KR100199860B1 - Reduction Method of Emissions - Google Patents

Abstract

A method is described for reducing the total emissions during cold start-up from an engine burning hydrocarbon fuels with a post-combustion reactor arranged upstream of the catalytic converter. This method involves (i) an exhaust / air mixture of sufficient concentration of hydrogen and oxygen to apply excessive fuel to the engine combustibility charge and to cause the resulting exhaust / air mixture to ignite with subsequent flames in the postcombustor when the postcombustor is close to ambient temperature. Immediately after the engine is first started, ) Ignite the exhaust / air mixture in the post-combustor immediately after the engine is first operated. In a preferred embodiment of the invention, the excess fuel and / or the additional air causes excess fuel after ignition takes place in the post-combustor to maintain a continuous flame in the post-combustor until at least a portion of the catalytic converter matrix reaches the light-off temperature. And / or additional air is regulated.

Description

Reduction Method of Emissions

1 is a schematic diagram of an engine having an intake and discharge system for realizing the invention.

2 is a graph showing the change in hydrogen and oxygen concentrations in the post-combustion, with the air / fuel ratio supplied to both the exhaust system and the engine and the air / fuel ratio supplied only to the engine.

3 is a graph showing the total emissions from an engine with a late combustor during the operating phase of the court's drive cycle plotted against the fuel / air ratio supplied to the engine.

* Explanation of symbols for main parts of the drawings

12: organ 14: pipe

16: post-combustor 18: igniter

20: Injector 22: Meter

24: Throttle 30: Pump

32: valve

The present invention relates to a method of operating an internal combustion engine with an internal combustion engine having a post-combustor to reduce the amount of emissions during room temperature startup.

Exhaust Catalytic Converter 300 With 400 After reaching a critical temperature called the light-off temperature in between, the mission is to reduce the unburned hydrocarbons, carbon monoxide and oxides in the nitrogen content of the off-gas. It is important to minimize the time spent by the catalyst to reach this temperature during cold start because many legislative release test drive cycles include cold start.

Several solutions have been proposed to reduce the light off time. The simplest solution is to place the catalyst very close to the engine so that it is heated by the exhaust gas before it is cooled by the exhaust system. Catalyst loading, called close-coupling, creates problems when the engine is operated at high speeds and high loads. Under such conditions, the exhaust gas temperature is 850 This is enough to cause permanent damage to the catalyst. Therefore, it is preferable to use one that is mounted slightly apart from an engine called an under-body catalyst without having a tightly coupled catalyst. Such mounting is safe at high speeds and high load operation, but reduces the preheating problem since the exhaust gas is cooled before it reaches the catalyst during the operation phase.

In order to speed up the heating of the catalytic converter, an external heat supply is proposed, in which an electric heater and a microwave heater are used. This proposal introduces significant additional cost and complexity, especially when power requirements are on the order of 2 to 3 kW, especially when there is a 12 volt supply requirement for currents of 166 to 250 amps.

It has been proposed to use chemical energy to reduce the light-off time by injecting and igniting fuel into the exhaust pipe. In this case, the complexity is exacerbated by the fact that the petroleum / air mixture is not reliably ignited when it is diluted from the engine to the exhaust gas, and if it does not, the hydrocarbon emissions on emissions increase abruptly and exacerbate the problem by cooling the catalyst. There is another complexity due to the need to ensure safety, and it is dangerous to have a fuel opening in the hot exhaust pipe.

Another proposal is to use a so-called thermal reactor that blocks the exhaust gas when it is still hot and injects air into the exhaust stream close to the exhaust port. If the mixture is set to be slightly rich, combustion will increase the temperature in the exhaust gas at a reduced rate. This proposal works, but the benefits it can achieve are limited. Typically the light-off time is reduced to about 2 minutes, which is insufficient to meet a more accurate permitted legal emission level.

Another suggestion is to use a post burner. The engine is again run with a rich mixture and the fresh air is added to the exhaust gas stream, but the mixture is then ignited, for example by sparks, to burn in a chamber arranged immediately upstream of the converter.

It is important to make a difference between the action initiated by ignition in the postcombustor and the action normally occurring at the catalytic converter surface. In late combustors, open flames are created that propagate through the gas and emit light that is not confined to the surface. Ignition is ignited by sparks, pilot flames or heated catalytic elements. When ignited, the flame is not confined to the igniter and the gas burns as if in an unconfined space.

The concept of a post-combustor is not new in itself and it is known since 1967 that it is possible to re-ignite fuel in the emission mixture under controlled conditions. CD Haynes's report, published by the Moter Industry Research Association of Great Britain (MIRA), under Report No. 1967/5, proposed the use of a post-combustion unit as a means of reducing pollution. The heat produced is simply dissipated in the heat sink. do. As a heat sink, as well as the matrix of the catalytic converter, the post-combustor works to reduce the light-off time of the converter.

The use of a late combustor to heat the exhaust gas before reaching the catalytic converter is proposed in particular in US Pat. No. 3,889,464 and the fuel for the postcombustor does not come from the exhaust gas. An advanced aspect of this idea, described in EP A 0 422 432, is the use of partially burnt combustion products in the exhaust gas to fuel the post-combustion. In the latter proposal, the mixture force to the engine is strengthened by diverting some of the measured air to flow directly into the exhaust pipe.

For the purpose of heating the catalytic converter to reduce the life-off time, the post-combustor has become the most efficient proposal. When the engine is operated with a properly enriched mixture and the exhaust system is preheated and fresh air is added to the hot exhaust gas, so-called cold flames occur in the exhaust system, allowing the mixture to re-ignite. This can reduce preheating time to less than one minute.

However, in the prior art proposals, it is necessary to wait some time after the engine is started before the gas can be ignited in the postcombustor. This means that the mixture that reaches the post-combustion system when the engine and exhaust system is cold loses most of its heat to the exhaust system and the cold flame generated by the gas when leaving the engine is passed through the cold exhaust manifold and down pipe. It weakens when it passes and becomes weaker when injecting additional cold air into the exhaust stream. The exhaust / air mixture cannot be ignited when there is no cold flame known to help ignite. Wait until the exhaust gas reaches the afterburner. The catalytic converter heats up rapidly to the life-off temperature when the postcombustor is activated, but during the initial stage before the postcombustor is ignited, the exhaust gas is released to the atmosphere without being cleaned by the postcombustion or by the catalytic converter.

Therefore, the invention seeks to have a system to ignite the post-combuster as soon as possible after the engine is first ignited to minimize the light off time of the catalytic converter and to mitigate the prior problems of the prior art.

According to the invention, there is provided a method of reducing the total amount of emissions during room temperature startup from an engine burning hydrocarbon fuels with a post-combustor arranged upstream of the catalytic converter and the method constitutes the next step.

Add excess fuel to the engine's combustible charge and the resulting exhaust / air mixture with a sufficient concentration of hydrogen and oxygen to keep the post-burner continuously sparking and igniting when the post-combustor is near ambient. Immediately after this first run, air is added to the engine exhaust to be present in the exhaust / air mixture.

Immediately after the engine is first run, the exhaust / air mixture in the postburner is ignited.

Preferably the exhaust / air mixture changes the excess fuel and / or additional air after ignition occurs in the post-combustor so that the post-combustor maintains a continuous flame until at least a portion of the catalytic converter matrix reaches the light-off temperature. By adjusting.

The minimum concentration of hydrogen and oxygen in the exhaust / air mixture depends on the gas flow conditions and the postcombustor design so that it can maintain a continuous flame and can be ignited in a cold postcombustor immediately after the engine is first run. For well mixed masses of gas sampled from the exhaust / air mixture of cold combustion bombs, the minimum values of experimentally produced hydrogen and oxygen concentrations are 3% and 6%, respectively. However, in practical situations with conventionally designed post-combustion reactors where the flow conditions around the ignition source are unstable and the mixing of additional air is not continued and the engine exhaust flow pulsates, the hydrogen concentration is typically 6% above 5% to enable ignition. It is necessary to be. Low concentrations may be used to maintain continuous flame after ignition, but should be well above the minimum of 3% and 6% for hydrogen and oxygen, respectively. Gas concentrations expressed in percentages throughout the specification are given in volume, not in mass.

The importance of hydrogen in the effluent mixture was not realized in the prior art and therefore the hydrogen concentration was not cited. However, it is inferred from the carbon dioxide concentrations required to achieve the improvements claimed in the prior art that the hydrogen concentration present in the actual post-combustor of the present invention is twice smaller than the hydrogen concentration required for ignition, and even under ideal conditions, less than 3% below the minimum combustibility limit. can do.

From this, it can be seen that the mechanism of action occurring in the prior art differs from that which depends on the present invention. In the prior art, if the exhaust gases are not cooled by passing through a cold exhaust system, the hot, partially burnt components will interact with each other at a slow rate, and under these conditions, if sufficient oxygen is present and an ignition source is provided, combustion will be It relies on the fact that it acts on hydrocarbons and carbon monoxide. However, some time is required to start the engine before it can be ignited in the post-combustion furnace, in which unburned hydrocarbons are released from the exhaust system. Adding air and increasing the mixture force increase the thermal action between the gases in the outlet, thus reducing the preheating time of the outlet system. However, this thermal action makes it more difficult to operate by lowering the concentration of gases that can be combusted in the mixture reaching the postcombustor.

Enriching the mixture supplied to the engine to increase the concentration of unburned hydrocarbons and carbon monoxide in the mixture reached at the postcombustor does not significantly reduce the preheating time (especially at idle speeds required for the first part of the legal drive cycle). It has a proven reverse productivity with a significant increase in the concentration of unburned hydrocarbons released before running the postburner.

In the prior art, increasing the fuel abundance supplied to the engine in the early stages of preheating the basic operation of the post-combustor relies on supplying hydrocarbons and carbon monoxide as fuel and increasing the concentration of this gas at the outlet. It only increases the total emissions emitted from the entire emissions system. If present in sufficient concentration, the present invention avoids this problem by first recognizing the important part made by hydrogen and using other mechanisms to ignite the postcombustor.

The improvement of the invention over the prior art is highlighted by the timing in the case of first engine operation. In the prior art, the post-combustor cannot run during the idling period of the first 20 seconds of the drive cycle because the exhaust gas becomes cold while the emission emissions follow the legal drive cycle in which they are measured. When the car is running under load, the temperature of the gas in the postcombustor rises quickly and after a few seconds, the postcombustion unit ignites. When activated, the post-combustor itself reduces the hydrocarbon emissions which increase the maximum force to raise the amount of heat produced to heat the catalytic converter. The total light / off time of the catalytic converter therefore extends to 30 seconds or more after the engine is first run.

In the present invention, the mixture force is reinforced immediately after or during cranking to achieve the required hydrogen concentration and the postcombustor is immediately ignited. The fuel abundance supplied to the engine for this purpose needs to be so dramatic that it requires an amount of fuel at a charge that can be burned by twice the fuel in stoichiometry. The actual level of abundance needs to be high to ensure that all the injected fuel does not form a burnable charge due to wall wetting.

Indeed, a strong ignition that follows a continuous flame that completely swallows the post-combustion chamber will occur less than a second after the engine is first run. Within 5 seconds, the front burner heat of the catalytic converter downstream of the postburner is reached and the postburner is turned off to prevent overheating of the catalyst.

Thus, in the invention, despite the importance of fueling the engine, the total emissions are reduced, but the hydrocarbons which do not burn before being released to the atmosphere and the post-combustor do not work, and as soon as the post-combustion exhausts, the catalytic converter itself purifies the exhaust gas emitted. Because you have a mission to do. In the prior art, on the other hand, untreated gases are released to the atmosphere for approximately the first 30 seconds of engine operation when the hydrocarbon emissions are worst and there is a consideration of the main rate of emissions given during the entire drive cycle.

In-depth exploration of the nature of the gas in the exhaust / air mixture reaching the post-combustor helps to clearly understand the invention. While starting with a rich mixture, the exhaust gases contain combustible components that include carbon monoxide, unburned hydrocarbons, and diluent gases including hydrogen and carbon dioxide, nitrogen, and water. The presence of hydrogen in the exhaust gas was absent in the prior art because hydrogen is not a combustion product, as is the preferred combustion for other gases present. The reason for the presence of hydrogen includes a mixture of carbon monoxide in which the combustion product equilibrates, known as water gas action, among other components of combustion products at high temperatures and pressures after abundant combustion inside the engine combustion chamber.

Hydrogen from this process is subsequently frozen when the temperature and pressure suddenly drop upon expansion as the gas is released during the engine exhaust stroke. This hydrogen is present in the exhaust gas and its concentration depends on the concentration of carbon monoxide and the H / C ratio of hydrocarbon fuels produced during abundant combustion.

Each combustion component in the exhaust gas has a critical concentration (flammability limit) that cannot form a mixture that can be ignited when cold. When air is mixed with the exhaust gas, the oxygen present in the mixture must reach a critical concentration unique to each fuel component so that it can be ignited. It should be noted that when fresh air is added to the exhaust gas stream, the concentration of the combustion components in the mixture is lowered and the oxygen concentration in the mixture must be distributed between air and the exhaust gas.

Extremely rich fuel measurement of sufficient amounts of constituents in the exhaust gas mixed with additional air to reach critical temperatures while simultaneously forming a mixture that can be ignited at ambient temperature with respect to the concentration of unburned hydrocarbons and carbon monoxide and the oxygen concentration in the exhaust / air mixture. Can't even make in. For this reason, the invention cannot be made by extrapolation from the results obtained in the prior art.

Instead, the invention is present in an exhaust gas that can simultaneously reach hydrogen and oxygen concentrations so that a sufficient amount of oxygen is mixed with additional air so that the engine is within the flammability limits for hydrogen at ambient temperature when supplied with a very rich mixture to the engine. It is therefore possible to ignite directly in the post-combustion chamber, avoiding the prior art operating zone and supplying the engine with the necessary excessively rich mixture.

It is ignited and the post-combustor of the prior art and the invention perform equally efficiently and quickly heat the catalytic converter to the light-off temperature in a few seconds. The basic difference between the prior art and the invention lies in the mechanism used to achieve ignition. With hydrogen, ignition is instantaneous and does not depend on the preheating rate of the exhaust system. Furthermore, experiments have shown that it is efficient over a wide range of ambient temperatures, including temperatures below zero degrees.

The heavy fuel abundance supplied to the engine causes the engine to heat unevenly and build up large amounts of carbon in the engine combustion chamber. Therefore, it is preferable to reduce the range of abundance as soon as ignited in the post-combustion and the resulting hydrogen and oxygen concentrations are kept above 3% and 6%, respectively, to maintain a stable flame.

The invention can lead to the ignition of the post-combustor shortly after the engine is started, so that the post-combustor can be operated simultaneously with the cranking of the engine. However, it is not necessary to measure the organ with an excessively rich mixture before cranking, and this is done just after the engine is started. This is necessary if the extra rich mixture interferes with the operation of the engine.

In an internal combustion engine that is ignited with a uniform charge of sparks, excess oxygen at the outlet is ensured by supplying the engine with an excessively rich mixture.

The method of realization of the invention is slightly different when applied to a layered charge engine. An example of such an engine is the direct injection of fuel into combustion chambers such as the FORD PROCO 4 administration, ORBITAL, and the diesel engine.

The effect of the occupied floor is made in the combustion chamber area of rich and weak mixture forces. Abundant areas are responsible for producing hydrogen, while weak areas contribute to the presence of oxygen in the exhaust system needed to mix with hydrogen to form a ignitable mixture. In such institutions, it is not proven necessary to inject additional air into the exhaust system or to enrich the mixture. However, it is necessary to throttle the suction in order to reduce the air content in the combustion chamber.

In both in-cylinder injections, the delayed injection timing allows fuel to enter the exhaust system directly, and this technique is used to increase the amount of heat released after the combustor is started.

The invention will be further described by way of example with reference to the accompanying drawings.

1 shows an engine 12 through which air is supplied through an air flow meter 22 and the air supply is controlled by a butterfly throttle 24. The fuel enters the air stream by the injector 20. The exhaust gas from the engine is guided by a pipe 14 to a catalytic converter made of two bricks 10a and 10b which are in front of the afterburner 16 with the spark igniter 18. Air is added to the exhaust gas flow in the exhaust pipe 14 by the pump 30 and the additional air flow is regulated by the valve 32.

In normal operation, the engine runs on stoichiometric fuel to air ratio and no fuel is added to the exhaust stream. The postburner 16 is inefficient and the three-way catalytic converter works satisfactorily to clean the exhaust gas in the usual way. The chemical action in the converter is initiated by the converter when it reaches the light on / off temperature, and the temperature of the exhaust gas, aided by the exothermic action occurring in the converter, causes the converter to be operated at a moderately high temperature to ensure that it operates correctly without assistance from the postcombustor. It serves to maintain.

The purpose of the post-combustor 16 is to reduce the light off time of the catalytic converters 10a and 10b. By injecting excessive fuel through the injector 20 so that the exhaust gas flow during operation contains combustible components, the engine moves and is injected by the pump 30 so that additional air is mixed with the binary components to form a combustible mixture and the post-combustor 16 The spark igniter 18 at) ignites the mixture to create a flame that heats the converter brick 10a. The invention relates to controlling additional air and excess fuel so that the mixture in the post-combustor 16 will ignite as soon as possible after the engine is first run.

FIG. 2 shows a map showing the concentration of hydrogen and oxygen in the post-combustion chamber with the overall air-to-fuel mixture supplied to the exhaust system and engine and the air-to-fuel mixture supplied to the substrate only. The vertical axis of the map represents the range of abundant mixture supplied to the engine and the right side of the horizontal axis represents the range of the entire mixture when additional air at the outlet is included in the chemical balance of the total air to fuel. The postcombustor should always be operated in the region on the right side of the vertical axis so that there is excess air in the postcombustor so that hydrogen and carbon monoxide interact with all the combustion gases of the hydrocarbon.

In the map of FIG. 2, there is a line depicting a uniform hydrogen concentration in the postburner at different operating conditions of the postburner and engine. The lines of uniform hydrocarbons and uniform carbon monoxide in the postcombustor can be drawn on this map but omitted. The invention allows the invention to identify the presence of hydrogen and oxygen as the main criterion to determine the flammability of the exhaust / air mixture at ambient temperature when it includes the combustible portions of carbon monoxide and hydrocarbons together with an unburned dilution of carbon dioxide, nitrogen and water. A limiting curve (flammable boundary) bounding the shaded areas on the map is identified by collecting samples of the exhaust / air mixture from the post-combustor under different operating conditions after mixing under stationary conditions in cold combustion bombs and evacuating the exhaust / air mixture. It can be ignited under ideal conditions at this ambient temperature.

The minimum condition for the ignition of the exhaust / air mixture from FIG. 2 is that the hydrogen concentration must, for example, exceed 6% by volume in oxygen at the point C and at least 3% in volume by volume. From a perspective view of the prior art, operating point A is used to achieve thermal action in the exhaust system and point B is used to ignite the postcombustor when the exhaust gas is kept hot and working. None of these points support cold ignition of the exhaust gases. Even point C does not actually support cold ignition, since it is less than ideal mixture conditions in conventionally designed post-combustion engines, the real engine relies on point D (more than 5% hydrogen, typically 6%) to achieve reliable cold ignition. If the ignition occurs, the fuel concentration can be reduced to return to the point close to point C, but it is too close to the flammability limit and cannot work satisfactorily when the flame is extinguished.

The absolute value of the air-to-fuel ratio shown on the map of FIG. 2 is different for different fuels depending on the stoichiometry of the fuel. However, the absolute values of hydrogen and oxygen concentrations required for stable combustion and reliable ignition in the post-combustor at ambient temperature remain the same despite the type of hydrocarbon fuel used.

The improvement made by the invention is shown by the graph in FIG. 3, where the total emissions during the operating phase of the legal drive cycle are drawn against the increasing fuel to air ratio supplied to the engine and D is plotted on the other operating points A in FIG. Well shown. When the mixture is concentrated from A to B and C, after the first 20 seconds of the idle cycle of the legal drive cycle, it is not successful to ignite the postcombustor until after the engine is under load. Through this period, untreated emissions continue to be released into the atmosphere, and the concentration of hydrocarbons contained increases with increasing fuel concentration. If the mixture is further concentrated to a certain threshold sufficient to overcome the hydrogen concentration present in the exhaust gas below the ideal mixture conditions in the later combustor, immediate ignition is possible but combustion becomes unstable. This threshold is, for example, ensured to be safely passed at point D, thereby ensuring immediate ignition and stable combustion by the much higher concentration of hydrogen present and the emissions of the atmosphere are the post-combustor which disposes of the pre-off emissions of the catalytic converter. Results in a very rapid reduction in combustion. After light-off, the catalytic converter has the task of purifying the exhaust gas. The critical period is reduced to a minimum when neither the postburner or catalytic converter is operated.

Prior art has never progressed to the point where there is a sudden change shown in FIG. 3 which signals the transition of ignition to another mechanism by hydrogen. Stepwise interpolation of the prior art with a clear increase in fuel concentration without understanding the important role played by hydrogen for ignition and the critical conditions that must be tripped over to achieve this increases emissions and leads to rough operation of the engine and severe cooling. Extend. This in turn does not cause significant drive problems and does not have sufficient emissions during the initial stages to exceed the permitted limits for the entire statutory drive cycle. All these factors require large and sudden ashing in the overconcentrated mixture, which is a preferred embodiment of the present invention, which is only needed for a short period of time, which makes the mixture ready to be ignited directly into the post-combustor, which eliminates the disadvantages of the prior art.

Claims (15)

A method of reducing the overall emissions during normal temperature startup from an engine combusting a combustible charge with hydrocarbon fuel and having a late combustor arranged upstream of the catalytic converter, when the late combustor is at a temperature close to ambient temperature, In order to ensure that the exhaust / air mixture is ignitable and combustible with a steady-state flame in the post-combustion unit, immediately after the engine is ignited, the exhaust gas of the engine is present in the exhaust / air mixture of hydrogen and oxygen of sufficient concentration. Applying excess fuel to the combustible charge in the engine, applying air, and igniting the exhaust / air mixture in the post-combustion unit immediately after the engine is ignited. The method of claim 1, wherein after the ignition has occurred in the post-continuum to maintain steady flame inside the post-combustor until at least a portion of the catalytic converter matrix reaches the light-off temperature, the excess fuel or additional air is changed. To reduce the emissions by which the exhaust / air mixture is controlled. The method of claim 1 wherein the hydrogen content of the off-gas / air mixture is greater than 5% by volume and the oxygen concentration is at least 6% by volume at or before ignition. 4. A method according to claim 3, wherein after ignition, the hydrogen concentration of the exhaust gas / air mixture is reduced while maintaining at least 3% by volume, and the oxygen concentration is maintained by at least 6% by volume. The method of reducing exhaust gas according to claim 3, wherein the fuel supply is changed so that the hydrogen concentration changes abruptly between the low concentration pack and the high concentration value. 2. A method according to claim 1, wherein the ignition source is operated continuously during the time that the flame inside the postburner is maintained. 2. The method of claim 1 wherein excess fuel is supplied to the engine and sufficient air is applied to the exhaust gas during cranking. 2. A method according to claim 1, wherein when the engine is first operated, excess fuel is supplied to the engine only after cranking and sufficient air is applied to the exhaust gas. 4. The method of claim 3 wherein the flame inside the post-combustor is extinguished after a sufficient time to initiate catalysis inside the catalytic converter. The exhaust gas according to claim 1, wherein the engine is an internal combustion engine that sparks with a uniform charge, and excess air is added directly to the exhaust air flow and supplies an excessively rich uniform mixture to the engine, whereby hydrogen is present in the exhaust gas. Method of reduction. The engine of claim 1, wherein the engine is an engine operating in bed occupancy, with the formation of a secondary layer in the combustion chamber region with an excessively rich and less concentrated mixture concentration, the former generating hydrogen, the latter A method of reducing off-gases such that it is present in the exhaust system of oxygen necessary to form an ignitable mixture. 12. The method of claim 11 wherein charge layer formation is achieved by injecting fuel directly into the combustion chamber. The method of reducing exhaust gas according to claim 1, wherein the engine is a spark ignition engine. The method of reducing exhaust gas according to claim 1, wherein the engine is a compression ignition engine. The method of reducing exhaust gas according to claim 1, wherein the engine is a two-stroke engine.