Exhaust system with heat accumulator

Abstract

An exhaust system for a combustion engine includes an exhaust pipe, and a heat accumulator housing in surrounding relationship to the exhaust pipe. Arranged in the heat accumulator housing are heat pipes to provide a heat transport of heat energy contained in exhaust gas. Heat energy thus withdrawn from the exhaust gas can be carried off via the heat pipes in the heat accumulator housing.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS[0001]This application claims the priority of German Patent Application, Serial No. 10 2011 103 109.3, filed May 25, 2011, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein.BACKGROUND OF THE INVENTION[0002]The present invention relates to an exhaust system for a combustion engine.[0003]The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.[0004]Combustion engines, e.g. Otto engines or Diesel engines, consume fuels for operation. As oil reserves are limited, it is desired to maximize performance of a combustion engine and thus exploitation of energy contained in the fuel. Due to the Carnot process, the efficiency of a combustion engine for converting energy contained in the fuel into mechanical ene...

AI Technical Summary

Benefits of technology

[0012]By arranging the heat accumulator about the exhaust pipe in accordance with the present invention, there is no need to integrate any elements in the exhaust gas tract, i.e. inside the exhaust pipe. Thus, there is no increase in the exhaust-gas back pressure. When the overall system of the combustion engine has reached its optimum operating temperature, heat energy contained in the exhaust gas can be used to charge the heat accumulator in the absence of any adverse effect on the exhaust gas after-treatment unit or other elements disposed in the exhaust tract.

[0016]Through selection of a zeolite material and dimensioning of the heat accumulator housing, the exhaust system according to the present invention can be best suited to the cold-start performance of the combustion engine for which the exhaust system is intended for use. In addition, active or passive open-loop and closed-loop control of the exhaust system is conceivable by which the exhaust system can be further modified to the respective operating state to be adjusted.

[0018]According to another advantageous feature of the present invention, the heat pipes can be arranged in parallel relationship to an exhaust-gas flow direction. It thus becomes possible to use especially short distances to conduct heat energy removed from the exhaust into the heat pipes and from there to carry it off via fluid located in the heat pipes. Thus, heat energy can be removed from the exhaust over a length of 50, 100 or also 200 mm and transferred by heat conduction through the heat accumulator housing into the heat pipe and carried off from there.

[0020]According to another advantageous feature of the present invention, several of the heat pipes can extend in parallel relationship within the heat accumulator housing and can be united in an end zone of the heat accumulator housing. As a result, several heat pipes which are small in diameter can be used to prevent the heat accumulator housing from being overdimensioned. The use of several small heat pipes in cross section enables enough heat quantity to be carried off from the heat accumulator and supplied to a respective heat sink in the region of the outlet of the heat accumulator housing via at least a central heat conduction in the form of a heat pipe. Overall, this leads to a particularly compact concept of the exhaust system according to the present invention.

[0023]According to another advantageous feature of the present invention, a thermal insulation can be formed on an outer surface area of the heat accumulator housing. Advantageously, the thermal insulation is a metal coating. As a result of thermal insulation on the outer side of the heat accumulator housing, heat dissipation to the ambient air is minimized. This ensures that the heat accumulator is able to optimally charge in the operating behavior and the stored heat quantity can be maintained over a longest possible time period without being wasted through dissipation to the ambient air. The thermal insulation may also be implemented in the form of a thermal insulating material, air gap insulation and / or in the form of a metallic film coating. In particular, it is possible to provide a reflection of heat energy in the heat accumulator by the surface of the metallic coating back into the heat accumulator. This, too, minimizes dissipation of the heat quantity to the ambient air.

Problems solved by technology

Combustion engines, e.g. Otto engines or Diesel engines, consume fuels for operation.

Due to the Carnot process, the efficiency of a combustion engine for converting energy contained in the fuel into mechanical energy is however limited to 40%.

In other words, ⅔ of chemical energy bound in fuel is not available for the actual purpose of the combustion engine, i.e. conversion of chemical energy into mechanical energy, but is lost as loss energy.

This requires, however, the use of heat exchangers in the region of the exhaust tract, causing a rise in the exhaust-gas back pressure so that the overall efficiency of the combustion engine is adversely affected.

Moreover, oftentimes a heat transfer medium, especially water, is used that in turn limits however efficiency and thus results in an inadequate solution.

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