Simulation method for two-stage plunger pressurized common rail fuel system of marine low-speed engine

Abstract

An objective of the disclosure is to provide a simulation method for a two-stage plunger pressurized common rail fuel system of a marine low-speed engine. The method includes: first setting initial status parameters, such as a control step of a system model, a total time of a calculation process, and structure parameters and pressures of components; and then establishing a mathematical model of a fuel booster unit, a mathematical model of a high-pressure fuel pipe and a mathematical model of a fuel injector based on a MATLAB simulation platform, and connecting input and output parameters of the models to realize data transfer between the models. By considering one-dimensional (1D) spatial fluctuations in the high-pressure fuel pipe, the disclosure establishes a high-precision model of the fuel system, which provides an effective method for designing and calculating detailed pressures in the common rail fuel system.

Claims

1. A simulation method for a two-stage plunger pressurized common rail fuel system of a marine low-speed engine, comprising the following steps: (1) setting initial parameters, such as a control step N.sub.t of the system, a total time N.sub.T (0<N.sub.t≤N.sub.T) of a calculation process, and structure parameters and pressures of a booster unit, a high-pressure fuel pipe and a fuel injector; (2) establishing a mathematical model of the fuel system, comprising a mathematical model of a fuel booster unit, a mathematical model of a high-pressure fuel pipe and a mathematical model of a fuel injector; and (3) connecting input and output parameters of the established models to realize data transfer between the established models: calculating real-time pressure changes and pressures of fuel flowing through each part of the fuel system in one step N.sub.t, and obtaining an injection pressure at this step; performing an iterative calculation on the fuel system model in N.sub.T/N.sub.t steps based on the status parameters in a previous step, to obtain injection pressure data for an entire working process of the fuel system.

2. The simulation method for a two-stage plunger pressurized common rail fuel system of a marine low-speed engine according to claim 1, wherein in step (1), the initial parameters that need to be set comprise: a control step N.sub.t of the system, a total time N.sub.T (0<N.sub.t≤N.sub.T) of a calculation process, a common rail servo oil pressure P.sub.s, diameters D.sub.1 and D.sub.2 of large and small plungers in the booster unit, a volume V.sub.y of a fuel booster chamber, a length L and diameter d.sub.hp of the high-pressure fuel pipe, and a volume V.sub.f of a fuel sump and a volume V.sub.in of a pressure chamber in the fuel injector.

3. The simulation method for a two-stage plunger pressurized common rail fuel system of a marine low-speed engine according to claim 1, wherein in step (2), the established mathematical model of the fuel system comprises a mathematical model of the fuel booster unit, a mathematical model of the high-pressure fuel pipe and a mathematical model of the fuel injector: (a) the mathematical model of the fuel booster unit is specifically established as follows: setting an electromagnetic signal I to drive a two-position three-way solenoid valve in the fuel booster unit to switch between open and close states to boost the low-pressure fuel; wherein, after boosting, a fuel pressure changes to $\Delta P_y=\left(\frac{E}{V_y\pm \Delta V_y}\right)\left(\frac{d\Delta V_y}{dt}-Q_{out}\right)$ wherein, ΔV.sub.z is a volume change of the fuel booster chamber, and Q.sub.out is a flow rate of fuel flowing into the high-pressure fuel pipe; (b) by considering one-dimensional (1D) fluctuations in a high-pressure fuel pipe, the mathematical model of the high-pressure fuel pipe is specifically established as follows: dividing a flow in the high-pressure fuel pipe according to a spatial length into sections for solving, to obtain: a forward pressure fluctuation in one control step N.sub.t in the length of L from a length of ΔL: $F=\left[\begin{array}{c}F\left(0\right)\\ F(\Delta L)\\ F(\Delta L+\Delta L)\\ \mathrm{.Math.}\\ F\left(L\right)\end{array}\right];$ a reverse pressure fluctuation from the current length of ΔL: $R=\left[\begin{array}{c}R\left(L\right)\\ R(L-\Delta L)\\ \mathrm{.Math.}\\ R(\Delta L)\\ R\left(0\right)\end{array}\right];$ forward and reverse pressure fluctuations in N.sub.T/N.sub.t steps from N.sub.t:
Fnd(L*+ΔL)=F(L*).Math.e.sup.−KN′, and Rnd(L*+ΔL)=R(L*).Math.e.sup.−KN′; wherein, K is a dissipation factor; and obtaining flow rates at an inlet and an outlet of the high-pressure fuel pipe as follows:
v(0)=[F(0)+R(0)]/(αρ), and v(L)=[F(L)+R(L)]/(αρ); (c) the mathematical model of the fuel injector is specifically established as follows: calculating a fuel pressure change in the fuel sump as follows: $\Delta P_f=\left(\frac{E}{V_f\pm \Delta V_f}\right)\left(Q_{\mathrm{in}}-Q_{out}\frac{d\Delta V_f}{dt}\right);$ wherein, ΔV.sub.f is a volume change of the fuel sump, Q.sub.in is a flow rate of fuel flowing from the high-pressure fuel pipe into the fuel sump, and Q.sub.out is a flow rate of fuel flowing into the pressure chamber; calculating a fuel pressure change in the pressure chamber as follows: $\Delta P_{\mathrm{in}}=\left(\frac{E}{V_{\mathrm{in}}}\right)\left(Q_{\mathrm{in}}-Q_{out}\right);$ wherein, Q.sub.in is a flow rate of fuel flowing from the fuel sump into the pressure chamber, and Q.sub.out is a flow rate of fuel injected from a nozzle; $Q_{\mathrm{in}}=\sqrt[1/2]{\frac{2\left(P_f-P_{\mathrm{in}}\right)}{\rho }}.Math.\mu .Math.A_{\mathrm{in}},$ wherein, A.sub.in is a flow area from the fuel sump to the pressure chamber; $Q_{\mathrm{out}}=\sqrt[1/2]{\frac{2\left(P_{\mathrm{in}}-P_0\right)}{\rho }}.Math.\mu .Math.A_{*},$ wherein, P.sub.0 is an in-cylinder pressure, and A* is a total area of the nozzle.

4. The simulation method for a two-stage plunger pressurized common rail fuel system of a marine low-speed engine according to claim 1, wherein in step (3), the connecting input and output parameters of the established models to realize data transfer between the models specifically comprises: applying $Q_{out}=v\left(0\right).Math.\frac{\pi .Math.d_{hp}^2}{4}$ to calculate a fuel pressure change ΔP.sub.y, to obtain a real-time fuel pressure in the booster chamber:
P.sub.y=P.sub.y0+ΔP.sub.y; applying $Q_{\mathrm{in}}=v\left(L\right).Math.\frac{\pi .Math.d_{hp}^2}{4}$ to calculate a fuel pressure change ΔP.sub.f, to obtain a real-time fuel pressure in the fuel sump:
P.sub.f=P.sub.f0+ΔP.sub.f; calculating real-time pressure changes and pressures of fuel flowing through each part of the fuel system in one step N.sub.t, and obtaining an injection pressure at this step; performing an iterative calculation on the fuel system model in N.sub.T/N.sub.t steps based on the status parameters in a previous step, to obtain injection pressure data for an entire working process of the fuel system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flowchart of the disclosure.

(2) FIG. 2 is a structural diagram of a fuel system.

(3) FIG. 3 shows a comparison of simulation and experimental results of an injection pressure of the fuel system.

DETAILED DESCRIPTION

(4) The disclosure is described in detail below with reference to the accompanying drawings and examples.

(5) As shown in FIGS. 1 to 3, the disclosure provides a modeling and simulation method for a two-stage plunger pressurized common rail fuel system of a marine low-speed engine. According to the overall flowchart as shown in FIG. 1, the method specifically includes the following steps:

(6) Step 1, set initial parameters of a system model, including:

(7) a control step N.sub.t of the system, a total time N.sub.T (0<N.sub.t≤N.sub.T) of a calculation process, a common rail servo oil pressure P.sub.s, diameters D.sub.1 and D.sub.2 of large and small plungers in the booster unit, a volume V.sub.y of a fuel booster chamber, a length L and diameter d.sub.hp of the high-pressure fuel pipe, a volume V.sub.f of a fuel sump and a volume V.sub.in of a pressure chamber in the fuel injector, a parameter of a needle valve component, and other related parameters.

(8) Step 2: establish a mathematical model of the fuel system, including a mathematical model of the fuel booster unit, a mathematical model of the high-pressure fuel pipe and a mathematical model of the fuel injector, where

(9) (a) the mathematical model of the fuel booster unit is specifically established as follows:

(10) set an electromagnetic signal I to drive a two-position three-way solenoid valve in the fuel booster unit to switch between open and close states to boost the low-pressure fuel;

(11) where, after boosting, a fuel pressure changes to

(12) 0$\begin{array}{cc}\Delta P_y=\left(\frac{E}{V_y\pm \Delta V_y}\right)\left(\frac{d\Delta V_y}{dt}-Q_{out}\right)& \left(1\right)\end{array}$

(13) where, ΔV.sub.z is a volume change of the fuel booster chamber, and Q.sub.out is a flow rate of fuel flowing into the high-pressure fuel pipe;

(14) ΔV.sub.z=S.sub.2.Math.H, where, H is obtained according to a mechanical motion equation of the plunger;

(15) (b) by considering one-dimensional (1D) fluctuations in the high-pressure fuel pipe, the mathematical model of the high-pressure fuel pipe is specifically established as follows:

(16) divide a flow in the high-pressure fuel pipe according to a spatial length into sections for solving, to obtain: a forward pressure fluctuation in one control step N.sub.t in the length of L from a length of ΔL:

(17) $\begin{array}{cc}F=\left[\begin{array}{c}F\left(0\right)\\ F(\Delta L)\\ F(\Delta L+\Delta L)\\ \mathrm{.Math.}\\ F\left(L\right)\end{array}\right]& \left(2\right)\end{array}$

(18) a reverse pressure fluctuation from the current length of ΔL:

(19) $\begin{array}{cc}R=\left[\begin{array}{c}R\left(L\right)\\ R\left(L+\Delta L\right)\\ \mathrm{.Math.}\\ R\left(\Delta L\right)\\ R\left(0\right)\end{array}\right]& \left(3\right)\end{array}$

(20) forward and reverse pressure fluctuations in N.sub.T/N.sub.t steps from N.sub.t:
Fnd(L*+ΔL)=F(L*).Math.e.sup.−KN′, and Rnd(L*+ΔL)=R(L*).Math.e.sup.−KN′  (4)

(21) where, K is a dissipation factor, which is specifically calculated as follows:

(22) assume that the flow in the pipe is a turbulent flow, and calculate a Reynolds number based on a current average flow velocity in the pipe according to the following formula:

(23) $\begin{array}{cc}\mathrm{Re}=\frac{\stackrel{\_}{V}{d}_{\mathrm{hp}}}{v}& \left(5\right)\end{array}$

(24) where, V is the average flow velocity in the pipe, and v is a kinematic viscosity;

(25) calculate a resistance coefficient λ of the fuel pipe according to a semi-empirical formula of the target fuel pipe, after obtaining the current Reynolds number; and

(26) obtain the dissipation factor according to

(27) $\begin{array}{cc}K=\lambda \frac{\stackrel{\_}{V}}{2d_{\mathrm{hp}}};& \left(6\right)\end{array}$

(28) obtain flow rates at an inlet and an outlet of the high-pressure fuel pipe as follows:
v(0)=[F(0)+R(0)]/(αρ), and v(L)=[F(L)+R(L)]/(αρ)  (7);

(29) where, α is a speed of sound, and ρ is a fuel density;

(30) (c) the mathematical model of the fuel injector is specifically established as follows:

(31) calculate a fuel pressure change in the fuel sump as follows:

(32) $\begin{array}{cc}\Delta P_f=\left(\frac{E}{V_f\pm \Delta V_f}\right)\left(Q_{\mathrm{in}}-Q_{out}+\frac{d\Delta V_f}{dt}\right)& \left(8\right)\end{array}$

(33) where, ΔV.sub.f is a volume change of the fuel sump, Q.sub.in is a flow rate of fuel flowing from the high-pressure fuel pipe into the fuel sump, and Q.sub.out is a flow rate of fuel flowing into the pressure chamber;

(34) calculate a fuel pressure change in the pressure chamber as follows:

(35) $\begin{array}{cc}\Delta P_{\mathrm{in}}=\left(\frac{E}{V_{\mathrm{in}}}\right)\left(Q_{\mathrm{in}}-Q_{out}\right)& \left(9\right)\end{array}$

(36) where, Q.sub.in is a flow rate of fuel flowing from the fuel sump into the pressure chamber, and Q.sub.out is a flow rate of fuel injected from a nozzle;

(37) $\begin{array}{cc}{Q}_{\mathrm{in}}=\sqrt[1/2]{\frac{2\left(P_f-P_{\mathrm{in}}\right)}{\rho }}.Math.\mu .Math.A_{\mathrm{in}}& \left(10\right)\end{array}$

(38) where, A.sub.in is a flow area from the fuel sump to the pressure chamber;

(39) $\begin{array}{cc}{Q}_{\mathrm{out}}=\sqrt[1/2]{\frac{2\left(P_{\mathrm{in}}-P_0\right)}{\rho }}.Math.\mu .Math.A_{*}& \left(11\right)\end{array}$

(40) where, P.sub.0 is an in-cylinder pressure, and A* is a total area of the nozzle.

(41) Step 3: connect input and output parameters of the established models to realize data transfer between the models:

(42) apply

(43) $Q_{out}=v\left(0\right).Math.\frac{\pi .Math.d_{hp}^2}{4}$
to calculate a fuel pressure change ΔP.sub.y, to obtain a real-time fuel pressure in the booster chamber:
P.sub.y=P.sub.y0+ΔP.sub.y  (12)

(44) apply

(45) 0$Q_{\mathrm{in}}=v\left(L\right).Math.\frac{\pi .Math.d_{hp}^2}{4}$
to calculate a fuel pressure change ΔP.sub.f, to obtain a real-time fuel pressure in the fuel sump:
P.sub.f=P.sub.f0+ΔP.sub.f  (13)

(46) calculating real-time pressure changes and pressures of fuel flowing through each part of the fuel system in one step N.sub.t, and obtaining an injection pressure at this step; performing an iterative calculation on the fuel system model in N.sub.T/N.sub.t steps based on the status parameters in a previous step, to obtain injection pressure data for an entire working process of the fuel system.

(47) Assuming j is a number of iterations, then an injection pressure is as follows:
P.sub.in(j+1)=P.sub.in(j)+ΔP.sub.in  (14)

(48) FIG. 3 shows a comparison of simulation and experimental results of the injection pressure of the fuel system, which indicates that the pressure fluctuations have good consistency.