Investigation of the Combustion Characteristics of GTL Diesel Fuel in a Constant Volume Combustion Chamber

The results of an optical investigation into the combustion characteristics of GTL (Gas-To-Liquids) diesel fuel are presented. The investigation was carried out using a high pressure, constant volume combustion chamber with optical access, fitted with a modern diesel injection system. Combustion images were captured under conditions which simulate those present in a diesel engine. A low sulphur diesel fuel meeting the European EN590 specification was used as a reference.

Image capture and subsequent analysis was performed by means of an AVL Visioscope system which used the two-colour method to yield quantitative information regarding flame temperature and soot concentration. Conditions in the combustion chamber are preset by combusting a pre-charge to generate the necessary pressure, temperature, and residual gas fraction. This allowed the effect of varying oxygen concentration at the start of diesel combustion to be investigated.

The results showed distinct differences in the experimentally determined soot concentrations and revealed that GTL has consistently lower levels of soot concentration in the flame than the reference fuel. The difference in flame temperature results between the fuels was small but a correlation of the soot concentration and flame temperature results revealed characteristic differences between the fuels that change systematically with EGR. GTL appeared to show improved relative combustion characteristics with increasing levels of EGR.