GB2106632A

GB2106632A - Fuel and gas mixing

Info

Publication number: GB2106632A
Application number: GB08225723A
Authority: GB
Inventors: John Philip Dobbs Hakluytt
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1981-09-11
Filing date: 1982-09-09
Publication date: 1983-04-13
Also published as: GB2106632B

Abstract

The present invention provides a method for mixing a liquid such as an oil based fuel with a gas such as air and and to apparatus for performing the method. Apparatus in accordance with the invention includes a liquid delivery tube (14) arranged to direct a high velocity liquid jet (15) onto a surface (12) which is shaped so as to direct droplets of the liquid formed by impact of the jet on the surface outwardly from the axis of the jet, and a gas pipe (10) or other means for directing a gas stream substantially coaxially with the jet wherein the gas stream disperses the liquid droplets. <IMAGE>

Description

SPECIFICATION Fuel/air mixers The present invention relates to methods for mixing a liquid such as an oil based fuel with a gas such as air, and particularly to such methods for use in gas turbine engines, and to apparatus for performing the methods.

It is increasingly important that combustion processes be completed efficiently (with minimum unburnt fuel) and with minimum production of noxious combustion gases such as (in gas turbine engines) the oxides of nitrogen. To this end it is desirable that fuel and air supplied to a combustion chamber be completely and evenly mixed. This is not easily achieved, particularly in the environment of a gas turbine engine which has a wide range of operating conditions.

Many systems have been proposed for mixing fuel and air for use in the combustion chambers of gas turbine engines. In one type of system fuel is emitted from a nozzle, referred to as an atomiser, in a fine spray and into an airstream into which it vapourises.

One disadvantage with this type of system is that when the mixture impinges on a surface before the fuel has fully vapourised the fuel tends to re-agglomerate.

According to the present invention, in a method for mixing a liquid and a gas, a high velocity liquid jet is allowed to impact on a surface where it is shattered into droplets which disperse into a gas stream flowing substantially co-axially with the jet.

The surface is preferably so shaped, by being, for example, convex or wedge-shaped, that the majority of droplets are directed away from the axis of the jet.

A typical apparatus for performing the invention has a cylindrical gas pipe with a, relative to the direction of gas flow, concave end piece on which is mounted a surface, the gas pipe having perforations radially outward of the surface, and a liquid delivery tube coaxially disposed within the gas pipe.

Some embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, of which: Figure 1 is an elevation, in section, of apparatus for performing the invention, and Figures 2a to 2e show alternative forms of surface for impaction of a liquid stream.

A cylindrical gas pipe 10 (Fig. 1) has a concave end piece 11 on which is mounted a convex surface 1 2. Perforations 1 3 in the pipe 10 lie radially outward of the surface 1 2.

A liquid delivery tube 14 extends co-axially within the pipe 10.

In use gas is blown along the pipe 10, as illustrated by the arrows X, and a stream 1 5 of liquid is ejected at high velocity from the tube 14. When the stream 1 5 impacts on the surface 1 2 it is atomised and is dispersed by the gas stream. The resultant mixture passes through the perforations 1 3 to, for example, a combustion chamber (not shown).

It will be realised that detailed design of the concave end piece 11, surface 1 2 and other features, for optimum performance of the apparatus, will depend on the characteristics of the liquid and gas to be mixed, on their delivery pressures, and on other factors. Surfaces other than the concave one illustrated in Fig. 1 may be advantageous, and other possible shapes are shown, by way of example, in Fig. 2.

It will be realised that the use of perforations 1 3 allows the apparatus to be formed as a unit with the liquid delivery tube 14 correctly aligned with the surface 1 2. This construction of necessity leaves webs extending between the pipe 10 and end piece 11. These webs can be disadvantageous as they may, for example, perform as flame stabilisers, overheat and be in danger of structural damage. The apparatus may alternatively be formed in situ as two separate items, one comprising pipe 10 and tube 14, the other comprising end piece 11 and convex surface 1 2. With this arrangement webs are avoided, but care is required in aligning the two items.

1. A method of atomising a liquid comprising directing a high velocity liquid jet onto a surface shaped to direct droplets of the liquid formed by impact of the jet on the surface outwardly from the axis of the jet, and directing a gas stream coaxially with the jet to disperse the liquid droplets.

2. A liquid atomiser for use in the method claimed in Claim 1, comprising a liquid delivery tube arranged to direct a high velocity liquid jet onto a surface which is shaped so as to direct droplets of the liquid formed by impact of the jet on the surface outwardly from the axis of the jet, and means for directing a gas stream substantially coaxially with the jet, wherein the gas stream disperses the liquid droplets.

3. A liquid atomiser as claimed in claim 2 wherein the means for directing a gas stream comprises a cylindrical gas pipe coaxially disposed over the liquid delivery tube.

4. A liquid atomiser as claimed in claim 2 or claim 3 wherein the surface is convex relative to the direction of the liquid jet.

5. A liquid atomiser as claimed in claim 3 or claim 4 wherein the cylindrical gas pipe has an end piece which is concave relative to the direction of gas flow and wherein the surface is mounted on the end piece, the gas pipe having perforations radially outwardly of the surface.

6. A liquid atomiser as claimed in claim 3 or claim 4 further including an end member which is concave relative to the direction of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Fuel/air mixers The present invention relates to methods for mixing a liquid such as an oil based fuel with a gas such as air, and particularly to such methods for use in gas turbine engines, and to apparatus for performing the methods. It is increasingly important that combustion processes be completed efficiently (with minimum unburnt fuel) and with minimum production of noxious combustion gases such as (in gas turbine engines) the oxides of nitrogen. To this end it is desirable that fuel and air supplied to a combustion chamber be completely and evenly mixed. This is not easily achieved, particularly in the environment of a gas turbine engine which has a wide range of operating conditions. Many systems have been proposed for mixing fuel and air for use in the combustion chambers of gas turbine engines. In one type of system fuel is emitted from a nozzle, referred to as an atomiser, in a fine spray and into an airstream into which it vapourises. One disadvantage with this type of system is that when the mixture impinges on a surface before the fuel has fully vapourised the fuel tends to re-agglomerate. According to the present invention, in a method for mixing a liquid and a gas, a high velocity liquid jet is allowed to impact on a surface where it is shattered into droplets which disperse into a gas stream flowing substantially co-axially with the jet. The surface is preferably so shaped, by being, for example, convex or wedge-shaped, that the majority of droplets are directed away from the axis of the jet. A typical apparatus for performing the invention has a cylindrical gas pipe with a, relative to the direction of gas flow, concave end piece on which is mounted a surface, the gas pipe having perforations radially outward of the surface, and a liquid delivery tube coaxially disposed within the gas pipe. Some embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, of which: Figure 1 is an elevation, in section, of apparatus for performing the invention, and Figures 2a to 2e show alternative forms of surface for impaction of a liquid stream. A cylindrical gas pipe 10 (Fig. 1) has a concave end piece 11 on which is mounted a convex surface 1 2. Perforations 1 3 in the pipe 10 lie radially outward of the surface 1 2. A liquid delivery tube 14 extends co-axially within the pipe 10. In use gas is blown along the pipe 10, as illustrated by the arrows X, and a stream 1 5 of liquid is ejected at high velocity from the tube 14. When the stream 1 5 impacts on the surface 1 2 it is atomised and is dispersed by the gas stream. The resultant mixture passes through the perforations 1 3 to, for example, a combustion chamber (not shown). It will be realised that detailed design of the concave end piece 11, surface 1 2 and other features, for optimum performance of the apparatus, will depend on the characteristics of the liquid and gas to be mixed, on their delivery pressures, and on other factors. Surfaces other than the concave one illustrated in Fig. 1 may be advantageous, and other possible shapes are shown, by way of example, in Fig. 2. It will be realised that the use of perforations 1 3 allows the apparatus to be formed as a unit with the liquid delivery tube 14 correctly aligned with the surface 1 2. This construction of necessity leaves webs extending between the pipe 10 and end piece 11. These webs can be disadvantageous as they may, for example, perform as flame stabilisers, overheat and be in danger of structural damage. The apparatus may alternatively be formed in situ as two separate items, one comprising pipe 10 and tube 14, the other comprising end piece 11 and convex surface 1 2. With this arrangement webs are avoided, but care is required in aligning the two items. CLAIMS

6. A liquid atomiser as claimed in claim 3 or claim 4 further including an end member which is concave relative to the direction of gas flow wherein the surface is mounted on the concave end member which is spaced from the gas pipe so as to define an annular gap extending around the periphery of the surface.

7. A liquid atomiser substantially as described herein with reference to the drawing.