Unthrottled Engine Operation with Variable Intake Valve Lift, Duration, and Timing

The part-load fuel consumption potential of unthrottled engine operation using variable valve actuation is evaluated for a single-cylinder version of the GM 3.4 L DOHC engine. The investigation focuses on evaluating the practical range of the early-intake-valve closing (EIVC) variable valve actuation strategy, which includes intake-valve-opening positions ranging from 360 to 420 crank-angle degrees ATDC, intake-valve durations ranging from 54 to 226 crank-angle degrees, and peak intake-valve lifts ranging from 0.75 to 4.5 mm. In addition to the experimental investigation, a one-dimensional simulation evaluation is completed to examine the potential of enhanced in-cylinder charge motion when implementing variable-valve actuation. A 7 % fuel consumption improvement is achieved for unthrottled engine operation when implementing the EIVC variable valve actuation strategy. This has been demonstrated at a part-load engine operating condition of 1300 rpm and 330 kPa net-mean-effective-pressure (NMEP) through the optimization of the intake-valve lift, duration, and timing while maintaining the conventional exhaust valve event. Along with this fuel consumption improvement, the engine-out HC emission level was 25 % higher and the engine-out NOx emission level was 25 % lower for unthrottled engine operation. Higher intake-valve velocities and in-cylinder charge motion could be achieved for unthrottled engine operation when using variable valve actuation; however, no significant combustion performance improvement was observed as a result of the enhanced charge motion.