A self-ignition temperature step prediction method, system and medium

Abstract

The application discloses a kind of self-ignition temperature step prediction method, system and medium, prediction method includes: judge whether the environment where positive standard fuel is there is droplet evaporation: if there is no droplet evaporation: collect gas phase temperature, pressure, equivalence ratio and n-heptane concentration proportion data, equivalence ratio and n-heptane concentration proportion are calculated to obtain the slope of initial temperature, based on pressure and n-heptane concentration proportion, cross temperature is calculated, so as to be based on gas phase temperature, the slope of initial temperature and cross temperature calculation obtains first temperature step;If there is droplet evaporation: collect gas phase temperature, pressure, equivalence ratio, droplet diameter and and liquid phase n-heptane concentration proportion data to calculate first temperature step.The application can predict the first stage temperature growth under different temperature, pressure, equivalence ratio, droplet diameter and n-heptane concentration condition, and prediction accuracy is good, both applicable to pure gas phase situation also applicable to have droplet evaporation situation, and simple operation.

Description

Technical Field

[0001] The present invention belongs to the field of temperature prediction, and in particular relates to a method, system and medium for predicting auto-ignition temperature step. Background Art

[0002] The internal combustion engine is one of the main sources of power for transportation worldwide, but it is also a major contributor to the consumption of fossil fuels and the production of environmental pollutants such as carbon dioxide (CO2), nitrogen oxides (NOx), and soot. Low-temperature combustion (LTC) is considered the most promising direction in engine research because it can improve combustion efficiency and reduce pollutant emissions.

[0003] Low-temperature combustion (LTC) engines exhibit two-stage autoignition due to low in-cylinder temperatures, pressures, and oxygen concentrations caused by early injection and high exhaust gas recirculation. This two-stage autoignition process involves two temperature jumps. The first temperature jump is the boundary between the first and second autoignition delays. The first temperature jump is approximately 200K, while the second temperature jump raises the temperature to over 2000K. Studying the first temperature jump provides insights into the timing and location of autoignition and flame propagation. This helps control the combustion path and avoid areas of high emission concentrations.

[0004] Positive reference fuel (PRF), also known as positive standard fuel, includes n-heptane and isooctane, whose reactivity is similar to that of diesel and gasoline, respectively. PRF is commonly used in reactivity controlled compression ignition (RCCI) and can increase the operating range of low-temperature autoignition. However, the stratification of the PRF number has a significant impact on the autoignition delay under medium and low temperature conditions, while the effect disappears under high temperature conditions. Moreover, under medium and low temperature conditions, the stratification of the PRF number can easily lead to a detonation mode, because a small change in the PRF number can cause a large difference in the autoignition delay. In addition, under conditions of droplet evaporation, due to the different evaporation characteristics of n-heptane and isooctane, the mixing ratio in the gas phase after the PRF droplets evaporate will also change, which increases the difficulty of controlling the combustion path. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above problems existing in the prior art and to provide a method, system and medium for predicting auto-ignition temperature step.

[0006] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0007] A method for predicting auto-ignition temperature step, the prediction method comprising:

[0008] Determine whether there is droplet evaporation in the environment of the positive standard fuel:

[0009] If there is no droplet evaporation: collect gas phase temperature, pressure, equivalence ratio and n-heptane concentration ratio data, calculate the slope of the initial temperature based on the equivalence ratio and n-heptane concentration ratio, calculate the crossover temperature based on the pressure and n-heptane concentration ratio, and then calculate the first temperature step based on the gas phase temperature, the slope of the initial temperature and the crossover temperature;

[0010] If a droplet evaporates:

[0011] Collect data on gas phase temperature, pressure, equivalence ratio, droplet diameter, and liquid phase n-heptane concentration ratio;

[0012] The equivalent ratio and the evaporation rate ratio of n-heptane to isooctane were dimensionlessized and fitted to the temporal evolution of the equivalent ratio and the evaporation rate ratio of n-heptane to isooctane in the gas phase under pure evaporation conditions.

[0013] Using explosion index analysis, key components are identified, variable models are constructed, and the evolution of concentrations of each component is calculated;

[0014] Using simplified low-temperature reaction pathways, the gas phase temperature evolution is calculated through the heat absorption and release of chemical reactions and evaporation.

[0015] According to the results of gas phase temperature evolution, the temperature before and at the start of low-temperature spontaneous combustion, the gas phase n-heptane concentration ratio, and the equivalence ratio are obtained;

[0016] The slope and crossover temperature corresponding to the evaporation of droplets are calculated based on the proportion of n-heptane concentration in the gas phase and the equivalence ratio at the start of low-temperature spontaneous combustion, thereby calculating the first temperature step.

[0017] Furthermore, the slope and crossover temperature calculation formulas when there is no droplet evaporation are as follows:

[0018]

[0019] Furthermore, the calculation formula for the first temperature step when there is no droplet evaporation is as follows: ΔT1=k(T0-T * ).

[0020] Furthermore, the quartic equation was used to fit the temporal evolution of the equivalent ratio and the evaporation rate ratio of n-heptane to isooctane in the gas phase under pure evaporation conditions. The calculation formula is as follows:

[0021]

[0022] where X hep,g is the concentration of n-heptane in the gas phase after evaporation. The calculation formula for the proportion of n-heptane concentration in the gas phase is:

[0023] X hep,f =X hep,g / (Xhep,g +X oct,g ).

[0024] Furthermore, the evaporation time scale is calculated based on the gas phase temperature and droplet diameter, and the calculation formula is as follows:

[0025]

[0026] Furthermore, the key components are ROO, O2QOOH and KET of n-heptane and isooctane.

[0027] Furthermore, the gas phase temperature evolution results are as follows:

[0028]

[0029] Furthermore, the calculation formula for the first temperature step when a droplet evaporates is as follows:

[0030] ΔT1=k(φ 1,start ,X hep,f,1 )×(T 1,start -T*(P,X hep,f,1 )).

[0031] like Figure 5 As shown, the present invention also provides a system for predicting auto-ignition temperature step, comprising

[0032] The droplet analysis module is used to determine whether there is droplet evaporation in the environment of the positive standard fuel;

[0033] a first analysis and processing module for collecting gas phase temperature, pressure, equivalence ratio, and n-heptane concentration ratio data when there is no droplet evaporation, calculating a slope of the initial temperature based on the equivalence ratio and the n-heptane concentration ratio, and calculating a crossover temperature based on the pressure and the n-heptane concentration ratio, thereby calculating a first temperature step based on the gas phase temperature, the slope of the initial temperature, and the crossover temperature;

[0034] The first analysis and processing module is used to collect data on gas phase temperature, pressure, equivalence ratio, droplet diameter, and liquid phase n-heptane concentration ratio when droplets evaporate; the equivalence ratio and the evaporation rate ratio of n-heptane to isooctane are dimensionlessly converted to fit the time evolution of the equivalence ratio and the evaporation rate ratio of n-heptane to isooctane in the gas phase under pure evaporation conditions; the key components are determined by explosion index analysis, a variable model is constructed, and the evolution results of the concentrations of each component are calculated; the gas phase temperature evolution results are calculated by using a simplified low-temperature reaction path through the heat absorption and release of chemical reactions and evaporation; based on the gas phase temperature evolution results, the temperature, gas phase n-heptane concentration ratio, and equivalence ratio corresponding to the moment before the start of low-temperature spontaneous combustion and the start of low-temperature spontaneous combustion are obtained; the slope and crossover temperature corresponding to the time when droplets evaporate are calculated based on the gas phase n-heptane concentration ratio and equivalence ratio corresponding to the start of low-temperature spontaneous combustion, thereby calculating the first temperature step.

[0035] The present invention also provides a computer storage medium having a computer program stored thereon, wherein the computer program implements the above prediction method when executed.

[0036] The beneficial effects of the present invention are:

[0037] 1. The present invention can predict the temperature growth in the first stage under different conditions of temperature, pressure, equivalence ratio, droplet diameter and n-heptane concentration with good prediction accuracy.

[0038] 2. The present invention predicts the first temperature step, is applicable to both pure gas phase and droplet evaporation, and is simple to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0040] Figure 1 This is a flow chart of the prediction method;

[0041] Figure 2 Schematic diagram of the first temperature step;

[0042] Figure 3 Schematic diagram of the relationship between the slope and cross temperature of the first temperature step and the initial temperature;

[0043] Figure 4 To simplify the key reaction diagram of low temperature chemical reaction pathway;

[0044] Figure 5 It is a system structure diagram of the present invention. DETAILED DESCRIPTION

[0045] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0046] like Figure 1 and Figure 2 A method for predicting auto-ignition temperature step is shown, and the prediction method includes:

[0047] Determine whether there is droplet evaporation in the environment of the positive standard fuel:

[0048] If no droplets evaporate:

[0049] Collect gas phase temperature T0, pressure P, equivalence ratio φ and n-heptane concentration ratio X hep,f As the initial condition, a homogeneous reaction simulation without evaporation was performed on the first reference fuel with different n-heptane concentration ratios.

[0050] The slope of the initial temperature is calculated based on the equivalence ratio and the proportion of n-heptane concentration, and the crossover temperature is calculated based on the pressure and the proportion of n-heptane concentration. Thus, the first temperature step is calculated based on the gas phase temperature, the slope of the initial temperature, and the crossover temperature.

[0051] According to the homogeneous reaction without evaporation, it is found that the first temperature increase has a linear relationship with the initial temperature, and its slope k is insensitive to the pressure P, and is affected by the equivalence ratio φ and the proportion of n-heptane concentration X. hep,f The temperature corresponding to the first temperature increase equal to zero is the crossover temperature T*, which is insensitive to the equivalence ratio φ and is mainly affected by the pressure P and the proportion of n-heptane concentration X. hep,f control.

[0052] The slope and crossover temperature are calculated as follows:

[0053]

[0054] According to the initial gas phase temperature T0, pressure P, equivalence ratio φ and n-heptane concentration ratio X hep,f Calculate the corresponding slope k and cross temperature T * .

[0055] Figure 3 This is a diagram showing the relationship between the slope k of the first temperature step and the initial temperature and the crossover temperature T*. Figure 3 , after the slope k and crossover temperature T have been calculated *, and the initial gas phase temperature T0 is determined, the first temperature step can be directly calculated using the formula. The first temperature step calculation formula is as follows: ΔT1=k(T0-T * ).

[0056] If a droplet evaporates:

[0057] Collect data on gas phase temperature, pressure, equivalence ratio, droplet diameter, and liquid phase n-heptane concentration ratio. In the presence of droplets, droplet evaporation will increase the equivalence ratio and the evaporation endotherm will reduce the gas phase temperature. In addition, due to the different properties of n-heptane and isooctane, the evaporation rates of the two are also different. Therefore, the gas phase temperature T0, pressure P, equivalence ratio φ, droplet diameter D0, and liquid phase n-heptane concentration ratio X are used to calculate the gas phase temperature. hep,l,0 is the initial condition.

[0058] In the presence of droplets, we first investigated the evolution of the equivalence ratio and evaporation rate under pure evaporation conditions. We nondimensionalized the equivalence ratio and the evaporation rate ratio of n-heptane to isooctane and used a quartic equation to fit the temporal evolution of the equivalence ratio and the evaporation rate ratio of n-heptane to isooctane in the gas phase under pure evaporation conditions.

[0059] The calculation formula is as follows:

[0060]

[0061] where X hep,g is the concentration of n-heptane in the gas phase after evaporation. The calculation formula for the proportion of n-heptane concentration in the gas phase is:

[0062] X hep,f =X hep,g / (X hep,g +X oct,g ).

[0063] Evaporation time scale τ eva It is an important parameter for calculating the equivalent ratio and the proportion of n-heptane. The evaporation time scale is calculated based on the gas phase temperature and droplet diameter. The calculation formula is as follows:

[0064]

[0065] The key components were determined by explosion index analysis. The key components were ROO, O2QOOH and KET of n-heptane and isooctane. A six-variable model was constructed to calculate the evolution of the concentration of each component.

[0066]

[0067] C=[C7H 15 O2,C8H 17 O2,O2C7H 14 OOH,O2C8H16 OOH,C7KET,C8KET] T

[0068] R=[k -8 [O2]C1,k -22 [O2]C2,0,0,0,0] T

[0069]

[0070] Using a simplified low-temperature reaction path, the gas phase temperature evolution results are calculated through the heat absorption and release of chemical reactions and evaporation.

[0071] Figure 4 In order to simplify the low-temperature reaction path, the present invention divides this low-temperature path into four parts based on the simplified low-temperature reaction path in the process of self-ignition of the first reference fuel droplet. The first part is from R to ROO, the second part is from QOOH to O2QOOH, the third part is the decomposition of the secondary oxygenation product, and the fourth part is the decomposition of KET. By calculating the heat release of each part of the reaction and the latent heat of evaporation during evaporation, the temperature change dT at each moment dt of the entire low-temperature self-ignition stage can be obtained, thereby calculating the temperature evolution of the entire low-temperature self-ignition stage. ΔH1, ΔH2, ΔH3, and ΔH4 represent the heat release of the four parts (the specific calculation details are not shown here), L eva As the latent heat of vaporization, C pmix is the constant pressure specific heat capacity of the mixed fuel, and the temperature change at each moment is expressed as:

[0072]

[0073] According to the evolution of gas phase temperature, the temperature is derived with respect to time to obtain the temperature growth rate. The moment when the temperature growth rate is first greater than 0 is taken as the time τ before the start of low-temperature spontaneous combustion. 1,start , thus obtaining the temperature T corresponding to the start of low-temperature spontaneous combustion 1,start , gas phase n-heptane concentration ratio X hep,f,1 and equivalence ratio φ 1,start .

[0074] According to the proportion of n-heptane concentration X at the beginning of low-temperature spontaneous combustion hep,f,1 and equivalence ratio φ 1,start , by substituting the slope and cross temperature formula without evaporation, we can calculate the slope k(φ 1,start ,X hep,f,1 ) and crossover temperature T*(P,X hep,f,1 ).

[0075] Using the formula ΔT1=k(φ 1,start ,X hep,f,1 )×(T1,start -T*(P,X hep,f,1 ))Calculate the first temperature step.

[0076] According to tests, the prediction error of the method of the present invention is only ±6%, and the prediction effect is good.

[0077] The present invention also provides a system for predicting auto-ignition temperature step, comprising

[0078] The droplet analysis module is used to determine whether there is droplet evaporation in the environment of the positive standard fuel;

[0079] a first analysis and processing module for collecting gas phase temperature, pressure, equivalence ratio, and n-heptane concentration ratio data when there is no droplet evaporation, calculating a slope of the initial temperature based on the equivalence ratio and the n-heptane concentration ratio, and calculating a crossover temperature based on the pressure and the n-heptane concentration ratio, thereby calculating a first temperature step based on the gas phase temperature, the slope of the initial temperature, and the crossover temperature;

[0080] The first analysis and processing module is used to collect gas phase temperature, pressure, equivalence ratio, droplet diameter and liquid phase n-heptane concentration ratio data when droplets evaporate; the equivalence ratio and the evaporation rate ratio of n-heptane to isooctane are dimensionless, and the time evolution law of the equivalence ratio and the evaporation rate ratio of n-heptane to isooctane in the gas phase under pure evaporation conditions is fitted; the explosion index analysis is used to determine the key components, construct a variable model, and calculate the evolution results of the concentration of each component; the simplified low-temperature reaction path is used to calculate the gas phase temperature evolution results through the heat absorption and release of chemical reaction and evaporation; according to the gas phase temperature evolution results, the temperature, gas phase n-heptane concentration ratio and equivalence ratio corresponding to the time before the start of low-temperature spontaneous combustion and the start of low-temperature spontaneous combustion are obtained; the slope and cross temperature corresponding to the gas phase n-heptane concentration ratio and equivalence ratio corresponding to the start of low-temperature spontaneous combustion are calculated, thereby calculating the first temperature step

[0081] A third aspect of the present invention further provides a computer storage medium having a computer program stored thereon, which implements the above method when executed. The storage medium may include any medium capable of storing program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0082] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0083] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A method for predicting auto-ignition temperature step, characterized in that: Prediction methods include: Determine whether there is droplet evaporation in the environment of the positive standard fuel: If there is no droplet evaporation: collect gas phase temperature, pressure, equivalence ratio and n-heptane concentration ratio data, calculate the slope of the initial temperature based on the equivalence ratio and n-heptane concentration ratio, calculate the crossover temperature based on the pressure and n-heptane concentration ratio, and then calculate the first temperature step based on the gas phase temperature, the slope of the initial temperature and the crossover temperature; If a droplet evaporates: Collect data on gas phase temperature, pressure, equivalence ratio, droplet diameter, and liquid phase n-heptane concentration ratio; The equivalent ratio and the evaporation rate ratio of n-heptane to isooctane were dimensionlessized and fitted to the temporal evolution of the equivalent ratio and the evaporation rate ratio of n-heptane to isooctane in the gas phase under pure evaporation conditions. Using explosion index analysis, key components are identified, variable models are constructed, and the evolution of concentrations of each component is calculated; Using simplified low-temperature reaction pathways, the gas phase temperature evolution is calculated through the heat absorption and release of chemical reactions and evaporation. According to the results of gas phase temperature evolution, the temperature before and at the start of low-temperature spontaneous combustion, the gas phase n-heptane concentration ratio, and the equivalence ratio are obtained; The slope and crossover temperature corresponding to the evaporation of droplets are calculated based on the proportion of n-heptane concentration in the gas phase and the equivalence ratio at the start of low-temperature spontaneous combustion, thereby calculating the first temperature step.

2. The method for predicting auto-ignition temperature step according to claim 1, characterized in that: The slope and crossover temperature calculation formulas when there is no droplet evaporation are as follows: Where k is the slope, is the equivalence ratio, X hep,f is the concentration ratio of n-heptane, T * is the crossover temperature, and P is the pressure.

3. The method for predicting auto-ignition temperature step according to claim 2, characterized in that: The calculation formula for the first temperature step when there is no droplet evaporation is as follows: ΔT1=k(T0-T * ); Where ΔT1 is the first temperature step and T0 is the initial gas phase temperature.

4. The method for predicting auto-ignition temperature step according to claim 1, characterized in that: The evolution of the equivalent ratio and the evaporation rate ratio of n-heptane to isooctane in the gas phase under pure evaporation conditions over time was fitted using the quartic equation. The calculation formula is as follows: where X hep,g is the concentration of n-heptane in the gas phase after evaporation. The calculation formula for the proportion of n-heptane concentration in the gas phase is: X hep,f =X hep,g / (X hep,g +X oct,g ); in, is the gas equivalent ratio, is the total equivalent ratio, t is the time, τ eva is the evaporation time scale, X oct,g is the isooctane concentration in the gas phase, X hep,1,0 is the initial n-heptane concentration ratio in the liquid phase, X oct,1,0 is the initial isooctane concentration ratio in the liquid phase, X hep,f is the percentage of n-heptane concentration.

5. The method for predicting auto-ignition temperature step according to claim 4, characterized in that: The evaporation time scale is calculated based on the gas phase temperature and droplet diameter, and the calculation formula is as follows: Where D0 is the droplet diameter and T0 is the initial gas phase temperature.

6. The method for predicting auto-ignition temperature step according to claim 5, characterized in that: The key components are ROO, O2QOOH and KET of n-heptane and isooctane, among which ROO is an alkyl peroxyl radical, O2QOOH is a peroxyhydroxyl radical, and KET is a ketone compound.

7. The method for predicting auto-ignition temperature step according to claim 6, characterized in that: The gas phase temperature evolution results are as follows: Among them, dT is the temperature change, ΔH1, ΔH2, ΔH3, ΔH4 represent the heat release of the four parts, is the mass evaporation rate, M is the molecular weight, L eva is the latent heat of vaporization, RU CGS is the gas constant, T is the temperature, dt is the time differential, C Pmix is the constant pressure specific heat capacity of the mixed fuel, P 0CGS For partial pressure.

8. The method for predicting auto-ignition temperature step according to claim 7, characterized in that: The calculation formula for the first temperature step when a droplet evaporates is as follows: ΔT1=k(φ 1,start ,X hep,f,1 )×(T 1,start -T*(P,X hep,f,1 )); Among them, φ 1,start is the equivalence ratio corresponding to the start of low-temperature spontaneous combustion, X hep,f,1 is the concentration ratio of n-heptane in the gas phase corresponding to the start of low-temperature spontaneous combustion, T 1,start is the temperature corresponding to the start of low-temperature spontaneous combustion, k is the slope, T * is the crossover temperature, and P is the pressure.

9. A system for predicting auto-ignition temperature steps, characterized by: include The droplet analysis module is used to determine whether there is droplet evaporation in the environment of the positive standard fuel; a first analysis and processing module for collecting gas phase temperature, pressure, equivalence ratio, and n-heptane concentration ratio data when there is no droplet evaporation, calculating a slope of the initial temperature based on the equivalence ratio and the n-heptane concentration ratio, and calculating a crossover temperature based on the pressure and the n-heptane concentration ratio, thereby calculating a first temperature step based on the gas phase temperature, the slope of the initial temperature, and the crossover temperature; The first analysis and processing module is used to collect data on gas phase temperature, pressure, equivalence ratio, droplet diameter, and the proportion of n-heptane concentration in the liquid phase when droplets evaporate. The module also non-dimensionalizes the equivalence ratio and the evaporation rate ratio of n-heptane to isooctane, and fits the temporal evolution of the equivalence ratio and the evaporation rate ratio of n-heptane to isooctane in the gas phase under pure evaporation conditions. Using explosion index analysis, the module identifies key components, constructs a variable model, and calculates the evolution of the concentrations of each component. Using simplified low-temperature reaction pathways, the gas phase temperature evolution is calculated through the heat absorption and release of chemical reactions and evaporation. According to the results of gas phase temperature evolution, the temperature before and at the start of low-temperature spontaneous combustion, the gas phase n-heptane concentration ratio and the equivalence ratio are obtained; based on the gas phase n-heptane concentration ratio and equivalence ratio corresponding to the start of low-temperature spontaneous combustion, the slope and crossover temperature corresponding to droplet evaporation are calculated, and thus the first temperature step is calculated.

10. A computer storage medium having a computer program stored thereon, characterized in that: When the computer program is executed, the prediction method according to any one of claims 1 to 8 is implemented.

Images