A gas turbine engine (GTE) may include multiple sets of nozzles that each deliver burn fuel to a combustion chamber within the GTE. These sets of nozzles may include, for example, a primary set of atomizer nozzles and a secondary set of air blast nozzles. During GTE start-up, it is generally desirable to bias up fuel flow to the atomizer nozzles relative to the air blast nozzles to achieve optimal engine lightoff conditions. However, after GTE start-up, it is generally desirable to provide even pressure and flow to the atomizer nozzles and the air blast nozzles to achieve an evenly distributed burn spray pattern in the combustion chamber. To address this need, fuel divider systems have been developed that bias up the pressure, and therefore the volume, of burn fuel supplied to the atomizer nozzles as a function of total metered burn fuel volume. When little burn fuel is supplied to the system during GTE start-up, the fuel divider system provides a relatively large pressure bias, and thus flow distribution, in favor of the atomizer nozzles. This bias decreases as the total burn fuel supplied to the system increases and ultimately disappears at a predetermined flow rate associated with typical engine run conditions, such as engine cruise. In this manner, the fuel divider system biases up fuel flow to the atomizer nozzles during engine lightoff conditions, while providing an equalized flow to the atomizer nozzles and the air blast nozzles during moderate to high flow engine run conditions.
Fuel divider systems of the type described above may further include an ecology valve. Upon cessation of GTE operation, the ecology valve removes a predetermined volume of burn fuel from the engine fuel manifold. In so doing, the ecology valve decreases the volume of fuel available for vaporization to the atmosphere and deters coking of the atomizer and air blast nozzles. When GTE operation is again initiated, the ecology valve returns the withdrawn fuel to the fuel engine manifold for combustion.
Although addressing the need to bias up fuel flow to the atomizer nozzles during engine start-up, conventional fuel divider systems of the type described above are limited in certain respects. As previously explained, such fuel divider systems bias up the pressure of the burn fuel supplied to the atomizer nozzles as a function of total burn fuel supplied to the system; consequently, such fuel divider systems also bias up the pressure of the burn fuel supplied to the atomizer nozzles during certain post start-up conditions, such as flight idle, wherein relatively little burn fuel is supplied to the fuel divider system and GTE. Unequal fuel distribution during such low flow post start-up conditions may result in an uneven burn spray pattern, which, in turn, may lead to heat-induced engine combustor distress in areas adjacent the atomizer nozzles. As a further limitation, fuel divider systems of the type described above permit the ecology valve to move, and thus prematurely reintroduce burn fuel to the engine fuel manifold, during GTE start-up procedures and potentially compromise ideal GTE start flow conditions.
It is thus desirable to provide a flow equalizing override assembly capable of being remotely actuated at a desired time (e.g., upon detection of GTE ignition) to equalize the flow output of a fuel divider system and thereby provide equalized flow to primary and secondary nozzles during post start-up conditions including low flow post start-up conditions, such as flight idle. It would also be desirable if, in embodiments wherein the override assembly is utilized in conjunction with a fuel divider system including an ecology valve, the flow equalizing override assembly permits ecology valve movement only after the override assembly has been remotely actuated and GTE start-up has been achieved. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended claims, taken in conjunction with the accompanying drawings and this Background.