Details of the Fluid Mechanic Conditions in the Combustion Vessel


Prior to an experiment, the vessel is heated to 458 K. This is the approximate temperature of combustible gases prior to spark ignition. A mixing fan mounted in the upper surface of the vessel runs throughout the entire simulation process. The fan serves to keep the temperature in the vessel uniform before and after spark ignition and up to the time of the diesel injection event. A fan that pulls gas from the center of the vessel and ejects it along the walls (view preburn) was found to provide the optimal uniformity in the core region of the vessel. Without the mixing fan, more significant temperature non-uniformities develop as a result of vertical thermal stratification of the gas in the vessel.


Spray A conditions

Velocity Estimates of the mean gas velocity induced by the fan were made using a particle tracking technique used to visualize the flow in the chamber (Siebers, 1998). The mean swirl velocity was approximately 0.7 m/s. This velocity is comparable to the velocity measured with LDV in the disk-shaped chamber (Naber, 1996), where the same mixing fan and fan speed were used. LDV measurements from this disk-shaped chamber also showed that the rms velocity was 0.7 m/s in the central core region of the vessel. Note that these gas velocities are small when compared to liquid (high-momentum) spray velocities (~400 to 600 m/s) and therefore, have little effect on the sprays. Schlieren movies of penetrating sprays show no deflection of the spray by the fluid motion inside the vessel (link to schlieren movie).

Time resolved Particle Image Velocimetry measurements in the ambient environment of Spray A, on the horizontal plane confirmed the findings of past work. The data is recommended for use by modelers as a typical vessel ambient condition after pre-ignition (link to spreadsheet).


Spray G conditions

For Spray G, the ambient conditions in the vessel have lower values of density and temperature. But the flow characteristics in the vessel follow the same behavior as Spray A. The ambient appears to follow a very slow recirculating flow downstream of the injector and towards the fan, which is located on the top left corner downstream of the spray. The recirculating motion is most likely induced by the rotation of the fan and the temperature gradients in the vessel. The fan is pulling gases towards the top left corner downstream of the spray. The heat distribution in the vessel, promotes a recirculation from the warmer top layers of gases to the colder bottom adjacent to the cold exterior walls and then upward from the bottom through the warm core. Time resolved Particle Image Velocimetry measurements in the ambient environment of Spray G is available for use by modelers (link to spreadsheet).