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The objective of this investigation was to evaluate the effects of a variable intake and exhaust valve timing in terms of opening, closing, opening duration, lift curve and number of active valves per pair on a four cylinder direct-injecting SI engine for the catalyst heating idling phase at the beginning of an NEDC emission test procedure. The first step evaluated the engine behavior at a reference point of operation. Its parameters in valve timing were adjusted to match the valve timing of the base production engine. The second step investigated the effects of an earlier exhaust valve opening while the exhaust valve closing time was kept and the exhaust valve opening duration was extended. The third step was to answer the question for the optimum number of exhaust valves in order to minimize the wall heat losses inside the cylinder head. The optimum 3V exhaust valve timing has been defined as the basis for exhaust valve timing for steps four and five.

A promising combustion technology for DISI downsizing engines is the Miller cycle. It is based on an early intake valve closing for the separation of effective and geometric compression ratio. Therefore IAV has prepared a turbocharged DISI test engine with a high geometric compression ratio. This engine is equipped with the Schaeffler “UniAir” variable valve train in order to investigate a variable Miller cycle valve timing in the turbocharged map area. The goal is to investigate whether and how a rapidly variable Miller cycle can influence the knocking behavior. Therefore its potential for a SI knock control can be evaluated. The investigated parameters in a steady-state engine dyno mode were the intake valve closing timing, the intake camshaft phasing and the ignition timing. A variable intake valve closing Miller cycle strategy, a variable intake camshaft phasing Miller cycle strategy and a state-of-the- art ignition timing strategy have been investigated.