Abstract:
Presented is a device that provides a correction factor to compensate for varying fuel and air properties in an ion signal sensed in combustion chamber of reciprocating and continuous combustion engines, on a predetermined basis during the combustion of conventional petroleum-based fuels, other alternate fuels, and renewable fuels. The device uses an ion current reference sensor device and a processing module to provide a correction factor to the ion signal(s). The ion current reference sensor device is positioned near the chamber(s) of the engine and fuel provided to the chamber(s) is routed to provide a diffusion flame and the resultant ion current from the flame is measured and provided to the processing module at discrete intervals during the combustion process. Alternatively, a pre-mixed flame is used. The processing module provides a scaling factor to be applied to the ion signal and/or calibration points used to detect combustion conditions.

Description:
BACKGROUND 
     Ion signals are used in a variety of controls for various types of engines in various industries such as light and heavy duty vehicles, locomotives, off-highway equipment, marine vessels and many industrial applications. For example, ion current has been used to detect knock and misfire in lean burn engines, to detect combustion instability in continuous combustion systems, to determine NO x  emissions, to control exhaust gas recirculation, etc. 
     An ion signal varies due to many factors, including A/F (air/fuel) ratio, flame proximity, humidity, and fuel properties. For example, the important fuel properties that affect ion current (and the combustion process) include hydrogen to carbon ratio, distillation range, volatility and cetane number. Variations in the design parameters from one engine to another and in the fuel properties affect the cylinder gas temperature and pressure, mixture formation, and the distribution of the equivalence ratio in the combustion chamber, all of which affect the formation of ions. The ion signal can be thought of as a single equation with many unknowns. While many of the unknowns have a small effect on the ion signal, they can be enough to reduce the effectiveness of the controls. 
     One example of the ion signal variation is shown in  FIGS. 7   a  and  7   b . Under the same conditions, the ion signal (labeled with reference numeral  700 ) exhibits a smaller or larger “second hump” depending on the fuel type.  FIG. 7   a  shows an incipient knock event where the fuel type is pure natural gas.  FIG. 7   b  shows an incipient knock event where the fuel type is a natural gas and propane mixture with other factors remaining the same. It can be seen that the ion signal variation resulting from a different fuel type is of the same order of magnitude as an incipient knock signal. As a result, the knock detection control isn&#39;t as effective with some fuels and could lead to erroneous detections. 
     BRIEF SUMMARY 
     Described herein is, among other things, a method and apparatus to compensate for varying fuel and air properties in an operating environment that detects and uses an ion current signal that changes as a result of the variation in the fuel and air properties. The method and apparatus account for the properties of varying fuel and air without requiring a complete analysis or understanding of the components influencing the ion current signal. Additionally, the method and apparatus does not require knowledge of the exact composition of the fuel or humidity. 
     The method and apparatus receive a reference ion current signal indicating a concentration of ions in a reference combustion chamber. A determination is made of whether the reference ion current signal has changed from a prior reference ion current signal. If the reference ion current signal has changed, a scaling factor is determined and transmitted to at least one controller that receives the ion current signal. The controller scales the ion current signal by the scaling factor. Alternatively, the controller scales at least one calibration point used in the controller to determine combustion conditions. 
     The scaling factor is periodically updated by receiving the sample of the reference ion current signal periodically. The scaling factor can be linear or non-linear. For example, it can be proportional to a square of a ratio of the reference ion current signal over the prior reference ion current signal, proportional to a natural logarithm of a ratio of the reference ion current signal over the prior reference ion current signal, etc. 
     The apparatus includes means for producing the reference ion current signal, means for receiving a reference ion current signal indicating a concentration of ions in the reference combustion chamber and processing means for determining if the reference ion current signal has changed from a prior reference ion current signal, for determining a scaling factor if the reference ion current signal has changed from a prior reference ion current signal and for transmitting the scaling factor to a controller that receives the ion current signal. 
     In one embodiment, the means for producing the reference ion current signal comprises an ion sensor located near a reference burner located in the reference combustion chamber where the reference burner is adapted to burn fuel and air. The ion sensor location is at a position such that the ion sensor can detect ions from flame produced by the reference burner. 
     Additional features and advantages will be made apparent from the following detailed description of illustrative embodiments, which proceeds with reference to the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the technologies described herein, and together with the description serve to explain the principles of the technologies. In the drawings: 
         FIG. 1  is a schematic view of a representative environment in which the technologies may operate; 
         FIG. 2  is a block diagram view of an ionization module that interacts with the technologies described herein; 
         FIG. 3  is a block diagram view of an embodiment of the technologies in the environment of  FIG. 1 ; 
         FIG. 4  is a block diagram view of an embodiment of the ion reference sensor module of  FIG. 3 ; 
         FIG. 5  is a flowchart illustrating the steps of compensating for varying fuel and air properties; 
         FIG. 6  is a flowchart illustrating an alternate embodiment of the steps of compensating for varying fuel and air properties; and 
         FIGS. 7   a  and  7   b  are graphs illustrating how the ion signal and cylinder pressure vary with a different mixture of fuel. 
     
    
    
     While the techniques will be described in connection with certain embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
     The apparatus and method described herein compensates for varying fuel and air properties in an ion signal without requiring complete analysis or understanding of the components influencing the ion signal. 
     Turning to the drawings, wherein like reference numerals refer to like elements, a suitable combustion engine environment in which the apparatus may operate in is shown in  FIG. 1 . The environment  100  includes an ionization module  102 , an air/fuel module  104 , a spark module  106 , and a reciprocating engine  108 . While a reciprocating engine  108  is shown, the apparatus may be used in other environments such as, for example, continuous combustion engines such as turbine engines. While the ionization module  102 , the air/fuel module  104 , the spark module  106  are shown separately, it is recognized that the modules  102 ,  104 ,  106 , may be combined into a single module or be part of an engine controller having other inputs and outputs. The reciprocating engine includes engine cylinder  110 , a piston  112 , an intake valve  114  and an exhaust valve  116 . An intake manifold  118  is in communication with the cylinder  110  through the intake valve  114 . An exhaust manifold  120  receives exhaust gases from the cylinder  110  via the exhaust valve  116 . The intake valve  114  and exhaust valve  116  may be electronically, mechanically, hydraulically, or pneumatically controlled or controlled via a camshaft. A spark plug  122  with a spark gap  124  ignites the air/fuel mixture in cylinder  110 . Spark module  106  controls ignition timing and provides power to the spark plug  122 . 
     In one embodiment, the exhaust manifold  120  is in fluid communication with EGR valve  130 . The EGR valve  130 , controlled by EGR module  132 , provides exhaust gas to the intake manifold  118 , preferably downstream of the throttle valve  128  for EGR control of the reciprocating engine  108 . For simplicity, the recirculation path from the EGR valve  130  to the intake is designated by arrows  134 . In some systems, the exhaust gas may be further cooled by means of a cooler in the exhaust gas recirculation path. Additionally, the exhaust valve  114  can be controlled with variable timing to assist in keeping some of the exhaust gas in the cylinder  108 . The air/fuel module  104  controls fuel injector  126  and may control throttle valve  128  to deliver air and fuel, at a desired ratio, to the engine cylinder  110 . The air/fuel module  104  receives feedback from the ionization module and adjusts the air/fuel ratio. The EGR module  132  used in some applications controls the amount of exhaust gas recirculated into the intake manifold and therefore into the cylinder. 
     The ionization module contains circuitry for detecting and analyzing the ionization signal. In the illustrated embodiment, as shown in  FIG. 2 , the ionization module includes an ionization signal detection module  140 , an ionization signal analyzer  142 , and an ionization signal control module  144 . In order to detect combustion conditions, the ionization module  102  supplies power to the spark gap  124  after the air and fuel mixture is ignited and measures ion current signals from the spark gap  124  via ionization signal detection module  140 . Alternatively a conventional ionization probe or other conventional device to detect ionization may be used to measure the ionization signals. Ionization signal analyzer  142  receives the ion current signal from ionization signal detection module  140  and determines if an abnormal combustion condition exists. The ionization signal control module  144  controls ionization signal analyzer  142  and ionization signal detection module  140 . The ionization signal control module  144  provides an indication to the air/fuel module  104 , spark module  106 , and EGR module  130  of combustion conditions. In one embodiment, the ionization module  102  sends the indication to other modules in the engine system such as an engine controller  146 . While the ionization signal detection module  140 , the ionization signal analyzer  142 , and the ionization signal control module  144  are shown separately, it is recognized that they may be combined into a single module and/or be part of an engine controller having other inputs and outputs. 
     Turning now to  FIGS. 3 and 4 , the apparatus shall be described in the reciprocating engine environment  100  described above. The apparatus may be used in other environments such as, for example, continuous combustion engines such as turbine engines and compression ignition engines. The apparatus provides an ion reference sensor module  160  that is positioned near the engine environment and receives fuel from the fuel line  162  that provides fuel to the fuel injectors  126  in reciprocating engine  108  and air from air line  164 . Alternatively, the air and fuel is pre-mixed and provided to the ion reference sensor module  160 . The ion reference sensor module  160  contains an ion sensor  166  that detects the concentration of ions produced by a flame burning at reference burner  168  in a reference combustion chamber  170  and a calibration module  172 . While  FIG. 4  shows a spark plug as an ion sensor, other types of ion sensors may be used. The flame should be as small as possible, similar to a pilot flame. In the description that follows, this flame shall be referred to as a pilot flame in describing the method. Note that the calibration module  172  may be part of ionization module  102  or part of other controllers such as an engine control unit (ECU). The reference burner  168  is mounted in the operating environment and uses the same fuel and air that is being consumed by the engine. Note that if EGR module  132  is used and the engine is operating with a high EGR rate (e.g., &gt;20%), the air sample for the reference burner should be taken after the EGR is mixed in with the intake so that the combustion uses air with the same characteristics used in the is not different than the air used in the engine combustion chamber (e.g., engine cylinder  110 ). The air/fuel ratio and quantity of gas provided to the reference combustion chamber  170  and burned by the reference burner  168  is controlled so that it is not changing. The air/fuel ratio (and quantity of gas) may be regulated opened-loop or closed-loop. The exhaust products are “dumped” upstream of any exhaust after-treatment of the engine  108  to reduce overall pollution from the engine  108 . 
     Turning now to  FIG. 5 , the reference burner  168  burns the flame consistently. The calibration module  172  periodically samples the reference ion current signal from ion sensor  166  indicating the concentration of ions in reference combustion chamber  170  (step  200 ). The ion current signal should be sampled as fast as the fuel mixture is expected to change. For example, in one embodiment the ion current signal is sampled at a 5 Hz rate for engines operating in landfill type applications while in other applications, the reference ion current signal is sampled between 10 Hz and 0.01 Hz, depending on the application. The reference ion current will increase or decrease with the composition of the fuel burned, the humidity of the air consumed, etc. 
     The calibration module  172  has processing means that determines how the reference ion current signal has changed (step  202 ). The calibration module  172  typically includes a variety of computer readable media. Computer readable media can be any available media that can be accessed by the components  102  and includes both volatile and nonvolatile media, removable and non-removable media. A scaling factor is determined based upon how the reference ion current signal has changed (step  204 ). The scaling factor is transmitted to the ionization module  102  (step  206 ). The transmission is likely to be over a network interface, such as for example, a Control Area Network (CAN) interface that is common in many engine applications. The scaling factor is a value that is used to scale ion current signals from spark gap  124  to compensate for a change in humidity, fuel property, etc. without knowledge of the change(s) and may also be used to scale calibration points used to detect abnormal engine conditions. Steps  200  to  206  are repeated during engine operation. 
     Turning now to  FIG. 6 , in an alternate embodiment, the processing means determines if the difference in the reference current ion signal is outside a predetermined threshold (step  208 ). If the difference in the reference current ion signal is not outside the predetermined threshold, the scaling factor is set to be the existing value and steps  202  and  208  are repeated. If the reference current ion signal is outside the threshold, the scaling factor is determined (step  204 ) and transmitted to the ionization module  102  (step  206 ). Steps  200 ,  204 ,  206 , and  208  are repeated, 
     The scaling factor can be linear or non-linear. For example, the scaling factor could be the ratio of the most recent reference ion current signal to the previous reference ion current signal, the square of the ratio of the most recent reference ion current signal to the previous reference ion current signal, the natural log of the ratio of the most recent reference ion current signal to the previous reference ion current signal, etc. 
     From the foregoing, it can be seen that the apparatus and method allows a direct correction of the ion current signal via the scaling factor because it is measured in the same manner as the in-cylinder/combustor ion current signals. The scaling factor accounts for all of the properties of varying fuel and air without requiring complete analysis or understanding of the components influencing the ion current signal. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the technologies (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventor for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventor intends for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.