Method and system for pre-ignition control
Methods and systems are provided for adjusting spark and/or fuel injection to a cylinder based on late combustion, partial burn, or misfire in a neighboring cylinder. A pressure sensor coupled to a cylinder exhaust port is used to sample exhaust pressure pulsations over a cylinder exhaust valve event, and accurately estimate an amount of residuals generated in and released from the cylinder as well as residuals received from the neighboring cylinder. Mitigating actions are performed in the cylinder in accordance before the occurrence of a pre-ignition event.
1. A method for an engine, comprising:
indicating imminent pre-ignition in a cylinder responsive to an amount of residuals received or generated in the cylinder, the amount of residuals based on a peak exhaust pressure amount and timing, and an intake manifold pressure; and
adjusting fueling of the cylinder based on the indication and further based on the amount of residuals.
2. The method of claim 1 , wherein the amount of residuals is based on the exhaust pressure amount relative to the intake manifold pressure as well as the peak exhaust pressure amount and timing, the amount of residuals increased as the exhaust pressure amount exceeds the intake manifold pressure, the amount of residuals further based on an exhaust pressure profile over an exhaust valve event.
3. The method of claim 1 , wherein the exhaust pressure amount is estimated by a pressure sensor coupled to an exhaust port of the cylinder over an exhaust valve event.
4. The method of claim 1 , wherein the indicating includes:
comparing a force generated by the amount of residuals at the cylinder relative to a force holding an exhaust valve seat of the cylinder closed; and
indicating imminent pre-ignition when the force generated by the amount of residuals is larger than the force holding the exhaust valve seat of the cylinder closed.
5. The method of claim 1 , wherein indicating imminent pre-ignition includes indicating pre-ignition may occur in the cylinder before an actual incidence of pre-ignition in the cylinder.
6. The method of claim 1 , further comprising, based on valve timing, determining whether the amount of residuals is released from the cylinder.
7. The method of claim 6 , wherein the cylinder is a first cylinder, the method further comprising, based on the valve timing, identifying a second cylinder receiving the amount of residuals from the cylinder.
8. The method of claim 1 , further comprising adjusting fueling of the cylinder based on a temperature of the amount of residuals.
9. The method of claim 8 , wherein the adjusting includes, when the temperature of the amount of residuals is lower than a threshold, enriching the cylinder; and when the temperature of the amount of residuals is higher than the threshold, disabling fuel to the cylinder or ceasing a compression stroke injection while maintaining an intake stroke injection of the cylinder.
10. The method of claim 1 , further comprising updating an estimate of internal EGR in the cylinder based on the amount of residuals.
11. The method of claim 10 , further comprising adjusting one or more of cylinder valve timing, cylinder spark timing, and an engine external EGR amount based on the updated estimate of internal EGR in the cylinder.
12. A method for an engine, comprising:
estimating an amount and temperature of exhaust residuals generated in a first cylinder based on exhaust pressure reading changes relative to intake manifold pressure readings over an exhaust valve event of the first cylinder, including by estimating exhaust pressure pulsations in each cylinder based on an amount and timing of a peak exhaust pressure during the exhaust valve event; and
adjusting fueling of a second cylinder based on the estimated amount and temperature of the residuals generated in the first cylinder.
13. The method of claim 12 , wherein the second cylinder receives at least a portion of exhaust residuals from combustion in the first cylinder.
14. The method of claim 13 , wherein the adjusting includes:
in response to the amount of residuals in the first cylinder being lower than a threshold amount and the temperature of the residuals being lower than a threshold temperature, enriching the second cylinder;
in response to the amount of residuals in the first cylinder being lower than the threshold amount and the temperature of the residuals being higher than the threshold temperature, selectively deactivating spark ignition or fuel to the second cylinder; and
in response to the amount of residuals in the first cylinder being higher than the threshold amount, selectively deactivating spark ignition and fuel to the second cylinder, wherein selectively deactivating fuel includes selectively deactivating delivery of fuel in at least a compression stroke to the second cylinder.
15. The method of claim 14 , further comprising estimating the portion of exhaust residuals received in the second cylinder from the first cylinder based on valve timing and further based on exhaust pressure reading changes over a valve event of the second cylinder, and increasing a degree of richness of the enriching as the portion increases.
16. The method of claim 13 , further comprising identifying the second cylinder based on the amount and temperature of exhaust residuals generated in the first cylinder and further based on valve timing.
17. The method of claim 12 , further comprising adjusting one or more of fueling, spark timing, and spark energy of the first cylinder based on the estimated amount and temperature of the exhaust residuals.
18. the method of claim 12 , further comprising estimating exhaust pressure pulsations in each cylinder based on instantaneous and peak exhaust pressure over the exhaust valve event, rather than an average exhaust pressure.