Fuel delivery system having an ecology valve
A fuel control system for a gas turbine engine is disclosed that includes a flow path carrying fuel from a fuel source to a combustion chamber, an ecology valve 124 for removing a quantity of fuel from the flow path, the ecology valve 124 being shiftable in a first direction from a first position to a second position and in a second direction from said second position to said first position and a fuel line 115 connected between the flow path and the ecology valve 124 for moving fuel between the flow path and the ecology valve 124 to bias the ecology valve 124 toward the second position, where the fuel line 115 is configured, such as by the inclusion of an orificed check valve 150 therein, to allow fuel to move therethrough away from the ecology valve 124 at a greater rate than toward the ecology valve 124.
1. A fuel control system for a gas turbine engine comprising:
a flow path carrying fuel from a fuel source to a combustion chamber;
an ecology valve for removing a quantity of fuel from said flow path, said ecology valve being shiftable in a first direction from a first position to a second position and in a second direction from said second position to said first position; and
at least one fuel line connected between said flow path and said ecology valve for moving fuel between said flow path and said ecology valve to bias said ecology valve toward said second position, said at least one fuel line including an orificed check valve to allow fuel to move through said at least one fuel line away from said ecology valve at a greater rate than toward said ecology valve.
2. The fuel control system of claim 1 including a manifold in said flow path, wherein said manifold is substantially emptied when said ecology valve moves into said first position.
3. The fuel control system of claim 2 wherein the orifice in said orificed check valve allows fuel to flow through said at least one fuel line toward said ecology valve at a first rate, said first rate being selected to allow said manifold to fill before said ecology valve is fully biased into said second position.
4. The fuel control system of claim 3 wherein said orificed check valve allows fuel to flow away from said ecology valve at a second rate greater than said first rate.
5. The fuel control system of claim 4 wherein said at least one fuel line comprises exactly one fuel line.
6. In a fuel control system for a gas turbine engine having a speed and a lightoff speed envelope, said system comprising a fuel flow path running from a metering valve to a gas turbine engine combustion chamber, said metering valve supplying a fuel flow to said flow path at a first rate, a first component of said fuel flow being directed to the combustion chamber and a second component of said fuel flow being directed to an ecology valve to bias the ecology valve toward a first position, said first rate being insufficient to supply adequate fuel to said combustion chamber and shift said ecology valve into said first position before the engine speed exceeds said lightoff speed envelope, the improvement comprising:
an orificed check valve in said fuel flow second component for limiting fuel flow toward said ecology valve.
7. The fuel control system of claim 6 wherein said engine has a maximum speed and wherein said lightoff speed envelope comprises from about 10 to about 15 percent of said maximum engine speed.