Alcohol in the tank: Methanol drive with energy recovery

In addition to gasoline, diesel fuel, natural gas and liquefied petroleum gas, there are other fuels basically suitable for use in vehicular drive systems. Owing to the different properties of the fuels, modifications to the engines are necessary in each specific case. As a matter of principle, alcohols like methanol and ethanol can basically also be used in the diesel engine, however their lower gross calorific value, the higher heat of vaporization and the required higher cooling performance constitute definite system drawbacks.

In a standard bus with methanol drive system introduced in 1981, Daimler-Benz took advantage of the heat of the coolant and methanol’s low boiling point of 65°C and, instead of the diesel engine, used a modified M 407 hG natural gas engine, many of whose parts were identical with a normal 11.5-liter production diesel. After a short preheating period of about two minutes before a cold start, the heat of the coolant sufficed to vaporize the methanol for use in the gas engine. Considering the short stops in urban regular service operation, any further warm-up usually was unnecessary.

Methanol operation and energy recuperation: The Mercedes-Benz O 305 test city bus on the test track in Stuttgart-Untertürkheim (1981). The vehicle was also tested in regular service.

With this configuration the circle was squared, as it were, and the methanol engine came close to a diesel direct injection unit in the utilization of energy. A diesel bus converted to methanol operation in June 1981 took up operation one month later in Auckland, New Zealand, as the world’s first methanol-powered public service bus. In early 1982 another methanol bus followed, going into practical operation with the Berlin local public transport service BVG. In May of the same year, a third methanol bus, a double-decker, went into service in Pretoria, South Africa. After two years of regular service and mileage of 100,000 kilometers, the Berlin methanol bus had given an extraordinarily good account of itself. It operated quietly, with low emissions, in particular with practically no particulate emissions, and impressed the drivers with its acceleration characteristics and its flexibility. As a result, BVG put seven more methanol buses into service in 1985. Methanol could be produced from natural gas or coal, but also from organic wastes, and was therefore considered a possible alternative fuel. The problem is not just the engine conversion, but even more so the provision of adequate fuel quantities and the establishment of a dedicated infrastructure for the fuel.