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 $\Delta .Math.P_y=\left(\frac{E}{V_y\pm \Delta .Math.V_y}\right).Math.\left(\frac{d.Math.\Delta .Math.V_y}{d.Math.t}-Q_{o.Math.u.Math.t}\right)$ 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: $F=\left[\begin{array}{c}F\left(0\right)\\ F(\Delta .Math.L)\\ F(\Delta .Math.L+\Delta .Math.L)\\ \mathrm{.Math.}\\ F\left(L\right)\end{array}\right];$ a reverse pressure fluctuation from the current length of ΔL: $R=\left[\begin{array}{c}R\left(L\right)\\ R(L-\Delta .Math.L)\\ \mathrm{.Math.}\\ R(\Delta .Math.L)\\ R\left(0\right)\end{array}\right];$ 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)]/(αφ; (c) the mathematical model of the fuel injector is specifically established as follows: calculating a fuel pressure change in the fuel sump as follows: $\Delta .Math.P_f=\left(\frac{E}{V_f\pm \Delta .Math.V_f}\right).Math.\left(Q_{\mathrm{in}}-Q_{o.Math.u.Math.t}.Math.\frac{d.Math.\Delta .Math.V_f}{d.Math.t}\right);$ 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: $\Delta .Math.P_{\mathrm{in}}=\left(\frac{E}{V_{\mathrm{in}}}\right).Math.\left(Q_{\mathrm{in}}-Q_{o.Math.u.Math.t}\right);$ 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; $Q_{\mathrm{in}}=\sqrt[1/2]{\frac{2.Math.\left(P_f-P_{\mathrm{in}}\right)}{\rho }}.Math.\mu .Math.A_{\mathrm{in}},$ wherein, A.sub.in is a flow area from the fuel sump to the pressure chamber; $Q_{\mathrm{out}}=\sqrt[1/2]{\frac{2.Math.\left(P_{\mathrm{in}}-P_0\right)}{\rho }}.Math.\mu .Math.A_{*},$ 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 $Q_{o.Math.u.Math.t}=v\left(0\right).Math.\frac{\pi .Math.d_{h.Math.p}^2}{4}$ 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 $Q_{\mathrm{in}}=v\left(L\right).Math.\frac{\pi .Math.d_{h.Math.p}^2}{4}$ 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

[0031] FIG. 1 is a flowchart of the disclosure.

[0032] FIG. 2 is a structural diagram of a fuel system.

[0033] FIG. 3 shows a comparison of simulation and experimental results of an injection pressure of the fuel system.

DETAILED DESCRIPTION

[0034] The disclosure is described in detail below with reference to the accompanying drawings and examples.

[0035] 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:

[0036] Step 1, set initial parameters of a system model, including:

[0037] 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.

[0038] 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

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

[0039] 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;

[0040] where, after boosting, a fuel pressure changes to

[00010]$\begin{array}{cc}\Delta .Math..Math.P_y=\left(\frac{E}{V_y\pm \Delta .Math.V_y}\right).Math.\left(\frac{d.Math.\Delta .Math.V_y}{d.Math.t}-Q_{o.Math.u.Math.t}\right)& \left(1\right)\end{array}$

[0041] 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;

[0042] ΔV.sub.z=S.sub.2.Math.H, where, H is obtained according to a mechanical motion equation of the plunger;

[0043] (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:

[0044] 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:

[00011]$\begin{array}{cc}F=\left[\begin{array}{c}F\left(0\right)\\ F(\Delta .Math.L)\\ F(\Delta .Math.L+\Delta .Math.L)\\ \mathrm{.Math.}\\ F\left(L\right)\end{array}\right]& \left(2\right)\end{array}$

[0045] a reverse pressure fluctuation from the current length of ΔL:

[00012]$\begin{array}{cc}R=\left[\begin{array}{c}R\left(0\right)\\ R\left(\mathrm{\Delta L}\right)\\ R\left(\mathrm{\Delta L}+\Delta .Math.L\right)\\ \mathrm{.Math.}\\ R\left(L\right)\end{array}\right]& \left(3\right)\end{array}$

[0046] 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)

[0047] where, K is a dissipation factor, which is specifically calculated as follows:

[0048] 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:

[00013]$\begin{array}{cc}\mathrm{Re}=\frac{\stackrel{\_}{V}.Math..Math.d_{\mathrm{hp}}}{v}& \left(5\right)\end{array}$

[0049] where, V is the average flow velocity in the pipe, and v is a kinematic viscosity;

[0050] 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

[0051] obtain the dissipation factor according to

[00014]$\begin{array}{cc}K=\lambda .Math.\frac{V}{2.Math.d_{\mathrm{hp}}};& \left(6\right)\end{array}$

[0052] 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);

[0053] where, α is a speed of sound, and ρ is a fuel density;

[0054] (c) the mathematical model of the fuel injector is specifically established as follows:

[0055] calculate a fuel pressure change in the fuel sump as follows:

[00015]$\begin{array}{cc}\Delta .Math..Math.P_j=\left(\frac{E}{V_f\pm \Delta .Math.V_f}\right).Math.\left(Q_{\mathrm{in}}-Q_{o.Math.u.Math.t}+\frac{d.Math.\Delta .Math.V_f}{d.Math.t}\right)& \left(8\right)\end{array}$

[0056] 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;

[0057] calculate a fuel pressure change in the pressure chamber as follows:

[00016]$\begin{array}{cc}\Delta .Math..Math.P_{\mathrm{in}}=\left(\frac{E}{V_{\mathrm{in}}}\right).Math.\left(Q_{\mathrm{in}}-Q_{o.Math.u.Math.t}\right)& \left(9\right)\end{array}$

[0058] 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;

[00017]$\begin{array}{cc}{Q}_{\mathrm{in}}=\sqrt[1/2]{\frac{2.Math.\left(P_f-P_{\mathrm{in}}\right)}{\rho }}.Math.\mu .Math.A_{\mathrm{in}}& \left(10\right)\end{array}$

[0059] where, A.sub.in is a flow area from the fuel sump to the pressure chamber;

[00018]$\begin{array}{cc}{Q}_{\mathrm{out}}=\sqrt[1/2]{\frac{2.Math.\left(P_{\mathrm{in}}-P_0\right)}{\rho }}.Math.\mu .Math.A_{*}& \left(11\right)\end{array}$

[0060] where, P.sub.0 is an in-cylinder pressure, and A⋅ is a total area of the nozzle.

[0061] Step 3: connect input and output parameters of the established models to realize data transfer between the models:

[0062] apply

[00019]$Q_{o.Math.u.Math.t}=v\left(0\right).Math.\frac{\pi .Math.d_{h.Math.p}^2}{4}$

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)

[0063] apply

[00020]$Q_{\mathrm{in}}=v\left(L\right).Math.\frac{\pi .Math.d_{h.Math.p}^2}{4}$

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)

[0064] 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.

[0065] 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)

[0066] 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.