Abstract:
A method for operating an engine is disclosed. The method may include supplying the engine with gas. The method may also include supplying the engine with hydrogen from a hydrogen source. Further the method may include charging a combustion chamber of the engine with a first amount of loaded gas, which may include a gas air mixture. The method may also include delivering, to the combustion chamber, a second amount of hydrogen. The second amount may be a predetermined fraction X of the first amount. The predetermined fraction may be selected to achieve a predetermined ratio λ of an actual amount of the air in the combustion chamber and a stoichiometric amount of the air in the combustion chamber. The hydrogen and the loaded gas may form a loaded gas mixture in the combustion chamber. The method may also include igniting the loaded gas mixture in the combustion chamber.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a procedure for running a spark-ignited gas engine with a combustion chamber and with a hydrogen source, said source supplying the engine with hydrogen, whereby the combustion chamber is being loaded with a gas air mixture. 
       Background 
       [0002]    EP 0 770 171 B1 discloses ignition devices for internal combustion engines, and more particularly hydrogen assisted jet ignition (HAJI) devices for improving combustion efficiency. In the present specification the term “hydrogen” is intended to include hydrogen and other fast-burning fuels. The benefits from the lean combustion approach are theoretically explained as follows. The excess air improves the engine&#39;s thermal efficiency by increasing the overall specific heats&#39; ratio, by decreasing the energy losses from dissociation of the combustion products, and by reducing the thermal losses to the engine cooling system. In addition, as the flame temperature drops with decreasing fuel air ratio, the NOx production is exponentially reduced and the excess air may promote a more complete reaction of CO and hydrocarbon fuel emission from crevices and quench layers. It further discloses that the effect of changing the main chamber fuel composition for the range of 1=1 to 3.5 at full throttle (full power) and smaller ranges at part throttle was studied and that even at full throttle it was possible to reduce the work per cycle wc (and the torque) to no load quantities by increasing the relative air/fuel ratio; whereas the lean limit for this engine with normal ignition is shown to occur at 1=1.64, there exists no lean limit with hydrogen assisted jet ignition, HAJI, within the usable range of wc. 
         [0003]    EP 0 770 171 B1 discloses that many attempts have been made to improve combustion efficiency. Such attempts included fuel stratification with a rich mixture in the spark plug region, divided or prechamber engines alone or in combination with stratification, and hydrogen enrichment of the whole fuel charge. None of these attempts have been entirely successful and the problems referred to above remain in evidence. 
       SUMMARY 
       [0004]    The object of the invention is to configure and arrange a combustion procedure for an Otto gas engine in such a manner that a higher rate of combustion is achievable. 
         [0005]    According to the invention, the aforesaid object is achieved in that a) the loaded gas air mixture is choked with hydrogen, i.e. the hydrogen is added to the air gas mixture or b) the combustion chamber is directly charged with hydrogen, in an amount of at most X % of the volume of the loaded gas as a proportion of the gas air mixture in dependency of a value lambda λ according to the following table, whereby this loaded mixture of hydrogen, air and gas is adjusted to a maximum value lambda λ of Y, according to the following table: 
         [0000]    
       
         
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 X [%] 
                 3.0 
                 8.0 
                 13.0 
                 33.0 
                 50.0 
                 80.0 
               
               
                   
               
             
             
               
                 Y 
                 1.8-2.1 
                 1.85-2.3 
                 1.9-2.4 
                 2.2-2.8 
                 2.5-3.5 
                 3.7-5.1 
               
               
                   
               
             
          
         
       
     
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  shows a schematic diagram of a supply chain of an engine generator unit with a H2 reformer; 
           [0007]      FIG. 2  shows a schematic diagram similar to  FIG. 1  with an electrically driven compressor; 
           [0008]      FIG. 3  shows a schematic diagram of a supply chain of an engine generator unit with a gas converter; and 
           [0009]      FIG. 4  shows a chart illustrating an exemplary variation of the parameter Y (or λ) with the parameter X. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    The maximum value lambda λ is defined as a range between the two values mentioned in the second line of this table. For example, in case of an amount of at most 3% hydrogen of the volume of the loaded gas the maximum value lambda λ is between 1.8 and 2.1. 
         [0011]    Further values for other amounts of hydrogen except the six values mentioned in the table above can be derived from the chart in  FIG. 4 . In this case, the additional gas proportion except hydrogen is methane. The combustion speed is adopted to be laminar with 15 cm/s. 
         [0012]    The Δ-graph is the top of the range for value Y and the □-graph is the bottom of the range for value Y, both in dependency of value X. 
         [0013]    To allocate a highly lean mixture leads to a combustion having a lower NOx (nitrogen oxide) portion and an increased rate of combustion. The increased rate of combustion allows a delayed ignition point, which leads to a higher degree of efficiency. 
         [0014]    In case of for example 3% hydrogen the value lambda λ should be 2.01 or less, i.e. the loaded mixture of hydrogen, air and gas can always be richer than the mentioned value Y (2.01), because a richer mixture is basically better ignitable than a leaner mixture. If the proportion of hydrogen is less than 3%, the mixture should be richer than said value Y (2.01) to allow a good ignition, i.e. a high rate of combustion. 
         [0015]    The mentioned values X and Y are six examples for the one skilled in the art as a basis for the adjustment of the values X and Y in a manner that the loaded mixture of hydrogen, air and gas is as lean as possible. 
         [0016]    Even a higher proportion of hydrogen in the amount of 100% is marketable, though other sources for hydrogen as claimed are necessary. In this case, the value lambda λ should be at most 9.8. As mentioned before, in case of less than 100% hydrogen, the mixture has to be a little richer than Y=9.8. In case of 80% hydrogen it has to be no leaner than 8.60. 
         [0017]    For all values mentioned before a deviation of +/−15% is possible, because of the further circumstances and conditions of the combustion. 
         [0018]    The hydrogen increases the rate of combustion and thus the efficiency of the engine. Additionally to this the very lean gas-air mixture in the combustion chamber having a value lambda λ above 1.81 leads to a combustion with a lower NOx (nitrogen oxide) portion. The increased rate of combustion allows a later point of ignition, which leads to a higher degree of efficiency. Further efficiency asset results in part from the methane for the oxidation reaction R3, R3′, because there is energy recharged with hydrogen, produced by using exhaust gas energy. 
         [0019]    The efficiency of the H2 production by a chemical reaction is not subject to restrictions like a thermo dynamic cyclic process. Therefore, the thermal exhaust energy used in this chemical process is reformed with a much better degree of efficiency, which leads to a better degree of efficiency overall. 
         [0020]    Moreover, recharging this produced hydrogen leads to a reduction of nitrogen oxide (NOx) and formaldehyde, i.e. methanal (CH 2 O) emissions, because the added hydrogen has a catalytic effect on the combustion. For this, the efficiency of the engine is increased, too. 
         [0021]    It can also be an advantage if the engine generating an exhaust gas stream is having a thermal reformer as source, said thermal reformer converting water into hydrogen according to the following reactions: 
         [0000]      MO red +H2O&lt;&lt;-&gt;&gt;MO OX +H2,   R1:
 
         [0000]      MO OX &lt;&lt;-&gt;&gt;MO red +O2,   R2:
 
         [0022]    and that the reformer is supplied with water and with heat from at least a part of the exhaust gas stream and that there are additional heating means, said heating means being powered by a part of the gas the engine is powered with in order to achieve the following exothermic oxidation reaction: 
         [0000]      CH4+O2&lt;&lt;-&gt;&gt;2H 2 O+CO 2 , or   R3:
 
         [0000]      C n H m + (n/2) O2&lt;&lt;-&gt;&gt; (m/2) H2+ n CO,   R3′:
 
         [0023]    whereby the heating means are thermodynamically coupled to the reformer and are additionally heating the reformer. 
         [0024]    Another procedure is possible, in which the engine generating an exhaust gas stream is having a converter, said converter converting higher HCs of the available gas to hydrogen, said HCs consisting of n carbon atoms and m hydrogen atoms according to at least one of the following reactions: 
         [0000]      C n H m + n H2O&lt;&lt;-&gt;&gt; (m/2+n) H2+CO, 
         [0000]      C n H m + (n/2) O2&lt;&lt;-&gt;&gt; (m/2) H2+ n CO, 
         [0000]      C n H m + n CO2&lt;&lt;-&gt;&lt; {m/2) H2+ 2n CO, 
         [0025]    whereby the converter is supplied with water, gas and with heat from at least a part of the exhaust gas stream. 
         [0026]    Alternatively, it can be advantageous if having a thermal reformer and additionally a converter is being used to generate hydrogen. 
         [0027]    Additionally, it can be advantageous if at least one compressor for loading said air-gas-mixture is driven via a motor, for example electrically. For this, the connected exhaust gas turbine can be eliminated. Therefore, the exhaust gas has a temperature that is 100° C. to 150° C. higher when entering the reformer. This higher temperature serves an improved operation of the reformer or the respective reactor in such that the heating means can generate less heating output. 
         [0028]    It can be advantageous if the engine has an exhaust gas turbine and at least one further generator for generating power, said further generator being driven mechanically via the exhaust gas turbine, said exhaust gas turbine being positioned downstream to the source. The energy available from the exhaust gas can be gained in this stage and used to generate energy for heating or powering processes. 
         [0029]    Additionally, it can be advantageous if only higher HCs, which have at least two or three carbon atoms, are converted in the converter. For optimization the methane number of the available gas it is more efficient to convert higher HCs first, i.e. methane itself must not be converted and therefore be joked with hydrogen. 
         [0030]    Other advantages and details of the invention are explained in the claims and in the description as well as shown in the figures. 
         [0031]    The schematic diagram in  FIG. 1  shows the supply chain of a spark-ignited gas engine  1  with an air-gas mixture. 
         [0032]    Starting from a gas mixer  11  at which the ambient air is mixed with the main combustion gas via an air port  11 . 1  and a gas port  11 . 2 , a fuel duct  12  is conducted via a compressor  8  and a fuel cooler  12 . 2  to the gas engine  1  or to a combustion chamber  1 . 1  of the gas engine  1 . A throttle valve  14  that is controlled based on the output of the gas engine  1  is provided in this fuel duct  12  immediately upstream to the gas engine  1 . The gas engine  1  is connected to a generator  26 , for example as part of a genset. 
         [0033]    The gas engine  1  comprises an exhaust gas duct  6  in which an exhaust gas turbine  2  is provided downstream to the gas engine  1  that is used to drive the above-mentioned compressor  8 . After passing through the exhaust gas turbine  2 , the exhaust gas is conducted through a reformer  5  where it dissipates heat to the reformer  5  or a first reactor  5 . 1  or a second reactor  5 . 2 , respectively. The exhaust gas passes the reformer  5 , in parallel, via two separate exhaust gas streams that are coupled or controlled, respectively, via a valve  16  for exhaust gas, and associated with the respective reactor  5 . 1 ,  5 . 2 . The valve  16  for exhaust gas is followed by a heat exchanger or superheater  17 , respectively, and a downstream evaporator  18  for a water circuit  19  described below. An exhaust gas heat exchanger  20  is provided downstream before the exhaust gas is carried off to the exhaust system not shown here. 
         [0034]    The water circuit or water duct  19  with the water port  19 . 1  is provided for supplying the reformer  5  with water for producing hydrogen. First, the water carried in it is preheated by a heat exchanger  12 . 1  for water coupled to the fuel duct  12 , wherein the heat is taken from the compressed exhaust gas-air mixture. Then the water is heated in the evaporator  18  mentioned above, and the vapor is overheated accordingly in the downstream superheater  17  before it is returned to one of the two reactors  5 . 1 ,  5 . 2  of the reformer  5  via a respective valve  21  for water, i.e. steam. The hydrogen that is produced during reformation is fed to the mixer  11  via a hydrogen duct  4  and a condenser  4 . 1 . The oxygen generated during hydrogen generation is carried off into the environment via a waste gate  5 . 3 . 
         [0035]    In order to achieve the temperatures required in the respective reactor  5 . 1 ,  5 . 2  or in the reformer  5 , respectively, the respective reactor  5 . 1 ,  5 . 2  additionally comprises heating means  7 . 1 ,  7 . 2  that are also supplied with the air-gas mixture fed to the gas engine  1 . For this purpose, the fuel duct  12  comprises a fuel valve  12 . 3  via which the required air-gas mixture is supplied via a fuel duct  13  and an air-gas valve  13 . 1  to the respective reactor  5 . 1 ,  5 . 2  or the respective heating means  7 . 1 ,  7 . 2 . The Co2 exhaust gas that is produced when operating the respective heating means  7 . 1 ,  7 . 2  is carried off via the waste gate  5 . 3 . 
         [0036]    In addition, the gas engine  1  comprises a cooling circuit  24  with a cooling water heat exchanger  24 . 1  for cooling the gas engine  1 . The cooling circuit  24  is also connected to an oil cooling exchanger  25 . 
         [0037]    According to the functional diagram shown in  FIG. 2 , the compressor  8  is driven by an electric motor  10 . The connected exhaust gas turbine  2  as shown in  FIG. 1  is eliminated. For this, the exhaust gas, when it enters the reformer  5 , has a temperature that is 100° C. to 150° C. higher. This higher temperature serves improved operation of the reformer  5  or the respective reactor  5 . 1 ,  5 . 2  in such that the heating means  7 . 1 ,  7 . 2  have to generate less heating output. 
         [0038]    Alternatively, there is an exhaust gas turbine  15  positioned downstream to the reformer  5  with a connected generator  15 . 1  for generating power. This power can be used for further heating means connected to the reformer  5  or the superheater  17  or the evaporator  18 , for example. 
         [0039]    In addition, there is a mixing section  9  within the hydrogen duct  4  in which ambient air or gas is admixed to the hydrogen via an air port  9 . 1  and a gas-port  9 . 2  to obtain a hydrogen-gas or a hydrogen-gas-air mixture the combustion chamber  1 . 1  is loaded with. 
         [0040]    The schematic diagram in  FIG. 3  shows the supply chain of a spark-ignited gas engine  1  with a gas converter. 
         [0041]    Starting from the gas mixer  11  at which the ambient air is added via the air port  11 . 1  and mixed with the combustion gas, provided via the gas duct  13 , the fuel duct  12  is conducted via the compressor  8  and the fuel cooler  12 . 2  to the spark-ignited gas engine  1  or to a combustion chamber  1 . 1  of the spark-ignited gas engine  1 . The throttle valve  14  that is controlled based on the output of the spark-ignited gas engine  1  is provided in this fuel duct  12  immediately upstream of the spark-ignited gas engine  1 . 
         [0042]    The compressor  8  is driven by an electric motor  10 . Therefore, there is no need for a connected exhaust gas turbine. The exhaust gas, when it enters a reformer  3  described below, has a temperature that is 100° C. to 150° C. higher as in case of an exhaust gas turbine. This higher temperature contributes to the enhanced operation of the reformer  3 . 
         [0043]    The spark-ignited gas engine  1  comprises the exhaust gas duct  6 , in which the reformer  3  for gas is provided downstream to the spark-ignited gas engine  1 . The heat of the exhaust gas is in part dissipated to the reformer  3  via a heat exchanger not shown here. 
         [0044]    Downstream to the reformer  3 , the exhaust gas turbine  15  is provided with a generator  15 . 1  coupled to it. Further expansion of the exhaust gas generates electricity that can also be used for the motor  10 . 
         [0045]    The exhaust gas turbine  15  is followed by the heat exchanger or superheater  17  and the evaporator  18  for a water circuit  19  described below. The exhaust gas heat exchanger  20  is provided downstream before the exhaust gas is carried off to the exhaust system not shown here. 
         [0046]    The water circuit or water duct  19  with the water port  19 . 1  is provided for supplying the reformer  3  with water vapor for producing reform gas. First, the water carried in it is preheated by the water heat exchanger  12 . 1  coupled to the fuel duct  12 , wherein the heat is taken from the compressed exhaust gas-air mixture. Then the water is heated in the evaporator  18  mentioned above, and the vapor is overheated accordingly in the downstream superheater  17  before it is discharged into the reformer  3 . 
         [0047]    A gas-steam mixing point  13 . 2  for adding combustion gas to the water vapor is provided between the evaporator  18  and the superheater  19 . The mixing point  13 . 2  is connected to a gas duct  13  via the gas valve  13 . 1  for gas. 
         [0048]    The reform gas that is produced during reformation can be fed to the mixer  11 , and thus to the air-gas mixture, for combustion in the spark-ignited gas engine  1  via a reform gas duct  4  and a condenser  4 . 1 . 
         [0049]    There is a mixing section  9  within the reform gas duct  4  with a air port  9 . 1  and a gas port  9 . 2  which allows mixing combustion gas and/or air to the reform gas before this mixture is injected into the combustion chamber  1 . 1 .