Using ion current signal for engine performance and emissions measuring techniques and method for doing the same

A system and method is provided for the use of the ion current signal characteristics for onboard cycle-by-cycle, cylinder-by-cylinder measurement. The system may also control the engine operating parameters based on a predicted NOx emission level, CO emission level, CO2 emission level, O2 emission level, unburned hydrocarbon (HC) emission level, cylinder pressure, or a cylinder temperature measurement according to characteristics of the ion current signal.

BACKGROUND

1. Field of the Invention

The present application relates to the use of the characteristics of an ion current sensor signal for onboard measurement of engine emissions such as NOR, CO, CO2, unburned hydrocarbon (HC), excess O2 in the exhaust and for onboard measurement of cylinder pressure and temperature and for the control of different engine parameters accordingly.

2. Description of Related Art

One existing technology in measuring NOx emissions utilizes a chemiluminescence detector (CLD) that samples gases to a chamber full with ozone (O3), where the chemical reaction between NO and O3 takes place producing luminescence proportional to the NO concentration. The CLD method is used only in research or during engine calibration and development as it requires very expensive instrumentation and maintenance. Another existing technology a sensor located in the exhaust pipe or with after treatment device which consists of Zirconia multilayer ceramics in metal housing. The NOx concentration in the exhaust gas is proportional to the electrical current controlling the electro-chemical pumps that adjusts the oxygen concentration in the cavities of the sensing element. The problem of this type of sensor is their slow time response and low sensitivity, and it requires recalibration due to signal drafting. Further, this type of sensors is unable to predict the concentration of NOx attributable to each engine cylinder accurately. This brings us to the conclusion that there is no in-cylinder, low cost technology that is capable of quantitatively and adequately predict the concentration of NOx produced in internal combustion engines.

Regarding CO, CO2, and unburned hydrocarbon (HC), there is no in-cylinder onboard sensor available to predict these emissions produced by the engine. As for excess O2 in the exhaust, one known sensor is the lambda sensor which is currently used by the auto industry. However, the use of the ion current sensor to predict excess O2 is a faster technology as the predictions are based on a cycle by cycle basis.

For cylinder pressure and temperature, pressure transducers are considered for this type of measurements. As cylinder pressure is measured and cylinder temperature is then calculated from the pressure trace. This is a reliable technology, however, the cost of a pressure transducer is still high compared to the use of the ion current sensor to predict cylinder pressure and temperature.

SUMMARY

A system and method is provided for an onboard in-cylinder pressure, temperature, and emissions measurements in an internal combustion engine. The system can be further used in controlling the engine based on a feedback signal from the measured parameters. The system acquires an ion current signal and controls the engine operating parameters based on the characteristics of the ion current signal.

Throughout the application examples will be provided with regard to NOx, pressure and temperature measurements, however, these principles can be applied to other in-cylinder variables as well and such applications are contemplated herein. In this application, it is understood that NOx refers to various emissions comprising Nitrogen and Oxygen, such as but not limited to NO and NO2.

The new technique gives the ion-current sensor, located inside the engine cylinder, the ability to detect and accurately measure the amount of different combustion resulted species on a cyclic basis. This fast response measuring technique can be applied in all engine cylinders in order to provide an onboard feedback signal to the contribution of each cylinder to certain emissions production.

The system offers a new cost effective and simple technique to measure pressure, temperature, and certain emissions inside the combustion chamber using the ion-current signal. The system also provides a fast cycle-by-cycle predictive technique to accommodate the engine transient operation. The feedback signal is sent to the engine ECU for better engine control, thereby producing less emissions with no modification to the engine.

The system is cost effective as the sensor involved is the ion sensor. The system provides a fast response emissions and engine performance measuring technique, as it depends on electron speed. The system is able to measure the disclosed parameters inside the combustion chamber and on a cycle-by-cycle basis. Further, the system is able to measure these parameters in every engine cylinder with no modifications required to the engine block. Accordingly, the system is well suited as an on-board tool for NOx, CO, CO2, unburned hydrocarbon (HC), excess O2, cylinder pressure and temperature measurement and provides an efficient, compact design for integration in production models.

Further objects, features and advantages of this application will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification.

DETAILED DESCRIPTION

Now referring toFIG. 1, a schematic view of an engine110is provided. For illustrative purposes the schematic shows a single cylinder of an engine, however, it is readily understood that multiple cylinders may be used in combination to form the engine. The cylinder112houses piston114allowing for reciprocating motion of the piston114within the cylinder112. The combustion chamber116is formed by the cylinder houses112, the piston114, and the cylinder head115. Air, a mixture of air and exhaust gases, or other mixtures of any fluid may be provided into the chamber116through an intake manifold118. The flow of air or mixtures made through the intake manifold118may be controlled by intake valve120. Fuel may be provided into the chamber by a fuel injector122. A spark plug124may is used to ignite of the fuel inside the combustion chamber116causing reciprocating motion of the piston114. After combustion, the exhaust gases in the chamber may be released through the exhaust manifold126. Further, the flow of exhaust may be controlled by an exhaust valve128located within the exhaust manifold126. As may be readily understood, combustion in the chamber116causes the piston114to move downward causing rotation of the crankshaft130. The inertia of a flywheel or combustion in other chambers will cause the crankshaft130to rotate further thereby causing a reciprocating motion of the piston114upward. The spark plug124can be turned on by the ECU150through an electrical command154. The spark plug124may also include a sensor132to monitor activity within the combustion chamber116during the entire cycle of the engine. The sensor132includes an ion current sensor, a pressure sensor, an optical sensor, or any combination of the above. These sensors may be standalone or integrated with the spark plug or the fuel injector122. Although certain aspects may be particularly useful for spark ignited engines, the application of this technology with regard to other internal combustion engines such as diesel engines is contemplated herein. In such scenarios, the ion current sensor may be placed within a glow plug. The sensor signal134may be provided to a combustion module140. The combustion module140includes an acquisition module142for acquiring the combustion signal and amplifier144for enhancing the combustion signal and a signal analysis module146to determine certain combustion characteristics based on the enhanced combustion signal. The combustion parameters148are then provided to an engine control module150. The engine control module150may then analyze the combustion parameters and control engine operation parameters based on the combustion parameters. In one implementation, the ion current signal may be used to control the engine operating parameters.

The engine control unit150includes a combustion controller152, a fuel delivery controller156and other engine controllers158. The combustion controller152may act as a master module that provides a control signal to different engine components such as the spark plug124(ignition system), the fuel delivery system162, or the injector122. The fuel delivery controller156provides a fuel delivery control signal160to an engine fuel delivery system162. The engine fuel delivery system controls the delivery of fuel to the injector122. The fuel from the tank166is delivered by the fuel pump164to the fuel delivery system162. The fuel delivery system162distributes the supplied fuel based on a signal160from the ECU150. The fuel is further supplied to the injector122through a fuel line168. In addition, the fuel delivery controller156is in communication electronically with the fuel injector122to control different injection parameters such as number of injection events, injection duration and timing as noted by line170. In addition, the other engine controllers158control other engine parameters such as engine speed, load, amount of exhaust gas recirculation, variable geometry turbocharger, or other units installed to the engine. Further, an output sensor180may be in communication with the crankshaft130to measure crank shaft position, and engine speed, torque of the crankshaft, or vibration of the crank shaft, and provide the feedback signal to the engine control unit150as denoted by line182.

Referring toFIG. 2, a graph is provided of the pressure, temperature, NOx, and corresponding ion current for an engine at cycle number30. Line210is the temperature and line212is the pressure in cylinder. Line214is the in-cylinder NOx measured using a fast NOx machine using an in cylinder sampling probe, while line216is the ion current profile. A high correlation between in-cylinder NOx and ion current profiles are apparent. In particular, it can be noticed that the peaks in the profile are the same in number and have similar spacing and relative amplitudes. In addition, the ion current signal is also affected by the cylinder pressure and temperature resulted from the combustion process.

Referring toFIG. 3, a graph is provided of the pressure, temperature, NOx, and corresponding ion current for an engine at cycle number8. Line310is the temperature and line312is the pressure in cylinder. Line314is the NOx, while line316is the ion current profile. Again, a correlation between the NOx and the ion current profile is apparent. In particular, it can be noticed that in this instance the NOx and ion current profiles have three peaks and also have similar spacing and relative amplitudes. It can be observed also that the ion current signal amplitude increased with the increasing cylinder pressure and temperature if compared with the previous graph shown inFIG. 2.

Now referring toFIG. 4, a graph of the pressure trace424, rate of heat release422, needle lift signal420, and ion current signal426is provided. Ion current signal parameters are shown in the graph to illustrate an algorithm to control engine operating parameters and indicate in-cylinder variables such as NOx, CO, CO2, unburned hydrocarbon (HC), excess O2, cylinder pressure and temperature based on the ion current signal. As examples of the parameters deduced from the ion current signal, the start of ion current signal (SIC) timing, which may be accomplished by various thresholding techniques, the ion current slope (m1, m2, m3, m4), where m1refers to the rate of ion current rise, m2is the rate of ion current decay, m3is the rate of the second peak decay, and m4is the rate of the ion current second peak rise. More slopes may be added depending on the number of peaks of each cycle-to-cycle ion current signal. The slope may be determined as the slope at which the ion current signal crosses an ion current threshold or may be the slope of the ion current signal at a specific position in degrees of the cycle. In some implementations, the slope may be determined at an offset position relative to an event such as the beginning of the ion current signal, the beginning of an ignition event, or some other characteristic marker of the cycle of the cylinder in which the ion current is measured. Further, the slope may be an instantaneous slope or may be an average slope, for example over a few degrees. The ion current delay (ICD) is another ion current parameter which is determined by a reference point which can be but not limited to the SOI (Start of Injection) (for example, as sensed by ECU) or the TDC (Top Dead Center) (for example, as sensed by the cam shaft sensor). Another parameter is the ion current amplitude (I1, I2, I3, . . . , Inin case of different peaks) for example, the first peak I1and second peak I2. The difference between two consecutive amplitudes (D1, . . . . , Dnin case of different peaks). The ion current peak to peak distance (P1, . . . , Pnin case of many peaks). The end of ion current signal timing (EOI), which may be accomplished by various thresholding techniques, and the total area under the curve (Ar) of the ion current signal, the area under the first bump (Ar1), and the area under the second bump (Ar2), and (Arn) for the area under the bump (n). Other parameters may be derived and will become readily apparent to persons skilled in the art

In one example, the relationship used to come up with measured parameters may be expressed as predicted parameter NOx=A*Fn(SOI)+B*Fn(m)+C*Fn(I)+L*Fn(P)+E*Fn(ICD)+F*Fn(Ar)+H*Fn(EOI)+K*Fn(D)+Y*Fn (SOI,m)+X*Fn (SOI, m, I)+ . . . etc. While the forgoing equation is exemplary, additional variables may be readily introduced. Such variables may include peak to peak, peak to end, peak to start, peak to start of injection, peak to top dead center, peak to end of injection, peak to start of combustion, peak amplitudes for each peak, or any of the other parameters mentioned herein and each of those variable may have their own weighting as indicated above. In addition, weighting factors such as A, B, C, L, E, F, H, K, Y, . . . , X may constants or may vary according to a look up table based on other parameters such as ion current sensor location inside the combustion chamber or the combustion chamber geometry. Further, it is anticipated that other relationship functions may be developed including linear, quadratic, root, trigonometric, exponential or logarithmic components or any combination thereof. In one particular example in accordance with the general equation provided above, NOx could be predicted according to a function:
NOx=A0+A1(Par1)+A2(Par2)+A3(Par3)+A4(Par4)+A5(Par1*Par2)+A6(Par1*Par3)+A7(Par1*Par4)+A8(Par2*Par3)+A9(Par2*Par4)+A10(Par1*Par2*Par3)+A1l(Par1*Par3*Par4)+A12(Par1^2*Par2^2*Par3^2*Par4^2)
where (Par) stands for an ion current parameter and (A) is a coefficient or weighting.

Now referring toFIG. 5, this graph illustrates the cycle-to-cycle NOx measurements for an engine transient operation at different engine operating conditions. As such, the graph represents a comparison between the NOx measured from the engine and the NOx predicted by the new technique depending on the function mentioned above. Line510represents the measured NOx percentage while line512represents the expected NOx calculated by the algorithm according to the ion current signal.

From the graph, it is clear that a good correlation between the measured NOx and the predicted NOx is achieved. The test was conducted based on a transient engine operating condition where engine operating parameters such as speed and load were varying. The engine was operated in transient test via an open ECU.

FIG. 6is a graph illustrating the correlation of the measured NOx and the predicted NOx as the engine operating parameters are varied. The x-axis of the graph is the measured NOx value and the y-axis of the graph is the predicted NOx value based on the ion current signal. Markers612are sample points that form a data cloud614. Line610is a linear fit based on the samples in the data cloud614. The linear correlation of the predicted NOx to the measured NOx is 93%.

Now referring toFIG. 7, a system is provided for determining the calibration between the ion current signal and the measured cylinder pressure, temperature, and NOx percentage in the exhaust. The experiments inFIGS. 1, 2, 4, 5, 6, 10, and 11were conducted on a multi-cylinder engine. The engine is equipped with a common rail injection system and a turbocharger. The engine specifications are shown in Table 2.

The engine system700includes an engine710with four cylinders712. Pistons reciprocate in the cylinders712to drive the crankshaft716. The crankshaft716may be connected to a dynamometer718. The dynamometer provides a load signal720to a processor714for combustion analyzing and data recording. Fuel is provided to the engine through a fuel rail722, pressure may be monitored in the fuel rail by a fuel sensor which may provide a fuel pressure signal724to the processor714. The fuel may be provided from the fuel rail722to the cylinder712through a fuel line726. The fuel may be provided through a fuel needle728. As such a needle lift signal730may be provided to the processor714for further analysis in conjunction with the other engine operating parameters. Further, a fuel flow meter is embedded within the fuel line726and is used to measure the fuel flow representing engine fuel consumption. It is understood that different fuel measurement devices could be used in this scenario.

Further, an ion current sensor734which may be the fuel injector or the spark plug or any electrically insulated probe may be located within the cylinder712to measure ion current. The ion current signal736may be provided to the processor714from the ion current sensor734. In addition, an inlet cylinder pressure sensor742may be located within the cylinder to measure cylinder pressure. The cylinder pressure signal744may be provided to the processor714by the pressure sensor742. The processor714uses the cylinder pressure signal744to calculate the cylinder temperature. Indicated Mean Effective Pressure (IMEP) and Brake Mean Effective Pressure (BMEP) for each engine cylinder is also calculated. It is understood that NOx, CO, CO2, unburned hydrocarbon (HC), excess O2, cylinder pressure and temperature can be predicted using the ion current signal by the processor714. Further, crank position sensor738may be connected to the crankshaft to provide an encoder signal740to the processor714, to track the various engine parameters based on the engine crank angle. In addition, a NOx measurement device746may be provided in an exhaust outlet748for each cylinder712. A NOx measurement signal750may be provided to the processor714by the NOx measurement device746. A lambda sensor is also available in the exhaust outlet748to measure excess oxygen. In addition, fast CO/CO2and unburned HC measurement devices are placed in the exhaust outlet748and used to provide a signal to the processor714.

Now referring toFIG. 8, a flow chart of a calibration procedure for NOx measurement using the ion current signal is provided. The method starts in block810. In block812, an ion sensor is positioned within the combustion chamber. In block814, the ion sensor is electrically connected to a power source through a positive terminal having a preset potential. In block816, the engine body is connected to the power source through a negative terminal. In block818, the NOx measurement device is connected to the engine exhaust port for measuring the actual NOx. In block820, the ion current signal is analyzed and calibrated with the NOx measurement device signal. In block822, a mathematical algorithm is developed for NOx prediction using the ion current signal. In block824, the algorithm is stored in a storage device for application to the engine control unit. The method ends in block826. The same calibration procedure may be used for the other disclosed parameters such as CO, CO2, unburned hydrocarbon (HC), excess O2, cylinder pressure and temperature

Now referring toFIG. 9, a method for controlling engine parameters based on the ion current signal characteristics is provided. The method900starts in block910. In block912, the calibration data is accessed by the engine control unit. In block914, an ion sensor signal is acquired. In block916, the ion sensor signal is analyzed to determine the weighting factors of the ion sensor pattern. In block918, the NOx prediction algorithm is applied to the ion sensor signal characteristics to estimate the amount of NOx during its formation in the combustion chamber. If the estimated NOx is not above a first threshold level, the method follows line928to block914, where the ion sensor signal is acquired again. If the estimated NOx is above a first threshold level, the method follows line930to block922. In block922, the engine control unit may change engine operation parameters of the engine to reduce the amount of NOx. In block924, the engine control unit determines if the estimated NOx is above a second threshold level. If the estimated NOx is not above a second threshold level, the method follows line928to block914where the ion sensor signal is acquired again and the method continues. If the estimated NOx is above the second threshold level, the method follows line923to block926. In block926, an error code is generated and/or an alert is provided to the user noting that the engine is experiencing emission problems outside of an acceptable range. The method then follows line928back to block914where the method continues.

Now referring toFIG. 10, this graph illustrates the cycle-to-cycle in-cylinder pressure measurements for an engine transient operation at different engine operating conditions. As such, the graph represents a comparison between the cylinder pressure measured using a pressure transducer and the cylinder pressure predicted by the new technique depending on the function mentioned above. Line1010represents the measured cylinder pressure while line1020represents the predicted cylinder pressure calculated by the algorithm according to the ion current signal.

Now referring toFIG. 11, this graph illustrates the cycle-to-cycle in-cylinder temperature for an engine transient operation at different engine operating conditions. As such, the graph represents a comparison between the cylinder temperature calculated from a measured cylinder pressure signal and the cylinder temperature predicted by the new technique depending on the function mentioned above. Line1110represents the calculated cylinder temperature while line1120represents the predicted cylinder temperature based on the ion current signal algorithm.