Methanol as fuel

A variety of specifications exists for methanol today, complemented with further sales specifications that are generally even stricter. Local regulations have further impact on the composition on the methanol on market, depending on intended use. The California Code of Regulations for instance require bitterant and odorant additives[1]. The quality requirement of methanol used as marine fuel is unknown but compared to methanol used in the chemical industry the acceptance of impurities such as water is higher [2]. An amount of water could even be beneficial to reduce the combustion temperature and thus lower NOx emissions. A lower quality product should imply a lower price but as the synthesis gas process represents a substantial part of the production cost the implications on price might not be that big. The demands on cleanness of transportation tanks and supply systems are however lower.

Blending

The use of alcohols as fuel has been practiced to a higher or lower degree for as long as the internal combustion engine has been available. Four alcohols are suitable to use as fuel: methanol, ethanol, propanol and butanol. In practice and previous use methanol and ethanol are the most suited from a practical point of view due to production methods, although British Petroleum has set up a demonstration plant to produce butanol for use as fuel. During the past decades the interest in ethanol has arisen and is a common additive to gasoline in Europe and the United States in an effort to lower CO2 emissions and reduce the dependence on oil. In China on the other hand methanol is used extensively and increasingly as an additive to gasoline. Alcohols blend well with gasoline and have been used in different concentrations for a long time. Ethanol is normally produced through fermentation, in the USA mostly from corn and in Brazil from sugarcane. A disadvantage with ethanol is that the production relies on large areas of farmland that could instead produce food; the production also relies on large amounts of fertiliser produced from oil. It is also possible to blend methanol and ethanol, with or without gasoline. The Junior World Rally Championship (Junior WRC) recently started to use an methanol-ethanol-gasoline mixture (37 %, 21% 42% respectively)[3] and Indy Car used a methanol ethanol mix (90% and 10% respectively) during the 2006 season. Methanol is also a common denaturant for ethanol.

Mixing alcohols with diesel is more difficult, this is particularly true for methanol as the two liquids separate very easily and an emulsifier is needed to stabilise the blend. Research on the subject of blending alcohols with diesel is scarce, at least in the public and academic domain and the only figure that was found is that a 3:2 volume relation of methanol to emulsifier is required [4] but the study is from 1984. Further development is likely to have been conducted but not found. Besides the poor mixing properties the low cetane number of methanol would probably require adding of an ignition improver, at least in a high-level blend (>5 %).

It is possible to run a diesel engine on methanol but as the cetane number is considerably lower than for diesel modifications to the ignition system is needed. This can be done in several ways. Conventional diesel can be used as pilot fuel to ignite the methanol but studies have shown that ignition with the help of glow plug could also work well.

Ignition improvers might be another route to use methanol in the diesel cycle. Scania is providing busses that run on a ethanol (95 vol%, 92.2 wt%) and 5 wt% ignition improver in the form of Beraid 3555 [5].

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