News | Published March 25 2020

The case for methanol, part two: Properties

Chemical and combustion properties

Methanol is the simplest alcohol and the molecule only contains one carbon atom. Diesel on the other hand is a complex mixture of mainly linear hydrocarbons comprising carbon chains from ten to 15 carbon atoms, averaging about 12. This leads to huge differences in combustion properties. Methanol burns very cleanly with a clear flame, and the gaseous products are essentially carbon dioxide and water.

In a deficiency of air, the emission may also contain trace amounts of carbon monoxide. In marked contrast, diesel will burn with a very luminous smoky flame and combustion does not go to completion. The products of combustion contain particulate carbon, and lower molecular weight carbon-containing compounds. The particulate carbon is clearly linked to many respiratory ailments which include some cancers. Such compounds will not be seen when using methanol fuels.

The other issue when discussing exhaust emissions is that of the nitrogen oxides, usually abbreviated to NOx, which also cause respiratory disease and also has implications on climate change. The NOx arises because nitrogen will react with oxygen at high temperatures. The higher the temperature, the higher the equilibrium concentration of NOx that will be formed. The temperatures within the combustion chambers are sufficiently high to generate significant levels of NOx.

Methanol has two main advantages over diesel fuel in that it has a lower ignition temperature in the combustion chamber, and that it also has a much greater “Latent Heat of Evaporation” which leads to further significant cooling in the engine. The net effect is a significantly lower level of NOx in the exhaust emissions. Methanol has a further advantage as well. It is an extremely pure chemical, essentially free from compounds that lead to the destruction of catalysts.

Consequently, a diesel engine vehicle fuelled by Avocet/Methanol would be able to use catalytic exhaust systems designed for cars, and with the lower starting levels of NOx, would improve greatly upon the exhaust emission requirements already in place for petrol engines.

Physical properties

Methanol is a clear free flowing flammable liquid that boils at 64.7°C. It is freely soluble in water, unlike diesel fuel, and has a dynamic viscosity of 0.594 centipoise at 20°C. This is much lower than that of regular road diesel fuel, 2.0 – 6.0 centipoise, and therefore flows much more easily. This factor could be important in fuel injection engines. It crystallises at -97.6°C and does not tend to “wax up” as the temperature falls below freezing, unlike diesel fuel. Thus, methanol could easily be used in extremely cold conditions and still remain free flowing.

Like water, methanol is a polar material and has a relatively high conductivity – 0.3E6 pico-siemens per metrecompared to non-polar hydrocarbon dielectrics such as petrol and diesel fuel –5 pico-siemens per metre.

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Authored by

Dr Bob Jennings
Director at Avocet Infinite Plc
March 25 2020

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