GB2099509A - Heating of aircraft fuel - Google Patents

Abstract

An aircraft fuel system includes a tank from which fuel is pumped to a fuel control unit by way of an oil/fuel heat exchanger to heat the fuel. In temperate ambient conditions a circuit control valve will be in a normal position (Figure 1) and the fuel will be heated by the cooler and flow by way of ports C and B to the control unit (Fig. 2 not shown). For lower-than- ambient conditions the valve will be moved so that some of the heated fuel flows from port B to the control unit and some of the heated fuel flows from port D to the tank, to heat the fuel therein. The valve has further positions (Figs. 3, 4 not shown). The throttling effect of ports O and E further heat the fuel. <IMAGE>

Description

SPECIFICATION Heating of aircraft fuel This invention relates to the heating of fuel used with aircraft engines.

Fuels currently used with aircraft engines have a freezing point in the region of-500C.

If aircraft fuels are made from fossilized materials such as shale oil, tar sands, or coal, the freezing point could be raised to about -290C. As a consequence, there would be a higher probability of the fuel freezing in a tank during a journey.

It is an object of this invention to heat the fuel in a fuel tank, and thus to reduce the tendency of the fuel to freeze.

According to this invention, an aircraft fuel system includes a tank for aircraft fuel, a highpressure pump for circulating fuel from the tank to a fuel control unit by way of a cooler, in which engine oil is cooled by fuel passing therethrough, and a valve having one position in which fuel from the cooler is supplied to the fuel control unit and another position in which some of the fuel from the cooler is supplied to the fuel control unit and some of the fuel from the cooler is supplied to the tank.

Conveniently, the high-pressure pump is a centrifugal pump, preferably of the high-speed type.

In the accompanying drawings: Figure 1 is a schematic arrangement of a system in accordance with one embodiment of the invention, Figure 2 shows the valve of Figure 1 in a position different from the one it has in Figure 1, Figure 3 shows that valve of Figure 1 in another different position, and Figure 4 shows the valve of Figure 1 in yet another different position.

Referring to the drawings, fuel from the tank is supplied, by way of a non-return valve and a boost pump to a high-pressure pump. Some heat will be added to the fuel by the high-pressure pump. The heated output from the high-pressure pump is supplied to one side of a fuel-cooled oil cooler and to port A of a circuit control valve.

In the position of the valve shown in Figure 1, which will be the normal position for temperate ambient conditions, all the fuel supplied by the high-pressure pump is further heated by the cooler and flows by way of ports C and B to a filter and then to a fuel control unit, of well-known form.

As the ambient and tank temperatures fall, the valve is moved to the position shown in Figure 2; alt the fuel supplied by the high-pressure pump is heated by the cooler and flows to port C. Some of that heated fuel flows from port B to the fuel control unit, and some of that heated fuel flows from port D back to the tank, thus adding heat to the fuel contained in the tank.

The flow of fuel from port D will be suitably restricted, for example by limiting the area of port D, to ensure that the flow of heated fuel from port B is sufficient to maintain the temperature of the filter at such a value that ice is prevented from forming in the filter.

Also, by restricting the flow of fuel from port D, the pressure energy of the fuel will be converted into heat, thereby increasing the heat content of the fuel flowing from port D back to tank.

If the ambient and tank temperatures fall even further, the valve is moved to the position shown in Figure 3. Some of the fuel supplied by the high pressure pump is fed by way of the oil cooler to port C. Of that fuel some flows from port B to the fuel control unit, and some flows from port D back to tank. Some of the fuel supplied by the highpressure pump is fed directly to port A and is then fed from port E to join the liquid from port D flowing back to the tank. The area of port E will be limited or a restrictor affecting the part of the fuel which flows through the valve from portAta ts pnr" E will be provided. This will cause the pressure energy of that fuel to be converted into heat. The flow from port D stays substantially constant.

The above sequence permits heat to be supplied to the tank preferentially from the fuelcooled oil cooler, large return flows from the highpressure pump'only being taken at lower ambient temperature conditions.

When the valve is moved to the position shown in Figure 4, some of the fuel from the highpressure pump is fed directly to port A and then by way of port B to the fuel control unit. Some of the fuel from the high-pressure pump is fed through the cooler to port C and this flows by way of ports D and E back to tank.

This position may be used to reduce any transient high fuel temperatures which might otherwise occur under hot ambient conditions with the engine throttled back to "altitude-idle fuel flow When the aircraft is on the ground, the fuel flow may be heated by passing it from a suitable connection through a suitable ground-based heating device.

Conveniently, the high-pressure pump is a centrifugal pump.

1. An aircraft fuel system including a tank for aircraft fuel, a high-pressure pump for circulating fuel from the tank to a fuel control unit by way of a cooler, in which engine oil is cooled by fuel passing therethrough, and a valve having one position in which fuel from the cooler is supplied to the fuel control unit and another position in which some of the fuel from the cooler is supplied to the fuel control unit and some of the fuel from the cooler is supplied to the tank.

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

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Heating of aircraft fuel This invention relates to the heating of fuel used with aircraft engines. Fuels currently used with aircraft engines have a freezing point in the region of-500C. If aircraft fuels are made from fossilized materials such as shale oil, tar sands, or coal, the freezing point could be raised to about -290C. As a consequence, there would be a higher probability of the fuel freezing in a tank during a journey. It is an object of this invention to heat the fuel in a fuel tank, and thus to reduce the tendency of the fuel to freeze. According to this invention, an aircraft fuel system includes a tank for aircraft fuel, a highpressure pump for circulating fuel from the tank to a fuel control unit by way of a cooler, in which engine oil is cooled by fuel passing therethrough, and a valve having one position in which fuel from the cooler is supplied to the fuel control unit and another position in which some of the fuel from the cooler is supplied to the fuel control unit and some of the fuel from the cooler is supplied to the tank. Conveniently, the high-pressure pump is a centrifugal pump, preferably of the high-speed type. In the accompanying drawings: Figure 1 is a schematic arrangement of a system in accordance with one embodiment of the invention, Figure 2 shows the valve of Figure 1 in a position different from the one it has in Figure 1, Figure 3 shows that valve of Figure 1 in another different position, and Figure 4 shows the valve of Figure 1 in yet another different position. Referring to the drawings, fuel from the tank is supplied, by way of a non-return valve and a boost pump to a high-pressure pump. Some heat will be added to the fuel by the high-pressure pump. The heated output from the high-pressure pump is supplied to one side of a fuel-cooled oil cooler and to port A of a circuit control valve. In the position of the valve shown in Figure 1, which will be the normal position for temperate ambient conditions, all the fuel supplied by the high-pressure pump is further heated by the cooler and flows by way of ports C and B to a filter and then to a fuel control unit, of well-known form. As the ambient and tank temperatures fall, the valve is moved to the position shown in Figure 2; alt the fuel supplied by the high-pressure pump is heated by the cooler and flows to port C. Some of that heated fuel flows from port B to the fuel control unit, and some of that heated fuel flows from port D back to the tank, thus adding heat to the fuel contained in the tank. The flow of fuel from port D will be suitably restricted, for example by limiting the area of port D, to ensure that the flow of heated fuel from port B is sufficient to maintain the temperature of the filter at such a value that ice is prevented from forming in the filter. Also, by restricting the flow of fuel from port D, the pressure energy of the fuel will be converted into heat, thereby increasing the heat content of the fuel flowing from port D back to tank. If the ambient and tank temperatures fall even further, the valve is moved to the position shown in Figure 3. Some of the fuel supplied by the high pressure pump is fed by way of the oil cooler to port C. Of that fuel some flows from port B to the fuel control unit, and some flows from port D back to tank. Some of the fuel supplied by the highpressure pump is fed directly to port A and is then fed from port E to join the liquid from port D flowing back to the tank. The area of port E will be limited or a restrictor affecting the part of the fuel which flows through the valve from portAta ts pnr" E will be provided. This will cause the pressure energy of that fuel to be converted into heat. The flow from port D stays substantially constant. The above sequence permits heat to be supplied to the tank preferentially from the fuelcooled oil cooler, large return flows from the highpressure pump'only being taken at lower ambient temperature conditions. When the valve is moved to the position shown in Figure 4, some of the fuel from the highpressure pump is fed directly to port A and then by way of port B to the fuel control unit. Some of the fuel from the high-pressure pump is fed through the cooler to port C and this flows by way of ports D and E back to tank. This position may be used to reduce any transient high fuel temperatures which might otherwise occur under hot ambient conditions with the engine throttled back to "altitude-idle fuel flow When the aircraft is on the ground, the fuel flow may be heated by passing it from a suitable connection through a suitable ground-based heating device. Conveniently, the high-pressure pump is a centrifugal pump. CLAIMS

1. An aircraft fuel system including a tank for aircraft fuel, a high-pressure pump for circulating fuel from the tank to a fuel control unit by way of a cooler, in which engine oil is cooled by fuel passing therethrough, and a valve having one position in which fuel from the cooler is supplied to the fuel control unit and another position in which some of the fuel from the cooler is supplied to the fuel control unit and some of the fuel from the cooler is supplied to the tank.

2. An aircraft fuel system as claimed in Claim in which the high-pressure pump is a centrifugal pump of the high-speed type.

3. An aircraft fuel system substantially as hereinbefore described with reference to the accompanying drawings.