GB2385433A

GB2385433A - Controlling an internal combustion spark ignited gas engine

Info

Publication number: GB2385433A
Application number: GB0203600A
Authority: GB
Inventors: Charles Gordon Hadfield Holt; Christopher Alan Shore
Original assignee: Heinzmann Co KG Fritz GmbH
Current assignee: Heinzmann Co KG Fritz GmbH
Priority date: 2002-02-15
Filing date: 2002-02-15
Publication date: 2003-08-20
Anticipated expiration: 2022-02-15
Also published as: GB2385433B; GB0203600D0

Abstract

A gas engine is controlled to constant speed even if the gas quality changes. With a calibrated throttle valve 11 and a special calibrated gas-metering block 19 comprising valve 5, temperature sensors 16, 10 and pressure sensors 6, 4, 23, 18, the gas flow and the air-fuel mixture flow are measured. Using these measurements and stored data together with the measured engine power (from kilowatt load sensor 16), the Wobbe index which represents the thermal heat of the gas is calculated. With this information the digital controller 7 positions the throttle valve 11 for sufficient mixture flow to maintain engine speed under changing load and the gas metering block is set for matching the air-fuel ratio for required emission values. The system can compensate for changing gas quality by calculating the Wobbe index without using a Lambda sensor.

Description

r Gas Metering and emissions control of an internal combustion spark

ignited Gas Engine.

5 Field of invention

This invention relates to gas metering and emissions control of an internal combustion spark ignited gas engine. To be more precise, it relates to the control of emissions of internal combustion spark ignited gas engines in power generation for use in island mode and parallel to an infinite grid.

Background.

Internal combustion gas engines are generally supplied with gas of various constituency and combustibility.

15 Neverlbeless customers and environmental regulations require modern gas engines to run reliably under various load conditions and gas qualities. The emissions of the gas engine under varying load conditions and gas qualities must be maintained within correct and specified values.

There are several methods of controlling the engine operation and emissions of an 20 internal combustion spark ignited gas engine. Usually they are of the closed loop type that is expensive to run and not reliable enough for cost effective industrial power generation. These methods require additional sensors such as oxygen, lambda and individual cylinder pressure detection. This type of closed loop control is unreliable due to the failing of intrusive sensing methods, cabling and wear of the many 25 components.

Previous practice for controlling the emissions of a gas engine is to have a pressure regulated gas supply feeding a Venturi gas mixer that in turn feeds the inlet manifold of the gas engine. The mixture ratio can be set with an adjusting screw on the mixer and will maintain emissions as long as the gas quality and pressure does not change.

30 The advantage of this approach lies in its simple structure.

There are other recognised processes for controlling the emissions of a gas engine and the art is as follows.

1. The relationship between the generated power and the manifold absolute pressure is sufficient to determine and control the Lambda. This method is described in the patent EP 0 259 382 of Jenbacher. A prerequisite for this method is that the gas quality does not change.

5 2. The relationship between the efficiency of the engine and the emissions at a given power is used for controlling the mixture flow and the air-fuel ratio. This is described in the patent EP 0 727 574 B1 of Deltec. According to this method the gas flow and airflow are measured to determine the engine efficiency.

10 A more advanced method than described in 1 and 2 above is the method of controlling the emissions of a gas engine having a precise gas metering control system with a direct connection to a speed and load governing system, which is calibrated in heat input (kilojoule). The advantage of this is that there is no need for unreliable Lambda sensing, has a fast reaction to engine load changes and has a good starting mixture 1 S control.

! i

Description of the invention.

The invention to be outlined in detail provides control of air-fuel ratio and emissions S of an internal combustion spark ignited gas engine for power generation with various gas qualities under various load conditions in island mode or parallel to an infinite grid. The aim of the invention is to provide a cost effective control of emissions under power generation conditions and especially the correct air-fuel ratio mixture upon 10 initial starting conditions. This invention uses the relationship between the theoretical fuel heat demand and the actual power output of a spark ignited gas engine by continually calculating the gas quality or Wobbe index. It is well known that the relationship between the gas-air mixture flow and power output relates to the emissions of the gas engine.

There are two distinct but combined parts of the invention: 1. Mixture flow control determined from the pressure difference across a defined throttle valve characteristic and theoretical power input compared with the precise and accurate power output of the engine with the calculation of the gas quality or 20 Wobbe index.

2. Gas-metering block being controlled by the theoretical heat input related directly to the throttle position.

The speed governor should be an integral part of this invention and sets the correct 25 mixture flow to the gas engine under all load conditions to maintain speed. If the load changes the position of the mixture valve will change to keep a constant speed.

With this invention the speed governor controls speed according to a given speed demand. This demand is subtracted from the actual measured speed and results in a speed error. The resultant error is processed by a three-term PID controller and the 30 resultant output is calibrated in heat and is the heating value of the fuel required to sustain the load applied to the engine.

It is a furler aim of this invention to make We engine operation stable against environmental influences. Therefore the governor, being Filly digital, has numerous I/O for determining external conditions. The precise mixture flow across the throttle

i valve is determined by upstream and down stream pressure sensors with an up stream temperature sensor for compensation of changes of the mixture temperature.

The secondary part of the invention is the control of the gas-metering block, which determines the exact flow of gas and is achieved by the use of a precise valve 5 positioning system and a fully calibrated flow characteristic valve.

The value of the throttle valve position relates to heat input and is passed to the fuel metering function. This function positions the gas metering valve so as to deliver the correct amount of gas fuel to match the governors heat input demand.

10 The gas valve displacement is calculated with reference to the calculated gas fuel quality represented by the Wobbe index. The pressures around the metering valve and the temperature upstream of the gas metering valve all combine to determine the real gas fuel quality.

The gas fuel quality is calculated from the real generated power. This value is passed 15 to look-up tables defined by arrays of measured power and heat inputs. The result is an estimated heat input required to balance the generated power. The estimated heat input is compared with the current governor mixture throttle position and the resultant error is integrated to provide an estimated gas quality Wobbe index. If Me gas quality reduces the governor reacts by demanding more gas-air mixture. The new mixture 20 valve position enters the fuel metering function and results in the gas-metering valve opening to provide more gas flow. The governor then cuts back its mixture fuel demand. The whole process is in closed loop and quickly finds a balanced position for all load conditions resulting in the correct air-fuel ratio. Within the algorithms there are boundaries to inhibit knocking and misfiring.

25 It is a further aim of this invention to improve the starting behaviour of the engine.

Therefor the controller recognises when the engine is starting by sensing speed and gas pressure. The controller turns on the servo drives for both gas and throttle valves.

Based on the known Wobbe index the position of both valves are chosen to give reliable firing and minimum start time.

30 When the engine reaches 80% of demand speed the gas and throttle valves are set to idle fuel positions.

In depth description of diagrams.

A further description of the invention is given below with schematic details of a

sample shown on 2 diagrams.

Diagram No. 1 portrays a schematic diagram of an emission control system and an S internal combustion spark ignited gas engine connected to an electrical generator.

Diagram number 2 is a pictorial diagram of a gas-metering block used for gas metering and supplying gas to an internal combustion spark i,,gnited gas engine connected to an electrical generator.

10 Overall system.

In diagram number 1 an electrical generator 13 is mechanically coupled to an internal combustion spark ignited gas engine 12 via a coupling with a starter ring gear 22 being used for speed sensing. The exhaust system 15 is connected to a turbine of a turbocharger 21, which in turn connects its shaft to a compressor 20 of the 15 turbocharger. The control unit 7 derives the speed of the gas engine from the speed pickup 14 placed at the starter ring gear ofthe engine. The integral speed governor in control unit 7 sets the position ofthe mixer throttle valvel 1 via an analogue positioner 8 and an electric actuator 9, which in turn is connected to the inlet manifold 17. The throttle valve is placed as close to the inlet manifold as possible.

20 The up stream throttle valve mixture temperature 10 and upstream throttle valve pressure 23 are monitored in conjunction with the down stream throttle valve pressure 18 and from this information the control unit 7 calculates a figure for the mixture flow through the throttle valve. The gas-air mixture flows through the throttle valve 11 from the gas-air mixture compressor 20, which is driven by the exhaust turbine 21.

25 The compressor 20 low-pressure input is derived from the gas air mixer 2 and this receives atmospheric air pressure via the air intake 1.

The gas air mixer receives gas from via the gas-metering block 19 and via a gas metering valve 5, which is connected to an electric actuator 3 * driven and positioned by the gas flow controller within control unit 7.

30 Inlet gas pressure 6 and outlet gas pressure 4 and gas inlet temperature 16 are sensed and the values sent to the gas flow controller in the unit 7. The control unit 7 calculates the gas flow from the pressures and temperature around the gas valve 5 that has previously been calibrated. The calibration of the valve 5 relates the flow across the valve 5 in direct relation to the valve position. The position of the valve S is

determined by the electric actuator 3 and has a non-contact feedback sensor sending the position signal to the electronic control unit 7.

The inlet of the gas-metering block is connected to the main gas supply without need of a pressure regulator. In special cases a mechanical regulator can be used.

5 With the engine running under load the governor within the electronic control unit 7 senses the speed of the engine with the speed pickup 14 and compares the speed to an internal reference speed set point. The resultant error is controlled via a three-term controller and the output of this controller is calibrated in thermal energy required to maintain the speed and load of the engine. This output positions the throttle valve via 10 a positioner 8 to the electric actuator 9 that in turn sets the position of the mixture throttle valvel 1 to give the correct mixture flow or thermal energy input.

The thennal energy requirement demand from the speed governor is not only sent to the throttle mixture valve 11 but also to a look-up table within the control unit 7 and this table gives a gas flow demand to the gas metering blockl9 to maintain the correct 15 gas flow for the load and speed ofthe gas engine 12 with concern to bow, stable engine operation and emissions.

During this open loop control the actual load of the engine is determined by a true kilowatt load sensor 16 and is compared with the thermal energy setting of the throttle valvel 1. From the two signals the actual thermal energy requirement from the true 20 kilowatt load signal is calculated within the control unit 7 and compared with the theoretical energy input from the governor in 7. The comparison of the two signals determines the Wobbe index of the gas. This in turn is compared with a reference Wobbe index in the control unit 7 and the error is integrated and sent to the control of the gas metering actuator to correct the gas flow to maintain speed and load. This 25 correction is continuously running until the Wobbe index error is balanced.

During the balancing of the Wobbe index the throttle valve gives the correct mixture flow, which has the correct gas thermal energy input derived from the gas-metering block. 30 Gas-metering block 19.

The gas inlet is fed via a pipe, size depending on the power of the gas engine and connects to the gas metering block upstream flange 28. The gas inlet pressure sensor 6 and the gas inlet temperature sensor 16 send the pressure and temperature signals to the control unit 7 in diagram number!.

- A fully calibrated gas flow valve 5 is connected via an actuator flexible coupling 26 to an electric actuator 3, which is positioned from the AFR controller 7 in diagram number 1.

The downstream gas pressure sensor 4 sends the pressure signal to the AFR control 5 unit 7 in diagram number 1. The controlled gas flow travels to the gas-air mixer via a pipe, which is connected to the gas-metering block via a gas pipe flange 24 The control unit 7 calculates the gas flow from the parameters, pressure upstream, pressure downstream and the upstream temperature. The flow calculation is fast and has the advantage of setting the gas flow immediately the governor demands a new throttle 10 valve position.

Key to diagram number 1.

Air Fuel Ratio Patent Drawing on page 1 of 2 1- AIR INTAKE 1 GAS TEMPERATURE.

2- MIXER 17- INLET MANIFOLD.

3- GAS VALVE ACTUATOR. 1 THROTTLE VALVE DOWN

STREAM PRESSURE.

DOWNSTREAM GAS PRESSURE. 19- GAS-METERING BLOCK

GAS METERING VALVE. 20- TURBOCHARGER.

UPSTREAM GAS PRESSURE. 21- EXHAUST TURBINE.

7- AFR CONTROLLER. 22- STARTER RING GEAR.

ANALOGUE POSITIONER. 23- THROTTLE VALVE UPSTREAM

PRESSURE.

9- THROTTLE VALVE ACTUATOR.

1 MIXTURE TEMPERATURE.

11- THROTTLE VALVE.

12- GAS ENGINE.

! Key to diagram No:2 Gas Metering Block on page 2 of 2 6 -GAS INLET PRESSURE SENSOR.

16-GAS INLET TEMPERATURE SENSOR

4 -DOWNSTREAM GAS PRESSURE.

24-DOWNSTREAM GAS PIPE MANIFOLD.

5 -GAS VALVE.

28-UPSTREAM GAS PIPE MANIFOLD.

3 -GAS VALVE ELECTRIC ACTUATOR'

26-ACTUATOR FLEXIBLE COUPLING.

27-STAINLES-STEEL HOUSING.

Claims

Claims.

1. Gas metering system and emissions control of an internal combustion spark ignited gas engine comprising: A gas metering block connected to a gas supply of varying gas pressure and 5 varying gas heat quality, said gas metering block controlling the gas flow of said gas, a fixed orifice venturi gas mixer connected to an air inlet and to said gas metering block and to a compressor of a turbocharger in case of a turbocharged engine, a mixture throttle valve placed directly before the intake manifold of the gas engine, a kilowatt sensor determining the true load of the engine, additional 10 sensors for temperatures, pressures and speed and an electronic digital control unit. This system is characterised in that the governor in the digital controller is calibrated in thermal heat requirement for the gas engine to maintain speed and load. The governor thennal heat set point is also one input to the gas metering 15 flow controller within the digital control unit. This is done to calculate the Wobbe index that in turn is used for compensation of changes in gas quality and pressure thus yielding good control of exhaust emissions and engine operation.

2. Gas metering system and emission control according to claim 1 having a 20 calibrated gas valve and being in closed loop control.

3. Gas metering system and emission control according to claim 1 or 2 having an inlet gas pressure no less than 60milli bar above atmospheric pressure.

25 4. Gas metering system and emission control according to one of claims 1 to 3 to control the gas flow under varying inlet pressures and gas qualities.

5. Gas metering system and emission control according to claim 4 having a calibrated valve with a map of the calibration within the digital control unit.

6. Gas metering system and emission control according to one of claims 1 to S having the gas flow additionally set by the governor energy mixture throttle set point. This being in open loop control.

7. Gas metering system and emission control according to one of claims 1 to with the throttle mixture control having a calibrated valve with a map of the characteristics within the digital control unit.

5 8. Gas metering system and emission control according to one of claims 1 to 7 with at engine start a quick positioning of the gas metering valve and the throttle valve based on the Wobbe index leading to a fast engine start with good emissions.

9. Gas metering system and emission control according to one of claims 1 to 8 10 with an additional oxygen sensor or an additional lambda sensor connected to the digital control unit for performing a feed back control of the lambda value.

Amendments to the claims have been filed as follows 1. Gas metering and emissions control system of an internal combustion gas Quelled engine comprising a gas metering block connected to a gas supply, said gas metering block controlling the flow of said gas, a gas mixer connected to air stream and to said gas metering block, a throttle valve controlling the gas and air mixture flow, additional sensors for mixture temperatures and pressures and engine speed and an electronic control unit which governs engine speed by regulating gas fuel flow and maintains emissions by controlling mixture flow equal to gas flow multiplied by the desired air to fuel ratio plus one.

2. Gas metering and emission control system according to claim 1 where the gas metering block and gas mixer are connected either upstream or downstream of a turbo or super-charger when applied with an engine so equipped.

3. Gas metering and emission control system according to one or more of claims 1 and 2 where a sensor measuring engine power is connected to the electronic control unit which estimates from the engine power and a programmed engine efficiency characteristic, the thermal power in the metered gas stream and by comparison with the metered gas flow, can calculate the actual heating quality of the gas fuel such that the system can maintain the desired emissions profile for the engine in applications where the gas fuel quality is unknown or variable.

4. Gas metering and emission control system according to one or more of claims 1 through 3 controlling gas flow by means of a gas metering block containing a gas valve calibrated in the electronic controller by means of programmed sizing and efficiency characteristics with respect to valve position, measurements of upstream pressure and temperature and differential or downstream pressure relative to the valve.

5. Gas metering and emissions control system according to one or more of claims 1 to 4 to control the gas flow under varying inlet pressures and gas qualities.

6. Gas metering and emission control system according to one or more of claims 1

through 5 controlling mixture flow by means of a throttle valve calibrated in the electronic controller by means of programmed sizing and efficiency characteristics with respect to valve position, measurements of upstream pressure and temperature and differential or downstream pressure relative to the throttle valve.

7. Gas metering and emission control system according to one or more of claims 1 through 6 whereby starting with unknown fuel gas quality is promoted by fixing the throttle valve at a programmed initial position and the gas valve is opened at a programmable rate until desired engine speed is exceeded whereupon the gas and throttle metering functions are reset to programmed no-load conditions and control thereafter passed to the speed governor function.

8. Gas metering and emissions control system according to one or more of claims 1 to 7 with an emissions sensor connected to the controller to modify the electronic controllers estimate of fuel gas quality to maintain the desired emissions set point".

9. Gas metering and emissions control system according to one or more of claims 1 through 8 where a separate speed governor controls the engine speed and load by means of the throttle valve but emissions are controlled by controlling gas flow to measured mixture flow divided by the desired (air:fuel ratio plus 1) when the mixture flow is calculated by the electronic controller by the previously stated method but using a throttle valve position sensor in lieu of the direct throttle position control.

10. Gas metering and emission control system according to one or more claims 1 through 9 where the throttle valve and its associated instrumentation is positioned ahead of the mixer such as to control air flow whereby emissions control is effected by the controller ensuring that air flow is maintained equal to gas flow multiplied by the desired air:fuel ratio.

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