Researchers Push Knock Control to the Edge

Scientists at Villanova University in suburban Philadelphia say tweaking the configuration of a standard engine knock control system can significantly boost fuel efficiency, lower emissions and increase torque without damaging the powerplant.

The three-member team reports on its work to date in the current International Journal of Engine Research.

Knock occurs when an engine's air-fuel mixture ignites prematurely. The resulting shock waves generate abnormally high temperatures and pressure within the cylinder that reduce torque, boost oxides of nitrogen emissions and can produce an audible rattle. Severe knock can damage the engine.

To avoid the problem, traditional controls use piezoelectric sensors to measure engine noise and compare it with condition sets that define the onset of knock. The system then retards ignition timing for one or more cylinders to avoid crossing the threshold.

The approach being developed at Villanova analyzes knock in terms of its statistical distribution rather than fixed sets of preconditions. The researchers say modifying a conventional knock controller accordingly gives the system faster transient response, more accurate spark adjustments and less variation in combustion patterns.