供油瞬态喷油杆内燃油结焦机理及规律数值研究

Numerical Studies on Mechanisms and Rules of Fuel Deposition at Transient Moment of Fuel Supply in a Fuel Injector

关键词:  通断循环供油  喷油杆  热冲击  燃油结焦  数值模拟

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

摘要:

为获得喷油杆通断循环供油工作模式下，供油瞬间燃油结焦速率陡增机理，本文建立起沿喷杆轴向的一维非稳态热-流-固耦合换热与燃油结焦计算模型。获得不同时刻壁温、油温与结焦速率等参数轴向分布。通过与连续供油模式下的结果对比，来分析供油瞬间灼热喷杆内壁对燃油热冲击的影响，以获得结焦速率陡增机理。结果表明：通断供油模式下，供油瞬间会迅速形成一尖锐的油温和结焦前体浓度峰值，结焦固相表面反应被迅速激发，结焦速率陡增。在喷杆前端（x=100mm）与底部（x=260mm）附近各存在一结焦速率峰值区域。通断供油模式下，在x=100mm和x=260mm位置处，每个周期供油起始时刻结焦速率峰值分别在5000μg/（cm²·h）和2000μg/（cm²·h）左右，远大于连续供油下的值。但供油结束时刻，供油模式的影响大幅下降。此外通断供油下，供油瞬间热冲击对燃油结焦的影响沿喷杆轴向逐渐减小。减小喷杆供油流量，热冲击的影响有所下降，且随时间先升高后降低。提高进口油温，热冲击的影响显著减小，且随供油时间逐渐降低。

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.