WO2022252578A1 - 一种实现天然气发动机超低排放的方法及*** - Google Patents

一种实现天然气发动机超低排放的方法及*** Download PDF

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WO2022252578A1
WO2022252578A1 PCT/CN2021/139941 CN2021139941W WO2022252578A1 WO 2022252578 A1 WO2022252578 A1 WO 2022252578A1 CN 2021139941 W CN2021139941 W CN 2021139941W WO 2022252578 A1 WO2022252578 A1 WO 2022252578A1
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catalytic converter
air
natural gas
low emission
twc
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PCT/CN2021/139941
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English (en)
French (fr)
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官维
盛利
林铁坚
宁德忠
刘志治
覃玉峰
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广西玉柴机器股份有限公司
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N11/00—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity
    • F01N11/007—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/08—Other arrangements or adaptations of exhaust conduits
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
    • F01N3/30—Arrangements for supply of additional air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
    • F01N3/30—Arrangements for supply of additional air
    • F01N3/303—Filtering additional air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B37/00—Engines characterised by provision of pumps driven at least for part of the time by exhaust
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1473—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method
    • F02D41/1475—Regulating the air fuel ratio at a value other than stoichiometry
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Definitions

  • the invention relates to the technical field of engine aftertreatment, and more specifically, it relates to a method and system for realizing ultra-low emission of natural gas engines.
  • Natural gas engines In order to meet the requirements of National VI emission regulations (GB17691-2018) for heavy-duty commercial vehicles and engines (emission limit requirements NOx control ⁇ 0.46g/kWh, CH4 ⁇ 0.5g/kWh, NMHC ⁇ 0.16g/kWh, NH3 ⁇ 10ppm), currently Natural gas engines generally adopt the combustion technology route of equivalent + EGR + TWC + ASC. First, the engine controls the original exhaust NOx, NMHC, CH4 and CO to a certain level through internal control technologies such as engine body design, combustion optimization and external cooling EGR strategy, and then combined with external purification (TWC+ASC) Emissions are controlled within the limits of China 6 emission regulations.
  • TWC+ASC external purification
  • the current technical solution of the three-way catalytic converter has high requirements on the control accuracy of the air-fuel ratio (as shown in Figure 1): there are certain differences in the most efficient conversion windows of NOx, CO and HC, and the exhaust gas concentration is lean or rich Neither can maximize the conversion efficiency of NOx, CO, and HC at the same time.
  • the use of the current scheme is limited by the air-fuel ratio window, and it is difficult to achieve ultra-low emission control. As a result, the overall engine emission has little margin compared with the national VI emission limit.
  • the technical problem to be solved by the present invention is to address the above-mentioned shortcomings of the prior art.
  • the first purpose of the present invention is to provide a method for realizing ultra-low emission of natural gas engines.
  • the second object of the present invention is to provide a system capable of realizing ultra-low emission of natural gas engines.
  • the present invention provides a method for realizing ultra-low emissions of natural gas engines, including:
  • the oxygen concentration is increased for the tail gas treated by the TWC catalytic converter, so that the NOx emission after the treatment by the SCR catalytic converter reaches the legal limit.
  • the oxygen concentration of the exhaust gas treated by the TWC catalytic converter is increased by sucking air from the atmospheric environment through Venturi air injection.
  • the oxygen concentration is increased by compressing the air.
  • the present invention provides a system for realizing ultra-low emission of a natural gas engine, including an engine, and the exhaust pipe of the engine is sequentially connected with a TWC catalytic converter, an air supply mechanism, an SCR catalytic converter, and an ASC catalytic converter.
  • the input end of the SCR catalytic converter is provided with an oxygen sensor, and the ECU of the engine is electrically connected to the air supply mechanism and the oxygen sensor respectively;
  • the engine controls the air-fuel ratio in the cylinder with the conversion efficiency of HC and CO in the TWC catalytic converter as the target, so that the HC and CO emissions after being treated by the TWC catalytic converter reach the legal limit;
  • the air replenishment mechanism controls the amount of air replenishment according to the detection value of the oxygen sensor to increase the oxygen concentration of the exhaust gas.
  • the air supply mechanism includes a Venturi tube, and an air supply pipe is provided on the outlet side of the Venturi tube.
  • the air supply pipe is respectively connected to a first branch pipe and a second branch pipe through a three-way joint, the first branch pipe is connected to the atmospheric environment, the first branch pipe is provided with a first control valve, and the second branch pipe is connected to the atmosphere.
  • the second branch pipe is provided with a second control valve, and the ECU is electrically connected to the first control valve and the second control valve respectively.
  • the compressed air source is a booster pump or a compressed air tank.
  • the exhaust pipe between the engine and the TWC catalyst is provided with a turbocharger, and the compressed air source is the turbocharger.
  • the air supply pipe is provided with an air filter.
  • the air supply pipe is provided with a one-way valve.
  • the present invention has the advantages of:
  • the conversion efficiency of HC and CO in the TWC catalytic converter is used as the target to control the air-fuel ratio in the cylinder, so that the air-fuel ratio control is in the high-efficiency conversion window of HC and CO, so that the TWC catalytic converter can efficiently convert HC and CO, and realize Ultra-low emissions of HC and CO; then increase the oxygen concentration to the tail gas treated by the TWC catalytic converter, so that the SCR catalytic converter can efficiently convert NOx, realize ultra-low emission of NOx, and meet the regulatory limit.
  • FIG. 1 is a schematic diagram of the TWC post-treatment reaction
  • Fig. 2 is a structural representation of the present invention
  • Fig. 3 is a structural schematic diagram of the air supply mechanism in the present invention.
  • 1-engine 2-exhaust pipe, 3-TWC catalytic converter, 4-gas supply mechanism, 5-SCR catalytic converter, 6-ASC catalytic converter, 7-oxygen sensor, 8-venturi tube, 9-supplement Air pipe, 10-first branch pipe, 11-second branch pipe, 12-first control valve, 13-compressed air source, 14-second control valve, 15-turbocharger, 16-air filter, 17-single to the valve.
  • a method for realizing ultra-low emissions of natural gas engines including:
  • the in-cylinder air-fuel ratio is controlled with the conversion efficiency of HC and CO in the TWC catalyst 3 as the goal, so that the air-fuel ratio control is in the high-efficiency conversion window of HC and CO, so that the TWC catalyst can efficiently convert HC and CO, and realize the conversion of HC and CO.
  • the SCR catalytic converter can efficiently convert NOx, realize ultra-low emission of NOx, and make the NOx emission treated by the SCR catalytic converter 5 reach the legal limit.
  • the exhaust gas continues to pass through the ASC, and the NH3 that has not participated in the reaction in the SCR reacts with O2 to purify the NH3 emission to a lower level, thereby achieving ultra-low emissions.
  • the oxygen concentration of the tail gas treated by the TWC catalytic converter 3 is increased by aspirating air from the atmospheric environment through Venturi air injection. Compressed air is used to increase the oxygen concentration when drawing air from the atmosphere is insufficient to meet the oxygen concentration requirement.
  • a system for realizing ultra-low emission of a natural gas engine comprising an engine 1, the exhaust pipe 2 of the engine 1 is sequentially connected with a TWC catalytic converter 3, an air supply mechanism 4, an SCR catalytic converter 5, an ASC catalytic converter 6, and an SCR catalytic converter 5
  • An oxygen sensor 7 is provided at the input end, and the ECU of the engine 1 is electrically connected to the air supply mechanism 4 and the oxygen sensor 7 respectively;
  • the engine 1 controls the air-fuel ratio in the cylinder with the conversion efficiency of HC and CO in the TWC catalytic converter 3 as the target, so that the HC and CO emissions after the treatment by the TWC catalytic converter 3 reach the legal limit;
  • the air replenishing mechanism 4 controls the amount of air supplemented according to the detection value of the oxygen sensor 7 to increase the oxygen concentration of the exhaust gas.
  • the air supply mechanism 4 includes a Venturi tube 8, the outlet side of the Venturi tube 8 is provided with an air supply pipe 9, and the air supply pipe 9 is respectively connected with a first branch pipe 10 and a second branch pipe 11 through a three-way joint, and the first branch pipe 10 is connected to the atmospheric environment , the first branch pipe 10 is provided with a first control valve 12, the second branch pipe 11 is connected with a compressed air source 13, the second branch pipe 11 is provided with a second control valve 14, and the ECU is electrically connected to the first control valve 12, the second Two control valves 14 .
  • the openings of the first control valve 12 and the second control valve 14 are regulated in real time by measuring the oxygen concentration and the target oxygen concentration, so that the oxygen concentration in the exhaust gas can fully meet the requirements of the system and ensure that the system achieves ultra-low emissions.
  • the compressed air source 13 is a booster pump or a compressed air tank.
  • the exhaust pipe 2 between the engine 1 and the TWC catalyst 3 is provided with a turbocharger 15
  • the compressed air source 13 is the turbocharger 15 .
  • Air supply pipe 9 is provided with air filter 16, can guarantee the cleanliness of air.
  • the gas supply pipe 9 is provided with a one-way valve 17 to prevent exhaust gas from leaking.
  • the conversion efficiency of HC and CO in the TWC catalytic converter is used as the target to control the air-fuel ratio in the cylinder, so that the air-fuel ratio control is in the high-efficiency conversion window of HC and CO, so that the TWC catalytic converter can efficiently convert HC and CO, and realize Ultra-low emissions of HC and CO; then increase the oxygen concentration to the tail gas treated by the TWC catalytic converter, so that the SCR catalytic converter can efficiently convert NOx, realize ultra-low emission of NOx, and meet the regulatory limit.
  • this proposal adds an SCR system, and the emission is controlled through the in-cylinder and after-treatment coordination, which makes the control more flexible, reduces the requirements for the control accuracy of the engine air-fuel ratio, and can increase the gas pollutant emission margin of the natural gas engine, thereby Improve vehicle emission endurance mileage.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)

Abstract

一种实现天然气发动机超低排放的方法，包括：采用TWC催化器（3）、SCR催化器（5）、ASC催化器（6）的排放控制方式；以TWC催化器（3）中HC和CO的转化效率为目标来控制缸内空燃比，使经过TWC催化器处理（3）后的HC和CO排放达到法规限值；对TWC催化器处理（3）后的尾气增加氧浓度，使经过SCR催化器处理（5）后的NOx排放达到法规限值。还提供了一种实现天然气发动机超低排放的***。本申请中TWC催化器对HC和CO进行高效转化；再对TWC催化器处理后的尾气增加氧浓度，使经过SCR催化器对NOx进行高效转化，实现超低排放，满足法规限值。

Description

一种实现天然气发动机超低排放的方法及*** 技术领域
本发明涉及发动机后处理技术领域，更具体地说，它涉及一种实现天然气发动机超低排放的方法及***。
背景技术
为满足重型商用车及发动机国六排放法规(GB17691-2018)要求(排放限值要求NOx控制≤0.46g/kWh，CH4≤0.5g/kWh，NMHC≤0.16g/kWh，NH3≤10ppm)，目前天然气发动机普遍采用当量+EGR+TWC+ASC的燃烧技术路线。首先发动机通过机内控制技术如发动机本体设计、燃烧优化和外部冷却EGR策略将原排NOx、NMHC、CH4和CO控制到一定水平，然后再结合机外净化的方式(TWC+ASC)将发动机总体排放控制在国6排放法规限值之内。
当前的技术方案三元催化器(TWC)对空燃比控制精度要求较高(如图1所示)：NOx与CO和HC的最高效转化窗口存在一定的差异，排气浓度偏稀或偏浓都无法使NOx、CO和HC的转化效率同时达到最高，使用当前方案受空燃比窗口的限制，较难以实现超低排放控制，导致发动机整体排放相对国六排放限值裕度不大，满足下一阶段排放法规存在很大技术挑战，特别是催化器的耐久性难以得到保证。
发明内容
本发明要解决的技术问题是针对现有技术的上述不足，本发明的目的一是提供一种可以实现天然气发动机超低排放的方法。
本发明的目的二是提供一种可以实现天然气发动机超低排放的***。
为了实现上述目的一，本发明提供一种实现天然气发动机超低排放的方法，包括：
采用TWC催化器+SCR催化器+ASC催化器的排放控制方式；
以TWC催化器中HC和CO的转化效率为目标来控制缸内空燃比，使经过TWC催化器处理后的HC和CO排放达到法规限值；
对TWC催化器处理后的尾气增加氧浓度，使经过SCR催化器处理后的NOx排放达到法规限值。
作为进一步地改进，通过文丘里空气引射方式从大气环境中吸取空气来增加TWC催化器处理后的尾气的氧浓度。
进一步地，当从大气环境中吸取空气不足以满足氧浓度需求时，通过压缩空气来增加氧浓度。
为了实现上述目的二，本发明提供一种实现天然气发动机超低排放的***，包括发动机，所述发动机的排气管依次连接有TWC催化器、补气机构、SCR催化器、ASC催化器，所述SCR催化器的输入端设有氧传感器，所述发动机的ECU分别电性连接所述补气机构、氧传感器；
所述发动机以TWC催化器中HC和CO的转化效率为目标来控制缸内空燃比，使经过TWC催化器处理后的HC和CO排放达到法规限值；
所述补气机构根据氧传感器的检测值来控制空气补充量来增加尾气的氧浓度。
作为进一步地改进，所述补气机构包括文丘里管，所述文丘里管的出口侧设有补气管。
进一步地，所述补气管通过三通接头分别连接有第一分管、第二分管，所述第一分管连通大气环境，所述第一分管上设有第一控制阀，所述第二分管连接有压缩空气源，所述第二分管上设有第二控制阀，所述ECU分别电性连接所述第一控制阀、第二控制阀。
进一步地，所述压缩空气源为增压泵或压缩气罐。
进一步地，所述发动机与TWC催化器之间的排气管设有涡轮增压器，所述压缩空气源为所述涡轮增压器。
进一步地，所述补气管设有空气过滤器。
进一步地，所述补气管设有单向阀。
有益效果
本发明与现有技术相比，具有的优点为：
本发明先以TWC催化器中HC和CO的转化效率为目标来控制缸内空燃比，使空燃比控制处于HC和CO的高效转化窗口，从而使TWC催化器对HC和CO进行高效转化，实现HC和CO超低排放；再对TWC催化器处理后的尾气增加氧浓度，使SCR催化器对NOx进行高效转化，实现NOx超低排放，满足法规限值。
附图说明
图1为TWC后处理反应原理图；
图2为本发明的结构示意图；
图3为本发明中补气机构的结构示意图。
其中：1-发动机、2-排气管、3-TWC催化器、4-补气机构、5-SCR催化器、6-ASC催化器、7-氧传感器、8-文丘里管、9-补气管、10-第一分管、11-第二分管、12-第一控制阀、13-压缩空气源、14-第二控制阀、15-涡轮增压器、16-空气过滤器、17-单向阀。
具体实施方式
下面结合附图中的具体实施例对本发明做进一步的说明。
参阅图2、3，一种实现天然气发动机超低排放的方法，包括：
采用TWC催化器3+SCR催化器5+ASC催化器6的排放控制方式；
以TWC催化器3中HC和CO的转化效率为目标来控制缸内空燃比，使空燃比控制处于HC和CO的高效转化窗口，从而使TWC催化器对HC和CO进行高效转化，实现HC和CO超低排放，使经过TWC催化器3处理后的HC和CO排放达到法规限值；
对TWC催化器3处理后的尾气增加氧浓度，使SCR催化器对NOx进行高效转化，实现NOx超低排放，使经过SCR催化器5处理后的NOx排放达到法规限值。尾气继续经过ASC，SCR中未参与反应的NH3与O2反应，将NH3排放净化至较低水平，从而实现超低排放。
在本实施例中，通过文丘里空气引射方式从大气环境中吸取空气来增加TWC催化器3处理后的尾气的氧浓度。当从大气环境中吸取空气不足以满足氧浓度需求时，通过压缩空气来增加氧浓度。
一种实现天然气发动机超低排放的***，包括发动机1，发动机1的排气管2依次连接有TWC催化器3、补气机构4、SCR催化器5、ASC催化器6，SCR催化器5的输入端设有氧传感器7，发动机1的ECU分别电性连接补气机构4、氧传感器7；
发动机1以TWC催化器3中HC和CO的转化效率为目标来控制缸内空燃比，使经过TWC催化器3处理后的HC和CO排放达到法规限值；
补气机构4根据氧传感器7的检测值来控制空气补充量来增加尾气的氧浓度。
补气机构4包括文丘里管8，文丘里管8的出口侧设有补气管9，补气管9通过三通接头分别连接有第一分管10、第二分管11，第一分管10连通大气环境，第一分管10上设有第一控制阀12，第二分管11连接有压缩空气源13，第二分管11上设有第二控制阀14，ECU分别电性连接第一控制阀12、第二控制阀14。通过实测氧浓度与目标氧浓度来实时调控第一控制阀12、第二控制阀14的开度，使尾气中氧浓度充分满足***的需求，保证***实现超低排放。
在一个实施例中，压缩空气源13为增压泵或压缩气罐。
在一个实施例中，发动机1与TWC催化器3之间的排气管2设有涡轮增压器15，压缩空气源13为涡轮增压器15。
补气管9设有空气过滤器16，可以保证空气的洁净度。补气管9设有单向阀17，防止尾气泄漏。
本发明先以TWC催化器中HC和CO的转化效率为目标来控制缸内空燃比，使空燃比控制处于HC和CO的高效转化窗口，从而使TWC催化器对HC和CO进行高效转化，实现HC和CO超低排放；再对TWC催化器处理后的尾气增加氧浓度，使SCR催化器对NOx进行高效转化，实现NOx超低排放，满足法规限值。
相比传统技术方案，本提案增加了SCR***，排放通过缸内和后处理协同控制，控制更加灵活，降低了对发动机空燃比控制精度的要求，可以提高天然气发动机气体污染物排放裕度，从而提高整车排放耐久里程。
以上仅是本发明的优选实施方式，应当指出对于本领域的技术人员来说，在不脱离本发明结构的前提下，还可以作出若干变形和改进，这些都不会影响本发明实施的效果和专利的实用性。

Claims (10)

  1. 一种实现天然气发动机超低排放的方法，其特征在于，包括：
    采用TWC催化器(3)+SCR催化器(5)+ASC催化器(6)的排放控制方式；
    以TWC催化器(3)中HC和CO的转化效率为目标来控制缸内空燃比，使经过TWC催化器(3)处理后的HC和CO排放达到法规限值；
    对TWC催化器(3)处理后的尾气增加氧浓度，使经过SCR催化器(5)处理后的NOx排放达到法规限值。
  2. 根据权利要求1所述的一种实现天然气发动机超低排放的方法，其特征在于，通过文丘里空气引射方式从大气环境中吸取空气来增加TWC催化器(3)处理后的尾气的氧浓度。
  3. 根据权利要求2所述的一种实现天然气发动机超低排放的方法，其特征在于，当从大气环境中吸取空气不足以满足氧浓度需求时，通过压缩空气来增加氧浓度。
  4. 一种实现天然气发动机超低排放的***，包括发动机(1)，其特征在于，所述发动机(1)的排气管(2)依次连接有TWC催化器(3)、补气机构(4)、SCR催化器(5)、ASC催化器(6)，所述SCR催化器(5)的输入端设有氧传感器(7)，所述发动机(1)的ECU分别电性连接所述补气机构(4)、氧传感器(7)；
    所述发动机(1)以TWC催化器(3)中HC和CO的转化效率为目标来控制缸内空燃比，使经过TWC催化器(3)处理后的HC和CO排放达到法规限值；
    所述补气机构(4)根据氧传感器(7)的检测值来控制空气补充量来增加尾气的氧浓度。
  5. 根据权利要求4所述的一种实现天然气发动机超低排放的***，其特征在于，所述补气机构(4)包括文丘里管(8)，所述文丘里管(8)的出口侧设有补气管(9)。
  6. 根据权利要求5所述的一种实现天然气发动机超低排放的***，其特征在于，所述补气管(9)通过三通接头分别连接有第一分管(10)、第二分管(11)，所述第一分管(10)连通大气环境，所述第一分管(10)上设有第一控制阀(12)，所述第二分管(11)连接有压缩空气源(13)，所述第二分管(11)上设有第二控制阀(14)，所述ECU分别电性连接所述第一控制阀(12)、第二控制阀(14)。
  7. 根据权利要求6所述的一种实现天然气发动机超低排放的***，其特征在于，所述压缩空气源(13)为增压泵或压缩气罐。
  8. 根据权利要求6所述的一种实现天然气发动机超低排放的***，其特征在于，所述发动机(1)与TWC催化器(3)之间的排气管(2)设有涡轮增压器(15)，所述压缩空气源(13)为所述涡轮增压器(15)。
  9. 根据权利要求5所述的一种实现天然气发动机超低排放的***，其特征在于，所述补气管(9)设有空气过滤器(16)。
  10. 根据权利要求5所述的一种实现天然气发动机超低排放的***，其特征在于，所述补气管(9)设有单向阀(17)。
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