System to enhance fuel flow measurement accuracy

A fuel flow measuring apparatus comprises a fuel conditioning cabinet, a fuel supply delivered through a fuel supply line, a fuel measurement cabinet, a fuel transfer line to transfer fuel from the fuel conditioning cabinet to the fuel measurement cabinet, a fuel delivery line extending between the fuel measurement cabinet and the internal combustion engine and to deliver fuel thereto, a first fuel return loop extending from the fuel delivery line to the fuel measurement cabinet, a second fuel return loop extending between the fuel measurement cabinet and the fuel conditioning cabinet and an intermediate cooling system comprising an intermediate cooling tank containing an intermediate coolant, an intermediate coolant line in serial thermodynamic communication with the first fuel return loop and the second fuel return loop to thermally connect the fuel flowing through both of the fuel conditioning cabinet and the fuel measurement cabinet to define an isothermic fuel stability.

FIELD OF THE INVENTION

Exemplary embodiments of the invention relate to systems for measuring mass fuel flow and, more particularly, to a laboratory's ability to accurately measure fuel mass flow without requiring that the test engine operate at steady state conditions until the fuel system thermal stability is established.

BACKGROUND

With increased governmental and consumer focus on motor vehicle fuel economy, the ability of manufacturers to develop fuel efficient engines has become of paramount importance. As part of this engineering effort is the ability to accurately measure the fuel economy of such engines as errors can be costly; on either the high or the low side of measurement.

In engine test cells, the density of fuel can change 0.1% per degree Celsius. Changes of fuel density during a test measurement introduce errors in mass flow calculations. Testing has shown a definite correlation between fuel temperature stability and fuel mass flow measurement accuracy. As a result, isothermal test cell fuel systems desirably enhance accuracy substantially. Jacketed fuel lines and large in-cell fuel reservoirs are one alternative but require significant test cell space which is generally not available. Some laboratories may attempt to attain stability through long stabilization times. This effectively compromises the ability to acquire accurate fuel flow measurements during transient conditions and adversely affects test cell productivity.

SUMMARY

In an exemplary embodiment a fuel flow measuring apparatus for an internal combustion engine comprises a fuel conditioning cabinet, a fuel supply configured to deliver fuel to the fuel conditioning cabinet through a fuel supply line, a fuel measurement cabinet (or subsystem), a fuel transfer line configured to transfer fuel from the fuel conditioning cabinet to the fuel measurement cabinet (or subsystem), a fuel delivery line extending between the fuel measurement cabinet (or subsystem) and the internal combustion engine and configured to deliver fuel thereto, a first fuel return loop extending from the fuel delivery line to the fuel measurement cabinet (or subsystem), a second fuel return loop extending between the fuel measurement cabinet (or subsystem) and the fuel conditioning cabinet and an intermediate cooling system comprising an intermediate cooling tank containing an intermediate coolant therein, an intermediate coolant line in serial thermodynamic communication with the first fuel return loop and the second fuel return loop to thereby thermally connect the fuel flowing through both of the fuel conditioning cabinet and the fuel measurement cabinet (or subsystem) to define an isothermic fuel stability therebetween.

DESCRIPTION OF THE EMBODIMENTS

The following description is merely exemplary in nature and is not intended to limit the present disclosure, its applications or uses. Referring to the FIGURE, a test cell10for testing various performance characteristics of an internal combustion engine12is illustrated. In the exemplary embodiment illustrated, the internal combustion engine is a 4-cylinder engine having a dead-headed or non-recirculating fuel system14, in which fuel entering a fuel rail does not return to the fuel system. Other types of fuel systems are contemplated.

A fuel flow measuring apparatus18includes a fuel conditioning cabinet20. In an exemplary embodiment the fuel conditioning cabinet20may include one or more fuel filters, fuel pumps and fuel pre-conditioners among other items (not shown) depending on the particular testing being conducted on the internal combustion engine12. Fuel enters the fuel conditioning cabinet20from a remote fuel supply22through fuel supply line24. In an exemplary embodiment, a fuel measurement cabinet (or subsystem)28may include one or more fuel flow measurement devices, fuel pressure controls, positive displacement pumps, variable displacement pumps, density sensors and fuel flow transducers among other items (not shown); again depending on the particular testing being conducted on the internal combustion engine12. Fuel enters the fuel measurement cabinet (or subsystem)28from the fuel conditioning cabinet20through fuel transfer line30. The purpose of fuel conditioning cabinet and fuel measurement cabinet (or subsystem)20and28respectively is to precisely condition the fuel passing therethrough (pressure, temperature, etc.) for introduction to the internal combustion engine12during testing. In another embodiment of the invention it is contemplated that the fuel flow measuring apparatus may comprise a single cabinet which would then be denominated simply as18in the FIGURE and could contain all of the equipment already indicated as resident in the individual cabinets20,28. A fuel delivery line32extends between the metering portion of the fuel measurement cabinet (or subsystem)28and the fuel rail16of the non-recirculating fuel system14for delivery of the precisely conditioned fuel thereto and to the engine12.

As indicated, one important aspect of the fuel condition is the temperature. Maintaining the fuel at a constant temperature during its residence time in both cabinets20and28as well as in fuel transfer line30is of significant importance if accurate measurements of engine fuel consumption are to be gathered. As such a first fuel return loop34is provided from the fuel delivery line32to the fuel measurement cabinet (or subsystem)28. In an exemplary embodiment, the fuel is delivered downstream of the metering portion36of the fuel line in the fuel measurement cabinet (or subsystem)28and, as such, in an exemplary embodiment, to an upstream portion of the fuel transfer line32. As a result of the first fuel return loop34, fuel is not allowed to become stagnant in the fuel delivery line32, due to the non-recirculating fuel system14, which could result in an undesirable increase in fuel temperature due to high ambient temperatures in the test cell10. In an exemplary embodiment, a second fuel return loop40is provided between the fuel measurement cabinet (or subsystem)28and the fuel conditioning cabinet20. The fuel return loop40extends from a location upstream of the metering portion36in the fuel measurement cabinet (or subsystem)28and returns fuel to the fuel supply line24in the fuel conditioning cabinet20.

In an exemplary embodiment, an intermediate cooling system42includes an intermediate coolant tank44which may be resident in the test cell10. The intermediate coolant tank44is maintained at a predetermined temperature through the use of a facility coolant supply58through thermodynamic transfer supply and return lines48,50, respectively. In one embodiment, a desired temperature of the intermediate coolant46in the intermediate coolant tank may be approximately 22 degrees Celsius. A temperature sensor52in signal communication with a controller54allows the controller to actuate a solenoid or other suitable valve member56to control the quantity of coolant/heating medium58flowing through the thermodynamic transfer supply and return lines48,50, to maintain the intermediate coolant46at the desired temperature. The intermediate coolant46is circulated through intermediate coolant lines60via intermediate coolant pump62in fluid communication therewith. The intermediate coolant lines60serially deliver intermediate coolant46to a first heat exchanger64disposed in thermodynamic communication with first fuel return loop34and to a second heat exchanger66disposed in thermodynamic communication with second fuel return loop40thereby thermally connecting the fuel flowing through both fuel conditioning cabinet and fuel measurement cabinet (or subsystem)20and28, respectively as well as fuel being returned from the non-recirculating fuel system14through first fuel return loop34. Following flow through the second heat exchanger66, intermediate coolant is returned to the intermediate coolant tank44.

The exemplary system described herein connects the circulating volumes (volumes in fuel conditioning cabinet and20,28, tubes, lines, fittings and associates equipment) by circulating a secondary coolant (i.e. intermediate coolant46) between heat exchangers64,66in each of these volumes. The intermediate cooling system42is designed to provide thermal stability to these fuel volumes (i.e. isothermal fuel stability) by means of a significant coolant mass and shared heat exchangers with a control system. In an exemplary embodiment, the temperature of the intermediate coolant46is controlled, via the controller54, to a temperature close to ambient temperature. By stabilizing the fuel temperature in the circulating volumes, the fuel density changes during a test measurement are minimized.