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Research Papers: Internal Combustion Engines

Development and Application of a Complete Multijet Common-Rail Injection-System Mathematical Model for Hydrodynamic Analysis and Diagnostics

[+] Author and Article Information
Andrea E. Catania, Alessandro Ferrari, Michele Manno

 IC Engines Advanced Laboratory, Politecnico di Torino, C.so Duca degli Abruzzi, 24 10129 - Torino (Italy)

J. Eng. Gas Turbines Power 130(6), 062809 (Aug 25, 2008) (13 pages) doi:10.1115/1.2925679 History: Received April 14, 2007; Revised October 15, 2007; Published August 25, 2008

A rather complete mathematical model for a common-rail injection-system dynamics numerical simulation was developed to support experimentation, layout, and control design, as well as performance optimization. The thermofluid dynamics of the hydraulic-system components, including rail, connecting pipes, and injectors was modeled in conjunction with the solenoid-circuit electromagnetics and the mechanics of mobile elements. One-dimensional flow equations in conservation form were used to simulate wave propagation phenomena throughout the high-pressure connecting pipes, including the feeding pipe of the injector nozzle. In order to simulate the temperature variations due to the fuel compressibility, the energy equation was used in addition to mass conservation and momentum balance equations. Besides, the possible cavitation phenomenon effects on the mass flow rate through the injector bleed orifice and the nozzle holes were taken into account. A simple model of the electromagnetic driving circuit was used to predict the temporal distribution of the force acting on the pilot-valve anchor. It was based on the experimental time histories of the current through the solenoid and of the associated voltage that is provided by the electronic control unit to the solenoid. The numerical code was validated through the comparison of the prediction results with experimental data, that is, pressure, injected flow rate, and needle lift time histories, taken on a high performance test bench Moehwald-Bosch MEP2000-CA4000. The novel injection-system mathematical model was applied to the analysis of transient flows through the hydraulic circuit of a commercial multijet second-generation common-rail system, paying specific attention to the wave propagation phenomena, to their dependence on solenoid energizing time and rail pressure, as well as to their effects on system performance. In particular, an insight was also given into the model capability of accurately predicting the wave dynamics effects on the rate and mass of fuel injected when the dwell time between two consecutive injections is varied.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Experimental hydraulic layout and transducers

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Figure 3

Pressure wave speed evaluation scheme

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Figure 4

Control plunger and nozzle

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Figure 5

Second order dynamic model for control plunger and needle

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Figure 7

Second order dynamic model for pilot valve

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Figure 8

Pilot-valve anchor and solenoid

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Figure 9

Electromagnetic model: (a) voltage and current at solenoid and (b) electromagnetic force on pilot valve

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Figure 10

Single injection (prail=1000bars,ET=1085μs): (a) pipe pressure at injector inlet, (b) injection flow rate, and (c) needle lift

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Figure 11

Single injection (prail=1000bars,ET=600μs): (a) pipe pressure at injector inlet and (b) injection flow rate

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Figure 12

Single injection (prail=1000bars,ET=1300μs): (a) pipe pressure at injector inlet and (b) injection flow rate

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Figure 13

Single injection (prail=1250bars,ET=1300μs): (a) pipe pressure at injector inlet and (b) injection flow rate

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Figure 14

Pilot and main injections (prail=1000bars,ETpil=300μs,ETmain=900μs): (a) pipe pressure at injector inlet (DT=1700μs), (b) injection flow rates (DT=1700μs), (c) pipe pressure at injector inlet (DT=2050μs), and (d) injection flow rates (DT=2050μs)

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Figure 15

Main and post injections (prail=1000bars,ETmain=800μs,ETpost=400μs): (a) pipe pressure at injector inlet (DT=850μs), (b) injection flow rates (DT=850μs), (c) pipe pressure at injector inlet (DT=1350μs), and (d) injection flow rates (DT=1350μs)

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