Process and Apparatus for the Cleaning of a Soot Filter

This invention relates to a procedure of cleaning of a soot filter in the exhaust system of a diesel engine under load and for all engine speeds, as well as an appropriate technique of this procedure with a functionally adapted combustion chamber in front of the soot filter, where a fuel nozzle and a specific ignition mechanism is built in.

Such a procedure is known from the German Publication 321994. With this the combustion works with secondary air supply, which is heated by a cylinder surrounding the combustion chamber before it actually arrives at the combustion chamber. There, the mixture of secondary air and the injected fuel is ignited by a glow plug. The hot combustion gas will be used for regeneration of an after-coupled soot filter.

The invention in question has the objective to achieve the burning up the soot in a soot filter for varying engine operating conditions in an effective yet constructively simple way.

According to the invention in question, this objective will be fulfilled by a method according to claim 1 and an apparatus according to claim 2, where the conducting of secondary air into the combustion chamber can be totally eliminated. Due to the fact that through the combustion chamber only a partial exhaust stream, comprised of less than about 25% of the total exhaust flow, is led therein and is, by means of an igniting-mechanism, ignited, the igniting conditions are easier to control. With proper dosage of the partial exhaust flow, it is possible to accomplish a consistent burning of the CO.sub.2 -portions that are still remaining in the exhaust flow, from 7 to 15% of the total exhaust flow. The engine exhaust, led into the combustion chamber, the temperature in which is a maximum of 400.degree. C., is intensely heated by the after burning in the combustion-chamber. It is possible, by means of the heated partial exhaust flow, which will be mixed again with the main exhaust main stream ahead of the soot filter, to raise the exhaust temperature of the total exhaust stream to about 700.degree. C. This temperature exceeds the ignition temperature of the burning soot in the soot filter. It is important for this increase in temperature, that at first only a portion of the exhaust will get ignited and burned with the injected fuel in the combustion chamber, and that the evaporated fuel be burned only partially, so that the mixing of the hot burning gas with other exhaust portions inside and or immediately following the combustion chamber can develop another afterburning of the added exhaust portions, with the result that the temperature of the total exhaust flow in front of the soot filter is noticeably higher than the temperature of the initial mixture.

It is possible to accomplish an extremely constant igniting and burning condition, because of the planned connection of the combustion-chamber with the ignition-chamber which is saturated with a partial exhaust flow. In addition, a certain method of procedure is preferred wherein the ignition chamber is located within the combustion chamber and wherein the ignition chamber is saturated by a first partial exhaust flow from a space created between the wall of the combustion chamber and the ignition chamber, and a second partial exhaust flow, and that both partial exhaust streams are mixed within the combustion chamber beyond the ignition chamber. Through this, as demonstrated above, a burning of the added partial exhaust flow takes place, thus, with this method only the first partial exhaust flow will be ignited in the ignition chamber, while the second partial exhaust flow exchanges heat with the wall of the ignition chamber which means it takes in limited heat but at the same time isolates the ignition chamber from the cooler surroundings. The portion of the first partial exhaust flow of the total exhaust flow preferably contains between 2% and 5%, and that of the second partial exhaust flow 15% to 20%. The mixing of both partial exhaust flows occurs within the combustion chamber, where provision is made for the second partial exhaust flow to rotate through the spiral shaped baffles between the ignition chamber and the wall of the combustion chamber. As a result an especially close mixing of both partial exhaust flows takes place, also creating the burning of the added partial exhaust flow. After the partial exhaust flows, expelled from the combustion-chamber, intermingle with the main exhaust flow, there results an afterburning with the remainder of the CO.sub.2 contained in the main exhaust flow.

Within the boundaries of the invention it is possible to build the combustion chamber either into a bypass pipe of the exhaust system or to have it surrounded by the exhaust pipe in such a way that the main exhaust flow is channeled by an outer annular chamber between the exhaust line and the wall of the combustion chamber. This method proves especially efficient in conserving energy and space.

A suitable design of the procedure is that the combustion chamber is positioned just about concentric into the exhaust pipe and is connected upwards to a chamber, where the wall curves against the flow of the exhaust and has an opening in the center. For the exact dosage of both partial exhaust flows another method can be provided by abutting the chamber to a diaphragm with a first opening for the dosage of the first partial exhaust flow and pointing to a second opening located radially outside the ignition chamber for the proper dosage of the second exhaust flow.

It is preferable for the ignition chamber to be a form of a Venturi nozzle, where the mouth of the fuel nozzle is placed just about in the most narrow part of the ignition chamber or close behind it.

Another suggestion for the procedure of the invention is that the ignition mechanism is surrounded by two ignition electrodes, which are guided through the exhaust pipe, the wall of the combustion chamber and the wall of the ignition chamber, so that their electrodes face each other close to the mouth of the fuel nozzle.

To achieve an especially balanced combustion process under safe ignition conditions in changing load conditions over the total range of revolutions of the diesel engine, it could be of further advantage that the end portion of the combustion chamber is void of any build-ins, and where the first and second partial exhaust flows mix, with perforations provided for the onward flowing of the portions of the main exhaust.

Here a small first partial exhaust enables the preservation of stable igniting conditions in conjunction with continued complete incineration of the exhausts with the remaining CO.sub.2 of the successively introduced portions of the partial exhaust flow. It does not matter, within the boundaries of the invention, what kind of a soot filter is used, for example the standard ceramic filter come into consideration as well as the so called ceramic swaddle filter, where steel pipes with punched holes are wrapped with a ceramic fiber.

Furthermore, within this invented method, an exhaust turbine could be in series. The fuel used for the function of the fuel nozzle can be matched according to the preference of the motor fuel, which has been given an advantageous additive to help the incineration process of the burning of the soot.

The supply of fuel into the fuel nozzle can be regulated according to the engine load; from an operating point of view, the hotter the engine exhaust in the regeneration area, the less fuel injected into the combustion chamber is needed.

The kind of ignition electrodes to be used are the ones which are used in heating systems, for example, and are readily available on the market.

The invention will be explained below with reference to the drawings.

FIG. 1 is a schematic view of the invented method in an exhaust system, located between the engine and soot filter.

FIG. 2 is an excerpt A of FIG. 1 with an alternative arrangement of the combustion chamber.

FIG. 3 is a lengthwise section through a combustion chamber, which is located inside the exhaust pipe.

FIG. 4 is an axial view taken at IV--IV in FIG. 3.

According to FIG. 1 a diesel engine (1) above a fuel tank (2) is provided with fuel. The suctioned air runs into the diesel engine (1) in an air suction line (4). An exhaust pipe (6) is connected to the exhaust manifold (5}of the diesel engine (1), which is connected with an exhaust pipe via a soot filter (7).

The soot filter (7) contains a ceramic insert (9) with channels running in the direction of the flow, where the unburned soot is collected. The fuel tank (2) is connected to the diesel engine (1) by a fuel line (10); another fuel line (11) which has a built in booster-pump (12) is then connected with a combustion chamber (13), where the exhaust line (6) is placed between the exhaust manifold (5) and the soot filter (7). For the afterburning, the fuel of the fuel line (11) is injected with partial exhaust, led through the combustion chamber (13) which is described in more detail in FIGS. 3 and 4.

FIG. 2 shows section A of FIG. 1 with an alternative position of the combustion chamber (13) which is built into a bypass line (15) branched off the exhaust line. The bypass line (15) is connected upwards with the exhaust line (6) by a scoop encasing the exhaust line (6), which is divided within the boundaries of the scoop, where the upstream position of the exhaust line ends in a narrowing (17).

FIG. 3 shows an axial section through the combustion chamber, which is located within the exhaust line (6). With its right end, the exhaust line (6) is connected through a flange with a section on the engine side (not shown) of the exhaust line (6). With the flange (19), provided on the left side, is the exhaust line, which is narrowing toward the left end, flanged with the casing of the soot filter (7). Through the combustion chamber (13), positioned inside the exhaust flow (6), the total exhaust stream running out of the exhaust line (6) according to arrow G, divided into one of the combustion chamber (13), that formed an outer annular chamber (42) formed between the combustion chamber (13) and the exhaust line (6) surrounding the total exhaust flow according to arrow (H) and a partial exhaust flow (10), which runs into one of the combustion chamber (13) through an opening of the chamber (21) connected in series. The chamber has a wall with an opening curved against the flow which is surrounded by the total exhaust flow (H). This wall (22) is connected to the side of the combustion chamber by a chamber (21) with an upstream diaphragm which has different openings. The other side of the diaphragm (23) connects to an ignition chamber (24) which has a narrowing like a Venturi nozzle.

First openings (26) in the diaphragm (23) join into the inside of the ignition chamber (24) through which a first partial exhaust flow according to arrow (T1) runs. A second partial exhaust flow according to arrow (T2) reaches a chamber (28) through a second opening (27) in the diaphragm between ignition chamber (24) and a cylindrical wall (29) portion in the combustion chamber (13). The chamber (28) as well as the inside of the ignition chamber (24) are open at their discharge end so that both exhaust streams (T1, T2) mix behind the ignition chamber (24) inside the combustion chamber (13). To achieve the best possible mixing, an annular chamber (30) between a cylindrical midsection of the ignition chamber (24) and the surrounding cylindrical wall section (29) of the combustion chamber (13) is provided with a baffle in form of a spiral, which then causes a spiralling of the second exhaust flow (T2). The end section (33) of the combustion chamber (13) which narrows into the direction of the exhaust stream joined at the ignition chamber (24) which is free of all builtins; the partial exhaust flows (T1 and T2) mix together, after leaving the downstream open combustion chamber (13). This exhaust mixture, whose temperature measures about 700.degree. C, teaches the soot filter and ensures the burning of the soot. The end section (33) of the combustion chamber (13) shows perforations (43), which cause an admixture of portions (T3) of the main exhaust flow (H) still within the combustion chamber (13). The rise in temperature through the afterburning flow depends on the first partial exhaust flow (T1) whose contents of unburned oxygen are ignited behind the fuel nozzle (34). Two ignition electrodes (35) which pass through the exhaust pipe (6) as well as the combustion chamber (13), and finally also through the wall of the ignition chamber face each other in a 90.degree. angle and serve as an ignition device. The electrodes (36) as displayed in FIG. 4 are positioned immediately next to the aperture (37) of the fuel nozzle (34) so that their ends face each other. The ignition electrodes (35) each have a porcelain body (38) which are surrounded by a steel pipe for heat protection. By means of a casing (40) attached to the steel pipe, the ignition electrodes (35) are anchored in the wall of the exhaust line (6); the inner end of the porcelain body (38) is held by a socket which is connected to the ignition chamber (24).

The fuel pipe (11) extends into the inside of the ignition chamber (24) through an opening (20) of the wall (22) of the chamber (21) and through a first opening (26) of the diaphragm (23) where it is connected with a fuel nozzle (34). Comparing the influx sections of the partial exhaust flow (T1) and (T2) as well as the main exhaust flow (H) to the height of the diaphragm (23) the proportion of the surfaces relate in a concrete example: FTl:FT2:FH=2:11:50. The cross section of the opening (20) in the chamber (21) equals approximately the sum of the first opening (26) and the second opening (27) in the diaphragm (23). An entry temperature of 400.degree. C. of the exhaust into the combustion chamber, after ignition in the ignition chamber (24) results in a temperature of about 1100.degree. to 1200.degree. C. of the first partial exhaust flow (T1). The mixing of the first partial exhaust flow (T1) with the second partial exhaust flow (T2) will now result in the burning of the gas mixture in the incineration portion (44) of the combustion chamber (13). Following this an afterburning develops of both partial exhaust flows (T1, T2) through the admixture to the main exhaust flow (H). This addition develops partially because of the perforations (43) in the incinerating chamber (44) mainly behind the combustion chamber (13) within the section (45) of the exhaust pipe (6) leading to the soot filter (7). As a result an exhaust mixture temperature of about 700.degree. C. is achieved, where the temperature is regulated accordingly through the injected fuel portion. This temperature is sufficient for the regeneration of the soot filter (7) through burning of the soot that is collected there.