Dynamic modeling of water-droplet spray injection in reciprocating-piston compressors
File(s)
Accepted version
Author(s)
Sapin, Paul
Simpson, michael
Kirmse, Christoph
Markides, Christos
Type
Conference Paper
Abstract
Water injection has historically been used in internal combustion engines to avoid premature ignition of the fuel-air mixture or to increase the power density of aviation engines. More recently, several innovative technologies have been developed based on injection of liquid into reciprocating-piston devices for energy conversion and storage. In the Dearman engine, liquid nitrogen is injected and rapidly evaporated by mixing with a heat transfer fluid within the cylinder to produce power. Water spray injection is also being developed for a variant of Compressed Air Energy Storage (CAES), where it is used to cool down the air during the compression process and achieve a near-isothermal compression, thus reducing both the compression work and the need for high temperature materials. Simulating the complex phenomena that take place inside a reciprocating-piston chamber during the evaporation of sprays is a time-consuming and expensive exercise in unsteady multiphase CFD. An alternative approach is presented in this paper, whereby a one-dimensional model is used to capture the overall performance of an air compressor with in-cylinder water-spray cooling. The gas phase (humid air) is considered using a zero-dimensional treatment, while the liquid water and evaporation process are handled using Lagrangian tracking. Thermo-physical properties of the humid air are derived from CoolProp. The pressure drop due to the intake and exhaust valves is calculated, as well as the unsteady heat transfer between the air-water mixture and the cylinder walls. Finally, the benefits of liquid-spray injection for CAES technologies are measured through the definition of a compression efficiency. This latter is predicted for various droplet diameters and rates of injection, and compared against a baseline (uncooled) compressor case. It is found that water-spray injection can improve the performance of CAES technologies: the maximum relative increase of the compression efficiency for the considered scenarios is 39 % (from an overall efficiency of 49.6 % for the baseline case to 68.9 % for the most efficient system).
Date Issued
2018-06-17
Date Acceptance
2018-04-18
Citation
ECOS 2018 - 31st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, 2018
Publisher
ECOS
Journal / Book Title
ECOS 2018 - 31st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems
Copyright Statement
© 2018 ECOS.
Source
ECOS 2018 - 31st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems
Publication Status
Published
Start Date
2018-06-17
Finish Date
2018-06-22
Coverage Spatial
Guimarães, Portugal