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Title: End-of-injection fuel dribble of multi-hole diesel injector: Comprehensive investigation of phenomenon and discussion on control strategy

Abstract

The needle shutdown of fuel injectors leads to an undesired fuel dribble that forms unburned hydrocarbons and decreases the engine thermal efficiency in modern engines. Understanding of the fuel dribbling process is of great importance to establish its minimization strategy for optimal use of conventional fuels. However, the detailed needle dynamics and in- and near-nozzle flow characteristics governing the fuel dribble process have not been thoroughly understood. In this study, the needle dynamics, in- and near-nozzle flow characteristics and fuel dribble of a mini-sac type three-hole diesel injector were investigated using a highspeed X-ray phase-contrast imaging technique at different injection pressures. The results showed that an increase in injection pressure increased the flow evacuation velocity at the needle close that induced a more intense fuel cavitation and air ingestion inside the nozzle. The fuel dribbling process showed a high shot-toshot deviation. A statistical analysis of 50-shot results exhibited two breakup modes of fuel dribble determined by the flow evacuation velocity at the needle close and presence of air ingestion. In the first mode, the fast breakup with a short residence time of fuel dribble occurred. Meanwhile, the dripping of undisturbed liquid column with a long residence time of fuel dribblemore » occurred in the second mode. An increase in injection pressure increased the population of the first mode due to more intense air ingestion that primarily caused by an increase in needle closing speed other than an increase in peak injection velocity. Based on the results, the formation mechanism and control strategies of the fuel dribble from modern diesel injectors were discussed.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1393203
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Energy; Journal Volume: 179
Country of Publication:
United States
Language:
English

Citation Formats

Moon, Seoksu, Huang, Weidi, Li, Zhilong, and Wang, Jin. End-of-injection fuel dribble of multi-hole diesel injector: Comprehensive investigation of phenomenon and discussion on control strategy. United States: N. p., 2016. Web. doi:10.1016/j.apenergy.2016.06.116.
Moon, Seoksu, Huang, Weidi, Li, Zhilong, & Wang, Jin. End-of-injection fuel dribble of multi-hole diesel injector: Comprehensive investigation of phenomenon and discussion on control strategy. United States. doi:10.1016/j.apenergy.2016.06.116.
Moon, Seoksu, Huang, Weidi, Li, Zhilong, and Wang, Jin. 2016. "End-of-injection fuel dribble of multi-hole diesel injector: Comprehensive investigation of phenomenon and discussion on control strategy". United States. doi:10.1016/j.apenergy.2016.06.116.
@article{osti_1393203,
title = {End-of-injection fuel dribble of multi-hole diesel injector: Comprehensive investigation of phenomenon and discussion on control strategy},
author = {Moon, Seoksu and Huang, Weidi and Li, Zhilong and Wang, Jin},
abstractNote = {The needle shutdown of fuel injectors leads to an undesired fuel dribble that forms unburned hydrocarbons and decreases the engine thermal efficiency in modern engines. Understanding of the fuel dribbling process is of great importance to establish its minimization strategy for optimal use of conventional fuels. However, the detailed needle dynamics and in- and near-nozzle flow characteristics governing the fuel dribble process have not been thoroughly understood. In this study, the needle dynamics, in- and near-nozzle flow characteristics and fuel dribble of a mini-sac type three-hole diesel injector were investigated using a highspeed X-ray phase-contrast imaging technique at different injection pressures. The results showed that an increase in injection pressure increased the flow evacuation velocity at the needle close that induced a more intense fuel cavitation and air ingestion inside the nozzle. The fuel dribbling process showed a high shot-toshot deviation. A statistical analysis of 50-shot results exhibited two breakup modes of fuel dribble determined by the flow evacuation velocity at the needle close and presence of air ingestion. In the first mode, the fast breakup with a short residence time of fuel dribble occurred. Meanwhile, the dripping of undisturbed liquid column with a long residence time of fuel dribble occurred in the second mode. An increase in injection pressure increased the population of the first mode due to more intense air ingestion that primarily caused by an increase in needle closing speed other than an increase in peak injection velocity. Based on the results, the formation mechanism and control strategies of the fuel dribble from modern diesel injectors were discussed.},
doi = {10.1016/j.apenergy.2016.06.116},
journal = {Applied Energy},
number = ,
volume = 179,
place = {United States},
year = 2016,
month =
}
  • Fuel phys­i­cal prop­er­ties are known to in­flu­ence in-noz­zle flow be­hav­ior, in turn af­fect­ing spray for­ma­tion in in­ter­nal com­bus­tion en­gines. A se­ries of 3D sim­u­la­tions was per­formed to model the in­ter­nal noz­zle flow in a five-hole mini-sac diesel in­jec­tor. The goal of the study was to eval­u­ate the be­hav­ior of two gaso­line-like fu­els (full-range naph­tha and light naph­tha) and com­pare them against n-Do­de­cane, se­lected from a palette used as a diesel sur­ro­gate. Sim­u­la­tions were car­ried out us­ing a multi-phase flow rep­re­sen­ta­tion based on the mix­ture model as­sump­tion with the Vol­ume of Fluid (VOF) method, and in­clud­ing cav­i­ta­tion ef­fects by means ofmore » the Ho­mo­ge­neous Re­lax­ation Model (HRM). Val­i­dated method­olo­gies from our pre­vi­ous stud­ies were em­ployed to ac­count for full nee­dle mo­tion. De­tailed sim­u­la­tions re­vealed the in­flu­ence of the fuel prop­er­ties on in­jec­tor per­for­mance, in­jected fuel en­ergy and propen­sity to cav­i­ta­tion. The three fu­els were com­pared with re­spect to global pa­ra­me­ters such as mass flow rate and area con­trac­tion co­ef­fi­cients, and lo­cal pa­ra­me­ters such as pres­sure and ve­loc­ity dis­tri­b­u­tion in­side the sac and ori­fices. Para­met­ric in­ves­ti­ga­tions were also per­formed to un­der­stand the fuel re­sponse to changes in the fuel in­jec­tion tem­per­a­ture, in­jec­tion pres­sure, and geom­e­try de­tails. Cav­i­ta­tion mag­ni­tude was ob­served to be strongly as­so­ci­ated with the val­ues of sat­u­ra­tion pres­sure. Ow­ing to their higher volatil­ity, the two gaso­line-like fu­els were ob­served to cav­i­tate more than n-Do­de­cane across all the in­ves­ti­gated con­di­tions. While at full nee­dle lift cav­i­ta­tion was re­duced for all fu­els, dur­ing the in­jec­tion tran­sients the gaso­line-like fu­els showed more propen­sity to cav­i­tate in­side the ori­fice and seat re­gions. This is ex­pected to have a pro­found in­flu­ence on noz­zle ero­sion. Al­though full-range and light naph­tha have lower den­si­ties com­pared to n-Do­de­cane, ow­ing to their lower vis­cos­ity, the mass flow rate dif­fer­ences be­tween the naph­tha fu­els and n-Do­de­cane were small. In conclusion, the analy­sis of fuel en­ergy con­tent showed that the higher lower heat­ing value (LHV) of light naph­tha helped com­pen­sate for the slightly lower to­tal de­liv­ered mass.« less
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  • Coal-water-slurry (CWS) engine tests designed to evaluate a new accumulator-based injection system are described in this paper The new injection system was found to improve CWS burnout considerably at both full and part engine loads. The peak cylinder firing pressure when operating with CWS was no higher than when operating with diesel oil. These data demonstrates the improved engine performance that can be achieved with the accumulator-based injection system.
  • Low-temperature combustion of diesel fuel was studied in a heavy-duty, single-cylinder optical engine employing a 15-hole, dual-row, narrow-included-angle nozzle (10 holes x 70/mD and 5 holes x 35/mD) with 103-/gmm-diameter orifices. This nozzle configuration provided the spray targeting necessary to contain the direct-injected diesel fuel within the piston bowl for injection timings as early as 70/mD before top dead center. Spray-visualization movies, acquired using a high-speed camera, show that impingement of liquid fuel on the piston surface can result when the in-cylinder temperature and density at the time of injection are sufficiently low. Seven single- and two-parameter sweeps around amore » 4.82-bar gross indicated mean effective pressure load point were performed to map the sensitivity of the combustion and emissions to variations in injection timing, injection pressure, equivalence ratio, simulated exhaust-gas recirculation, intake temperature, intake boost pressure, and load. High-speed movies of natural luminosity were acquired by viewing through a window in the cylinder wall and through a window in the piston to provide quasi-3D information about the combustion process. These movies revealed that advanced combustion phasing resulted in intense pool fires within the piston bowl, after the end of significant heat release. These pool fires are a result of fuel-films created when the injected fuel impinged on the piston surface. The emissions results showed a strong correlation with pool-fire activity. Smoke and NO/dx emissions rose steadily as pool-fire intensity increased, whereas HC and CO showed a dramatic increase with near-zero pool-fire activity.« less