The influence of timed coolant injection on compressor efficiency

G. G. Jacobs, L. Liebenberg

Research output: Contribution to journalArticle


Timed injection of coolant during the onset of the compression stroke in a reciprocating compressor aimed at achieving quasi-isobaric conditions during the initial part of the compression stroke was investigated as a means of improving compressor efficiency. It is found that an isobaric cooling process followed by an isothermal compression process requires less energy than an isothermal compression process for the same boundary conditions. Achieving isobaric cooling in a real reciprocating compressor would require sudden and significant cooling during the onset of compression. A simplified process model of a real reciprocating compressor was created. It modelled the timed cooling process as a polytropic process with reduced polytropic index. An experimental compressor, equipped with a coolant injection system, was constructed. Dry baseline tests and tests with continuous and timed coolant injection were conducted. It was found that timed injection during the onset of compression, while also keeping the suction valve closed to prevent additional suction air inflow, yields an additional compression work-saving advantage over continuous coolant injection for the same set of boundary conditions. The simplified process model and numerical simulation were validated against the experimental results and were found to agree well with the experimental results.

Original languageEnglish (US)
Pages (from-to)175-189
Number of pages15
JournalSustainable Energy Technologies and Assessments
StatePublished - Dec 1 2016
Externally publishedYes


  • Compressor efficiency
  • Coolant injection
  • Quasi-isobaric
  • Quasi-isothermal
  • Reciprocating compressor

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Energy Engineering and Power Technology

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