Numerical Study on Premixed Charge Compression Ignition (PCCI) Combustion for Down-Sized Diesel Engine Using Converge 2020-32-2308
Diesel vehicle market have been recognized the need for change. In order to meet the strengthened emission regulations, innovative combustion technologies that can maintain power and improve fuel efficiency are becoming important solutions for diesel engines. This study deals with the goal of homogeneous combustion formation through changes in injection angle of conventional diesel engines. The conventional diesel engines show local combustion and has the limitation of generating exhaust gas including wall wetting phenomena. On the other hand, the appropriate injection angle optimization for the piston bowl shape can reduce wall wetting and form a homogeneous mixture overall in combustion. This study used 1D thermodynamic simulation to validate the conventional 4-cylinder diesel engine and compared to the test results to obtain modeling accuracy. To describe combustion behavior under 1D environment, multi-injection was used to increase the mixing time between air and fuel, which increases the temperature inside the cylinder, evaporates the fuel and creates a in-cylinder mixture and combustion processes. Secondly, detailed combustion analysis was performed using 3D CFD for spray combustion by creating a homogeneous mixture with change in injection angle, and the detailed combustion behavior was visualized. As a result, the optimized injection can provide enhanced egg motion, and optimal Heat Release Rate (HRR) can cause the soot to oxidize. Also optimized injection angles that can reduce the wall wetting were predicted to prevent incomplete combustion by forming homogeneous mixture. The emission results from homogenous mixture confirmed that nitrogen oxide (NOx) and particulate matter(PM) were reduced after combustion, and the results of unburned hydrocarbon(UHC) and carbon monoxide(CO) were confirmed by varying injection angle with reduced wall wetting. This can meet the premixed charge compression ignition (PCCI) by reducing emissions of NOx and PM. Furthermore, changing the injection angle for complete combustion can be an indicator for small diesel engines by connecting with early injection strategies, which is our future work scope.