WO2008012005A1

WO2008012005A1 - Spark-ignited internal combustion engine for gaseous fuels, and method for the operation of such an internal combustion engine

Info

Publication number: WO2008012005A1
Application number: PCT/EP2007/006310
Authority: WO
Inventors: Martin Bechtold; Frank Jacobi; Martin Matt; Jörg SIEVERT; Klaus Wunderlich
Original assignee: Daimler Ag
Priority date: 2006-07-28
Filing date: 2007-07-17
Publication date: 2008-01-31
Also published as: DE102006035077A1

Abstract

Spark-ignited internal combustion engines for gaseous fuels are known in prior art. Catalytic converters for aftertreating exhaust gases are also known in prior art, said catalytic converters being rapidly heated during the warm-up period of the internal combustion engine by afterburning fuel in the emission system. The invention relates to a spark-ignited internal combustion engine (1) that is operated by means of gaseous fuel and comprises an emission system (7) with an exhaust gas aftertreatment device (9), upstream of which a mixture of air and gaseous fuel provided for afterburning can be delivered in order to increase the exhaust gas temperature. The air is supplied from a secondary air pump (11) while the gaseous fuel is supplied from a fuel gas tank (14). A mixing device (12) for mixing air and gaseous fuel is provided, said mixing device (12) supplying a mixture of air and gaseous fuel at a certain ratio. The invention applies to spark-ignited internal combustion engines for gaseous fuels.

Description

FORCED INTERNAL COMBUSTION ENGINE FOR GASEOUS FUELS AND METHOD FOR OPERATING SUCH A COMBUSTION ENGINE

The invention relates to a foreign-fired internal combustion engine for gaseous fuels with the features of the preamble of claim 1 and a method for operating a foreign-fired internal combustion engine for gaseous fuels with the features of the preamble of claim. 7

German Offenlegungsschrift DE 102 49 274 A1 discloses a gas-fueled internal combustion engine in which a gas-air mixture is introduced into the exhaust system upstream of the catalytic converter for the purpose of rapid heating of the catalytic converter. From an air filter, air is pumped into the exhaust system by a secondary air pump. In order to improve afterburning of the exhaust gas and heating of the catalyst, gaseous fuel is supplied to the air from the secondary air pump from a gas tank via a gas valve. With the method shown, it is not possible to achieve an accurate metering of the gaseous fuel in order to produce a good fuel gas and a good mixing with the air. Depending on the operating point, different pressures prevail in the exhaust system, as a result of which different amounts of air are pumped through the secondary air pump into the exhaust system. The Problem of this device is therefore in the exact mixing of the amount of fuel to the amount of secondary air.

The object of the invention is in contrast to provide a foreign-fired internal combustion engine for gaseous fuels available, in addition to the heating of a catalyst during cold start air and gaseous fuel is introduced in the correct mixing ratio in the exhaust system. Another object of the invention is to provide a method of operating such an internal combustion engine.

This object is achieved by an internal combustion engine with the features of claim 1 and by a method for operating an internal combustion engine with the features of claim 7.

The inventive, externally ignited internal combustion engine for gaseous fuels has a mixing device for mixing air and gaseous fuel. The mixer provides a mixture of air and gaseous fuel in a particular ratio.

Future exhaust gas legislation requires efficient catalyst heating at the start of the internal combustion engine to quickly reach the operating temperature of the catalytic converter and reduce exhaust emissions. According to the state of the art of petrol-gasoline, this is produced by a rich fuel-air mixture, which is supplied with air in the exhaust tract via a secondary air pump. By the after-reaction of the unburned fuel components and the carbon monoxide with the injected air in the exhaust system, a strong temperature increase in the exhaust gas is achieved, which is the catalyst brings quickly to operating temperature. In internal combustion engines with gaseous fuels, such as natural gas (CNG, compressed natural gas), but only a very low enrichment is possible, whereby a catalyst heating by subsequent Lufteinblasen and post-reaction is not effectively possible. The additional fuel gas necessary for a post-reaction is therefore not achieved by enrichment of the mixture in the cylinder, but is blown together with the secondary air into the exhaust system upstream of the catalyst. Since the injected air volume fluctuates and depends on the exhaust backpressure, it is essential for a good afterburning to be able to regulate the amount of fuel supplied as well. This is done by means of a mixing device with which a certain ratio of supplied air and additionally injected gaseous fuel is adjustable.

Since the pressure in the air line from the secondary air pump to the exhaust system is dependent on the exhaust pressure in the exhaust system and therefore fluctuates, it is advantageous if the ratio of the air supplied from the secondary air pump and additionally injected, gaseous fuel is independent of the pressure of the supplied air adjustable , In this way, effective afterburning is possible at different exhaust pressures in different operating conditions at any time.

The ratio of the supplied air and the gaseous fuel to each other is fixed in the mixing device or controllable in a more complex design by a control unit depending on the operating point of the internal combustion engine. The mixing device is constructed so that at least one check valve and a pressure control valve are provided. Thus, the air from the secondary air pump can be attributed to the gaseous fuel.

The mixing device is constructed so that in each case at least one check valve and a pressure regulating valve are provided for the air and the gaseous fuel. The pressure control valves in the air or fuel line are arranged within the mixing device and are regulated by the respective other gas flow so that a predetermined ratio of the two gases is maintained. Any type of mixing device that adjusts a predetermined ratio of the two gases is usable, but a simple and less susceptible structure is preferable. With such a mixing device, a fuel-air mixture in the correct mixing ratio is injected into the exhaust system at each exhaust back pressure.

The inventive method for operating an externally ignited, operated with gaseous fuel internal combustion engine is characterized in that for the rapid heating of an exhaust gas treatment device, air and gaseous fuel is fed into an exhaust system upstream of an exhaust aftertreatment device. The exhaust aftertreatment device is designed for example as a 3-way catalyst. The air and the gaseous fuel burn in an exothermic reaction and heat the catalyst at the start of the engine quickly to its operating temperature. By means of a mixing device, the amount of fuel is metered independently of the exhaust back pressure depending on the amount of air and / or the air pressure. As a result, both a lack of air and an excess of air in the fuel gas for afterburning avoided. The air and the gaseous fuel are mixed in the mixing device. In this way, a good mixing of the two gases is guaranteed until it enters the exhaust system. If the two gases are already mixed in the mixing device, no further devices or processes are necessary in order to introduce the two gases into the exhaust system for good afterburning. By means of this method, at the start of the internal combustion engine and at low exhaust gas temperatures outside the warm-up, the catalyst can be heated in order to achieve the highest possible pollutant conversion in the catalyst.

In a further embodiment of the method according to the invention is set in lean operation of the internal combustion engine in the mixing device rich fuel-air mixture and added to the exhaust gas. Internal combustion engines with gaseous fuel, such as natural gas, can be operated with a lean mixture in certain operating ranges without combustion incidents occurring. In order to achieve an exothermic after-reaction in the exhaust system in this case, however, a rich fuel-air mixture is adjusted in the mixing device.

In a further embodiment of the method according to the invention, a late ignition timing is set at stoichiometric operation of the internal combustion engine, in order thereby to delay the combustion. In addition, a stoichiometric fuel-air mixture is adjusted by the mixing device and added to the exhaust gas upstream of the catalyst. In a further embodiment of the invention, the ratio between the amount of air and the amount of gaseous fuel is regulated in the mixing device with pressure regulating valves connected in cross. In this way, a correct ratio between the amount of air and the amount of gaseous fuel is always set at different pressures in the exhaust system.

Further advantages, features and combinations of features will become apparent from the description and the drawings. An embodiment of the invention is shown in simplified form in the drawing and explained in more detail in the following description.

Showing:

Fig. 1 is a schematic representation of

Internal combustion engine and Fig. 2 is a schematic representation of the mixing device.

In Fig. 1 is a schematic representation of an internal combustion engine 1 for gaseous fuels, such as natural gas, shown. Such internal combustion engines are known by the term CNG (Compressed Natural Gas) internal combustion engine. The gaseous fuel is hereinafter referred to as fuel gas. The internal combustion engine 1 consists of a motor housing 2 with a cylinder head, not shown, which is shown in four-cylinder in-line construction. However, other cylinder numbers and arrangements are also conceivable. On the intake side, a throttle valve 3 and an intake system 4 are arranged on the internal combustion engine 1. The intake air flows through an air filter 5 and the throttle valve 3 in the intake system 4 and is passed over four individual intake 6 in the cylinder head.

On the exhaust side, an exhaust system 7 is provided on the internal combustion engine 1, which collects the exhaust gases from the internal combustion engine 1 in an exhaust manifold 8 and from there an exhaust aftertreatment system 9, such as a catalyst, passes. From there, the cleaned exhaust gases leave the exhaust system 7 into the environment via a silencer (not shown).

Furthermore, an air line 10, a secondary air pump 11, a mixing device 12 and a plurality of secondary air lines 13 are arranged in the immediate vicinity of the internal combustion engine 1. In the mixing device 12, the air with fuel gas from a fuel gas tank 14 is intensively mixed and then close to several, in particular four secondary air lines 13 of the exhaust system 7 close the internal combustion engine 1 is supplied. In this case, each secondary air line 13 is connected to a single exhaust manifold pipe 15 upstream of a collection point 16. In an embodiment not shown, a central introduction of the secondary air can be provided in a manifold of the exhaust system 7. This fuel gas-air mixture reacts exothermally or burns due to the hot exhaust gas in the exhaust system 7 and brings in this way the exhaust system 7 downstream catalyst 9 quickly to its operating temperature. This is required when starting and warming up the internal combustion engine 1. However, it is also possible, in the case of operating states of low exhaust gas temperature, to heat the catalytic converter 9 by means of a secondary reaction by means of secondary air injection and addition of fuel gas. A rich fuel mixture for combustion in the internal combustion engine 1 with a pure Lufteinblasung for post-reaction, as is the case with conventional gasoline petrol engines is not possible in internal combustion engines with fuel gas in the entire desired air ratio. Therefore, additional fuel gas must be supplied to the secondary air. In a lean operation of the internal combustion engine 1, that is, in an operation with excess air in the combustion chamber, a rich fuel-air mixture, that is, a mixture with lack of air, blown into the exhaust system 7 for afterburning, so as to exothermic reaction by afterburning obtained, which heats the catalyst 9.

Since the exhaust pressure in the exhaust system 7 is subject to strong fluctuations, the amount of air that is pumped by the secondary air pump 11 against the exhaust pressure in the exhaust system 7, also varies. The secondary air pump 11 is usually designed as a simple, electrically or mechanically driven pump, which is not readjusted to pressure fluctuations on the pressure side, but is controlled only to an operating state or standstill. A fluctuating back pressure on the pressure side can not be compensated by such a pump, which means that at different pressures in the exhaust system 7 different amounts of air are pumped through the secondary air pump 11. In order to avoid an expensive air mass meter for detecting the secondary air quantity or secondary air mass, a mixing device 12 is provided. Due to the pressure conditions in the air supply via the secondary air pump and the fuel gas supply, the mixing device 12 always sets a predetermined ratio of air quantity to gas quantity. 2, a possible embodiment of such a mixing device 12 is shown schematically. The mixing device 12 has a first supply line 17 for air from the secondary air pump 11 and a second supply line 18 for the fuel gas from the fuel gas tank 14 and for the fuel gas-air mixture formed later a leading-off line 19 to the four secondary air lines 13. In both supply lines 17, 18, the air or the fuel gas flows in each case to a pressure regulating valve 20; 21, whose control pressure from the other medium via a connection 22; 23 from a check valve 24; 25 is formed. The pressure control valves 20, 21 are each connected in cross with the check valves 24, 25.

The air is pumped by the secondary air pump 11 via the first supply line 17 into the first pressure regulating valve 20. From there, the air flows through the first check valve 24 into the mixing chamber 26. The fuel gas flows from the fuel gas tank 14 via the second supply line 18 in the second pressure control valve 21. The fuel gas is in the fuel gas tank 14 under high, but filling-dependent pressure and therefore does not need to be pumped become. From the second pressure control valve 21, the fuel via the second check valve 25 also flows into the mixing chamber 26. In the mixing chamber 26 in the mixing device 12 fuel gas and air is mixed, so that a fuel gas-air mixture is formed, which leaves the mixing device 12 and on the away Line 19 continues to flow into the four secondary air lines 13 or via a central introduction, not shown, in the exhaust system 7. Through the connections 22, 23 are the pressure control valves 20, 21 with the check valves 24, 25 of the other medium in such a cross in combination that at any time a predetermined mixing ratio between air and fuel gas is adjusted. This happens independently of the pressure in the exhaust system 7 and the dependent pressure that the secondary air pump 11 generates.

In an operation of the internal combustion engine 1 with excess air, so-called lean operation, and at low exhaust gas temperature, it is possible controlled by a controller 27 to shift the ratio of air and fuel gas in the mixing device 12 in the direction of a fuel gas excess, thereby increasing To achieve exothermic after-reaction in the exhaust system 7.

There are also other types and designs of the mixing device 12 as the shown possible. However, it is necessary that the mixing ratio between air and fuel gas in the mixing device 12 can be set independently of the exhaust gas back pressure in the exhaust system 7.

Claims

DaimlerChrysler AGPatent claims

1. Foreign-ignited, with gaseous fuel-powered internal combustion engine (1) with an exhaust system (7) with an exhaust aftertreatment device, wherein upstream of the exhaust aftertreatment device for increasing the exhaust gas temperature for Nachverbrennung provided mixture of air and gaseous fuel can be supplied, wherein the air from a secondary air pump ( 11) and the gaseous fuel originate from a fuel gas tank (14), characterized in that a mixing device (12) is provided for mixing air and gaseous fuel, which is a mixture of air and gaseous fuel in a certain ratio of air and gaseous fuel provides.

2. Internal combustion engine according to claim 1, characterized in that in the mixing device (12), the ratio of the supplied air and the gaseous fuel is independent of the pressure of the supplied air adjustable.

3. Internal combustion engine according to claim 1 or 2, characterized in that in the mixing device (12), the ratio of the supplied air and the gaseous fuel fixed or controlled by a control unit (27) operating point dependent.

4. Internal combustion engine according to one of claims 1 to 3, characterized in that the mixing device (12) has at least one check valve (24, 25) and at least one pressure regulating valve (20, 21).

5. Internal combustion engine according to one of claims 1 to 4, characterized in that the mixing device (12) for the air and the gaseous fuel in each case at least a first and a second check valve (24, 25), and at least a first and a second pressure regulating valve ( 20, 21).

6. Internal combustion engine according to claim 5, characterized in that in the mixing device (12) both the first check valve (24) of the air and the second pressure control valve (21) of the gaseous fuel and the second check valve (25) of the gaseous fuel and the first Pressure control valve (20) of the air are interconnected.

7. A method for operating a spark-ignited, operated with gaseous fuel internal combustion engine (1) with an exhaust system (7) with an exhaust aftertreatment device, wherein upstream of the exhaust aftertreatment Device for increasing the exhaust gas temperature is supplied to a post-combustion intended mixture of air and gaseous fuel, wherein the air from a secondary air pump (11) and the gaseous fuel from a fuel gas tank (14), characterized in that for rapid heating of the exhaust aftertreatment device (9 Air and gaseous fuel in an exhaust system (7) upstream of the exhaust aftertreatment device (9) is supplied, wherein by means of a mixing device (12) regardless of the exhaust back pressure, the amount of fuel is metered depending on the amount of air and / or the air pressure.

8. A method for operating an internal combustion engine according to claim 7, characterized in that when lean operation of the internal combustion engine (1) in the mixing device (12) set a rich fuel-air mixture and the exhaust gas is mixed.

9. A method for operating an internal combustion engine according to claim 8, characterized in that at stoichiometric operation of the internal combustion engine (1) a late Zündzeitpunktlage is set and in the mixing device (12) a stoichiometric fuel-air mixture is added.

10. A method for operating an internal combustion engine according to claim 8 or 9, characterized in that in the mixing device (12), the ratio between the

Air quantity and the amount of gaseous fuel with is regulated by cross-connected pressure control valves (20, 21).