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6637 |
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Tuesday, May 04, 2021, Hall 1 11:30 AM Applications |
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Project study of gel formation in engine coolants - and considerations for the development of further improved coolant compositions |
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Alexander Rehmer* / Solvay Fluor GmbH, Germany Andreas Haas / Arteco, Jurgen de Kimpe/ Arteco, Serge Lievens/ Arteco, Hans-W. Swidersky/ Solvay, Deutschland |
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During recent years, gel blockage in engine coolant systems with aluminium heat exchangers produced by CAB (controlled atmosphere brazing - using non-corrosive flux) is getting more and more attention in the automotive industry. A general understanding of the gel formation processes in engine coolants and the role that flux residues present on internal surfaces of brazed heat exchangers may or may not have, is of significant interest. In the first part of the presentation, the correlation between literature description of gels and real field service parts with gel-like deposit will be shown. Based on the analytical results of gel samples collected from field service parts, the simulation of gel formation in engine coolants with comparable chemical compositions was investigated under laboratory conditions. It was possible to obtain gels with and without the presence of post-brazed flux residue. Parameters affecting the level of gel formation include: • Flux residue quantity • Time, temperature and pH • Coolant composition (Si-OAT vs P-OAT) • Dissolved aluminium ions To the best of our knowledge, no artificially synthesized laboratory gel samples with similar chemical composition as gel sample from field service parts have been reported so far. The paper summarises gel generation mechanisms in automotive engine coolants and illustrates the complexity of these gels. Flux residue is only one of several parameters in the gel formation process. Some results indicate that gel in Si-OAT engine coolants can be generated without the presence of post-braze flux residue. In the second part, the focus is on the development of further improved coolant compositions. The formation of gels and precipitates of coolants under thermal stress in the presence of processing aids and gel promoting impurities remains a major issue for the development of modern combustion engine coolants. The presentation elaborates on a strategy to reduce the tendency of coolants to form gels and precipitates with the help of novel additives. In this context the challenge for coolant formulators is to reduce to a minimum gel formation by novel additives, preserving nevertheless the major generally required performance parameters - such as corrosion protection, hard water stability and resistance against thermal stress. Results on static and dynamic corrosion and heat transfer test will be presented. |