Research Papers

The Deviation Function Method of Rotary Engine Design by Geometric Parameters

[+] Author and Article Information
Sarah Warren Rose

Teaching Associate
Department of Mechanical
and Aerospace Engineering,
University of California,
Los Angeles, CA 90095
e-mail: sarahwarren@ucla.edu

Daniel C. H. Yang

Department of Mechanical
and Aerospace Engineering,
University of California,
Los Angeles, CA 90095
e-mail: dyang@seas.ucla.edu

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received September 11, 2012; final manuscript received February 13, 2014; published online March 21, 2014. Editor: Shapour Azarm.

J. Mech. Des 136(5), 051004 (Mar 21, 2014) (7 pages) Paper No: MD-12-1462; doi: 10.1115/1.4026867 History: Received September 11, 2012; Revised February 13, 2014

Rotary engines require seals inserted into each rotor apex to maintain contact with the housing and prevent leaks during internal combustion. These seals are called apex seals and their effectiveness directly influences the engine operation and efficiency. The deviation function (DF) method of rotary engine design has several advantages over the conventional design method with regard to the apex seals, and also finds many more possibilities. The DF method can be used to incorporate the profile of the apex seal into the design process and the rotor profile itself. In the DF method, the seal profile is used as a generating curve and the housing bore profile is a generated curve. The housing is conjugate to the apex seal, and therefore conforms to the seal profile, unlike the conventional rotary engine. Another advantage the DF method has over the conventional method is that different apex seal profiles can be used, resulting in a larger variety of rotary engine designs. This paper introduces the DF method of rotary engine design and selection by the geometric parameters rotor radius, R, and eccentricity, l. In conventional rotary (Wankel) engine design, these parameters are used as a ratio called the K factor. The K factor uniquely identifies a conventional rotary engine profile and is therefore used to associate performance criteria such as displacement, compression ratio, and apex sealing. The DF method can be used to employ the same ratio as a selection tool. Instead of a single profile for each K factor, there is a range of possible DF-designed engine profiles associated with each R/l ratio. The resulting design flexibility is shown using two example deviation functions and the design criteria swept area and maximum theoretical compression ratio. Furthermore, the R/l ratio is not an indication of apex sealing effectiveness because the DF method of rotary engine design and selection separates the engine profile geometry from the apex seal geometry. An apex sealing index is presented to show how the DF method can be used to quantify, analyze, and improve apex sealing.

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Fig. 1

Deviation function method

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Fig. 2

Generating curve g1 represents half of an apex seal profile

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Fig. 3

Housing profile g2

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Fig. 4

Generating rotor flanks, conjugate curve g3

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Fig. 5

The geometric parameters of a rotor profile

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Fig. 6

The rotor tip radius can be determined by r1+e1(0)

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Fig. 7

Maximum compression ratio for arc-based DF engines

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Fig. 8

The theoretical compression ratio for nonarc-based DF engines

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Fig. 9

Radius of curvature of an apex seal profile

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Fig. 10

Clearance Δt between apex seal and housing

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Fig. 11

Average sealing index for arc-based housing profiles



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