Spontaneous combustion temperature step prediction method and system and medium

Abstract

The invention discloses a spontaneous combustion temperature step prediction method and system and a medium, and the method comprises the steps: judging whether there is droplet evaporation in the environment where positive standard fuel is located: if there is no droplet evaporation, collecting the gas phase temperature, pressure, equivalence ratio and n-heptane concentration ratio data, and calculating the slope of the initial temperature based on the equivalence ratio and the n-heptane concentration ratio; calculating to obtain a cross temperature based on the pressure and the n-heptane concentration ratio, and calculating to obtain a first temperature step based on the gas phase temperature, the slope of the initial temperature and the cross temperature; if liquid drops are evaporated, collecting gas phase temperature, pressure, equivalence ratio, liquid drop diameter and liquid phase n-heptane concentration ratio data to calculate a first temperature step; the method can predict the first-stage temperature increase under the conditions of different temperatures, pressures, equivalence ratios, droplet diameters, n-heptane concentrations and the like, is good in prediction precision, is suitable for a pure gas phase condition and a droplet evaporation condition, and is simple to operate.

Description

Technical Field

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

[0002] The internal combustion engine is one of the main sources of power for transportation in the world, but it is also a major factor in consuming fossil fuels and producing 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 experience two-stage autoignition due to low in-cylinder temperature, pressure and oxygen concentration caused by early injection and high exhaust gas recirculation. There are two temperature jumps in the two-stage autoignition process, and the first temperature step is the dividing line between the first and second autoignition delays. The first temperature step is about 200K, while the second temperature step increases the temperature to more than 2000K. The study of the first temperature step helps us understand the autoignition timing, autoignition location and flame propagation. These can help us control the combustion path and avoid areas with high emission concentrations.

[0004] Positive standard fuel (PRF), also known as positive standard fuel, includes n-heptane and isooctane, whose reactivity is similar to diesel and gasoline, respectively. PRF is usually used in reactivity controlled compression ignition (RCCI) and can increase the operating range of low-temperature autoignition. However, the stratification of PRF number has a significant effect on the autoignition delay under medium and low temperature conditions, while the effect disappears under high temperature conditions. And under medium and low temperature conditions, the stratification of 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 the condition 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 the evolution of the equivalent ratio and the evaporation rate ratio of n-heptane to isooctane in the gas phase under pure evaporation conditions with time was fitted.

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

[0014] Using simplified low-temperature reaction paths, the gas phase temperature evolution results are 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 beginning of low-temperature spontaneous combustion, the temperature corresponding to the concentration ratio of gas phase n-heptane, and the equivalent ratio are obtained;

[0016] According to the proportion of n-heptane concentration in the gas phase and the equivalence ratio corresponding to the start of low-temperature spontaneous combustion, the slope and crossover temperature corresponding to the evaporation of droplets are calculated, and thus the first temperature step is calculated.

[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 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, and 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 the 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 there is droplet evaporation 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 autoignition temperature step, comprising

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

[0033] The first analysis and processing module is used to collect gas phase temperature, pressure, equivalence ratio and n-heptane concentration ratio data when there is no droplet evaporation, calculate the slope of the initial temperature based on the equivalence ratio and the n-heptane concentration ratio, calculate the crossover temperature based on the pressure and the n-heptane concentration ratio, and calculate the 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 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 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; according to 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 moment when low-temperature spontaneous combustion starts 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 moment when low-temperature spontaneous combustion starts, thereby calculating the first temperature step.

[0035] The present invention also provides a computer storage medium on which a computer program is stored, and 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, and the prediction accuracy is good.

[0038] 2. The present invention predicts the first temperature step, which is applicable to both the pure gas phase and the droplet evaporation, and is easy 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 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 crossover 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 block diagram of the present invention. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

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

[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 And as the initial condition, a homogeneous reaction simulation without evaporation was carried out 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 crossover temperature T * .

[0055] Figure 3 This is a schematic diagram of 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 the 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 endothermicity 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, the evolution of the equivalence ratio and evaporation rate under pure evaporation is first explored. The equivalence ratio and the evaporation rate ratio of n-heptane to isooctane are dimensionless, and the evolution of the equivalence ratio and the evaporation rate ratio of n-heptane to isooctane in the gas phase under pure evaporation conditions with time is fitted using a quartic equation.

[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 explosion index analysis was used to determine the key components, which 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 simplified low-temperature reaction paths, 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 according to 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 reaction and the latent heat of evaporation during evaporation, the temperature change dT at each moment dt in 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 evaporation, 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 time when the temperature growth rate is greater than 0 for the first time 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 crossover temperature formula without evaporation, we can calculate the slope k(φ 1,start ,X hep,f,1 ) and the 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] After testing, 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 autoignition temperature step, comprising:

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

[0079] The first analysis and processing module is used to collect gas phase temperature, pressure, equivalence ratio and n-heptane concentration ratio data when there is no droplet evaporation, calculate the slope of the initial temperature based on the equivalence ratio and the n-heptane concentration ratio, calculate the crossover temperature based on the pressure and the n-heptane concentration ratio, and calculate the 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 evolution law of the equivalence ratio and the evaporation rate ratio of n-heptane to isooctane in the gas phase under pure evaporation conditions with time is fitted; the key components are determined by explosion index analysis, and a variable model is constructed to calculate the evolution results of the concentrations of each component; 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; according to 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 moment when low-temperature spontaneous combustion starts 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 moment when low-temperature spontaneous combustion starts, thereby calculating the first temperature step

[0081] The third aspect of the present invention also provides a computer storage medium, on which a computer program is stored, and the computer program implements the above method when executed. The storage medium may include: a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and other media that can store program codes.

[0082] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0083] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for predicting autoignition 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 the evolution of the equivalent ratio and the evaporation rate ratio of n-heptane to isooctane in the gas phase under pure evaporation conditions with time was fitted. Using explosion index analysis, key components are determined, variable models are constructed, and the evolution results of the concentrations of each component are calculated; Using simplified low-temperature reaction paths, the gas phase temperature evolution results are 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 beginning of low-temperature spontaneous combustion, the temperature corresponding to the concentration ratio of gas phase n-heptane, and the equivalent ratio are obtained; According to the proportion of n-heptane concentration in the gas phase and the equivalence ratio corresponding to the start of low-temperature spontaneous combustion, the slope and crossover temperature corresponding to the evaporation of droplets are calculated, and thus the first temperature step is calculated.

2. The method for predicting auto-ignition temperature step according to claim 1, characterized in that: The slope and crossover temperature calculation formulas for no droplet evaporation are as follows:

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 * ).

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 )。 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:

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.

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:

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 there is droplet evaporation is as follows: ΔT1=k(φ 1,start ,X hep,f,1 )×(T 1,start -T*(P,X hep,f,1 ))。 9. A system for predicting autoignition temperature step, characterized in that: include A droplet analysis module is used to determine whether there is droplet evaporation in the environment of the positive standard fuel; The first analysis and processing module is used to collect gas phase temperature, pressure, equivalence ratio and n-heptane concentration ratio data when there is no droplet evaporation, calculate the slope of the initial temperature based on the equivalence ratio and the n-heptane concentration ratio, calculate the crossover temperature based on the pressure and the n-heptane concentration ratio, and calculate the 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 gas phase temperature, pressure, equivalent ratio, droplet diameter and liquid phase n-heptane concentration ratio data when droplets evaporate; the equivalent ratio and the evaporation rate ratio of n-heptane to isooctane are dimensionless, and the evolution law of the equivalent ratio and the evaporation rate ratio of n-heptane to isooctane in the gas phase under pure evaporation conditions with time 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; Using simplified low-temperature reaction paths, the gas phase temperature evolution results are 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 beginning of low-temperature spontaneous combustion, the gas phase n-heptane concentration ratio and the equivalent ratio are obtained; according to the gas phase n-heptane concentration ratio and the equivalent ratio corresponding to the beginning of low-temperature spontaneous combustion, the corresponding slope and crossover temperature when droplets evaporate 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.

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