CN115422686B - Engine performance improvement method based on accurate local heat insulation of combustion chamber - Google Patents

Abstract

An engine performance improvement method based on precise local insulation of the combustion chamber. This method is based on the calculation of the heat flow density and fuel-air equivalence ratio of various parts of the combustion chamber wall, and selects some areas for heat insulation treatment, so as to improve the heat flow distribution in areas with less heat flow distribution. There is no heat insulation in the place to alleviate the intake air heating. At the same time, it can effectively alleviate the near-wall combustion problem of the highly intensified diesel engine, making the combustion more complete. In addition, it also alleviates the deterioration of the charging efficiency, thereby comprehensively improving engine performance.

Description

An engine performance improvement method based on precise local insulation of the combustion chamber

Technical field

The present invention relates to the field of engine technology, and in particular to a method for improving engine performance through local heat insulation of a combustion chamber.

Background technique

In order to reduce heat loss and improve the thermal efficiency of the engine, combustion chamber insulation technology is widely used. The use of heat insulation technology to improve engine thermal efficiency will inevitably lead to the deterioration of charging efficiency. The reason is that the use of heat insulation technology causes the temperature of the cylinder wall to be too high, causing the fresh charge to be heated during the intake stroke, and the fresh air The density decreases and the intake air quality decreases.

In order to solve this problem, many studies have adopted the form of partial insulation, that is, insulating part of the combustion chamber, which can help alleviate the deterioration of charging efficiency. However, when selecting the heat insulation area, only the macro area is selected, such as only insulating the piston, or only insulating a certain characteristic part of the piston, without refining the selection of the heat insulation area. This leads to the thermal insulation of some insignificant areas, which has basically no benefit in improving thermal efficiency, but aggravates the deterioration of inflation efficiency.

On the other hand, as the degree of strengthening of diesel engines continues to increase, the injection pressure and fuel injection volume increase significantly, which inevitably leads to an increase in the amount of fuel attached to the wall. The oil film formed by the spray hitting the wall has a lower evaporation rate, resulting in oil and gas mixing. Poor combustion, incomplete combustion and excessively high emissions of unburned hydrocarbons and carbon monoxide, especially during the cold start phase of the engine. This phenomenon is more serious.

Research has found that the insulated combustion chamber is coated with a thermal barrier coating on the surface of the metal wall, which increases the surface temperature of the wall, which is conducive to strengthening wall-coated combustion and alleviating a series of problems caused by the slow evaporation rate of wall-coated oil film and low wall temperature. However, when the current research uses partial insulation technology, the selection of the insulation area does not consider the impact on Coanda combustion.

Contents of the invention

The present disclosure provides a universal partial insulation method, which comprehensively considers the comprehensive impact of the insulation area on thermal efficiency, charging efficiency and Coanda combustion, and provides theoretical support for the selection of the insulation area of the engine combustion chamber.

The engine performance improvement method provided by this disclosure based on precise local insulation of the combustion chamber includes the following steps:

Step 1. Establish a three-dimensional simulation model of the fuel engine;

Step 2. Use the three-dimensional simulation model established in Step 1 to calculate the heat flow density q on each wall of the combustion chamber during the engine working cycle, and at the same time calculate the mixture equivalence ratio distribution φ in the combustion chamber at the end of injection;

Step 3. Convert the heat flux density values of each wall of the combustion chamber calculated in Step 2 into the cycle average heat flux density values:

q _i is the heat flow density value at each moment in step 2, and n is the number of times the heat flow density result of an engine cycle is output;

Step 4. Normalize the circulating average heat flux density value of each wall of the combustion chamber calculated in step 3:

Step 5. Based on the normalized heat flux value of the combustion chamber wall, select the area for heat insulation treatment;

Step 6. Based on the fuel-air equivalence ratio distribution in the combustion chamber at the end of injection calculated in step 2, select the area for heat insulation treatment;

Step 7: Perform Boolean addition between the area selected in step 5 and the area selected in step 6, and perform Boolean subtraction between the operation result and the cylinder side wall area below the first ring groove when the piston is at top dead center. , determine the area that will ultimately be insulated.

Further, the specific method of step 1 includes:

Converge software is used to establish a CFD three-dimensional simulation model of the engine. The model includes a turbulence model, a spray model, and a combustion model. The RNGk-ε model is used as the turbulence model, the KH-RT model is used as the spray breakup model, and the SAGE model is used as the combustion model;

The first type of boundary condition is used to set the boundary conditions in the CFD model, that is, the wall temperature of each boundary is set.

Further, in step 2, the heat flux q is output every 1°CA.

Further, in step 5, select an area with a normalized heat flow density value exceeding 0.5 as a heat insulation treatment area, that is, apply a thermal barrier coating to the area with a heat flow density value exceeding 0.5 for heat insulation, and apply thermal barrier coating to other areas. No insulation.

Furthermore, in step 6, the area near the combustion chamber wall with a fuel-to-air equivalence ratio exceeding 2 is selected as the heat insulation treatment area.

Compared with the existing technology, the beneficial effects of the present disclosure are: ① Selection of the combustion chamber heat insulation area based on heat flow distribution can achieve efficient heat insulation, that is, selecting the combustion chamber wall area with high heat flow density for heat insulation to effectively Prevent heat dissipation and improve thermal efficiency; do not insulate areas with less heat flow distribution to alleviate intake air heating; ② Selecting the combustion chamber insulation area based on equivalence ratio distribution can effectively alleviate the near-wall combustion problem of highly intensified diesel engines. Make combustion more complete; ③ It achieves efficient heat insulation while mitigating the deterioration of charging efficiency and strengthening near-wall combustion.

Description of the drawings

The above and other objects, features and advantages of the present disclosure will become more apparent by describing the exemplary embodiments of the present disclosure in more detail with reference to the accompanying drawings, wherein the same reference numerals are generally used throughout the exemplary embodiments of the present disclosure. Represents the same parts.

Figure 1 shows a flow chart of a partial thermal insulation method for a diesel engine according to the present disclosure.

Detailed ways

Preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the preferred embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

The present disclosure provides a method for improving engine performance through precise local insulation of the combustion chamber. The specific steps of an exemplary embodiment are shown in Figure 1, including:

Step 1. Use engine CFD simulation software to establish a three-dimensional simulation model of a diesel engine.

As a preference, this embodiment uses Converge software to establish a CFD simulation model of a certain diesel engine, which includes a turbulence model, a spray model, and a combustion model. Among them, the turbulence model uses the RNGk-ε model, the spray breakup model uses the KH-RT model, the combustion model uses the SAGE model, and the Soot and NOx emission models are turned on. The setting of boundary conditions in this CFD model adopts the first type of boundary conditions, that is, setting the wall temperature of each boundary:

Step 2. Use the CFD model established in Step 1 to calculate the heat flux density q on each wall of the combustion chamber during the engine working cycle, and at the same time calculate the mixture equivalence ratio distribution φ in the combustion chamber at the end of injection.

In this embodiment, the combustion chamber wall includes: piston, cylinder head, and cylinder liner. As a preference, the heat flux q is output every 1°CA.

Step 3. Convert the heat flow density values of each wall of the combustion chamber calculated in Step 2 into the cycle average heat flow density value:

q _i is the heat flow density value at each moment in step 2, and n is the number of times the heat flow density result is output in one engine cycle. Since it is output every 1°CA, n here is 720.

Step 4: Normalize the cycle average heat flux value calculated in step 3.

Step 5. Select the heat insulation area based on the normalized heat flow density value of each wall of the combustion chamber: It is preferred to conduct heat insulation treatment in the area where the normalized heat flow density value exceeds 0.5, that is, apply heat to the area where the heat flow density value exceeds 0.5. Barrier coating is used for thermal insulation, and other areas are not thermally insulated.

Step 6. Select the heat insulation area based on the fuel-to-air equivalence ratio distribution in the combustion chamber at the end of injection calculated in step 2: Apply a thermal barrier coating to the area near the combustion chamber wall with a fuel-to-air equivalence ratio exceeding 2 for insulation and strengthening. Burns near the wall while reducing heat loss.

Step 7. Considering that the friction caused by the contact between the cylinder side wall and the piston ring causes the area below the first ring groove when the piston is at the top dead center to be coated with thermal barrier coating, the final spray area of the thermal barrier coating is: : Perform a Boolean addition operation on the area where the heat flow density exceeds 0.5 in step 5 and the area where the fuel-to-air equivalence ratio exceeds 2 near the combustion chamber wall in step 6, and compare the operation result with the cylinder below the first ring groove when the piston is at top dead center. A Boolean subtraction operation is performed on the side wall surface area to obtain the final heat insulation treatment area.

The above technical solutions are only exemplary embodiments of the present invention. For those skilled in the art, on the basis of the application methods and principles disclosed in the present invention, it is easy to make various types of improvements or modifications, not limited to The methods described in the above specific embodiments of the present invention are therefore only preferred and do not have a restrictive meaning.

Claims (5)

1. An engine performance improvement method based on precise local insulation of the combustion chamber, including the following steps: Step 1. Establish a three-dimensional simulation model of the fuel engine; Step 2. Use the three-dimensional simulation model established in Step 1 to calculate the heat flow density q on each wall of the combustion chamber during the engine working cycle, and at the same time calculate the mixture equivalence ratio distribution φ in the combustion chamber at the end of injection; Step 3. Convert the heat flux density values of each wall of the combustion chamber calculated in Step 2 into the cycle average heat flux density values: q _i is the heat flow density value at each moment in step 2, and n is the number of times the heat flow density result of an engine cycle is output; Step 4. Normalize the circulating average heat flux density value of each wall of the combustion chamber calculated in step 3: Step 5. Based on the normalized heat flux value of the combustion chamber wall, select the area for heat insulation treatment; Step 6. Based on the fuel-air equivalence ratio distribution in the combustion chamber at the end of injection calculated in step 2, select the area for heat insulation treatment; Step 7: Perform Boolean addition between the area selected in step 5 and the area selected in step 6, and perform Boolean subtraction between the operation result and the cylinder side wall area below the first ring groove when the piston is at top dead center. , determine the area that will ultimately be insulated. 2. The method of claim 1, wherein the specific method of step 1 includes: Converge software is used to establish a CFD three-dimensional simulation model of the engine. The model includes a turbulence model, a spray model, and a combustion model. The RNGk-ε model is used as the turbulence model, the KH-RT model is used as the spray breakup model, and the SAGE model is used as the combustion model; The first type of boundary condition is used to set the boundary conditions in the CFD model, that is, the wall temperature of each boundary is set. 3. The method of claim 1, wherein in step 2, the heat flux q is output every 1° CA. 4. The method according to any one of claims 1 to 3, characterized in that in step 5, an area with a normalized heat flow density value exceeding 0.5 is selected as a heat insulation treatment area, that is, in the heat flow area Areas with a density value exceeding 0.5 are coated with thermal barrier coatings for thermal insulation, and other areas are not thermally insulated. 5. The method of claim 4, wherein in step 6, a region with a fuel-to-air equivalence ratio exceeding 2 near the wall of the combustion chamber is selected as a heat insulation treatment area.