Taking diesel-ignited direct injection natural gas (NG) engine as the research object, the synergistic control of intake pressure and NG injection timing on the organization of in-cylinder mixture and combustion process was analyzed under the condition of low load (1300rpm) by numerical simulation, in order to achieve low HC emission and high thermal efficiency. The results show that by improving intake pressure, the NG jet momentum, squeeze flow and turbulent motion in cylinder are enhanced, which is beneficial to the stratification of mixture, gradual ignition and combustion rate in cylinder. In addition, too prior injection results in more combustible mixture entering the cylinder clearance, leading to incomplete combustion; too late injection causes too late combustion, reducing the power capability and thermal efficiency. By optimal matching the intake pressure and NG injection timing, a higher indicated thermal efficiency (ITEg) of 49.03% can be obtained when the intake pressure is 0.2MPa and the injection timing is -10°CA ATDC with a lower NOx emission level without using EGR technology.
Keywords natural gas direct injection engine, diesel ignition, injection strategy, intake pressure, combustion process