US20060204910A1

US20060204910A1 - High efficiency fuel injection system for gas appliances

Info

Publication number: US20060204910A1
Application number: US11/080,830
Authority: US
Inventors: Yu-Shan Teng
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-03-14
Filing date: 2005-03-14
Publication date: 2006-09-14

Abstract

A unique control system is provided for fuel injection gas appliances to achieve efficient combustion by controlling the proportion of fuel and air variables. The combustion control system provides active feedback control of the combustion event and includes at least one detection sensor e.g. CO₂CO sensor and O₂, to trigger the modulation of a gas valve to adjust pressure and gas flow to the combustion chamber of a gas appliance. A processor receives the concentration signal from the detection sensor to generate a proportionate control signal to modulate a pressure regulator of the gas valve thereby to control future combustion events to achieve maximum fuel combustion efficiency. Accordingly, the injection system varies the proportion of air to fuel inflow to a prescribed optimum range achieving efficient fuel combustion.

Description

BACKGROUND OF THE INVENTION

The present invention relates to an improved method and apparatus for fuel injection for gas appliances.
Gas appliances such as heaters serve as floor heaters, space heaters, room heaters, central furnaces, clothes dryers and cooking ranges. Existing gas heating appliances typically employ manually operated gas valves to regulate and control gas flow to burners for combustion to generate heat from the burning of natural or propane gas.
The fixed orifice in a conventional gas valve, however, is not capable of active adjustment of pressure and flow rate of gas into the burner resulting in inefficient combustion i.e. too little heat and too much exhaust generated from a gas-heating appliance.
Excessive gas flow with inadequate air in the combustion mixture, or vise versa, will cause less heat and excess exhaust. Moreover, various ambient conditions such as altitudes in different parts of the world, are variable factors that can contribute to combustion efficiency. The components of conventional gas heating appliances are generally fixed and not self-adjusting to account for these various ambient conditions.
Those skilled in the art have recognized a significant need for a variety of control systems that utilizes the concentration of carbon dioxide.
U.S. Pat. No. 6,398,118 issued to Rosen, et al., discloses a system for monitoring and modifying the quality and temperature of air within a conditioned space including a blower unit, a damper unit for selectively admitting outside air into the conditioned space, a temperature moderating unit and a control unit.
The Rosen system relates to the art of conditioning indoor living and working and other enclosed public spaces. More particularly, the patent discloses a system in which the carbon dioxide (CO₂) level is monitored and controlled by apparatus in which the CO₂sensor and support circuitry is integral with a thermostat which also serves to conventionally control the temperature range within the conditioned space.
The principle of operation of the CO₂sensor is stated to be that, the cell constituting the cathode, anode and solid electrolyte, becomes susceptible to readily measurable change in accordance with the CO₂concentration at the cell. This known effect appears to be due to a chemical reaction between the CO₂and the electrolyte which must be selected to enhance the extent of the change in accordance with the gas of interest. Combinations of electrodes and electrolytes suitable for the purpose are discussed, for example, by S. Azad, S. A. Akbar, S. G. Mhaisalkar, L. D. Birkefeld and K. S. Goto in the Journal of the Electrochemical Society, 139, 3690 (1992). One suitable combination which gives very good results for measuring CO₂concentration is: platinum (Pt) for the cathode, reference electrode 30; silver (Ag) for the anode, sensing electrode 31; and a mixture of Na₂CO₃, BaCO₃and AG₂SO₄as the solid electrolyte.
U.S. Pat. No. 6,286,482 issued to Flynn, et al., discloses a premixed charge compression ignition engine, and a control system, which effectively initiates combustion by compression ignition and maintains stable combustion while achieving extremely low oxides of nitrogen emissions, good overall efficiency and acceptable combustion noise and cylinder pressures. The Flynn engine and control system effectively controls the combustion history, that is, the time at which combustion occurs, the rate of combustion, the duration of combustion and/or the completeness of combustion, by controlling the operation of certain control variables providing temperature control, pressure control, control of the mixture's autoignition properties and equivalence ration control. The combustion control system provides active feedback control of the combustion event and includes a sensor, e.g. pressure sensor, for detecting an engine operating condition indicative of the combustion history, e.g. the start of combustion, and generating an associated engine operating condition signal. A processor receives the signal and generates control signals based on the engine operating condition signal for controlling various engine components to control the temperature, pressure, equivalence ration and backlash or autoignition properties so as to variably control the combustion history of future combustion events to achieve stable, low emission combustion in each cylinder and combustion balancing between the cylinders.
The Flynn patent discloses a strategy for controlling the start and direction of combustion by varying the air/fuel mixture autoignition properties. The autoignition properties of the air/fuel mixture may be controlled by injecting gas, e.g. air, oxygen, nitrogen, ozone, carbon dioxide, exhaust gas, etc., into the air or air/fuel mixture either in the intake system.
U.S. Pat. No. 6,392,536 issued to Tice, et al. discloses a multi-function detector which has at least two different sensors coupled to a control circuit. In a normal operating mode the control circuit, which would include a programmed processor, processes outputs from both sensors to evaluate if a predetermined condition is present in the environment adjacent to the detector. In this mode the detector exhibits a predetermined sensitivity. In response to a failure of one of the sensors, the control circuit processes the output of the remaining operational sensor or sensors so that the detector will continue to evaluate the condition of the environment with substantially the same sensitivity.
U.S. Pat. No. 5,644,068 issued to Okamoto, et al. discloses a gas sensor of the thermal conductivity type suitable for the quantitative analysis of the fuel vapor content of a fuel-air mixture. The Okamoto gas sensor comprises a sensing element and a compensating element , each of which includes an electrically-heated hot member incorporated into a Wheatstone bridge circuit powered by a constant current supply circuit. The constant current supply circuit is adjusted and regulated such that the hot member of the sensing element is heated with an electric current of such an intensity that corresponds to a point of transition (Y) at which, at the interface of the hot member and the mixture, the predominant mode of heat transfer changes from thermal conduction to natural convection.
The dislosures of the foregoing patents are hereby incorporated by this reference.
While recognizing the advantages of control systems utilizing carbon dioxide as possible parameter, these systems do not strive to achieve combustion efficiency through the recognition of carbon dioxide, carbon monoxide and oxygen gas concentration as a critical factors for active feedback control. The present invention achieves these goals.

SUMMARY OF THE INVENTION

The present invention relates to an improved method and apparatus for fuel injection for gas appliances.
A unique control system is provided for fuel injection gas appliances to achieve efficient combustion by controlling the proportion of fuel and air variables. The combustion control system provides active feedback control of the combustion event and preferably includes a CO₂CO sensor and O₂to trigger the modulation of a valve to adjust pressure and gas flow to combustion chamber of gas appliance. A processor receives the concentration signals from the sensors and generates control signals based on the concentration signal for controlling a pressure regulator of the gas valve so as to variably control future combustion events to achieve maximum fuel combustion efficiency. Accordingly, the control signal varies the proportion of air to fuel inflow to a prescribed optimum range achieving efficient fuel combustion.
The present invention achieves improved combustion efficiency by adjustment of pressure and fuel flow related to changing ambient conditions. One embodied system comprises a CO₂sensor to measure the concentration of carbon dioxide out of combustion chamber of a gas heating appliance and relay the signal to an electronic circuitry; after receiving the signal, the electronic circuitry will activate a device to adjust pressure regulator of a gas valve to a prescribed optimum range.
In one embodied form, the present invention provides an improved method and apparatus for achieving high efficiency of combustion by comprising active feedback control means based upon detection of the concentration of carbon dioxide. Assuming fixed exhaust gas flow from combustion, if the concentration level of carbon dioxide exceeds about nine percent (9%), the control means will accordingly decrease the air flow into the burner of the gas heating appliance. If the concentration of carbon dioxide in the exhaust gas is less than seven percent (7%), the control means will proportionately increase the intake air flow to the combustion chamber. Thus greatest combustion efficiency can be achieved by monitoring and maintaining the concentration of carbon dioxide within a range of between about 7 to 9 percent.
In a second embodiment, the inventive system comprised a CO₂sensor, CO sensor, O₂sensor to trigger the modulation of gas valve to adjust pressure of gas pressure and gas flow to combustion chamber of gas appliance. In operation, modulation will take place in a range of concentration. For instance, in the case of CO₂, modulation is within the range of 7 percent to 9 percent. Gas pressure and flow will be adjusted in responding to changes of concentration, way before CO₂reaches 7 percent or 9 percent. Actually, modulation of gas value can be to such an extent of virtually shutting down gas flow to a halt.
The inventive system comprises a processor that receives the qualitative and quantative signal from the carbon dioxide sensor and provides feedback control to an electronic control unit (ECU). ECU receives the sensor signal and processes the signal to determine the appropriate adjustment, if any, to the flow of air to be mixed with fuel for combustion in the burner unit. The signal reflecting the carbon dioxide concentration in the exhaust gas is then compared to a predetermined database of desired airflow adjustment values. Based on the comparison of the actual airflow to the desired airflow adjustment value, the ECU then generates a plurality of output signals, for variably controlling a pressure regulator of a gas intake flow valve and other respective components of the system so as to effectively ensure, that the future carbon dioxide concentration in the exhaust gas is maintained within the prescribed optimum range.
The combustion control scheme is most preferably implemented in software contained in ECU that includes a central processing unit such as a micro-controller, micro-processor, or other suitable micro-computing unit. Accordingly, the unique system achieves high efficiency combustion in a wide variety of gas heating appliances.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional side view of one embodied CO₂sensor and Pitot tube in accordance with the present invention.
FIG. 2 is a side sectional view illustrating the system components and placement of a CO₂sensor in the control processor in accordance with the present invention.
FIG. 3 is a schematic sectional view depicting a gas valve in accordance with one embodied form of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A unique control system os provided for fuel injection heating appliances to achieve efficient combustion by controlling the proportion of fuel and air variables. The combustion control system provides active feedback control of the combustion event and includes a CO₂CO sensor and O₂to trigger the modulation of a gas valve to adjust pressure of gas pressure and gas flow to combustion chamber of gas appliance. A processor receives the concentration signals from the sensors and generates control signals based on the concentration signal for controlling a pressure regulator of the gas valve so as to variably control future combustion events to achieve maximum fuel combustion efficiency. Accordingly, the control signal varies the proportion of air to fuel inflow to a prescribed optimum range achieving efficient fuel combustion.
In one embodied form, the present invention provides an improved method and apparatus for achieving high efficiency of combustion by comprising active feedback control means based upon detection of the concentration of carbon dioxide. Assuming fixed exhaust gas flow from combustion, if the concentration level of carbon dioxide exceeds about nine percent (9%), the control means will accordingly decrease the air flow into the burner of the gas heating appliance. If the concentration of carbon dioxide in the exhaust gas is less than seven percent (7%), the control means will proportionately increase the intake air flow to the combustion chamber. Thus greatest combustion efficiency can be achieved by monitoring and maintaining the concentration of carbon dioxide within a range of between about 7 to 9 percent.
In a second embodiment, the inventive system comprised a CO₂sensor, CO sensor, O₂sensor to trigger the modulation of gas valve to adjust pressure of gas pressure and gas flow to combustion chamber of gas appliance. In operation, modulation will take place in a range of concentration. For instance, in the case of CO₂, modulation is within the range of 7 percent to 9 percent. Gas pressure and flow will be adjusted in responding to changes of concentration, way before CO₂reaches 7 percent or 9 percent. Actually, modulation of gas value can be to such an extent of virtually shutting down gas flow to a halt.
The sensor module provides a 0-4 VDC output scaled to 0-2000 ppm CO₂. The sampling method for detection of the carbon dioxide concentration may be either flow through or diffusion and can be configured to measure ppm levels up to 5%. The modules include self-calibration algorithm that eliminates the need for on-going calibrations.
The CO sensor is operational to trigger the modulation of gas valve to lower the amount of gas flow to combustion chamber of gas appliance. If the concentration is less than 65 PPM, the sensor is not activated. Preferably, the CO sensor accumulates concentration up to 65 PPM of carbon monoxide in one hour.
The O₂sensor is operational to trigger the modulation of gas valve to lower the amount of gas flow to combustion chamber of gas appliance. If the level is over 19.5 percent, the sensor is not activated.
The system may use conventional shut off mechanisms for instance disclosed in U.S. Pat. No. 5,838,243, which is hereby incorporated by this reference.
After generating the sensor concentration signal, the control processor will determine the desired adjustment of air inflow by setting the pressure regulator of a gas valve to a prescribed optimum range.
In this respect the CO₂Sensor module communicates over an asynchronous, UART interface at 9600 baud, no parity, 8 data bits, and 1 stop bit. When the host computer of PC communicates with the sensor, the host computer sends a request to the sensor, and the sensor returns a response. The host computer acts as a master, initiating all communications, and the sensor acts as a slave, responding with a reply.
Preferably, sensor commands and replies are wrapped in a secure communications protocol to insure the integrity and reliability of the data exchange. One suitable communications protocol for the serial interface and the command set for the module CO₂Sensor are set forth below.
Each command to the sensor consists of a length byte, a command byte, and any additional data required by the command. Each response from the sensor consists of a length byte and the response data if any. Both the command to the sensor and the response from the sensor are wrapped in a communications protocol layer.

- Command: <length><command>additional_data>
- Response: <length><response_data>

The communications protocol consists of two flag bytes (0xFF) and an address byte as a header, and a two-byte CRC as a trailer. In addition, if the byte 0xFF occurs anywhere in the message body or CRC trailer, the protocol inserts a null (0x00) byte immediately following the 0xFF byte. The inserted 0x00 byte is for transmission purposes only, and is not included in the determination of the message length or the calculation of the CRC.

- Header Message Body Trailer
- <flag><flag><address><Command/Response><crc_Isb><crc_msb>

When receiving a command or response, the flags and any inserted 0x00 bytes must be stripped from the message before calculating the verification CRC. A verification CRC should be computed on all received messages from the sensor and compared with the CRC in the message trailer. If the verification CRC matches the trailer CRC, then the data from the sensor was transmitted correctly with a high degree of certainty.
In response to the concentration signal from the sensor module the air flow from a gas valve will be adjusted by pressure regulator before it flows to burner, prior to combustion chamber. If concentration of carbon dioxide is more than 9 percent (9%), gas flow will be adjusted upward to increase its mixture with air; and if concentration of carbon dioxide is less than 7 percent (7%), gas flow will be adjusted downward to decrease its mixture with air.
In the CO₂module, a bus interfaces to both an external processor and the A/D converter which is collecting the CO₂data. When the module is collecting data, its serial shift clock is configured to generate its own internal clock. That is, the module is said to be operating in “master” mode. When the CO₂module is communicating with an external processor, it relies upon the external processor to supply the clock pulse, called the “slave” mode.
Thus, to an external process, the CO₂module appears as a slave on the bus. The external processor is the master, meaning that it provides the SK clock signal for both sending and receiving data across the bus. From the CO₂module's point of view, during communications with an external processor, is SI (serial in) and SK (serial clock) are inputs, and its SO (serial out) is an output. Additionally, there are two digital handshake lines that an external processor uses to communicate with the CO₂module.
Every data exchange between an external processor and the CO₂module starts with the external processor sending a request data-packet—several bytes—to the CO₂module. The CO₂module then responds by returning a response data-packet to the external processor. The request data packet contains a command byte, and perhaps one or more parameter bytes.
After receiving each byte in a request data packet, the CO₂module raises the UB_ACK handshaking line. When it is ready to receive the next byte it lowers UB_ACK. The external processor must send the next byte to the CO₂module within 10 milliseconds from the time the UB_ACK line goes low. This handshaking between bytes provides flow control and insures that the external processor does not overrun the CO₂module's input buffer and that the CO₂module does not wait indefinitely for the external processor to send the next byte. After receiving the final byte of the request data-packet, the CO₂module again raises UB_ACK.
When the CO₂module has processed the request and is ready to send the first byte of the response data-packet, the CO₂module lowers UB_ACK. The external processor has 10 milliseconds from the time the UB_ACK lines goes low in order to start the clock and receive the byte. After transmitting the byte, the CO₂module raises UB_ACK, and lowers it again when it is ready to transmit the next byte. The process continues until all bytes of the response data-packet have been transmitted to the external processor. The 10 millisecond time limit insures that the CO₂module does not wait indefinitely for the external processor to start the clock to receive the byte.
After sending the final byte in a response, the CO₂module raises UB_ACK and leave it high. The external processor then raises UB_REQ, concluding the data interchange. UB_REQ must stay high longer than a specified minimum before the external processor lowers it to start the next data exchange.
At the conclusion of a response data packet, the CO₂module will wait approximately 100 milliseconds after the final UB_ACK goes high before initiating its return to master mode and the resuming of data collection. If the external processor raises and lowers UB_REQ during this delay interval, the module stays in slave mode and immediately services the new request. The delay interval gives the external processor the opportunity to send a series of commands in rapid succession to the module. Note that the CO₂module is not functioning as a sensor while it is in the slave mode.
The raising of UB_REQ, together with the expiration of the delay time interval, is the signal to the CO₂module to return to Microwire master mode and resume its A/D converter data collection. Microwire mode conversion and re-initialization for data collection is a time consuming process, and the module has only three opportunities during the process to abort and respond to a new UB_REQ. Hence, for non-PPM/Temperature request, it is most time-efficient to start the next UB_REQ during the delay interval following the previous request.
If the external processor needs to terminate an incomplete data exchange it raises the UB_REQ line. When the CO₂module see this, it discards the contents of its communication buffers and then respond by raising the UB_ACK.
If the CO₂module needs to terminate an incomplete data exchange, it raise UB_ACK. If UB_ACK remains high longer than the maximum time specified for UB_ACK High Between Bytes, then the external processor must recognize this as termination of an incomplete data exchange. For example, if the CO₂module receives bytes that do not correspond to a valid request data-packet then it raises UB_ACK and holds it high, signaling termination of an incomplete data exchange.
The CO₂module starts a 10 millisecond timeout timer each time it lowers UB_ACK. The external processor must respond by starting the serial shift clock within this interval so that the module can transmit or receive the pending byte. If the external processor fails to start the clock, the CO₂module presumes that the communication has been aborted and will raise UB_ACK.
If either the external processor or the CO₂module terminates a data exchange, no new communication can be initiated until both UB_ACK and UB_REQ have return to the high state. The new command then starts with the external processor lowering UB_REQ as described above.
The inventive system comprises a processor that receives the qualitative and quantitave signal from the carbon dioxide sensor and provides feedback control to an electronic control unit (ECU). ECU receives the sensor signal and processes the signal to determine the appropriate adjustment, if any, to the flow of air to be mixed with fuel for combustion in the burner unit. The signal reflecting the carbon dioxide concentration in the exhaust gas is then compared to a predetermined database of desired airflow adjustment values. Based on the comparison of the actual airflow to the desired airflow adjustment value, the ECU then generates a plurality of output signals, for variably controlling a pressure regulator of a gas intake flow valve and other respective components of the system so as to effectively ensure, that the future carbon dioxide concentration in the exhaust gas is maintained within the prescribed optimum range.
The combustion control scheme is most preferably implemented in software contained in ECU that includes a central processing unit such as a micro-controller, micro-processor, or other suitable micro-computing unit. Accordingly, the unique system achieves high efficiency combustion in a wide variety of gas heating appliances.

Claims

1. A high efficiency fuel injection system for gas appliances, the system comprising in combination:

a) means for qualitative and quantitative sampling of combustion exhaust gas from a appliance;

b) sensor means for detecting the concentration of a component selected from the group consisting of carbon dioxide, carbon monoxide and/or oxygen and combinations thereof present in the combustion exhaust gas;

c) means converting the detected concentration of said component to a digital value signal for relay to a central processor unit;

d) means for comparing the carbon dioxide concentration value signal with a stored desired concentration value;

e) means for continuously entering the digital value signal into a computer and comparing the value signal with the desired concentration value;

f) means for converting the digitized values to calibrated values;

g) means for calculating the desired air flow for optimum combustion efficiency from the calibrated value;

h) means for directing the signal derived from the computer to a regulator valve for adjusting the concentration of fuel and air for future combustion.