Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Oxidation of hydrocarbons in internal combustion engines

Unburnt hydrocarbon emissions from internal combustion engines result from several different mechanisms. Each is essentially a process in which some fuel or fuel/air mixture does not burn during normal flame propagation in the engine. The project team has developed and implemented a one dimensional model describing the desorption of hydrocarbons from oil layers and carried out parametric studies examining the adsorption and desorption of iso-octane and toluene in squalene. The effect of oil temperature has also been studied and a theoretical analysis to predict the time scales of possible secondary oxidation of the desorbed fuel from oil layers carried out using numerical tools.

Hydrocarbon oxidation under typical engine conditions was studied in a single cylinder Ricardo E6 engine. This engine was modified to allow small quantities of hydrocar bon to be injected during the post combustion phase at defined moments in time. Study was then made of post-flame oxidation of unburnt hydrocarbons and exhaust emissions measured. The mechanisms of fuel desorption from oil layers and further fuel oxidation were also carried out in a constant volume pressure chamber using advanced laser techniques.

Based on emission measurements and a knowledge of the pressure and temperature conditions of the exhaust gases during expansion and exhaust strokes, an interpretation of important chemical processes and physical conditions for hydrocarbon emission formation were made. The pressure variation in the constant volume chamber indicated that the oil film temperature is the key parameter in reducing the unburnt hydrocarbon emissions in internal combustion engines caused by fuel desorption from the oil layer. Desorption was reduced when the oil layer was 100 C or more. The theoretical analyses indicate that some fuel is left unburnt after about 10 ms, for example at about 590 degrees of crank angle. Before that time all fuel desorbed from the oil appears to be oxidised.

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