Abstract:
A method for determining fuel dilution of diesel engine lubricating oil in a diesel engine. A first table contains a soot compensation factor, respectively, for each weight of oil selected among a predetermined range of oil weights. A second table contains fuel dilution levels for a plurality of predetermined compensated viscosity ratios. After determining the weight of the oil in the engine a first viscosity of the oil at a first temperature and a second viscosity of the oil at a second temperature are measured. Next, either a ratio or a difference of the first and second viscosities is determined. Using the ratio, soot in the oil is compensated using a soot compensation factor of the first table which is respective of the oil to thereby provide a compensated viscosity ratio. Finally, the compensated viscosity ratio is compared with the second table to thereby determine the fuel dilution level.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to detecting diesel engine lubricating oil contamination and, more particularly, to a method of detecting diesel fuel dilution levels of diesel engine lubricating oil used in diesel engines.  
       BACKGROUND OF THE INVENTION  
       [0002]     Many design modifications have been applied to diesel engines, hereinafter referred to as engines, for the purpose of reducing the emission levels and improving fuel efficiency. One possible way to reduce the NO x  in the exhaust gas is to post-inject a small amount of diesel fuel, hereinafter referred to simply as “fuel”, into the cylinder, called post-injection. Because diesel fuel is very fluid, under several malfunction conditions of the diesel engine, hereinafter referred to simply as an “engine”, for example imperfect combustion and piston ring blow-by, the fuel can pass through the piston seals and get into the engine lubricating oil, hereinafter referred to simply as “oil”, thereby contaminating the oil, herein referred to as “fuel contaminated oil”.  
         [0003]     The process of fuel (diesel fuel) mixing with the oil (engine lubricating oil) resulting in fuel contaminated oil is herein referred to as “fuel dilution”. The amount of fuel dilution, or the fuel dilution level, may be expressed as a percent defined as the fraction of the amount of fuel, by volume or weight, preferably, by volume, with respect to the total amount of the fuel contaminated oil, by volume or weight, preferably by volume. For example, a fuel dilution of 5%, or a fuel dilution level of 5%, of 1000 ml of a fuel contaminated oil consists of 50 ml of fuel and 950 ml of oil. After the fuel contaminates the oil, the fuel contaminated oil&#39;s viscosity is lowered compared to the oil&#39;s (non-fuel contaminated) viscosity at a given temperature. At a given fuel dilution level, for example 7% to 10%, the fuel contaminated oil starts to lose its lubricating qualities, especially at high temperature, about 100 degrees C. or greater, whereupon engine parts can become stressed enough to result in untoward consequences, as for example the bearings failing. Post-injection thus requires a method to measure the fuel dilution level in order to alert the driver to change the oil to avoid engine failure.  
         [0004]     Accordingly, what is needed in the art is a method to determine the diesel fuel dilution level in order to alert the driver to change the oil to avoid engine failure.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention is a method to measure the diesel fuel dilution level of fuel contaminated diesel engine lubricating oil utilizing viscosity information in conjunction with engine lubricating oil soot contamination information.  
         [0006]     Most current oils are multi-weighted. Above, approximately, 100 degrees C. viscosity modifiers in multi-weighted oils become active. The present invention utilizes temperatures at or below, approximately, 100 degrees C. such that viscosity modifiers in multi-weighted oils do not become active.  
         [0007]     It is known in the art that viscosity changes with temperature in a predetermined temperature range, for example from 60 degrees C. to 100 degrees C., are different for different weights of oil. The reason for this is that the temperature dependence of the viscosity of a fluid, such as oil, follows an activated behavior (an Arrhenius plot) with an activation energy that is a fixed fraction of the heat of vaporization (W. J. Moore, Physical Chemistry, Addison-Wesley, 1964) which in turn is a function of the molecular weight of the fluid. Thus, a very different temperature dependence of viscosity between fuel and oil is also expected. After fuel is added into oil, the viscosity of the fuel contaminated oil drops, but since the viscosity of the fuel contaminated oil is also a function of the weight of the oil, a measurement of the viscosity of the fuel contaminated oil alone cannot be used as an indicator of fuel dilution levels. Furthermore, viscosity changes by fuel dilution are smaller at higher temperatures and larger at lower temperatures. For example, at 60 degrees C. pure, fresh 15W40 oil having a viscosity of 47 cst drops to a viscosity of 38 cst with a fuel dilution level of 5%, whereas at 100 degrees C. pure, fresh 15W40 oil having a viscosity of 14.7 cst drops to 12.6 cst 38 cst with a fuel dilution level of 5%. Thus, viscosity measurements are less sensitive to fuel dilution levels as the temperature is increased.  
         [0008]     There is an additional issue specific to the oil: the diesel combustion process generates soot that can get into the oil, thereby producing a soot contaminated oil. The soot contaminated oil&#39;s viscosity is increased compared to the oil&#39;s (non-soot contaminated) viscosity at a given temperature. The amount of soot contamination, or soot concentration, can be expressed as a percentage in an analogous manner as previously described for fuel dilution. The impact of increased soot concentration on the viscosity of the oil is similar of that of fuel dilution, but in the opposite direction. In general, the oil can be simultaneously contaminated with fuel and soot, herein referred to as “fuel-soot oil”. Thus, a measurement of viscosity of fuel-soot oil alone can give a false sense of security: the fuel-soot oil can display no variation in viscosity while having lost its lubricating quality if soot and fuel are simultaneously present. This could conceivably be addressed by looking at the fuel-soot oil viscosity&#39;s temperature dependence, but experimentation shows that fuel dilution reduces the viscosity ratio (lower temperature viscosity/higher temperature viscosity) of fuel contaminated oil or fuel-soot oil while soot increases the viscosity ratio of soot contaminated oil or fuel-soot oil.  
         [0009]     One method to determine oil viscosity is given in U.S. Pat. No. 6,810,717 B2, issued on Nov. 2, 2004, and assigned to the assignee hereof, the entire disclosure of which is hereby incorporated herein by reference. One method to determine soot content in diesel engine oil is given in United States Patent Application Publication No. US 2004/0036487 A1, assigned to the assignee hereof, the entire disclosure of which is hereby incorporated herein by reference.  
         [0010]     In a first preferred embodiment of the present invention, the fuel dilution level is determined through a soot compensated viscosity ratio for a given weight of oil.  
         [0011]     It is well known in the art, theoretically and empirically, that with fresh, clean oil in the engine, the ratio of viscosity at a first temperature to the viscosity at a second temperature, wherein the first temperature is, preferably, lower than the second temperature, for example, a first temperature of 60 degrees C. and a second temperature of 100 degrees C., uniquely determines the weight of the oil. Alternatively, by definition, the weight of the oil is the viscosity at a predetermined temperature, for example 40 degrees C., and can be determined, therefore, by measuring the viscosity at the predetermined temperature. To be described later, a unique soot compensation factor can be empirically determined for a given weight of oil, whereby different weights of oil have different unique soot compensation factors independent of fuel dilution levels, which are then stored in a first look-up table. The unique soot compensation factor for a given weight of oil is used to produce a compensated viscosity ratio from the measurements of the viscosity at the first and second temperatures, whereby the fuel dilution level can be ascertained from a second look-up table containing fuel dilution levels for various compensated viscosity ratios which are unique for the given weight of oil, wherein different weights of oil have unique entries of fuel dilution levels for various compensated viscosity ratios for each weight of oil stored in the second look-up table.  
         [0012]     In a second preferred embodiment of the present invention, the fuel dilution level is determined through a soot compensated viscosity difference for a given weight of oil.  
         [0013]     By definition, the weight of the oil is the viscosity at a predetermined temperature, for example 40 degrees C., and can be determined, therefore, by measuring the viscosity at the predetermined temperature. To be described later, a unique soot compensation factor can be empirically determined for a given weight of oil, whereby different weights of oil have different unique soot compensation factors independent of fuel dilution levels which are then stored in a third look-up table. The unique soot compensation factor for a given weight of oil is used to produce a compensated viscosity difference from the measurements of the viscosity at the first and second temperatures, whereby the fuel dilution level can be ascertained from a fourth look-up table containing fuel dilution levels for various compensated viscosity differences which are unique for the given weight of oil, wherein different weights of oil have unique entries of fuel dilution levels for various compensated viscosity differences for each weight of oil stored in the fourth look-up table.  
         [0014]     Many variations in the embodiments of present invention are contemplated as described hereinbelow in more detail. Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0015]     The description herein makes reference to the accompanying drawings, wherein like reference numerals refer to like parts throughout the several views.  
         [0016]      FIG. 1  is a graph of plots of viscosity ratios versus soot percentages for various fuel dilution levels.  
         [0017]      FIG. 2  is a graph of plots of soot compensated viscosity ratios versus soot percentages for various fuel dilution levels.  
         [0018]      FIG. 3  is a graph of plots of fuel dilution levels versus average soot compensated viscosity ratios.  
         [0019]      FIG. 4  is a graph of plots of calculated fuel dilution levels versus actual fuel dilution levels.  
         [0020]      FIG. 5  is a graph of plots of viscosity differences versus actual fuel dilution levels for various soot percentages.  
         [0021]      FIG. 6  is a graph of plots of ratios of viscosity differences versus actual fuel dilution levels for various soot percentages.  
         [0022]      FIG. 7  is a graph of plots of soot compensated viscosity differences versus actual fuel dilution levels for various soot percentages.  
         [0023]      FIG. 8  is a graph of plots of calculated fuel dilution levels versus actual fuel dilution levels. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]     By example, 15W40 oil is used in the plots of  FIGS. 1 through 9 .  FIGS. 1 through 4  pertain to the first preferred embodiment of the present invention, wherein fuel dilution level is determined through a soot compensated viscosity ratio for a given weight of oil.  FIGS. 5 through 8  pertain to the second preferred embodiment of the present invention, wherein fuel dilution level is determined through a soot compensated viscosity difference for a given weight of oil.  
         [0025]     Referring firstly to the first preferred embodiment of the present invention,  FIG. 1  is a graph  100  of plot curves  102  through  112  of viscosity ratios versus soot percentages for various fuel dilution levels wherein each curve corresponds to a particular fuel dilution level and each viscosity ratio is the ratio of the viscosity at 60 degrees C. to the viscosity at 100 degrees C. at a particular soot percentage and a particular fuel dilution level. Curve  102  corresponds to a fuel dilution level of 0% (ie., zero percent). Curve  104  corresponds to a fuel dilution level of 1%. Curve  106  corresponds to a fuel dilution level of 2%. Curve  108  corresponds to a fuel dilution level of 3%. Curve  110  corresponds to a fuel dilution level of 4%. Curve  112  corresponds to a fuel dilution level of 5%. The curves  102  through  112  show that soot contamination (soot %) has the same effect on viscosity ratios independent of the fuel dilution level since the slopes of the curves are almost the same. Therefore, the viscosity ratios can be compensated for the error introduced by soot contamination by using the soot percent (ie., soot %) level to do the compensation.  
         [0026]      FIG. 2  is a graph  200  of curves  102 ′ through  112 ′ of soot compensated viscosity ratios (compensated viscosity ratios). In this regard, each curve  102 ′ through  112 ′ corresponds to a respective curve  102  through  112  of  FIG. 1 , as identified by priming, wherein: curve  102 ′ corresponds to a fuel dilution level of 0%; curve  104 ′ corresponds to a fuel dilution level of 1%; curve  106 ′ corresponds to a fuel dilution level of 2%; curve  108 ′ corresponds to a fuel dilution level of 3%; curve  110 ′ corresponds to a fuel dilution level of 4%; and curve  112 ′ corresponds to a fuel dilution level of 5%. Each viscosity ratio of  FIG. 1  may be soot compensated to yield a soot compensated viscosity ratio of  FIG. 2  by subtracting the product of the average slope of the curves  102  through  112  and the soot percent at that viscosity ratio from the viscosity ratio.  
         [0027]     For example, the average slope of the curves  102  through  112  of  FIG. 1  is, numerically, approximately 0.012, which is the soot compensation factor. Point  114  of  FIG. 1  has a viscosity ratio of, approximately, 3.095 at 4% soot and a fuel dilution level of 4%. The product of 0.012 (ie., the soot compensation factor) times 4 (ie., the soot percent) is 0.048 (ie., a compensation value). Subtracting 0.048 (ie., the compensation value) from 3.095 (ie., the viscosity ratio) yields 3.047, which is the soot compensated viscosity ratio at the point  114 ′ of  FIG. 2  and which corresponds to the viscosity ratio at the point  114  of  FIG. 1 .  
         [0028]     The average slope of the curves  102  through  112  is the soot compensation factor for the given weight of oil (15W40). It can be seen in  FIG. 2  that the soot compensated viscosity ratios have, approximately, the same value for all soot percent at a given fuel dilution level wherein the fuel dilution levels of curves  102 ′ through  112 ′ correspond to the fuel dilution levels of curves  102  through  112 , respectively, of  FIG. 1 .  
         [0029]      FIG. 3  is a graph  300  of fuel dilution levels versus average soot compensated viscosity ratios (average compensated viscosity ratios) of  FIG. 2  for each particular fuel dilution level of  FIG. 2 . Each point  302  through  312  is obtained from  FIG. 2  by dividing the sum of the soot compensated viscosity ratios by the number of soot compensated viscosity ratios for a given fuel dilution level. For example, point  310 , having a fuel dilution of 1% at a soot compensated viscosity ratio of, approximately, 3.163 is obtained by summing the soot compensated viscosity ratios  220  through  230  of  FIG. 2  and dividing by 6, the number of soot compensated viscosity ratios  220  through  230  for a fuel dilution level of 1%. The straight line  314  is the best fit through the points  302  through  312 .  
         [0030]     In the example of  FIG. 3 , the equation of the straight line  314  is:
 
 Y=− 26.78 X+ 85.84  (1)
 
 where Y is the fuel dilution level in percent and X is the average soot compensated viscosity ratio. 
 
         [0031]      FIG. 4  is a graph of plots of calculated fuel dilution levels  402  through  412  using equation (1) versus actual fuel dilution levels. The dotted straight line  414  represents the best fit through the points  402  through  412 .  
         [0032]     The average slope of the curves  102  through  112 , the soot compensation factor, and the best fit straight line  414 , equation (1), are unique for the given weight of oil 15W40 in the example of the depicted figures. Each different weight of oil will have a unique soot compensation factor and unique best fit straight line. This is due to the dependence of the activation energy characterizing the temperature dependence of different fluids on their molecular weight, as previously described. For each different weight of oil of interest, the soot compensation factors and best fit straight lines can be empirically determined and stored, as for example in a vehicle sensor memory or in a vehicle microprocessor memory, in first and second look-up tables, respectively.  
         [0033]     The first preferred embodiment of the present invention may be implemented as follows.  
         [0034]     With fresh, clean oil in the engine, a viscosity measurement is made at a predetermined temperature, which measurement is indicative of the weight of the oil. Alternatively, a first ratio of the viscosity (first viscosity ratio) measured at 60 degrees C. and at 100 degrees C. is determined, whereby the viscosity ratio uniquely determines the weight of the oil. For example, point  116  of  FIG. 1  having a viscosity ratio, numerically, of, approximately, 3.2 determines that the weight of oil is 15W. This determines the correct entries in the first and second look-up tables yielding, in this case, a soot compensation factor of, for example, 0.012 from the first look-up table and the best fit line, equation (1), from the second look-up table. At a later time, the soot contamination level (ie., soot percent, or soot %) is measured and a second ratio of the viscosity (second viscosity ratio) measured at 60 degrees C. and at 100 degrees C. is determined. The second viscosity ratio and soot compensation factor determine a soot compensated viscosity ratio. For example, point  114  having a viscosity ratio, numerically, of, approximately, 3.095, has a soot compensated viscosity ratio, numerically, of, approximately, 3.047 at point  114 ′, as previously described. From equation (1) the soot compensated viscosity ratio yields the fuel dilution level in percent. For example, the soot compensated viscosity ratio of, approximately, 3.047 at point  114 ′ yields a fuel dilution level of 4% using equation (1) corresponding to the actual fuel dilution level in percent of point  114  in  FIG. 1 . Subsequent fuel dilution levels are obtained in a similar manner.  
         [0035]     Referring now to the second preferred embodiment of the present invention,  FIG. 5  is a plot  500  of viscosity differences versus fuel dilution levels in percent for various soot percents, wherein each viscosity difference is the difference between the viscosity at 60 degrees C. and the viscosity at 80 degrees C. at a particular soot percent and a particular fuel dilution level. Viscosity differences  502  correspond to a soot contamination of 5%. Viscosity differences  504  correspond to a soot contamination of 4%. Viscosity differences  506  correspond to a soot contamination of 3%. Viscosity differences  508  correspond to a soot contamination of 2%. Viscosity differences  510  correspond to a soot contamination of 1%. Viscosity differences  512  correspond to a soot contamination of 0%.  
         [0036]      FIG. 6  is a graph  600  of ratios of viscosity differences versus fuel dilution levels for various soot percents, wherein the ratios of viscosity differences are the ratios of the viscosity differences  502  through  512  of  FIG. 5  at a given fuel dilution level to the viscosity difference at 0% soot at the same given fuel dilution level of  FIG. 5 .  FIG. 6  shows that each of the ratios of the viscosity differences  602  through  612  are almost constant for same level of soot contamination (soot percent, or soot %) independent of the fuel dilution level. Therefore, the ratios of the viscosity differences  502  through  512  of  FIG. 5  can be compensated for the error introduced by soot contamination by using the soot percent to do the compensation.  
         [0037]     A graph  700  of the soot compensated viscosity differences  702  through  712  of the viscosity differences  502  through  512  of  FIG. 5  are shown in  FIG. 7 . Each of the viscosity differences  502  through  512  of  FIG. 5  may be soot compensated to yield soot compensated viscosity differences  702  through  712  by dividing the viscosity difference  502  through  512  at a given soot contamination level (ie., soot percent, or soot %) by the average ratio of the viscosity difference at the same given soot contamination level. For example, the average ratio of the viscosity difference at 5% soot is, approximately, 1.30, numerically, from  FIG. 6 . Point  514  of  FIG. 5  has a viscosity difference of, approximately, 27, numerically, at 5% soot and a fuel dilution level of 2%. The ratio of 27/1.30 is 20.8 which is the soot compensated viscosity difference at point  714  of  FIG. 7 , corresponding to the viscosity difference of 27 at the point  514  of  FIG. 5 . The average of the ratios of the viscosity differences  602  through  612  at a given soot contamination level (ie., soot percent, or soot %) is the soot compensation factor for the given weight of oil for the given soot contamination level. For example, the average of the ratios of the viscosity differences  602 , approximately 1.30, numerically, is the soot compensation factor for 5% soot for the given weight of oil, 15W40 in this case, whereas the average of the ratios of the viscosity differences  604 , approximately 1.20, numerically, is the soot compensation factor for 4% soot for the given weight of oil, 15W40 in this case.  
         [0038]     In the example of  FIG. 7 , the equation of the straight line  722  is:
 
 A=− 1.0109 B+ 22.688  (2)
 
 where A is the fuel dilution level in percent and B is the average soot compensated viscosity difference for a given soot contamination. 
 
         [0039]      FIG. 8  is a graph  800  of calculated fuel dilution levels  802  through  812  using equation (2) versus actual fuel dilution levels. The straight line  814  represents the best fit through the points  802  through  812 .  
         [0040]     The average of the ratios of the viscosity differences  602  through  612  for a given soot contamination level (ie., soot percent, or soot %), the soot compensation factor, and the best fit straight line  722 , equation (2), are unique for the given weight of oil 15W40 in the example of the depicted figures. Each different weight of oil will have a unique soot compensation factor for a given soot contamination level and unique best fit straight line. This is due to the dependence of the activation energy characterizing the temperature dependence of different fluids on their molecular weight, as previously described. For each different weight of oil of interest, the soot compensation factors for each given soot contamination level and best fit straight lines can be empirically determined and stored, for example in a vehicle sensor memory or a vehicle microprocessor memory, in third and fourth look-up tables, respectively.  
         [0041]     The second preferred embodiment of the present invention may be implemented as follows.  
         [0042]     With fresh, clean oil in the engine, a viscosity measurement is made at a predetermined temperature, which measurement is indicative of the weight of the oil. Alternatively, a first ratio of the viscosity (first viscosity ratio) measured at 60 degrees C. and at 100 degrees C. is determined, whereby the viscosity ratio uniquely determines the weight of the oil. This determines the correct entries in the third and fourth look-up tables.  
         [0043]     At a later time, the soot contamination level (ie., soot percent, or soot %) is measured and a difference of the viscosity (second viscosity difference) measured at 60 degrees C. and at 80 degrees C. is determined. The soot contamination level determines the soot compensation factor for the given weight of oil, 15W40 in this case, from the third look-up table. For example, point  518  of  FIG. 5  having a viscosity difference, numerically, of, approximately, 25.5, has a soot compensation factor, of, approximately, 1.30, numerically, from  FIG. 6 , as previously described, and produces a soot compensated viscosity difference of, approximately, 19.6, numerically at point  718  of  FIG. 7 . Equation (2), in the fourth look-up table, using the soot compensated viscosity difference yields the fuel dilution level in percent. For example, the soot compensated viscosity difference of, approximately, 19.6, numerically, at point  718  yields a fuel dilution level of 3% using equation (2) corresponding to the actual fuel dilution level in percent of point  518  in  FIG. 5 . Subsequent fuel dilution levels are obtained in a similar manner.  
         [0044]     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.