Abstract
Spray guided stratified combustion for minimizing nitrogen oxides (NOx) emissions have been studied. Conducted for this purpose are experimental studies using a single cylinder test engine over a wide range of EGR (Exhaust Gas Recirculation) rate and temperature. An in-house developed combustion system with a multi-hole nozzle of 18 holes and a flat piston is applied for the study. Multiple injection strategy is applied at a typical light load operation at low engine speed. The test results have indicated that NOx emissions in spray-guided stratified operations generally depend on carbon dioxides (CO2) concentration of induction gas into the cylinder and the limit of the maximum CO2 decides minimum NOx emissions. On the other hand, combustion speed is influenced by both the temperature and CO2 concentration of induction gas. Consequently, induction gas heating extends the limit of maximum EGR rate to reduce NOx emissions, keeping combustion rate and stabilities as well as HC emissions. The minimum NOx emission index has been proved to be approximately 1g/kg_fuel, which is far less than the other combustion system for spark ignited gasoline engines like homogeneous lean burn and stratified combustion with wall controlled method and even close to some controlled auto-ignition (CAI) combustion. Low NOx emissions have been realized by a practical combustion system with intensive internal EGR instead of induction gas heating.
Keywords:Direct Injection Gasoline Engine, Spray, EGR, NOx emissions, Auto ignition