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The design and adjustment of modern engines is limited by combustion behavior of the fuels. In the application of present fuels knock is the dominating factor, usually defined as Research -and Motor Octane Numbers (RON and MON). Alternative fuels prove to be different in some cases. So some engines react more sensitive with regard to knock as to be expected from the octane numbers when oxygenated fuels are utilized. In the application of alcohol fuels pre-ignition is an important factor besides knock, mainly in case of methanol. The investigation of pre-ignition and knock effects in high compression alcohol engines answers the question how the adjustment parameters such as air-fuel ratio, ignition timing and the temperatures of intake air and water will have an influence. As pre-ignition is a fuel property, a relation to other fuel properties, for instance octane numbers, is expected. It was found that the knock sensitivity gives a correlation to pre-ignition effects.

A standard Volkswagen 4-cylinder swirl-chamber Diesel engine was used to test the performance of alcohol-Diesel fuel blends, the alcohols involved being ethanol and methanol. The fuels had a content of oxygenate components of about 30% by volume. A solubilizer was added to prevent phase separation. The blend remained stable down to −20°C. The Diesel fuel used in the blend had a low cloud point and CFPP rating. At the Volkswagen research test facility, the fuel blends were tested for performance, exhaust emissions and fuel economy. In order to obtain detailed information on customer acceptance the alcohol-Diesel fuel blends are now being tested in a fleet of 30 Bundespost vehicles in the Ruhr region. The article discusses customer response, vehicle performance and wear.

Methanol as a fuel for spark ignition engines offers a lot of advantages in comparison to gasoline. Results of a prototype passenger car fueled with pure methanol show promising aspects of lower energy consumption, higher energy output and more favorable emission figures. Modifications on the engine are limited, the unfavorable cold start and warm up behavior of pure methanol can be eliminated by the use of suitable additives.

Most of the present LPG passenger cars and light trucks on the road are based on production gasoline engines. Various retrofit systems for LPG use are offered from different producers. The necessity for a large range of adaptibility to various engine types leaves limited space for individual optimization. Lack of equipment in some service stations is another reason for limited performance of many LPG vehicles on the road. Only the careful selection of a suitable LPG equipment and its best adaptation to the engine makes the full utilization of all advantages of this excellent engine fuel possible. Still better results can be obtained if the engine-vehicle concept is optimized to the LPG fuel as well. A lean burn engine promises low emissions at good performance, where the economy of the vehicle i. e. the operation costs depend on the local fuel prices in the different countries.