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Physical limitations of water based coolants

engine cooling

Chemical limitations of water based coolants


A review of water based engine coolants
The Economax Engine Cooling System represents a major step forward in engine cooling technology. To fully appreciate the radical improvements facilitated by Economax, it is useful to review current cooling technology.

Over the last 100 years engine design and efficiency has improved significantly. In stark contrast engine coolants have remained mostly unchanged since the 1930’s and are still based on a mixture of Ethylene Glycol (EG), water and corrosion inhibitors. All such mixtures have inherent physical and chemical limitations that restrict engine performance and effect reliability.

Physical limitations of water based coolants
Within an engine cooling system the hottest surfaces are those adjacent to the combustion chamber, specifically the cylinder liners and cylinder head. Evans have proven that in these areas EG-Water mixtures regularly cross the thermal boundary that separates efficient Nucleate Boiling (B in Fig.1) from inefficient Critical Heat Flux.

CHF is synonymous with the condition ‘Departure from Nucleate Boiling’ or DNB. When DNB occurs in an engine cooling system a layer of steam bubbles form adjacent to the engine hot-spots (A in Fig.1). Because steam dissipates less than 1/30th of the heat that water does, local metal temperatures over-heat rapidly.

This over-heating leads to several problems including; thermal distortion of the cylinder head and liners, pre-ignition (aka engine knock), liner pitting, boil-over and after-boil. Over-heating is the most common cause of engine down-time and responsible for >50% of catastrophic engine failures.

Chemical limitations of water based coolants
Although water is cheap and readily available, it is also the root cause of corrosion within engine cooling systems (see Fig.2). Hence the necessity to add corrosion inhibitors. Corrosion inhibitor formulations have changed many times over the years, but not always for the better.

Nitrite, silicate, borate and azole based products have been around for many years, with Organic Acid Technology (OAT) inhibitors appearing more recently. OAT formulations are often branded as ‘Long-Life’ based on their five year life-span, compared with 1-2 years for standard antifreeze formulations.

Although OAT-EG-Water mixtures are now used in most new car engines, they have proven less successful in Heavy Duty Diesel Engine (HDDE) cooling systems. After several years of trying OAT based products many OEMs and fleet operators reverted to nitrite and/or Hybrid OAT (HOAT) formulations. One reason for this u-turn was that OAT formulations offer little protection against liner pitting - a major problem in HDDE.

To maintain effective inhibitor levels it is often necessary to retro-dose with Supplemental Coolant Additives or SCAs. It is common for SCA’s to be under or over dosed leading to accelerated corrosion rates, cylinder liner pitting or blocking up of radiator channels with congealed inhibitor.



Evans Cooling Systems UK | Unit 5 | Europa Way | Swansea West Business Park | Fforestfach | Swansea | SA5 4AJ
01792 572299 | 01792 561606 | uksales@evanscooling.uk.com

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