Methanol as Fuel in Internal Combustion Engines ICE

In contrast to gasoline, which is a complex mixture containing many different hydrocarbons and some additives, methanol is a simple chemical. It contains about half the energy density of gasoline, which means that 2 L of methanol contains the same energy as 1 L of gasoline. Even though methanol's energy content is lower, it has a higher octane rating of 100 (average of the research octane number (RON) of 107 and motor octane number (MON) of 92) which means that the fuel/ air mixture can be compressed to a smaller volume before it is ignited by the sparkplug. This allows the engine to run at a higher compression ratio (10-11

to 1 against 8-9 to 1 for gasoline engines) and thus also more efficiently than a gasoline-powered engine. Efficiency is also increased by methanol's higher "flame speed" which enables a faster and more complete fuel combustion in the cylinders. These factors explain why, despite having half the energy density of gasoline, less than double the amount of methanol is necessary to achieve the same power output. This is true even in engines that are only modified gasoline engines and not specifically designed for methanol's properties. Methanol-specific engines however provide even better fuel economy [116]. Methanol also has a latent heat of vaporization which is about 3.7 times higher than gasoline, so that methanol can absorb a much larger amount of heat when passing from the liquid to gaseous state. This helps to remove heat away from the engine so that it may be possible to use air-cooled radiators instead of heavier, water-cooled systems. For similar performance to a gasoline-powered car, a smaller, lighter engine block, reduced cooling requirements, better acceleration and mileage are to be expected from methanol-optimized engines in the future [116]. In addition, methanol vehicles have low overall emissions of air pollutants such as hydrocarbons, NOx, SO2, and particulates.

Some problems remain, however, which arise mainly from the chemical and physical properties of methanol, and these need to be addressed. Methanol, not unlike ethanol, is miscible with water in all proportions. It has a high dipole moment as well as a high dielectric constant, making it a good solvent for ionizable substances such as acids, bases, salts (contributing to corrosion problems) and some plastic materials. Gasoline on the other hand, as already mentioned, is a complex mixture of hydrocarbons, the majority of which have low dipole moment, low dielectric constant and are non-miscible in water. Gasoline is therefore a good solvent for non-polar, covalent materials.

Due to the different chemical characteristics of gasoline and methanol, some of the materials used in gasoline distribution, storage, devices and connectors are predictably often incompatible with methanol. Methanol, consequently, can corrode some metals, including aluminum, zinc and magnesium, though it does not attack steel or cast iron [123]. Methanol can also react with some plastics, rubbers and gaskets, causing them to soften, swell or become brittle and fail, resulting in eventual leaks or system malfunction. Therefore, systems built specifically for methanol use must be different from those used for gasoline, but are expected to be only marginally, if at all, more expensive. Specific lubricating engine oils and greases that are compatible with methanol but already exist must be further developed.

With pure methanol, cold start problems can occur because it lacks the highly volatile compounds (butane, isobutane, propane) generally found in gasoline, which provide ignitable vapors to the engine even under the most frigid conditions [108]. The addition of more-volatile components to methanol is usually the preferred solution. In FFVs using M85 for example, the 15% gasoline provides enough vapors to allow the motor to start even in the coldest climates. Another possibility is to add a device to vaporize or atomize methanol into very small droplets which are easier to ignite.

Technical problems have to be expected during the development of any new technology. The technological difficulties facing methanol as a blending component or substitute for gasoline in ICE vehicles however, are relatively easy to solve and, indeed, the majority of them have already found solutions.

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Guide to Alternative Fuels

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