Predictions of Charge Drift in a Concept Electrosprayed DISI Engine

[+] Author and Article Information
Geraldo C. S. Nhumaio

School of Mechanical, Aerospace and Civil Engineering, University of Manchester, Sackville Street, P.O.Box 88, Manchester, M60 1QD, UKgeraldo.nhumaio@talk21.com

A. Paul Watkins

School of Mechanical, Aerospace and Civil Engineering, University of Manchester, Sackville Street, P.O.Box 88, Manchester, M60 1QD, UK

The flow is of compressed turbulence type where the effects of compression enter the dissipation of turbulence kinetic energy equation through the source term.

Charge induction is used to charge(semi) conducting liquids. In the present case of hydrocarbons the technique used is charge injection, in which the charging electrode is embedded into the fluid.

J. Fluids Eng 128(5), 903-912 (Jan 31, 2006) (10 pages) doi:10.1115/1.2243299 History: Received September 29, 2005; Revised January 31, 2006

Limited to nonvaporizing spray cases, this work discusses the transport of charged droplets within a cylinder of a motored axisymmetric model electrosprayed direct injection spark ignition (eDISI) engine with electrified walls. The concept engine investigated here is assumed to operate with an electrostatic atomizer previously studied for application in fuel burners [Yule, 1994, Fuel, 74(7), pp. 1094–1103]. A split/multiple injection strategy is employed in which three pulses of 5mg each are made at crank angles of 80, 150 and 300 deg ATDC of the intake, which fall within the intervals for stable combustion of either early or late injection modes of operation of DISI engines [Jackson, 1997, SAE Paper No. 970543]. The direct Simulation Monte Carlo (DSMC) approach embodied in an in-house CFD research code is used to simulate the discrete phase flow with the electrical charge distribution for different instants within the computational cells being computed by simple addition of the droplet charges residing in particular cells at particular instants of time. It is shown in the half engine cycle investigated that the use of charged sprays in eDISI engines may help to reduce the in-cylinder wall-wetting phenomenon. In addition, pockets of highest electrical charge are found to populate the region near the spark plug by 345 deg CA, which may be a path for improved combustion efficiency.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Illustration of charge induction (left) and charge injection (right) techniques used for semi-conducting liquids and insulators, respectively. (a) Charge induction technique: used in fluids with resistivities in the range 104 to 106Ωm, e.g. agricultural, coat and paint spraying and xerocopy, laser and ink jet printing. The polarity of charged droplets is opposite to that of the charging field. (b) Charge injection technique: used in fluids with resistivities in the range 1012 to 1016Ωm, e.g. hydrocarbon fuels. The polarity of charged droplets is the same as that of the charging field. Negative (electron emission) potential is favored over positive potential (field ionization), since it requires field intensities lower by a factor of ∼10 to inject the same amount of charge (1).

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Figure 2

Image charges at the interface between two dielectrics (16)

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Figure 3

Droplet frequency distributions derived from charge induction (22)

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Figure 4

Simplified geometry of the investigated concept eDISI engine

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Figure 5

Tested cases for grid calibration

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Figure 6

Computational grid used in the study with the piston near the TDC (a) and BDC (b), respectively

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Figure 7

Distribution of the injected spray for numerical validation

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Figure 8

PDA measured (23) and computed U and V velocity profiles for 1.67cm3∕s and −1.80C∕m3 using a 250μm diameter atomizer orifice

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Figure 9

Cumulative number of piston-impinging droplet parcels of an uncharged spray during the intake stroke

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Figure 10

Droplet locations and gas velocity vectors of uncharged (left) and charged (right) cases at different stations of the flow development

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Figure 11

Charge distribution (in μC) as function of time

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Figure 12

Film thickness on the piston surface 2ms after the third pulse of uncharged and charged sprays

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Figure 13

Cumulative number of impinging drop parcels from a charged spray subjected to various electrical boundary conditions

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Figure 14

Droplet locations and gas velocity vectors for a charged spray with neutral boundaries at the station 225deg CA




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