关键词: 通断循环供油;喷油杆;热冲击;燃油结焦;数值模拟

Abstract: In order to investigate mechanisms of rapid increase of fuel deposition rate at the transient moment of fuel supply under the on-off cycle mode in a fuel injector， one-dimensional unsteady heat-fluid-solid coupled heat transfer and fuel deposition model along the axial direction of fuel injector was established. Axial distributions of wall temperature， oil temperature and fuel deposition rate at different fuel supply moments were obtained. By comparing with results of continuous fuel supply mode， effects of thermal shock caused by the hot inner wall of fuel injector at the moment of fuel supply on fuel deposition were analyzed， so as to obtain mechanisms of sharp increase of fuel deposition. Results show that at the beginning of each on-off cycle， sharp peak values of oil temperature and deposition precursor are formed rapidly after fuel supply. The solid-phase surface reaction which leads to fuel deposition is excited rapidly， so the deposition rate increases sharply. There is respectively a peak area of fuel deposition rate near the front （x=100mm） and bottom （x=260mm） of the injector. Under the on-off mode， at x=100mm and x=260mm， peak values of deposition rate at the beginning of each cycle are respectively about 5000μg/（cm²·h） and 2000μg/（cm²·h）， which are much higher than those under the continuous fuel supply mode. However， at the end of fuel supply， influences of fuel supply mode are greatly reduced. Besides， under the on-off mode， influences of thermal shock on fuel deposition decrease along the axial direction of the injector. When the inlet flow rate is reduced， effects of thermal shock are smaller than those under the baseline condition， and first increase with time and then decrease. With the increase of inlet oil temperature， effects of thermal shock become smaller significantly， and gradually decrease with the fuel supply time.

Key words: On-off cyclic fuel supply;Fuel injector;Thermal shock;Fuel deposition;Numerical simulation