Influence of compressor oil from natural gas filling stations on the operation of CNG vehicles

E.ON Ruhrgas has carried out tests on an engine test bed to determine the extent to which the gas supply system in natural gas vehicles will tolerate oil entrained in the compressed natural gas (CNG). This article discusses the results. The tests have shown that the potential level of oil ingress from a CNG filling station will not normally cause any problems during driving operation, provided that the compressor is operated within its design parameters and wear and maintenance levels are acceptable. Under the test conditions, which had been adapted to operating conditions on the road, about 90 per cent of the added oil burned almost completely inside the engine. About 10 per cent of the oil collected on supply system components as a liquid without, however, forming any solid or wax-like deposits that could cause malfunctioning. The tests carried out as part of the EU's "InGAS" project were also aimed at defining a realistic and meaningful limit for compressor oil levels in natural gas used as a vehicle fuel for a national or international standard. Given the findings of the tests, it is proposed to define a maximum content which is above the level normally found during measurements at CNG filling stations but below the level selected for these tests. This level could be 40-50 mgoil/kgnatural gas.