CA1155946A - Combustion control system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An improved combustion control system for an engine having an exhaust conduit and fuel and air inlet lines. The control system comprises temperature and oxygen sensor means for interpositioning in the engine exhaust conduit for (a) admitting engine exhaust gases thereinto, and (b) for emitting electrical signals representative of or analogous to both engine exhaust temperatures and engine exhaust oxygen content. Signal comparator/controller means is coupled to the sensor means for emitting discrete unitary electrical signals deriva-tive of the temperature and oxygen-content signals. Fuel regulating means is interpositioned in the fuel inlet line and is coupled to the comparator/controller means and responsive to the discrete, unitary signals for regulating fuel conduct through the fuel inlet line.
The improvement comprises transducer means comprised by the fuel regulating means for transforming the unitary, electrical signals into analogous fluid pressures.

Description

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In a practical engine combustion control system some elemental quantity shoulcl be monitored which is directly related to air-fuel ratio but only remotely related to other engine variables. This elemental quantity is uncombined oxygen subsisting in the engine exhaust. By monitoring or sensing oxygen in the engine exhaust, and using its analog to modulate a closed-loop, air-fuel ratio control system one can dispense with the necessity of measuring other variables related to air-fuel ratioO In addition, with such an arrangement, the air-fuel ratio could be automatically adjusted to compensate for small changes in fuel (gas) BTU contenta There are two prime reasons for such a control system. One is increased fuel economy, as a result of running an engine lean. Norma]ly, running an engine near its lean limit is not done without a person on hand to ma]~e manual adjustments and thus avoid misfiring. It is an object of this system to allow engine operation near the lean limit without the necessity of making manual adjust-ments.
The other principal reason for such a control system is that it offers lowered emissions of ~x~ HC and CO. By proper system manipulation of the air~fuel ratio, exhaust emissions can be greatly reduced without the need for a catalytic converter. ~ow in the event the even lower emissions are required, the object con rol system can be used in addition to a catalytic converter. In this latter circumstance, such a converter could be reduced in ~ .

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size and cost as compared to one sized to operate without such a control system.
It is a particular object of this invention, then, to disclose such a closed-loop, air-fuel ratio, engine combustion control system designed especially to be used with gas-fueled engines which are either naturally-aspirated or turbocharged.
A feature of the present invention, from a broad aspect thereof, is to provide an improved combustion control system for an engine having an exhaust conduit and fuel and air inlet lines. The control system comprises temperature and oxygen sensor means for interpositioning in the en~ine exhaust conduit for (a) admitting engine exhaust gases thereinto, and (b) for emitting electrical signals representative of or analogous to both engine exhaust temperatures and engine exhaust oxygen content.
Signal comparator/controller means is coupled to the sensor means for emitting discrete unitary electrical signals derivative of the temperature and oxygen-content signals.
Fuel regulating means is interpositioned in the fuel inlet line and is coupled to the comparator/controller means and responsive to the discrete, unitary signals for regulating fuel conduct through the fuel inlet line. The improvement comprises transducer means comprised by the fuel regulat-ing means for transforming the unitary, electrical signals into analogous fluid pressures.

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Further o~jects of this invention, as well as th~ novel features thereof, will become more apparent by reference to the following description, taken in conjunction with the accompanying figures in which:
Figure 1 is a schematic diagram depicting the novel engine combustion control system, according to an emboaiment thereof, in operative association with a gas-fueled engine;
Figure 2 is a vertical cross-sectional view of the zirconium sensor, of the Figure 1 system, interposed in the exhaust conduit of the engine;
Figure 3 is a vertical, cross-sectional view of the gas engine regulator valve, of the Figure 1 system, modified~ accord-ing to the invention, to accommodate a trim-control gas cylinder;
and Figure 4 is a diagrammatic illustration of a portion of a system similar to that of Figure 1 modified to accommodate a plur-ality of gas-well fuel sources of disparate BTU values.
As shown in Figures 1 through 3, the novel combustion control system 10 comprises a zirconium oxygen and temperature sensor 12 interposed in the exhaust conduit 14 of a gas-fueled engine I6~
The sensor 12 has a pair of output lines 18 and 20 through which analogous, electrical signals representative of the oxygen content of the exhaust, and the exhaust temperature, are conducted to a comparator/controller 22. The comparator/controller 22, in turn, generates a unitary signal representative of ~i.e., derivative from) the oxygen and temperature signals, which derivative signal is transmitted by a line 24 to a current-to-pressure transducer 26. A gas line 28 from a supply (not shown) has tap-off line 30 which, via a pressure reducer 32, supplies gas under pr~ssure to the transducer 26. ~Jith variations in exhaust temperatur~ and 1 ~5~
oxygen content, of course, the derivative signal will manifest complementary excur~ions or modulations. Accordingly, pursuant to the modulations of the derivative signal from the comparator/
controller 22, the transducer 26 provides an excursive or modu-lated fluid pressure to a gas cylinder 34 fixed to the lower endof a gas engine regulator valve 36 via line 37.
As shown, and as is standard with such regulator valves, valve 36 comprises a pressure chamber 38 compartmented by a dia-phragm 40, and fuel chamber 42 ~7ith an orificed valve seat 44 and a val~ing element 46. A heavy spring 48 biases the pressure-- responsive diaphragm 40 and valving element 46 to an "open" posi-tion whereby fuel gas from the line 28 is freely admitted there-through, supplying a given gas flow to the engine 16. Depending upon the oxygen content and the temperature of the exhaust and, more directly, the pressure in line 37, the gas cylinaer 34 either - opposes or yields to the biasing of spring 48; consequently, the gas cylinder 34 provides a trim control of the fuel flow.
As shown in detail, in Figure 3, the gas cylinder 34 comprises a cylinder 90 in which a piston 92 is reciprocatably disposed. A
rolling diaph.ragm-seal 94, carried by piston 92, fluid-seals be-tween the upper and lower ends of the cylinder. The piston 92 carries a rod 96 which penetrates into valve 36, the terminal end of the rod 96 effecting an abutting engagement with the VAlVing element 46 (in valve 36). A spring 98 biases the piston 92 towards the lower end of the cylinder 90, and line 37 (which carries the excursive or modulated "trimming" gas pressure) communicates with an orifice 100 formed in the lower end wall of the cylinder~
The spring 48 in the regulator valve 36 is initially adjusted ~in the absense of a signal from line 3~) so that the engine 16 is in a "rich" running mode. ~.pneumatic, trimming signal from line _4_ : . ' ' ' ~ , .
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37 will tend to lean the air-fuel mixture to the engine in pro-portion to the amplitude of the signal. Any change in the mixture will be reflected in the oxygen concentration in the exhaust and thus the control loop of the novel system 10 is closed. The sys-tem 10 trims the fuel gas to the engine 16 in response to variousensine operating parameters (load changes, etc.) which are reflected in the exhaust oxygen content. The system 10 maintains the oxygen concentration at a predetermined level (set point) and thus maintains the required or optimum air-fuel ratio. In this embodiment, line 28 provides fuel (gas) at approximately twenty-- five psi, and the reducer 32 supplies a quantity thereof to the transducer 26 at approximatel~T twenty psi. From the latter, then, the line 37 addresses the pneumatic trimming signal to the gas c~rlinder 34 with an amplitude taken from a range of approximately two to twenty psi and, specifically in this embodiment, with à
swing of from approximately three to fiftenn psi.
The comparator/controller 22, per se, is not a subject of this invention. Such devices, as well as current-to-pressure -transducers 26, are commercially available and, consequently, the structure and circuitry thereof are not set out herein; the same are well known to those skilled in this art. However, it may be useful to briefly outline the functioning of the comparator~con-troller 2~. The sensor 1~ provides the aforesaid temperature and oxygen-content signals to an analyzer (comprised by the comparator/
controller); the latter produces a composite signal there~rom. The compos-te signal is presented to a comparator (also comprised by the device) which determines any difference in the ~alue thereof against a optimum, predetermined value or "setpoint" (priorly noted~. In turn, pursuant to any deviation in the composite sig-na; vis-a-vis the setpoint value, the comparator/controller 22 ~ :LS59~
produces the aforesaid derivative signal, of from perhaps one-half to eight milliamperes of current, but from one to five ma. in this embodiment, to the transducer 26. Means (not shown) are provided, of course, for adjusting the setpoint value for given engine oper-ating conditions and loads. According to this first en~odimentof the invention, the comparator/controller 22 has a single (albeit variable) setpoint.
According to an alternative en~odiment, the comparator/con-troller 22 has a pair of setpoints -- for the following reason:
very rapid engine load transients, as might be encountered in a generator set, give rise to special requirements with regard to ~( an air-fuel ratio control system. An engine 16 running very "lean"
at low load with, for example, six percent oxygen in the exhaust, will have little reserve if the load is increased or decreased lS very rapidly. To avoid this problem, the system 10 has an input signal from the engine manifold vacu~ (which varies with load).
` A pressure transducer 50 throughconnected with the manifold senses both absolute ~alues, and rate of change, of manifold depression.
Thus the line 52, carrying the sign~l from transducer 50 provides a means of switching setpoints in the comparator/controller 22 from one to another of the pair of setpoints. By way of example: run-ning the engine 16 an 23/1 aix-fuel ratio and six percent oxygen in the exhaust, as a first setpoint, it will be possible to switch to one percent oxygen, as the other setpoint, until the effect of the load transient is over, and then switch back to the six percent setpoint. This will allow the engine 16 to recover smoothly.
It is somewhat common in prior art combustion control systems to employ a zirconium sensor 12 in the exhaust system or conduit 14. However, we have determined that the prior art arrangements ex?erience a surging of pressure, within the sensor, which gives `~ ~6-~039-IR-~P
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poor, spurious oxygen-content readings. For this reason we have employed a surge bottle 54 or plenum chamber in the discharge line 56 of the sensor 12 in order that exhaust pressure surges will be substantially eliminated. Within the chamber 58 of the sensor 12, a substantially uniform pressure will obtain, as the surge bottle 54 effectively absorbs and damps the pressure surges.
The remainder of the sensor 12 is rather conventional. It com-prises a housing 60 and a heater 62, the latter two elements being separated by insulation 64. The probe 66 terminates in a head 68 (from whence the oxygen-content and temperature signals are trans-mitted). The orifice 70 admits exhaust gases, from the conduit 14, ~( into the chamber 58. Port 72 releases the gases to line 56 and the interposed surge bottle 54.
As noted earlier, the s~stem 10 is usable with naturally~

aspirated or turbocharged engines. In the former case, the up?er compartment 74 of the valve 36 is vented to the atmosphere. In the latter case, compartment 74 is communicated with the engine carburetor intake 76 via line 78 (Fiqure 1).
Engine-compressor apFlicatlons o~ the system 10 in ~ gas field or patch will o~ten dictate that an engine 16 must run on gas from any well in the patch. A problem arises when the fuel gas BTU valve varles from one well to the next. A small change in BTU valve is automatically compen~ated for by the control system 10, however, large variations would have to be compensated for by adjusting the force of spring 48 in the gas regulator valve 36.
The Figure 4 embodiment indicates how this matter can be handled with more facility. Each well 80, 80a, 80b, etc. has a regulator valve 36, 36a, 36b, etc~ which is adjusted for proper engine per-formance for the BTU valve of the associated well. I'hus, whenever an operator switches gas wells, a properly a~justed regulator valve ~039-IR-EP
5~4~6 is switched at the same timeO The regulator valves 36, 36a, and 36b, are all commonly coupled to the transducer 26 via lines 37, 37a, and 37b. Too, the valves are commonly coupled via lines 82, 82a, and 82b to a well-selector valve 84; the latter, via line 86, supplies the fuel (gas) to the engine 16.
While we have described our invention in connection with specific embodiments thereof, it is to be clearly understood that this is done only by way of example; and not as a limitation to the scope of our invention as set forth in the objects thereof and in the appended claims.

(''' ` ' This is a division of Canadian patent application Serial Number 362,611 filed October 17, 1980 entitled "An Improved Combustlon Control System".

Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An improved combustion control system for an engine having an exhaust conduit and fuel and air inlet lines, comprising temperature and oxygen sensor means, for interpositioning in the engine exhaust conduit, for:
(a) admitting engine exhaust gases thereinto, and (b) for emitting electrical signals representative of or analogous to both engine exhaust temperatures and engine exhaust oxygen content; signal comparator/controller means, coupled to said sensor means, for emitting discrete, unitary electrical signals derivative of said temperature and oxygen-content signals; and fuel regulating means, for interpositioning in said fuel inlet line, coupled to said comparator/controller means and responsive to said discrete, unitary signals for regulating fuel conduct through said fuel inlet line, wherein the improvement comprises:
transducer means comprised by said fuel regulating means for transforming said unitary, electrical signals into analogous fluid pressures.

2. An improved combustion control system, according to claim 1 wherein:
said fuel-regulating means further comprises a fuel regulator valve;

said valve has first means normally operative for admitting fuel at a given rate of flow therethrough and alterably operative for diminishing fuel flow there-through to less than said given rate, and second means, responsive to fluid pressure, coupled to said first means and alterably operative of the latter to effect a diminished fuel flow through said valve to less than said given rate.

3. An improved combustion control system, according to claim 2, wherein:
said transducer means comprises an electrical current-to-fluid pressure transducer, for transforming excursive, electrical-current signals into analogous, excursive fluid-pressures;
said transducer having a fluid-pressure outlet;
and said second means is in fluid-flow communication with said fluid-pressure outlet of said transducer.

4. An improved combustion control system, according to claim 3, wherein:
said fuel regulator valve has a fuel inlet port for admitting therethrough fuel under pressure;
said transducer has a fluid-pressure inlet; and said inlet port and said fluid-pressure inlet are in fluid-flow communication.