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2 2019

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Numerical study of fuel and turbulence distributions in an automotive-sized scavenged pre-chamber

Bolla Michele, Shapiro Evgeniy, Kotzagianni Maria, Kyrtatos Panagiotis, Tiney Nick, Boulouchos Konstantinos

Combustion Engines

2019

R. 58, nr 1

61--67

This article presents a numerical study of the fuel and turbulence distributions in a pre-chamber at spark-time. The study has been conducted in the framework of the H2020 Gas-On project, dealing with the development of a lean-burn concept for an automotive-sized gas engine equipped with a scavenged pre-chamber. The test case considered studies a 7-hole pre-chamber with circumferentially-tilted orifices mounted on the cylinder head of a rapid compression-expansion machine (RCEM), consistent with the experimental test rig installed at ETH Zurich. An accurate description of turbulence and fuel distributions are key quantities determining the early flame development within the pre-chamber. Both quantities have an influence on the overall combustion characteristics and therefore on the engine performance. For this purpose, computational fluid dynamics (CFD) is employed to complement experimental investigations in terms of data completeness. The performance of the Reynolds-averaged Navier-Stokes (RANS)-based turbulence model is compared with large-eddy simulation (LES) through ensemble averaging of multiple LES realizations, in which the fuel injection rate evolution into the pre-chamber has been perturbed. Overall, RANS results show that the distributions of the turbulent kinetic energy and fuel concentration at spark-time agree well with the LES ensemble-averaged counterparts. This constitutes a prerequisite in view of the combustion phase and the accuracy reported provides further confidence in this regard.

Prediction of secondary flow losses in an entrance duct to a low-pressure turbine

Jonak P., Borzęcki T., Kubacki S.

Archives of Mechanics

2019

Vol. 71, nr 1

65--90

Secondary flow features and total pressure losses by means of the total pressure loss coefficient are discussed in an entrance duct, named a turbine central frame (TCF), to a four-stage low-pressure turbine (LPT) of aero-engine. The massaveraged total pressure losses are also analysed at outlets from selected components of the low-pressure turbine. The Reynolds-averaged Navier–Stokes (RANS) technique has been employed for prediction of mean flow characteristics. The numerical results are compared with experimental data obtained in Polonia Aero Lab in Zielonka (Poland). Good agreement is obtained between measured and predicted global flow characteristics and the pressure coefficient on a surface of an inlet guide vane. The high values of the loss coefficient are observed at endwalls, in cores of streamwiseoriented vortex structures near to the endwalls and in the wakes behind the vanes. It is found that the endwall losses contribute by far the most to the total losses at the outlets from the turbine central frame and first vane-row and they become lower at an outlet f rom the first blade-row and at outlets form consecutive vane- and blade-rows.