Effects of primary breakup modeling on spray and combustion characteristics of compression ignition engines

Journal Article · Tue Jun 15 04:00:00 EDT 2010 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2010.02.018· OSTI ID:21318368

Som, S; Aggarwal, S K ^[1]

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1. Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL 60607 (United States)

Injector flow dynamics and primary breakup processes are known to play a pivotal role in determining combustion and emissions in diesel engines. In the present study, we examine the effects of primary breakup modeling on the spray and combustion characteristics under diesel engine conditions. The commonly used KH model, which considers the aerodynamically induced breakup based on the Kelvin-Helmholtz instability, is modified to include the effects of cavitation and turbulence generated inside the injector. The KH model and the new (KH-ACT) model are extensively evaluated by performing 3-D time-dependent simulations with detailed chemistry under diesel engine conditions. Results indicate that the inclusion of cavitation and turbulence enhances primary breakup, leading to smaller droplet sizes, decrease in liquid penetration, and increase in the radial dispersion of spray. Predictions are compared with measurements for non-evaporating and evaporating sprays, as well as with flame measurements. While both the models are able to reproduce the experimentally observed global spray and combustion characteristics, predictions using the KH-ACT model exhibit closer agreement with measurements in terms of liquid penetration, cone angle, spray axial velocity, and liquid mass distribution for non-evaporating sprays. Similarly, the KH-ACT model leads to better agreement with respect to the liquid length and vapor penetration distance for evaporating sprays, and with respect to the flame lift-off location for combusting sprays. The improved agreement is attributed to the ability of the new model to account for the effects of turbulence and cavitation generated inside the injector, which enhance the primary breakup. Results further indicate that the combustion under diesel engine conditions is characterized by a double-flame structure with a rich premixed reaction zone near the flame stabilization region and a non-premixed reaction zone further downstream. This flame structure is consistent with the Dec's model for diesel engine combustion (Dec, 1997), and well captured by a newly developed flame index based on the scalar product of CO and O{sub 2} mass fraction gradients. (author)

• OSTI ID: 21318368
• Journal Information: Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 6 Vol. 157; ISSN CBFMAO; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

33 ADVANCED PROPULSION SYSTEMS
CARBON MONOXIDE
CAVITATION
COMBUSTION
COMPARATIVE EVALUATIONS
COMPRESSION
COMPUTERIZED SIMULATION
DIESEL ENGINES
DISTANCE
DROPLETS
Diesel combustion
EXHAUST GASES
FLAMES
FORECASTING
Flame lift-off
HELMHOLTZ INSTABILITY
IGNITION
Kelvin-Helmholtz model
LENGTH
MASS
MASS DISTRIBUTION
MATHEMATICAL MODELS
Primary breakup
SIZE
SPRAYS
STABILIZATION
THREE-DIMENSIONAL CALCULATIONS
TIME DEPENDENCE
TURBULENCE
VAPORS
VELOCITY
ZONES