Patent Publication Number: US-8527179-B2

Title: Method and device for measuring the emissions of engines

Description:
The invention pertains to a method and a device for determining specific nitrogen oxide emissions of an internal combustion engine. 
     In the course of the ongoing climate debate, climate protection rules and regulations that specify limits on exhaust gas emissions for individual means of transportation have been established in many areas of passenger and freight traffic. These limits are usually related to a certain value such as, e.g., km, kWh or the like. 
     Such limits are also increasingly being imposed on rail vehicles, as well as on waterborne traffic. For the maritime transport sector, for example, the Marpol Convention stipulates in Annex VI that the exhaust emissions of a ship be set in relation to the engine power, i.e., in the form of, e.g., grams of pollutant per kilowatt of power and operating hour. Currently, the emissions of sulfur oxides (SO x ) and nitrogen oxides (NO x ) are regulated. 
     Other sectors such as, e.g., stationary engines for various applications are subject to similar regulations or comparable directives and limits are currently being prepared. 
     Compliance with limits is usually verified while the engines are mounted on corresponding test stands during type approvals, design tests, etc. On these test stands, the complete measuring technology is available in the form of stationary measuring devices because the test stand is, after all, specifically designed for verifying the corresponding limits, parameters, factors, etc. Since there is an increasing number of instances in which it is necessary or required to verify compliance with limits in the field, i.e., during the actual operation of engines, e.g., in a locomotive or on a ship, there is a need for reliable and mobile measuring systems that make it possible to quickly and easily verify on-site whether the internal combustion engines are in compliance with the respective limits. However, it is frequently difficult or impossible to also carry out a direct on-site measurement of all operating parameters for determining the emission values that are measured on a test stand. For example, it is frequently impossible to determine the instantaneous power output or the current fuel consumption without complicated alterations or modifications of the machine itself. 
     The invention therefore is based on the objective of developing a method and a device for easily determining specific exhaust gas performance figures of an internal combustion engine in real time and under realistic conditions. 
     According to the invention, this objective is attained in that the emission mass flow or a specific exhaust gas component mass flow is determined as a first operating parameter and the engine power output is determined as a second operating parameter, in that the specific exhaust gas component mass flow and the engine power output are respectively derived or determined from at least one measured quantity that deviates from the operating parameter, and in that the specific emission (exhaust gas performance figures) is calculated as the quotient of the specific exhaust gas component mass flow and the engine power output. A measured quantity that deviates from an operating parameter refers, in particular, to a measured quantity that physically differs from the operating parameter. The exhaust gas component preferably consists of NO x . However, the method can also be used for other exhaust gas components such as, for example, SO x . 
     Since the operating parameters are derived from measured quantities that can be acquired more easily, it is possible to utilize a method and a measuring system that do not require complicated and costly alterations. Consequently, such a method can be used on different engines at any location and allows a reliable real-time control of the exhaust gas performance figures and/or exhaust gas limits. 
     It is practical to determine the two operating parameters for different load conditions of the engine. If applicable, a summation of the operating parameters is also carried out. 
     It is particularly practical that the operating parameters belonging to a certain load stage are multiplied with weighting factors that are adapted to the intended use of the engine prior to the summation, wherein the weighting factors may be stored, for example, in a table. In this case, it is possible, in particular, to take the individual load stages into consideration to a different degree in the performance figures. For example, a marine diesel engine primarily runs slightly below full load such that the weighting factor may be higher in this case than at idle speed while an automobile is primarily operated at partial load or lower and the pollutant emission therefore can or must be weighted higher in this load range. 
     The specific exhaust gas performance figures is preferably defined as the corrected specific exhaust gas component mass flow per kilowatt of engine power and per operating hour and simply referred to as the specific emission performance figures below. 
     In a first embodiment of the invention, the engine power is determined from the current torque and the engine speed, wherein the torque is determined, for example, by means of a strain gauge on the shaft. 
     According to a second embodiment of the inventive emission performance figures determination, the engine power is calculated from the fuel mass flow and the specific fuel consumption of the engine, wherein the specific fuel consumption is a value that is provided by the manufacturer and indicates, e.g., in the form of a table or diagram, the corresponding fuel consumption at the respective engine power. Due to the determination of the instantaneous fuel consumption, the power can be, e.g., simply read out in the table or interpolated based on the table values. 
     It may occasionally be difficult or impossible to arrange a fuel mass flow sensor on or in the supply lines of the engine, which is why it may be sensible to calculate the fuel mass flow from the exhaust gas mass flow and the stoichiometric air requirement. A simple observation of the reaction equation makes it possible to recalculate the fuel mass flow from the exhaust gas quantity. 
     In this case, the stoichiometric air requirement results from the chemical composition of the fuel, particularly the mass fractions of carbon, hydrogen and, if applicable, sulfur. 
     Since it may also be difficult to measure the exhaust gas mass flow, the fuel mass flow can be recalculated from the combustion air mass flow and the excess air factor. In this case, the excess air factor takes into consideration that not all of the air (oxygen) is required for the combustion and therefore cannot be included in the fuel calculation. 
     The excess air factor is determined from the composition of the exhaust gas in this case, particularly the volume concentration of carbon dioxide CO 2  and, if applicable, CO, as well as, if applicable, hydrocarbons HC. The measuring expenditure can also be reduced in this case by calculating the carbon dioxide fraction from the oxygen volume concentration. 
     The combustion air mass flow can be measured with a hydrometric vane or a similar measuring device. However, it can also be calculated if the air intake of the engine cannot be accessed. 
     For this purpose, the speed, the volumetric displacement and the number of cylinders of the engine, the charge air pressure and the charge air temperature downstream of the intercooler, i.e., prior to the admission into the engine, the ambient temperature, the air pressure and the relative humidity are determined and the combustion air mass flow is calculated therefrom. 
     When using an engine without an intercooler or turbocharger, the corresponding measured values are processed analogously, wherein the intake air replaces the charge air in this case and the intake air temperature and the normal ambient pressure are used instead of the charge air temperature and the charge air pressure. 
     Several options are available for determining the power depending on which types of sensors are available and which locations of the engine are accessible. In the worst-case scenario, it may suffice to carry out a simple oxygen measurement in the exhaust gas by inserting a thin probe through a small opening in the exhaust gas system, as well as to determine the charge air pressure and charge air temperature together with the ambient parameters and the engine speed. All other data can then be calculated from these measured values, the fuel parameters and the known engine data. 
     The determination of the exhaust gas component mass flow, particularly the nitrogen oxide mass flow, can be realized similarly. A direct determination of the mass flow also may be occasionally difficult in this case because it is problematic to carry out the volume flow rate measurement required for this purpose in larger exhaust gas stacks such as, e.g., on ships. 
     Consequently, it is necessary to determine the volume concentration, e.g., of nitrogen oxides, by means of a gas sensor and to calculate the mass flow therefrom. Some commercially available NO x  sensors determine the concentration in dry exhaust gas such that the measuring result is processed with a dry-humid correction factor for further use. 
     Corresponding measuring methods and sensors generally also make it possible to directly carry out a measurement of the O 2 , NO x , SO x  and/or HC concentration on humid exhaust gas. A recalculation into a humid mass flow is no longer required in this case. 
     This dry-humid correction factor is defined by the volume concentration of CO and CO 2 , as well as by the ambient conditions such as the absolute air pressure, the relative humidity and the temperature. 
     The NO x  concentration in humid exhaust gas formed in this way is recalculated into an NO x  mass flow together with the humid exhaust gas mass flow, wherein the exhaust gas mass flow was already measured or determined during the power determination and therefore is already available in the form of a value or can be determined in accordance with the same method. 
     Depending on the application and the specifications, the resulting value of the NO x  mass flow is now processed with a special NO x  weighting factor in order to obtain a value that is comparable, for example, to test stand values of the engine. This weighting factor is determined from the air temperature and the air pressure of the intercooler, as well as the ambient conditions such as the absolute air pressure, the relative humidity and the temperature. 
     Consequently, this method is universally applicable and can be easily carried out, especially in the field. Particularly on a vehicle that is in operation such as, for example, a ship, this makes it possible to realize the measurement of the exhaust gas parameters in the exhaust gas with a simple probe in the vicinity of the engine rather than having to carry out complicated exhaust gas mass flow measurements in the exhaust gas stack. The probe preferably features a flange or the like such that it can be mounted on the stack or the exhaust gas outlet and protrudes into the engine exhaust gases in the mounted position in order to take an exhaust gas sample. 
     The exhaust gas sample is preferably taken with a heated or unheated hose, wherein certain precautions, for example, as described in DE 196 31 002 C2, need to be taken when using an unheated hose in order to prevent a transition of the exhaust gas component into exhaust gas moisture. 
     The real-time determination of the exhaust gas parameters and the exhaust gas performance figures furthermore allows an optimization of the combustion process in the engine because it is possible to observe directly and under realistic operating conditions how changes of the input parameters and engine adjustments affect the exhaust gas concentration and ultimately also influence the fuel consumption. 
     According to one embodiment of the invention, the humid exhaust gas may be abruptly cooled before it comes in contact with the sensors. This can be realized, for example, in a cooling trap or in a gas cooler that is arranged in the flow of the extracted exhaust gas upstream of the sensors. In this case, it is advantageous that the analyzed exhaust gas components are not bound in the humid exhaust gas. 
     In order to easily take the exhaust gas sample for the described method, a device for carrying out the method may be provided with a probe for extracting exhaust gas that features a flange for being mounted on the exhaust gas outlet of the internal combustion engine. Consequently, this probe can be quickly and nondestructively mounted in the exhaust gas flow, for example, in the exhaust gas stack of a ship over an extended period of time and/or without any effort on the part of the personnel. 
     The method is described in greater detail below with reference to the drawings, namely in the form of the exemplary determination of the weighted nitrogen oxide parameter GAS NOx  according to directive Marpol 73/78 Annex VI that is simply referred to as Marpol below. 
    
    
     
       In the drawings: 
         FIG. 1  shows a schematic arrangement for determining the exhaust gas performance figures; 
         FIG. 2  shows a flow chart for determining the weighted nitrogen oxide performance figures; 
         FIG. 3  shows a flow chart of a first method for determining the engine power output; 
         FIG. 4  shows a flow chart of a first method for determining the corrected nitrogen oxide mass flow; 
         FIG. 5  shows a flow chart of a second method for determining the engine power output, and 
         FIG. 6  shows a flow chart of a second method for determining the corrected nitrogen oxide mass flow. 
     
    
    
       FIG. 1  shows a device for determining the nitrogen oxide performance figures that can be used, for example, for carrying out measurements aboard a ship. 
     The central component of the system is a measuring device  30  that is connected to an exhaust gas probe  31  via a hose and that is suitable for measuring the exhaust gas volume concentrations of the exhaust gas components O 2 , CO, CO 2 , NO x , SO 2  and HC, as well as other quantities. For this purpose, the measuring device features a pump that takes in exhaust gas through the probe tip and pumps the exhaust gas through a sensor section in the measuring device. The measuring device has a modular design such that other sensors can be easily inserted into the measuring section in case additional measured values such as, for example, SO x  are required for other or future applications. 
     It furthermore contains corresponding devices for processing the gaseous analyte such as, e.g., filters, a gas drying module, for example, with a gas cooler, etc. If so required, the exhaust gas probe  31  and its hose may feature filters as well (e.g., also on the probe tip) and are designed in such a way that the gas components to be measured are prevented from binding on the surfaces, etc. 
     In another exemplary embodiment, a combination of the probe  30  and the measuring device  31  used as an analyzer is realized in the form of one unit, i.e., without an intermediate hose, and arranged directly on the exhaust gas duct. 
     The measured exhaust gas values  38  are forwarded to a central measured value acquisition device  32 . 
     The device furthermore features measuring devices for ambient parameters  35  and engine parameters  36  that are transmitted to the central measured value acquisition device  32  via radio or cables. These parameters can also be read in, e.g., at an engine management interface. 
     The measurement data in the central measured value acquisition device  32  can be retrieved by at least one computer  33 , on which a suitable program for carrying out the calculation of the performance figures is loaded. If applicable, table data  37  of the engine and fuel manufacturers is also available to the program for the calculation. A corresponding measurement log  34  may be directly output as a result of the calculation. It is also possible to permanently monitor the measurement data with the computer  33  such that a current value of the exhaust gas performance figures can be calculated and displayed at any time. It would also be conceivable to arrange the display directly at the control station or even on the bridge of a ship such that the on-board engineer or the captain can monitor the exhaust gas emissions of the engine at any time. This may make it possible to detect malfunctions of the engine in a timely fashion and to prevent more significant damages. 
       FIG. 2  shows a flow chart of the method for determining the weighted nitrogen oxide parameter GAS NOx    1  that describes the nitrogen oxide mass emission in the exhaust gas per kilowatt of power and operating hour. Consequently, the method includes the determination of the power  2  and of the nitrogen oxide mass flow  3 . The power  2  and the nitrogen oxide mass flow  3  are determined at different load stages of the engine and the values are weighted with a weighting factor  4 . The nitrogen oxide parameter is calculated in accordance with the formula shown in Step  5 : 
     
       
         
           
             
               GAS 
               NOX 
             
             = 
             
               
                 
                   ∑ 
                   
                     i 
                     = 
                     1 
                   
                   n 
                 
                 ⁢ 
                 
                   
                     GNOX 
                     i 
                   
                   · 
                   
                     W 
                     Fi 
                   
                 
               
               
                 
                   ∑ 
                   
                     i 
                     = 
                     1 
                   
                   n 
                 
                 ⁢ 
                 
                   
                     P 
                     i 
                   
                   · 
                   
                     W 
                     Fi 
                   
                 
               
             
           
         
       
     
     The weighting factors  4  take into consideration that an engine is primarily operated in a certain load range depending on the respective application. On ships, this is also dependent on the type of drive. For example, the diesel engine of a diesel-electric drive will always run at full speed such that the voltage being generated has the correct frequency. Consequently, the pollutant emissions of a diesel-electric drive is negligible at slow speeds because the engine is usually not operated in this range. On ships with direct drives, in contrast, the engine speed is reduced when traveling slowly such that the pollutant emissions contribute a portion to the total emissions in this case. 
     In one application, for example, the emissions can be measured with the described method at 10%, 50% and 100% of the full load of the internal combustion engine and inserted into the formula. 
     In another application that needs to comply with other regulations such as, for example, the aforementioned diesel-electric drives, the emissions are only measured, for example, at 100% of the full load of the internal combustion engine and no summation according to the above formula is carried out. 
     In conventional applications, the emissions are measured at three to five load points, but these numbers may also differ depending on the corresponding directives or requirements. 
     The calculation described in Step  5  can also be used for other specific performance figures and would even be suitable for calculating, for example, the customary motor vehicle performance figure of CO 2  emission per kilometer. A weighting of different power stages could also be sensible in this case. 
     The power  2  and the nitrogen oxide mass flow  3  can be determined with different methods. A first method for determining the power is illustrated in  FIG. 3 . 
     In this case, a torque measurement  6  is carried out on the shaft of the engine in order to determine the power  2 . For example, a strain gauge is arranged on the shaft for this purpose and the measured tension is converted into a torque. Along with the speed  7  of the engine, the power  2  can be easily calculated in accordance with the formula P i =T·2π·n, particularly if the shaft parameters are used for converting the measured bridge voltage into the torque. 
     If the engine drives an electric generator, a determination of the power  2  can be alternatively realized by determining the electric power output of the generator, particularly with consideration of the generator efficiency and/or the transmission ratio of a transmission arranged in the drive train between the engine and the generator. 
     However, if the torque  6  cannot be measured, for example, because the shaft is inaccessible and no strain gauge can be attached, the power determination method described in  FIG. 4  does not require a torque measurement and only has simple metrological requirements. 
     In a first step, the intake air mass flow  13  is calculated from the engine speed  7 , the number of cylinders  8 , the volumetric displacement  9 , the charge air pressure  10  and the charge air temperature  11  downstream of the intercooler, as well as the ambient conditions  12  such as the absolute air pressure, the relative humidity and the temperature. 
     In a second step that needs to be carried out simultaneously and under identical conditions, the volume concentration of carbon dioxide  14  and, if applicable, carbon monoxide  15 , as well as, if applicable, hydrocarbons  16 , is measured in the dry exhaust gas. For example, a probe is inserted into the exhaust gas duct of the engine for this purpose such that exhaust gas is drawn into a measuring device by means of said probe and passed over different sensors in this device. 
     Alternatively, the CO 2  volume concentration CO 2  can also be calculated from the oxygen concentration O 2, measured  (in %) and the maximum CO 2  quantity CO 2, max  that can be produced from the fuel, namely in accordance with the formula 
     
       
         
           
             
               CO 
               2 
             
             = 
             
               
                 
                   CO 
                   
                     2 
                     , 
                     max 
                   
                 
                 · 
                 
                   ( 
                   
                     
                       21 
                       ⁢ 
                       % 
                     
                     - 
                     
                       O 
                       
                         2 
                         , 
                         gemessen 
                       
                     
                   
                   ) 
                 
               
               
                 21 
                 ⁢ 
                 % 
               
             
           
         
       
     
     An excess air factor  17  that indicates how much of the intake air was not required for the combustion can be calculated from the three values. 
     A combustion air or exhaust gas mass flow  18  is calculated from the intake air mass flow  13  and the excess air factor  17 . 
     At the same time, the stoichiometric air requirement  19  is calculated from the specific composition of the fuel  20  in another step, wherein the composition is a value provided by the fuel manufacturer. The calculation therefore can also be carried out in advance and the result can be buffered. In this case, the interesting components are the carbon, sulfur and hydrogen fractions in the fuel. 
     The fuel mass flow  21  can be determined based on the combustion air mass flow  18  and the stoichiometric air requirement  19  by observing the reaction equation and the molar mass balance. 
     In a last step, the power  2  of the engine is calculated or interpolated from the fuel mass flow  21  with the specific fuel consumption  22  that is provided by the engine manufacturer in table form. 
       FIG. 5  shows a first method for determining the nitrogen oxide mass flow GNOX that is required for calculating the nitrogen oxide performance figures in addition to the power. One important part of the method is the determination of the nitrogen oxide volume concentration  23  in the dry exhaust gas. This requires a sensor in the exhaust gas flow, wherein this sensor is advantageously arranged in the same measuring device that is also provided, among other things, for measuring the carbon dioxide  14 . In the simplest case, it suffices to install a corresponding sensor module into the gas path of the measuring device for this purpose such that the installation expenditures are very low. 
     The NO x  concentration needs to be converted into the volume concentration in the humid exhaust gas  25  for additional processing with the aid of a dry-humid correction factor  24  that was calculated from the ambient conditions  12  that were already determined during the power determination and the carbon dioxide concentrations  14 ,  15 . 
     The fuel mass flow  26  is measured in a parallel step, for example, by installing an impeller flow meter into the fuel supply line or in a non-invasive fashion by means of clamp-on sensors. The humid exhaust gas mass flow  27  is calculated from the fuel mass flow  26 , as well as the excess air factor  17  and the stoichiometric air requirement  19  that were already calculated during the power determination. 
     The humid NO x  mass flow  28  in the exhaust gas is calculated from the humid exhaust gas mass flow  27  and the NO x  concentration  25  in a next step. 
     However, since the nitrogen oxide performance figures cannot be affected by ambient influences such as the humidity, an NO x  humidity correction factor needs to be calculated in another step from the ambient conditions  12  that were already determined during the power determination, as well as the charge air pressure  10  and the charge air temperature  11  downstream of the intercooler, i.e., prior to the admission into the engine. 
     In a last step, the NO x  mass flow  3  required for determining the nitrogen oxide performance figures is calculated from the humid NO x  mass flow  28  and the NO x  humidity correction factor  29 . 
       FIG. 6  shows another method for determining the NO x  mass flow  3  that can be distinguished merely from the method according to  FIG. 5  with respect to the determination of the fuel mass flow. 
     In this case, the calculated value from the power determination according to  FIG. 4  is used as fuel mass flow  21 . This makes it possible to eliminate a measurement of the fuel mass flow and the method can be significantly simplified because it is usually not possible to subsequently or temporarily arrange a mass flow sensor on an engine. 
     The invention pertains to a method and a device for determining specific emissions as exhaust gas performance figures of an internal combustion engine. The method is characterized in that the emission mass flow that is also referred to as exhaust gas mass flow, particularly the exhaust gas component mass flow  3 , in which the exhaust gas component preferably consists of NO x , is determined as a first operating parameter and the engine power output  2  is determined as a second operating parameter, in that the exhaust gas component mass flow  3  and the engine power output  2  are respectively derived from at least one measured quantity that deviates from the operating parameter, and in that the exhaust gas performance figures are calculated as the quotient of the corrected exhaust gas component mass flow  3  and the engine power output  2 . 
     A method and a device are provided for determining specific emissions as an exhaust gas characteristic of an internal combustion engine. The method is characterized in that the exhaust gas mass flow ( 3 ) is determined as the first operating parameter and the engine power output ( 2 ) as the second operating parameter, the nitrous oxide mass flow ( 3 ) and the engine power output ( 2 ) are derived from a respective measured value that deviates from the operating parameter and the exhaust gas characteristic is calculated as a quotient from the corrected exhaust gas mass flow ( 3 ) and the engine power output ( 2 ).