Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Analysis and Design of a Lightweight High Specific Power Two-Stroke Polygon Engine

[+] Author and Article Information
K. R. Anderson

Professor of Mechanical Engineering
e-mail: kranderson1@csupomona.edu

A. Clark

e-mail: anclark@csupomona.edu

D. Forgette

e-mail: Daniel.T.Forgette@jpl.nasa.gov

M. Devost

e-mail: medevost@csupomona.edu

R. Okerson

e-mail: raokerson@csupomona.edu

T. Wells

e-mail: twells@cmu.edu
Solar Thermal Alternative Renewable
Energy Laboratory,
Mechanical Engineering Department,
California State Polytechnic
University at Pomona,
3801 West Temple Avenue,
Pomona, CA 91768

S. Cunningham

e-mail: stevec@butteindustries.com

M. Stuart

e-mail: martins@butteindustries.com
Butte Industries, Inc.,
Burbank, CA 91501

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received October 30, 2013; final manuscript received November 12, 2013; published online December 12, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(4), 041508 (Dec 12, 2013) (8 pages) Paper No: GTP-13-1391; doi: 10.1115/1.4026049 History: Received October 30, 2013; Revised November 12, 2013

Current trends in engine design have pushed the state of the art regarding high power-to-weight ratio gasoline engines. Newly developed engine systems have a power-to-weight ratio near 1 hp per pound. The engine configuration presented herein makes it possible to package a large number of power producing pistons in a small volume, resulting in a power-to-weight ratio near 2 hp per pound, which has never before been realized in a production engine. The analysis and design of a lightweight two-stroke 6-sided in-plane polygon engine having a geometric compression ratio of 15.0, an actual compression ratio of 8.8, and a piston speed of 3500 ft/min are presented in this investigation. Typical results show that for a hexagonal engine with 2 in. diameter pistons and 1.25 in. stroke, a single piston displacement is 7.85 cubic in., while the total engine displacement is 47. 1 cubic in. Full power at 12,960 rpm at an air flow rate of 353 cubic feet per minute affords 0.444 cubic ft/min/hp for specific power. For an efficiency of 21%, the blower power is 168 hp. Our air-flow analysis shows that the power of the engine does not depend on the number of pistons, but rather on the volume of the gas-air mixture which passes through the engine. System level engineering of power output, kinematic modeling, air-flow modeling, efficiency, scavenging predictions, crankshaft sizing, and weight estimates are presented.

Copyright © 2014 by ASME
Topics: Engines , Pistons , Design , Air flow
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Fig. 1

Basic configuration of the polygon engine showing pistons arranged in a hexagonal array with one side dedicated to the crank shaft

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Fig. 2

Cut-away view of the 6-sided 5-piston polygon engine

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Fig. 3

Displacement of the even and odd pistons about their center position as a function of the crank shaft angle

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Fig. 4

The model fuel-air cycles for the two types of chambers, which give the correct power for the CR125 engine but conservatively overestimates the maximum pressure

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Fig. 5

Scavenging efficiency versus delivery ratio

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Fig. 6

Compressible flow function for air plotted against the upstream/downstream pressure ratio

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Fig. 7

Air flow model results, 4000 rpm, 4 psi manifold pressure

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Fig. 8

Blowback due to rpm

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Fig. 9

Blowback due to manifold pressure

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Fig. 10

Finite element analysis of the crankshaft

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Fig. 11

Torque profile as a function of the crank shaft angle for a single arc engine of five pistons

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Fig. 12

Single and double arc engines showing the ability to stack the rings of pistons

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Fig. 13

Torque profile as a function of the crank shaft angle for a double-arc engine of 10 pistons




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