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Piston Ring Friction Losses in a Free Piston Engine with Variable Frequency
Journal Article
03-15-04-0025
ISSN: 1946-3936, e-ISSN: 1946-3944
Sector:
Topic:
Citation:
Bade, M., Subramanian, J., Clark, N., and Famouri, P., "Piston Ring Friction Losses in a Free Piston Engine with Variable Frequency," SAE Int. J. Engines 15(4):483-497, 2022, https://doi.org/10.4271/03-15-04-0025.
Language:
English
Abstract:
Free piston linear engines (FPLE) directly convert the piston reciprocating
motion into electricity using an integrated linear alternator. Unlike
conventional crankshaft engines, the FPLE’s motion is variable and is not
restricted between the predefined or fixed dead centers. The variable FPLE
motion is governed by the system of forces acting on the translator
(reciprocating) mechanism. In some cases, energy storage devices like stiff
mechanical springs are used in the FPLE system for increasing frequency and
power density. Variations in the forces acting on the reciprocating mechanism
will significantly influence the dynamics, in-cylinder thermodynamics, and
mechanical friction losses of FPLE. While the researchers til today focused on
finding the piston ring frictional characteristics for one design and operating
point, no investigation was performed to understand how different design and
operating variables impact the frictional characteristics of a free piston
engine. Furthermore, no investigation was carried out so far for a free piston
engine with a dominant energy storage system (i.e., stiff mechanical springs).
The novelty of this article lies in analyzing and understanding the effect of
the alternator’s moving mass and spring stiffness on FPLE dynamics and piston
ring frictional characteristics. Two different cases are considered. The first
case deals with the calculation of piston ring frictional losses for different
spring stiffness at the same operating frequency. The second case deals with the
calculation of piston ring frictional forces for different spring stiffnesses
with constant translator moving mass. The piston rings’ power losses on average
remained constant for all the spring stiffness values in Case I. This loss value
corresponds to 3.01% of the total fuel energy input. In Case II, the frictional
power losses increased as the spring stiffness was raised. In this case, the
frictional losses increased from 2.12% to 3.37% of the fuel energy with spring
stiffness.