Abstract:

In this paper， the impact of injection pressure and injection duration on the combustion characteristics of a natural gas engine using active jet ignition mode is studied. The test conditions are selected under conditions where the intake air pressure is maintained at 0.08 MPa while the injection duration of natural gas at the inlet is kept at 18 ms. The active injection pressure of natural gas in the jet chamber is adjusted to increase from 0.5 MPa to 3.0 MPa with an increment interval of 0.5 MPa and the injection duration increases from 1 ms to 5 ms， with an increment interval of 1 ms. The engine speed is kept at 800 r/min and the spark timing is fixed at -24°CA ATDC for all the conditions. The experimental results show that the active jet ignition mode can increase the peak heat release rate and accelerate the combustion rate compared with the passive jet ignition mode. Large COV is observed with too low active injection pressure and too short injection duration while the COV decreases （COV<1.5%）with the increase of injection pressure or injection duration. The combustion stability is insignificantly impacted by the injection pressure or injection duration once the COV is below 1.5%. Besides that， the peak in-cylinder pressure and peak heat release rate increase as the injection pressure or injection duration increases. Under such conditions， the combustion rate in the initial stage is accelerated while the overall combustion duration becomes longer. Higher indicated thermal efficiency is realized under lower injection pressure and shorter injection duration at fixed ignition time. The highest indicated thermal efficiency is realized when the injection pressure is 0.5 MPa and the injection duration is 2~5 ms， with an increase of 2. 8% of the optimized indicated thermal efficiency.

Key words: active jet ignition, natural gas, injection pressure, injection duration, combustion rate