Use of Dynamic Valving to Achieve Residual-Affected Combustion

Studies have been conducted to assess the potential of variable valve actuation to initiate homogeneous charge compression ignition (HCCI) through reinduction of exhaust from the previous combustion cycle. As opposed to strategies which induce HCCI through use of either intake or exhaust throttling, use of exhaust reinduction incurs no pumping penalty, making it particularly attractive as a method for achieving efficient, light-load combustion. Using a fully flexible electrohydraulic valve actuation system, tests were conducted on a single-cylinder research engine using three strategies: late exhaust valve closing, late intake valve opening (used in conjunction with the exhaust valve being left open throughout the intake stroke), and a combination of the two. Results show that IMEP values from ∼30-55% of unthrottled SI combustion output could be obtained by varying the valve timings used to implement reinduction. Phasing of autoignition was found to depend strongly on exhaust valve closing time. Peak pressures during HCCI were as large as those found for unthrottled SI combustion (at MBT timing) despite the fact that only a fraction of the work output was produced in HCCI mode.