Natural gas engines with fuel quality determination
Systems and methods for automatic calibration of large industrial engines in applications where the quality of the fuel supply is unknown and/or variable over time, particularly engines that drive compressors on a natural gas well site. A combination of throttles and an oxygen sensor are disclosed, whereby the combination involves a mass-flow-air (MFA) throttle and a mass-flow-gas (MFG) throttle to determine the mass flow of air and mass flow of gas. As a response to exhaust gas oxygen level readings, the mass flow measurements are used to determine real time air-fuel ratios. An algorithm uses the air-fuel ratios as input data, wherein a microcontroller adjusts the throttles to meet engine performance demands. Additionally, using the air-fuel ratio data and suggested engine OEM calibration specifications as block multiplier inputs, particular fuel properties can be accurately interpolated, thereby enabling automatic calibration of the engine and other interventions as desired.
1. A system comprising:
a) a mass-flow throttle operatively connected with an internal combustion engine for controlling a mass flow through an intake manifold of the internal combustion engine, wherein the mass flow is a mass flow of a gaseous fuel or air or a mixture of the air and the gaseous fuel; and
b) one or more processors for controlling operation of the system, the processors having data communication with a database correlating fuel quality measures with a plurality of possible values for a particular condition that characterizes the operation of the internal combustion engine, the one or more processors being programmed to:
determine via the mass-flow throttle a current measure of the mass flow through the intake manifold of the internal combustion engine;
determine a current air-fuel ratio from the current measure of the mass flow;
determine via the database an ideal air-fuel ratio based on a current operating condition of the internal combustion engine;
determine an ideal value for the mass flow based on the ideal air-fuel ratio;
calculate an error based on a difference between the current measure of the mass flow and the ideal value for the mass flow;
compare the error with a fuel property table including fuel properties associated with measures of error, the measures of error having been programmed in the fuel property table;
interpolate one or more properties of the gaseous fuel based on information in the database; and
adjust the operation of the internal combustion engine when the one or more interpolated properties require an adjustment of an operating condition of the internal combustion engine.
2. The system of claim 1 , wherein the mass-flow throttle is one of:
a mass-flow-gas (MFG) throttle configured to receive and quantify a quantity of the gaseous fuel; or
a mass-flow-air (MFA) throttle positioned downstream of the MFG throttle, the MFA throttle being configured to receive and quantify a quantity of the air.
3. The system of claim 2 , further comprising:
an oxygen sensor positioned in an exhaust manifold associated with the internal combustion engine, the exhaust manifold positioned downstream of the MFG throttle and the MFA throttle, the oxygen sensor being configured to sense an oxygen content in the gaseous fuel.
4. The system of claim 1 , wherein the database correlating fuel quality measures with the plurality of possible values for the particular condition comprises a fuel property database, where the fuel property database comprises information including fuel properties and air-fuel ratio adjustments of the internal combustion engine.
5. The system of claim 4 , wherein the fuel property database comprises one or more of British Thermal Unit values or Methane Number values for known fuels.
6. The system of claim 4 , wherein the fuel property database comprises one or more of engine spark advances and load limits for known fuels.
7. The system of claim 1 , wherein the processors are programmed to adjust the operation of the internal combustion engine to achieve a target phi value.
8. The system of claim 1 , wherein the mass-flow throttle further comprises:
a throttle blade position sensor configured to detect a position of a throttle blade of the mass-flow throttle;
a temperature sensor configured to take temperature readings of a fluid passageway of the mass-flow throttle; and
an upstream pressure sensor disposed upstream of the throttle blade and a downstream pressure sensor disposed downstream of the throttle blade, each pressure sensor configured to take pressure readings of the fluid passageway, and
wherein the one or more processors are further configured to use readings from the throttle blade, the temperature sensor, the upstream pressure sensor and the downstream pressure sensor in performing determinations and calculations.
9. A method for controlling operation of a system comprising a) a mass-flow throttle operatively connected with an internal combustion engine for controlling a mass flow through an intake manifold of the internal combustion engine, wherein the mass flow is a mass flow of a gaseous fuel or air or a mixture of the air and the gaseous fuel; and b) one or more processors, the processors having data communication with a database correlating fuel quality measures with a plurality of possible values for a particular condition that characterizes the operation of the internal combustion engine, the method comprising:
determining, via the mass-flow throttle, a current measure of the mass flow through the intake manifold of the internal combustion engine;
determining a current air-fuel ratio from the current measure of the mass flow;
determining, via the database, an ideal air-fuel ratio based on a current operating condition of the internal combustion engine;
determining an ideal value for the mass flow based on the ideal air-fuel ratio;
calculating an error based on a difference between the current measure of the mass flow and the ideal value for the mass flow;
comparing the error with a fuel property table including fuel properties associated with measures of error, the measures of error having been programmed in the fuel property table;
interpolating one or more properties of the gaseous fuel based on information in the database; and
adjusting the operation of the internal combustion engine when the one or more interpolated properties require an adjustment of an operating condition of the internal combustion engine.
10. The method of claim 9 , wherein the mass-flow throttle is one of:
a mass-flow-gas (MFG) throttle configured to receive and quantify a quantity of the gaseous fuel; or
a mass-flow-air (MFA) throttle positioned downstream of the MFG throttle, the MFA throttle being configured to receive and quantify a quantity of the air.
11. The method of claim 10 , wherein the system further comprises:
an oxygen sensor positioned in an exhaust manifold associated with the internal combustion engine, the exhaust manifold positioned downstream of the MFG throttle and the MFA throttle, the oxygen sensor being configured to sense an oxygen content in the gaseous fuel.
12. The method of claim 9 , wherein the database correlating fuel quality measures with the plurality of possible values for the particular condition comprises a fuel property database, and wherein the fuel property database comprises information including fuel properties and air-fuel ratio adjustments of the internal combustion engine.
13. The method of claim 12 , wherein the fuel property database comprises one or more of British Thermal Unit values or Methane Number values for known fuels.
14. The method of claim 12 , wherein the fuel property database comprises one or more of engine spark advances and load limits for known fuels.
15. The method of claim 9 , comprising adjusting the operation of the internal combustion engine to achieve a target phi value.
16. The method of claim 9 , wherein the mass-flow throttle further comprises:
a throttle blade position sensor configured to detect a position of a throttle blade of the mass-flow throttle;
a temperature sensor configured to take temperature readings of a fluid passageway of the mass-flow throttle; and
an upstream pressure sensor disposed upstream of the throttle blade and a downstream pressure sensor disposed downstream of the throttle blade, each pressure sensor configured to take pressure readings of the fluid passageway,
wherein the method comprises using readings from the throttle blade, the temperature sensor, the upstream pressure sensor and the downstream pressure sensor in performing various determinations and calculations.