Low-Temperature Combustion/Diesel Combustion Simulation Vessel
Optically accessible diesel combustion simulation vessel
Investigating diesel engine combustion processes is challenging due to the many factors that affect the in-cylinder environment where diesel fuel jet mixing occurs. The temperature, pressure, density, and composition of the in-cylinder gases as well as fuel injector conditions have a direct effect on combustion and emission formation processes. In the CRF's Low-Temperature Combustion Diesel Combustion Simulation Vessel, a wide range of ambient (charge gas) environments can be simulated at the time of fuel injection, allowing the effect of each variable to be assessed. The capabilities of the facility are unique in the world. With full optical access, the following ambient conditions can be simulated:
- Ambient gas temperatures from 700 K to 1300 K
- Ambient gas densities from 7 kg/m3 to 60 kg/m3
- Ambient gas oxygen concentrations from 0% to 21%
These conditions span or exceed those typically experienced in a diesel engine.
Planar laser-induced incandescence images at four orifice diameters. Ambient gas temperature, density, and oxygen concentration were 1000 K, 14.8 kg/m
3, and 21%, and the orifice pressure drop was 1400 bar.
Current research focuses on methods of achieving low-flame temperature and low-sooting diesel combustion. The ultimate goal is to define conditions that will enable engines with high, diesel-like efficiencies but with reduced engine-out nitrogen oxide and particulate matter emissions. Advanced optical diagnostics are used to study fundamental aspects of diesel combustion and soot formation. Data are being obtained for a range of ambient gas temperatures, ambient gas densities, injection pressures, injector orifice diameters, and fuel types.
Schematic of combustion vessel
Our research shows that diesel combustion that does not undergo any soot formation and that also has a low-flame temperature can be produced at some injector and ambient conditions. For example, planar laser-induced incandescence images to the right show that soot formation decreases as injector-tip orifice diameter is reduced and that there is no detectable soot when using a 50-micron orifice. In addition, the 50-micron orifice fuel jet remains soot-free as ambient gas oxygen concentration is reduced from 21% to 10%-a condition where flame temperatures are low and NO
x formation is minimal.
The knowledge base created by this research on low-temperature diesel combustion fundamentals is being used by engine manufactures to help design higher efficiency, emission-compliant engines. The datasets obtained in the combustion vessel also provide an opportunity for combustion and soot model development and verification in well-characterized conditions. Improvements in these models are needed to allow faster and more reliable optimization of engine performance and minimization of emissions.
