Environmentally sound coolant for combustion engines

An efficient cooling system is capable of dissipating large volumes of heat and in doing so it can enhance the performance of combustion engines. Mono ethylene glycol (MEG) with a volume share of up to 50 per cent is added to conventional coolants in order to lower the freezing point. MEG has the drawback of disintegrating when temperatures rise above 165°C and the resulting disintegration product may cause corrosion damage. That is why it is necessary to add inhibitors and stabilisers. The aim of this FVV project was to find thermally stable and more environmentally sound alternatives for MEG. To this end, 24 substances were investigated with regard to their thermal stability and physical-chemical properties. The substances triethylene glycol, sodium propionate, diethylene glycol and potassium acetate have the potential to replace MEG as a freezing point lowering medium, owing to their high thermal stability. To calculate this potential, further analysis of corrosion and cavitation behaviour, especially when coolant additives are applied, is necessary.

Motivation

The cooling system influences the performance of combustion engines: The larger the volume of dissipated heat, the more efficiently the engine can work. Thus it is possible to reduce fuel consumption and emissions. A volume share of up to 50 per cent MEG is added to water in conventional coolants in order to lower the freezing point. To counter the thermal disintegration of MEG when temperatures rise above 165°C and the resulting corrosion damage, it is necessary to add inhibitors and stabilisers. This creates a demand for thermally stable and environmentally acceptable alternatives to MEG.

Methodology

From the 140 potential substances and compounds that lower the freezing point, 24 were selected for further investigation. The thermal stability and the physical-chemical properties (specific thermal capacity, density, viscosity, vapour pressure curve, boiling point, evaporation enthalpy, flashpoint and thermal conductivity) were the focus of the investigations. Reactors with pressure monitoring were used to test thermal stability. The ph-values, conductivity and refraction index were determined before and after the reactor tests – the composition was analysed using chromatography procedures. The mixture of substances was assessed on the basis of the experimental data.

Result

The substances triethylene glycol, sodium propionate, diethylene glycol and potassium acetate have the potential to replace MEG as a freezing point lowering medium, owing to their high thermal stability. To calculate this potential, further analysis of corrosion and cavitation behaviour, especially when coolant additives such as corrosion inhibitors, defoamers and hard water stabilisers are applied, is necessary. Testing at established testing facilities according to FVV test guidelines R530/2005 – for example at a modular hot testing facility or a cavitation chamber – could make an important contribution here.

Documentation

AlFreD – Alternative Freezing Point Depressants | Requirements for coolants of modern combustion engines based on alternative additives for freezing point depression | Project No. 1169

Themis