Predictive model-based spark control
In certain embodiments, remarkable improvements in H 2 -ICE performance may be achieved with the combination of Active Scavenge Prechamber technology and Predictive Model-Based Spark Control to overcome the drawbacks of known combustion technologies. In certain embodiments, advanced combustion modeling and simulations of the ignition process including the spark event, the arc-travel and stretching, and resulting flame propagation may be used to predict the relationship between the spark energy/power, the flow within the electrode gap, and the flame development (SOC) for different engines, different spark plugs and at various conditions. This information may be used to adjust the spark energy/power characteristic during the same cycle spark event, to minimize the SOC variations and to significantly reduce the propensity to combustion anomalies, such as backfire, knock and preignition, that prevent achieving high engine power densities and efficiencies.
1. A method of controlling the start of combustion in an internal combustion engine, comprising:
providing a prechamber comprising:
an external surface and an internal surface enclosing a prechamber volume;
one or more ejection ports communicating between the external surface and the internal surface for introducing a fuel-air mixture into the prechamber volume;
a spark-gap electrode assembly, comprising:
a primary electrode disposed within the prechamber volume; and
one or more ground electrodes disposed within the prechamber volume and offset from the primary electrode to form one or more electrode gaps;
introducing a spark across at least one of the one or more electrodes gaps to ignite the fuel-air mixture;
measuring the initial trend of spark voltage or spark current of the spark;
determining whether the spark was initiated at the leading edge or trailing edge of the electrode gap;
determining whether the flow at the location of the spark is fast or slow; and
adjusting a power of the spark based on whether the spark was initiated at the leading edge or trailing edge and whether the flow of the spark is fast or slow to control the initial rate of flame propagation by adjusting the ignition delay to maintain a substantially constant start of combustion.
2. The method of claim 1 , wherein the one or more electrode gaps have a surface-to-volume ratio between about 2 mm −1 and about 4 mm −1 .
3. The method of claim 2 , wherein the surface-to-volume ratio of the one or more electrode gaps varies proportionally with BMEP from about 2 mm −1 for engine power density of about 10 bar BMEP to about 4 mm −1 for engine power density of about 20 bar BMEP.
4. The method of claim 1 , wherein the fuel-air mixture has uniform flow velocity distributions in the prechamber volume and electrode gap that vary by less than 50% from cycle to cycle.
5. The method of claim 1 , wherein the power of the spark is adjusted by predetermined amounts determined using combustion simulations and stored in one or more ignition control module lookup tables to achieve a target start of combustion value and to achieve stable engine operation.
6. The method of claim 1 , wherein the power to the spark is increased if the spark was initiated at the leading edge.
7. The method of claim 6 , wherein the power of the spark is increased inversely proportional to the flow velocity at the location of the spark.
8. The method of claim 1 , wherein the power to the spark is decreased if the spark was initiated at the trailing edge.
9. The method of claim 8 , wherein the power of the spark is decreased inversely proportional to the flow velocity at the location of the spark.
10. The method of claim 1 , wherein the determining steps comprise comparing the initial trend of spark voltage or spark current of the spark with predetermined spark waveforms.
11. The method of claim 10 , wherein the predetermined spark waveforms are determined by considering at least one of whether the spark initially is located between the leading edge and trailing edge and whether the spark initially has a flow velocity between an average leading edge velocity and an average trailing edge velocity.
12. The method of claim 1 , wherein the step of adjusting the power of the spark is performed in the same cycle in which the spark was introduced to achieve a target start of combustion.
13. The method of claim 1 , further comprising determining an arc blowout condition exists when a steep, short increase of the spark voltage is detected to be exponential or a sinusoidal ringing.
14. The method of claim 1 , further comprising determining that a stable flame condition exists when either of the following is detected: (1) a flat trend of the spark voltage after a voltage breakdown event followed by a later rate of increase that is above a predetermined value; or (2) an immediate increase in spark voltage after a voltage breakdown event that is not exponential or a sinusoidal ringing and that has a rate of increase below a predetermined value.
15. The method of claim 1 , further comprising determining that a flame quenching or slow combustion condition exists when either of the following is detected: (1) decreasing spark voltage after a voltage breakdown event indicating insufficient arc travel and stretching from the leading edge of the electrodes; or (2) increasing spark voltage at a rate above a predetermined value after a voltage breakdown event indicating an arc blowout is predicted from the trailing edge or leading edge of the electrodes.
16. The method of claim 1 , further comprising determining that a fast combustion or knock condition exists when an increasing spark voltage within a predeterminate range is detected after a voltage breakdown event.
17. The method of claim 1 , further comprising predicting the start of combustion based on one or more of engine design, fuel characteristics and one or more operating conditions using at least one of the spark voltage or the spark current trends after a voltage breakdown event.
18. A high energy programmable ignition system for internal combustion engines comprising:
at least one of a spark voltage sensor for sensing a spark voltage from one or more spark gap electrodes in a prechamber and a spark current sensor for sensing a spark current from one or more spark gap electrodes in a prechamber; and
an ignition control module configured to
receive at least one of the spark voltage and the spark current from the one or more spark gap electrodes,
measure the initial trend of spark voltage or spark current of the one or more spark gap electrodes;
determine whether the spark was initiated at the leading edge or trailing edge of the one or more spark gap electrodes;
determine whether the flow at the location of the spark is fast or slow;
adjust a power to the spark based on whether the spark was initiated at the leading edge or trailing edge and whether the flow of the spark is fast or slow to control the initial rate of flame growth by adjusting the ignition delay to maintain a substantially constant start of combustion.
19. The system of claim 18 , wherein the ignition control module is configured to adjust the power of the spark by predetermined amounts determined using combustion simulations and stored in one or more ignition control module lookup tables to achieve a target start of combustion value and to achieve stable engine operation.
20. The system of claim 18 , wherein the ignition control module is configured to increase the power to the spark if the spark was initiated at the leading edge.
21. The system of claim 20 , wherein the ignition control module is configured to increase the power of the spark inversely proportional to the flow velocity at the location of the spark.
22. The system of claim 18 , wherein the ignition control module is configured to decrease the power to the spark if the spark was initiated at the trailing edge.
23. The system of claim 22 , wherein the ignition control module is configured to decrease the power of the spark inversely proportional to the flow velocity at the location of the spark.
24. The system of claim 18 , wherein the ignition control module is configured to compare the initial trend of spark voltage or spark current of the spark with predetermined spark waveforms.
25. The system of claim 24 , wherein the predetermined spark waveforms are determined by considering at least one of whether the spark initially is located between the leading edge and trailing edge and whether the spark initially has a flow velocity between an average leading edge velocity and an average trailing edge velocity.
26. The system of claim 18 , wherein the ignition control module is configured to adjust the power of the spark in the same cycle in which the spark was introduced to achieve a target start of combustion.
27. The system of claim 18 , wherein the ignition control module is configured to determine an arc blowout condition exists when a steep, short increase of the spark voltage is detected to be exponential or a sinusoidal ringing.
28. The system of claim 18 , wherein the ignition control module further is configured to determine that a stable flame condition exists when either of the following is detected: (1) a flat trend of the spark voltage after a voltage breakdown event followed by a later rate of increase that is above a predetermined value; or (2) an immediate increase in spark voltage after a voltage breakdown event that is not exponential or a sinusoidal ringing and that has a rate of increase below a predetermined value.
29. The system of claim 18 , wherein the ignition control module further is configured to determine that a flame quenching or slow combustion condition exists when either of the following is detected: (1) decreasing spark voltage after a voltage breakdown event indicating insufficient arc travel and stretching from the leading edge of the electrodes; or (2) increasing spark voltage at a rate above a predeterminate value after a voltage breakdown event indicating an arc blowout is predicted from the trailing edge or leading edge of the electrodes.
30. The system of claim 18 , wherein the ignition control module further is configured to determine that a fast combustion or knock condition exists when an increasing spark voltage within a predetermined range is detected after a voltage breakdown event.
31. The system of claim 18 , wherein the ignition control module further is configured to predict the start of combustion based on one or more of engine design, fuel characteristics and one or more operating conditions using at least one of the spark voltage or the spark current trends after a voltage breakdown event.