FI104108B - Method and apparatus for reducing nitrogen oxide emissions from internal combustion engines - Google Patents

Description

104108

Method and apparatus for reducing nitrogen oxide emissions from internal combustion engines

The invention relates to a method according to the preamble of claim 1 and to a device according to the preamble of claim 5 for carrying out this method.

In a known process of this type, the nitrogen oxides contained in the exhaust gas and a reducing agent in the catalyst coupled downstream of the engine to which the reducing agent and the exhaust gases are fed. The catalyst required in this known process (SCR = Selective Catalytic Reduction) requires not only high stand-by costs but also large space, since SCR catalysts for superhigh stoichiometric combustion engines are substantially larger than, for example, three-way catalysts for Otto engines. In addition, there will be increased maintenance costs. In this case, the starting point is that particulates contained in the exhaust gas of diesel engines in particular contaminate the catalyst. This results in a power limitation if short cleaning intervals are not maintained.

Nevertheless, SCR catalysts have a very limited service life. In addition, the SCR catalyst requires a relatively high temperature of 280 to 350 ° C in order to achieve sufficiently high rates of conversion of nitric oxide. But then, all engine starts produce relatively long operating times, with little or no reduction in nitric oxide if the engine does not have an additional engine heater, which again generates a high additional power requirement. Another drawback is that the system consisting of the catalyst and the reductant dosing system responds very slowly to changes in the load, i.e. changes in the nitric oxide and exhaust mass flow, which, in the case of such changes, results in either periodic increases in nitrogen oxide A further disadvantage is that the catalyst provides a significant increase in flow resistance, which can affect the operation of the exhaust gas compressor connected after the engine. This is especially true for two-stroke engines where the catalyst must be positioned before the exhaust supercharger due to the required high temperature. In this case, it is often necessary to equip the engine with an auxiliary fan, which smoothes the airflow without fluctuations in the passage, in order to enable stable operation of the exhaust compressor. But such a helicopter also has high availability and operational costs.

However, it is known from DE 2 742 609 that an additional amount of CnH is injected into the combustion chamber, primarily in the form of normal fuel, to reduce the formation of nitric oxide. This injection must occur when the 2,104,108 fire event is fully running. Accordingly, it is a question of after-injection of fuel to the actual combustion event. With this, free oxygen is bound before it reacts with nitrogen to form nitric oxide. In contrast, this known process thus takes place in contrast to the state of the art, whereby nitrogen oxides from combustion are subsequently reduced, thereby preventing the formation of nitrogen oxides from the outset. In this case, it is to be noted that the effect thus obtained is only negligible, since the nitrogen produced by combustion when bound by oxygen is an advantage over the fuel injected afterwards. In addition, it should be noted that at least a portion of the fuel injected into the fully running combustion event after combustion is burned and thus not available for the desired reaction. DE 2 742 609 thus provides no useful information for reducing the drawbacks of the prior art.

JP A 63-140862 also discloses a prior art solution.

JP A 1-318716 discloses an internal combustion engine from which the present invention starts, and which is already known to inject ammonia into the combustion chamber as an NOx reducer before opening the exhaust valve. Thus, the aim is to achieve an effective reduction of nitrogen oxide emissions from combustion.

It is an object of the present invention to further improve this prior art technique in a simple and inexpensive manner such that said emission reduction is achieved without the need for a catalyst. In this case, it must be ensured that the reducing agent, on the one hand, no longer burns and, on the other hand, that there is sufficient time to react with the nitrogen oxides and adjust the spraying of the reducing agent as desired.

·· 25 A methodical solution to this object is apparent from the characterizing part of claim 1.

Thus, the process of the invention ensures that the injected reducing agent no longer participates in combustion without the injector time of the reducing agent being too late so that no further reaction with NOx can take place (e.g. due to a cold combustion chamber) and the amount of reducing agent is optimal. ^

By injection of the reductant according to the invention into the combustion chamber, after the combustion has passed the peak, the reaction takes place with the reducing agent and nitrogen. and, as the experiments show, preferably without the use of catalyst 35. The measures of the invention thus completely avoid the drawbacks of the prior art. Injection of the reductant into the combustion chamber 3,104,108 eliminates the cost of manufacturing and maintaining the catalyst so far, as well as the space requirement of the catalyst and the flow resistance provided by the catalyst. The elimination of the flow resistance caused by the catalyst also ensures that the exhaust gas compressor 5 connected after the engine is guaranteed stable operation under all conditions. The direct injection of the reducing agent into the combustion chamber also ensures that the same high efficiency is maintained even with long operating times. Another particular advantage of the measures of the invention is to see that full efficiency can be achieved when the engine is started, and without the need to heat the engine while it is stationary. Furthermore, the measures according to the invention ensure that changes in the spray rates of the reducing agent are effective immediately, which enables the spray rates to be adjusted depending on the load or speed or the like.

The device implementing the method according to the invention, in turn, is characterized by what is stated in the characterizing part of claim 5.

15 These measures provide a robust and correspondingly undisturbed system with minimal space and energy requirements. In the design of the injection equipment, it is preferable to refer to the fuel injection equipment. This ensures high performance with a long service life combined with a low cost structure.

Preferred and convenient embodiments are set forth in claims 6-8. Thus, the pressure-generating apparatus may be suitably constructed as an injection pump, which provides a particularly simple and inexpensive design and guarantees particularly good durability.

In another preferred embodiment, each injection nozzle may be constructed as a multi-hole nozzle. This allows for a good distribution of the injected reducing agent over the entire combustion chamber under its influence.

Other appropriate embodiments and advantageous developments of the above operations will be apparent from the following description of an exemplary embodiment with reference to the accompanying drawing, in which Figure 1 is a sectional view of a diesel engine having a device for injecting a reducing agent; from the nozzle.

The principle structure and mode of operation of a diesel engine are known in itself and therefore do not require any further explanation in this context.

The diesel engine shown in principle in Figure 1 includes a plurality of adjacent cylinders 1, which are closed by means of a cylinder head 2 104108 disposed thereon. Each cylinder 1 includes a running up and down piston 3 operable with the crankshaft which defines the movable boundaries of the combustion chamber 4 to which the fuel is injected. The cylinder head 2 has air and exhaust suction and discharge valves 5 and an injection nozzle 6 5 for injecting fuel. Injection nozzle 6 is connected to the fuel injection pump 8 by a high pressure line 7. Fuel injection occurs when the piston has sealed the intake air.

Diesel engines of this type are operated with an excess of air (lambda> 1), resulting in a superchiometric combustion with a high nitrogen oxide content of 10 (NOx). However, in order to reduce nitrogen oxide emissions in these types of engines, combustion exhaust gas is reacted with a reducing agent. Suitable reducing agents are ammonia and / or urea or similar non-hydrocarbon substances. As the reductant reacts with the nitrogen oxides contained in the exhaust gas, nitrogen and water are formed in the form of water vapor and thus harmless substances.

The reaction of the reducing agent with nitric oxides takes place at that time. in the engine in combustion chamber 4. For this purpose, the reducing agent is injected into the combustion chamber. Accordingly, there is another injection device for the reducing agent adjacent to the fuel injection system. These two injection devices can be operated independently of each other, whereby the fuel and the reducing agent can be injected independently. In order to inject the reducing agent, it is used in the form of a solution, deliberately in the form of an aqueous solution. The so-called piston 3 suitable additives may be added to the reducing agent to prevent corrosion and / or corrosion.

Here, the injection equipment of the reducer comprises an injection nozzle 9 located above the cylinder head 2, which is connected to the injection pump 11 by means of a high pressure line 10. Naturally, it would be conceivable to have several, preferably equally spaced, injection nozzles. The injection pump 11 for the reducing agent may be further developed in its construction and mode of operation by the construction of fuel pumps 30 known per se. The reducer injection pump 11e may be mounted to the side of the engine housing and may be driven by a camshaft 12 powered by the engine crankshaft which may extend over a plurality of adjacent injection pumps 11. By way of example, instead of an injection pump, the reducing agent could be conveyed to a pressure vessel and the injection could be effected by means of electric 35 or hydraulically controlled valves. In any case, the reducing agent is injected at a pressure such that fogging occurs in the combustion chamber 4, thereby achieving favorable reaction conditions.

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Since the reductant must react with nitrogen oxides from combustion, the reductant is injected only after the combustion has already exceeded its 5 peak points. In the case presented here, the reductant is injected only after the combustion has already reached perfection and is thus substantially completed. It occurs with most diesel engines of this type after the ignition top 35-40 °. In order to react, as far as possible, the injected reducing agent with the total amount of exhaust gas, as stated above, the reducing agent 10 is sprayed as evenly as possible over the entire combustion chamber affected by the injection. Accordingly, the injection pump 9 is constructed as a multi-point nozzle, thereby generating a plurality of injection jets. Their shower position is set so that the fire compartment is completely covered.

The amount of reducing agent required increases with the amount of fuel and is therefore load dependent. The start of the injection depends on the primary engine speed and also the load. As the RPM increases, the start of the reducing agent injection is delayed so that sufficient time is available for the desired reaction. Injection of the reducing agent should not be too early, since the reducing agent is still on. In an individual case, 20 optimization must be performed by determining the appropriate characteristic.

Ko. For converting a type of characteristic curve into practice, the device may comprise adjusting devices 13 having a controller 14, in which the characteristic curve is programmed, by means of which the means for changing the amount of injection and changing the start of the injection are adjustable. Equipment of this type is known per se based on fuel pumps. The camshaft 12 is adjusted to change the start of the injection. The pistons having the peripheral guide edges of the injection pump are rotated to change the amount of injection, as shown by the apparatus 15.

The system of Figure 1 includes a reduction injector nozzle 9 located at the outermost edge of the combustion chamber. But of course one could think of Ψ '·. also so that there is, in addition to or alternatively, a central nozzle injection nozzle.

This type of reduction injector nozzle may be combined with a fuel injection nozzle into a dual nozzle 16 on the basis of Figure 35. The dual nozzle 16 underlying Figure 2 comprises two nozzle needles 17, 18, each adjusting its own injection channel 19, 20, 6 104108, one of which, shown here to the left, is pressurized by a reducing agent and the other, shown here to the right, is fueled. Here, the injected injection channels 19, 20 and the nozzle needles 17, 18 placed therein could also be coaxial with respect to each other.

5 All you have to do is make sure that both spraying systems are completely independent of each other. The injection channel 19 provided on the reducer, in the form of a plurality of nozzle holes 21, enters the combustion chamber, which improves the uniformity of distribution as already mentioned above. The corresponding multiple hole arrangement may also be on the fuel side.

Only one preferred embodiment of the invention is described in greater detail above, without, however, limiting the invention in any way. Of course, it is possible to use the method according to the invention, of course, not only in the case of diesel engines, but also in the case of gas engines, diesel gas engines and alternative fuel engines.

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Claims (8)

1. A method for reducing nitrous oxide emissions from internal combustion engines, in particular self-igniting, air-fueled internal combustion engines, primarily hydrocarbon-free reducing agents, primarily from ammonia and / or urea-fueled combustion, has already passed its climax, or has already ceased combustion, and at the start of injector reduction at the earliest angle of the crankshaft 10 35 ° after the ignition head, whereupon the injector disintegrates and distributes uniformly in the injector varies with load and / or RPM and / or environmental conditions. Process according to Claim 1, characterized in that the reducing agent is injected in the form of an aqueous solution. Method according to one of the preceding claims, characterized in that an additive having lubricating and / or corrosion inhibiting properties is added to the reducing agent. A method according to any one of the preceding claims, characterized in that the reducing agent is sprayed at spray pressure. Apparatus for carrying out the method according to any one of the preceding claims, in a combustion engine, in particular a self-igniting, air-powered internal combustion engine, in particular a diesel engine having an injectable reduct an engine-driven pressure-generating device connected thereto, wherein the injection nozzle or nozzles (9) are / are located on the cylinder head (2), the nozzle or nozzles (9) having a jet position such that the fire-µ 30 space (4) and the regulator spraying apparatus has a regulating apparatus (13) including a regulator (14), characterized in that the regulator (14) is programmed with appropriate characteristics for the injection rate and / or speed and / or ambient of the regulator i Depending on the circumstances, the onset of spraying can be varied. Apparatus according to claim 5, characterized in that the pressure generating apparatus is constructed as an injection pump (11). 104108 Apparatus according to Claim 5 or 6, characterized in that the injection nozzle (s) (9) are / are constructed as multi-hole nozzle (s). 7 104108 Device according to Claim 5 or 6, characterized in that the device 5 has at least one central injection nozzle (16) having two nozzle needles (17, 18), one of which is located in the fuel injection system. and one is placed in the billing system of the reducer. • * ψ: · i: r 104108