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In this paper, pressure fluctuation in a high-pressure common rail system has been investigated through numerical simulation method. By establishing a three-dimensional (3D) model and one-dimensional (1D) simulation model of a high-pressure common rail system validated by the experiment, three essential parameters (needle lift, injection pulse width, and the pressure in common rail) of the common rail system were investigated, and their effects on pressure waves’ characteristics were evaluated with a 1D model. Combined with the results of the 3D simulation, the pressure wave generation, propagation, and fuel flow vector in high-pressure pipelines are studied. The results illustrated how each geometric parameter affects the pressure fluctuations. The pressure waves mainly include the expansion wave generated by the fuel injector spray and the compression wave generated during the fuel supply, and the pressure waves are reflected and superimposed in the process of propagation.

Two-stroke engines have to face the problems of insufficient charge for short intake time and the loss of intake air caused by long valve overlap. In order to promote the power of a two-stroke poppet valve diesel engine, measures are taken to help optimize intake port structure. In this work, the scavenging and combustion processes of three common types of intake ports including horizontal intake port (HIP), combined swirl intake port (CSIP) and reversed tumble intake port (RTIP) were studied and their characteristics are summarized based on three-dimensional simulation. Results show that the RTIP has better performance in scavenging process for larger intake air trapped in the cylinder. Its scavenging efficiency reaches 84.7%, which is 1.7% higher than the HIP and the trapping ratio of the RTIP reaches 72.3% due to less short-circuiting loss, 11.2% higher than the HIP.

Mechanical load and thermal load are the two main barriers limiting the engine power output of heavy duty (HD) diesel engines. Usually, the peak cylinder pressure could be reduced by retarding combustion phasing while introducing the drawback of higher thermal load and exhaust temperature. In this paper, Miller cycle with late intake valve closing was investigated at high speed high load condition (77 kW/L) on a single cylinder HD diesel engine. The results showed the simultaneous reduction of mechanical and thermal loads. In the meanwhile, higher boosting pressure was required to compensate the Miller loss of the intake charge during intake and compression process. The combustion temperature, cylinder pressure, exhaust temperature and NOx emission were reduced significantly with Miller cycle at the operating condition. Furthermore, the combustion process, smoke number and fuel consumption were analysed.

Three-phase sequential turbocharging system with two unequal-size turbochargers is developed to improve fuel economy performance and reduce emission of the automotive diesel engine, which satisfies wide range of intake flow demand. However, it results in complicated transient control strategies under frequently changing operating conditions. The present work aims to optimize the control scheme of boost system and fuel injection and evaluate their contributions to the improvement of transient performance. A mean value model for diesel engine was built up in SIMULINK environment and verified by experiment for transient study. Then a mathematical model of optimization issue was established. Strategies of control valves and fuel injection for typical acceleration and loading processes are obtained by coupled calculating of the simulation model and optimization algorithm.

The intake process plays an important role in the operation of internal combustion engines. In the present study, a three-dimensional transient simulation of a four-valve diesel engine was performed using Large Eddy Simulation (LES) model based on software CONVERGE. The mean velocity components in three directions through the intake valve curtain, the flow separation around the intake valves, the influences of inlet jet on turbulence flow field and cycle-to-cycle variation were investigated in this work. The result shows that the mean velocity distributes non-uniformly near the valve curtain at high valve lifts. In contrast, the mean velocity distribution is uniform at low valve lifts. It is found that the flow separation occurs at valve stem, valve seat and valve sealing through the outlet of the helical port. In contrast, flow separation is only observed in the valve seat through the outlet of the tangential port.

In diesel engines, valve avoiding pit (VAP) is often designed on the top of the piston in order to avoid the interference between the valves and the piston during the engine operation. With the continued application of the downsized or high power density diesel engines, the depth of VAP has to be further deepened due to increased valve lift for more air flow into and out of the cylinder and decreased piston top clearance for less HC/CO and soot emissions. The more and more deepening of VAP changes the combustion chamber geometry, the top clearance height and the injector relative position to the piston crown. In this paper, a 3-D in-cylinder combustion model was used for a heavy duty diesel engine to investigate the effects of the depth of VAP on combustion process and emissions. Five depths of VAP were designed in this study. In order to eliminate the influence of compression ratio, the piston clearance height was adjusted for each VAP depth to keep the same compression ratio.

Due to increasingly stringent emission and fuel consumption regulations, diesel engines for vehicle are facing more and more technical challenges. Engine downsizing technology is the most promising measures to deal with these challenges at present. With the enhancement of power density, a small engine displacement with a high turbocharging technique becomes popular. In order to increase the intake mass flow rate on a downsizing diesel engine, the tilting axis of intake valve was chosen to enlarge the intake valve diameter and decrease the arc radius of intake ports. Thus cylinder head had to be redesigned to meet this demand. Geometry of cylinder head made a notable effect in organization of in-cylinder flow, fuel-air mixing quality and further combustion characteristics. 3-D CFD was a convenient and economical tool to explore effects of geometry of cylinder head on the combustion process.

In the present paper, a three-dimensional (3D) internal flow field model of an electronic unit pump (EUP) fuel system oil drainage progress was established, including solenoid valve model, control valve model, high-pressure oil passage, and the plunger cavity model. From the microscopic point of view, the flow characteristics, such as pressure, velocity, and turbulence kinetic energy, are analyzed by using Fluent. This paper uses the combination of one-dimensional (1D) software AMESim and 3D software Fluent to achieve the purpose. The pressure curve of the high-pressure pipe is extracted from the control valve module of the 1D EUP fuel system model, and the velocity curve of the plunger movement is extracted from the plunger pump module. The two sets of curves are dynamically linked to the flow field calculation with a User-Defined Function (UDF), and the flow field change of the single pump fuel system control valve is calculated by Fluent.

Increasing rail pressure is the development trend of high-pressure common rail system. When the rail pressure reaches ultrahigh range, fuel leakage of precision coupling components could have a significant impact on system performance. In order to investigate the effects of system and structure parameters on the leakage characteristics of precision coupling components, guide the design of ultrahigh-pressure common rail system, simulations were carried out. Variation of fuel leakage were studied with different structure and system parameters. A three-dimensional model of oil film with eccentric was developed to simulate eccentric between two parts of coupling component. The leakage in control valve component increases with common rail pressure; however, there is no obvious change in leakage of control piston component with rail pressure.

Displacement downsize is an exciting technology for IC engines in recent years in order to reduce both toxic emissions and fuel consumption simultaneously. The key point of this technology is to increase power density so that a downsized engine has power output high enough to replace a bigger displacement one. This paper describes a research into the power output enhancement by combustion system optimization. This research work was conducted on a single-cylinder diesel engine with a displacement of 2.8L. The aim of the research is to increase engine power output from current 73kW to 150kW. The power output was firstly boosted to 92kW by virtue of increasing intake pressure, reducing intake flow resistance, optimizing cam profile, modifying fuel injection system and optimizing combustion parameters. As a result, a satisfied heat release pattern was obtained with the achievement of the power target.

In this study, effects of altitude on free diesel spray morphology, macroscopic spray characteristics and air-fuel mixing process were investigated. The diesel spray visualization experiment using high-speed photography was performed in a constant volume chamber which reproduced the injection diesel-like thermodynamic conditions of a heavy-duty turbocharged diesel engine operating at sea level and 1000 m, 2000 m, 3000 m and 4500 m above sea level. The results showed that the spray morphology became narrower and longer at higher altitude, and small vortex-like structures were observed on the downstream spray periphery. Spray penetration increased and spray angle decreased with increasing altitude. At altitudes of 0 m, 1000 m, 2000 m, 3000 m and 4500 m, the spray penetration at 1.45 ms after start of injection (ASOI) were 79.54 mm, 80.51 mm, 81.49 mm, 83.29 mm and 88.92 mm respectively, and the spray angle were 10.9°, 10.8°, 10.7°, 10.4°and 9.8° respectively.

Two-stroke cycle is one of the most effective methods to increase the torque and power output of a four-stroke engine due to the doubled firing frequency compared to four-stroke cycle at the same engine speed. As the two-stroke cycle lacks separate intake and exhaust strokes, the positive pressure difference between intake and exhaust ports is required to drive fresh charge into the cylinder, and is affected by intake port structures due to the different amounts of short-circuited fresh charge during scavenging process. To evaluate the effects of intake port structures on the high-load performance of a boosted poppet-valved two-stroke diesel engine, one-dimensional gas dynamic model and three-dimensional computational fluid dynamics model were established and used to predict the high-load performance of the boosted two-stroke diesel engine with top-entry intake ports, inclined side-entry intake ports, and side-entry intake ports, respectively.

Downsizing as a main-stream technology was widely used for design of future diesel engines in order to meet the increasingly stringent demands of emissions regulation and reduction of CO2 production. Design of intake system faces a considerable challenge accordingly. Discharge coefficient and swirl ratio as two main factors of intake port design have been widely investigated by researchers. However, these two parameters indicate a trade-off relationship. Therefore, it is difficult for a classical intake system to achieve a good balance between sufficient air charge and decent air-fuel radial mixing quality. A 1 L twin-intake-port single-cylinder diesel engine was studied in this paper. A swirl control valve designed to adjust the effective flow area of the filling port, was installed between the intake manifold and the intake filling port in order to achieve variation of swirl ratio. And there is no control valve for the intake spiral port.

Swirl ratio in the cylinder of a diesel engine is an important parameter for air/fuel mixing and combustion process. The swirl intensity generated by an intake port is measured on a steady flow rig. The swirl ratio at the end of intake process in the engine is then estimated from the steady flow test results by equations which have already been established by Ricardo and AVL. However, the existing equations are deduced from a series of assumptions. Three of them affect swirl ratio estimation significantly: a) volumetric efficiency of an engine is 100%; b) the pressure drop through the intake ports is constant during the intake process in engine operation; c) no burned gas residual is trapped in the cylinder. An accurate estimation of swirl ratio is essential during the engine combustion system development.

The two-stroke operation is one of the most effective approaches to significantly increase the torque and power of a 4-stroke engine without the necessary requirement of intensifying the engine. Scavenging process is one of the key factors determining the performance of the two-stroke engine. In this work, a structure of top entry intake ports with poppet valves was employed on a 2-stroke single cylinder diesel engine with the conventional horizontal intake ports replaced. By this way, the reversed tumble flows in the cylinder were formed during the intake process to improve the scavenging performance of 2-stroke operation. In the meanwhile, the effects of valve timings and intake port structures on scavenging processes were estimated respectively through the1D and 3D simulation of the gas exchange process.

Piston bowl geometry has important effects on diesel engine combustion. Especially for a high power density engine, much more fuel requires to burn across the cylinder in a short period after the top dead centre (TDC). Therefore the piston bowl geometry plays a critical role for the air/fuel mixing process and the combustion process. In this paper, a 3-D in-cylinder combustion modeling was carried out for a high power density engine. The ω type of bowl shape was described by seven independent parameters. Five of them are conducted to investigate their effects on the combustion process. The results show that the bowl diameter has significant effects on combustion both in the pre-mixing combustion period and in the diffusion combustion period. There exists an optimized bowl diameter value to obtain a highest indicated power. The re-entrant angle has an important effect on pre-mixing combustion and there also exists an optimized value to reach a highest indicated power.