Three-dimensional pressure field measurement method for spray flame measurement in optical engine

Abstract

The invention discloses a three-dimensional pressure field measurement method for spray flame measurement in an optical engine, and belongs to the technical field of optical imaging applied to spray flame measurement in the optical engine. The implementation method comprises the following steps of: establishing a Cartesian coordinate system in the transparent cylinder of the optical engine, and applying a tomographic particle image velocity measurement method to the diagnosis of a spray flow field or a flame combustion process in the transparent cylinder of the optical engine; and calculating first-order derivatives of the three-dimensional velocity field distribution in time and three space directions. And substituting the first-order derivatives of time and space into a Navier Stokes equation to calculate and obtain pressure gradient field distribution in three space directions. And calculating the three-dimensional pressure relative distribution of the whole space to be measured relative to the pressure reference point through a direct integration method. A real pressure value at the pressure reference point is determined through a cylinder pressure sensor in the optical engine, and then three-dimensional pressure field distribution of the whole space to be measured is obtained.

Description

[0001] This invention belongs to the field of optical imaging technology applied to the measurement of spray flames inside optical engines, and particularly relates to a three-dimensional pressure field measurement method. Background Technology

[0002] With the continuous development of engine diagnostic technology, optical testing has become a widely adopted method both domestically and internationally for analyzing the internal working processes of engines. Compared with traditional invasive measurements, optical testing can negligibly disturb the in-cylinder flow and combustion processes, and can obtain more comprehensive experimental data on faster time scales and multi-dimensional spatial scales. In the past decade, with the improvement of testing equipment performance and the refinement of computational imaging technology, optical measurement technology has gradually expanded from traditional one-dimensional (single-point or single-line) and two-dimensional (planar) measurements to three-dimensional spatial measurements to meet the measurement requirements of high turbulence and strong spatial specificity of internal engine processes. However, since the principle of optical testing technology is to directly measure specific optical signals (such as chemiluminescence, Rayleigh / Raman / Mie scattering, laser-induced fluorescence / incandescence / breakdown spectroscopy, etc.) to quantitatively calculate the physical parameters of the measured area (such as velocity, temperature, free radical concentration, etc.), it is indirect in terms of data acquisition and requires a strong correspondence between the measured physical parameters and the optical signals (e.g., the laser-induced fluorescence signal of OH free radicals has an approximately linear relationship with the free radical concentration, and the spatial distribution of particle Mie scattering signals can be used to directly calculate the velocity field distribution). Due to the indirect nature of optical testing, the measurement difficulty will increase significantly when calculating physical parameters (such as pressure) that are weakly correlated with the intensity of optical signals. The spatial resolution of the measurement results will decrease significantly, or even become dimensional, and may introduce large experimental errors, making it impossible to meet the measurement needs of complex internal processes of internal combustion engines.

[0003] On the other hand, the spatial distribution and dynamic changes of in-cylinder pressure during the operation of an internal combustion engine are crucial for engine design and performance optimization. Under normal operating conditions, although most simulation results show that the internal pressure of an internal combustion engine is basically uniform at various times, for certain key steps, such as spraying and ignition, the pressure field simulation results show significant spatial inhomogeneity. This non-uniform pressure distribution changes rapidly over time, significantly affecting the phase change, diffusion, and mixing processes of fuel in the spray, as well as the development and propagation of the initial ignition nucleus, thus altering the engine's heat release patterns and operating efficiency. Therefore, accurately measuring the in-cylinder pressure field at various times under normal operating conditions is beneficial for analyzing the engine spraying and combustion processes at a microscopic scale, thereby diagnosing and predicting engine performance. For abnormal in-cylinder pressure conditions occurring under certain extreme conditions (such as gasoline engine knocking, super knocking, and diesel engine rough combustion), pressure field measurement can quickly resolve the transient three-dimensional pressure distribution, thereby determining the spatial location of pressure fluctuations and monitoring their propagation patterns, providing experimental evidence for improving internal combustion engine combustion strategies and combustion chamber structures. Therefore, developing a three-dimensional full-dimensional transient pressure field quantitative measurement technology for the complex in-cylinder pressure distribution of internal combustion engines under multiple operating conditions is an important development method in the field of engine optical diagnostics. Summary of the Invention

[0004] Existing pressure field distribution measurement techniques do not consider the impact of the three-dimensionality of complex flow fields on the spatial pressure field distribution, and can only measure single-point or two-dimensional pressure field distributions. The purpose of this invention is to provide a three-dimensional pressure field measurement method for measuring spray flames inside optical engines. This method obtains the three-dimensional velocity field distribution of the measured space through tomographic particle velocimetry. The first derivatives of the three-dimensional velocity field with respect to time and space are substituted into the Navier-Stokes equations to obtain the spatial pressure field gradient distribution. Through direct integration, the relative pressure field distribution of the entire field within the measured area relative to a pressure reference point is obtained. The true pressure at the pressure reference point is determined based on the pressure values ​​measured by the sensor, thus obtaining the three-dimensional pressure field distribution of the entire field. Because tomographic particle velocimetry has high temporal resolution, this invention has the advantage of transient measurement and can meet the measurement requirements of high-turbulence flow fields. Due to the convenience and ease of operation of the direct integration method, this invention has the advantages of low computational cost and high computational efficiency.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] To address the diagnostic problem of spray flow field and flame combustion process within the transparent cylinder of an optical engine, this invention discloses a three-dimensional pressure field measurement method for measuring spray flames within an optical engine. A Cartesian coordinate system is established inside the transparent cylinder of the optical engine, and existing tomographic particle image velocimetry technology is applied to diagnose the spray flow field or flame combustion process inside the transparent cylinder, obtaining a high-time-resolution three-dimensional velocity field distribution within the cylinder. The first derivatives of the three-dimensional velocity field distribution with respect to time and three spatial directions are calculated using the central difference method. These first derivatives with respect to time and space are then substituted into the Navier-Stokes equations to calculate the pressure gradient field distribution in the three spatial directions. The three-dimensional relative pressure distribution of the entire test space with respect to a pressure reference point is calculated efficiently and with low computational cost using the direct integration method. The actual pressure value at the pressure reference point is determined using a cylinder pressure sensor inside the optical engine, thereby obtaining the three-dimensional pressure field distribution of the entire test space. The three-dimensional pressure field measurement method for measuring spray flames within an optical engine disclosed in this invention includes the following steps: Step 1: The test objects include the spray flow field and flame combustion process within the optical engine. The optical engine is derived from modifying the cylinder of an existing engine with a transparent material, allowing the internal flow field and combustion process to be observed through optical detection. A three-dimensional Cartesian coordinate system o-xy is established within the transparent cylinder. Based on this coordinate system, the three-dimensional space to be measured is discretized into several cubic micro-elements, called voxels, with the side length of each voxel defined as the spatial step size h. The three-dimensional velocity field distribution of the spray flow field or flame combustion process inside the optical engine cylinder is measured using tomographic particle image velocimetry (TPV). The velocity component in the x-direction is defined as u, the velocity component in the y-direction as v, and the velocity component in the x-direction as ω. Based on the time resolution of TPV, the time variable of the measurement process is defined as Δt, with a time step of Δt.

[0007] Step 2: Using the central difference method, calculate the spatial and temporal derivatives of the three-dimensional velocity field inside the transparent cylinder.

[0008]

[0009] The first derivative of the velocity field component u with respect to the y-direction in space is

[0010]

[0011] The first derivative of the velocity field component u with respect to the z-direction in space is

[0012]

[0013] The first derivative of the velocity field component v with respect to the x-direction in space is

[0014]

[0015] The first derivative of the velocity field component v with respect to the y-direction in space is

[0016]

[0017] The first derivative of the velocity field component v with respect to the z-direction in space is

[0018]

[0019] The first derivative of the velocity field component w with respect to the x-direction in space is

[0020]

[0021] The first derivative of the velocity field component w with respect to the y-direction in space is

[0022]

[0023] The first derivative of the velocity field component w with respect to the z-direction in space is

[0024]

[0025] The first derivative of the velocity field component u with respect to time t is

[0026]

[0027] The first derivative of the velocity field component v with respect to time t is

[0028]

[0029] The first derivative of the velocity field component w with respect to time t is

[0030]

[0031] Step 3: Based on the Navier-Stokes equations and the first derivative of the three-dimensional velocity field within the cylinder calculated in Step 2 with respect to space and time, calculate the components of the pressure gradient in the three spatial directions within the measured region. Since the viscous term contributes an order of magnitude smaller to the pressure field in turbulent flow than other factors, the viscous term is ignored in the calculation to reduce computational cost and improve computational efficiency.

[0032] Step 3.1: The Navier-Stokes equations are as follows:

[0033]

[0034] Where p represents the pressure field. Represents the pressure field gradient. Let be the Hamiltonian operator, u represent the three-dimensional velocity vector, and v be the dynamic viscosity of the fluid. Due to the high turbulence in the flow field within the engine cylinder, the effect of the viscous term can be neglected, reducing computational complexity and improving efficiency. A simplified Navier-Stokes equation is used.

[0035]

[0036] Step 3.2: Decompose the Navier-Stokes equations in three spatial directions according to the simplified Navier-Stokes equations in equation (14).

[0037]

[0038] in, Let x, y, and z represent the components of the pressure gradient in the spatial directions, respectively. Substituting the first derivatives of the in-cylinder flow field calculated in step 2 into equation (15), the components of the pressure gradient in the three spatial directions are calculated.

[0039] Step 4: Apply the direct integration method to calculate the true pressure field distribution based on the components of the pressure gradient in the three spatial directions within the test area obtained in Step 3.

[0040] Step 4.1: Define voxel A as the pressure reference point and voxel B as any point within the space to be measured. A line segment from point A to point B passes through q voxels within the space to be measured. The coordinate difference between points A and B is x... n y n and z n For each voxel q traversed by line segment AB, sum the gradients in each spatial direction, then average them based on the actual coordinate differences, and finally sum the averages of the three spatial directions to calculate the relative pressure difference between points A and B.

[0041]

[0042] By performing Equation 15 on all discrete voxels in the space to be measured with respect to point A, the relative pressure distribution of the space to be measured relative to the pressure value at point A is calculated.

[0043] Step 4.2: Based on the position of the cylinder pressure sensor, obtain the spatial location of point A from Step 4.1. The pressure reference value at point A is the actual pressure value measured by the cylinder pressure sensor. Based on the actual pressure value at point A, the true three-dimensional pressure field distribution of the space to be measured is then obtained.

[0044] The process also includes step 5: based on the actual distribution results of the three-dimensional pressure field obtained in step 4, the spray penetration distance, diffusion range, and local combustion pressure distribution are analyzed to check whether the fuel injection parameters are reasonable and whether the combustion atmosphere is good, and to evaluate the fuel injection parameters and the combustion process. In addition, the obtained spray diffusion and combustion pressure are also used to detect fuel impact against the walls and local material load, which can provide a reference for combustion design optimization and solve engineering problems related to excessive local load on the engine.

[0045] Beneficial effects:

[0046] 1. Existing pressure field detection methods do not consider the highly three-dimensional nature of the flow field caused by the high turbulence within the cylinder. Traditional one-dimensional and two-dimensional measurements cannot meet the requirements for detecting and diagnosing complex flow fields. This invention discloses a three-dimensional pressure field measurement method for measuring spray flames inside an optical engine. It obtains the three-dimensional velocity field distribution within the optical engine cylinder using existing tomographic particle image velocimetry, and then calculates the three-dimensional pressure field distribution within the cylinder based on the three-dimensional velocity field and Navier-Stokes equations. Compared to one-dimensional and two-dimensional measurements, three-dimensional measurement improves the accuracy of detection in terms of dimensionality, enabling a more detailed diagnosis of the in-cylinder spray flow field development and combustion conditions.

[0047] 2. The three-dimensional pressure field measurement method disclosed in this invention for measuring spray flames inside optical engines employs a direct integration method to calculate the relative pressure field distribution of all points in space with respect to a certain pressure reference point, based on the pressure field gradient calculated according to the Navier-Stokes equations. This simple and intuitive direct integration method achieves low computational cost and high efficiency in calculating the relative pressure field distribution.

[0048] 3. The three-dimensional pressure field measurement method for measuring spray flames inside optical engines disclosed in this invention obtains the three-dimensional velocity field of the area to be measured using tomographic particle image velocimetry. The three-dimensional pressure field is then solved using this velocity field, enabling the acquisition of three-dimensional pressure field information. This significantly improves the accuracy and comprehensiveness of pressure field measurement, providing more accurate design references for related engineering issues such as injection pressure, pulse width, timing, and the matching of the combustion chamber piston crown shape with the injector. Furthermore, the application of this invention is not limited to piston internal combustion engines; this method is also applicable to other complex flow fields that can be optically diagnosed. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the direct integration method provided by the present invention.

[0050] Figure 2 The following is a flowchart illustrating the implementation process of this invention. Detailed Implementation

[0051] To better illustrate the purpose and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples.

[0052] like Figure 1 The three-dimensional pressure field measurement method for measuring spray flames inside an optical engine disclosed in this embodiment has the following specific implementation steps:

[0053] Step 1: The current optical engine's transparent cylinder is made of quartz glass with a refractive index of 1.4, an outer diameter of 132 mm, and an inner diameter of 92 mm. A three-dimensional Cartesian coordinate system o-xyz is established inside the transparent cylinder of the optical engine. The origin o is located at the center of mass of the transparent cylinder, and the x, y, and z axes are arranged according to the Cartesian right-hand coordinate system. Based on the coordinate system, the three-dimensional space to be measured is discretized into several cubic micro-elements, called voxels, and the side length of the voxels is defined as the spatial step h = 0.5 mm. The three-dimensional velocity field distribution of the spray flow field or flame combustion process inside the optical engine cylinder is measured using the tomographic particle image velocimetry method. The velocity component in the x-direction is defined as u, the velocity component in the y-direction as v, and the velocity component in the z-direction as w. The time variable is t, and the time step is defined as Δt according to the time resolution in tomographic particle image velocimetry technology.

[0054] Step 2: Calculate the first derivatives of the three-dimensional velocity field of the flow field inside the transparent cylinder with respect to space and time using the central difference method.

[0055] The first derivative of the velocity field component u with respect to the x-direction in space is

[0056]

[0057] The first derivative of the velocity field component u with respect to the y-direction in space is

[0058]

[0059] The first derivative of the velocity field component u with respect to the z-direction in space is

[0060]

[0061] The first derivative of the velocity field component v with respect to the x-direction in space is

[0062]

[0063] The first derivative of the velocity field component v with respect to the y-direction in space is

[0064]

[0065] The first derivative of the velocity field component v with respect to the z-direction in space is

[0066]

[0067] The first derivative of the velocity field component w with respect to the x-direction in space is

[0068]

[0069] The first derivative of the velocity field component w with respect to the y-direction in space is

[0070]

[0071] The first derivative of the velocity field component w with respect to the z-direction in space is

[0072]

[0073] The first derivative of the velocity field component u with respect to time t is

[0074]

[0075] The first derivative of the velocity field component v with respect to time t is

[0076]

[0077] The first derivative of the velocity field component w with respect to time t is

[0078]

[0079] Step 3: Based on the Navier-Stokes equations and the first derivatives of the three-dimensional velocity field within the cylinder calculated in Step 2, determine the spatial and temporal components of the pressure gradient in the three spatial directions within the test region. Ignoring the non-dominant viscous terms in the turbulence, the Navier-Stokes equations are:

[0080]

[0081] Decompose the Navier-Stokes equations in Equation 28 in three spatial directions

[0082]

[0083] in, Let x, y, and z represent the components of the pressure gradient in the spatial directions, respectively. Substituting the first derivatives of the in-cylinder flow field calculated in step 2 into equation (29), the components of the pressure gradient in the three spatial directions are calculated.

[0084] Step 4: Application Figure 2 The direct integration method shown defines voxel A as the pressure reference point and voxel B as any point within the space to be measured. A line segment from point A to point B passes through q voxels within the space to be measured, and the coordinate difference between points A and B is x. n yn and z n For each voxel q traversed by line segment AB, sum the gradients in each spatial direction, then average them based on the actual coordinate differences, and finally sum the averages of the three spatial directions to calculate the relative pressure difference between points A and B.

[0085]

[0086] By performing Equation 30 on all discrete voxels in the space to be measured with respect to point A, the relative pressure distribution of the space to be measured relative to the pressure value at point A is calculated.

[0087] Step 4.2: Based on the position of the cylinder pressure sensor, obtain the spatial location of point A from Step 4.1. The pressure reference value at point A is the actual pressure value measured by the cylinder pressure sensor. Based on the actual pressure value at point A, the true three-dimensional pressure field distribution of the space to be measured is then obtained.

[0088] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A three-dimensional pressure field measurement method for measuring spray flames inside an optical engine, characterized in that: Includes the following steps, Step 1: The test objects include the spray flow field and flame combustion process inside the optical engine; the optical engine is derived from modifying the cylinder of an existing engine with a transparent material, so that the flow field and combustion process inside the cylinder can be observed through optical detection methods; a three-dimensional Cartesian coordinate system o-xyz is established inside the transparent cylinder, and the three-dimensional space to be measured is discretized into several cubic micro-elements, called voxels, according to the coordinate system, and the side length of the voxel is defined as the spatial step h; the three-dimensional velocity field distribution of the spray flow field or flame combustion process inside the optical engine cylinder is measured using the tomographic particle image velocimetry method, and the velocity component in the x-direction is defined as u, the velocity component in the y-direction is defined as v, and the velocity component in the z-direction is defined as w; according to the time resolution of the tomographic particle image velocimetry technology, the time variable of the measurement process is defined as t, and the time step is Δt; Step 2: Calculate the first derivatives of the three-dimensional velocity field of the flow field inside the transparent cylinder with respect to space and time using the central difference method; The first derivative of the velocity field component u with respect to the x-direction in space is The first derivative of the velocity field component u with respect to the y-direction in space is The first derivative of the velocity field component u with respect to the z-direction in space is The first derivative of the velocity field component v with respect to the x-direction in space is The first derivative of the velocity field component v with respect to the y-direction in space is Step 2: Calculate the first derivatives of the three-dimensional velocity field of the flow field inside the transparent cylinder with respect to space and time using the central difference method; The first derivative of the velocity field component u with respect to the x-direction in space is The first derivative of the velocity field component u with respect to the y-direction in space is The first derivative of the velocity field component u with respect to the z-direction in space is The first derivative of the velocity field component v with respect to the x-direction in space is The first derivative of the velocity field component v with respect to the y-direction in space is The first derivative of the velocity field component v with respect to the z-direction in space is The first derivative of the velocity field component w with respect to the x-direction in space is The first derivative of the velocity field component w with respect to the y-direction in space is The first derivative of the velocity field component w with respect to the z-direction in space is The first derivative of the velocity field component u with respect to time is: The first derivative of the velocity field component v with respect to time t is The first derivative of the velocity field component w with respect to time t is Step 3: Based on the Navier-Stokes equations and the first derivatives of the three-dimensional velocity field of the flow inside the cylinder with respect to space and time calculated in Step 2, calculate the components of the pressure gradient in the three spatial directions within the region to be measured. Since the viscous term contributes an order of magnitude less to the pressure field than other factors in turbulent flow, the viscous term is ignored in the calculation. Step 4: Apply the direct integration method to calculate the true pressure field distribution based on the components of the pressure gradient in the three spatial directions within the test area obtained in Step 3.

2. The three-dimensional pressure field measurement method for measuring spray flames inside an optical engine as described in claim 1, characterized in that: Step 3 is implemented as follows: Step 3.1: The Navier-Stokes equations are as follows: Where p represents the pressure field. Represents the pressure field gradient. Let be the Hamiltonian operator, u represent the three-dimensional velocity vector, and v be the dynamic viscosity of the fluid; due to the high turbulence in the flow field within the engine cylinder, the effect of the viscous term can be neglected; the simplified Navier-Stokes equations are used. Step 3.2: Decompose the Navier-Stokes equations in three spatial directions according to the simplified Navier-Stokes equations in equation (14). in, Let x, y, and z represent the components of the pressure gradient in the spatial directions respectively. Substitute the first derivatives of the in-cylinder flow field calculated in step 2 into equation (15) to calculate the components of the pressure gradient in the three spatial directions. in, Let x, y, and z represent the components of the pressure gradient in the spatial directions respectively. Substitute the first derivatives of the in-cylinder flow field calculated in step 2 into equation (15) to calculate the components of the pressure gradient in the three spatial directions.

3. The three-dimensional pressure field measurement method for measuring spray flames inside an optical engine as described in claim 2, characterized in that: Step 4 is implemented as follows: Step 4.1: Define voxel A as the pressure reference point and voxel B as any point within the space to be measured; the line segment from point A to point B passes through q voxels within the space to be measured, and the coordinate difference between points A and B is x. n y n and z n For each voxel q traversed by line segment AB, sum the gradients in each spatial direction, then average them according to the actual coordinate difference, and finally sum the averages of the three spatial directions to find the relative pressure difference between points AB. By performing Equation 15 on point A for all discrete voxels in the space to be measured, the relative pressure distribution of the space to be measured relative to the pressure value at point A is calculated. Step 4.2: Based on the position of the cylinder pressure sensor, obtain the spatial position of point A in step 4.1; the pressure reference value of point A is the actual pressure value measured by the cylinder pressure sensor; based on the actual pressure value of point A, obtain the actual three-dimensional pressure field distribution of the space to be measured.

4. The three-dimensional pressure field measurement method for measuring spray flames inside an optical engine as described in claim 1, 2, or 3. Its features are: It also includes step 5: based on the actual distribution results of the three-dimensional pressure field obtained in step 4, analyze the spray penetration distance, diffusion range, and local pressure distribution of combustion, detect whether the fuel injection parameters are reasonable and whether the combustion atmosphere is good, and evaluate the fuel injection parameters and combustion process; in addition, the obtained spray diffusion and combustion pressure are also used to detect the fuel wall impact and local material load.

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