Abstract:
An on-board vapor reclamation system and method includes an air inlet into an on-board diesel fuel tank and a fuel vapor/air mixture outlet from the fuel tank. A pump or a suction fan is operable to drive air from the air inlet through the tank and a fuel vapor/air mixture out the fuel vapor/air mixture outlet at a flow rate which maintains a fuel vapor concentration in the tank to less than a predetermined value corresponding to the lower explosive limit to reduce fire and explosive hazards and to reduce harmful emissions. A condenser subsystem is fluidly connected to the fuel vapor/air mixture tank outlet and is configured to condense fuel vapor in the fuel vapor/air mixture delivered to the condenser subsystem at the required flow rate. Condensed fuel vapor from the condenser subsystem is returned to the fuel tank to save fuel and increase mileage.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of and priority to U.S. Provisional Application Ser. No. 61/520,580 filed Jun. 9, 2011 under 35 U.S.C. §§119, 120, 363, 365, and 37 C.F.R. §1.55 and §1.78, which is incorporated herein by this reference. 
     
    
     GOVERNMENT RIGHTS 
       [0002]    This invention was made with U.S. Government support under Contract No. DTF53-07-D-0003 awarded by Federal Railroad Administration. The Government may have certain rights in the invention. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The invention relates, in one embodiment, to diesel vapor reclamation in locomotive fuel tanks. 
       BACKGROUND OF THE INVENTION 
       [0004]    It is known that diesel vapor emissions at locomotive refueling stations is problematic. In addition, the inventors hereof discovered that en route the diesel fuel temperature in the locomotive diesel fuel tank can reach temperatures higher than 100° F. This is due to the fact that the fuel pump delivers fuel to the engine manifold at a certain rate but, at any engine RPM, unused fuel, now heated in the engine manifold, is returned to the fuel tank. Warm ambient temperatures and heat transfer from engine components can also heat the fuel producing additional fuel vapor. 
         [0005]    The result is that the fuel vapor in the fuel tank can also exceed 100° F. Even at concentrations of fuel vapor as low as 3000 ppm in air, fuel vapor can reach or exceed the diesel fuel lower explosive limit (LEL). In the case of a puncture to the fuel tank due to a collision or derailment, combustible fuel vapor can escape the tank and cause a fire or explosive hazard with flash-back into the tank. 
         [0006]    Traditional vapor recovery systems used at automobile gas stations and the like are not well suited for use on board a diesel locomotive. Still, U.S. Pat. Nos. 5,367,882; 6,786,700; 6,616,418; 5,220,799; 7,270,155; 6,834,686 are incorporated herein by this reference. 
         [0007]    Unless otherwise stated above, however, the subject matter of this background section is not admitted prior art and instead is provided only to explain the context of the novel invention described herein. 
       SUMMARY OF THE INVENTION 
       [0008]    In one aspect, the subject invention features an on board locomotive reclamation system which maintains a low fuel vapor concentration in the diesel locomotive fuel tank to prevent fire and explosive hazards and to provide fuel vapor recovery to lessen environmental pollution and to improve fuel economy. Even if only 0.1% of the fuel is recovered, the fuel cost savings could potentially exceed millions of dollars per year. 
         [0009]    Featured is an on-board vapor reclamation system comprising an air inlet into an on-board diesel fuel tank, a fuel vapor/air mixture outlet from the fuel tank, and a pump or a suction fan operable to drive air from the air inlet through the tank and a fuel vapor/air mixture out the fuel vapor/air mixture outlet at a flow rate which maintains a fuel vapor concentration in the tank to less than a predetermined value below the explosive limit to prevent explosions and fires and to reduce emissions. A condenser subsystem is fluidly connected to the fuel vapor/air mixture tank outlet and is configured to condense fuel vapor in the fuel vapor/air mixture delivered to the condenser subsystem at the required flow rate. A return line delivers condensed fuel vapor from the condenser subsystem to the fuel tank to reduce fuel loss and to increase mileage. 
         [0010]    In one version, the pump is disposed between the fuel tank fuel vapor/air mixture outlet and the condenser unit. Alternatively, a suction fan is attached to the exit end of the condenser. Preferably, the pump and condenser subsystem are disposed on or over the fuel tank. 
         [0011]    A data acquisition module including one or more sensors may be included. One typical sensor is a fuel vapor sensor. 
         [0012]    In one design, the condenser subsystem includes an inlet duct connected to the fuel vapor/air mixture outlet, a heat exchanger, and an outlet duct connected to the return line. The inlet duct has diverging walls and the outlet duct has converging walls. A chiller delivers a coolant fluid to the heat exchanger and receives warmed fluid from the heat exchanger. Further included is an outlet from the condenser to atmosphere for air in the vapor/air mixture. In this way, the predetermined vapor concentration value in the tank is maintained at less than 3000 ppm. 
         [0013]    Also featured is an on-board vapor reclamation method comprising urging air into an on-board diesel fuel tank and driving a fuel vapor/air mixture out of the fuel tank at a flow rate which maintains a fuel vapor concentration in the tank to less than a predetermined value corresponding to the lower explosive limit. The fuel vapor in the fuel vapor/air mixture is condensed and liquid fuel is returned to the fuel tank. Urging air into the on-board diesel fuel tank preferably includes pumping or sucking the air/fuel vapor mixture out of the tank and providing an air inlet into the tank. 
         [0014]    Also featured is a locomotive comprising a diesel fuel tank, an air inlet into the diesel fuel tank, and a fuel vapor/air mixture tank outlet. A pump proximate the diesel fuel tank is operable to drive air from the air inlet through the tank and the fuel vapor/air mixture out the fuel vapor/air mixture outlet at a flow rate which maintains the fuel vapor concentration in the tank to a less than a predetermined value corresponding to the lower explosive limit. A condenser subsystem is proximate the diesel fuel tank and fluidly connected to the fuel vapor/air mixture tank outlet and configured to condense fuel vapor in the fuel vapor/air mixture delivered to the condenser at the required flow rate. A return line returns liquid fuel from the condenser subsystem to the diesel fuel tank. 
         [0015]    The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0016]    Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: 
           [0017]      FIG. 1  is a block diagram showing the primary components associated with one example of an onboard locomotive vapor reclamation system in accordance with the invention; 
           [0018]      FIG. 2  is a diagram showing the primary components associated with the condenser subsystem depicted in  FIG. 1 ; 
           [0019]      FIG. 3A  is a schematic three dimensional view of a preferred vapor condenser as depicted in  FIG. 2 ; 
           [0020]      FIG. 3B  is a schematic front view of the vapor condenser shown in  FIG. 3A ; 
           [0021]      FIG. 3C  is a schematic end view of the vapor condenser shown in  FIG. 3B ; 
           [0022]      FIGS. 4A-4C  are schematic views showing the vapor condenser of  FIG. 3  in place over a locomotive fuel tank; and 
           [0023]      FIGS. 5A-5B  are schematic three dimensional views showing a locomotive diesel fuel tank and various components of an example of the onboard vapor reclamation system of the subject invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer. 
         [0025]      FIG. 1  shows locomotive fuel tank  10  and fuel pump  12  delivering liquid diesel fuel to engine manifold  14 . Fuel which is not used depending on the engine RPM is returned to fuel tank  10  on one or more lines  16 . This fuel is heated by the hot fuel injectors and the engine manifold, however, and by other engine components raising the temperature of the fuel in the fuel tank to temperatures higher than 100° F. producing fuel vapor in tank  10  also at high temperatures. 
         [0026]    Presently, no known locomotive fuel reclamation systems have been designed or employed. The result is environmental pollution especially at locomotive refueling stations, high temperature fuel vapor which can cause fires and/or explosions, and a missed opportunity to reclaim liquid fuel from the fuel vapor to improve efficiency and mileage. 
         [0027]    In one example, the invention features a pump  20  (which may be a suction pump or a fan, blower, or the like) having a capacity sufficient to drive air from the air inlet  22 , through the fuel tank  10 , and out of the tank at outlet  24  at a flow rate which maintains the fuel vapor concentration in the tank to approximately 1500 ppm or less which is typically lower than 50% of the lower explosive limit (LEL). 
         [0028]    In one example of a laboratory test on a scaled tank, with an air flow rate of 2.5 cubic feet pre minute (cfm) through the tank, the fuel vapor concentration in air within the tank vapor space was reduced to less than 45 percent LEL. For a full scale locomotive fuel tank, the fuel vapor suction pump or fan capacity can be selected in order to maintain the fuel vapor concentration well below the LEL of diesel fuel used that precludes formation of hazardous vapor condition within the fuel tank. Vapor concentrations less than about 3000 ppm may be acceptable. 
         [0029]    Here pump  20  is located at the exit end of condenser  40  to draw the air and fuel vapor mixture out of tank  10  which urges air into the tank via inlet  22 . The air and vapor mixture is delivered to condenser subsystem  24  which outputs air at  26  and produces, from the fuel vapor, liquid fuel delivered back to diesel fuel tank  10  on return line  28 . 
         [0030]    Condenser unit  24  is configured to condense all or most of the fuel vapor at the flow rate of the air/fuel vapor mixture delivered to the condenser by pump  20  which, as noted above, has a capacity sufficient to maintain a low fuel vapor concentration in the fuel tank. The result is fuel savings and less environmental pollution especially at refueling stations where it is expected there will be very little fuel vapor in tank  10 . 
         [0031]    Data acquisition module  30  may be included along with an optional controller. In one example, data acquisition module  30  is linked to one or more sensors such as vapor sensor as shown at  32  or a thermocouple for measuring fuel or fuel vapor temperature. The controller (e.g., a microprocessor or microcontroller) may be programmed or otherwise configured to control pump  20  and/or condenser subsystem  24  based on the vapor concentration in tank  10 . 
         [0032]    One preferred condenser subsystem  24 ,  FIG. 2  includes vapor condenser  40  with inlet duct  42  having diverging walls, heat exchanger  44 , and outlet duct  46  with converging walls. Chiller unit  50  delivers a cooled refrigerant or coolant fluid to heat exchanger  44  in a closed loop and receives the warmer refrigerant or coolant fluid from the heat exchanger as shown. 
         [0033]    For the reclamation capacity required in the laboratory test on scaled tank, this heat exchanger  44  was 5.12 inches thick, 29.53 inches wide, and 28.75 inches tall. Inlet duct  42  was 16.31 inches long and outlet duct  46  was 19.12 inches wide. 
         [0034]    As shown in  FIGS. 4-5 , the low profile onboard reclamation system is typically disposed on or over fuel tank  10  (e.g., between the tank and the catwalk above it). The fuel vapor outlet pipe from the tank is connected to the vapor condenser  40 ,  FIG. 4A  and a suction pump or fan  20  is fitted at the exit end of the condenser. The ambient air inlet pipe  22   a ,  FIG. 4B  has an opening at the opposite side of the tank to prevent fuel outflow in the event of the locomotive rollover. The condenser  40  is cooled down by the circulating coolant from the chiller unit  50  that condenses the diesel vapor present in the mixture of diesel vapor and air into liquid fuel and this is returned back to the tank  10 . 
         [0035]    During monitoring of an actual locomotive fuel tank in service, it was determined that the fuel reached temperatures of 50° F. above ambient. In a test bed, the reclaimed fuel was nearly identical to the No. 2 diesel fuel employed in the tank. In particular, the heat flow rate per unit mass between the reclaimed fuel and the original fuel was almost identical. Analyzing the reclaimed fuel using gas chromatography-mass spectrometry revealed that almost all the component hydrocarbon constituents of the original diesel fuel were present in the reclaimed fuel. 
         [0036]    The typical locomotive fuel tank and the scaled down test tank have complex internal baffle arrangements which would generate turbulent flow of fuel vapor and air in the vapor space when ambient air is inlet through a vent pipe and the vapor mixture is sucked out for condensation at the opposite end. The main objective of the experimental analysis was to simulate the distribution of fuel vapor concentration within the vapor space, vapor temperature variation and the flow characteristics of the mixture of fuel vapor and air at a given fuel temperature and inlet air flow rate. In order to model the mass transfer between the fuel and air inside the test tank, a reaction equilibrium state between the diesel fuel and air was assumed to exist on the liquid fuel surface. The vapor pressure in the air just above the liquid surface is equal to the saturation pressure of the fuel corresponding to the fuel surface temperature. A surface vaporization reaction was defined through diffusion process. The vapor generation rate is a function of the molar concentration gradient of fuel vapor in a thin boundary layer near the liquid fuel surface. A relation between the equilibrium vapor pressure (in PSIA) and the inverse of temperature, expressed in degrees Rankine (° R) for diesel fuel was determined. 
         [0037]    A robust software package which has been widely applied to computational fluid dynamics (CFD) was used. It can efficiently deal with the fluid dynamics, heat and mass transfer, and multi-phase flow. 
         [0038]    The ambient air temperature is assumed to be 50° F., which was the laboratory temperature during the laboratory scale test. Through the inlet to the test tank, dry air with no fuel content was introduced at a rate of 150 ft 3 /hour (4.25 m 3 /hr). The air flow velocity at the inlet was 11.2 ft/sec (3.42 m/sec). A mixture of air and fuel vapor was driven out of the tank at the opposite end through the outlet pipe. The ambient pressure was assumed one atmospheric pressure. For simplicity, the liquid fuel surface temperature was assumed to be maintained at 120° F. due to controlled continuous heating. The measured temperature variation of the fuel within the tank varied by about 1 to 2° F. Material properties for diesel fuel, fuel vapor, air and the mixture were used from a standard material database. The diffusion coefficient of No. 2 diesel vapor was 6.2193×10 −6  m 2 /sec. 
         [0039]    The results of simulations show that the flow of the mixture of fuel vapor and air within the tank is somewhat turbulent due to the staggered positioning of the baffle plates that also project above the liquid fuel surface, thus creating partially obstructed flow path within the tank. The flow velocity is rather low (about 0.8 ft/sec or 0.25 m/sec) in the vapor space, but it increases to 11.7 ft/sec (3.5 msec) while exiting through the outlet pipe because of the small diameter of the pipe used in the test tank. Due to the relatively cold air entry, the air-inlet end temperature is found to be at 299° K (78.8° F.) and the outlet end mixture temperature is seen to reach 322° K (120.2° F.). The fuel vapor mole fraction values vary from as low as 0.00039 at the inlet air end to as high as 0.00264 at the vapor exit end of the tank. This maximum mole fraction value corresponding to the steady fuel temperature of 120° F. is very close to the analytically predicted value of 0.00265 from the equilibrium vapor pressure data. The mole fraction or vapor volume fraction at any temperature can be estimated by expressing the vapor pressure as a fraction of the atmospheric pressure (14.7 psi). The vapor mass fraction distribution shows a variation from 0.000642 (0.0642%) at inlet air end to a maximum value of 0.0128 (1.28%) at the exit end. This steady state vapor fraction value permits estimation of maximum possible fuel vapor recovery potential from the laboratory test tank and also that of the locomotive fuel tank by suitably scaling up. 
         [0040]    The purpose of conducting a proof-of-concept laboratory test was to demonstrate the feasibility of diesel vapor reclamation. In this test, a ¼ th  scale steel tank of one half of an SD70 locomotive fuel tank was used. The tank incorporated two rows of baffles similar to the ones provided in one half of SD70 fuel tank on one side of its main longitudinal baffle. 
         [0041]    A small vapor condenser unit was developed using three radiator units offering large finned surfaces for fuel vapor cooling. All four immersion heaters of the test tank were fitted with thermostat controls for ease of regulating the fuel temperature during the test. The test tank was filled with 15 gallons of No. 2 diesel fuel which had a depth of 3.8 in inside the tank and completely covered all the immersion heating coils. 
         [0042]    At the start of the test, all four heaters were switched on and regulated to gradually heat the fuel at a steady rate of about 2° F.-3° F. per minute. The liquid fuel and vapor temperatures inside the tank were monitored at mid-point of the tank by a dual channel thermometer and the data were recorded. Simultaneously, the Fuel-vapor to Air Ratio (FAR) readings from an Infrared sensor-based gas detector were monitored and recorded by the data acquisition computer. Prior to the test, the gas detector unit was calibrated by the manufacturer using 0.6% Propane in air as the “Span Gas” and using appropriate calibration factors so as to express the No. 2 diesel vapor concentration in air in terms of its percent Lower Explosive Limit (LEL). Because of the long duration nature of the test, automatic recording of test data was performed at a slow rate of once every 10 to 20 seconds. When the fuel temperature reached about 110° F., the thermostats were adjusted to maintain an almost steady temperature of the fuel and the temperature and FAR data were recorded. With the FAR value in the tank vapor space reaching 0.3% (i.e. 50% LEL) for the No. 2 diesel fuel used in the test, the detector unit&#39;s visual “Alarm” started flashing, set-off by the preset trigger setting. At this point, after noting down the fuel and vapor temperature readings and corresponding FAR value within the tank vapor space, the coolant circulation by the chiller unit to the condenser was started and compressed air flow passing through an air-dryer unit was used at a slow rate of about 1.0 cubic feet per minute under standard atmosphere condition (scfm) to 2.5 scfm or 150 cubic feet per hour (scfh). Any variation in FAR value within the tank was recorded and vapor condensation into liquid fuel in the vapor condensation unit was noted down. By maintaining a constant airflow rate and a steady temperature of fuel, an equilibrium or nearly steady condition could be reached between vapor generation and vapor transport from the tank by the air-flow through the tank that indicated a nearly steady value of FAR (with slight fluctuations) within the tank vapor space. 
         [0043]    As a part of exploring the feasibility of greater condensation of the fuel vapor in the condenser, an attempt was made to further lower the temperature of the circulating coolant of the chiller unit below 60° F. down to 40° F. by using a mixture of Glycol and water as the circulating chilling fluid. The effectiveness of vapor condensation was assessed by measuring temperatures and drawing the mixture of fuel vapor and air near the entrance and exit points of the vapor condensation unit during the test. 
         [0044]    Another parameter that was varied for exploration purpose during the test was the air flow rate. This was varied from 1.0 scfm or 60 cubic feet per hour under standard atmospheric condition (scfh) to 2.5 scfm (150 scfh) and also briefly ran at 5.0 scfm (300 scfh). In each case the stability of FAR value within the tank vapor space and the rate of vapor condensation, judged by the condensed fuel dripping rate from the condenser unit, were noted. During later part of the test, the fuel temperature was raised from 120° F. to nearly 130° F. for a short duration. This was done with a view to assess the rate of vapor formation at still higher fuel temperature which may be part of railroad operational scenario. It is believed that the maximum fuel temperature inside fuel tank could reach as high as 125° F. to 140° F. prior to refueling of the tank in long-haul freight operations of SD70 locomotives. By noting down the condensed fuel collected in the graduated measuring flask, it was possible to evaluate an average rate of fuel vapor condensation per hour for steady values of fuel temperature at 120° F., FAR value and air flow condition within the tank. On completion of the test, acquired data from all the instruments were downloaded for further analysis. The cooled down fuel from the test tank was disposed of following the standard hazmat disposal procedure of QNA. 
         [0045]    The following is a summary of the test results. It was generally possible to maintain a nearly steady fuel temperature within the tank with thermostatic control of the heater units. Appreciable amount of diesel vapor were formed in the tank vapor space at fuel temperatures above 105° F. At around 115° F. to 120° F., the vapor concentration in air (FAR) mostly varied between 45% to 65% LEL. The effects of varying the air flow rate through the test tank on the fuel and fuel vapor temperatures were investigated. For fuel temperatures at 105° F. and 120° F., the air flow rate varied between 1 scfm (60 scfh) and 5 scfm (300 scfh). It is observed that at fuel temperature of 105° F., a higher air flow rate had resulted in considerable decrease in the vapor temperature inside the tank, which is mostly due to the low temperature (50° F.) of the inlet air. However, at fuel temperature of 120° F., and corresponding air flow rate of 2.5 scfm (150 scfh), both fuel and vapor temperatures at mid-point of tank appeared to be nearly remaining steady close to 120° F. 
         [0046]    During the laboratory test, for a nearly steady fuel temperature maintained first at 105° F. and later at close to 120° F. with inlet air flow rate of 2.5 scfm (150 scfh), the variation of fuel temperature shows that the mixture of fuel vapor and air was sufficiently cooled down to nearly 40° F. while traversing through the chilled radiator units of the condenser thereby condensing a part of the vapor into liquid fuel. The variation of Fuel-vapor to Air Ratio (FAR) expressed as percent LEL with time while the fuel temperature had remained close to 120° F. with slight fluctuations. The FAR values most of the time varied between 45% LEL to 65% LEL, which translates into 0.27 (% v/v) to 0.39 (% v/v) or diesel vapor volume fraction in air under equilibrium condition. These values are slightly different than the values computed from the vapor pressure versus temperature but close to the predicted values obtained from simulation results. 
         [0047]    During the test while the fuel temperature remained nearly 120° F., the condensed fuel collection rate was recorded at 20 milli-liter (ml) or 0.676 ounce over a period of 42 minutes. This amounted to an average vapor condensation rate of about 28.5 ml per hour or 0.964 ounce/hour. The collected condensed fuel was analyzed to assess its suitability for combustion in a locomotive diesel engine. The heat flow rate or specific heat of the fuel was analyzed along with a sample of ‘as received’ (neat) No. 2 diesel fuel employed in the test using a Differential Scanning calorimeter (DSC) instrument. The result of this analysis shows the heat flow rate per unit mass (slope of the curve up to 100° C. or 212° F.) is almost identical between the two samples analyzed. In order to verify the composition of various hydrocarbon compounds in the recovered fuel one sample each of the neat No. 2 diesel and the recovered (condensed) fuel were analyzed using Gas Chromatography-Mass Spectrometry (GC-MS). It was observed that almost all component hydrocarbon constituents are present in both samples, although the recovered fuel sample is seen to have a slightly different proportion of lighter and heavier constituents compared to those of the neat diesel sample, which is as expected due to the repeated heating and cooling cycles of the same fuel within the test tank. 
         [0048]    The reasons for lower than expected vapor condensation in the condenser unit was investigated and it is believed that the fuel vapor recovery through condensation in the condenser unit was only partial and most part of the fuel vapor got lost to the exhaust air going out of the condenser unit. This happened despite maintaining the chilling unit fluid circulation at 40° F. The primary reason for this could be due to the inadequate diffusion of inlet mixture of fuel vapor and air at entrance through a 0.825 in diameter pipe into the condenser unit at a high flow velocity of about 11 ft/sec (at 2.5 scfm air flow rate) and consequent impingement of this high velocity flow over only a small fraction of the finned radiator surface area. The characteristic smell of profuse diesel vapor in the exhaust air from the condenser unit as well as measurement of FAR value by MSA&#39;s XIR unit revealed that much of the fuel vapor did not get condensed and was lost in the exhaust air. 
         [0049]    Using the equilibrium of diesel vapor partial pressure and volume fraction in air relationship with temperature, it is possible to estimate the expected value of fuel vapor condensation per hour from the above test scenario. From the No. 2 diesel vapor equilibrium curve at fuel temperature of 120° F., the fuel vapor volume fraction in air can be computed to be 0.265% (v/v). Corresponding mass ratio of diesel vapor to air is obtained by multiplying with the ratio of molecular weight of diesel vapor to that of air. 
         [0050]    Therefore, the vapor to air mass ratio=0.265*130/29=1.19%=0.0119. The corresponding value of mass fraction predicted from the analysis is 0.0128 or 1.28%, which is slightly higher because the model uses a Molecular Weight of 140 for the Diesel fuel (corresponding to C 10 H 22 ), instead of 130 as recommended. 
         [0051]    For a nearly steady state airflow rate of 2.5 scfm, mass of air per minute=0.193375 lb/minute. This mass of air flow translates to a mass flow rate of diesel vapor=0.193375*0.0119=0.0023 lb/minute, or 0.1381 lb/hour. Assuming an ideal laboratory scale condenser unit with well-diffused vapor flow within it to have a vapor to fuel conversion efficiency of approximately 90%, the realizable diesel fuel mass per hour=0.1243 lb/hour. This would imply a condensed fuel collection rate of 66.43 ml/hour or 2.246 ounce/hour. Comparing this value with the condensed fuel collection rate of 28.5 ml/hour (0.964 ounce/hour) from the laboratory test, it represents only 43% recovery capability of the tested condenser unit under the test conditions and a loss of over 50% fuel vapor to the exhaust air/environment. 
         [0052]    In order to offer a better solution, two alternative approaches were explored, namely (a) reduction in mixture flow velocity through the condenser unit for better diffusion within the condenser unit by lowering the inlet air flow rate through the tank, and (b) design and test a new condenser unit with a higher diffusion capacity to ensure larger spread of vapor over entire radiator frontal surface and much reduced flow velocity through the condenser. 
         [0053]    The first alternative was evaluated during the laboratory test, when the air flow rate was reduced to 1 scfm. This had resulted in improper mixing of the fuel vapor (in the vapor space), which is heavier than air and therefore remained close to the fuel surface. The vapor content in the mixture exiting the tank and entering the condenser unit was found to be low which resulted in very small or no condensed fuel flow during that part of the test. 
         [0054]    The second alternative results in a steady state flow condition at 120° F. fuel temperature and 2.5 scfm (150 scfh) air flow rate which produced close to equilibrium level fuel vapor content (volume fraction) in air. In order to permit efficient condensation of most fuel vapor, a relatively larger new condenser unit design was made to be tested in the laboratory, as well as used as the prototype condenser unit for integration with a locomotive fuel system.  FIGS. 3A-3C  show this new condenser unit. 
         [0055]    For the SD70 tank, in order to maintain the same airflow velocity through the tank vapor space, the scaled up airflow rate should be 32 times larger than that of the test tank or about 80 scfm (4,800 scfh). Assuming that the fuel temperature in the tank remains between 110° F. to 120° F. for about 15 hours prior to refueling during a long-haul freight operation lasting several days, the diesel vapor mass transported to and condensed in the condenser unit may be expected to be=0.1243*80/2.5=3.977 lb/hour. This amounts to about 59.6 lb for a 15 hour period or corresponding to every refueling. The above analysis is based on the assumption that an equilibrium state of diesel vapor mass fraction is maintained within the tank for the indicated airflow rate of 80 scfm. This fuel recovery translates to about 8.4 gallons over a 15 hour period, or 0.56 gallon per hour under the above operating conditions. Assuming that corresponding to every refueling of an average 3000 gallons of diesel, it is possible to recover condensed fuel vapor equal to nearly 8.4 gallons of reusable fuel, the recovery potential is 0.28%. The collective benefit for a class I railroad operating a few hundreds or thousands of locomotives can therefore be substantial. According to the Norfolk Southern (NS) communicated fuel consumption statistics available for 2009, NS had consumed approximately 392 million gallons of diesel fuel during 2009. Assuming a possible upper bound fuel saving of 0.28% through fuel vapor recovery, this would have translated into a potential 1.1 million gallons of diesel fuel saving per year for one Class I railroad. As a lower-bound value or worst case scenario, assuming only a 50% fuel vapor recovery efficiency of the Diesel Vapor Recovery Unit (DVRU), the fuel recovery potential would be 0.14% of refueling diesel (representing consumption), and corresponding to each refueling operation, which is still a large overall fuel saving per year for combined class I railroads. 
         [0056]    For the diesel vapor recovery process, with an optimized design of vapor recovery system, it should be possible to achieve an appreciable percentage saving, since this reclamation process is dependent on the time-span of diesel vapor generation due to prolonged operation of locomotive at elevated fuel temperatures close to its flash point between refueling. 
         [0057]    Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. 
         [0058]    In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended. 
         [0059]    Other embodiments will occur to those skilled in the art and are within the following claims.