KR20050013996A - Spark ignition engine including three-way catalyst with nox storage component - Google Patents

Abstract

Spark engines include three-way catalysts (TWCs) containing NOx storage components, stoichiometric air-to-fuel ratios during normal operation, and stoichiometric air-to-roads during a limited ratio of engine speed / road maps. Control the air-to-fuel ratio of the engine for lean operation of the fuel ratio, determine the amount of NOx contacting the TWC during lean driving operation in response to data input from the sensor means, and thereby the remaining NOx of the TWC An exhaust system comprising an engine control unit that is configured to determine storage capacity and to return the air-to-fuel ratio stoichiometrically when the remaining NOx storage capacity is less than a predetermined value, the arrangement being continuously Compared to running a spark ignition engine in stoichiometry mode, it is practical to prevent sending more NOx to the atmosphere during engine cycles. .

Description

Spark Ignition Engine INCLUDING THREE-WAY CATALYST WITH NOX STORAGE COMPONENT

A heterogeneous catalyst capable of the simultaneous conversion of nitrogen oxides (NOx), carbon monoxide (CO) and unburned hydrocarbons (HC) in the exhaust gas from a stoichiometrically operated spark-ignition combustion engine is known as a three-way catalyst (TWC). have. NOx reduction easily occurs above the TWC when the air-to-fuel ratio is rich in stoichiometry, while the CO and HC reactions are hindered by insufficient oxygen (O ₂ ). On the lean side, CO and HC conversions are high, but NOx reduction is difficult due to excess oxidizing species. Thus, an effective three-way conversion takes place in a relatively narrow air-to-fuel ratio window. Indeed, oxygen sensors are used to detect the lambda composition of the upstream exhaust gases of the TWC and to adjust the air-to-fuel ratio and thus to balance the exhaust gases.

Typical TWCs are platinum (Pt) and / or palladium (Pd) as oxidation catalyst and rhodium (Rh) as reduction catalyst, and oxygen storage components (OSC), for example ceria-zirconia, on suitable high surface area oxide supports, such as alumina. Mixed oxides. Various small amounts of base metal catalyst promoters, stabilizers and hydrogen sulfide inhibitors can be added. For further details, see WO 98/03251, which is incorporated herein by reference.

The result of using the detected oxygen concentration to control the air-to-fuel ratio is that there is a time delay associated with the adjusted air-to-fuel ratio. This causes disturbances around the control set point. Therefore, when operating in abundance, it is necessary to provide a small amount of O ₂ to consume unreacted CO and HC. Conversely, when the exhaust gas is slightly oxidized, excess O ₂ needs to be consumed. One development in the TWC technology adopted to reduce the disturbances associated with disturbances has been the inclusion of O ₂ storage components in the TWC composition. This component adsorbs (or absorbs) O ₂ in the lean environment and releases it in the rich environment, thus effectively extending the time the exhaust gas is at the set point. Where during the acceleration, a greater amount of HC fuel is needed to maintain the air-to-fuel ratio, this can be provided, for example, by adjusting the fuel injection period.

More recently, there has been a movement towards lean operation of gasoline combustion engines, for example in gasoline direct injection engines. The principle is to improve fuel economy by operating in stoichiometric lean (thus reducing CO ₂ emissions). The main problem in pursuing this strategy is that lean environments inhibit NOx reduction in TWC. One technique developed to address this problem is variously called NOx absorbers / catalysts, lean NOx traps (LNTs) or NOx traps and is based on acid-base washcoat chemistry. It involves the adsorption (or absorption) and storage of NOx in the catalyst washcoat during lean operating conditions and release under enriched operation. The released NOx is catalyzed by nitrogen as it is in TWC.

Typical NOx trap compositions include Pt and Rh on high surface area oxide supports such as Al ₂ O ₃ and NOx storage components such as barium oxide (BaO, eg EP 0758713, incorporated herein by reference). . In general, the loading of the NOx storage component in the NOx trap washcoat can be up to 50% by weight or even higher.

The main problem with the use of NOx trap technology is that it requires very careful and complex engine control to provide rich regeneration of NOx storage components. In addition, many feedback sensors are used to control the function of the NOx trap NOx storage capability, for example sensors that evaluate cumulative engine-out NOx manufacturing using stored engine maps and NOx trap temperature sensors, because NOx storage that absorbs NOx. This is because the efficiency of the components is temperature dependent.

In the art of TWC, it is known to use small amounts (1-3 percent) of BaO or lanthanum oxide (La ₂ O ₃ ) to stabilize the gamma-Al ₂ O ₃ component from sintering during high temperature aging. Base metal catalyst promoters such as barium (Ba), cerium, lanthanum, magnesium, calcium and strontium can also be used (see WO 98/03251 mentioned above).

In WO 99/00177 (incorporated herein by reference) of the present inventors, the present inventors describe a catalytic converter for a lean burn (lean burn) internal combustion engine, such as a direct injection gasoline engine, comprising a catalyst component capable of storing NOx. do. In one embodiment, the catalytic converter comprises a first inner layer having a first platinum group metal (PGM) such as Pt and a NOx storage component such as Ba, and Rh supported on a non-Al ₂ O ₃ support. Supported layered catalysts having a second outer layer containing the same second, different PGM, and optionally OSC, such as a mixed oxide of ceria and zirconia.

Japanese Unexamined Patent Publication (KOKAI) No. 5-317,652 (incorporated herein by reference) describes a substrate and a catalyst comprising an alkaline-earth metal compound and Pt loaded on the substrate. The specification observes that the car is often accelerated and decelerated during urban driving. As a result, this can cause the air-to-fuel ratio to change frequently from the range of values close to the stoichiometric point to the fuel rich side, during a more stable state, for example idle. For example, to lower fuel consumption during urban driving conditions, the gasoline engine is operated on the fuel lean side, such as an air-to-fuel ratio of 23: 1 (weight / weight) or less. The catalyst is designed to adsorb (or absorb) NOx over alkaline earth metals and to release and reduce stored NOx using natural fluctuations to the rich side of the air-to-fuel ratio during lean operating conditions, thus the NOx storage capacity of the alkaline earth metal compound. Play it.

US patent no. 5,575,983 (herein incorporated by reference) is disclosed in Japanese Unexamined Patent Publication No. Observe that the NOx absorption capacity of the catalyst of 5-317,652 is lowered by sulfates. To prevent this, it proposes a catalyst comprising Pt or Pd supported on lithium-stabilized Al ₂ O ₃ and rare earth elements including alkali metals, alkaline earth metals and lanthanum (La).

The inventors of the Japanese Unexamined Patent Publication (KOKAI) No. 5-317, 652 and US patent no. The use of lean-burn gasoline engines other than direct injection gasoline engines, such as those described in 5,575, 983, has not been widely accepted in the vehicle industry and one reason for this is the difficulty in controlling NOx emissions to meet existing and future emission legislation. Believe.

The present invention provides a catalyst and air-to-operation to operate at stoichiometric air-to-fuel ratios during normal operating conditions and to run at a lean of stoichiometric air-to-fuel ratios during a limited ratio of engine speed / road map. A spark ignition engine comprising an exhaust system comprising an engine control unit programmed to control a fuel ratio. In particular, the present invention relates to an engine wherein the catalyst is a three-way catalyst (TWC) comprising a NOx storage component.

1 is a graph showing the HC conversion to temperature after aging of the TWC containing the NOx storage component according to the invention, the TWC at the present state of the art and the NOx trap.

Figures 2, 3 and 4 are graphs showing the% conversion of CO, HC and NOx to lambda for each of the TWCs comprising the NOx storage component according to the present invention, the TWC and NOx trap formulations at the current state of the art.

The inventors now surprisingly find that spark ignition engines, such as port fuel injection gasoline engines, which are engines containing TWCs containing NOx storage components, are available during lean driving conditions, while avoiding the need for expensive and complex control systems. It has been found that it can work in a way that benefits from increased fuel economy.

According to one aspect, the present invention provides a catalyst and engine for operating at stoichiometric air-to-fuel ratios during normal operating conditions and for operating at lean stoichiometric air-to-fuel ratios during a limited ratio of engine speed / road map. A spark ignition engine comprising an exhaust system comprising an engine control unit programmed to control an air-to-fuel ratio of a catalyst, wherein the catalyst comprises a three-way catalyst (TWC) comprising a NOx storage component, the engine The control unit determines the amount of NOx contacting the TWC during lean driving operation in response to the data input from the sensor means, thereby determining the remaining NOx storage capacity of the TWC, and the remaining NOx storage capacity is less than the predetermined value. Is further programmed to return the air-to-fuel ratio to stoichiometry when the batch is continuously spark point in stoichiometric mode. Compared with the engine operation, characterized in that to substantially prevent the sending of more NOx during the engine cycle into the atmosphere.

As used herein, "engine cycle" means the period between key on and key off.

The present invention regenerates NOx storage components, for example, by accelerating natural fluctuations in rich lambda values in the composition of the exhaust gas of a spark ignition engine operated at stoichiometric air-to-fuel ratio during acceleration. NOx stored in the NOx storage component is generally not released, and the NOx storage component is not regenerated under lambda = 1 state, that is, a rich state of lambda = 1 is required. We have also devised a catalyst which promotes the regeneration of the NOx storage component in the TWC, which catalyst is used in preferred embodiments according to the invention.

The present invention provides many very practical advantages. One such advantage is that the vehicle output by the spark ignition engine can be operated on fuel that saves more than similar vehicles operated continuously in stoichiometric conditions. Such increased efficiency can result in lower CO ₂ emissions in the legal test cycle for the vehicle. Lower CO ₂ emissions in the test cycle, the law is interpreted to lower CO ₂ emissions in the "real world" driving conditions. Thus, the vehicle according to the invention can be more "environmentally friendly". Moreover, in countries where taxation (so-called "green tax") is based on the amount of CO ₂ emitted by vehicles, such as the United Kingdom, this can reduce the tax burden on consumers.

The second such advantage is that it can allow a current vehicle comprising a spark ignition engine to accommodate the advantages of the present invention by updating certain components. This is accomplished by simply replacing the existing TWC with a TWC containing sufficient NOx storage components and (i) driving the engine at a lean stoichiometric air-to-fuel ratio during a limited ratio of engine speed / road map and (ii) sensor means. To determine the amount of NOx contacting the TWC during the lean operation in response to data inputs, thereby determining the remaining NOx storage capacity of the TWC and when the remaining NOx storage capacity is less than a predetermined value. It can be programmed by the engine control unit to program the return to the stoichiometry and thereby substantially prevent sending more NOx to the atmosphere during engine cycles as compared to running a spark ignition engine in stoichiometric mode continuously. have.

According to a particularly preferred embodiment, the finite ratio of engine speed / road map is engine idle. This is a particularly advantageous arrangement for providing a safety device system for regenerating NOx storage components. This is because the only thing that can happen to the engine after idle is that it is accelerated and then the exhaust gas that contacts the TWC is temporarily enriched before the engine control unit returns the exhaust gas equivalently. Even if the engine is switched off after idle, NOx can be stored at key on, after which the engine will accelerate. Thus, this preferred arrangement regenerates the NOx storage component by taking advantage of the natural fluctuations toward the composition of the exhaust gas during acceleration. For similar reasons, a limited ratio of engine speed / road map may include low speed operation where the level of NOx emitted by the engine is up to 10 times or more, such as 5 or 2 times or more than during engine idle.

A very real advantage of this preferred arrangement is that it avoids the need for complex and expensive sensors and controls to meet emission laws that currently burden the adoption of NOx traps.

Many means for inputting data into the engine control unit to determine the amount of NOx contacting the TWC, and thus the NOx storage capacity of the NOx storage component, can be used alone or in any mechanical / electronically viable combination. Many sensor means necessary for collecting this information are included in the engine and / or vehicle equipped with the engine and used by the engine control unit for controlling the engine and / or other functions of the vehicle. This is why it is possible to adopt the present invention by updating the vehicle engine control unit with a TWC containing a NOx storage component.

Such selected data that can be used to monitor the NOx storage capacity remaining in the TWC of the present invention includes: the predetermined or predicted time elapsed from the start of the lean driving operation by sensing the state of the appropriate clock means; Air flow over the TWC or manifold vacuum; Ignition timing; Engine speed; Throttle position; Exhaust gas redox reaction compositions using, for example, lambda sensors, preferably linear lambda sensors; The amount of fuel injected from the engine; Where the vehicle comprises an exhaust gas recirculation (EGR) circuit, the position of the EGR valve and thereby the detected amount of EGR; Engine coolant temperature; And the amount of NOx detected upstream and / or downstream of the TWC, where the exhaust system comprises a NOx sensor. When a clock embodiment is used, the predicted time can then be adjusted in response to the data entry.

The spark ignition engine can be operated during normal operating conditions at stoichiometric air-to-fuel ratios. In one embodiment, the engine may be output by gasoline and the engine may be of the port fuel injection or direct injection type. Optionally, the engine can be fueled using alternative fuels such as liquefied petroleum gas (LPG), natural gas (NG), methanol, ethanol or hydrocarbon mixtures including hydrogen gas. The present invention can be used in all grades of sulfur-containing fuels, but particularly efficient are those that contain less than 50 ppm by weight of sulfur, most preferably less than 10 ppm by weight of sulfur.

The present invention may utilize any known TWC composition provided that sufficient NOx storage components are included to perform the desired function.

Typical TWC compositions comprise at least one PGM and may be selected from the group consisting of Pt, Pd, Rh, ruthenium, osmium and iridium and any combination of two or more thereof.

Many NOx storage components are disclosed in the prior art and can be used with the present invention. Typical NOx storage components are alkali metals such as potassium or cesium, for example alkaline earth metals of magnesium, calcium, strontium or Ba, rare earth metal lanthanide metals, preferably La, or any practical combination of two or more thereof, for example And mixed oxides.

Conventional components of the TWC at the present technical level are OSCs and these can also be included in the TWC, with utility according to the invention. In fact, it is common knowledge for those skilled in the art that the NOx trap composition does not contain OSC because the OSC aids in the combustion of HC at the stoichiometric point and at its slightly rich point. This property counters the need for a system that includes a NOx trap composition that regenerates the NOx storage component using reducing species such as HC in the exhaust gas and results from the air-to-fuel ratio adjustment. Thus, the presence of OSC in the NOx trap composition will result in increased fuel consumption for the same amount of NOx storage component compared to the OSC-free NOx trap composition.

Known OSCs are manganese-based compounds supported on optionally stabilized ceria, perovskite, NiO, MnO ₂ , Al ₂ O ₃ containing mixed oxides (see PCT / GB01 / 05124, incorporated herein by reference). ), Mixed oxides of manganese and zirconium (see WO 99/34904, incorporated herein by reference), Pr ₂ O ₃ or any combination of two or more thereof. The ceria stabilizer can be zirconium, lanthanum, aluminum, yttrium, praseodymium or neodymium.

Preferred TWCs for use in the present invention comprise a first PGM, preferably Pt, and a NOx storage component in the first, inner layer and a second PGM, preferably Rh, in the OSC and the second outer layer.

This arrangement is advantageous for the following reasons. During the stoichiometric operation, the Rh / OSC component is active for NOx reduction and other reactions while the Pt component is active for oxidation reactions. During the oxygen rich state, Rh is relatively inert and Pt is active against NO, HC and CO oxidation, while the produced NO ₂ is stored in the adsorbent as nitrate.

Then, when returning to lambda = 1, the OSC component in the second layer prevents the stored NOx from "meeting" the reducing gas so that the NOx remains stored as nitrate. Rh is active against NOx reduction by CO and Pt is active against oxidation of HC and CO.

When accelerated, gas mixing is abundantly deflected, reducing the OSC material so that stored NOx is released when the nitrate becomes thermodynamically unstable. The released NOx is then reduced by the Rh layer with excess reducing agent.

According to a further aspect, the invention provides a vehicle comprising an engine according to the invention.

TWCs are generally located in two positions in the vehicle according to their intended purpose: a close-coupled position, where the TWCs are arranged as close as possible to the exhaust manifold; And in one or both of the subfloor locations. The reason for placing the TWC in the closely doubled position is to control the release immediately after the cold start, because many controlled emissions are emitted during the legal test cycle immediately after the cold start. By placing the TWC close to the engine, the catalyst is contacted by the hot exhaust gas immediately after key on and thus reaches the light off temperature for CO and HC oxidation faster than the TWC in the cooler, subfloor position. However, once the exhaust system has risen to a temperature for effective three-way conversion, the underfloor catalyst bears much of the burden of treating the exhaust gas. In the meantime, the closely doubled TWC is exposed to very high temperatures, for example 1000 ° C. Indeed, one vehicle manufacturer requires testing of a closely double TWC for 50 hours at catalyst bed temperatures of at least 970 ° C and below 1010 ° C. At this kind of temperature, catalysts can lose activity when materials lose their surface area through sintering events, migration of active species into pores, and component interactions. Thus, it can be expected that the TWC, which is in a closely doubled position, will lose some of its activity compared to fresh catalyst. NOx storage components may also lose NOx storage capacity through this high temperature aging due to loss of surface area.

Especially in the TWC located in the closely doubled position, the loss of NOx storage capacity through high temperature aging is not desirable in the present invention, but if some of the NOx storage activity is maintained, the advantages of the present invention are still obtained. Thus, in embodiments of the present invention, fresh TWCs contain sufficient NOx storage components to maintain sufficient NOx storage capacity, for example, after high temperature aging in a tightly ventilated position.

According to a further aspect, the present invention provides an engine control unit for a spark ignition engine comprising an exhaust system comprising a TWC comprising a NOx storage component, wherein the engine control unit is stoichiometric air-to-bed during normal operating conditions. To control the air-to-fuel ratio of the engine to operate at fuel ratio and to operate at stoichiometric lean during a limited ratio of engine speed / road map, and to contact the TWC during lean driving operation in response to data input from the sensor means. Determine the amount of NOx, thereby determining the remaining NOx storage capacity of the TWC and returning the air-to-fuel ratio stoichiometrically when the remaining NOx storage capacity is below a predetermined value, the batch being continuously It is practical to send more NOx to the atmosphere during the engine cycle compared to operating a spark ignition engine in stoichiometric mode. It intended to prevent.

According to a further aspect, the present invention provides a method of treating the exhaust gas of spark ignition engine operation at stoichiometric air-to-fuel ratio during normal operating conditions, wherein the engine comprises an exhaust comprising a TWC comprising a NOx storage component. A system comprising: controlling the engine air-to-fuel ratio to operate in stoichiometric lean during a limited ratio of engine speed / road map and applying the TWC during lean driving operation in response to data input from the sensor means; Determining the amount of NOx contacted, thereby determining the remaining NOx storage capacity of the TWC and returning the air-to-fuel ratio to stoichiometry when the remaining NOx storage capacity is below a predetermined value, the batch Substantially sending more NOx to the atmosphere during engine cycles as compared to running a spark ignition engine in stoichiometric mode. It is to prevent.

In order that the present invention may be more fully understood, the following examples are provided by way of illustration only and with reference to the accompanying drawings.

Example 1- Total Hydrocarbon Complexing

Three catalyst washcoats were tested. Comparative catalyst A is the current state of the art Pt / Rh TWC on a high surface area support which is thermally stable at a ratio of 5Pt: 1Rh and total precious metal loading at 60 g ft ⁻³ .

Catalyst B is a TWC comprising a NOx storage component according to the invention supported on the same substrate. It included a first inner layer of high surface area Al ₂ O ₃ impregnated with NOx storage components such as Pt and BaO, and a second outer layer of mixed oxide OSC impregnated with Rh. The ratio of Pt: Rh and the total precious metal loading were the same as for catalyst A.

Comparative catalyst C is a NO x trap composition comprising a high surface area Al ₂ O ₃ -based mixed oxide support impregnated with Pt, Rh and a NO x storage component. The ratio of Pt: Rh was 6: 1 and the total precious metal loading was 70 g ft ^-3 .

Each washcoat was coated onto a 4.66 x 6 inch (11.9 x 15.2 cm) ceramic substrate of 400 cells (cpsi) 62 cells cm ^-2 per square inch of 0.15 mm wall thickness and the resulting coated substrate was 10% 0. Aged by hydrothermal reaction at 800 ° C. for 5 hours under ₂ /10% H ₂ O / balance nitrogen.

The catalyst was adapted to the exhaust of a four-cylinder 2.0-litre Port Fuel Injection bench mounted engine controlled by a Bosch ME7 control system. The catalyst temperature was increased by the control of a heat exchanger installed in the exhaust line before the catalyst. The temperature ramp rate was 14 ° C./min.

The results for HC complexing (reaction is promoted at 50% efficiency at that temperature) are shown in Figure 1, from which it can be seen that the HC complexing temperature for catalyst B is similar to that of comparative catalyst A. It can also be seen that the HC complexing temperature of Comparative Catalyst C is approximately 30 ° C. higher than Comparative Catalyst A.

These results indicate that the TWC containing the NOx storage component (catalyst B) has very similar activity for HC activity compared to the TWC (comparative catalyst A) of the present state of the art, despite the presence of the NOx storage component. Shows that NOx traps (comparative catalyst C) perform less well than catalyst B or comparative catalyst A, although with higher Pt loading.

Example 2

Disturbed Lambda Scan

The same engine as in Example 1 was used to provide a catalyst injection temperature of 450 ° C. Lambda scans were performed at a frequency of 1 Hz using 10% disturbance (cycles between lambda = 1 values below 10%, ie less than 0.147 lambda, and up to 10% greater than lambda = 1 (1.147 lambda)). These conditions were chosen to stimulate the exhaust gas composition at the inlet to the TWC disposed in the exhaust system including a lambda sensor upstream of the catalyst inlet providing feedback to the engine control unit to maintain the lambda = 1 condition.

The results are shown in FIGS. 2, 3 and 4. As can be seen, TWC (catalyst B) containing NOx storage components performs similarly to TWC (catalyst A), whereas NOx traps (comparative catalyst C) have more lambda scan performance despite having more Pt. Dropped (indicating poor conversion).

Example 3

Engine testing

In a bench test cell, a direct flow strain gauge was installed on a four cylinder, 1.8 liter, 1997 model, Mitsubishi direct injection engine from a vehicle calibrated for the Japanese market. The catalyst substrate prepared according to Example 1 was mounted at approximately 30 cm close double position from the engine exhaust manifold. Substrate volume represented 22% engine cleaning volume (ESV). The concentrations of NOx, HC, CO ₂ , CO and 0 ₂ were measured using a dual bank MEXA (Motor Exhaust Gas Analyser) 9500 sensor that allows for continuous measurement of gas concentrations upstream and downstream of the catalyst. Catalyst injection temperature was measured by thermocouple.

The engine was run from one of two sets of maps: one for uniform mode and the other for lean, stratified mode. The base map for ignition and injection timing and duration was generated by first recording data from the ECU of the vehicle containing the same model of engine as used in the bench test and then basing the map on this information by reverse engineering. . In the uniform mode, the engine was operated at a range of engine speeds and loads and a supplemental map to the base map was generated for the best emissions of NOx, CO and HC emissions under λ = 1 operation. The lean, layered mode was mapped by matching the torque achieved in the uniform mode at the same speed and load requirements.

Prior to testing, the engine was warmed up completely at idle. In the homogeneous mode, the engine was then operated so that the inlet temperature for the closely doubled catalyst was 300 ° C. It was then switched to lean, stratified operation, and the EGR valve position was adjusted until the engine-out NOx was 300 ppm. The EGR valve position was recorded and called a lean set point. The engine was switched back to the uniform mode and the EGR valve was closed. The abundance setting was obtained by increasing the fuel injector pulse width to obtain lambda 0.80. A series of lean / rich cycles was operated as follows. In lean mode, the EGR valve was in the lean setpoint position until the system's NOx efficiency dropped below 75%. The engine then switched back to uniform mode for 15 seconds with fuel injector duration at the rich set point. The cycle was repeated five times and the results obtained for each cycle were recorded. The exhaust system was mounted on the engine and the data were collected in lean, layered mode at 300 ° C. catalyst injection temperature, which is typical of catalyst injection temperature for closely double TWC in the exhaust system of port fuel injection, following the protocol and during idle.

Table 1 shows the NOx storage efficiencies for each of Comparative Catalysts A and C and B which store NOx, and in particular how each catalyst stores 30, 40, 50 and 60 mg of NOx. Thus, the NOx trap (comparative catalyst C) stores 60 mg NOx at 97% efficiency, i.e. 97% of the NOx contacting the catalyst is stored, whereas the TWC (comparison catalyst A) stores 60 mg NOx at 9% efficiency. During the time it took to store, ie, store 60 mg of NOx, the catalyst escaped 91% of the NOx contacting it.

The results of Examples 1, 2, and 3 show that TWCs containing NOx storage components maintain TWC performance despite including NOx storage components and that NOx storage capacity is several times higher than TWC compositions of current state of the art. Shows.

Claims (36)

A catalyst comprising a three-way catalyst (TWC) containing a NOx storage component, and a stoichiometric air-to-fuel ratio during normal operating conditions at stoichiometric air-to-fuel ratio and during a limited ratio of engine speed / road map In a spark ignition engine comprising an exhaust system comprising an engine control unit programmed to control an air-to-fuel ratio of an engine for driving at lean, the engine control unit is lean in response to data input from sensor means. Determine the amount of NOx contacting the TWC during operation, thereby determining the remaining NOx storage capacity of the TWC, and returning the air-to-fuel ratio to stoichiometry when the remaining NOx storage capacity is less than a predetermined value. More programmed, the layout is more during the engine cycle compared to running a spark ignition engine in continuous stoichiometric mode. Spark ignition engine characterized in that to prevent the sending of NOx into the atmosphere substantially. The engine of claim 1, wherein the limited ratio of engine speed / road map is engine idle. 3. An engine according to claim 1 or 2, wherein the limited ratio of engine speed / road map includes an operating state in which the level of NOx emitted by the engine is up to 10 times or more than at engine idle. 4. An engine according to claim 1, 2 or 3, characterized in that it comprises a clock and sensor means and the data input comprises a predetermined or predicted time elapsed from the start of the lean driving operation. The engine of claim 4, wherein the predicted time is subsequently adjusted in response to data input. 6. A method according to any one of claims 1, 2, 3, 4 or 5, characterized in that the sensor means detects airflow above the TWC and the data input comprises the detected value. engine. An engine according to any of the preceding claims, wherein the sensor means detects the manifold vacuum and the data input comprises the detected value. An engine according to any of the preceding claims, characterized in that the sensor means detects the ignition timing and the data input comprises the detected value. An engine according to any one of the preceding claims, wherein the sensor means detects the engine speed and the data input comprises the detected value. An engine according to any one of the preceding claims, wherein the sensor means detects the throttle position and the data input comprises the detected value. Engine according to any of the preceding claims, wherein the sensor means is a lambda sensor, preferably a linear lambda sensor, and the data input comprises a lambda value detected upstream and / or downstream of the TWC. An engine according to any one of the preceding claims, wherein the sensor means detects the amount of fuel injected from the engine and the data input comprises the detected value. An engine according to any one of the preceding claims, including an exhaust gas recirculation (EGR) circuit, wherein the sensor means detects the position of the EGR valve and the data input comprises a detected amount of EGR. An engine according to any one of the preceding claims, wherein the sensor means detects the engine coolant temperature and the data input comprises the detected value. An engine according to any of the preceding claims, wherein the sensor means comprises a NOx sensor and the data input comprises an amount of NOx detected upstream and / or downstream of the TWC. An engine according to any of the preceding claims, wherein it is a gasoline engine. 17. The engine of claim 16, wherein it is a port fuel injection engine. 17. The engine of claim 16, wherein it is a direct injection engine. 16. An engine according to any one of claims 1 to 15, which is fueled by a hydrocarbon mixture comprising liquefied petroleum gas, natural gas, methanol, ethanol or hydrogen gas. An engine according to any of the preceding claims, wherein the TWC comprises at least one platinum group metal (PGM). 21. The engine of claim 20, wherein the at least one PGM is platinum (Pt), palladium, rhodium (Rh), ruthenium, osmium and iridium and any combination of two or more thereof. 23. An engine according to claim 21 or 22, wherein the NOx storage component comprises an alkali metal, an alkaline earth metal or a rare earth metal or a combination of any two or more thereof. The engine of claim 22, wherein the alkali metal is potassium or cesium. 23. The engine of claim 22 wherein the alkaline earth metal is magnesium, calcium, strontium or barium. 23. The engine of claim 22 wherein the rare earth metal is a lanthanide metal, preferably lanthanum. 26. The engine of any one of claims 20 to 25, wherein the TWC further comprises an oxygen storage component (OSC). 27. The method of claim 26, wherein the OSC is selected from manganese-based compounds supported on selectively stabilized ceria, perovskite, NiO, MnO ₂ , alumina containing mixed oxides, mixed oxides of manganese and zirconium, Pr ₂ O ₃ or any of them. An engine comprising at least two combinations. 28. The engine of claim 27 wherein the ceria stabilizer is zirconium, lanthanum, aluminum, yttrium, praseodymium or neodymium. 2. The TWC according to claim 1, characterized in that the TWC comprises a first PGM, preferably Pt, and a NOx storage component in the first, inner layer and a second PGM, preferably Rh, in the OSC and the second outer layer. engine. A vehicle comprising an engine according to any of the preceding claims. 31. The vehicle of claim 30, wherein the TWC is in a closely doubled position. 32. A vehicle according to claim 30 or 31, wherein the fresh TWC contains sufficient NOx storage component to maintain sufficient NOx storage capacity after high temperature aging. An engine control unit for a spark ignition engine comprising an exhaust system comprising a TWC comprising a NOx storage component, the engine control unit operating at a stoichiometric air-to-fuel ratio during normal operating conditions and having a limited ratio of engine speed / During the road map, the air-to-fuel ratio of the engine is controlled to operate in stoichiometric lean, and in response to data input from the sensor means to determine the amount of NOx contacting the TWC during lean driving operation, thereby It is programmed to determine the remaining NOx storage capacity and return the air-to-fuel ratio to stoichiometry when the remaining NOx storage capacity is below a predetermined value, and this batch is continuously compared to the spark ignition engine operation in stoichiometric mode. Engine control characterized by substantially preventing the sending of more NOx to the atmosphere during the cycle unit. A method of treating the exhaust gases of spark ignition engine operation at stoichiometric air-to-fuel ratio during normal operating conditions, wherein the engine comprises an exhaust system comprising a TWC comprising a NOx storage component, the method comprising Controlling the engine air-to-fuel ratio to operate at stoichiometric lean during engine speed / road map and determining the amount of NOx contacting the TWC during lean driving operation in response to data input from the sensor means, thereby Determining the remaining NOx storage capacity of the TWC and returning the air-to-fuel ratio to stoichiometry when the remaining NOx storage capacity is below a predetermined value, the batch continuously operating spark ignition engine in stoichiometric mode. To substantially prevent sending more NOx to the atmosphere during engine cycles. Engine as substantially described herein with reference to the accompanying embodiment. A method of treating an exhaust gas of a spark ignition engine substantially as described herein with reference to the accompanying embodiment.