Solid-State 1H NMR Spin-Lattice Relaxation in Combustion Chamber Deposits from a Gasoline Direct Injection Engine 2004-01-0042
Combustion chamber deposits from a gasoline direct injection stratified charge SI engine were analyzed using solid-state 1H inverse recovery NMR spectroscopy, before and after thermal desorption (TD). The engine was run with a typical European base fuel, containing 9.8% MTBE.
Before TD, solid-state 1H NMR showed two broad peaks representing aliphatics and aromatics. The results showed that T1 (the relaxation time) of the aliphatics was significantly longer than T1 of the aromatics in the deposits. Deposits taken from the piston bowl, with the lowest volatility content, showed the shortest T1. In comparison, piston squish and piston bowl deposits, with higher volatility content showed a longer T1. After TD, T1 of the aliphatics was shorter than the corresponding T1 of the aromatics. A decreasing T1 of aliphatics may be used for following a transition from a liquid (engine oil), via a semi-solid deposit to a solid carbon backbone. This may give a rough measure of the engine oil content of the deposits.