An investigation into the characteristics and optimisation of a high-pressure common rail injection system

  • Nao Hu

Student thesis: Doctoral Thesis

Abstract

The primary aim of this research was to predict the emissions and fuel savings when replacing a mechanical fuel oil injection system with a high pressure common rail one. The work in this study consists of two parts. In the first part, a novel routine is proposed for the optimisation of electronic fuel injectors and their dynamic response, including the needle valve opening delay and the needle valve closing delay (The needle valve opening delay refers to the delay between the control signal being trigged and the needle valve being fully open; the needle valve closing delay refers to the delay between the control signal deactivating and the needle valve being fully closed).Two injectors (Type-I and Type-II) were included; their one-dimensional (1D) models were built in AMESim software and validated respectively.A parametric study on the Type-I fuel injector was conducted before the optimisation process in order to examine the effects of various parameters including the control piston diameter (CPD), control oil (i.e. the fuel oil used for control in a typical solenoid electronic fuel injector) inlet passage diameter (IPD) and control oil outlet passage diameter (OPD) on injection characteristics, i.e. injection rate, injection mass, needle valve lift and control chamber pressure.Then, the optimisation of the injector dynamic response was investigated by the proposed routine in modeFRONTIER software. In detail, the routine included the following steps: First, a random sequence was adopted in the design of experiment (DOE) type. Then, an NSGA-II (Non-dominated Sorting Genetic Algorithm II) algorithm was selected. Next, a whole electronic fuel injector model was chosen, where the displacements of the needle valve were generated.These data were first written into an input file, and to do this, appropriate writing and reading rules needed to be developed. The text file was read by the MATLAB code, where the control signal and needle valve displacement timings were calculated. The valve opening delay and the valve closing delay were thus obtained from these timings. Additionally, a constraint was set between the control oil inlet passage diameter and control oil outlet passage diameter in that the former should be smaller than the latter in each run.The CPD, OPD and IPD were the three design parameters to be varied in the optimisation process of the Type-I fuel injector at a specific rail pressure. However, three more design parameters (the spring preload force (SPF), nozzle orifice number (NZN) and nozzle orifice diameter (NZD)) were involved in the optimisation process of the Type-II fuel injector under three different rail pressures (80 MPa, 120 MPa and 160 MPa).The optimal design with the best trade-off between the valve opening delay and the valve closing delay of each fuel injector was singled out via a scattering chart. Results show that the optimum Type-I fuel injector achieved reductions of 40% and 25% of the baseline design on the valve opening delay and valve closing delay respectively. The optimal design of the Type-II fuel injector also achieved a huge reduction at all three rail pressures.Specifically, the valve opening delay was reduced by 29.8%, 29.2% and 20.9%, and the valve closing delay was reduced by 25.6%, 24.5% and 30.1% at 80 MPa, 120 MPa and 160 MPa rail pressures respectively. RSM (response surface method) contour maps were used to study the interactions between design parameters. Results indicated that the CPD, IPD and OPD and their interactions are influential design parameters for the valve opening delay, while the IPD has a dominant effect on the valve closing delay.. A large CPD together with a large IPD was found to increase the valve opening delay dramatically. Surprisingly, the effects of the spring preload force (SPF) on the valve closing delay are noticeable at low rail pressures. The valve closing d
Date of Award1 Mar 2016
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsLloyds Register of Shipping & University of Strathclyde
SupervisorPeilin Zhou (Supervisor) & (Supervisor)

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