Study On Effect Of EGR On Gasoline Engine Based On Hydrogen Injection Strategy

In recent years, Chinese automobile market develops in good shape, whose positive long-term developing features keep constant. It is the rigid demand for process of modernization, but China is also faced with various problems from the automotive industries. Except the external factors such as national policies and economic situation et al., it is necessary for the automotive industries to address the energy and environment. With the national vigorously promoting energy saving and low emission, vehicle development must accept this challenge. As the most clean energy in the 21 st century, hydrogen provides new inspiration for the future development of the automobile. In this paper, under the National Natural Fund Project "Study on Energy-saving Mechanism of HEV Equipped with Lean-burn Gasoline Engine with Hydrogen Direct Injection System and Local ",this paper is aimed at high NOx emissions at lean burn operations. Therefore, the introduction of EGR combined with hydrogen injection strategies to control NOx is proposed, which is to verify the power performance and emission performance of gasoline-hydrogen blends engine combined with EGR by experimental test.By the initial pilot experiments to develop a more comprehensive test program, the proposed hydrogen injection strategies mainly contain hydrogen fraction, hydrogen injection timing and engine speed control, which can affect the flow status of hydrogen in cylinder, while EGR rate is determined by the levels of NOx control. Based on the modification of laboratory, 1.8T Gasoline Direct Injection for the original machine test bench is built with the installation of hydrogen direct injection and gasoline intake injection combined with self-developed electrical control systems. Through the peak torque, the peak cylinder pressure, the cylinder pressure angle corresponding to its peak flame development duration and rapid combustion duration, it is to explore the effects of various parameters on combustion performance, while the CO, HC and NOx emissions are detected to observe emission performance. The conclusions in this study are summarized as follows:1. With the increase of hydrogen, peak cylinder pressure is increasing, while the corresponding peak cylinder pressure angle is constantly advanced and peak heat release rate is also increasing. Additionally, with the increase of hydrogen fraction, the combustion process becomes faster and better. With the advance in injection timing, the peak cylinder pressure is rising. However, compared to hydrogen injection at the intake stroke, hydrogen injection at compression stroke combined with reasonable hydrogen injection pressure, hydrogen injection timing and ignition timing can have the greater potential to improve cylinder combustion state. As the engine speed increases, the peak cylinder pressure is relatively close to the top dead center. Hydrogen addition has a very significant effect on flame propagation speed and improvement of combustion status.2. When the engine keeps constant speed, it is not easy to use large hydrogen fraction for the small EGR rate. Flame development duration and rapid combustion duration are prolonged with the increase of EGR rate. Hydrogen addition has a greater impact on rapid combustion duration, but hydrogen fraction has little effect on rapid combustion duration. Thereby, it is possible for the use of small hydrogen fraction with small EGR rate to achieve both increase of the torque and improvement of rapid combustion duration.3. For specified hydrogen injection timing, the torque decreases sharply with the increase of engine speed for larger EGR rate without hydrogen addition, but this phenomenon becomes less obvious after hydrogen addition.4. For a given hydrogen fraction, it is possible to delay the hydrogen injection timing at small EGR rate, but hydrogen injection timing should be advanced at large EGR rate, which can increase the torque to some degree. The advance in the hydrogen injection timing can increase the combustion speed after hydrogen addition.5. After the study on CO, HC, NOx emissions versus EGR rate at different hydrogen injection timings, hydrogen fraction, the engine speed, it can be found that the increase of hydrogen fraction can avail improving CO, HC emissions, while the advance of hydrogen injection timing also can play a positive role. Hydrogen addition has great effect on NOx emission. With the increase of hydrogen fraction, NOx emissions significantly increase. However, the introduction of appropriate EGR rate, low NOx emissions can be achieved, but also the torque can be significantly increased.