The present application is a 371 of International application PCT/EP2010/003608, filed Jun. 16, 2010, which claims priority of DE 10 2009 033 082.8, filed Jul. 3, 2009, the priority of these applications is hereby claimed and these applications are incorporated herein by reference.
The invention concerns a method for automatically controlling a gas engine, in which both a fuel volume as a fraction of an air/fuel mixture is determined as a function of a set volume flow and a mixture pressure of the air/fuel mixture in the intake manifold upstream of the intake valves of the gas engine is determined as a function of a set volume flow.
Gas engines are often used as power plants for emergency generators, standby-ready units, or combined heat and power (CHP) installations. In these applications, the gas engine is operated at a combustion air ratio of, for example, 1.7, i.e., in a lean operation with air excess. Typically, the gas engine has a gas throttle valve for setting the gas fraction in the air/fuel mixture, a mixer for mixing the combustible gas with the air, a compressor as part of an exhaust gas turbocharger, a cooler and a mixture throttle valve. The mixture throttle valve serves to set the filling of the working cylinders and thus the torque of the gas engine. The filling of the working cylinders in turn is computed from the pressure of the air/fuel mixture with other parameters otherwise held constant, for example, at constant intake manifold temperature, at constant engine speed, and at constant combustion air ratio.
DE 10 2007 045 195 B3 discloses an automatic control method for a stationary gas engine with a generator, in which a speed controller uses a speed control deviation to determine a controller torque as a correcting variable. The controller torque in turn and the actual speed are used to determine a set volume flow by means of an efficiency input-output map. The set volume flow is both the input variable for controlling the gas throttle valve and the input variable for setting the mixture pressure in the intake manifold. The central element is the parallel control of the two control elements as a function of the same actuating variable, in this case, the set volume flow. The mixture pressure in the intake manifold is set via a cascade closed-loop pressure control system for the intake manifold. In this intake manifold closed-loop control system, the set intake manifold pressure represents the reference input and the measured intake manifold pressure is the controlled variable. The gas motor and the generator then constitute the controlled system. The set intake manifold pressure is computed from the set volume flow, taking into account the actual speed of the gas engine, the temperature in the intake manifold, and constants. Constant values include, for example, the combustion air ratio and a stoichiometric air requirement. The method we have been describing has been found to be effective in actual practice. However, the effect of different gas grades (volume fraction) within the same family of gases on the emission values remains critical.
DE 699 26 036 T2 also describes a method for automatically controlling a gas engine, in which a control signal for controlling the mixture throttle valve is computed from the speed control deviation by a PID controller. A correction value is determined, likewise as a function of the speed control deviation, and is then used to change the control signal for the gas throttle valve. However, the objective of the method is to suppress engine speed oscillations that develop after a change in the set engine speed.
Proceeding from an automatic control method with parallel control of the gas throttle valve and mixture throttle valve and cascade closed-loop pressure control system for the intake manifold, the objective of the invention is to minimize the effect of a different gas grade on the automatic control method.
The effect of a different gas grade is minimized by computing a deviation of the controller torque, i.e., the correcting variable of the speed controller, from the generator torque, and the set intake manifold pressure is corrected on the basis of this deviation. The deviation is a measure of the amount by which the energy content of the gas actually being used, for example, biogas, deviates from the energy content of the reference gas. The gas engine is calibrated to this reference gas on a test bench, with natural gas being used as the reference gas. For the gas being used on site, which occurs as a mixed gas comprising gases of a known family of gases, the fuel parameters must be known. These are the calorific value, the stoichiometric air requirement, and the density. The fuel parameters are then stored in the system as fixed values. The speed controller, by which the controller torque is computed, uses natural gas as the reference. The set intake manifold pressure is corrected by computing a corrected value from corrected input variables, namely a corrected set volume flow, a corrected combustion air ratio, and a corrected air requirement.
The corrected set volume flow is computed by multiplying the set volume flow by the square of the deviation. The corrected combustion air ratio is computed from a reference combustion air ratio and the deviation, where the reference combustion air ratio is computed by an input-output map as a function of the controller torque and the actual speed of the gas engine. The corrected air requirement is determined by a recursive method, likewise as a function of the deviation.
The use of the method of the invention offers the advantage that despite variation of the gas grade, the power output of the gas engine remains unchanged. Therefore, a gas engine that is being operated with, for example, biogas, has the same power output as a gas engine operated with natural gas. If the volume fraction of the combustible gas varies, the set intake manifold pressure is adjusted by the method of the invention, so that the power output remains unchanged in this case as well. Therefore, the volume fraction does not have to be known. As a consequence, the pollutant emissions are the same as for the reference gas. Since the method is based on the same sensor signals that are already being used, no modification or supplementation of the sensor technology or of the engine control unit is necessary. Therefore, gas engines that have already been delivered can be retrofitted with the method of the invention without any problem, for example, during maintenance. Compared to automatic control of the combustion air ratio, parallel control of the gas throttle valve and the mixture throttle valves as a function of the same actuating variable offers the advantage of a reduced response time and more precise transient oscillation with improved adjustability of the total system. As a result, smooth automatic control of the engine output is obtained.
The drawings show a preferred embodiment of the invention.
The mode of operation of the gas engine 1 is determined by an electronic engine control unit 14 (GECU). The electronic engine control unit 14 contains the usual components of a microcomputer system, for example, a microprocessor, interface adapters, buffers and memory components (EEPROM, RAM). Operating characteristics that are relevant to the operation of the gas engine 1 are applied in the memory components in the form of input-output maps/characteristic curves. The electronic engine control unit 14 uses these to compute the output variables from the input variables. The following input variables are shown in
The system has the following general functionality: A fuel volume flow supplied to the mixer 7 is adjusted by the position of the gas throttle valve 6. The position of the A-side mixture throttle valve 10 defines an A-side mixture volume and thus the A-side intake manifold pressure pRRA in the A-side intake manifold 12 upstream of the intake valves of the gas engine 1. The B-side intake manifold pressure pRRB upstream of the intake valves of the gas engine 1 is determined by the B-side mixture throttle valve 11.
The set speed nM(SL), for example, 1500 rpm, which corresponds to a frequency of 50 Hz, is preset by the system controller 15 as the desired output. At a point A, a speed control deviation dn is computed from the set speed nM(SL) and the actual speed mM(IST). A speed controller 16 in turn uses the speed control deviation dn to compute the controller torque MR as a correcting variable. In practice, the speed controller 16 is realized as a PIDT1 controller. The controller torque MR is the first input variable of a consumption input-output map 17. The second input variable is the actual speed nM(IST). A set volume flow V(SL) is determined by the consumption input-output map 17 as a function of the two input variables. The set volume flow V(SL) is the input variable for both a volume adjustment unit 31 and a mixture quantity unit 18. The set volume flow V(SL) is adjusted by the volume adjustment unit 31 at least as a function of the generator torque MGen. The output variable of the volume adjustment unit 31 is an adjusted set volume flow Va(SL), which is the input variable of the gas throttle valve 6. An electronic processing unit integrated in the gas throttle valve 6 assigns to the value of the adjusted set volume flow Va(SL) a corresponding cross-sectional area and a corresponding angle. A fuel volume flow as a gas fraction of the air/fuel mixture is set by the gas throttle valve 6.
The mixture quantity unit 18 combines the computation of the set intake manifold pressure and a cascade closed-loop pressure control system for the intake manifold. The conversion of the set volume flow V(SL) in the mixture quantity unit 18 is shown in
The block diagram in
A reference combustion-air ratio LAMr is assigned to the controller torque MR and the actual speed nM(IST) by an input-output map 21. The reference combustion-air ratio LAMr is the first input variable of a correction unit 22. The second input variable is a reference air requirement LMINr, which in the present case is constant. The reference air requirement LMINr represents the stoichiometric air requirement for the complete combustion of one cubic meter of the reference gas. The third input variable is the deviation yS. The correction unit 22 uses the following relation to compute the corrected combustion air ratio LAMk:
LAMk=LAMr+[(1−ys2)/LMINr] (1)
The output variable of the correction unit 22, i.e., the corrected combustion air ratio LAMk, is the first corrected input variable of a computing unit 25 for determining the set intake manifold pressure pRR(SL). A correction unit 23 computes a corrected air requirement LMINk as a function of the deviation yS. The correction unit 23 is shown in
pRR(SL)=2·yS2·T1·p0·[1+LAMk·LMINk]·Vk(SL)/[LG·VH·nM(IST)·T0] (2)
where yS is the deviation, T1 is the temperature measured in the intake manifold, p0 is the standard air pressure at mean sea level (1013 hPa), LAMk is the corrected combustion air ratio, LMINk is the corrected air requirement, Vk(SL) is the corrected set volume flow, LG is the volumetric efficiency, VH is the stroke volume of the cylinder, nM(IST) is the actual speed of the gas engine, and T0 is standard temperature (273.15K). In the drawing (
xS={HUO−[HUr·ETA·(1/yS2)]}/[HUO−HUU] (3)
where xS is the mixing parameter. The constant HUO represents the greatest calorific value to be adopted for the fuel that is actually being used, for example, biogas. The constant HUU represents the smallest calorific value to be adopted for the fuel that is actually being used. The constant HUr represents the calorific value of the reference fuel, here: natural gas. To determine the constants HUO and HUU, it is necessary to know the provenience and the family of gases to which the fuels belong. These constants are not varied in the operation of the gas engine. The mixing parameter xS is then supplied to an efficiency input-output map 28, which determines a new efficiency ratio ETA as a function of the mixing parameter xS and the ignition point ZZP. The efficiency ratio ETA can be obtained as the ratio of an actual efficiency to a reference efficiency determined on the test bench with the use of the reference fuel (natural gas). The new efficiency ratio ETA is then fed back to the computing unit 27, in which the mixing parameter xS is then recomputed from the new efficiency ratio ETA by formula (3). The recursive loop is repeatedly passed through until a termination criterion is recognized. A termination criterion occurs when the recursive loop 26 has been passed through i times. Alternatively, a termination criterion is present when the difference between two recursively computed mixing parameters is less than a limit. When the termination criterion has been recognized, the last mixing parameter computed is set as the valid value. The recursive loop 26 is followed by a filter 29, typically a PT1 filter, which filters the mixing parameter that has been set as valid. A computing unit 30 uses the filtered mixing parameter xSF and constant values K to compute the corrected air requirement LMINk, which is further processed in the functional block 19 shown in
LMINk=xSF·LMINu+(1−xSF)·LMINo (4)
where LMINu is the minimum air requirement of the fuel that is actually used and LMINo is the maximum air requirement of the fuel that is actually used, which are the constants. The mixing parameter xSF is further processed internally, for example, for adjustment of the fuel density and the ignition point.
The invention was described with reference to a gas engine that powers a generator. Instead of a generator, a standby-ready unit or a combined heat and power (CHP) installation can also be used. In this case, the generator torque MGen then corresponds to the torque delivered by, for example, the standby-ready unit.
Number | Date | Country | Kind |
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10 2009 033 082 | Jul 2009 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2010/003608 | 6/16/2010 | WO | 00 | 1/3/2012 |
Publishing Document | Publishing Date | Country | Kind |
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WO2011/000474 | 1/6/2011 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
4854283 | Kiyono | Aug 1989 | A |
5463993 | Livshits | Nov 1995 | A |
5577474 | Livshiz et al. | Nov 1996 | A |
5775304 | Kono | Jul 1998 | A |
6021755 | Maddock et al. | Feb 2000 | A |
6340005 | Keast | Jan 2002 | B1 |
6522024 | Takaoka et al. | Feb 2003 | B1 |
6945221 | Baeuerle | Sep 2005 | B2 |
6959691 | Ueda | Nov 2005 | B2 |
7082924 | Ruedin | Aug 2006 | B1 |
7150264 | Kobayashi et al. | Dec 2006 | B2 |
7174250 | Barba | Feb 2007 | B2 |
7263425 | Bleile | Aug 2007 | B2 |
7650222 | Shiraishi | Jan 2010 | B2 |
7654247 | Shiraishi | Feb 2010 | B2 |
7747378 | Shiraishi | Jun 2010 | B2 |
7778761 | Böckhoff et al. | Aug 2010 | B2 |
7801668 | Ito | Sep 2010 | B2 |
7813865 | Martin | Oct 2010 | B2 |
8306722 | Whitney et al. | Nov 2012 | B2 |
8340885 | Baldauf et al. | Dec 2012 | B2 |
8364381 | Kar et al. | Jan 2013 | B2 |
20040024518 | Boley | Feb 2004 | A1 |
20080140298 | Morimoto et al. | Jun 2008 | A1 |
20080162014 | Shinohara et al. | Jul 2008 | A1 |
20090076709 | Shiraishi | Mar 2009 | A1 |
20090076712 | Bockhoff et al. | Mar 2009 | A1 |
20090192698 | Smuda | Jul 2009 | A1 |
20090228186 | Bischoff et al. | Sep 2009 | A1 |
20100242937 | Baldauf | Sep 2010 | A1 |
20100256890 | Baldauf | Oct 2010 | A1 |
20120109499 | Klaser-Jenewein | May 2012 | A1 |
Number | Date | Country |
---|---|---|
102007056623 | Oct 2004 | DE |
69926036 | Apr 2006 | DE |
102007045195 | Mar 2009 | DE |
102007045195 | Mar 2009 | DE |
102007045195 | Mar 2009 | DE |
102007056623 | May 2009 | DE |
102008006708 | Aug 2009 | DE |
2039916 | Feb 2008 | EP |
Number | Date | Country | |
---|---|---|---|
20120109499 A1 | May 2012 | US |