Experimental study of a novel valvetrain system on SI engine efficiency and emissions

Abstract

Strict emissions legislations and continuous race for improvement of fuel economy urge to develop more efficient and cleaner IC engines for commercial and private use. Engine downsizing has been shown as an effective means to reduce the vehicle’s fuel consumption but the full potential of engine downsizing is limited by the knocking combustion at boosted operations and the presence of pumping loss at part load conditions. A variable valve train system can be used to minimise the knocking combustion by implementing Miller and Atkinson cycles through alteration of the effective compression ratio (ECR) at high load via Early Intake Valve Closure (EIVC) or Late Intake Valve Closure (LIVC), as well as reducing the pumping loss at part load. In this work, a single cylinder direct injection Spark Ignition (SI) gasoline engine equipped with an electro-mechanical valvetrain system named iVT (intelligent Valve Technology) by Camcon was set up and used to investigate the potential benefits of the iVT. Engine experiments were carried out at 1500 and 3000rpm with various valve profiles including EIVC and LIVC with single and two intake valve mode as well as early intake Maximum Opening Position (MOP) at 35% and 40% MOP. Their effects on engine performance and emissions were measured and analysed at 4, 6, 9 and 12.6bar net IMEP. Results showed that EIVC and LIVC profiles were successful in reducing the fuel consumption with two valve mode at low loads thanks to lower pumping loss and at high loads where spark timing was knock limited. Those profiles also resulted in lower emissions. In particular, the LIVC profile reduced the NOX concentration by up to 20% at low loads due to lowest ECR. Single valve mode operations also provided improved fuel economy at 4bar and 12.6bar net IMEP when combined with EIVC profiles. However, the most significant reduction in ISFC was achieved with early MOP. With combination of LIVC and early MOP, ISFC was reduced by up to 5.4% at low load and by up to 7.1% at high load compared to the baseline profile at 1500rpm.