The study presents a one-dimensional, transient and compressible flow models of a commercial Common Rail Injector (CRI) and a prototype of a single-fuel Hydraulically actuated Electrically controlled Unit Injector (HEUI) developed at the University of New South Wales (UNSW) in conjunction with local industry. The unique feature of the UNSW HEUI is the fact that it uses diesel fuel as the driver for pressure amplification within the unit injector. The work undertaken is part of a wider study aimed at optimization of the design of diesel injectors for dual-fuel systems to reduce green house gas emissions. The contribution of this thesis is the development of the model of the UNSW HEUI injector, which can be used to investigate possible modifications of the injector for its use in dual-fuel injection systems.The developed models include electrical, mechanical and hydraulic subsystems present in the injectors. They are based on Kirchhoff??s laws, on the mass and momentum conservation equations and on the equilibrium of forces. The models were implemented in MATLAB/SIMULINK graphical software environment, which provides a high degree of flexibility and allows simulation of both linear and nonlinear elements. The models were used to perform sensitivity analysis of both injectors. The sensitivity analysis has revealed that the temperature of the solenoid coil is one of the critical parameters affecting the timing and the quantity of the fuel injection of both injectors. Additional critical parameters were found to be the dimensions of the piston of the CRI, the stiffness of the needle spring of the HEUI and the dimensions of the intensifier of the HEUI. The models also revealed that in the case of pilot injections the speed of the solenoid is the major limiting factor of the performance. The developed models provide better understanding of the issues and limitations of the injectors. They give detailed insight into their working principles. The investigations of the models permit making quantitative analysis of the timing of the HEUI solenoid and to evaluate the proposed change of the direction of the pressure acting on the HEUI solenoid plunger.
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