Engine Combustion Control System

In a practical engine combustion control system some elemental quantity should 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 ratio. In addition, with such an arrangement, the air-fuel ratio could be automatically adjusted to compensate for small changes in fuel (gas) BTU content.

There are two prime reasons for such a control system. One is: increased fuel economy, as a result of running an engine lean. Normally, running an engine near its lean limit is not done without a person on hand to make 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 adjustments.

The other principal reason for such a control system is that it offers lowered emissions of NO.sub.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. Now, in the event the even lower emissions are required, the object control system can be used in addition to a catalytic converter. In this latter circumstance, such a converter could be reduced in 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.

Another object of this invention is to set forth 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 means coupled to said sensor means for inhibiting engine exhaust gas pressure surges therewithin.

Yet another object of this invention is to disclose 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.

Further objects of this invention, as well as the novel features thereof, will become more apparent by reference to the following description, taken in conjunction with the accompanying figures in which:

FIG. 1 is a schematic diagram depicting the novel engine combustion control system, according to an embodiment thereof, in operative association with a gas-fueled engine;

FIG. 2 is a vertical cross-sectional view of the zirconium sensor, of the FIG. 1 system, interposed in the exhaust conduit of the engine;

FIG. 3 is a vertical, cross-sectional view of the gas engine regulator valve, of the FIG. 1 system, modified, according to the invention, to accommodate a trim-control gas cylinder; and

FIG. 4 is a digrammatic illustration of a portion of a system similar to that of FIG. 1 modified to accommodate a plurality of gas-well fuel sources of disparate BTU values.

As shown in FIGS. 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 16. 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 pressure to the transducer 26. With variations in exhaust temperature and oxygen content, of course, the derivative signal will manifestcomplementary excursions or modulations. Accordingly, pursuant to the modulations of the derivative signal from the comparator/controller 22, the transducer 26 provides an excursive or modulated fluid pressure to a gas cylinder 34 fixed to the lower end of 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 diaphragm 40, and fuel chamber 42 with an orificed valve seat 44 and a valving element 46. A heavy spring 48 biases the pressure-responsive diaphragm 40 and valving element 46 to an "open" position whereby fuel gas from the line 28 is freely admitted therethrough, 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 cylinder 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 FIG. 3, the gas cylinder 34 comprises a cylinder 90 in which a piston 92 is reciprocatably disposed. A rolling diaphragm-seal 94, carried by piston 92, fluid-seals between 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 absence of a signal from line 37) so that the engine 16 is in a "rich" running mode. A pneumatic, trimming signal from line 37 will tend to lean the air-fuel mixture to the engine in proportion 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 system 10 trims the fuel gas to the engine 16 in response to various engine 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 thereto to the transducer 26 at approximately twenty psi. From the latter, then, the line 37 addresses the pneumatic trimming signal to the gas cylinder 34 with an amplitude taken from a range of approximately two to twenty psi and, specifically in this embodiment, with a swing of from approximately three to fifteen 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/controller 22. The sensor 12 provides the aforesaid temperature and oxygen-content signals to an analyzer (comprised by the comparator/controller); the latter produces a composite signal therefrom. The composite signal is presented to a comparator (also comprised by the device) which determines any difference in the value thereof against a optimum, predetermined value or "setpoint" (priorly noted). In turn, pursuant to any deviation in the composite signal vis-a-vis the setpoint value, the comparator/controller 22 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 operating conditions and loads. According to this first embodiment of the invention, the comparator/controller 22 has a single (albeit variable) setpoint.

According to an alternative embodiment, the comparator/controller 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 very rapidly. To avoid this problem, the system 10 has an input signal from the engine manifold vacuum (which varies with load). A pressure transducer 50 through connected with the manifold senses both absolute values, and rate of change, of manifold depression. Thus the line 52, carrying the signal 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: running the engine 16 an 23/1 air-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 experience a surging of pressure, within the sensor, which gives 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 comprises 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 transmitted). 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 system 10 is usable with naturally-aspirated or turbocharged engines. In the former case, the upper 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 (FIG. 1).

Engine-compressor applications of the system 10 in a gas field or patch will often dictate that an engine 16 must run on gas from any well in the patch. A problem arises when the fuel gas BTU valve varies from one well to the next. A small change in BTU valve is automatically compensated 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 FIG. 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 performance for the BTU valve of the associated well. Thus, whenever an operator switches gas wells, a properly ajdusted regulator valve is switched at the same time. 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.