Combustion chamber deposits (CCDs) from a gasoline direct injection stratified charge SI engine were analysed. The engine was run with two fuels: a typical European base fuel, containing 9.8% MTBE, and a low volatility worst case fuel. The worst case fuel is a standardized European fuel, CEC RF 86-A-96, prone to form deposits. It contains high amounts of aromatics and olefins but no MTBE. The deposits were analyzed in several ways; thermal desorption followed by gravimetric analysis, fast neutron activation analysis and solid-state 13C nuclear magnetic resonance spectroscopy.
Up to 50% of the deposits, formed inside the GDI engine, consist of volatiles. The composition of the deposits is strongly related to the composition of the engine oil.
The fraction of volatiles in the deposits decreased in the order: cylinder head, piston squish surface and piston bowl. The deposits from the piston squish surface contained the highest fraction of oxygen, about 30 %.
The non-volatile part of the deposits was highly oxidized. The organic oxygen in the non-volatile part was found in different types of carbon compounds: oxygenated aliphatics, carboxyls and carbonyls.
The fuels used in this study apparently did not significantly affect the content of oxygen and the volatile organic found in the deposits.