The Initial Spark
The history of Autogas begins in the mid 1930’s, LPG had been discovered in Germany only a few years earlier as a condensate when compressing refinery off-gas to extract gasoil. It was being sold in cylinders as propane and butane or as a less refined mixture of both components, which was marketed under the names Ruhrgasol and Leuna-Gas (amongst others), depending on its origin.
At the same time countries with a low supply of oil like England and Germany began experimenting with alternative fuels in search of alternatives to fuel their growing car fleets. Ultimately striving for self-reliance, no option was to be left untested. Among others, experiments were conducted with natural gas (methane) and LPG.
In 1934 Germany kicked off a programme to increase independence from oil imports. The following year in 1935 several alternatively fuelled vehicles (three diesel, one each fuelled with methane, LPG and methanol as well as two steam powered) were presented at the international automobile fair in Berlin. By 1942 Autogas systems had becoming very popular due to the scarcity of conventional fuels. The supply of LPG was plentiful: As aviation grade and other liquid fuels were being synthesised from lignite, considerable volumes of LPG were co-synthesised. Unlike in other markets, German Autogas consumption was about 50 times higher than what was delivered to households for cooking.
These first generation systems were developed for spark ignition engines and heavy duty diesel engines (dual fuel). The liquefied fuel stored in cylinders or fixed tanks is fed in liquid phase to a converter which vaporises the fuel and regulates the pressure to a set value. The gas is then fed into a mixer located in front of the throttle valve at the beginning of the intake system. The mixer restricts the diameter of the intake accelerating the flow of air at the narrowest point thus locally reducing the pressure. The mixture composition is regulated through the interaction between the regulated pressure and the amount of air flowing through the venturi. Manual adjustments can be made to ensure satisfying operation across the entire speed and load ranges. The system is entirely mechanically operated and has very few moving parts. Slightly more complex systems, relying on a diaphragm to regulate the gas flow depending on manifold pressure were developed in the US.
The technical solutions elaborated in those years set the reference for decades to come. The simple technology spread to other countries and was used in the south of France and in Italy (with both LPG and natural gas). Its main principles are still used today on carburetted engines, like those found on motor scooters or in generators. Even the advent of electronically controlled carburettors and early fuel injection systems did not change the robust and reliable technology.
Modern emissions, electronic controls
Stricter emission standards forced the widespread introduction of three-way catalysts in the exhaust system of every car. The mixture needed to be monitored more precisely in order to maintain the air-fuel ratio needed for correct catalyst operation with on-board diagnostics systems (EOBD) monitoring the quality of combustion. Electronic controls were added to venturi systems to enable finer adjustments to the mixture needed for correct operation of the catalyst. This formed the second generation of developments.
Because the risk of a backfire dramatically increases with longer intakes and larger plenums, venturi systems are less suited for these more modern types of engines. Later iterations did away with the mixer altogether and delivered the fuel directly before the intake of each cylinder. Apart from mitigating the backfire risk, these systems were much more precise in terms of fuel distribution and the loss of power normally associated with Autogas could be reduced drastically. These constant flow injection systems of the third generation were equipped with a variable valve controlled by the electronics to regulate the flow. The completely independent electronics include their own timing tables for the injection and drive the car independent of the original electronics.