small Volumetric Rotary Expansion Device

Single stage expansion devices are currently studied for small scale size power plant, often in combination with Organic Rankine Cycles for the employment of solar, geothermal, biomass or waste heat energies.A volumetric rotary single-stage expander was chosen in this study as expansion device for such type of plants. Its main characteristics and performances are discussed as a function of both the working conditions (fluid type, inlet temperature) and the working parameters (rotating speed, admission and recompression grades, valves advance).These analyses were carried out with numerical and experimental techniques. The analysis of the effects of the working condi- tions on the expander performances was carried out through a numerical model created with the simulation tool AMESim. At the same time, a prototype was built and experimented with compressed air to validate the model used by means of air mass flow rate, torque and indicated cycle. This way the isentropic and mechanical efficiency are discussed.The validation of the model was carried out by comparison with the experimental data collected at the engine test bench by operating the engine with compressed air. The indicated cycle, the air mass flow rate and the delivered torque were used as parameters of comparison. Moreover an experimental analysis at the fluid dynamic bench was carried out to validate the numerical 3D CFD model of the valves.The part load performances of this expansion device were studied by hypothesizing different control strategies and comparing them in terms of efficiency reduction respect to the design point. The influence of valves advance was also discussed.

The Valve Timing Optimization of the Diesel Engine Based on Response Surface Methodology

To study the effect of valve timing on the diesel engine performance, the simulation model of diesel engine was established with AVL BOOST and its accuracy was proved. The volumetric efficiency is one of the important indicators to evaluate engine performance. The volumetric efficiency as optimization objective and valve timing were optimized and discussed by using Box-Behnken test method and the response surface methodology. Optimization result shows that volumetric efficiency of the diesel engine can been increased by 6.42% under rated speed.

Application of Multi-Objective Genetic Algorithm (MOGA) for Design Optimization of Valve Timing at Various Engine Speeds

This paper aims to demonstrate the effectiveness of Multi-Objective Genetic Algorithm Optimization and its practical application on the automobile engine valve timing where the variation of performance parameters required for finest tuning to obtain the optimal engine performances. The primary concern is to acquire the clear picture of the implementation of Multi-Objective Genetic Algorithm and the essential of variable valve timing effects on the engine performances in various engine speeds. Majority of the research works in this project were in CAE software environment and method to implement optimization to 1D engine simulation. The paper conducts robust design optimization of CAMPRO 1.6L (S4PH) engine valve timing at various engine speeds using multiobjective genetic algorithm (MOGA) for the future variable valve timing (VVT) system research and development. This paper involves engine modelling in 1D software simulation environment, GT-Power. The GT-Power model is run simultaneously with mode Frontier to perform multiobjective optimization.

EFFECT OF VALVE TIMING AND EXHAUST BACK PRESSURE ON THE PERFORMANCE OF GASOLINE ENGINE BY

Today, studying the parameters that affected on the gasoline engine performance becomes very important for the popular using of this type of engines. In spite of the previous studies concerning the economic fuel consumption, some aspects still need more investigations. There are many investigations concerning the internal combustion engine performance. In previous researches the effect of valve timing on engine performance and detonation were studied. In this work, the effect of changing exhaust back pressure with variable intake valve timing on the engine performance was theoretically studied. It was found that the fuel consumption decreased and engine performance improved. The validity of the simulation technique was checked by comparing its results with those from experimental results then a good agreement was noticed.

Effects of valve timing and intake flow motion control on combustion and time-resolved HC & NOx formation characteristics

In SI engines, valve events have a major influence on volumetric efficiency, fuel economy and exhaust emissions. Moreover, swirl and tumble motions in the intake charge also improve combustion speed and quality by stratifying the mixture as well as intensifying the mixing rate of air and fuel. This paper investigates the behaviors of an engine and the combustion phenomenon for various intake valve timings and intake charge motions using CVVT system and port masking schemes. Test condition includes a part load and a cold idle condition inclusive of a cold start of the engine. Time-resolved HC and NOx emissions were also measured at an exhaust port to examine their formation mechanisms and behaviors with fast response HC/NOx analyzers. In conclusion, the fast burning of fuel and improved combustion quality by enhanced charge motions reduced unburned HC emissions, and advancing the intake valve opening reduced HC as well as NOx. Furthermore, HCs during the cold transient phase and idle conditions decreased with recalibrated start parameters such as lean air-fuel ratio and spark retardation via the enhancement of intake charge motions.

Valve timing effect on the cooling performance of a 4 K pulse tube cooler

Generally, a compressor together with a rotary valve system generates the pressure oscillation in GM-type cryocoolers. The timing of the rotary valve, which is one of the key operating parameters for cryocoolers, determines the relationship between intake and exhaust processes. A systematic investigation of valve timing effects on cooling performance of a two-stage 4 K pulse tube cooler (PTC) is reported. The experiments show that the optimization of valve timing can considerably improve the cooling performance for both stages. For the same PTC, a performance comparison for operation on different compressors with various input powers ranging from 0.5 to 6.0 kW is also presented.

Theoretical and experimental investigation of effect of valve timing on volumetric efficiency in an IC engine

Volumetric efficiency is a typical parameter that is effected by almost all constructive, aerodynamic and thermal parameters through a simple or complicated relation. In this study, the effect of valve timing, which is a highly dynamic parameter, has been investigated. Beside the original one, thirteen new camshafts have been produced without changing the angles that valves are open. New camshafts are then produced by shifting the valve-open period. All camshafts are used to determine volumetric efficiency at various engine speeds.