Adsorption-based Structural Characterisation of Combustion Chamber Deposits

It has been recognized that carbonaceous engine deposits, which accumulate on the internal surfaces of spark-ignition engines, can adversely affect engine performance. One mechanism by which this occurs is the adsorption and desorption of fuel components and combustion products during the engine cycle. We have studied the structural properties of these deposits and their adsorption behaviour, under different conditions, to try to understand their impact on the engine operation. Combining experimental and simulation techniques, it is possible to evaluate the internal structure of activated carbon adsorbents and determine their pore size distribution (PSD). We have applied this methodology to the study of combustion chamber deposits (CCDs). This will give a better understanding of the phenomena of adsorption and desorption on a molecular level. Experimental adsorption isotherms were measured in a step-by-step volumetric rig from 4.0×10^-2 to 20 bar, at 278 and 298 K, in deposits produced by a road-test engine. The adsorption of ethane in carbon pores with slit-like geometry was simulated using grand canonical Monte Carlo simulation (GCMC). Elemental analysis revealed that the combustion chamber deposits contained the range of components that are usually presented in the lubricating oil, including P, Ca and Zn. It has also been shown that these materials are thermally stable up to 600 K.