CA2549215C - Improved carbureted natural gas turbo charged engine - Google Patents

Improved carbureted natural gas turbo charged engine Download PDF

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Publication number
CA2549215C
CA2549215C CA2549215A CA2549215A CA2549215C CA 2549215 C CA2549215 C CA 2549215C CA 2549215 A CA2549215 A CA 2549215A CA 2549215 A CA2549215 A CA 2549215A CA 2549215 C CA2549215 C CA 2549215C
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Canada
Prior art keywords
fuel
valve
flow
linear
carburetor
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CA2549215A
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French (fr)
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CA2549215A1 (en
Inventor
Howard Malm
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Rem Technology Inc
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Rem Technology Inc
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Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02BINTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B37/00Engines characterised by provision of pumps driven at least for part of the time by exhaust
    • F02B37/12Control of the pumps
    • F02B37/18Control of the pumps by bypassing exhaust from the inlet to the outlet of turbine or to the atmosphere
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02BINTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B37/00Engines characterised by provision of pumps driven at least for part of the time by exhaust
    • F02B37/12Control of the pumps
    • F02B37/18Control of the pumps by bypassing exhaust from the inlet to the outlet of turbine or to the atmosphere
    • F02B37/183Arrangements of bypass valves or actuators therefor
    • F02B37/186Arrangements of actuators or linkage for bypass valves
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D19/00Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/02Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with gaseous fuels
    • F02D19/021Control of components of the fuel supply system
    • F02D19/023Control of components of the fuel supply system to adjust the fuel mass or volume flow
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02MSUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M21/00Apparatus for supplying engines with non-liquid fuels, e.g. gaseous fuels stored in liquid form
    • F02M21/02Apparatus for supplying engines with non-liquid fuels, e.g. gaseous fuels stored in liquid form for gaseous fuels
    • F02M21/0203Apparatus for supplying engines with non-liquid fuels, e.g. gaseous fuels stored in liquid form for gaseous fuels characterised by the type of gaseous fuel
    • F02M21/0215Mixtures of gaseous fuels; Natural gas; Biogas; Mine gas; Landfill gas
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02MSUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M21/00Apparatus for supplying engines with non-liquid fuels, e.g. gaseous fuels stored in liquid form
    • F02M21/02Apparatus for supplying engines with non-liquid fuels, e.g. gaseous fuels stored in liquid form for gaseous fuels
    • F02M21/04Gas-air mixing apparatus

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Output Control And Ontrol Of Special Type Engine (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)

Abstract

A control system for a turbo charged natural gas engine generally uses a butterfly valve for fuel control upstream of a carburetor and provides non-linear flow response during opening and closing. According to the invention, a flow compensator compensates for the non-linear response. A throttle valve position sensor acts in association with a controller which compares the throttle valve position signal with a predetermined set point and thereby opens or closes the waste gate of the turbo charger which effects oxygen content in the exhaust.

Description

TITLE
IMPROVED CARBURETED NATURAL GAS TURBO CHARGED ENGINE
INTRODUCTION
[0001] This invention relates to a control system for a carbureted natural gas engine and, more particularly, to an improved control system for air/fuel ratio and for the governor of a natural gas carbureted turbo charged engine.
BACKGROUND OF THE INVENTION
[0002] Natural gas powered engines are used pervasively for various applications and are particularly used in association with gas compression and electric power generation. Many of these engines are generally smaller type engines typically in the range of 200HP to 800HP. These existing engines have certain disadvantages including relatively high exhaust emissions which typically contain nitrogen oxides also known as NOx. In many jurisdictions, regulations place an upper limit on the nitrogen oxide emissions; hence the engines require technology to limit and control these emissions. These engines often are turbo charged and waste gates used with the turbo charger on such engines are typically controlled only by the turbo charger compressor pressure and therefore serve only to limit the maximum turbo charger pressure output. The costs of operation of these engines together with the cost of existing control systems are relatively high. It would be advantageous to provide a control system for less cost and which control system would increase engine efficiency, reduce nitrogen oxides emissions and reduce engine exhaust temperatures by providing increased or otherwise appropriately controlled air with the fuel for increased efficiency in combustion.
[0003] The replacement of the existing control systems on natural gas engines is difficult. It would further be advantageous to install an improved control system on existing engines relatively inexpensively in addition to supplying such a control system on OEM engines.
- 4 -SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided a method of controlling a natural gas engine, said method comprising the steps of opening and closing an air/fuel throttle valve associated with a carburetor, opening and closing a fuel valve upstream of said carburetor to vary the supply of fuel from a fuel source to said carburetor, said fuel valve having a non-linear fuel flow response as said fuel valve is opened and closed, compensating for said non-linear fluid flow response passing through said fuel valve as said fuel valve is opened and closed and providing a PID controller having an output modified by said compensation for said non-linear fluid flow response, said non-linear flow response compensation being a non-linear curve which is inverse to said flow characteristics of said fuel valve.
- 5 -According to a further aspect of the invention there is provided a control system for a natural gas engine, said control system comprising an air/fuel throttle valve operable to be associated with a carburetor, a fuel valve having non-linear fuel flow response as said fuel valve is opened and closed, said fuel valve being located upstream of said carburetor and associated with the supply of fuel to said carburetor from a fuel source, and a flow compensator to compensate for said non-linear flow of fuel passing through said fuel valve as said fuel valve is opened and closed, a PID
controller associated with said flow compensator and having an output which is modified by said flow compensator, said flow compensator compensating for said non-linear flow of fuel by generating a curve which is inverse to said flow of fuel passing through said fuel valve.
-6-BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0012] Specific embodiments of the invention will now be described, by way of example only, with the use of drawings in which:
- 7 -[0013] Figure 1 is a diagrammatic schematic illustrating a control system for a natural gas engine which utilises air compressed by the turbo charger for waste gate control according to the PRIOR ART;
[0014] Figure 2A is a diagrammatic view illustrating a control system incorporated into a natural gas engine and which particularly illustrates a butterfly type fuel valve according to a first embodiment of the invention;
- 8 -[0015] Figure 2B is a diagrammatic flow chart illustrating the proportional integral derivative (PID) controller, a compensator and an actuator for the fuel valve used in the control system of Figure 1A;
[0016] Figure 3A is a diagrammatic schematic illustrating a control system installed on a natural gas engine according to a further aspect of the invention and particularly illustrating an oxygen sensor used for compensating and controlling the fuel valve;
[0017] Figure 3B is a diagrammatic flow chart illustrating a proportional integral derivative (PID) controller with a compensating algorithm which generates the actuator of the air/fuel throttle valve used with the control system of Figure 2A;
[0018] Figure 3C is a diagrammatic flow chart illustrating a waste gate PID used with the throttle position sensor used for actuator control;
[0019] Figure 4 is a diagrammatic schematic illustrating a waste gate control and bypass arrangement used when
- 9 -instrument gas may be present in the vicinity of the hot exhaust gases emanating from the turbo charger according to a further aspect of the invention;
[0020] Figure 5A is a diagrammatic schematic of an alternative pressure control for the waste gate illustrating control pressure applied above the diaphragm of the waste gate; and [0021] Figure 5B illustrates the non-linear exhaust oxygen response for a butterfly type valve used for gas flow control.
DESCRIPTION OF SPECIFIC EMBODIMENT
[0022] Referring now to the drawings, a natural gas turbo charged carbureted engine is illustrated generally at 100 in Figure 1, with its turbo charger being generally illustrated at 101 and its carburetor being generally shown at 102. The natural gas fuel source 103 provides the natural gas used as fuel which enters the engine 100 through carburetor 102.
- 10 -[0023] The turbo charger 101 is powered by the hot exhaust gases leaving the engine 100 through exhaust manifold 104. The turbo charger 101 uses atmospheric air 110 which enters the turbo charger 101 through duct 111. The air is compressed by the turbo charger 101 and leaves the turbo charger 101 through duct 112 which duct 112 provides the compressed air to the carburetor 102.
[0024] The hot gases passing to the turbo charger 101 from exhaust manifold 104 leave the turbo charger 101 and are exhausted to the atmosphere through exhaust duct 113. A
waste gate generally illustrated at 114 may be used to reduce the volume of hot engine gases entering the turbo charger 101 by bypassing a portion of the hot engine gases from passing through turbo charger 101.
[0025] An air/fuel throttle valve 120 is associated with the carburetor 102. Throttle valve 120 is generally in the form of a butterfly valve and is conveniently operated by a governor 121 which runs off the engine rpm. If the engines rpm falls, the governor 121 instructs the throttle valve 120 to open to a greater position thereby admitting more air-fuel mixture to engine 100 and if the engine rpm increases,
- 11 -the governor 121 instructs the throttle valve 120 to move to a more closed position thereby restricting air-fuel flow to the engine 100. This is known technology and part of the prior art as indicated in Figure 1.
[0026] Referring to Figure 2A, a fuel flow valve 124 is used to admit the natural gas fuel to the carburetor 102. An oxygen sensor (UEGO) 122 is mounted so as to measure the oxygen in the exhaust duct 113 and a controller 123 measures the output of the oxygen sensor 122 and a user set point which is close to or at the optimum oxygen/fuel ratio. The controller 123 will accordingly provide a change in position for the fuel flow valve 124 to either admit more or less fuel to the carburetor 102 based on the optimum value of oxygen in the exhaust as measured by the oxygen sensor 122.
[0027] The fuel flow valve 124 conveniently takes the form of a butterfly type valve and is controlled by actuator 130. Butterfly valves are useful since they are simple in operation and inexpensive. Reference is made to Figure 5B
where PID output is a function of the percentage of oxygen in the exhaust. However, there are non-linearities associated with butterfly type valves as it is apparent that
- 12 -such valves have non-linear flow changes as the valve opens and closes. This non-linear valve characteristic output makes it difficult to adjust the controller to give a fast response for all outputs. To enhance the operation of the valve 124, a proportional integral derivative (PID) controller 131 (Figure 2B) is located upstream from the actuator 130 and a flow compensation algorithm is incorporated in a compensator 132 located between the controller 131 and the actuator 130.
[0028] For the same reasons described above in association with fuel flow valve 124, the air/fuel throttle valve 120 (Figure 2A) suffers from non-linear fuel flow when the throttle valve 120 is opened and closed. When the governor 121 (Figure 2A) is of the mechanical type, a throttle position sensor 133 is operably connected to the throttle valve 120 in order that the angle position of the throttle valve 120 can be measured and recorded. A second PID controller 134 obtains this position of the throttle valve 120 from throttle position sensor 133 and determines the difference between such position and an optimum and predetermined set point as entered into the controller 134.
- 13 -[0029] The output of the controller 134 will then reflect this difference. The controller 134 is operably connected to the waste gate 101 by way of a pressure transducer 140. The controller 134 and pressure transducer 140 will thereby open and close the waste gate valve 101 thereby increasing or decreasing the pressure of the compressed air leaving turbo charger 101 and entering carburetor 102 through duct 112.
Thus, the air/fuel throttle valve 120 is under the direction of the controller 134 which allows the governor 121 to operate in a more limited range for which the governor 121 may be more precisely turned.
[0030] A further aspect of the invention relates to engines which utilise a governor 142 which is electronically controlled as opposed to being mechanically controlled and reference is made to Figure 3B where the waste gate control system described in association with Figure 2A and which is associated with throttle position sensor 133 is not required. A PID
controller 160 operably connected with the engine speed sensor 161 will change the output of the controller 160. A
flow compensation algorithm is incorporated in a compensator 143 and will correct for the inherent non-linear flow
- 14 -characteristics of the throttle valve 120 which will allow optimum tuning of the controller 160 and therefore the throttle valve 120. The compensator 143 effectively inverses the non-linear action of the air/fuel throttle valve 120 so that a substantially linear response is similar to the oxygen-PID output curve illustrated in Figure 5B.
[0031] A further aspect of the invention relates to the use of instrument gas being used for pneumatic devices instead of instrument air. Instrument gas is commonly pressurized natural gas and it is desirable to isolate this gas from the hot exhaust gases emanating from the turbo charger 101. Reference is made to Figure 4 where a pneumatic relay 143 is used. The relay 143 is controlled by the instrument gas acting on the pressure transducer 144. If it desired to open the waste gate 114, relay 143 will be activated by pressure transducer 144 which will allow the compressed air in duct 112 to travel through line 150 to relay 143 and thence to the waste gate 114 where it will open the waste gate 114 and allow a portion of the exhaust in the exhaust manifold 104 to escape directly to the exhaust stack 113 without driving the turbo charger
- 15 -101 so that the speed of the turbo charger 101 will be reduced which will, in turn, reduce the pressure of the compressed air in duct 112.
[0032] In the event of failure of the control system, apparatus may conveniently be used to return the waste gate control to that of the original system.
[0033] Reference is again made to Figure 4 where default equipment is added to the circuit by way of a solenoid valve 151 which opens in the event of a control system failure. A
pressure regulator 152 may also be provided to reduce the pressure in line 150 if required.
Opening the solenoid valve 151 will allow the compressed air in duct 112 and line 150 to be applied to the waste gate 114 directly.
[0034] Many modifications will readily occur to those skilled in the art to which the invention relates and the specific embodiments herein described should be taken as illustrative of the invention only and not as limiting its scope as defined in accordance with the accompanying claims.

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of controlling a natural gas engine, said method comprising the steps of opening and closing an air/fuel throttle valve associated with a carburetor, opening and closing a fuel valve upstream of said carburetor to vary the supply of fuel from a fuel source to said carburetor, said fuel valve having a non-linear fuel flow response as said fuel valve is opened and closed, compensating for said non-linear fluid flow response passing through said fuel valve as said fuel valve is opened and closed and providing a PID controller having an output modified by said compensation for said non-linear fluid flow response, said non-linear flow response compensation being a non-linear curve which is inverse to said flow characteristics of said fuel valve.
2. A method as in claim 1 wherein said fuel valve having said non-linear flow response is a butterfly type valve.
3. A control system for a natural gas engine, said control system comprising an air/fuel throttle valve operable to be associated with a carburetor, a fuel valve having non-linear fuel flow response as said fuel valve is opened and closed, said fuel valve being located upstream of said carburetor and associated with the supply of fuel to said carburetor from a fuel source, and a flow compensator to compensate for said non-linear flow of fuel passing through said fuel valve as said fuel valve is opened and closed, a PID controller associated with said flow compensator and having an output which is modified by said flow compensator, said flow compensator compensating for said non-linear flow of fuel by generating a curve which is inverse to said flow of fuel passing through said fuel valve.
4. A control system as in claim 3 wherein said fuel valve is a butterfly type valve, said butterfly type valve having said non-linear fuel flow response.
CA2549215A 2006-06-01 2006-06-01 Improved carbureted natural gas turbo charged engine Active CA2549215C (en)

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CA2549215C true CA2549215C (en) 2015-10-27

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US9181901B2 (en) 2009-11-03 2015-11-10 Indian Institute Of Science Producer gas carburettor
CH708276A1 (en) * 2013-07-04 2015-01-15 Liebherr Machines Bulle Sa Gas engine.

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