Ultrasonic-densiometer mass flow sensor for use in flow metering units

A fuel delivery system uses a volumetric flow sensor and a densiometer to measure a mass flow rate of the fuel. A densiometer may be a coriolis mass flow sensor etched into a small circuit chip. As fuel flows past the densiometer a density of the fuel and characteristic slope as a function of temperature is determined. At least one temperature sensor is also located on the circuit chip to provide accurate temperature of the fuel to correspond to the fuel density reading. Piezoelectric crystals in the volumetric flow sensor generate and receive a sound wave. By analyzing the sound wave signals the volumetric flow rate of fluid through the volumetric flow sensor can be calculated. At least one temperature sensor is also placed on the volumetric flow sensor to correct for any thermal expansion of an inner diameter of the volumetric flow sensor and for final mass flow calculation. The density and temperature information from the densiometer and the volumetric flow and temperature information from the volumetric flow sensor are used to determine the density of the fuel at the volumetric flow sensor. By using the density calculated at the volumetric flow sensor and using the volumetric flow information an accurate mass flow rate of the fuel at the volumetric flow sensor can be calculated.

BACKGROUND OF THE INVENTION

This invention relates to a pressure regulating fuel delivery system suitable for a gas turbine engine, having a pressure regulator, together with an ultrasonic sensor and a densiometer to accurately measure the mass flow of fuel to the engine.

Conventional fuel delivery systems for gas turbine engines are expensive and include numerous complex parts. A typical fuel delivery system is controlled by scheduling fuel flow based upon a fuel metering valve position and a linear variable displacement transducer to provide feedback. The metering valve position is adjusted in closed loop to maintain the desired engine speed (and power setting). A low accuracy dual rotor turbine meter to measure totalized mass flow after the fuel metering unit. The totalized flow is used as a double check for the wing tank fuel level gauges. The dual rotor turbine meter is a volumetric device with limited accuracy, therefore it is not used for engine health monitoring.

The fuel metering valve, dual rotor turbine meter, linear variable displacement transducer, pressure regulator, and other components, are all quite complicated. The metering valve also creates a pressure drop within the system that generates extra heat in fuel and decreases the efficiency of the oil cooling system. Therefore, what is needed is a system that reduces heat load, eliminates the fuel metering valve, dual rotor turbine meter, and linear variable displacement transducer, and accurately measures the instantaneous and totalized mass flow to the burner, for engine health monitoring.

SUMMARY OF THE INVENTION

A pressure setting fuel delivery system uses an ultrasonic volumetric flow sensor and a densiometer to measure a mass flow rate of the fuel.

A densiometer having a coriolis mass flow sensor etched into a small chip is located within the fuel delivery system. Preferably, for durability reasons, the densiometer is at a location having lower fuel temperatures and pressures. As fuel flows past the densiometer a density of the fuel is determined for a given temperature and a slope verses temperature determined and continuously updated. At least one temperature sensor is also located on the chip to provide accurate temperature of the fuel to correspond to the fuel density reading.

An ultrasonic flow sensor is positioned in the system such that fuel flows through the ultrasonic flow sensor and is discharged from fuel nozzles into the engine. Piezoelectric crystals within the ultrasonic flow sensor generate and receive a sound wave. By analyzing the sound wave signals the fluid velocity and a corresponding volumetric flow rate of fluid through the ultrasonic flow sensor can be calculated. At least one temperature sensor is also placed on the ultrasonic flow sensor to correct for any thermal expansion of an inner diameter of the ultrasonic flow sensor when analyzing the sound wave signals, and for converting the volumetric flow to mass flow.

The density and temperature information from the densiometer and the volumetric flow rate and temperature from the ultrasonic flow sensor are sent to an electronic engine controller (EEC). Using the information the EEC can determine the density of the fuel at the ultrasonic flow sensor and thus the true mass flow rate of the fuel. The EEC can then send this information to aircraft systems that monitor total and instantaneous fuel consumption for engine health monitoring.

Accordingly, the present invention provides a fuel metering unit that eliminates the fuel metering valve, dual rotor turbine meter, linear variables displacement transducer, and other complicated and expensive components typically found in prior art fuel delivery systems, while providing accurate mass flow rate information.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A fuel delivery system10is shown schematically inFIG. 1. The system10is preferably for use in delivering fuel to a gas turbine engine12. Fuel from a boost pump system14passes through a fuel filter16. The fuel flows from the fuel filter16through an ultrasonic volumetric flow sensor18and is discharged from fuel nozzles20into the engine12. Due to the ability of the ultrasonic flow sensor18to withstand high temperatures, it may be located immediately prior to the fuel nozzles20as shown in the present embodiment. However, other locations for the ultrasonic flow sensor18can also be utilized to provide volumetric flow information.

Between the fuel filter16and the ultrasonic flow sensor18a portion of the fuel is directed toward a pressure-regulating valve24which can be used to adjust the fuel pressure in the fuel line26prior to the fuel nozzles20. By decreasing pressure within the fuel line26the flow rate of the fluid through the ultrasonic flow sensor18and out of fuel nozzles20is decreased. Inversely, as the pressure in the fuel line26is increased, the flow rate of the fuel through the ultrasonic flow sensor18and the fuel nozzles20is increased. Thus, the pressure regulating valve24is used to adjust the mass flow rate of the fuel into the engine12.

Excess fuel is bypassed by the pressure regulating valve24and flows back to the boost pump system14where it later cycles through the system again. Additionally, a portion of the fuel that passes through the fuel filter16also passes through a fine filter28. Fuel from the fine filter28flow through coriolis densiometer30then joins the fuel from the pump22to cycle back to the boost pump system14. A Minimum Pressure and Shut-Off Valve (MPSOV)31is located between filter16and ultrasonic flow sensor18. The MPSOV31opens as pressure builds and allows flow to the engine. It also is controlled by a separate solenoid (not shown) to allow shutting off the fuel flow and stopping the engine12.

FIG. 2is a side view of the ultrasonic flow sensor18. Fluid enters the ultrasonic flow sensor18at a first end32and exits the ultrasonic flow sensor18through the sidewall34near a second end36. Piezoelectric crystals38are positioned along the ultrasonic flow sensor18. As shown there are two sets of piezoelectric crystals38placed at 90-degree intervals on the sidewall34of the ultrasonic flow sensor18. Two of the piezoelectric crystals38, for redundancy, generate a sound wave, while the other two piezoelectric crystals38receive the sound wave. By analyzing the sound wave signals received by the piezoelectric crystals38the velocity and the volumetric flow rate of fluid through the ultrasonic flow sensor18can be calculated. The piezoelectric crystals38create two direct sonic flow paths40through the ultrasonic flow sensor18. One of the flow paths40is shown inFIG. 3. Alternately, the piezoelectric crystals38may be arranged to have a reflective flow path.

Referring toFIG. 3the ultrasonic flow sensor18may utilize a flow straightening device, such as flow straightening tubes41. At least one temperature sensor42is also placed on the ultrasonic flow sensor18. The temperature sensor42is preferably a resistance temperature device (RTD). Other types of temperature sensors are known and may also be used. In the embodiment shown there are two temperature sensors42, for redundancy (shown inFIG. 4). The temperature recorded by the temperature sensor42is used to correct for any thermal expansion of an inner diameter44(shown inFIG. 3) of the ultrasonic flow sensor18that affects the volumetric flow rate and to calculate the local fuel density based on the slope of the density as determined by a densiometer30. The temperature can be used to make any necessary adjustments when analyzing the sound wave signals.

Referring toFIGS. 5 and 6, a side and end view of a micro coriolis densiometer30is shown. The densiometer30is a coriolis mass flow sensor46etched into a small circuit chip48. This type of densiometer30may be as known. Acceptable densiometers and can be best identified for example by visiting the web page of, Integrated Sensing Systems, at www.mems-issys.com. The densiometer30is ideal for providing instantaneous density readings. As the fuel flows past the densiometer30a density of the fuel is determined by the coriolis flow sensor46. At least one temperature sensor50is also located on the computer chip48. The temperature sensor50is used to provide accurate temperature of the fuel to correspond to the fuel density reading. Calibration for the coriolis flow sensor46is also embedded on the computer chip48so that it may be used in any fuel system without requiring matched sets. Of course, other fluid density meters may be used.

Referring back toFIG. 1, the density and temperature information from the densiometer30is sent to an electronic engine controller (EEC)52. The EEC52also receives the volumetric flow and temperature information from the ultrasonic flow sensor18. Density and temperature for a known material have a linear relationship with one another. Thus, knowing the density of a fluid at one temperature the density at another temperature can be calculated. Using this the EEC52can determine the density of the fuel at the ultrasonic flow sensor18from the temperature at the ultrasonic flow sensor18, and the temperature and density at the densiometer30. By using this relationship to calculate density at the ultrasonic flow sensor18the densiometer30may be located remotely from the ultrasonic sensor. Preferably, the densiometer30is located in a portion of the fuel system10that is not subject to high temperatures. The system shown has the densiometer30located between the fine fuel filter and a return flow of the fuel to the boost system. Other locations may be desired depending on the design or the application, such as the boost pump circuit of the wing tank.

Using the density calculated at the ultrasonic flow sensor18and using the volumetric flow information, an accurate mass flow rate of the fuel at the ultrasonic flow sensor18can be calculated. The EEC52then sends this information to the aircraft system for the purpose of monitoring instantaneous mass flow and totalized mass flow.