New findings on combustion behaviour of oxygenated synthetic Diesel fuels

New results were obtained on pollutants evolution during the combustion of four oxygenated fuels, whichwere compared with n-tetradecane and n-octane combustion. Three different techniques were adopted on a single cylinder direct injection diesel engine, equipped with optical accesses: two-colour pyrometry for the measurement of in-cylinder soot loading, high speed cinematography for the visualization and analysis of spray and combustion, fast sampling valve for the measurements of in-cylinder combustion products. In particular, the sampling line downstream of the fast sampling valve was adapted for the in-cylinder aldheydes measurements. Heat release analysis and fast sampling valve have shown that CO formation rate and heat release rate during the diffusion phase of combustion increase with the fuel oxygen content. Acetylene concentrations are influenced by fuel cetane number and oxygen content but, at the same fuel cetane number, they decrease when oxygen content increases. In-cylinder aldheydes concentrations are connected with premixed phase fraction of combustion and then influenced by fuel cetane number. In comparison with n-tetradecane fuel combustion, high burning rate and low visible flame distribution were observed through high speed cinematography tests. when oxygenated fuels were burned. Investigation on in-cylinder soot loading showed a great difference between the combustion behavior of ethers and glycolethers. The glycolethers show lower soot loading at the same fuel oxygen content.