Internal combustion engine with a fuel reformer and ammonia generator

The present invention relates to an internal combustion engine which is used in particular in motor vehicle having a reformer for generating hydrogen, whereby the reformer has a single operating mode in which it generates as much reformate as needed or even more for purification of the maximum quantity of exhaust gas generated, whereby a distributor apparatus is situated at the output end of the reformer and the distributor apparatus is connected at the output end to an intake train of the internal combustion engine and to an ammonia generator, whereby the ammonia generator is connected at the output end upstream from an SCR catalyst to an exhaust train of the internal combustion engine, whereby the distributor apparatus allocates the reformate between the intake train and the ammonia generator as a function of the operating state of the internal combustion engine.

CLAIM FOR PRIORITY

This application claims the benefit of German Application No. DE 10 2004 028 651.5, filed Jun. 15, 2004 and is incorporated herein by reference.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an internal combustion engine, in particular in a motor vehicle, having a reformer for generating hydrogen.

(2) Description of Related Art

It is known in general that reformers may be used in aftertreatment of exhaust gas, in particular diesel engine exhaust gas. Their function is to generate hydrogen, which is converted to ammonia, for example, in additional steps. To do so, fuel, e.g., diesel, is mixed with air and enters an autothermal reactor that operates mostly without external heating. A gas mixture comprised mainly of hydrogen, carbon dioxide, nitrogen and water is formed there at approximately 700° C. Ammonia produced from hydrogen in additional steps can convert the nitrogen oxides present in the exhaust into harmless nitrogen and water in a catalytic converter (SCR catalyst, where SCR stands for selective catalytic reduction) designed specifically for this purpose. It is known in general here that such reformers may be positioned in the full stream, in a substream (bypass) or between the intake and exhaust sides of the engine.

BRIEF SUMMARY OF THE INVENTION

The present invention is concerned with the problem of providing an improved embodiment for an internal combustion engine having a reformer of the type mentioned in the preamble; this embodiment also reliably includes in particular fast and high load spreads of the dynamically operated internal combustion engine and can nevertheless be implemented economically.

This problem is solved according to the present invention by the object of the independent claim. Advantageous embodiments are the object of the dependent claims.

The present invention is based on the general idea of providing a reformer for generating hydrogen for an internal combustion engine, said reformer having a single operating mode in which it generates as much reformate or more than needed for purification of the maximum quantity of exhaust gas. A distributor apparatus situated at the output end of the reformer is connected at its output to an intake train of the internal combustion engine and also to an ammonia generator. At the output end, the ammonia generator is connected upstream from an SCR catalyst to an exhaust train of the internal combustion engine. The distributor apparatus divides the reformate between the intake train and the ammonia generator (depending on the operating state of the internal combustion engine).

The reformer has only a single operating mode, so the distributor apparatus connected downstream from it can control very rapid and very high load spreads due to a demand-oriented allocation of the reformate between the intake train and the ammonia generator as a function of the operating state of the internal combustion engine. Reformate is always available in sufficient quantity for purification of the exhaust gas, so that nitrogen oxide emissions by the dynamically operated internal combustion engine can be followed only through demand-oriented allocation of reformate between the exhaust train and the intake train. In addition, the inventive arrangement and design of the reformer and/or the distributor apparatus can adapt to sudden great changes in pressure, a respective educt supply being ensured in all operating states, i.e., even during load peaks, in particular in an exhaust system with a particulate filter. Due to the constant generation of reformate, a simplified mode of operation is achieved, so that a simpler embodiment of the reformer and/or a supply of air and fuel can be achieved. In a lower load range in which the reformer generates more reformate than needed for purification of the exhaust gas, the reformate stream not needed is supplied to the intake train of the internal combustion engine and thus converted to mechanical power through combustion in the internal combustion engine, so that essentially no increase in consumption is to be expected in comparison with a modulable reformer when this is taken into account accordingly in the fuel supply to the internal combustion engine.

The reformer is expediently a partial oxidation reformer (POX reformer). Such POX reformers have long been used successfully, improving the cold start performance of an internal combustion engine, thus permitting a more protective engine warm-up.

According to an advantageous embodiment of the inventive approach, a cooler is provided between the reformer and the distributor apparatus and/or between the distributor apparatus and the ammonia generator and/or between the distributor apparatus and the intake train. The cooler is preferably tied into a heating circuit for heating the internal combustion engine and/or heating an interior space of a vehicle equipped with said internal combustion engine and/or heating an oxidation catalyst of the exhaust train in a cold start. The cooler is preferably tied into a heating circuit for heating the internal combustion engine and/or an interior of a vehicle equipped with said internal combustion engine and/or an oxidation catalyst of the exhaust train in a cold start. Placing the cooler between the reformer and the distributor apparatus according to the first alternative makes it possible to heat the reformate generated in the reformer to the optimum temperature for downstream process steps such as generation of ammonia. At the same time, the heated reformate is already supplied to the distributor apparatus, so that it can be allocated at the optimum temperature between the exhaust train and the intake train of the internal combustion engine.

In an advantageous embodiment of the inventive approach, the reformate is introduced into the intake train upstream from a charger. The reformate, which is generated in the reformer and is additionally heated correctly, for example, is therefore introduced in a demand-oriented process into the intake train of the internal combustion engine. For example, a fluid-driven turbocharger, driven by combustion exhaust gases, or a mechanically driven compressor may be provided as the charger, each of these having the function of compressing the fresh air intake and supplying it in compressed form to the internal combustion engine.

Additional important features and advantages of this invention are derived from the subclaims, the drawing and the respective description of the figures with reference to the drawing.

It is self-evident that the features mentioned above and those to be explained in greater detail below may be used not only in the particular combination given but also in other combinations or alone without going beyond the scope of the present invention.

A preferred exemplary embodiment of this invention is depicted in the drawings and explained in greater detail in the following description.

DETAILED DESCRIPTION OF THE INVENTION

According toFIG. 1, an internal combustion engine1has an engine or an engine block2with an intake train3connected to it at the input end and an exhaust train4connected to it at the output end. The internal combustion engine1may be installed in a motor vehicle (not shown) and/or may drive such a motor vehicle. A charger5, designed here as an exhaust gas turbocharger tied into the exhaust train4at the drive end accordingly, is preferably situated in the intake train3. Alternatively, the charger5may be designed as a mechanical charger, e.g., a compressor driven by the internal combustion engine1. The charger5serves in a known way to compress fresh air supplied to the engine block2, thus permitting an increase in the power and efficiency of the internal combustion engine1.

Downstream from the charger5, an oxidation catalyst6may be situated in the exhaust train4, resulting in purification of the exhaust gas in the form of decreasing the carbon monoxide and hydrocarbon emissions by oxidizing these substances to carbon dioxide and water.

At the output end of the oxidation catalyst6, a particulate filter7, in particular a soot filter, may be situated downstream in the exhaust train4, filtering the exhaust gas to remove the fine particles, in particular soot particles, from the exhaust gas, thus preventing their release. Further downstream in the exhaust train4, an SCR catalyst8may be situated downstream from the particulate filter7to reduce the nitrogen oxides present in the exhaust gas to water and nitrogen. Ammonia is also needed for chemical reduction of nitrogen oxides to water and nitrogen; according toFIG. 1, ammonia is generated by an ammonia generator9and added to the exhaust train4upstream from the SCR catalyst8, expediently downstream from the particulate filter7.

The ammonia generator9is connected at the input end to an output end of a distributor apparatus10, which has the job of dividing the reformate stream between the ammonia generator9, i.e., between the exhaust train4at one end, and the intake train3at the other end in a demand-oriented process.

To do so, the distributor apparatus10is flow-connected at the input end to an output end of a reformer11and at the output end is connected to both the intake train3as well as the ammonia generator9and by way of the latter also to the exhaust train4. The reformer11is designed to generate hydrogen, which is converted to ammonia, for example, in ammonia generator9in subsequent steps. The starting materials, namely air and fuel, needed to generate the reformate, i.e., hydrogen, are supplied to the reformer11by a fan13and a fuel supply14according toFIG. 1.

In contrast with controllable and/or modulable reformers of the traditional output, which must be capable of handling very rapid and very large load spreads because they must adjust to the nitrogen oxide emissions of the dynamically operated internal combustion engine, the reformer11with the inventive internal combustion engine1has only a single operating mode in which it generates as much reformate as needed or even more for the maximum quantity of exhaust gas produced. The distributor apparatus10has the function of distributing the reformate between the intake train3and the ammonia generator9as a function of the operating state of the internal combustion engine. The advantage is the simplified static mode of operation due to the constant generation of reformate in addition to a simpler and thus less expensive design of the reformer11and/or the fan13and the fuel supply14. The (sub)stream of the reformate not needed for exhaust gas purification is converted to mechanical power by combustion in the engine block2, so there is no increase in consumption in comparison with a modulating reformer if the reformate feed is taken into account accordingly during operation of the fuel injection system. The distributor apparatus10is therefore suitably coupled to a corresponding control (not shown here) of the injection system.

The reformer11may be designed, for example, as a partial oxidation reformer (POX reformer). Such a POX reformer oxidizes the hydrocarbons present in the fuel in a catalytic or thermal reaction together with atmospheric oxygen to form hydrogen, carbon monoxide and carbon dioxide. The energy required to accomplish this is normally supplied by combustion (oxidation) of a portion of the hydrocarbons in the process itself.

According to another embodiment of the inventive approach, it is conceivable for a cooler15to be provided between the reformer11and the distributor apparatus10and/or between the distributor apparatus10and the ammonia generator9and/or between the distributor apparatus10and the exhaust train3. Since this is an optional approach, the cooler15is shown with broken lines inFIG. 1. The cooler15may be tied into a heating circuit (not shown) for heating the internal combustion engine1and/or heating an interior of a vehicle equipped with said internal combustion engine1and/or an oxidation catalyst6of the exhaust train4in a cold start. The “heating circuit” is expediently the “cooling circuit” of the internal combustion engine1, which is already provided anyway, for cooling the engine block2during hot operation. The cooler15between the distributor apparatus10and the ammonia generator9may be used for heating the reformate stream discharged from the distributor apparatus10to the ammonia generator9.

Additionally or alternatively, the distributor apparatus10may also be connected at the output end to a burner16, the reformate then being distributed among the intake train3, the ammonia generator9and the burner16as a function of the operating state of the internal combustion engine1. It is conceivable here for some or all of the reformate stream to be supplied to the burner16in a cold start and to be burned there and for the resulting heat of combustion to be supplied via a heat exchanger (cooler) to an appropriate heating circuit for heating the engine block2and/or the internal combustion engine1and/or a vehicle equipped with such an internal combustion engine1. High nitrogen oxide emissions usually do not occur in a cold start of the internal combustion engine1, so the reformate can be supplied completely to the burner16via the respective heat exchanger (not shown).

In another expansion stage (not shown), the system may also be equipped with the burner16for auxiliary heating. The burner16has the additional advantage that in the case of deceleration of the vehicle, when a release of mechanical power is not desired, the reformate thereby generated can be burned. In winter, this heat of combustion may be utilized to partially or completely compensate for the cooling of the engine cooling circuit, which is often associated with deceleration of a vehicle, e.g., in prolonged downhill driving, and to thereby maintain a high level of heating comfort.

An exhaust gas aftertreatment system, e.g., the catalytic converter6, may also be heated with the burner16or an additional burner (not shown), e.g., in a cold start, so that it rapidly reaches its operating temperature. The burner heat may of course also be used to support regeneration of the particulate filter, if present.

According to an advantageous refinement of the inventive approach, it is also possible to provide for the charger5to be used for fresh air supply to the reformer11. A substream of compressed intake air can be branched off here at the pressure end of the charger5and sent to the reformer11over a supply line17. The fan13may advantageously then be eliminated and/or replaced by the feed line17, thus resulting in a simplified design and an inexpensive variant at the same time.

In summary, the essential features of the inventive approach can be characterized as follows:

According to this invention, a reformer11having a single operating mode is to be provided with an internal combustion engine such that it generates as much reformate as needed or even more for purification of the maximum quantity of exhaust gas generated. The reformer11is flow-connected at the output end to an input end of a distributor apparatus11, which divides the reformate stream at the output end according to demand, i.e., as a function of the operating state of the internal combustion engine1, between the intake train3and the ammonia generator9.

The inventive approach offers the advantage of a simple embodiment of the reformer11with a simplified mode of operation with constant production of reformate while at the same time converting the portion of the reformate stream not needed for exhaust gas purification into mechanical power by combustion in the internal combustion engine1. This yields continuous reformer operation in particular without any significant increase in consumption in comparison with a modulating reformer.