Patent Application
20090013687
1. Field of the Invention
The present invention is related to a system for monitoring the performance of a turbocharged reciprocating internal combustion engine.
2. Disclosure Information
Reciprocating internal combustion engines, such as diesel and spark-ignited engines frequently utilize turbocharging. In essence, most turbochargers are configured as a single shaft gas turbine engine having a compressor and turbine wheel attached for rotation on a common shaft. Because the turbine and, particularly the compressor, are aerodynamic devices using airfoil sections, turbochargers are subject to certain operational difficulties inherent to aero machinery, such as compressor surge or stall. Compressor surge is a condition characterized by separation of flow from certain of the compressors rotating and static surfaces. Severe surge may cause high frequency, oscillating airflow, resulting in large unbalanced forces which may quickly damage the turbocharger and the engine to which it is attached. Accordingly, engines have been monitored to detect operation tending toward surge. When operation tending toward surge is detected, the engine may be derated, causing a loss of horsepower output.
Turbocharged engines typically have extensive air piping extending from the turbocharger to the engine cylinders. Such piping has many joints and potential leak paths, particularly where an intercooler is employed in the air piping system. Unfortunately, leaks in the air piping system or intercooler may create the appearance of a compressor surge, because of a decrease in the engine's inlet manifold pressure, when no surge is present. This in turn may be the cause of unneeded derating of the engine, again when there is no surge problem. On the other hand, air piping, including intercoolers, may also be subject to plugging, and this may cause compressor surge.
It would be desirable to have the capability to detect leaks or obstructions in charge air piping extending between a turbocharger and the engine's cylinders, so as to avoid spurious compressor surge determinations, unneeded deration, and, in certain cases, engine damage.
According to an aspect of the present invention, a system for monitoring operation of a multicylinder turbocharged reciprocating engine includes a speed detection system for determining the rotational speed of the turbocharger and a mass flow detection system for determining the actual flow rate of charge air to the engine cylinders. An onboard controller, which is operatively connected with the speed detection system and the flow detection system, compares the actual charge air flow rate with a predetermined flow rate corresponding to the turbocharger's rotational speed. The predetermined flow rate is determined based upon a trend analysis of the rotational speeds and corresponding mass flow rates of a population of same-design engines, with the controller setting a condition flag if the actual charge air flow rate is less than the predetermined flow rate.
According to another aspect of the present invention, the determined rotational speed of the turbocharger and the determined actual flow rate are corrected for mach number.
According to another aspect of the present invention, the population of same-design engines from which the trend analysis is drawn includes a population of engines having turbocharger and air induction system design characteristics which are generally equivalent to the turbocharger and air induction system design characteristics of the engine being monitored, and with the population of engines having actual air charge flow rates which are generally congruent with the predetermined flow rates. In other words, the population of engines used to establish a trend analysis is a population of engines without either charge air leaks, or plugging of the charge air handling system.
According to another aspect of the present invention, a trend analysis may be performed by a regression analysis or other analytical technique, with the results of the regression analysis being stored within a memory contained within the controller, either in tabular form, or as an analytical expression.
According to another aspect of the present invention, a method for monitoring operation of a multicylinder turbocharged reciprocating engine includes determining the rotational speed of the turbocharger with a speed detection system, and determining the actual flow rate of charge air through the engine cylinders, with a flow detection system. Then, the method further includes comparing the actual charge air flow rate with a predetermined flow rate corresponding to the turbocharger's rotational speed, with an onboard controller operatively connected with the speed detection system and the flow detection system. As described above, a predetermined flow rate is preferably based upon a trend analysis stored within the controller, of turbocharger rotational speeds and corresponding mass flow rates of a population of same-design engines without either charge air leaks or plugging of the charge air handling system.
The method further includes setting a condition flag indicating that a charge air leak or flow obstruction exists downstream of the turbocharger if the actual charge air flow rate is less than a predetermined flow rate.
According to another aspect of the present invention, the method may also include derating the power output of the engine if the charge air condition flag is set.
According to another aspect of the present invention, in a broader sense the invention includes monitoring at least one operating parameter predictive of the turbocharger's output, and generating a parametric output signal corresponding to the value of the at least one operating parameter. Then, after determining the actual mass flow rate of charge air to the engine cylinders, the method includes comparing the actual charge air flow rate with a predetermined flow rate corresponding to the monitored operating parameter, using an onboard controller which receives a parametric output signal and the results from the flow detection system.
It is an advantage of a method and system according to the present invention that false positive detections of compressor surge may be avoided.
It is yet another advantage of a method and system according to the present invention that potentially dangerous leaks of high pressure, extremely hot, compressed air being discharged from a turbocharger compressor may be diagnosed in a timely fashion, so as to permit repairs to be made before engine performance is compromised.
It is yet another advantage of a method and system according to the present invention that unneeded horsepower derations and even failures of engines may be avoided, along with the extra costs, such as increased fuel consumption, associated with spurious determinations of compressor surge.
It is yet another advantage of a method and system according to the present invention that leaks or obstructions in the air piping extending from a turbocharger to an engine's cylinders may be detected well before any noticeable degradation in engine performance occurs.
Other advantages, as well as features of the present invention, will become apparent to the reader of this specification.
As shown in
As shown in
In a first embodiment according to the present invention, controller 30 receives a signal from a rotational speed sensor (one of sensors 34) associated with turbocharger 14. Such sensors are commonly used in internal combustion engines and are known to those skilled in the art. A mass flow detection system for engine 10 may include, for example, a sensor providing direct measurement of the flow either through a hot wire anemometer, or through a speed-density system using manifold pressure, engine speed, and charge air temperature. If a speed-density system is employed, engine a mass flow rate may be calculated with the following expression:
Mass Flow Rate=K*MAP*RPM/(MAT)
where:
MAP=manifold absolute pressure;
RPM=engine speed;
MAT=charge air absolute temperature; and
K=a constant determined for a particular engine.
Mass flow rate may be corrected for mach number by multiplying the raw mass flow value by a correction factor as follows:
Correction Factor=sqrt(TIA/Ref_Temp)/(BAP/Ref_Pressure).
Where:
TIA=turbo inlet absolute temperature; and
BAP=barometric pressure.
Similarly, turbocharger speed may be corrected for mach number by the formula:
Corrected Turbo Speed=sensed turbo speed/sqrt(TIA/Ref_Temp).
Having determined the mass flow and turbo speed of a particular engine, the process according to an aspect of the present invention may be continued according to the flow diagram of
Curve A may be captured within controller 30 either as a lookup table or as an analytical expression. In either event, as engine 10 is monitored, and mass flow and turbo speed are determined, the process according to
Beginning at block 50 of
If the charge air leak or obstruction confirmed at block 66 is sufficiently severe that the engine's operation approaches curve B of
According to another aspect of the present invention, the method of
Although the present invention has been described in connection with particular embodiments thereof, it is to be understood that various modifications, alterations, and adaptations may be made by those skilled in the art without departing from the spirit and scope of the invention set forth in the following claims.
