Four-valve Diesel Engine Research Articles

The full-parametric development of the intake ports by using genetic algorithm in a four-valve diesel engine

In-cylinder flow characteristics, which are mainly determined by the intake ports, have a decisive influence on the mixture formation and combustion process of internal combustion (IC) engines. To develop the optimum intake ports in a four-valve diesel engine, the full-parametric design method coupled with genetic algorithm (GA) and artificial neural network (ANN) was adopted in this study. Different from previous studies, the full-parametric templates for the tangential and helical ports were established. Then, to improve the precision of the CFD result which was used to train the ANN, the near-wall region affected by viscosity was resolved by the “enhanced wall treatment” during the simulation process. Besides, considering the interaction between the outlets of adjacent intake ports in the four-valve engine, the ANN was divided into three parts to better predict the flow performance of the combined intake ports. Finally, the developed intake ports based on ANN and GA were machined to the flow box and validated by the steady flow test. The low deviation of 4.71% in swirl ratio between the design target and the experiment result confirms that this method can be well applied to the development of the intake ports in a four-valve diesel engine.

2-Stroke RCCI Engines for Passenger Cars

Reactivity Controlled Compression Ignition (RCCI) is one of the most promising solutions among the low temperature combustion concepts, in terms of thermal efficiency and pollutant emissions. However, for values of brake mean effective pressure higher than 10 bar, in-cylinder peak pressure rise rates tend to be too high, limiting the specific power of any 4-Stroke (4S) engine. Such a limitation can be canceled by moving to the 2-Stroke (2S) cycle. Among many alternatives, the “Uniflow” scavenging system with exhaust poppet valves on the cylinder head allows the designer to reproduce the same identical combustion patterns of a 4-stroke RCCI engine, while increasing the indicated power output. The goal of the paper is to explore the potential of a 2-stroke RCCI engine, on the basis of a comprehensive experimental campaign carried out on a modified automotive 2.0 L, 4-stroke, four-cylinder, four-valve diesel engine. The developed prototype can run with one cylinder operating in 4-stroke RCCI mode (gasoline–diesel), while the others work in the standard diesel mode. A One Dimensional-Computational Fluid Dynamics (1D-CFD) model has been built to predict the performance of the same prototype, when operating all four cylinders in RCCI mode. In parallel, an equivalent 2-stroke RCCI virtual engine has been developed, by means of 1D-CFD simulations and empirical assumptions. A numerical comparison between the 4S and the 2S engines is finally presented, in terms of performance and emissions at full load. The study demonstrates that a 2S RCCI engine can maintain all of the advantages of the RCCI combustion, strongly reducing the penalization in terms of performance, in comparison to a standard 4S diesel engine.

Airflow Characteristics Investigation of a Diesel Engine for Different Helical Port Openings and Engine Speeds

Intake airflow characteristics are essential for the performance of diesel engines. However, previous investigations of these airflow characteristics were mostly performed on two-valve engines despite the difference between the airflow of two-valve and four-valve engines. Therefore, in this study, particle image velocimetry (PIV) investigations were performed on a four-valve diesel engine. The investigations were conducted under different engine speeds and helical port openings using a swirl control valve (SCV). The results suggest that the position of the swirl center does not significantly shift with different engine speeds and helical port openings, as the dynamics of the flow remained closely similar. The trends of the airflow characteristics can be best observed during the compression stroke. A higher engine speed increases the angular velocity of the engine more compared to the increase of the airflow velocity and results in a lower swirl ratio of the flow. On the other hand, a higher engine speed leads to a higher mean velocity and the variation of velocity results in a larger turbulence intensity of the flow. Increasing the helical port opening brings a reduction in the swirl ratio and turbulence intensity as more airflow from the helical port disturbs the airflow from the tangential port.

Flow Field Influence Analysis of Combination Intake Port to Port and In-Cylinder for a Four-Valve Diesel Engine

Intake port structure directly affects the flow characteristics and combustion process of diesel engine, and then affects the comprehensive performance of diesel engine. To the intake ports of a four-valve direct injection diesel engine, the flow characteristics are analyzed on the four combined intake ports : (1) helical (left) and tangential (right), (2) tangential (left) and helical (right); (3) helical (left) and helical (right); and (4) tangential (left) and tangential (right).And the influence of air flow in four combined intake ports to in-cylinder gas flow is also analyzed. Results show that the helical and tangential combination intake ports flow velocity increases with the valve lift increases, and small turbulence arises at the valve guide lug, and the intake flow velocity of the minimum cross-section of the junction of the guiding section and the helical section is the maximum. The air flow in- cylinder moves from top cylinder head bottom to the cylinder bottom, the air flow is enlarged gradually by the small-scale irregular swirl, which eventually converges to a single swirl. The turbulence kinetic energy is very big when the air is just entering the cylinder, the flow space expands rapidly, and the dissipation of turbulent kinetic energy is very significant with the gas moves to the bottom of the cylinder.

Investigation on the Effects of Internal EGR by Variable Exhaust Valve Actuation with Post Injection on Auto-ignited Combustion and Emission Performance

Variable valve mechanisms are usually applied to a gasoline combustion engine to improve its power performance by controlling the amount of intake air according to the operating load. These mechanisms offer one possibility of resolving the conflict of objectives between a further reduction of raw emissions and an improvement in fuel efficiency. In recent years, variable valve control systems have become extremely important in the diesel combustion engine. Importantly, it has been shown that there are several potential benefits of applying variable valve timing (VVT) to a compression ignition engine. Valve train variability could offer one option to achieve the reduction goals of engine-out emissions and fuel consumption. The aim of this study was to investigate the effects on part load combustion and emission performance of internal exhaust gas recirculation (EGR) by variable exhaust valve lift actuation using a cam-in-cam system, which is an electronically variable valve device with a variable inside cam retarded to about 30 degrees. Numerical simulation based on GT-POWER has been performed to predict the NOx reduction strategy at the part load operating point of 1200 rpm in a four-valve diesel engine. A GT-POWER model of a common-rail direct injection engine with internal EGR was built and verified with experimental data. As a result, large potential for reducing NOx emissions through the use of exhaust valve control has been identified. Namely, it is possible to utilize heat efficiently as recompression of retarded post injection with downscaled specification of the exhaust valve rather than the intake valve, even if the CIC V1 condition with a reduction of the exhaust valve has a higher internal EGR rate of about 2% compared to that of the CIC V2 condition.

Numeric Investigation of Gas Distribution in the Intake Manifold and Intake Ports of a Multi-Cylinder Diesel Engine Refined for Exhaust Gas Stratification

In-cylinder exhaust gas recirculation (EGR) stratification, generally achieved by supplying EGR asymmetrically into intake ports on a four-valve diesel engine, is sensitive to trapped exhaust gas in the intake manifold and intake ports that is caused by the continuous supply of EGR during the valve-close periods of the intake valves. The subject of this study is to evaluate the distribution of trapped exhaust gas in the diesel intake system using commercial Star-CD software (version 4.22.018). Numeric simulations of the intake flow of fresh air and recycled exhaust in the diesel intake system were initialized following previous experiments that were conducted on a reformed six-cylinder diesel engine by supplying CO2 instead of EGR to the tangential intake port alone to establish CO2 stratification in the first cylinder. The distributions of the intake CO2 in the intake manifold and intake ports under the conditions of 1330 r/min and 50% load with different mass flow rates of CO2 are discussed. This indicates that CO2 supplied to one intake port alone would escape to another intake port, which not only weakens the CO2 stratification by diminishing the mass fraction disparity of the CO2 between the two intake ports of cylinder 1, but also influences the total mass of CO2 in the cylinder. There is 4% CO2 by mass fraction in the intake port without CO2 supply under the condition that the CO2 mass flow rate is 5 kg/h during the intake process, and 10% CO2 under the condition of 50 kg/h.

Experimental and Modeling Study of the Effect of Manufacturing Deviations on the Flow Characteristics of Tangential Intake Port in a Diesel Engine

The intake port flow characteristics in an internal combustion engine significantly affect its power output, fuel economy, and emissions. To optimize the flow characteristics in the intake port, increasing attention has been paid to its design process. However, the casting and machining processes of the intake port are underappreciated, which may introduce significant deviations, leading to undesirable variation of intake port flow and subsequent deterioration in engine combustion and emissions. In this paper, steady flow tests were carried out on a four-valve diesel engine to investigate how and to what extent the casting and machining deviations of the intake port influence the in-cylinder flow characteristics. The results show that these deviations lead to the variation of swirl ratio up to 20%. Then, computational fluid dynamics (CFD) simulation was conducted for understanding the reason. It is indicated that higher tolerance is needed during the casting and machining processes. For example, in order to control the variation of swirl ratio within 10%, the inclined angle should be controlled at less than 1 deg, the eccentric distance should be restricted to less than 0.5 mm, and the swelling thickness should be limited to less than 1 mm.

Experimental Study on Diesel Engine Intake Ports with Reverse Engineering Technology

Compared the principle and application effect of non-contact measuring data collecting method of intake ports: the nondestructive scanning method and laser scanning method. A intake port was developed for a four-valve diesel engine with reverse engineering technology, and different core boxes of intake port were made respectively by different measureing and manufacturing method, and were investigated in the steady-flow test with the original cylinder head of the diesel engine. The results show that the performance of the metal core box based on laser scanning is consistent with the original cylinder head. Compared with the epoxy resin core box based on nondestructive scanning method, the metal core box based on laser scanning can satisfy the requirement of development of intake port.

3D Numerical Simulation on the Variable Swirl Intake Process of Diesel Engine

To study the flow and swirl characteristics in the variable swirl intake system of a four-valve diesel engine, a numerical simulation with using the three dimensional CFD software AVL-FIRE, was calculated on the intake flow in three types of inlet of the engine. Two swirl-control valve plans are posed and a better plan was selected through the comparative study. The result shows that with a lager valve lift the flow characteristic of spiral inlet is better than that of tangential inlet, and in the opposite case the results are also opposite. The double inlets make the swirl torque increase. When a swirl-control valve is set in the spiral inlet, the variable swirl effect is better, and it ensures better flow capacity and larger swirl ratio range.

Intake and in-cylinder flowfield modelling of a four-valve diesel engine

A three-dimensional unsteady turbulent compressible Navier-Stokes solver, KIVA3V, was utilized in the present study to investigate the intake and in-cylinder flowfield of a four-valve direct injection compression ignition engine. Successful modelling of internal combustion engine configurations is highly dependent upon the generation of a quality grid with the correct boundary conditions. The preprocessor of the KIVA3V computer code, K3PREP, was improved, and a complete grid for a four-valve/cylinder single-cylinder caterpillar diesel test engine, CAT3401, was generated. The complete grid consisted of four moving valves, two intake ports, two exhaust ports, and the port runners. Predicted global in-cylinder flow quantities were compared against experimental data. It was found that the intake process was well modelled by KIVA3V with this complete grid. It was also found that important complex flow structures are developed during the intake stroke. While many of these structures decay during the compression stroke, swirl and tumble can survive. The effect of increased swirl ratio at the end of the compression stroke for the CAT3401 engine with a piston bowl is clearly observed in this study. This is important for aiding in good fuel spray atomization. The formation, development, and break-up of tumble flow are seen, contributing to an increase in turbulent kinetic energy at the end of the compression stroke. Other researchers have substantiated this phenomenon for this type of engine flow. The complete engine flowfield, i.e. the inlet jet, pressure variation in the intake runner and ports, and formation of swirl in the intake ports, is also clearly shown in the prediction. The homogeneity of the in-cylinder flow characteristics and temperature field is also studied. Results of these simulations aid in the improved understanding of the intake process and its influence on direct injection compression ignition engine flowfields.

In-cylinder swirl formation process in a four-valve diesel engine

An experimental study is presented on the steady flow in a four-valve diesel engine rig by using hot-wire anemometry. Through the analysis of the in-cylinder three-dimensional flow field of a four-valve diesel engine, the in-cylinder swirl formation process at various valve lift was investigated. A new criterion is proposed for predicting the emergence of a stable-swirl formation interface, based on swirl angular momentum flux. A stable-swirl formation interface exists when the main swirl angular momentum flux is nearly equal to the in-cylinder air total angular momentum flux.

A Parallel, Unstructured-Mesh Methodology for Device-Scale Combustion Calculations

Los Alamos National Laboratories is developing a parallel, unstructured-mesh, finite-volume CFD methodology for the simulation of chemically reactive flows in complex geometries. The methodology is embodied in the Chad (Computational Hydrodynamics for Advanced Design) code. In this report we give an overview of the Chad numerical methodology and present parallel scaling results for calculations of flows in a four-valve Diesel engine.