GB2076055A - Cooling i.c. engine exhaust gases - Google Patents

Abstract

Exhaust gases pass within a heat exchanger (10) over the external surface of a hollow cooling element (19) and baffles (18) cause the gases to follow a circuitous path towards and away from the cooling element. Water is passed through the cooling element and the exhaust gases pass from the heat exchanger to atmosphere via a water bath (12). The elbows (14, 15) and the exchanger wall (17) define water cooling passages. <IMAGE>

Description

SPECIFICATION A new or improved heat exchanger Description of Invention From one aspect, this invention relates to a heat exchanger suitable for cooling the exhaust gases expelled from internal combustion engines in general and the internal combustion engines of locomotives used in underground mines in particular.

Known devices for cooling exhaust gases expelled from internal combustion engines in underground locomotives are arranged to provide the exchange of heat between the gases and a cooling fluid. Such devices commonly consist of a chamber through which the gases pass whilst the cooling fluid flows in contact with the external surfaces of the walls of the chamber. Heat exchange takes place with as much of the exhaust gases as come into contact with the internal surfaces of the walls.

Gases leaving a heat exchanger of the known kind generally pass through a flame trap before entering a water bath conditioning unit. Because the temperature of the exhaust gases has not been cooled sufficiently by the heat exchanger, it is required that further cooling means be included in the arrangement. Thus, it is often necessary to separate the flame trap widely from the heat exchanger to allow the gases further opportunity for cooling, and the conditioning unit requires additional cooling means to overcome the loss of water through evaporation. Such an additional cooling means includes the water jacketing of the unit and the provision of condensing tubes downstream of the unit to recoup water losses resulting from evaporatipn.

According to the invention there is provided a heat exchanger for cooling exhaust gases from an internal combustion engine, said heat exchanger comprising an exhaust gas inlet, baffles arranged for constraining the flow of the gases to circuitous paths within the exchanger, an exhaust gas outlet, and an element suitable for containing a cooling fluid, the element comprising a thermally conductive wall for separating the gases from the cooling fluid.

According to a second aspect of the invention, there is provided a combination comprising a heat exchanger according to the first aspect of the invention, an internal combustion engine and an exhaust gas conditioning unit, wherein an exhaust pipe connects the exhaust gas output means of the engine with the inlet of the heat exchanger, and a pipe from the outlet of the heat exchanger leads to the exhaust gas conditioning unit.

The invention achieves a greater reduction in exhaust gas temperature than do known arrangements. This enables the associated conditioning unit to be less expensive. Less water is required to wash the gas and condensing tubes are no longer needed because losses by evaporation are reduced. It is no longer necessary that the conditioning unit be water jacketed.

Preferably the combination does not include a flame trap between the heat exchanger and the conditioning unit.

One example of a heat exchanger embodying the invention will now be described with reference to the accompanying drawing which shows a cross-section of a heat exchanger connected to an internal combustion engine and a conditioning unit.

The heat exchanger 10 shown in the drawing receives exhaust gases from an internal combustion engine 11 and the exhaust gases pass from the heat exchanger to a conditioning unit 12.

The inlet 1 3 of the heat exchanger is connected to the internal combustion engine by a water cooled exhaust pipe 14. Preferably (but. not shown in the drawing) the inlet is also water cooled. A similar exhaust pipe 1 5 connects the outlet 1 6 of the haat exchanger with the conditioning unit, both exhaust pipes including flexible element so that limited relative movement of the engine, heat exchanger and conditioning unit does not stress connections with the pipes excessively.

The heat exchanger 10 comprises a double walled outer envalope 1 7 through which a cooling fluid passes. The inlet 13 and outlet 16 are formed in the outer envelope adjacent to opposite ends thereof so that exhaust gases must pass along the length of the exchanger. Baffles 1 8 are provided to cause the gases to follow circuitous paths from the inlet to the outlet. The baffles are arranged with their faces opposing the flow of the exhaust gases, alternate baffles providing annular and central passages for the exhaust gases.

An element 1 9 projects perpendicularly to the faces of the baffles 1 8 from an internal surface of an end wall 22 of the exchanger. The element comprises a coaxial inner pipe 20 and outer pipe 21. A cooling fluid such as water passes from a reservoir (not shown) into the inner pipe 20. At the tip 26 of the element there is sufficient clearance between the open end of the inner pipe and the closed end of the outer pipe for the fluid to pass from one to the other. The fluid then leaves the outer pipe and the heat exchanger via the space between the outer and inner walls 23 and 24.

The outer pipe 21 is formed of a thermally conductive material. Thus heat is transferred from hot exhaust gases in contact with the outer pipe to the cooling fluid contained within the pipe and is then carried away from the heat exchanger. The element enables heat transfer to take place in a central portion of the heat exchanger. The inner pipe conducts the coldest fluid to undergo heat transfer to the end of the element. As the fluid returns by the outer pipe, it increases in temperature. Heat transfer also take place between the exhaust gases and cooling fluid in the double walled outer envelope 17.

A heat exchanger may comprise a plurality of elements 10. When the heat exchanger is not in use, the end wall 22 may be removed to enable inspection and cleaning of the elements and the inside of the heat exchanger to take place. The central openings of the baffles mounted on the outer envelope 1 7 may be sufficiently large to permit baffles mounted on the exterior of the element 19 to pass through these central openings so that the element 19 can be withdrawn from the chamber defined by the envelope 17.

The combination of heat exchanger, internal combustion engine and conditioning unit are intended for use in locomotives for underground mines. The use of locomotives in such circumstances imposes important safety requirement in the treatment of the exhaust gases.

The more efficient heat exchanger now described reduces the requirement for other units in the combination. An exhaust flame trap can be placed immediately after the heat exchanger and before the conditioning unit without the surface temperature of the interconnecting pipe between the heat exchanger and conditioning unit creating a hazard or contravening regulations. In some circumstances a flame trap may not be needed at all. The conditioning unit is of a standard form, being a water bath designed to wash the exhaust gases. A lower temperature of exhaust gas entering the conditioning unit reduces the loss of water by evaporation. A vertical float switch 25 shuts down the engine 11 in the event of the water level falling too low.

Claims (12)

1. A heat exchanger for cooling exhaust gases from an internal combustion engine, the heat exchanger comprising an exhaust gas inlet and an exhaust gas outlet and being characterised by baffles for constraining the flow of gasses from the inlet to the outlet to circuitous paths within the heat exchanger and further characterised by an element for containing a cooling fluid, the element comprising a thermally conductive wall for separating the exhaust gases from the cooling fluid.

2. A heat exchanger according to Claim 1 wherein said element projects from an internal surface of a wall of the heat exchanger.

3. A heat exchanger according to Ciaim 2 wherein said element comprises concentric inner and outer pipes. the outer pipe being constituted by said thermally conductive wall and the inner pipe being open at both of its ends.

4. A heat exchanger according to any preceding claim wherein the exhaust gas inlet and the exhaust gas outlet are adjacent to opposite ends of the heat exchanger.

5. A heat exchanger according to any preceding claim wherein said element is elongated and rectilinear and wherein the baffles have faces substantially perpendicular to the length of the element.

6. A combination comprising an internal combustion engine, a heat exchanger and an exhaust gas conditioning unit, wherein an exhaust pipe connects the exhaust gas output means of the engine with an inlet of the heat exchanger and a pipe from an outlet of the heat exchanger leads to the exhaust gas conditioning unit, characterised in that the heat exchanger is in accordance with any preceding claim.

7. A combination according to Claim 6 wherein there is no flame trap between the heat exchanger and the conditioning unit.

8. A method of cooling exhaust gases discharged from an internal combustion engine wherein the exhaust gases follow a circuitous path which repeatedly leads towards and away from the external surface of a hollow cooling element and are then passed through a liquid bath to the ambient atmosphere and wherein a fluid coolant is passed through the interior of the cooling element to extract heat therefrom.

9. A heat exchanger substantially as herein described with reference to and as shown in the accompanying drawings.

10. A combination comprising a heat exchanger, internal combustion engine and conditioning unit substantially as herein described with reference to and as shown in the accompanying drawing.

11. A method substantially as herein described with reference to and as shown in the accompanying drawing.

12. Any novel feature or novel combination of features disclosed herein or as shown in the accompanying drawing.