Résumé de rapport

Using natural gas in electric vehicle fuel cells

Methanol and natural gas can both be used as fuel for vehicles powered by fuel cells, provided there is a cheap, compact reformer available for conversion to hydrogen. Full life cycle efficiency favours natural gas since nowadays methanol is mostly produced from natural gas at 65-70% efficiency. Natural gas is also readily available from the public supply network and it can be compressed and stored in tanks.

The potential for using natural gas as a fuel for electric vehicles powered by fuel cells was investigated. It developed a system study with a compressed natural gas (CNG) reformer to supply hydrogen to fuel cells in electric vehicles. The system successfully increased the range of the vehicles. However, more work is needed to improve the quality of the reformate and to reduce the size of the system before it can be considered for commercial development.

A system study was carried out to assess energy use, range and driving performance. The researchers used an existing electric car, the Hotzenblitz (which is manufactured by one of the project partners), equipped with a 1 kW fuel cell back-up system. The key component of the system design was the hydrogen generator, consisting of the natural gas reformer and the gas management system. These two components were developed by 2 of the partners, FhG-ISE and TNO. Two experimental set-ups of reforming reactors capable of supplying hydrogen to a 1 kW and 5 kW fuel cell were developed and operated in a brass board (storage tank and reformer combined). Proton Exchange Membrane (PEM) fuel cells were considered for the system envisaged because of their high power density and compactness, but they are very sensitive to carbon monoxide (CO), so levels of CO in the reformate were measured. The potentially deleterious effects of sulphur compounds in natural gas on the performance of the reformer and the fuel cell were investigated.

Studies with the electric vehicle showed that, for urban use at low average speeds, the range depended on the CNG tank capacity, rather than on the battery capacity. The maximum daily range could increase from 90 km to 250 km if the car was refuelled regularly with natural gas. When the reformer needed to power, a 5 kW fuel cell was operated under a range of conditions, the methane conversion varied between 85-92% and the efficiencies between 55-58%. The lowest achievable CO content of the reformat was 0.7 vol%. However, since PEM fuel cells are very sensitive to CO, this indicates that additional gas clean-up would be needed. Traces of sulphur compounds were identified in the natural gas, but these could be removed in a desulphurisation system, based on active carbon, at a low cost.