The Simulation Research Of Diesel Emission Control Technologies Based On Injection Rates

Recently, researches are gradually focused on the reduction of NOx emission of diesel engines. By adopting multiple injections or HCCI technique, NOx emission can be sharply reduced. In the process of analyzing multiple injections and HCCI technique, simulation plays an important role with its outstanding characteristics such as shout period, low cost and informative solutions can be achieved. Simulation analysis originates from project data and provides optimized solution to project application.AVL Boost and AVL Fire simulation software are used to set up the model of the original diesel engine. On the base of that, multiple injections and HCCI technique are applied to optimize its NOx emission. The ignition process of HCCI is mainly influenced by chemical reaction rates, which demands a specific combustion model, so its influence is only analyzed on AVL Fire. In the simulation of multiple injection, AVL Boost can be used to calculate various cases. The best one is selected from the calculated cases and is applied in AVL Fire for further CFD simulation.Meticulous design of injection duration, injection timing and injection interval is carried out. Two types of multiple injections which can obviously reduce NOx emission are obtained. The idea of the design is described below:one or two pilot injections are realized around700°CA. The injected fuel should be burned to improve the temperature in cylinder, so that the ignition delay of main injection can be decreased or even ignite the fuel injected during the main injection. The simulation results show that it can reduce the peak combustion pressure and the mean combustion temperature. NOx emission can meet the restriction of Tier Ⅱ or Tier Ⅲ. Meanwhile, the output power is reduced and the BSFC is increased.In the simulation of HCCI which is realized by early injections, if the injected fuel is burned in premixed combustion, the peak combustion pressure will be too high, which can easily cause shock. In order to ensure the stability of working process, the peak pressure can be reduced through EGR technique under part load. The simulation results show that the NOx emission can meet the restriction of Tier Ⅲ.