Combustion products, exhaust emissions and engine exhaust deposits formed on thermocouples, positioned after the heat exchanger of an engine power plant, were analyzed chemically. The engine was a lean burn 18W28SG 50 Hz (Wärtsilä NSD, Trollhättan Sweden) fuelled with natural gas equipped with a catalyst (Süd-Chemie NMHC catalyst).
The exhaust emissions were sampled using the off-line bottle-in-bag (BiB) method and were analyzed by gas chromatography/flame ionization (GC/FID). Heavier organic compounds and aldehydes were separately collected using adsorption cartridges. The combustion products measured in the emissions were mainly ethene, propene and formaldehyde indicating normal combustion of the fuel in the engine.
Organics contained in the engine exhaust deposits were extracted using three different extraction methods: thermal desorption (TD), liquid extraction (LE) and super critical fluid extraction (SFE). The extracts were analyzed by GC/MS. The chemical composition of the deposits before and after TD and LE was characterized using solid-state 13C NMR. The amount of oxygen in the deposits was measured using cyclic fast neutron activation analysis (cFNAA).
A substantial part of the deposits (77 weight %) consisted of extractable organics. The remaining part of the deposits consisted of a carbon structure rich in aromatics and aliphatics. The amount of oxygen in the deposits was about 17 weight %.
As expected, the results demonstrated that the deposits originated from engine oil. This was shown clearly using GC/MS analysis of components desorbed or extracted from the deposits combined with NMR of deposits.