With the growing use of oxygenates as gasoline supplements, there is an increasing need to establish how such fuels will perform in cars in the market, particularly with respect to their impact on existing gasoline specifications and vehicle fuel system design.
One area which is attracting considerable attention at the present time is vehicle/fuel driveability performance, especially since oxygenates, when blended with gasoline, have a tendency to increase volatility as well as octane number. It is essential therefore that fuel volatility criteria and limits are established for gasolines containing oxygenated components.
Road trials have recently been carried out in Italy with the aim of identifying the hot weather driveability characteristics of a wide range of fuels and cars. The oxygenate types assessed included methanol and 50/50 blends of methanol and tertiary butyl alcohol (TBA) in blend with gasoline at concentration levels of up to 15 per cent volume and methyl tertiary butyl ether (MTBE) at concentrations of up to 20 per cent volume, at different levels of volatility.
Whilst oxygenate concentrations had little effect on driveability performance, there were differences in performance between oxygenate types. For example, in some cars gasolines containing methanol/TBA were shown to advantage over all other fuels tested, even gasoline. On the other hand, fuels with methanol gave inferior performance in some cars. On an overall basis, however, fuels containing methanol, methanol/TBA or MTBE were considered to perform equally as well as gasoline although the rating characteristics displayed by the methanol blends in some cars could, if widespread, impose difficulties in setting volatility specifications.
The authors conclude that methanol alone or methanol/TBA in blend with gasoline at concentration levels of up to 15 per cent volume, or MTBE up to 20 per cent volume concentration should give acceptable hot weather driveability performance if fuels are manufactured to existing gasoline specifications. Of perhaps greater interest is that use of methanol/TBA may even offer benefits over non oxygenated gasoline in some cars in the form of improved performance.