阅读说明：本技术 一种防止压气机上游混合气冷凝的方法及装置 (Method and device for preventing upstream mixed gas of gas compressor from condensing ) 是由 王文将 刘义强 金昶明 钱鹏飞 于 2019-10-28 设计创作，主要内容包括：本发明涉及一种防止压气机上游混合气冷凝的方法及装置,所述方法包括步骤：根据发动机的当前工况,计算水蒸气占比值,水蒸气占比值包括：第一水蒸气占比值、第二水蒸气占比值和第三水蒸气占比值,第一水蒸气占比值表征为再循环废气环境中水蒸气的占比χ-e,第二水蒸气占比值表征为大气环境中水蒸气的占比χ-a,第三水蒸气占比值为表征为压气机上游混合气环境中水蒸气占比值χ-m；根据水蒸气占比值,计算出EGR率的限制值；根据EGR率的限制值,对EGR率的目标值进行限制；根据限制后的所述EGR率的目标值,获取EGR的实际流量；根据实际流量调整所述EGR率的限制值,以防止压气机冷凝现象的发生；本发明能够避免引入再循环废气导致在压气机上游出现冷凝现象。(The invention relates to a method and a device for preventing mixed gas at the upstream of a gas compressor from condensing, wherein the method comprises the following steps: calculating a water vapor ratio value according to the current working condition of the engine, wherein the water vapor ratio value comprises the following steps: a first water vapor fraction value, a second water vapor fraction value, and a third water vapor fraction value, the first water vapor fraction value being characterized as a water vapor fraction χ in a recirculated exhaust gas environment e The second water vapor proportion is characterized as the water vapor proportion chi in the atmospheric environment a The third water vapor proportion ratio is characterized as the water vapor proportion ratio chi in the mixed gas environment at the upstream of the air compressor m (ii) a Calculating a limit value of the EGR rate according to the water vapor ratio; limiting the target value of the EGR rate according to the limit value of the EGR rate; acquiring the actual flow of the EGR according to the limited target value of the EGR rate; adjusting the limit value of the EGR rate according to the actual flow to prevent the condensation phenomenon of the compressor; the invention can avoid the condensation phenomenon at the upstream of the compressor caused by introducing the recirculated waste gas.)

1. A method for preventing the condensation of a mixture upstream of a compressor is characterized by comprising the following steps:

calculating a water vapor ratio value according to the current working condition of the engine, wherein the water vapor ratio value comprises the following steps: first water vapor ratio, secondA water vapor fraction value and a third water vapor fraction value, the first water vapor fraction value being characterized as the water vapor fraction χ in the recirculated exhaust gas environment_eAnd the second water vapor proportion value is characterized as the water vapor proportion chi in the atmospheric environment_aAnd the third water vapor proportion ratio is characterized as the water vapor proportion chi in the mixed gas environment at the upstream of the air compressor_m；

Calculating a limit value of an EGR rate according to the water vapor ratio;

limiting the target value of the EGR rate according to the limit value of the EGR rate;

controlling the actual opening degree of EGR according to the limited target value of the EGR rate, and acquiring the actual flow of the EGR based on the actual opening degree;

and adjusting the limit value of the EGR rate in the compressor according to the actual flow so as to prevent the condensation phenomenon of the compressor.

2. The method for preventing condensation of the mixture upstream of the compressor according to claim 1, wherein the formula for calculating the limit value of the EGR rate from the water vapor fraction value is:

3. the method for preventing the condensation of the mixture upstream of the compressor as recited in claim 1, wherein the calculation formula of the first water vapor ratio is selected by determining whether a value of the air-fuel ratio λ is greater than a predetermined value.

4. The method for preventing the condensation of the mixture upstream of the compressor as set forth in claim 3, wherein when the value of the air-fuel ratio λ is not greater than the preset value, the first water vapor ratio is calculated by the formula:

wherein A is CO₂The molar concentration of (c);

b is H₂The molar concentration of O;

d is N₂The molar concentration of (c);

f is CH_nThe molar concentration of (c).

5. The method for preventing the condensation of the mixture upstream of the compressor according to claim 4, wherein the calculation formula of the first water vapor proportion value includes the following calculation formula:

F＝1-λ

wherein lambda is an air-fuel ratio which represents the mass ratio of air to fuel in the compressor;

n is a carbon to hydrogen ratio, which characterizes the atomic ratio of carbon atoms to hydrogen atoms;

x is N in air injected into compressor₂Relative to O₂Volume fraction of (a);

y is CO in air injected into compressor₂Relative to O₂Volume fraction of (a);

z is the ratio of water vapor in air injected into compressor to O₂Volume fraction of (a).

6. A method of preventing condensation in a mixture upstream of a compressor as set forth in claim 3, wherein said air is combusted as it is being compressedThe value of the ratio lambda is larger than the preset value, and the calculation formula of the first water vapor ratio is as follows: the calculation formula of the first water vapor ratio is as follows:

wherein A is CO₂The molar concentration of (c);

b is H₂The molar concentration of O;

d is N₂The molar concentration of (c);

e is O₂The molar concentration of (c).

7. The method for preventing the condensation of the mixture upstream of the compressor according to claim 6, wherein the calculation formula of the first water vapor ratio value includes the following calculation formula:

wherein lambda is an air-fuel ratio which represents the mass ratio of air to fuel in the compressor;

n is a carbon to hydrogen ratio, which characterizes the atomic ratio of carbon atoms to hydrogen atoms;

x is N in air injected into compressor₂Relative to O₂Volume fraction of (a);

y is CO in air injected into compressor₂Relative to O₂Volume fraction of (a);

z is the ratio of water vapor in air injected into compressor to O₂Volume fraction of (a).

8. A method for preventing condensation of a mixture upstream of a compressor as set forth in claim 3, wherein said second water vapor fraction value is calculated by the formula:

wherein, P_aIs the pressure of the atmosphere;

T_ais the temperature of the atmosphere;

RH_ais the relative humidity;

P_s(T_a) Is the saturated water vapor pressure of the atmospheric environment.

9. A method for preventing condensation of a mixture upstream of a compressor as set forth in claim 3, wherein said third water vapor fraction value is calculated by the formula:

wherein, P_mThe pressure of the mixed gas at the upstream of the compressor;

T_mthe temperature of the mixed gas at the upstream of the gas compressor;

RH_mrelative humidity of the mixed gas;

P_sm(T_m) The saturated vapor pressure of the mixture at the upstream of the compressor.

10. An apparatus for preventing condensation of a mixture upstream of a compressor, comprising:

the first calculation module is used for calculating a water vapor ratio value according to the current working condition of the engine, and the water vapor ratio value comprises the following steps: the first water vapor ratio,A second water vapor fraction value and a third water vapor fraction value, the first water vapor fraction value being characterized as the water vapor fraction χ in the recirculated exhaust gas environment_eAnd the second water vapor proportion value is characterized as the water vapor proportion chi in the atmospheric environment_aAnd the third water vapor proportion ratio is characterized as the water vapor proportion chi in the mixed gas environment at the upstream of the air compressor_m；

The second calculation module is used for calculating a limit value of the EGR rate according to the water vapor proportion value;

a target value limiting module for limiting a target value of the EGR rate according to the limit value of the EGR rate;

the actual flow obtaining module is used for controlling the actual opening degree of EGR according to the limited target value of the EGR rate and obtaining the actual flow of the EGR based on the actual opening degree;

and the execution module is used for adjusting the limit value of the EGR rate in the compressor according to the actual flow so as to prevent the condensation phenomenon of the compressor.

Technical Field

The invention relates to the technical field of EGR (exhaust gas recirculation), in particular to a method and a device for preventing mixed gas at the upstream of a gas compressor from condensing.

Background

With the development of economy, the automobile industry also develops, and the increase of the number of automobiles also causes problems, such as environmental pollution, energy exhaustion and the like, especially environmental pollution, and each year, the emission of exhaust gas of automobiles is large, resulting in certain environmental pollution.

Currently, many automobile manufacturers adopt an Exhaust Gas Recirculation (EGR) technique, in which a part of Exhaust Gas generated in an oil extraction machine or a gasoline engine is led out of an Exhaust pipe, and an appropriate amount of Exhaust Gas is led into an intake pipe through a control valve such as an EGR valve to be mixed with fresh air, and the Exhaust Gas is introduced into a fuel chamber to participate in combustion, because the Exhaust Gas contains a large amount of carbon dioxide, the carbon dioxide cannot be combusted but can absorb a large amount of heat, thereby reducing the combustion temperature of the air-fuel mixture in the cylinder, and reducing NO_xThe production amount of (a).

However, in automobiles supercharged engines incorporating EGR technology are used, where EGR technology is divided into high pressure EGR and low pressure EGR, where low pressure EGR technology typically mixes fresh air and cooled recirculated exhaust gas upstream of the compressor, high pressure EGR technology typically mixes fresh air and exhaust gas in the intake manifold, where fresh air in the atmosphere is unsaturated humid air, typically at temperatures between-40 ℃ and 40 ℃, whereas as the main components of recirculated exhaust gas are carbon dioxide and water vapour, the cooled temperature is above 100 ℃, when two fresh air and recirculated exhaust gas of different temperatures are mixed, the high temperature gas will transfer heat to the low temperature gas, the mixed gas temperature being intermediate between the temperatures of the two source gases.

From the thermodynamic knowledge, when the temperature of the humid air is lower than the temperature corresponding to the saturated water vapor pressure, the water vapor condensation phenomenon occurs, the temperature continues to decrease, and water drops occur. It can be seen that the recirculated high temperature exhaust gas is mixed with relatively cool fresh air and condensation may occur. Since the fresh air and recirculated exhaust gas mix upstream of the compressor, after condensation occurs, water droplets can accelerate into the compressor, causing damage to the blades.

Therefore, the above problems need to be solved by those skilled in the art.

Disclosure of Invention

In view of the above problems in the prior art, an object of the present invention is to provide a method and an apparatus for preventing condensation of a mixture upstream of a compressor, which can avoid the occurrence of condensation upstream of the compressor due to the introduction of recirculated exhaust gas.

In order to solve the above problems, the present invention provides a method for preventing the condensation of a mixture gas upstream of a compressor, comprising the steps of:

calculating a water vapor ratio value according to the current working condition of the engine, wherein the water vapor ratio value comprises the following steps: a first, second, and third water vapor fraction value, the first water vapor fraction value being characterized as the water vapor fraction χ in the recirculated exhaust gas environment_eAnd the second water vapor proportion value is characterized as the water vapor proportion chi in the atmospheric environment_aAnd the third water vapor proportion ratio is characterized as the water vapor proportion ratio chi in the mixed gas environment at the upstream of the air compressor_m；

Calculating a limit value of an EGR rate according to the water vapor ratio;

limiting the target value of the EGR rate according to the limit value of the EGR rate;

controlling the actual opening degree of EGR according to the limited target value of the EGR rate, and acquiring the actual flow of the EGR based on the actual opening degree;

and adjusting the limit value of the EGR rate in the compressor according to the actual flow so as to prevent the condensation phenomenon of the compressor.

Further, the formula for calculating the limit value of the EGR rate from the water vapor proportion value is:

further, the calculation formula of the first water vapor proportion value is selected by judging whether the value of the air-fuel ratio lambda is larger than a preset value.

Further, when the value of the air-fuel ratio λ is not greater than the preset value, the calculation formula of the first water vapor proportion value is as follows:

wherein A is CO₂The molar concentration of (c);

b is H₂The molar concentration of O;

d is N₂The molar concentration of (c);

f is CH_nThe molar concentration of (c).

Further, in the formula for calculating the first water vapor proportion value, the formula for calculating the value a, the value B, the value D and the value F is respectively as follows:

F＝1-λ

wherein lambda is an air-fuel ratio which represents the mass ratio of air to fuel in the compressor;

n is a carbon to hydrogen ratio, which characterizes the atomic ratio of carbon atoms to hydrogen atoms;

x is N in air injected into compressor₂Relative to O₂Volume fraction of (a);

y is CO in air injected into compressor₂Relative to O₂Volume fraction of (a);

z is the ratio of water vapor in air injected into compressor to O₂Volume fraction of (a).

Further, when the value of the air-fuel ratio λ is greater than the preset value, the calculation formula of the first water vapor proportion value is as follows: the calculation formula of the first water vapor ratio is as follows:

wherein A is CO₂The molar concentration of (c);

b is H₂The molar concentration of O;

d is N₂The molar concentration of (c);

e is O₂The molar concentration of (c).

Further, in the formula for calculating the first water vapor proportion value, the formula for calculating the value a, the value B, the value D and the value E is respectively as follows:

wherein lambda is an air-fuel ratio which represents the mass ratio of air to fuel in the compressor;

n is a carbon to hydrogen ratio, which characterizes the atomic ratio of carbon atoms to hydrogen atoms;

x is N in air injected into compressor₂Relative to O₂Volume fraction of (a);

y is CO in air injected into compressor₂Relative to O₂Volume fraction of (a);

z is the ratio of water vapor in air injected into compressor to O₂Volume fraction of (a).

Further, the calculation formula of the second water vapor proportion value is as follows:

wherein, P_aIs the pressure of the atmosphere;

T_ais the temperature of the atmosphere;

RH_ais the relative humidity;

P_s(T_a) Is the saturated water vapor pressure of the atmospheric environment.

Further, the calculation formula of the third water vapor proportion value is as follows:

wherein, P_mThe pressure of the mixed gas at the upstream of the compressor;

T_mthe temperature of the mixed gas at the upstream of the gas compressor;

RH_mrelative humidity of the mixed gas;

P_sm(T_m) The saturated vapor pressure of the mixture at the upstream of the compressor.

The invention also provides a device for preventing the upstream mixed gas of the compressor from condensing, which comprises:

the first calculation module is used for calculating a water vapor ratio value according to the current working condition of the engine, and the water vapor ratio value comprises the following steps: a first, second, and third water vapor fraction value, the first water vapor fraction value being characterized as the water vapor fraction χ in the recirculated exhaust gas environment_eThe second water vapor fraction value being characterized as water vapor in the atmospheric environmentRatio chi_aAnd the third water vapor proportion ratio is characterized as the water vapor proportion chi in the mixed gas environment at the upstream of the air compressor_m；

The second calculation module is used for calculating a limit value of the EGR rate according to the water vapor proportion value;

a target value limiting module for limiting a target value of the EGR rate according to the limit value of the EGR rate;

the actual flow obtaining module is used for controlling the actual opening degree of the EGR according to the limited target value of the EGR rate and obtaining the actual flow of the EGR based on the actual opening degree;

and the execution module is used for adjusting the limit value of the EGR rate in the compressor according to the actual flow so as to prevent the condensation phenomenon of the compressor.

Due to the technical scheme, the invention has the following beneficial effects:

according to the method and the device for preventing the upstream mixed gas of the gas compressor from condensing, a relational expression of the water vapor ratio and the corresponding humidity and the EGR rate limit value is established in an engine control link through atmospheric environmental parameters and the temperature and the pressure of the upstream mixed gas of the gas compressor, the EGR rate limit value is controlled through controlling the water vapor ratio and the corresponding humidity, the target value of the EGR rate is further controlled, and the phenomenon of condensation on the upstream of the gas compressor caused by introducing recirculated waste gas is avoided.

Drawings

In order to more clearly illustrate the technical solution of the present invention, the drawings used in the description of the embodiment or the prior art will be briefly described below. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.

FIG. 1 is a flow chart of a method for preventing condensation of a mixture upstream of a compressor according to an embodiment of the present invention;

FIG. 2 is a flowchart of step S104 provided by the embodiment of the present invention;

FIG. 3 is a schematic structural diagram of an apparatus for preventing condensation of a mixture upstream of a compressor according to an embodiment of the present invention;

fig. 4 is a schematic structural diagram of an actual traffic acquiring module according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

Reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic may be included in at least one implementation of the invention. In the description of the present invention, it is to be understood that the terms "upper", "lower", "left", "right", "top", "bottom", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," and the like are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein.

Example one

The embodiment provides a method and a device for preventing mixed gas at the upstream of a compressor from condensing, as shown in figure 1

The method comprises the following steps:

s101, calculating a water vapor ratio value according to the current working condition of the engine, wherein the water vapor ratio value comprises the following steps: a first, second, and third water vapor fraction value, the first water vapor fraction value being characterized as the water vapor fraction χ in the recirculated exhaust gas environment_eAnd the second water vapor proportion value is characterized as the water vapor proportion chi in the atmospheric environment_aAnd the third water vapor proportion ratio is characterized as the water vapor proportion chi in the mixed gas environment at the upstream of the air compressor_m；

S102, calculating a limit value of an EGR rate according to the water vapor ratio;

s103, limiting the target value of the EGR rate according to the limit value of the EGR rate;

s104, controlling the actual opening degree of EGR according to the limited target value of the EGR rate, and acquiring the actual flow of the EGR based on the actual opening degree;

and S105, adjusting the limit value of the EGR rate in the compressor according to the actual flow so as to prevent the compressor from condensing.

Specifically, the EGR rate is a ratio of a mass of recirculated exhaust gas to a total mass of intake air for a cylinder of a compressor in the engine.

As shown in fig. 2, the step of obtaining the actual flow rate of EGR based on the limited target value of the EGR rate includes the steps of:

s201, acquiring a target value of the EGR rate after limitation;

s202, determining the target opening degree of the EGR valve according to the target value of the EGR rate, and sending an opening and closing instruction of the EGR valve based on the target opening degree;

s203, controlling the opening and closing of the EGR valve according to the opening and closing instruction to obtain the actual opening degree of the EGR valve;

and S204, determining the actual flow of the EGR according to the actual opening degree.

Specifically, the formula for calculating the limit value of the EGR rate from the water vapor proportion value is:

further, the formula of the limit value of the EGR rate is derived from a defined formula of the mass EGR rate, the defined formula of the mass EGR rate being

Wherein m is_eFor the mass of the recirculated exhaust gas, m_aIs the mass of atmospheric air.

Further, according to the relationship between mass and molar mass: M-n-M, the formula defining the mass EGR rate translates to:

can also be expressed as:wherein the molar mass M of the exhaust gas_eRelationship of value of air-fuel ratio λ:

further, when the deviation value of the exhaust gas molar mass with respect to the air molar mass is within ± 0.3%, it can be assumed that the gas molar mass is equal to the air molar mass, which is 28.97 g/mol.

Further, when the atmospheric air and the recirculated exhaust gas are mixed, the water vapor content in the mixed gas is the sum of the water vapor content in the atmospheric air and the water vapor content in the recirculated exhaust gas, i.e. chi_mn_m＝χ_an_a+χ_en_e。

Further, the formula of the EGR rate is obtained by combining the formula of the water vapor content with the formula of the mass EGR rate, and the formula of the EGR rate is subjected to limit value calculation to form a limit value formula of the EGR rate.

Specifically, the calculation formula of the first water vapor proportion value is selected by judging whether the value of the air-fuel ratio lambda is larger than a preset value.

Further, the preset value is 1.

Specifically, when the value of the air-fuel ratio λ is not greater than the preset value, the calculation formula of the first water vapor proportion value is:

wherein A is CO₂The molar concentration of (c);

b is H₂The molar concentration of O;

d is N₂The molar concentration of (c);

f is CH_nThe molar concentration of (c).

Further, in the formula for calculating the first water vapor proportion value, the formula for calculating the value a, the value B, the value D and the value F is respectively as follows:

F＝1-λ

wherein lambda is an air-fuel ratio which represents the mass ratio of air to fuel in the compressor;

n is a carbon to hydrogen ratio, which characterizes the atomic ratio of carbon atoms to hydrogen atoms;

x is N in air injected into compressor₂Relative to O₂Volume fraction of (a);

y is CO in air injected into compressor₂Relative to O₂Volume fraction of (a);

z is the ratio of water vapor in air injected into compressor to O₂Volume fraction of (a).

Specifically, when the value of the air-fuel ratio λ is greater than the preset value, the calculation formula of the first water vapor proportion value is: the calculation formula of the first water vapor ratio is as follows:

wherein A is CO₂The molar concentration of (c);

b is H₂The molar concentration of O;

d is N₂The molar concentration of (c);

e is O₂The molar concentration of (c).

Further, in the formula for calculating the first water vapor proportion value, the formula for calculating the value a, the value B, the value D and the value E is respectively as follows:

wherein lambda is an air-fuel ratio which represents the mass ratio of air to fuel in the compressor;

n is a carbon to hydrogen ratio, which characterizes the atomic ratio of carbon atoms to hydrogen atoms;

x is N in air injected into compressor₂Relative to O₂Volume fraction of (a);

y is an implantCO in air in compressor₂Relative to O₂Volume fraction of (a);

z is the ratio of water vapor in air injected into compressor to O₂Volume fraction of (a).

Specifically, the calculation formula of the second water vapor proportion value is as follows:

wherein, P_aIs the pressure of the atmosphere;

T_ais the temperature of the atmosphere;

RH_ais the relative humidity;

P_s(T_a) Is the saturated water vapor pressure of the atmospheric environment.

Specifically, the calculation formula of the third water vapor proportion value is as follows:

wherein, P_mThe pressure of the mixed gas at the upstream of the compressor;

T_mthe temperature of the mixed gas at the upstream of the gas compressor;

RH_mrelative humidity of the mixed gas;

P_sm(T_m) The saturated vapor pressure of the mixture at the upstream of the compressor.

As shown in fig. 3, the apparatus for preventing condensation of the mixture upstream of the compressor includes:

the first calculation module 10 is configured to calculate a water vapor proportion value according to a current operating condition of the engine, where the water vapor proportion value includes: a first, second, and third water vapor fraction value, the first water vapor fraction value being characterized as the water vapor fraction χ in the recirculated exhaust gas environment_eAnd the second water vapor proportion value is characterized as the water vapor proportion chi in the atmospheric environment_aAnd the third water vapor proportion ratio is characterized as the water vapor proportion chi in the mixed gas environment at the upstream of the air compressor_m；

The second calculation module 20 is used for calculating a limit value of the EGR rate according to the water vapor proportion value;

a target value limiting module 30 for limiting a target value of the EGR rate based on the limit value of the EGR rate;

an actual flow rate obtaining module 40, configured to control an actual opening/closing degree of the EGR according to the limited target value of the EGR rate, and obtain an actual flow rate of the EGR based on the actual opening/closing degree;

and the execution module 50 is used for adjusting the limit value of the EGR rate in the compressor according to the actual flow so as to prevent the compressor from condensing.

As shown in fig. 4, the actual flow rate obtaining module 40 includes:

a target value acquisition unit 401 for acquiring a target value of the EGR rate after restriction;

a target opening degree acquiring unit 402 configured to determine a target opening degree of the EGR valve according to the target value of the EGR rate;

an instruction sending unit 403, configured to send an opening/closing instruction of the EGR valve based on the target opening/closing degree;

an actual opening and closing degree obtaining unit 404, configured to control opening and closing of the EGR valve according to the opening and closing instruction, and obtain an actual opening and closing degree of the EGR valve;

and an actual flow rate determining unit 405 configured to determine an actual flow rate of the EGR according to the actual opening degree.

The embodiment provides a method and a device for preventing condensation of a gas compressor upstream mixed gas, which can establish a relation between a water vapor ratio and corresponding humidity and an EGR rate limit value through atmospheric environmental parameters and the temperature and pressure of the gas compressor upstream mixed gas in an engine control link, control the EGR rate limit value through controlling the water vapor ratio and the corresponding humidity, further perform the EGR rate target value, and avoid the condensation phenomenon at the gas compressor upstream caused by introducing recirculated exhaust gas.

It should be noted that, for the sake of simplicity, the foregoing method embodiments are described as two series of acts, but those skilled in the art should understand that the present invention is not limited by the described order of acts, as some steps may be performed in other orders or simultaneously according to the present invention. Similarly, the modules of the device for preventing the mixture upstream of the compressor from condensing refer to computer programs or program segments for performing one or more specific functions, and the distinction between the modules does not mean that the actual program code is also necessarily separate. Further, the above embodiments may be arbitrarily combined to obtain other embodiments.

In the foregoing embodiments, the descriptions of the embodiments have respective emphasis, and reference may be made to related descriptions of other embodiments for parts that are not described in detail in a certain embodiment. Those of skill in the art will further appreciate that the various illustrative logical blocks, units, and steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate the interchangeability of hardware and software, various illustrative components, elements, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design requirements of the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present embodiments.

The foregoing description has disclosed fully preferred embodiments of the present invention. It should be noted that those skilled in the art can make modifications to the embodiments of the present invention without departing from the scope of the appended claims. Accordingly, the scope of the appended claims is not to be limited to the specific embodiments described above.