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After validation of the numerical model against published laser doppler anemometry (LDA) experimental data (Pitcher et al., 2003), numerical calculations have been carried out to investigate the in-cylinder transient flow structure of a controlled auto-ignition (CAI) engine running at speeds of 1,500 rpm and 2,000 rpm. The geometry configuration of the engine is imported into the computational fluid dynamics (CFD) code used in this study. The simulations take into account the movement of the inlet, exhaust valves and the piston. To simulate an engine in controlled auto-ignition (CAI) mode, the same valve timing that allows 36% gas residuals was applied to the model. The evolution of the flow pattern inside the cylinder at the symmetrical cross section is described. Also, the turbulence intensity (TI), the turbulent kinetic energy (TKE) and turbulent dissipation rate (TDR) are described for a better understanding of the effect of engine speed on the turbulences generated. The effects of engine speed on fresh charge velocity are also revealed.

The purpose of this paper is to assess a phenomenological zero‐dimensional model (0‐D model) in order to evaluate both the in‐cylinder tumble motion and turbulence in high‐performance engine, focusing on the capability and sensitivity of the model.

The study was performed using a four‐valve pentroof engine, testing two different intake ports. The first one was a conventional port and the second one was design in such a way to promote tumble. CFD simulations for admission and compression strokes under different engine conditions were carried out. Then, the in‐cylinder entrance mass and mean velocities from CFD were imposed as boundary conditions in the 0‐D model.

Marked discrepancies between 0‐D model and CFD results were found. As expected, for the original port, CFD results displayed a poor tumble generation during the admission period. It was followed by a fast degradation of the tumble momentum along the compression stroke due to it was not dominant over the other two momentum components. 0‐D model overestimated the entrance‐tumble but underestimated the vortex degradation along the compression stroke, resulting in higher tumble predictions, thereby it is not recommended for low‐tumble engines. As for the modified port, 0‐D model assumptions were closer to the in‐cylinder flow field from CFD, but results underestimated the entrance‐tumble during the intake stroke and predicted excessive tumble at the end of the compression stroke. Summarizing, 0‐D model neither showed sensitivity to changes in the intake port because of the scarce information about the entrance‐flow field nor it was not suitable to evaluate the tumble degradation.

The limitations of the current model were highlighted, given possible guidelines in order to improve it.

A multidimensional calculation method is used to investigate the flow in a motored two‐stroke engine. The governing equations are written in a moving‐coordinate system such that the grid can move with the piston. Grid lines are added into or deleted from the computational domain, depending on opening or closure of the ports. The EPISO algorithm is modified and adopted as the solution procedure. Calculations are performed on an engine of loop‐scavenged type. Details of the gas exchange process and the flow structure in the cylinder are shown. The effects of the engine speed, inlet discharge coefficient and the angle of boost port are examined.

Investigations are carried out with the aim of improving performance of a diesel engine with the design modification on piston crown to stimulate the uniform combustion by inducing turbulence in the incoming charge.

A stirrer is introduced at the top of the piston so as to inculcate more turbulence to the incoming charge by improving the rate of fuel vaporization. Whirling motion is created in the combustible mixture by providing rotating blades on the cavity/bowl of the reciprocating piston head. By putting a simple link mechanism, the oscillatory motion of connecting rod will rotate the blade by an angle of 60°.

The investigations are carried out with and without swirl piston at 17.5 compression ratio and 200 bar injection pressure by varying injection timings.

Finally, the result shows that by using the modified piston, nearly 3 per cent of efficiency increased and 31 per cent of NOx emissions are reduced compared to that of a normal piston with 80 per cent load at standard injection timing.

The purpose of this paper is to study the effect of piston position on the in-cylinder swirling flow in a simplified model of a large two-stroke marine diesel engine.

Large eddy simulations with four different models for the turbulent flow are used: a one-equation model, a dynamic one-equation model, a localized dynamic one-equation model and a mixed-scale model. Simulations are carried out for two different geometries corresponding to 100 and 50 percent open scavenge ports.

It is found that the mean tangential profile inside the cylinder changes qualitatively with port closure from a Lamb-Oseen vortex profile to a solid body rotation, while the axial velocity changes from a wake-like profile to a jet-like profile. The numerical results are compared with particle image velocimetry measurements, and in general, the authors find a good agreement.

Considering the complexity of the real engine, the authors designed the engine model using the simplest configuration possible. The setup contains no moving parts, the combustion is neglected and the exhaust valve is discarded.

Studying the flow in a simplified engine model, the setup allows studies of fundamental aspects of swirling flow in a uniform scavenged engine. Comparing the four turbulence models, the local dynamic one-equation model is found to give the best agreement with the experimental results.

An axisymmetric two‐dimensional computer program employing the Large Eddy Simulation (LES) and SIMPLE‐C method coupled with preconditioned conjugate gradient methods is applied to the turbulent flows in the compression‐expansion strokes for various combustion chamber geometries under realistic engine conditions. The squish area percent of piston crown is changed (SQ = 0 percent for flat piston model, SQ = 46 percent for shallow bowl piston model and SQ = 76 percent for deep bowl piston model) under engine speeds (500∼1,500rpm) for the purpose of investigating the heat transfer performance. Comparison was made of present heat flux results and earlier experimental and numerical results. It is shown that the numerical method can predict the turbulence with reasonable accuracy. The results show that the configuration of piston crown for squish area percent can obviously enlarge the surface heat flux of wall boundaries in reciprocating engines.

This paper aims to present the effects of varying different operating parameters such as Start of Injection (9 to 21 deg bTDC), compression ratio (16 to 12.5), fuel injection pressure (400 to 1,400 bar) and exhaust gas recirculation (0 to 25 per cent) on the performance and emissions of the engine for constant engine speed of 1,600 rpm.

Simulation results were validated with experimental data available in the literature for baseline configuration. The effect of each parameter on the performance characteristics such as pressure and temperature, emission characteristics such as NO_x and soot are presented and discussed. Optimization has been carried out based on the regression equations developed from the simulation results to obtain the optimum set of the parameters to achieve the desired performance and emissions. Numerical simulations have been performed for the optimized set and compared with the reference engine.

Results of optimization showed that there was a simultaneous reduction in NO_x and soot while maintaining the same level of performance as that of the baseline case.

Based on the present work, it can be said that lesser emissions are achieved in terms of NO_x and soot while maintaining the same performance in terms of peak pressure.

The high‐speed engine cannot compete with these fuel consumptions on a b.h.p. basis, but on a basis of indicated power there is little to choose, under optimum conditions, as is seen by comparison of the data in Figs. 7 and 8.

IT has been stated above that the rate of heat transfer is closely proportional to the temperature difference between the plate and the free air stream, and over the laminar portion it will also be proportional to the conductivity of the air. It remains to consider to what extent the actual temperature of the air in the boundary layer will influence the rate of heat transfer. The conductivity of air increases with temperature by reason of the increased molecular velocities, and we might expect, therefore, that the hotter the surface the greater will be the rate of heat transfer per unit of temperature difference above that of the air. This is, in fact, found to be the case.

THE work which forms the subject matter of this paper relates to a device for reducing the air resistance of an air‐cooled radial engine. The device is one which can be added to the engine without completely enclosing the cylinders, either singly or collectively, in streamline casings of the conventional type, which usually render the engine inaccessible.