Abstract:
Apparatus and method are described for enhancing performance of an alcohol fueled engine during cold conditions, with such enhancement being particularly effected by generation of ether to assist cold operation including starting and/or to achieve reduced emissions during cold running. Dimethyl ether is generated by catalytic dehydration of vaporized methanol using a catalyst, preferably fluorinated alumina. Apparatus is disclosed for generating dimethyl ether on board as needed for immediate mixing with combustion air and methanol and/or for storage to enable later mixing of the dimethyl ether with combustion air and methanol to effect subsequent cold starts and/or cold running operations.

Description:
FIELD OF THE INVENTION 
     This invention relates to alcohol fueled engines, and relates, more particularly, to enhancing performance of methanol fueled, internal combustion engines during cold conditions. 
     BACKGROUND OF THE INVENTION 
     It has been heretofore shown that alcohol can be utilized to fuel an internal combustion engine, and it has also been heretofore shown that methanol can be produced efficiently and economically from a variety of feedstocks, including natural gas, coal and biomass. Methanol has, therefore, been widely considered as a replacement for gasoline and diesel fuel when petroleum supplies become scarce, and it has been suggested that the use of methanol to fuel vehicle engines would improve air quality by appreciably decreasing unburned hydrocarbon emissions (as compared, for example, with gasoline fueled vehicle engines). 
     The use of methanol to fuel a spark ignition (Otto cycle) internal combustion engine, however, has heretofore faced a significant cold start and/or cold running operation problem not normally found with respect to gasoline and diesel engines (although diethyl ether is now commercially offered as a cold start fluid even for such engines). 
     Now known methanol fueled vehicle engines have been found to be difficult to start at ambient temperatures below 10° C. due to the low vapor pressure and high heat of vaporization of methanol. In addition, even when a methanol fueled engine was somehow started, the associated vehicle was found to have poor driveability and/or high carbon monoxide (CO) and unburned hydrocarbon emissions were found to be emitted from the engine. 
     Various apparatus and methods have been heretofore suggested in an attempt to solve these problems, including the use of fuel and carburetor heaters to assist fuel vaporization, the use of methanol dissociation reactors to generate highly combustible gases, and the addition of volatile compounds to the methanol fuel. 
     With respect to electrical heating of an air/methanol fuel mixture to thereby allow cold starting at low temperatures, the required electrical power has been found to increase dramatically with decreasing temperatures and increasing engine load, and this has limited the useful application of electrical heating to conditions of moderate temperatures and low engine speeds and loads. 
     With respect to methanol dissociation, methanol can be dissociated according to the reaction: 
     
         CH.sub.3 OH→2 H.sub.2 +CO 
    
     with the reaction being highly endothermic and occurring in the presence of a catalyst above 250° C. The gaseous fuel produced is combustible over a wide range of temperatures and air/fuel ratios and therefore would theoretically allow cold starting to below any practical temperature. Electrically heated reformers suggested for heating the catalyst, however, have adversely affected performance of the resulting dissociation unit due to long warm-up periods required to bring the catalyst up to the reaction temperature, the large amounts of electrical power consumed, and/or the large size required for the unit. In addition, methanol dissociation catalysts are not compatible with gasoline (gasoline is usually added to methanol fuel to increase its flame luminescence for safety reasons). 
     With respect to additives, a number of additives have also been heretofore suggested and/or utilized for addition to methanol fuel to increase the vapor pressure of fuel to assist cold starting, and such suggested additives include butane, isopentane, winter grade gasoline, and, in some cases, dimethyl ether. While one or more of these additives have resulted in a fuel that would allow the engine to be reliably started at a lower temperature, such additives have heretofore not been shown to be sufficiently effective in providing a fuel that would allow the engine to be started at the lowest temperature at which gasoline fueled engines are commonly required to start by vehicle manufacturers (i.e., -30.4° C. (-30° F.)) and/or have not been generated on-board the utilizing vehicle. Moreover, at least some of these additives have been known to create other problems, including fuel system vapor lock at moderate temperatures, high evaporative emissions, and/or increase fuel costs. 
     With respect to the use of methanol to fuel an engine, it has also been suggested that a compression ignition engine (diesel cycle) could be modified for such use by converting methanol to dimethyl ether, continuously aspirating the dimethyl ether into the engine with combustion air and injecting methanol directly into the cylinder (see U.S. Pat. No. 4,422,412). 
     With particular respect to the generation and use of dimethyl ether, it is known that dimethyl ether can be generated by dehydration of methanol. It is also known that dimethyl ether can be generated using a number of different catalysts, with dimethyl ether formation apparently occurring over Lewis acid sites, Bronsted acid sites, or both, depending upon the particular catalyst utilized. Alumina, for example, is a widely used catalyst for dehydration of alcohol, and its activity appears to be mostly due to the presence of Lewis acid sites. 
     While equilibrium conversion of methanol to dimethyl ether has been found to be achievable using a number of catalysts, the rate at which the dehydration reaction proceeds has been found to differ depending upon the particular catalyst used. In order to increase dehydration activity, it has also been heretofore suggested that an alumina catalyst could be appropriately modified, and, accordingly, phosphated alumina, silicon-coated alumina, and titania-containing alumina have been suggested for use in this connection. 
     Thus, while different apparatus and/or methods have been heretofore suggested and/or utilized, apparatus and method providing a satisfactory solution to the cold starting and cold running operation problem has not been heretofore found for alcohol fueled, and, more particularly, methanol fueled, internal combustion engines. 
     SUMMARY OF THE INVENTION 
     This invention provides apparatus and method for enhancing performance of an alcohol fueled engine, and, more particularly, a methanol fueled engine, during cold conditions, which apparatus and method provides a solution for cold start problems and/or greatly reduces emissions during cold running operations. 
     In this invention, an ether, and, more particularly, dimethyl ether, is generated on-board the vehicle and mixed with combustion air and alcohol, and, more particularly, methanol when dimethyl ether is to be generated, to provide reliable cold starts and/or cold running operation to temperatures below about -30.4° C. The required ether can be generated and used at the time needed and/or can be generated and stored for future use. 
     With respect to dimethyl ether, the ether is generated by catalytic dehydration of methanol and the generated dimethyl ether is then mixed with the combustion air and methanol (or a mixture of methanol and gasoline), and a number of catalysts may be utilized, with fluorinated alumina being the now preferred catalyst. 
     It is therefore an object of this invention to provide enhanced performance of an alcohol fueled engine, and, particularly, a methanol fueled engine, during cold conditions. 
     It is still another object of this invention to provide an improved apparatus and method for on-board generation of ether from alcohol, and, particularly, dimethyl ether from methanol, and use of the ether to improve alcohol fueled engine performance during cold conditions. 
     It is another object of this invention to provide an improved apparatus and method for generation of ether from alcohol, and, particularly, dimethyl ether from methanol, and mixing of the ether with a mixture of alcohol, gasoline and combustion air to improve alcohol fueled engine performance during cold conditions. 
     It is another object of this invention to provide an improved apparatus and method for on-board generation and use of dimethyl ether to improve performance of a spark ignition engine. 
     It is still another object of this invention to provide an improved apparatus and method for producing dimethyl ether using fluorinated alumina as a catalyst. 
     It is another object of this invention to provide an apparatus for generating ether, and particularly dimethyl ether, on-board as needed for immediate mixing with combustion air and alcohol, and, particularly, methanol, to improve cold start and/or cold running operation of an internal combustion engine. 
     It is still another object of this invention to provide an apparatus for generating ether, and, particularly, dimethyl ether, on-board and storing the same for later mixing with alcohol, and, particularly, methanol, during subsequent cold starts or cold running operations. 
     With these and other objects in view, which will become apparent to one skilled in the art as the description proceeds, this invention resides in the novel construction, combination, arrangement of parts and method substantially as hereinafter described, and more particularly defined by the appended claims, it being understood that changes in the precise embodiments of the herein disclosed invention are meant to be included as come within the scope of the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings illustrate complete embodiments of the invention according to the best mode so far devised for the practical application of the principles thereof, and in which: 
     FIG. 1 is a graphical illustration of a known saturated vapor/air equivalence ratio versus temperature for methanol; 
     FIG. 2 is a graphical illustration of known vapor pressure versus temperature for selected fuels; 
     FIG. 3 is a graphical illustration of the known thermodynamic equilibrium for a methanol dehydration reaction; 
     FIG. 4 is a block and schematic view illustrating apparatus according to this invention for generating dimethyl ether on board for immediate mixing with methanol; 
     FIG. 5 is a cut-away side view illustrating the dehydration reactor unit shown in FIG. 4; 
     FIG. 6 is a graphical illustration of methanol conversion versus temperature for selected catalysts; 
     FIG. 7 is a graphical illustration of dehydration of methanol with 15 volume percent gasoline over a 0.3% fluorinated alumina catalyst; 
     FIG. 8 is a graphical illustration of dehydration of methanol over a 0.3% fluorinated alumina catalyst; 
     FIG. 9 is a typical graphical illustration of the power requirements for the methanol dehydration reactor unit shown in FIG. 5; 
     FIG. 10 is a flow chart illustrating typical operation for apparatus as shown in FIG. 4; 
     FIG. 11 is a block and schematic view illustrating a second embodiment of the apparatus of this invention utilized to generate dimethyl ether on-board and store the same for subsequent cold start and/or cold running operations; and 
     FIG. 12 is a block and schematic diagram illustrating typical operation of the apparatus as shown in FIG. 11. 
    
    
     DESCRIPTION OF THE INVENTION 
     As illustrated by the graph of FIG. 1, mixtures of air saturated with methanol are not combustible at temperatures below 12° C. In this invention, ether, preferably dimethyl ether, is generated on-board a vehicle having an internal combustion engine mounted thereon, and the ether is then mixed with combustion air and the alcohol from which the ether was derived (methanol where dimethyl ether is generated) to provide for reliable cold starting and/or enhanced cold running operation of the engine, as well as reducing emissions under cold conditions. 
     Dimethyl ether (DME) is generated on-board by catalytic dehydration of methanol according to the following reaction: 
     
         2 CH.sub.3 OH→CH.sub.3 OCH.sub.3 +H.sub.2 O+Heat 
    
     As illustrated by FIG. 2, DME has a vapor pressure between that of propane and butane, and DME has wide flammability limits so as to be capable of enabling engine cold starting and/or running to temperatures below about -30.4° C. 
     The methanol dehydration reaction is exothermic, but some energy input is required to vaporize the liquid methanol. The energy required to dehydrate methanol to dimethyl ether is, however, far less than that required to dissociate methanol to hydrogen and carbon monoxide, as is illustrated in Table I as follows: 
     
                       TABLE I______________________________________Energy Required To Dehydrate and Dissociate MethanolProcess      Dehydration    Dissociation______________________________________Vaporization  12,114 cal/gm-mole                       12,114 cal/gm-mole&amp; SuperheatingDehydration  -3,220 cal/gm-moleDissociation                21,660 cal/gm-moleTotal         8,894 cal/gm-mole                       33,774 cal/gm-moleWater        -5,260 cal/gm-moleCondensationTotal         3,634 cal/gm-molePower for    323 Watts      1,227 Watts1 kg/hrWith Water   132 WattsCondensation______________________________________ 
    
     As illustrated in Table I, 12,114 cal/gm-mole is required for both reactions to vaporize the methanol and heat it to the necessary reaction temperature of 350° C. Methanol dehydration is exothermic with a net energy requirement of 8,894 cal/gm-mole, and if the water from the reaction is condensed and used to vaporize the methanol, only 3,634 cal/gm-mole is required to dehydrate the methanol. Methanol dissociation, on the other hand, is highly endothermic requiring a total of 33,774 cal/gm-mole. While methanol dehydration is utilized as discussed hereinafter, a combination of dehydration and dissociation might be utilized, at least in some instances. 
     The power required to dehydrate and dissociate methanol at a rate of 1 kg/hr is also illustrated in Table I, with the steady state power required to dehydrate methanol to dimethyl ether being much less than to dissociate methanol. The thermodynamic equilibrium for the methanol dehydration reaction, is shown in FIG. 3. 
     An on-board system 18 for generating DME from methanol and then substantially immediately mixing the generated DME with methanol and combustion air for providing the fuel mixture to a methanol fueled internal combustion engine is illustrated in FIG. 4. 
     As shown, methanol 20 is stored in tank, or reservoir, 22 and is pumped therefrom by pump 24 to fuel injector 26 through line, or conduit, 28, with pressure regulator 30 being connected between line 28 and tank 22. Methanol is injected by fuel injector 26 into passage, or mixing area, 32 (formed by passage walls 34). The methanol is injected into mixing area 32 as a finely dispersed aerosol and is vaporized within mixing area 32 by combustion air then present within the mixing area (providing such air is sufficiently heated). The methanol is mixed at mixing area 32 with incoming air passing through air cleaner 36 and past throttle 38. The mixture is then fed into cylinder 40 of the methanol fueled engine when inlet valve 42 is opened in conventional manner (while piston 44 is retracted and exhaust valve 46 is closed). It should be appreciated that while only one cylinder is illustrated in FIG. 4, an engine will normally have a plurality of cylinders as is conventional with internal combustion engines (either spark ignition engines or combustion ignition engines). 
     As also shown in FIG. 4, methanol from tank 22 is also pumped by pump 24 to fuel injector 50. Fuel injector 50 is connected to the input side of reactor 52 of methanol dehydration unit 54. Methanol injected into reactor 52 by fuel injector 50 is caused to be vaporized, heated and catalytically converted to dimethyl ether, with the DME generated by reactor 52 being supplied from the outlet side 56 of reactor 52 into passage, or mixing area, 32 for mixing with combustion air and methanol thereat. 
     As also indicated in FIG. 4, the operation is controlled by fuel control unit 58, which unit can be, for example, an engine control computer such as is now included in many automotive vehicles. Fuel control unit 58 is connected with temperature switch 60 (sensitive to the temperature of cylinder 40) and provides electrical output signals to fuel injectors 26 and 50, and also provides electrical output signals for controlling heating of vaporizer, superheater and catalytic sections 62, 64 and 66, respectively, of reactor 52. 
     Reactor 52 is preferably electrically heated and is designed to operate at or near equilibrium conversion of methanol to DME at a neat methanol flow rate of 1 kg/hr which is more than half of the idle fuel requirements of a 1.6 liter engine. Since the reactor is intended for on-board vehicle use, it is compact and lightweight, and for warm-up from cold ambient temperatures (of about -20° C.) to operating temperature, requires less than 15 seconds. While not specifically shown, all power requirements can be provided by the vehicle&#39;s conventional (normally 12 volt) battery/alternator system. 
     Reactor 52 is shown in greater detail in FIG. 5. As shown, methanol injected by injector 50 is sprayed into vaporizer, or boiler, section 62. Section 62 is heated by heater coil 70 so that the methanol is vaporized while at vaporizer section 62. The vaporized methanol from vaporizer section 62 is then directed to superheater section 64 where the vaporized methanol is heated by superheating coils 72 to the necessary reaction temperature (i.e., 350° C.). 
     Nichrome 80 is preferred for use as superheater coil wires 72. A design wire temperature of 850° C. has been used to gain long life, and such wires may be operated up to 1100° C. for short periods if necessary. As also shown in FIG. 5, insulation 74 may be provided for superheater section 64, as needed. 
     The heated vaporized methanol is then coupled through screen 76 to catalytic section 66. Heat is supplied to catalytic section 66 by coil 78 adjacent to catalyst 80. At catalytic section 66, the heated vaporized methanol is dehydrated to generate dimethyl ether. The thus generated DME is then coupled from the reactor at outlet nozzle 82 at output side 56 of reactor 52 (outlet nozzle 82 opens into passage 32 as indicated in FIG. 4). 
     Reactor 52 is designed to fit inside a standard 11/2 inch butt weld, pipe &#34;T&#34; 84. The low operating pressure of the system allows the use of a thin wall, for the &#34;T&#34;. Flanges 86 may be welded to the &#34;T&#34;, if desired, so that the flange facings contain the sections, or subassemblies, of the reactor, whereby each subassembly can be easily removed for analysis, repair or reconfiguration with minimal disturbance to the rest of the reactor. 
     As also indicated in FIG. 5, vaporizer section 62 is defined by electrically heated copper tube 90 (1 inch OD) upon which the methanol from fuel injector 50 is sprayed. Vaporizer specifications are set forth in Table II as follows: 
     
                       TABLE II______________________________________Design Specifications for Electrical VaporizerParameter       Specification______________________________________Methanol Flow Rate           1 kg/hrBoiling MethanolPower           370 WHeat Flux       280 kW/m.sup.2Heating Wires   Nichrome 80/20Ribbon cross section           0.0126 in. × 3/32 in.Length          17 cmResistance      0.25 ohmConfiguration   Wrapped around 0.5 mm mica           insulator and Copper Tube at           5/32 in. center to center           distance.BoilerCopper tubeOD              1 in.Wall thickness  0.065 in.Length          1 in.Area            3.8 cm.sup.2TemperaturesTube wall       75° C.Wire            400° C.______________________________________ 
    
     Methanol is fed to the vaporizer, or boiler, section 62 by electronic fuel injector 50 (which injector may be a conventional injector such as manufactured and sold by Bosch, or example). The methanol is injected into a cone shaped pattern so that the methanol impinges on boiler wall 90 which is maintained approximately 10° C. above the boiling point of the methanol. The vapor heat transfer mechanism was assumed to be nucleate boiling, and nichrome wire ribbon 70 was used to heat the copper tube forming the boiler wall. 
     Helical coils of Nichrome wire are utilized as superheater coils 72 of superheater section 64, with the heating elements being sized to bring the temperature of the vaporized methanol up to the 350° C. reactor temperature (four sets of wires, each having a nominal 10 volt drop, were utilized). Design specifications for the superheater are summarized in Table III as follows: 
     
                       TABLE III______________________________________Design Specifications for ElectricallyOperated SuperheaterParameter          Specification______________________________________Methanol Flow Rate 1 kg/hr.Temperature Rise   60° C. to 350° C.Power Required     70 WOverall Heat Transfer              26 W/m.sup.2 KCoefficientLog-Mean Temperature              630° C.DifferenceArea Required      34 cm.sup.2Wire HeaterType               NichromeDiameter           0.032 in.Length             240 cmNumber of Segments 4Resistance;        1.25 ohmeach segmentWeight             6 gConfiguration      4 electrically parallel              helically coiled wires.              Leading 2 sets are              controlled separately from              the second 2 sets.______________________________________ 
    
     Four catalysts were selected for possible use in catalytic section 66, including a high surface area γ-alumina, a phosphated γ-alumina (containing a phosphorous-to-alumina ratio of 1.0), an amorphous silica-alumina, and fluorinated γ-alumina (with 0.3 wt % F.). 
     Although a fair amount of literature exists regarding the use of fluorine to increase catalyst acidity, no mention has been found of the use of fluorinated alumina for methanol dehydration. Fluorine incorporated in an oxide catalyst replaces surface O or OH. Because fluorine is very electronegative, it polarizes the lattice more than the group it has replaced, thus increasing the acidity of both Bronsted and Lewis sites. Only small amounts of fluorine are necessary for increasing acid strength. It has been found that the first 0.5 wt% of HF added was the most effective and appeared to remain on the surface to influence acid sites in proportion to surface area covered. Larger amounts of acid react with bulk alumina to form crystallites of basic aluminum fluoride. As brought out hereafter, fluorinated alumina is the now preferred catalyst for use in this invention. 
     Each of the selected catalysts was tested, and the results are summarized in Tables IV through IX as follows: 
     
                       TABLE IV______________________________________Methanol Dehydration over 0.1653 g Silica-Aluminadiluted with 2.08 g quartz.  Meth-  anol                         MethanolTemper-  Feed            Product mole %                               Conversionature  Rate    whsv    DME   H.sub.2 O                             MeOH  DME   H.sub.2 O(C.)   (g/hr)  (1/hr)  %     %    %     %     %______________________________________250    0.384   2.32    30.0  30.4 39.7  60.2  60.5250    0.853   5.16    21.0  22.1 56.9  42.5  43.7200    0.384   2.32     8.0   8.6 83.3  16.2  17.2200    0.853   5.16     4.6   5.0 90.3   9.3  10.0250    0.853   5.16    19.0  19.0 62.0  38.0  30.0300    0.853   5.16    39.0  39.3 21.7  78.2  78.3300    1.82    11.02   29.1  28.7 42.3  57.9  57.6350    1.82    11.02   39.3  40.3 20.4  79.3  79.8350    0.853   5.16    41.8  42.8 15.4  84.5  84.8250    0.853   0.85    19.0  19.3 61.7  38.1  38.4______________________________________ 
    
     
                       TABLE V______________________________________Methanol Dehydration over 0.1652 g Phosphated Alumina(P/A1 = 1.0) diluted with 2.168 g quartz.  Meth-  anol                         MethanolTemper-  Feed            Product mole %                               Conversionature  Rate    whsv    DME   H.sub.2 O                             MeOH  DME   H.sub.2 O(C.)   (g/hr)  (1/hr)  %     %    %     %     %______________________________________250    0.853   5.16    14.0  14.1 71.8  28.0 28.3250    0.384   2.32    18.7  18.7 62.6  37.4 37.4200    0.384   2.32     2.8   2.7 94.5   5.6  5.3200    0.853   5.16     1.9   1.7 96.5   3.7  3.4250    0.853   5.16    14.0  13.3 72.6  27.9 26.9300    0.853   5.16    42.2  41.5 16.3  83.8 83.6300    1.82    11.01   32.9  32.1 35.0  65.3 64.7350    1.82    11.01   42.1  42.4 15.5  84.5 84.6350    4.68    4.68    36.3  33.8 29.9  70.8 69.3350    0.853    0.853  42.5  42.8 14.7  85.2 85.3250    0.853   0.85    11.4  11.7 76.9  22.9 23.3______________________________________ 
    
     
                       TABLE VI______________________________________Methanol Dehydration over undiluted0.9708 g Phosphated-Alumina (P/A1 = 1).  Meth-  anol                         MethanolTemper-  Feed            Product mole %                               Conversionature  Rate    whsv    DME   H.sub.2 O                             MeOH  DME   H.sub.2 O(C.)   (g/hr)  (1/hr)  %     %    %     %     %______________________________________250    4.68    5.16    11.1  11.7 77.1  22.4  23.3200    4.68    5.16     1.5   1.5 97.0   3.1   2.9250    4.68    5.16    14.1  13.3 72.5  28.0  26.8300    4.68    5.16    43.1  43.9 13.1  86.8  87.0350    4.68    5.16    42.7  43.2 14.1  85.8  86.0250    4.68    5.16    11.8  12.4 75.8  23.7  24.7______________________________________ 
    
     
                       TABLE VII______________________________________Methanol Dehydration over 0.1653 g γ-Aluminadiluted with 2.167 g quartz.  Meth-  anol                         MethanolTemper-  Feed            Product mole %                               Conversionature  Rate    whsv    DME   H.sub.2 O                             MeOH  DME   H.sub.2 O(C.)   (g/hr)  (1/hr)  %     %    %     %     %______________________________________250    0.853   5.16    30.5  30.4 39.1  61.0  60.9250    0.384   2.32    34.5  34.5 31.1  68.9  68.9200    0.384   2.32     7.7   8.6 83.7  15.6  16.9200    0.853   5.16     5.2   6.0 88.9  10.4  11.8250    0.853   5.16    30.4  30.4 39.3  60.7  60.7300    0.853   5.16    42.8  43.4 13.8  86.1  86.2300    1.82    11.0    39.1  40.1 20.7  79.1  79.5300    4.68    28.3    27.6  29.7 42.8  56.2  58.1350    4.68    28.3    42.0  43.0 15.0  84.8  85.2350    7.4     44.8    34.3  33.6 32.1  68.1  67.7250    0.853   5.16    31.5  31.2 37.3  62.8  62.6______________________________________ 
    
     
                       TABLE VIII______________________________________Methanol Dehydration over 0.1654 g Fluorinatedγ-Alumina diluted with 2.202 g quartz.  Meth-  anol                         MethanolTemper-  Feed            Product mole %                               Conversionature  Rate    whsv    DME   H.sub.2 O                             MeOH  DME   H.sub.2 O(C.)   (g/hr)  (1/hr)  %     %    %     %     %______________________________________250    0.853   5.16    30.1  32.1 37.8  61.4  62.9250    0.384   2.32    37.3  39.7 23.0  76.5  77.6200    0.384   5.16     9.3  11.2 79.5  18.9  22.0200    0.853   5.16     5.8   7.3 86.9  11.7  14.4250    0.853   5.16    31.0  30.9 38.0  62.0  61.9300    0.853   5.16    42.0  43.9 14.1  85.6  86.1300    1.82    11.00   39.9  41.8 18.4  81.3  82.0300    4.68    28.30   31.0  26.9 42.1  59.5  56.2350    4.68    28.30   37.4  34.1 28.6  72.3  70.4350    7.4     44.74   39.9  41.4 18.8  80.9  81.5350    4.68    28.30   39.7  41.1 19.2  80.5  81.0300    4.68    28.30   33.3  31.1 35.5  65.2  63.6250    0.853   5.16    32.4  33.1 34.5  65.2  65.8250    0.853   5.16    27.7  25.7 46.6  54.3  52.4350    7.4     44.74   40.4  39.6 20.0  80.2  79.8350    11.75   71.04   40.0  38.0 22.0  78.4  77.5350    17.38   105.00  35.6  35.3 29.1  71.0  70.8350    24.01   145.20  32.1  30.9 37.0  63.4  62.5250    0.853   5.16    30.0  29.3 40.7  59.5  59.0250    1.82    11.00   16.9  16.3 66.9  33.5  32.7250    4.68    28.30   12.0  11.3 76.7  23.9  22.8250    0.384   2.32    39.0  38.6 22.4  77.7  77.5250    0.853   5.16    28.0  26.7 45.3  55.2  54.1250    7.4     44.74    9.5   9.8 80.7  19.1  19.5301    7.4     44.74   31.7  29.8 38.5  62.2  60.7300    4.68    28.30   32.1  31.2 36.7  63.6  62.9300    17.38   105.08  20.3  16.9 62.7  39.3  35.0300    24.01   145.16  12.5  11.0 76.6  24.5  22.3250    0.853   5.16    29.8  28.7 41.5  58.9  58.1______________________________________ 
    
     
                       TABLE IX______________________________________Methanol with 15 vol % unleaded gasoline additive.Dehydration over 0.1654 g Fluorinated γ-Aluminadiluted with 2.202 g quartz.  Meth-  anol                         MethanolTemper-  Feed            Product mole %                               Conversionature  Rate    whsv    DME   H.sub.2 O                             MeOH  DME   H.sub.2 O(C.)   (g/hr)  (1/hr)  %     %    %     %     %______________________________________250    0.853   5.16    32.6  28.0 39.4  62.4  58.7300    6.3     38.09   34.2  28.7 37.1  64.8  60.7350    14.8    89.48   36.1  30.4 33.5  68.4  64.5350    20.4    123.34  33.8  31.1 35.1  65.8  63.9250    0.853   5.16    33.4  30.7 35.9  65.0  63.1______________________________________ 
    
     For purposes of comparison, the catalyst activities are shown in FIG. 6. Conversion of methanol to DME is shown for each catalyst at a weight hourly spaced velocity (WHSV) of 5.16/hr. At this low WHSV, the γ-Alumina and 0.3% F./γ-Alumina were practically identical in activity. These two catalysts were also compared at a WHSV of 45/hr. At the increased space velocity, the fluorinated alumina was more active. 
     Several early runs were made with the silica-alumina catalyst in both diluted and undiluted beds, and the silica-alumina was tested at temperatures ranging from 200° C. to 350° C., and at space velocities ranging from 2.32 to 11.02 g MEOH/hr-g catalyst. As with each catalyst run, the catalyst was tested at &#34;baseline&#34; conditions of 250° C. and 5.16 WHSV at start-of-run (SOR) and end-of-run (EOR) to monitor any activity loss. From Table IV, a slight loss in activity over the length of the run is observed (42-43% methanol conversion at SOR, and 38% conversion at EOR). 
     The second catalyst tested was the phosphated alumina, with a ratio P/A1=1.0 (&#34;AlPO 4  &#34;). Both the phosphated alumina, and the fluorinated alumina produced a peak attributed to formaldehyde (the peak disappeared after about 30 minutes of testing). 
     The phosphated alumina was tested at temperatures ranging from 200° C. to 350° C., and at space velocities from 2.32 to 28.3 WHSV (Tables V and VI). The silica-alumina was more active at lower temperatures (200-250° C.), but the phosphated alumina was more active at the higher temperatures (300-350° C.). At 350° C. and 5.2 WHSV the conversion obtained from both catalysts is the same--about 85%, the equilibrium conversion. The phosphated alumina also lost some activity during the run; conversion at 250° C., 5.2 WHSV dropped from about 28% to 23% at EOR. 
     In order to test the validity of results from diluted catalyst beds, the phosphated alumina was tested undiluted. Methanol conversion at identical temperature and space velocity is the same (within experimental error) for both diluted and undiluted beds (Tables V and VI). For example at 250° C., 5.16 WHSV, EOR conversion was 23% in the diluted bed and about 24% in the diluted bed. At 200° C., 5.16 WHSV, conversion was 3.4-3.7% in the diluted bed and 2.9-3.1% in the undiluted bed. 
     The third catalyst tested in the reactor system was γ-alumina The γ-alumina was found to be more active than either the silica-alumina or the phosphated alumina. The increased activity is especially apparent at the larger space velocities (45/hr, FIG. 6). At 350° C., the γ-alumina provided 68% methanol conversion at a space velocity as high as 44.7 g MEOH/hr-g catalyst the γ-alumina also did not appear to deactivate as did the first two catalysts: EOR conversion at 250° C. and 5.2 whsv was 62-63%, while SOR and middle-of-run (MOR) activities at these conditions were about 61% methanol conversion (Table VII). 
     Based on the encouraging results with the high-surface area γ-alumina, fluorine was applied to increase surface acidity. A fluorinated catalyst with 0.3 wt% F was prepared. The catalyst was tested over three operating days. The fluorinated γ-alumina was tested at temperatures from 200° C. to 350° C., and at space velocities as high as 145.2 g MEOH/hr-g catalyst (Table VIII). 
     The fluorinated alumina was found to be the most active catalyst for methanol dehydration. Even at 350° C. and 145.2 WHSV, conversion of 62% was observed. The fluorinated catalyst did not lose significant activity over the three days (approximately 30 hours) of running. At SOR, methanol conversion was about 62% at 250° C. and 5.2 WHSV; at EOR on the third day the conversion was 58-59% at those conditions. 
     A final run was performed with the same fluorinated catalyst to determine the effect of impurities in the methanol feed. A mixture of 15 volume % unleaded gasoline and 85 volume % methanol was prepared. The fluorinated catalyst was started up with pure methanol, then feed was switched to the gasoline blend. After exposure at 350° C. and WHSV of 89-123 (based on the methanol flow rate), the catalyst feed was switched back to pure methanol. The catalyst was not deactivated by the use of the gasoline/methanol blend. SOR and EOR conversion at the baseline conditions was 58-62% and 63-65%, respectively (Table IX). The catalyst maintained activity in the gasoline/methanol mixture equivalent to the pure methanol (FIG. 7). 
     A second order model based on methanol concentration and an Arrhenius law dependence on temperature fit the data well. If C is the concentration of methanol then the second order model for methanol conversion is 
     
         r.sub.d =k·C.sup.2,                               (1) 
    
     where 
     r d  =conversion rate of methanol to DME and water, g methanol/hr·g catalyst. 
     C=concentration of methanol, g methanol/g feed. 
     k=second order rate constant, (g feed)2·g methanol/hr·g catalyst. 
     The rate constant, k, is expected to follow the Arrhenius law for temperature dependence 
     
         k=k.sub.o e.sup.-E a/.sup.RT                               (2) 
    
     with 
     k o  =apparent pre-exponential factor 
     E a  =apparent activation energy, cal/mol 
     R=gas constant, 1.987 cal/mol·K, 
     T=absolute temperature, K. 
     Introducing the dimensionless fractional conversion 
     
         x=C/C.sup.o                                                (3) 
    
     where C o  is the methanol concentration (g methanol/g feed) at the reactor inlet, and substitution into equation provides 
     
         r.sub.d =k.sub.o ·e.sup.-E a/RT (C.sup.o).sup.2 (1-x).sup.2. (4 
    
     For an ideal plug flow reactor, with (mass) flow rate, F, and differential catalyst weight, dW c , the design equation is 
     
         d(C·F)/dW.sub.c -r.sub.d.                         (5) 
    
     Distance through the reactor, z, and the superficial cross-sectional flow area, A, of the reactor are related to the differential catalyst weight, dW c , by 
     
         dW.sub.c =.sub.ρb ·A·dz,             (6) 
    
     where .sub.ρb is the catalyst bulk density, g/m 3 . Since there is no change in moles as the reaction proceeds, and with the inlet mass feed flow rate of F o , equation 5 combined with equation 3 becomes 
     
         r.sub.d =-F.sub.o ·C.sup.o ·(dx/dW.sub.c). (7) 
    
     Combining equations 4 and 7, and rearranging yields ##EQU1## The ratio W c  /F o  is the reciprocal of the weight hourly space velocity, WHSV. Equation 8 is integrated from the inlet of the reactor with known feed concentrations to the reactor outlet. Thus ##EQU2## the term, C o  ·(W c  /F o ), is the reciprocal of the WHSV based on methanol rather than total gas feed rate. This term was used to compare the catalyst activities when gasoline was added to the methanol. Bear in mind that 
     
         k=3.156×10.sup.10 ·e.sup.-23,000/RT.        (11) 
    
     The apparent activation energy, E a  =23,000 cal/mol, and the apparent pre-exponential factor, k o  =3.156×10 10 , were determined by linear regression of the linear equation form of equation 9 combined with equation 2, 
     
         ln[x/(1-x)]=ln[k.sub.o ·C.sup.o ·(W.sub.c /F.sub.o)]+E.sub.a /R·(1/T).                     (12) 
    
     In this case ln[x/(1-x)] is the dependent variable, and 1/T is the independent variable. A plot of ln[x/(1-x)] versus 1/T gave straight lines for each value of W c  /F o . 
     The predicted dependence of the conversion on the WHSV of the reactor and inlet feed concentration of methanol for the fluorinated γ-alumina is shown in FIG. 8. The second order kinetic model adequately describes the observed methanol conversions at 250-350° C., and 2.32-145 WHSV. 
     Reactor 52 was sized using catalyst performance data as brought out above to operate at 95% of equilibrium conversion of methanol to dimethyl ether and at a temperature of 350° C. This yielded a WHSV of 40/hr and a total catalyst loading of 25g. A reactor length of 62 cm (2.5 inches) was chosen to provide a ratio of reactor length to catalyst particle diameter of 90, which is more than adequate to avoid channeling and to provide for effective catalyst utilization and conversion. 
     The thermal conductivity of the catalyst is needed to calculate the time required to preheat the reactor. Since an experimental value for this material does not exist, a value was estimated. The value calculated was 20% lower than those earlier reported by others for similar catalysts. The lower value was used to provide a conservative determination of the time required to heat the reactor. 
     The thermal conductivity of the catalyst indicated that heating the catalyst from the outside of the tube would take longer than the 15 s targeted at the outset of the design. Thus, wire heaters were placed inside of the reactor and spaced about 1/8 inch apart. To maintain a constant wire temperature of 850° C., the power to the preheaters were made to follow the typical curve shown in FIG. 9. This curve was generated by solution of the time dependent heat transfer equation in radial coordinates using a Crank-Nicholson finite difference technique. 
     Pressure drop in the catalyst bed was calculated for flow through packed columns. Ground catalyst and pellet densities indicated that the catalyst has a macropore void fraction of 0.5-0.6. Pressure drop through the reactor was calculated to be less than 7 kPa (1 psi). The design specifications for the electrically preheated catalyst bed are set forth in Table X as follows: 
     
                       TABLE X______________________________________Design Specifications for Electrically PreheatedCatalyst Bed.Parameter          Specification______________________________________ReactorMaterial           Stainless SteelTube Outside Diameter              5/8 in.Wall thickness     0.035 in.Catalyst           Preheated γ-AluminaWeight             25 gParticle Diameter  0.6-0.8 mmPreheaterMaximum Power Input              460 WPreheat time       15 sWire Heaters       NichromeDiameter           0.032 in.Length             2 each, 8 in.Resistance         0.42 ohmDesign Temperature 850° C.Maximum Temperature              1100° C.Maximum Current    10 A______________________________________ 
    
     The methanol dehydration reaction is exothermic which results in the products having a temperature approximately 200° C. higher than the reactants. Some of the reaction heat will be lost through the reactor insulation, and superheater outlet temperature can be reduced to control the catalyst bed temperature. 
     The reactor has two distinct control modes - the initial heat-up to reaction temperature, and load following cold engine operation. 
     During the reactor heat-up transient, an open loop, power-time program can be used as typically shown in FIG. 9. Catalyst bed power decreases with time to maintain a relatively constant wire temperature. Just before the start of methanol flow, the vaporizer power will be turned on to pre-heat it to 75° C. The superheater has very little thermal mass and will be powered-up just before the start of methanol flow. 
     During engine operation, the reactor control will be in a load following mode, and a DME flow demand signal will be generated based on engine temperature and load as indicated by the flow diagram of FIG. 10. This will be translated into a signal to control the electronic fuel injectors. 
     Catalytic bed heating will be turned off after methanol flow is begun since the dehydration reaction is exothermic. Vaporizer and superheater power will follow methanol flow in an open loop mode. Superheater power will be reduced, as a percentage of vaporized power, with continuing reactor operation to control reactor temperature. 
     Reactor 52 has a total system weight of 1.2 kg, as shown in Table XI as follows: 
     
                       TABLE XI______________________________________Weights of Electrically Heated Reactor ComponentsComponent           Weight (g)______________________________________Boiler               30Superheater          32Reactor              50Inner Flange         50Container           1040TOTAL               1202 (2.6 lbs.)______________________________________ 
    
     The overall dimensions of the reactor are 27.7 cm (10.5 inches)×11.4 cm (4.5 inches)×7.0 cm (2.75 inches) and occupies less than 840 cm 3  (130 in. 3 ) of space. 
     DME is added to combustion air and methanol only during start-up or for a short period of cold running operation (until the engine has been running for a sufficient time to heat above cold running). It is not intended that the DME be added on a continuous basis during running (other than during the initial cold running). During cold starting and cold running, it has been found that injection of 5% to 30% DME with respect to total fuel provides best results. 
     An alternate embodiment 94 of an on-board system for generating DME from methanol and storing the DME for later use is shown in FIG. 11. System 94 is designed to supply DME to the engine at the time of cold start from stored DME produced during previous engine operation, and could, of course, supply dimethyl ether at other times, as needed, to enhance engine operation, particularly cold operation. A DME storage container 96 is provided, and is sized to provide 1 kg/hr of DME to the engine for 40 minutes or a capacity of 670 g. The DME generating portion of the system recharges the storage at 0.5 kg/hr. The system must operate at a pressure of 15 atm. so that the DME can be stored in liquid form at temperatures up to 60° C. 
     As shown in FIG. 11, methanol stored in tank, or reservoir, 98 is pumped by pump 100 to fuel injector 102. Methanol is injected by fuel injector 102 into passage, or mixing area, 104 (formed by passage walls 106). Air passes through air cleaner 108 and is passed by throttle 110 to passage 104 for combining with methanol thereat (which methanol is vaporized at mixing area 104 if sufficiently heated combustion air is present at the mixing area). The air/methanol mixture is coupled to cylinder 112 with injection into the cylinder occurring when inlet valve 114 is open (with piston 116 retracted and exhaust valve 118 closed). 
     As also indicated in FIG. 11, methanol is also pumped from tank 98 by pump 100 to boiler/superheater 120 of methanol dehydration and storage unit 122, and the output from superheater 120 is coupled through reactor 124 to condenser 126 (having fan 128 driven by motor 130 connected therewith). Generated DME is coupled from condenser 126 and stored in receptacle, or tank, 96 until needed. When needed, the DME is withdrawn from tank 96 and supplied to fuel injector 132 (as by pumping, for example) for injection into passage 104 for combination thereat with methanol and air. As also indicated in FIG. 11, operation of injectors 102 and 132 is controlled by electrical output signals from fuel control unit 134, which unit also receives an input from temperature sensor 136 (connected to sense the temperature of cylinder 112). 
     FIG. 12 illustrates operation of the system of FIG. 11. As indicated, superheater 120 can be heated by engine exhaust (after the engine has reached operating temperature which is estimated to be 5 to 10 minutes after engine start). The superheated methanol flows from superheater 120 into catalyst reactor 124 where the dehydration takes place, and the reaction products are condensed in air cooled heat exchanger 126. The DME is separated from the water and un-reacted methanol by gravity in the storage vessel, and the water and un-reacted methanol are fed to the engine for disposal. 
     Boiler/superheater 120 is a once-through design and uses a single 1/8 in. tube with the minimum standard wall thickness (0.030 inches). The tubing is coiled helically inside a larger tube through which the exhaust gas flows. The design specifications for boiler superheater 120 are summarized in Table XII as follows: 
     
                       TABLE XII______________________________________Boiler/Superheater Heat Exchange Specifications forExhaust Heated Methanol ConverterParameter               Specification______________________________________Methanol Flow Rate      0.5 kg/hrBOILER SECTIONOverall Heat Transfer Coefficient                   44 W/m.sup.2 KLog Mean Temperature Difference                   320° C.Power Required          185 WArea Required           130 cm.sup.2SUPERHEATER SECTIONOverall Heat Transfer Coefficient                   43 W/m.sup.2 KLog Mean Temperature Difference                   120° C.Heat Transfer Rate      35 WArea                    38 cm.sup.2CONFIGURATION           1/8 in. OD                   tubing in 3/4                   in. helical                   coil inside a 1                   in. exhaust                   tubeWEIGHT1/8 in. Tubing          560 g1 in. Tubing            1375 gPRESSURE DROPMethanol Side           60 psi                   (415 kPa)Exhaust Side            0.4 psi                   (2.75 kPa)______________________________________ 
    
     An electrically heated reactor was selected for the system to avoid using exhaust gas diverter valves to control reactor temperature. The size of the catalyst bed was assumed to be the same as used in the electrically heated reactor as described hereinabove. 
     Specifications for the condenser are summarized in Table XIII: 
     
                       TABLE XIII______________________________________Condenser Heat Exchanger SpecificationsParameter               Value______________________________________Methanol Flow Rate   0.5 kg/hrGAS/GAS COOLINGOverall Heat Transfer                8 W/m.sup.2 KCoefficientLog Mean Temperature 340° C.DifferenceHeat Transfer Rate   165 WArea                 600 cm.sup.2CONDENSATIONOverall Heat Transfer                45 W/m.sup.2 KCoefficientLog Mean Temperature 66° C.DifferencePower Required       150 WArea Required        495 cm.sup.2TOTAL AREA           1095 cm.sup.2CONFIGURATION        1/8 in. OD tubing                arranged in bundles                1/4 in. center to                center and 8-12 in.                long. Requires 1/3-                1/2 hp motor to                drive cooling fan.WEIGHTTubing               300 gFan + Motor          1000 gPRESSURE DROPDME/Methanol/Water Side                negligibleAir                  none, 1.5 m/s                superficial                velocity.______________________________________ 
    
     Ambient cooling air is blown by fan 128 over a configuration of 1/8 inch tubes in a manifold approximately 20.32 cm (8 in.)×20.32 cm (8 in.), and 2-3 tubes deep. The condensate flows by gravity into separation vessel 96. The line between the condenser and separator is equipped with check valve 138 to maintain superheater pressure after the system is turned off. At 87% conversion, the water and methanol condenses the mixture. The average condensate is 35% methanol and water by weight. The methanol/water condense over the temperature range 160° C. to 80° C. 
     As shown in FIG. 12, separator vessel 96 consists of a schedule 40, 3 inch diameter×8.25 inch long pipe 140 mounted vertically. A cone 142 is welded or flanged into the bottom of the pipe. The condensate enters at the top of the vessel, water/methanol mixture is drawn off from the bottom of the vessel, and DME is drawn off at some point above the water/methanol effluent port. 
     Two level control systems (one of which includes float 146, level sensor 148, level control 150, valve control 152 and valve 154, and the other of which includes float 158, level sensor 160, level control 162, valve control 164, valve 166 and pump motor control 168) determine if water/methanol is purged from the system into the water intake, and if the DME level is sufficient to shut off the reactor. These valves work on a float system since the DME is 65% as dense as the water/methanol. 
     When the level of DME in the storage vessel reaches a predetermined height, this level is sensed by level sensor 160 and level control 162 causes motor control 168 to turn off pump 100. The water/methanol mixture is maintained at a constant level by level control 148 (connected to level sensor 150) causing venting of liquid through valve 154 (controlled by valve control 152 connected with level control 150) to the engine intake manifold. A pressure relief valve 170 is also incorporated into the system to vent any non-condensibles that may enter the system. 
     The solubility of DME in water at 24° C. and 5 bar is 35%. At 80° C. and 1 bar DME is soluble in water to 7%. It is unknown how soluble DME is in a 35% methanol/water mixture. Correcting these values for temperature, decreases the solubility by a factor of 4 at 60° C. The hotter the mixture is during separation, the less DME is lost in the water/methanol phase. Thus, an 8-10% loss of DME in the water is expected from a first order analysis. There is the possibility that DME is more soluble in methanol/water mixtures, or that DME is miscible with a methanol water phase. 
     The freezing point of the water/methanol mixture is -35° C. If the reactor achieves an equilibrium DME/water/methanol mixture at an effluent temperature of 200° C., the mixture could freeze at -22° C. This combination of effluent temperature and equilibrium are unlikely to occur, so small amounts of water/methanol remaining in the separator would not freeze until well below -20° C. If conditions colder than -35° C. are expected for the operation, heat tracing on the lines would be necessary to thaw them prior to running the reactor system. The DME which dissolves in the water/methanol phase would further lower the freezing point of the mixtures (probably at least 10° C.) since its normal freezing point is -140° C. 
     In the event that DME, water, and methanol form a miscible system at the temperatures and pressures encountered in the storage and dehydration system, the single phase mixture could be utilized for starting the engine. Engine efficiency, however, would be lower because some of the ignition energy of the fuel would normally go into raising the pressure of the system would be consumed to vaporize the water. 
     Stream numbers (1 through 7), indicated in FIG. 12, are associated with percentages and temperatures according to Table XIV as follows: 
     
                       TABLE XIV______________________________________Steam Number1           2       3       4     5   6     7Temperature (°C.)-20         500     350     450   60  60   60______________________________________% DME   0       0       0     43    43  90   4% MeOH  100     0       100   13    13  10   357______________________________________ 
    
     Start-up of the system is delayed until exhaust gas temperature reaches 500° C. (as sensed by temperature sensor 172). Methanol is then caused to be pumped into boiler/superheater 120 and a reactor electric pre-heater is turned on (temperature sensor 174 and temperature control 176 are connected with the electric pre-heater). Temperature sensor 178 senses the output of reactor 124 (temperature sensor 178 is connected with temperature control 180 to control valve 164, and temperature sensor 182 senses the output of condensor 126 (temperature sensor 182 is connected with temperature control 184 to control fan motor 130). After initial electric preheat has been applied, the reactor temperature is controlled by diverting exhaust gas around the boiler/superheater. 
     An estimate of system weight is summarized in Table XV as follows: 
     
                       TABLE XV______________________________________Weights of Components for Exhaust Heated Reactor               WeightComponent           (g)______________________________________Boiler/Superheater  1935Reactor              50Condenser            300DME Separator/Storage               9400______________________________________ 
    
     The largest single component is the DME separator/storage vessel. 
     As can be appreciated from the foregoing, this invention provides heretofore unavailable systems and methods for enhancing performance of an alcohol fueled engine, and, more particularly, a methanol fueled engine to achieve reliable cold starts and/or enhanced engine operation under cold conditions.