DE10346983B4 - Method and a device for controlling a fuel-air mixture of an internal combustion engine operated with gaseous fuel - Google Patents

Abstract

Method for controlling a fuel-air mixture of an internal combustion engine operated with gaseous fuel as a function of a respective operating state, in which the fuel is mixed in a gas-air mixer with the intake air sucked by the internal combustion engine (1) and the internal combustion engine (1) is supplied , characterized in that a venturi mixer (2) is used as the gas-air mixer, that at the gas-air mixer (2) a the air mass flow passing through this corresponding actual pressure difference .DELTA.p _is measured and with a for the respective operating state the internal combustion engine (1) predetermined target pressure difference Ap _{is to} be compared, that the target pressure difference Ap _{is to} be set in accordance with a power requirement of the internal combustion engine such that the target pressure difference Ap _will continue p _abs (a function of an absolute pressure at the venturi mixer 2), in particular in response to an absolute pressure p _{abs of} the supplied Combustion air and _air of the supplied combustion air is predetermined in dependence on a temperature T, and that a mixing ratio and / or a mass flow of the fuel-air mixture in the sense of an approximation of the actual pressure difference Dp _and the target pressure difference Ap _{is to} be set.

Description

The The invention relates to a method and a device for regulation a fuel-air mixture of a gaseous fuel-powered internal combustion engine dependent on from the respective operating state, wherein the gaseous fuel in a gas-air mixer, in particular a venturi mixer, mixed with sucked by the engine air and the Internal combustion engine supplied becomes.

With gaseous Fuel-powered internal combustion engines, called gas engines for short in big Number in the field of stationary Energy conversion used. These are fueled operated under atmospheric conditions gaseous is.

In order to it in the engine to a combustion, d. H. Oxidation of the fuel comes, the fuel with a known, dependent on its type ratio with Air from the environment can be mixed. This happens with motors in size up to one usable mechanical power of about 3000 kW usually outside of the combustion chamber with the aid of a gas mixer (Venturi gas mixer). The gas mixer uses its geometry and known physical laws, around the gaseous Fuel and the air sucked in by the engine in one of the mass flow (Flow) largely independent, constant ratio to mix with each other. This mixture is then used to burn the engine fed.

by virtue of known chemical-physical laws has the composition of the gas-air mixture has a significant influence on the properties such as power, efficiency and emission of air pollutants, such as nitrogen oxides, carbon monoxide and unburned Hydrocarbons. To these properties in the desired It is known to affect the mixing ratio of Gas and air with the help of external interference depending on engine operating variables such as For example, the engine power changed specifically.

From the DE 38 87 609 T2 is known a control device for a venturi carburetor of a gas engine, in which for the purpose of a load-dependent control of the fuel-air mixture in the Venturi tube a the air mass flow passing through this representative pressure difference and in a gas pressure regulator on mechanical ways to adjust the Gaszumessung is used. Furthermore, from the DE 693 06 056 T2 a control system for adjusting the air-fuel ratio of a gas engine is known in which calculated from a number of engine parameters, a target value of the gas-air ratio in the manner of an engine identifier and with a measured actual value for the gas-air ratio is compared. From a measured at the gas supply line, the mass flow of the gas supplied pressure difference and the gas-air ratio, in turn, the mass flow of the combustion air to be supplied to the engine is calculated net. Because of the measurement and calculation of the volume flows, this system is complex and can be inaccurate.

From the AT 384 279 B it is known to be known in the intake line to detect the actual pressure of the gas-air mixture and to compare with a predetermined for the respective operating condition of the engine target pressure. Furthermore, the engine power is detected. A power demand is assigned a target pressure of the gas-air mixture. Wear-related engine modifications or calorific value changes can not be taken into account with this control method.

The The object of the invention is to provide a method and device for regulating a fuel-air mixture of a gaseous fuel operated Specify internal combustion engine, with a little effort an accurate Regulation of the fuel-air mixture depending on the operating state the internal combustion engine possible is.

The The object is achieved by a method having the features of the claim 1 and by a device having the features of claim 5 solved.

advantageous embodiments and further developments of the invention are specified in the respective subclaims.

The invention provides a method for controlling a fuel-air mixture of an internal combustion engine operated with gaseous fuel as a function of the respective operating state, in which the fuel in a gas-air mixer, in particular a Venturi mixer with air sucked by the internal combustion engine mixed and the internal combustion engine is supplied. According to the invention, it is provided that an actual pressure difference Δp corresponding to the air mass flow passing through the mixer _is removed and compared with a desired pressure difference Δp _soll predetermined for the respective operating state of the internal combustion engine, and that the mixing ratio and / or the mass flow of the fuel Air mixture in the sense of an equalization of actual pressure difference .DELTA.p _is and target pressure difference .DELTA.p _{soll is} set.

Preferably, the desired pressure difference Δp _{soll is} predetermined as a function of the power requirement of the internal combustion engine.

According to a preferred embodiment of the invention, it is provided that the desired pressure difference Δp _{soll is provided} as a function of the absolute pressure p _abs at the Venturi mixer, in particular as a function of the absolute pressure p _{abs of} the supplied combustion air.

According to another preferred embodiment of the invention, it is provided that the desired pressure difference Δp _{soll is} predetermined as a function of the temperature T _{air of} the supplied combustion air.

According to a further preferred embodiment of the invention, it is provided that the desired pressure difference Δp _{soll is} predetermined as a function of one or more of the following parameters: engine speed n, mixture temperature T _Gem .

Preferably, the desired pressure difference Δp _{soll is} read out as a function of the variables mentioned from a stored characteristic field.

According to a preferred embodiment of the invention, it is provided that the approximation of the actual pressure _difference Dp and the target pressure difference Ap _should done by the actual pressure difference Dp _is measured and compared with the predetermined target pressure difference Ap _{is to} be compared, the mass flow _is the supplied to the mixer gaseous fuel in the sense of reducing the difference between actual pressure difference .DELTA.p and target pressure difference Ap _{is to} will change the power delivered by the internal combustion engine is measured, the mass flow of the supplied guide from the mixer to the engine th fuel-air mixture _in the sense of a reduction of the difference between the actual pressure difference Ap and target pressure difference Ap _{is to} be changed, and the aforementioned steps are repeated until the difference between the actual pressure difference Ap _and target pressure difference Dp _to below a predetermined tolerance limit.

Further, the invention provides a device for controlling a fuel-air mixture of an internal combustion engine operated with gaseous fuel in dependence on the respective operating state, with a gas-air mixer, in particular a Venturi mixer for mixing the fuel with the combustion air sucked by the internal combustion engine , And provided with a, in particular electronic, motor controller for adjusting an adjusting the mass flow of the fuel supplied to the mixer actuator in response to the motor controller supplied, representing the engine operating state input variables. According to the invention it is provided that representing a pressure measuring device for detecting a to the mixer passes through the air mass flow at the mixer actual differential pressure Ap _is provided, and that the motor controller for adjusting the fuel-air mixture in the sense of an approximation of the measured actual pressure difference .DELTA.p _is and a predetermined for the respective operating condition of the internal combustion engine target pressure difference Δp _{soll is} provided.

Preferably, the engine controller is provided that the target pressure difference Δp _{soll is set} in dependence on the power requirement of the internal combustion engine.

According to a preferred embodiment of the invention, the engine governor is provided so that the target pressure difference Δp _soll in dependence on the absolute pressure p _abs at the mixer, in particular special depending on the absolute pressure p _{abs of} the supplied combustion air is specified.

According to another preferred embodiment of the invention, the engine governor is provided so that the target pressure difference Δp _{soll is} predetermined as a function of the temperature T _{air of} the supplied combustion air.

According to a further preferred embodiment of the invention, the engine governor is provided for presetting the desired pressure difference Δp _soll as a function of one or more of the following parameters: engine speed n, mixture temperature T _gem .

Preferably, the engine controller is provided with a memory device in which a map is stored, from which the target pressure difference Δp _{soll is} readable in dependence on the variables mentioned.

According to a preferred embodiment of the invention, the engine governor for equalizing the actual pressure difference .DELTA.p _is and the target pressure difference .DELTA.p _soll provided by the actual pressure difference .DELTA.p _is measured and compared with the predetermined desired pressure difference .DELTA.p _soll , the mass flow of the _is mixers supplied gaseous fuel in the sense of reducing the difference between actual pressure difference .DELTA.p and target pressure difference Ap _{is to} be changed, the power delivered by the internal combustion engine is measured, the mass flow of the supplied from the mixer to the engine fuel-air mixture in the sense of _is reduction of the difference between the actual pressure difference Ap and target pressure difference Ap _{is to} be changed, and repeats the above steps until the difference between the actual pressure difference Δp _is and target pressure difference Δp _soll falls below a predetermined tolerance limit.

in the The following will be an embodiment of Invention explained with reference to the drawing.

It shows:

1 a circuit diagram of an embodiment in which method and apparatus for controlling the fuel mixture of a gaseous fuel-powered internal combustion engine with a gas-powered piston engine are realized;

2 a control scheme, based on which the principle for controlling the fuel mixture is to be explained according to the embodiment; and

3 a flowchart of a program according to which the scheme according to the embodiment runs.

In 1 is an internal combustion engine 1 represented in the form of a gas-powered piston engine. This is operated with gaseous fuel, which via a gas supply line 13 fed and in a gas-air mixer 2 mixed with combustion air from the internal combustion engine 1 on an air intake pipe 12 aspirated and then continue on an intake 14 the intake ports of the internal combustion engine 1 is supplied. The gas-air mixer 2 is designed in the manner of a known Venturi mixer, in which the air intake pipe 12 sucked in air in a constriction 2a is accelerated with reduced cross-section with simultaneous pressure reduction. The gas supply line 13 in which an actuator 4 is arranged, opens at the circumference, typi cally over several circumferentially distributed holes in the constriction 2a of the Venturi mixer 2 , The actuator 4 is a flow-limiting valve, which via a coupled actuator drive 4a is adjustable.

In the further course of the intake 14 is the compressor 10b an exhaust gas turbocharger 10 arranged, its turbine 10a in the exhaust tract 15 the internal combustion engine 1 is arranged and driven by the exhaust gas thereof. The compressor 10b the exhaust gas turbocharger 10 downstream is a mixture cooler 11 to cool off the compressor 10b compressed gas-air mixture and a throttle valve 9 that with a throttle valve drive 9a coupled and is adjustable by this.

An electronic engine controller 3 is used to control the air-fuel ratio of the venturi mixer 2 produced gas-air mixture in claims to a number of input variables or input parameters that can be fed from corresponding sensors. The sizes or parameters provided by the sensors represent the respective operating state of the internal combustion engine 1 ,

A pressure measuring device 5 attached to the venturi mixer 2 is provided which supplies an output signal which _is a differential pressure Dp between the air intake pipe 12 before the constriction 2a and the pressure in the narrowing 2a itself reproduces and thus according to Bernoulli's law the mass flow of the air intake pipe 12 represents supplied combustion air. A pressure measuring device 6 gives the absolute pressure p _abs of the air intake pipe 12 sucked combustion air in front of the Venturi mixer 2 again. A temperature measuring device 7 gives the temperature T _air in the air intake pipe 12 sucked combustion air again. Another temperature measuring device 8th in the intake tract 14 in front of the inlets of the internal combustion engine 1 is arranged, generates an output signal T _gem , which is the temperature of the compressor 10b the exhaust gas turbocharger 10 compacted, through the mixture cooler 11 cooled gas-air mixture after passing the throttle 9 and more or less immediately before delivery to the combustion chambers of the internal combustion engine 1 represents. A speed sensor 16 and a power sensor 17 on the internal combustion engine 1 generate respective output signals, the speed n and the output mechanical power P _mech the internal combustion engine 1 represent.

All these variables T _air , p _abs , Δp _is , T _gem , as well as speed n and mechanical power P _mech are via appropriate inputs to the engine governor 3 fed for processing. Outputs of the motor controller 3 are with the throttle valve drive 9a for a throttle position adjustment 9 and with the actuator drive 4a for adjusting the actuator 4 connected. Also located on the engine governor 3 Other inputs and outputs for other signals and functions for operating the internal combustion engine 1 as display and control functions.

In a not specifically shown storage device of the electronic engine controller 3 is stored a multi-dimensional characteristic field, which for each regular operating condition of the internal combustion engine 1 a reference value or setpoint Δp _soll specifies that the air mass flow in the air intake pipe 12 for optimum operation of the internal combustion engine 1 represented under the respective applicable operating conditions.

For controlling the mixing ratio of the Venturi mixer 2 generated gas-air mixture is at the Venturi mixer 2 the pressure difference Ap _is taken off, which on the the air intake pipe 12 supplied air mass flow corresponds, and with the for the respective operating condition of the internal combustion engine 1 predetermined, read from the characteristic field set pressure difference .DELTA.p _{soll is} compared. About the actuator drive 4a becomes the actuator 4 and over the throttle valve drive 4a the throttle 9 adjusted so that the mixing ratio and / or the mass flow of the air and thus the fuel-air mixture in the sense of an approximation of the measured actual pressure difference .DELTA.p _{is set} to the predetermined by the characteristic field desired pressure difference .DELTA.p _soll .

The predetermined pressure difference Δp _soll specified in the characteristic field is primarily dependent on that of the power sensor 17 measured power demand P _mech and from the speed sensor 16 measured speed n of the internal combustion engine 1 , This gives, so to speak, the "coarse adjustment" of the setpoint pressure difference Δp _soll stored in the characteristic field. The other parameters that the electronic engine controller 3 are supplied as input variables, namely at the pressure measuring device 6 measured absolute pressure p _{abs of} the intake air at the temperature measuring device 7 measured temperature T _air thereof, as well as by the temperature measuring device 8th Measured mixture temperature T _Gem additionally provide, as it were, the "fine adjustment" of the desired pressure difference Δp _soll in the characteristic field.

The approximation of the pressure measuring device 5 measured actual pressure difference .DELTA.p _is and from the characteristic field of the electronic engine controller 3 in dependence on said input parameters read target pressure difference Ap _{is to} carried out in such a manner that the actual pressure difference Dp _is measured and compared with the predetermined target pressure difference Ap is compared _to the mass flow of the venturi mixer 2 via the gas supply line 13 supplied gaseous fuel by means of fuel through the drive 4a controlled actuator 4 _in the sense of a reduction of the difference between the actual pressure difference Ap and target pressure difference Ap is changed _to that of the internal combustion engine 1 delivered power through the power sensor 17 is measured, the mass flow of the Venturi mixer 2 over the intake tract 14 supplied gas-air mixture by the drive 9a driven throttle 9 _and in terms of a further reduction of the difference between actual pressure difference .DELTA.p target pressure difference Ap _{is to} be changed, and the aforementioned steps are repeated until the difference between the measured actual pressure difference _is Ap and the predetermined target pressure difference Ap _{should be} smaller than is a predetermined tolerance limit.

When a deviation between the actual pressure difference Dp _and the target pressure difference Ap is so _to the venturi mixer 2 supplied gas volume by means of the actuator 4 changed. As a result, the composition of the internal combustion engine also changes 1 supplied gas-air mixture, which in turn is a change of the internal combustion engine 1 delivered power P _mech . In order to keep an externally specified nominal power P _mech constant, is now again by means of the motor controller 3 the position of the throttle 9 and thus that of the internal combustion engine 1 mixture supplied amount varies, in turn, a change in the intake air quantity and hence a change in the measured differential pressure Ap _is at the gas-air mixer 2 entails.

The described process is repeated until the measured pressure difference Ap _is Ap and the nominal difference _should match from the map or below a predetermined tolerance limit. Because for a certain power demand P _mech a clear relationship between the by the actuator 4 controlled amount of gas supplied and that through the throttle 9 indirectly via the total amount of the mixture controlled amount of the air intake pipe 12 sucked in air, ie there is only a correct mixing ratio of the gas-air mixture at the Venturi mixer 2 If optimal operation is to take place for the operating state defined by said operating parameters, it is possible to regulate the fuel mixture in the manner mentioned.

2 shows a control scheme of the regulation of the fuel-air mixture. A deviation of the measured actual power from the specified target power ( 210 ) leads to a change in the position of the throttle valve. A particular throttle position means the flow rate of an actual air amount and an actual gas amount. A deviation of the Venturi mixer 2 measured actual pressure difference .DELTA.p _is of the through the map of the engine controller 3 predetermined target pressure difference Dp _to ( 230 ) leads to a change in the target gas quantity to be supplied, which deviates from the actually supplied gas quantity ( 220 ) again causes a change in the actual power.

3 Finally, a flowchart for a program as it can be used to control the fuel-air mixture according to an embodiment of the invention. In step 302 becomes a target power for that of the internal combustion engine 1 delivered power P _mech specified. In step 305 is the actually delivered actual power P _mech by means of the power _sensor 17 measured. In step 310 a comparison is made between the target power and the actual power. Insists Difference between the two, done in step 315 a change in the position of the throttle 9 , which causes a change of air quantity and gas quantity, step 320 , Then in step 322 using the map, a calculation of the desired pressure difference Δp _soll . Was in step 310 If the target power and the actual power match, this calculation is made in step 322 directly bypassing the steps 315 and 320 , In step 325 a measurement of the actual pressure difference Δp _{is made} at the Venturi mixer 2 , In step 330 Δp _soll and Δp _are compared. In case of deviation, a change takes place via the gas supply line 13 supplied amount of gas by means of the actuator 4 and then a return to step 305 If there is no deviation, the return is from step 330 Immediately to measure the actual power in step 305 ,

The control algorithms described above are examples, the control can of course be done in a different manner, with the aim of the pressure differences .DELTA.p _soll and .DELTA.p _{is to be} equalized.

Claims (8)

Method for controlling a fuel-air mixture of a gaseous fuel-operated internal combustion engine as a function of a respective operating state, in which the fuel in a gas-air mixer with the internal combustion engine ( 1 ) sucked combustion air mixed and the internal combustion engine ( 1 ), characterized in that the gas-air mixer is a Venturi mixer ( 2 ) is used on the gas-air mixer ( 2 ) an actual air pressure corresponding to this passing through the air pressure difference .DELTA.p _is measured and with a for the respective operating state of the internal combustion engine ( 1 It _is compared that the target pressure difference Δp _{soll is} predetermined as a function of a power requirement of the internal combustion engine, that the target pressure difference Δp _soll further in dependence on an absolute pressure p _abs at the Venturi mixer ( 2 ), in particular as a function of an absolute pressure p _{abs of} the supplied combustion air and as a function of a temperature T _{air of} the supplied combustion air is predetermined, and that a mixing ratio and / or a mass flow of the fuel-air mixture in the sense of an approximation of the actual pressure difference .DELTA.p _is and the target pressure difference .DELTA.p _{soll is} set. Method according to Claim 1, characterized in that the desired pressure difference Δp _{soll is} predetermined as a function of the following parameters: engine speed n, mixture temperature T _Gem . A method according to claim 1 or 2, characterized in that the desired pressure difference Δp _{soll is} read out as a function of said variables from a stored map. Method according to one of claims 1 to 3, characterized in that the approximation of the actual pressure _difference Dp and the target pressure difference Ap _should done by the actual pressure difference Dp _is measured and compared with the predetermined target pressure difference Ap _{is to} be compared, the mass flow of the mixer ( 2 _Is) supplied gaseous fuel in the sense of reducing the difference between actual pressure difference .DELTA.p and target pressure difference Ap is changed _to one (of the internal combustion engine 1 ) is measured, the mass flow of the mixer ( 2 ) to the internal combustion engine ( 1 _Is) supplied to the fuel-air mixture in the sense of reducing the difference between actual pressure difference .DELTA.p and target pressure difference Ap _{is to} be changed, and the aforementioned steps are repeated until the difference between the actual pressure _difference Ap and target pressure difference Ap _{is to} falls below a predetermined tolerance limit. Device for controlling the fuel-air mixture of a gaseous fuel-operated internal combustion engine ( 1 ) depending on a respective operating state, with a gas-air mixer for mixing the fuel with the engine ( 1 ) sucked combustion air, and with an electronic engine governor ( 3 ) for adjusting a mass flow of the mixer ( 2 ) supplied fuel limiting actuator ( 4 ) in dependence on the engine governor ( 3 ), the respective operating state of the internal combustion engine representing input variables, characterized in that the gas-air mixer is a Venturi mixer ( 2 ) is that on the gas-air mixer ( 2 ) a pressure measuring device ( 5 ) for detecting a the the mixer ( 2 ) passing through the air mass flow representing actual differential pressure .DELTA.p _is provided that the engine governor ( 3 ) _Is for setting the air-fuel mixture in the sense of an approximation of the measured actual pressure difference Ap and one (for the respective operating state of the internal combustion engine 1 ) predetermined target pressure difference Ap _is intended that the engine governor ( 3 ) is provided so that the target pressure difference Δp _{soll is} specified as a function of a power requirement of the internal combustion engine that the engine governor ( 3 ) is provided so that the desired pressure difference Δp _soll in dependence on the absolute pressure p _abs at the gas-air mixer ( 2 ), in particular as a function of an absolute pressure p _{abs of} the supplied combustion air and in dependence on a temperature T _{air of} the supplied combustion air is specified. Device according to claim 5, characterized in that the engine governor ( 3 ) It can be seen that the target pressure difference Δp _{soll is} predefined as a function of the following parameters: engine speed n, mixture temperature T _gem . Device according to claim 5 or 6, characterized in that the engine governor ( 3 ) is provided with a memory device in which a map is stored, from which the target pressure difference Ap _{should be} readable in dependence on the variables mentioned. Device according to one of claims 5 to 7, characterized in that the engine governor ( 3 ) _Is .DELTA.p the approximation of the actual pressure difference and the target pressure difference Ap _{is to} be provided by the actual pressure _difference Ap measured and compared with the predetermined target pressure difference Ap _{is to} be compared, a mass flow of the gas-air mixer ( 2 _Is) supplied gaseous fuel in the sense of reducing the difference between actual pressure difference .DELTA.p and target pressure difference Ap is changed _to one (of the internal combustion engine 1 ) is measured, a mass flow of the mixer ( 2 ) to the internal combustion engine ( 1 _Is) supplied to the fuel-air mixture in the sense of reducing the difference between actual pressure difference .DELTA.p and target pressure difference Ap _{is to} be changed, and the aforementioned steps are repeated until the difference between the actual pressure _difference Ap and target pressure difference Ap _{is to} falls below a predetermined tolerance limit.