This project deals with R&D for compressed natural gas (CNG) and biogas vehicles. CNG and biogas (upgraded to CNG equivalent quality) consist mainly of methane. Therefore, the terminology "methane vehicles" will be used in the subsequent text for these vehicles. Methane vehicles have the potential to reduce the local traffic based air pollution problems (ozone, NO2, particulate matter) as well as the greenhouse gas emissions (CO2-equivalent) significantly. The use of methane as motor vehicle fuel assists the effort for a diversification of the transport fuel market (that has today an 98% crude oil dependency) and allows the usage of preprocessed biogenic methane, produced waste (organic waste, sewage sludge, liquid manure, unburned wood).To use this potential, the methane vehicle technolgoy needs to be improved.
The traditional gasoline-to-CNG-coversion technology was often disapointing regarding reliability, efficiency, costs, functions and so on. Due to the development of methane-powered vehicles by the automotive industry, a strong improvement was initiated. Besides engine optimization, the main R&D aspects for methane vehicles are the optimization of the catalytic converter's methane conversion ability with (cost driven) low loading of platin group metals (PGM) and the simultaneous improvment in durability.
As methane is a potent greenhouse gas, the technology to assure methane emissions near zero is not only important to fulfill the demanding hydrocarbon emission limits given by the emission legislation but it is also crucial for the superb overall ecological performance of methane vehicles.
In the first phase, the actual project included the evaluation of the catalytic converter specification on the dynamic engine dynamometer (Fig. 1 and 2). Thereby, fresh and aged catalytic converters were systematically investigated and evaluated regarding their conversion efficiency and their dynamic oxygen storage and oxygen release behaviour. With the knowledge this first phase, technical specifications for optimized catalytic converters were eleborated and prototypes of such catalytic converters were produced.
In the second phase, three prototype vehicles for field testing were equipped with these optimized catalytic converters. The vehicles were (and still are) operated in cooperation with Novatlantis, a sustainability network in the ETH-domain, in the so called "Pilotregion Basel" at different administration offices and companies. The emission behavior of the vehicles is monitored every 5'000 km for emissions stability in the official European driving cycle as well as in the real world driving cycle CADC on a chassis dynamometer (Fig. 3). The surface of the catalytic converters is analysed regarding poisoning, sintering and phase transformation after the field testing for further improvements.
Results:The conversion efficiency of the catalytic converters could be increased while the coating with PGM elements could be significantly reduced (reduced costs) and the emission stability was strongly improved (no deterioration visible until the actual mileage of 20'000 km). Conventional high-PGM technologies showed a clear worsening of emissions within this mileage.