Research Papers: Gas Turbines: Structures and Dynamics

Predicting Gas Leakage in the Rotary Engine—Part I: Apex and Corner Seals

[+] Author and Article Information
Mathieu Picard

Department of Mechanical Engineering,
Massachusetts Institute of Technology,
77 Massachusetts Avenue,
Cambridge, MA 02139
e-mails: mpicard@mit.edu;

Tian Tian

Department of Mechanical Engineering,
Massachusetts Institute of Technology,
77 Massachusetts Avenue,
Cambridge, MA 02139
e-mail: tiantian@mit.edu

Takayuki Nishino

Powertrain Division,
Mazda Motor Corporation,
3-1 Shinchi, Fuchu-cho, Aki-gun,
Hiroshima 730-8670, Japan
e-mail: nishino.tak@mazda.co.jp

1Present address: Assistant Professor, Department of Mechanical Engineeering, Université de Sherbrooke, Sherbrooke, QC J1N 0T2, Canada.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received September 10, 2015; final manuscript received October 1, 2015; published online November 17, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(6), 062503 (Nov 17, 2015) (8 pages) Paper No: GTP-15-1444; doi: 10.1115/1.4031873 History: Received September 10, 2015; Revised October 01, 2015

The Wankel rotary engine offers a greater power density than piston engines, but higher fuel consumption and higher hydrocarbon emissions, in large part due to poor gas sealing. This paper presents a modeling approach to evaluate the gas leakage of apex and corner seals in rotary engines. The apex seal is modeled as a deformable beam and its dynamics is coupled with the gas flows around the seal. It is shown that the main leakage mechanisms are: (1) corner seal clearance leakage, (2) leakage around the apex seal through the spark plug cavities, and (3) flank leakage at high speed. The side piece corner orifice and the trailing spark plug cavity also contribute to leakage, but to a lesser extent. Leakage through the seal–housing interface is negligible as the apex seal can conform to the distorted shape of the rotor housing.

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Fig. 1

Apex seals, corner seals, and side seals are required to prevent the high-pressure gases in the working chamber from leaking to the neighboring chambers and to the side of the rotor

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Fig. 2

The model iterates to find the position of every cross section that satisfies Newton's second law, taking into account the external forces and the seal inertia and rigidity: (a) reference position and (b) calculated position of every cross section

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Fig. 3

The displacement of every cross section is defined by two translations and one rotation: (a) reference position and (b) displacements

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Fig. 4

The dominant forces on the apex are included, except for the hydrodynamic pressure as it does not significantly influence dynamics and leakage: (a) body force and spring force, (b) asperity contact reaction forces, and (c) gas pressure

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Fig. 5

The effect of the two springs is modeled as four local forces: (a) springs and (b) spring forces

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Fig. 6

Running face clearance is calculated as a function of the displacements and housing distortion

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Fig. 7

Flank clearance includes the seal and groove wear

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Fig. 8

The model includes all the gas flow paths around the apex seal

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Fig. 9

Gas in the apex seal groove can flow to the corner seal groove and then leak through the corner seal clearance: (a) rotor side view, (b) section view A–A, and (c) close-up view C of the apex seal, corner seals, and their grooves

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Fig. 10

Through the corner seal clearance, gas can flow in or out of the groove toward or from the trailing chamber, the leading chamber, and the side of the rotor

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Fig. 11

The side piece is designed to prevent a large apex seal-side housing clearance. A small orifice remains nevertheless once the side piece closes the end clearance. (a) Initial position and (b) position in operation.

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Fig. 12

Gas leaks around the apex seal running face through the spark plug cavities: (a) position of the spark plugs and (b) leakage path around the apex seal through the spark plug cavity

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Fig. 13

The measured worn shapes of the groove and seal flanks are used in the dynamics and leakage calculations: (a) close-up view of the trailing flank clearance and (b) close-up view of the leading flank clearance

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Fig. 14

The predicted groove pressure at 2000 rpm full load fits with experiments. Leakage is dominated by flow through the leading spark plug cavity and the corner seal clearance.

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Fig. 15

Corner seal and leading spark plug leakage mechanisms dominate at 2000 rpm

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Fig. 16

The apex seal can conform to the rotor housing when the chamber pressure is high so running face leakage is low: (a) amplified shape of rotor housing distortion, (b) clearance at low gas pressure (90 CA), and (c) clearance at high gas pressure (450 CA)

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Fig. 17

Apex seal can conform to the groove flank distorted shape when gas pressure is high: (a) amplified shape of groove distortion, (b) leading flank displacement at low gas pressure (90 CA), and (c) trailing flank at high gas pressure (450 CA)

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Fig. 18

At 8000 rpm full load, flank leakage becomes important because of pressure lag that modifies apex seal dynamics

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Fig. 19

At high speed, groove flank leakage is as important as corner seal and leading spark plug leakage

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Fig. 20

Gas pressure distribution forces the low-pressure flank open at the end of expansion due to groove pressure lag compared to chamber pressure. The section view shown is taken at 10% of the seal length and at 570 CA. (a) Pressure and forces on the apex seal and (b) close-up view of the groove flanks.




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