Asynchronicity in opposed-piston RCMs: Does it matter?

S. Scott Goldsborough, Song Cheng, Dongil Kang, Joseph P. Molnar, Yuri M. Wright, Christos E. Frouzakis

Research output: Journal article publicationJournal articleAcademic researchpeer-review

Abstract

Rapid Compression Machines (RCMs) are widely utilized to study combustion phenomena at engine-relevant conditions, and significant efforts are typically made to create a quiescent environment, particularly for investigations of autoignition chemistry. Opposed-piston configurations can be advantageous due to shorter compression times and reduced surface area to volume ratios. Each side must be actuated simultaneously, but this can be challenging in practice. These devices, like most RCMs, utilize hydraulics for actuation, speed control and arrestation of the piston at the end of the stroke; there is no mechanical control or linkage of the two piston trajectories. To quantify the magnitudes and effects of piston asynchronous behavior, this work employs both detailed experimental measurements and, for the first time, high-fidelity, Direct Numerical Simulation (DNS). The boundary conditions are carefully considered applying insight from high-resolution linear variable differential transformer (LVDT) measurements of the piston trajectory and a zero-dimensional kinematics model of the piston-shaft assembly. Sufficient resolution in the piston crevice region is used. The complicated fluid dynamical behavior that can evolve during piston compression and the ensuing delay processes due to offset timings from toffset = 0–10 ms is elucidated. It is found that near toffset = 6 ms and beyond, the boundary layer on the face of the first-seating piston can be sufficiently perturbed, due initially to reemergence of gas from the crevice of the first-seating piston, so that the adiabatic core can become degraded at long ignition delay times. Substantial mixing of colder gas into the interior of the reaction chamber can alter the measurements, similar to effects previously observed for improper piston crevice configuration. Experimental techniques to mitigate asynchronous behavior are discussed and demonstrated.

Original languageEnglish
Article number105406
JournalProceedings of the Combustion Institute
Volume40
Issue number1-4
DOIs
Publication statusPublished - Jan 2024
Externally publishedYes

Keywords

  • Direct numerical simulation
  • LVDT
  • Piston asynchronicity
  • Rapid compression machines

ASJC Scopus subject areas

  • General Chemical Engineering
  • Mechanical Engineering
  • Physical and Theoretical Chemistry

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