Figure 8 shows the CFD The resultant flowfield close to TC has an results of u values for the bowl-in piston influence on the turbulence intensity, which geometry in the diametric plane 4 mm below will be discussed below.
The computed results are shown with and without the compressibility Summarizing the flowfield results, the jet-like effects in the 1 equation. Examination of the character of the intake flow interacting with computed results reveals large variation in u the cylinder walls and the moving piston right through the induction and compression creates a large-scale rotating flow pattern process. Initial high turbulence sets in within the cylinder.
The flowfield is observed to undergo large-scale changes during intake and subsequently in the compression process. Between the two CRs with bowl-in-piston geometry there is no distinct change in the fluid flow pattern in the intake and early part of the compression process.
However, in the last stages of compression and the early part of expansion, the fluid velocities near the edge of the bowl are largely different, the high CR creating large shear zones near to the edge of the bowl. Between the flat head and bowl-in-piston geometries, the swirl and tumble ratios are about the same during the intake process. During compression, the swirl ratio is found to Fig. However, CA there is one distinct difference observed between the two geometries: owing to shear in the high-velocity jet entering 1.
In the case of bowl-in-piston the cylinder. In the flat piston geometry there is further to which there is a fall in turbulence evidence of a single tumbling vortex intensity with commencement of intake valve during the early part of the closure. The turbulence fluctuation, u , again compression, and this is dissipated increases beyond the intake valve closure much earlier than the completion of owing to increased fluid movement, and it the compression process.
These results are The effect of these flow patterns on the comparable with and without allowance for the turbulence generation is discussed below. Beyond the intake valve closure, [22], as shown in Fig. These experiments are opposing trends in the variation of u with CA conducted on a production diesel engine of are found. The comparison is made considering the values.
This feature is unaltered piston speeds of 4. The even when the compressibility effect is comparison of the u0 between the two results accounted for by choosing a constant of A similar solution is obtained about inlet valve closure. In this time period, adapting a finer grid of 0. The bottom plot solid line shows the variation in instantaneous piston speed normalized with the mean piston speed 5. The dotted line is the intake valve lift profile of the CFD geometry.
The maximum intake valve lift for ref is 8. However, other experimental studies in the literature suggest a trend of increase in u for certain bowl-in-piston geometries, namely a re-entrant configuration compared Fig. Coming to the present comparison, account for reaction conditions in earlier work even though the bowl geometries are different, by the present authors [13, 14].
It is clear from nevertheless a similar trend in the turbulence the figure that variation in u with time is close intensity behaviour is expected considering the to being independent of CR; this is consistent bowl shape in the experimental work [22] not with the observations made by Lancaster [24] to be of the completely re-entrant type. Figure 10 shows the comparison of u for both piston Next, the mass-averaged u and lI as a function geometries.
The variation in u0 with time is of CR are shown in Fig. In the later part of the in the bowl region of the geometry. These compression process, it is evident that decline time-varying mass-averaged data have been in u is faster in the case of the flat geometry.
The absence of a turbulence-generating mechanism such as squish in the case of flat geometry is evident. However, it is important to recognize the role of the tumbling vortices, taking note of the literature. Floch et al. Their study indicates the breakdown of the tumbling vortices prior to TC to be responsible for enhancement of turbulence along with decline in the tangential Fig.
It is further consistent with the experimental observations observed that, in the case of swirl, the rotating of Schapertons and Thiele [4]. A general motion is conserved during the compression observation at all time steps indicates the TKE process, thereby contributing to turbulence to be of high intensity in the central region of generation to a lesser extent on account of the bowl, decreasing towards the walls.
Similarly, Urushihara Further revealing information from the contour et al. It is also observed that variation in mean velocity that tends to be the TKE is marginally lower 5 per cent at generated by the tumbling motion. In the higher CR, probably owing to enhanced present study there is evidence of tumble dissipation of kinetic energy on account of vortex breakdown with flat piston geometry increased fluid movement during the squish and much earlier than TC, and this, apart from the reverse squish period.
Lastly, comparison of the absence of squish, appears to be responsible TKE of the two piston geometries reveals for the faster decline in u substantial enhanced TKE for bowl-in-piston geometry compared with the flat piston. In the Next, the spatial distribution of turbulence case of flat geometry, the TKE is more or less kinetic energy TKE at crank angles close to TC uniform throughout the combustion chamber. SAE paper , , Vol. Three-dimensional computations on engine geometry are able to capture the generic 3.
Watkins, A. SAE paper , experimental observations available in the , Vol. The presence of high shear zones near to the edge of the bowl during 4. Schapertons, H. SAE paper geometry. Q2 trends in turbulence intensity around TC that are different from the experimental data 5. Haworth, D. This is thought to be Huebler, M. SAE geometry. These motored turbulence parameters, namely the turbulence intensity and length scale, have 6.
Trigui, N. Use been used as input for zero-dimensional of experimentally measured in-cylinder thermodynamic modelling by considering a flow field data at IVC as initial simple rapid distortion process to account for conditions to CFD simulations of reaction conditions in earlier publications [13, compression stroke in I. The zero-dimensional modelling is able to feasibility study.
SAE paper , make reasonably accurate predictions at , Vol. Jones, P. Full cycle well with the experimental results obtained on computational fluid dynamics a high compression ratio gas engine with calculations in a motored four valve biomass-derived producer gas as the fuel [15].
It appears that the enhanced fluid movement during the reverse 8. Strauss, T. Combustion in a swirl significantly modifies the burn rate. However, chamber diesel engine simulation by it might be possible to gain insight into some of computation of fluid dynamics.
SAE these aspects more precisely by adapting paper , , Vol. Reuss, D. Particle 1. Versteeg, H. Q1 calculations. Lebrere, L. Engine flow calculations using a Reynolds stress Khalighi, B. Ekchian, A. Flow combustion in a four-valve engine with visualization study of intake process of intake variations. SAE paper , an internal combustion engine. SAE , Vol. Q3 paper , , Vol. Bauer, W. Flow characteristics in Arcoumanis, C. Some features of this site may not work without it.
Search Deep Blue. This collection. Log in. Research Collections. Dissertations and Theses Ph. Teledyne Continental Motors developed variable compression ratio pistons for both cu.
The variable compression ratio piston consisted of a moveable top that used engine oil pressure to extend the piston top for the highest compression ratio. To limit peak cylinder pressure, a pressure relief valve in the piston allowed the piston top to move downward, thereby reducing compression ratio Grundy et al.
Ford patented a similar concept in the s Caswell Mercedes has also experimented with a similar concept Joshi Articulated cylinder head. Saab introduced its system at the Geneva Motor Show. In the Saab system, one side of the cylinder head with integrated cylinders is attached to the crankcase with a hinge, and a lifting mechanism is placed on the other side of the crankcase.
The cylinder head can pivot up by four degrees to increase the volume of the combustion chambers, thereby lowering the compression ratio. Saab claimed that the technology could change the compression ratio from to while the engine was running Evans Rocker arm. Peugeot introduced its system at the Geneva Motor Show. In the Peugeot system, each piston is attached to a rocker arm and the center of the rocker arm is connected to the crankshaft. An intermediary gear is added to the other end of the rocker arm.
Hydraulic jacks in the engine block next to the cylinders manipulate a gear rack to raise or lower the rocker arm gear in order to change the length of the piston stroke, thereby changing the volume of the combustion chamber and, consequently, the compression ratio Evans Eccentric big end rod bearing.
The eccentric wheel includes a gear that meshes with a ring gear. Rotating the ring gear will adjust the position of the eccentric wheel, thereby adjusting the clearance volume at top dead center. Eccentric crankshaft bearing. Gomecsys has developed a fourth-generation variable compression ratio engine. This system houses the crankshaft bearings within eccentric wheels contained within the cylinder block. Rotating the eccentric wheels changes the clearance volume at top dead center.
FEV has developed a similar variable compression ratio engine shown in Figure O. Eccentric piston pin. An eccentric piston pin has also been proposed as a means of varying the clearance volume at top dead center.
Multi-link rod-crank.
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