The optically accessible combustion vessel as shown in Figure A.1 is a high-pressure combustion vessel which enables combustion studies including spray, ignition, and flame investigations at a maximum pressure of 345 bar (5000 psia) with full-field, multi-axis, optical access. This high-pressure vessel is based upon the design and operation of the Sandia National Laboratory combustion vessel (http://www.sandia.gov/ecn/dieselSprayCombustion.php). The vessel is formed by the intersection of three cylinders creating a cubical chamber with a volume of 1.1L. On each of the six faces of the cube is a removable sapphire window for nearly complete optical access to the combustion chamber. On each vertex of the combustion chamber, there are eight instrument and actuator access ports that contain valves, pressure transducers, etc.
With a gas mixing system including a 10L mixing vessel, the gas composition inside the vessel can be generated to provide an inert environment for the study of vaporizing non-reacting sprays as well as high dilution conditions over a range of percent oxygen. The same gas mixing system can be used to provide virtually any composition of gaseous fuels for combustion studies as well. The gas mixing system mixes up to seven components (of any gas desired), and is currently configured with O2, N2, CO, CO2, H2, C2H2, and CH4. The combustion vessel provides the ideal environment to investigate the fundamental spray, vaporization, and ignition characteristics of the gaseous and liquid fuels and supports advanced chemical kinetics, auto-ignition, and CFD combustion modeling efforts for these fuels.
The operating range of the combustion vessel in comparison to the TDC compression conditions of a naturally aspirated and a highly boosted, 10 bar boost, compression ignition engine is shown in Figure A.2. As can be seen the combustion vessel is able to attain and exceed the thermodynamic conditions experienced in advanced IC engines. It is also seen that the critical temperature and pressure for various fuels are often exceeded prior to fuel injection. The operational range of the combustion vessel not only covers the conditions expected in advanced engine technologies, but to conditions well above these. This is key since the engine efficiency and operation demands of the future will continue to rise.
The ignition system is configurable. The housing that holds the electrode-fan assembly is shown in Figure A.3. The figure shows two electrodes and a single fan (left) which have been optimized for the preburn, lean combustion that has been used extensively in the diesel combustion studies.
The speed and direction of rotation of the fans is configurable, allowing researchers to easily vary the fluid velocity vector at the source of ignition. The flow field is characterized by using PIV system when dual fans are operational as shown in Figure A.3. Note that spark ignition system can be readily reconfigurable such as a single fan with two electrodes (left in Figure A.3) and dual fans with a spark plug (right in Figure A.3) depending on experimental requirement. Both fans in this case have a 25.4 mm outer diameter with eight straight vanes with 30 deg attack angle. Fan speed for this test is set at 8000 rpm to enhance mixing and homogeneous preburn mixture to minimize temperature variations in space at the time of fuel injection. The measurement condition for velocity field is 15oC and ambient pressure. The result indicates that the maximum averaged flow velocity observed is about 1 m/s. Since the high-pressure fuel spray lies in a momentum-driven jet, the surrounding gas turbulent levels induced by fan motion affects the spray minimal.
The entire AFCL, including the gas mixing system, data acquisition, process control, and all safety and operator alert systems are separated from the lab in a control room and fully automated using A&D Technology data acquisition and process control equipment.