17th International Symposium on Application of Laser Techniques to Fluid Mechanics, Lisbon, Portugal, July 07 – 10, 2014

1.6.4

Sensitivity Study of Cycle-to-Cycle Variation to Air Filling Parameters of a SI Engine

Y. Cao1,2,*, L. Thomas2, J. Borée2, S. Guilain1

1: Renault s.a.s, Powertrain engineering and technologies Department, 1 Allée Cornuel, 91510 Lardy 2. Institut Pprime, CNRS, ISAE-ENSMA, Université de Poitiers, 86962 Futuroscope Chasseneuil, France

• Correspondent author: yujun.cao@ensma.fr

Keywords: 2D-2C PIV, CCV, SI Engine, Triple Decomposition

The goal of this work is to study the sensitivity of CCV to two air filling parameters of a gasoline engine: the inlet valve closing (IVC) and the engine stroke. The model case is referred as case 1. The IVC of case 2 is set 20 CAD earlier than case 1 and case 3 has a higher engine stroke (+11%). The phased 2D-2C PIV data set is obtained in vertical and horizontal planes at low frequency. Integral characteristics (see Table 1) are first compared. A detailed analysis of velocity field is proposed during the intake stroke. Thanks to the 1D simulation of the full flow bench, two key information concerning valve flow: mass flow rate and kinetic energy flux, are computed to complete the PIV measurements. At 270 CAD, the three-dimensional flow states are examined to study the flow structure. A clear tumbling flow is observed in the reference case 1. By changing the IVC in case 2, the geometric confinement is very large when mass flow rate is high (before 90 CAD). We may infer that this leads to the intense fluctuating velocities observed in the region of the flow interaction with piston and liner wall. Consequently, the mean flow tumbling structure at 270 CAD is weak. Besides, the modification of the engine stroke (case 3) modifies the global intensity of the mass flow, which influences both the coherent motion and the turbulent structure. Thus, the internal flow is similar to case 1 before the tumble breakdown. In the pent-roof region, 𝐾 𝜃 and 𝑘 𝜃 are defined as respectively the averaged kinetic energy of the mean flow and the mean fluctuating kinetic energy at phase 𝜃 . The measurements are acquired each 10 CAD between 270 CAD and TDC (Fig.1 and 2). A tumble breakdown is observed in the first case: 𝐾(!) decreases exponentially beyond 300 CAD (see Fig 1), the superscript number denotes the case number. 𝐾(!) begins at much lower level, reaches its maximum later (at 320 CAD) and experiences a less significant decrease. An earlier intake valve opening and closing leads here to internal flows that are less structured and to an unsuccessful transfer from large-scale flow to small-scale turbulence. One can note that 𝑘(!)/𝑘(!) = 1.84 at TDC (see Fig.2). Finally we notice that the spatially averaged kinetic energy of the mean flow evolves in a rather unexpected way for case 3: the tumble breakdown occurs at the same rate but about 20 CAD earlier than for case 1. For the rather moderate geometrical modification performed here, we indeed observe a complete modification of the mean flow orientation in the symmetry plane, leading to a secondary maximum of 𝐾(!) at about 350 CAD. This particular behaviour during the end of the compression stroke is confirmed by horizontal PIV planes not displayed here for brevity. Although cases 1 and 3 seemed to have very similar evolutions before mid-compression stroke, no significant increase of 𝑘(!) is detected near TDC. On the contrary, a continuous increase is detected with 𝑘 ! /𝑘 ! =1.1 at TDC. Using a resemblance coefficient, conditional statistics is then applied to distinguish the properties of families of flow configurations near TDC. A triple decomposition is performed. The conditional analysis is proposed in the full paper.

Case 1 2 3

K 14.2 10.8 15.1 k 5.2 5.5 5.6

k/(K+k) 27% 34% 27% Rt 1.2 0.9 1.1

Table 1 Integral quantities in tumble plane. K and k unit: [m2.s-2]. Rt: no unit

Fig. 1 Kinetic energy of the mean flow K

Fig. 2 Mean fluctuating kinetic energy k

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k(θ)

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