The HCCI Simulation Of The Natural Gas-hydrogen Engine Based On The Chemical Reaction Kinetics

Natural gas has been used widely in motor engine as one alternative fuel. However, it has disadvantages on auto-igniton, combustion velocity and exhaust emission. So it's meaningful to do the HCCI simulation of HCNG engine based on the chemical reaction kinetics to have a deeper understanding for the fuel characteristics and combustion model of HCNG engine.This paper used CHEMKIN code to simplify the detailed mechanism for the combustion of natural gas and finally got a simplified mechanism that includes 29 species and 60 elementary reactions. The simplified result was verified by comparing the test in a HCNG and then combined with hydrogen combustion mechanism to form the hybrid mechanism. The hybrid one was also verified by the comparison of simulation results and test results in constant volume combustion bomb model.The single zone HCCI combustion model was built for HCNG engine based on chemical kinetics. The effects of hydrogen addition amount in HCNG engine in performance and emission were analyzed. And the influence of the change of parameters such as equivalent ratio, intake temperature, compression ratio and engine speed was researched as well as the EGR condition and the function of exhaust gases. With the increasing addition of hydrogen, the change of maximum temperature and pressure in cylinder were not changed much as well as the CH2 O as a intermediate product. But the ignition time was advanced and the emission of NO increased for a while and then decreased for the change of combustion velocity and chamber volume.The misfiring limit will be widen when the hydrogen is enriched. Then the theoretical reason for the effects of hydrogen addition to ignition time is analyzed. The enriched hydrogen produces many H atoms by chain-reaction which lead to positive influence to the concentration of freedom radicals and so the ignition time is advanced. The higher intake temperature and compression ratio would advance the ignition time while the higher engine speed will delay. But the combustion time will be reduced by the increasing of intake temperature and engine speed. The top combustion temperature and pressure will increase linearly with a higher equivalent ratio. In the EGR condition in HCNG engine, the combustion temperature and pressure is lower when the EGR ratio is higher as well as the NO emission. The HCCI combustion operating area was determined. The ?-T diagram of NO was also constructed which could be referred for the low-emission combustion routine design for HCNG engine.