Development of optical diagnostic techniques to correlate mixing and auto-ignition processes in high pressure Diesel jets

A tracer laser-induced fluorescence (LIF) technique for the visualization of fuel distribution in the presence of oxygen was developed and then used sequentially with high speed chemiluminescence imaging to study the correlation between the inking and auto-ignition processes of high pressure Diesel jets. A single hole common rail Diesel injector allowing high injection pressures up to 150 MPa was used. The reacting fuel spray was observed in a high pressure, high temperature cell that reproduces the thermodynamic conditions which exist in the combustion chamber of a Diesel engine during injection. Both free jet and flat wall impinging jet configurations were studied. Several tracers were first considered with the objective of developing a tracer-LIF technique in the presence of oxygen. 5-nonanone was selected for its higher fluorescence efficiency. This technique was subsequently combined with high speed chemiluminescence imaging to study the correlation between mixing and auto-ignition. In the free jet configuration and for the parameter range studied, it was found that auto-ignition is preferentially located in rich regions of the upstream mixing zone. Also, in the jet wall configuration, auto-ignition appears in the centre of the jet and propagates towards the periphery, in the vicinity of the wall.