Load Control Using Late Intake Valve Closing in a Cross Flow Cylinder Head

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Load Control Using Late Intake Valve Closing in a Cross Flow Cylinder Head

Johansson, Bengt / Söderberg, Fredrik

A newly developed cross flow cylinder head has been used for comparison between throttled and unthrottled operation using late intake valve closing. Pressure measurements have been used for calculations of indicated load and heat-release. Emission measurements has also been made. A model was used for estimating the amount of residual gases resulting from the different load strategies.Unthrottled operation using late intake valve closing resulted in lower pumping losses, but also in increased amounts of residual gases, using this cylinder head. This is due to the special design, with one intake valve and one exhaust valve per camshaft. Late intake valve closing was achieved by phasing one of the camshafts, resulting in late exhaust valve closing as well. With very late phasing - i.e. low load - the effective compression ratio was reduced. This, in combination with high amount of residual gases, resulted in a very unstable combustion.The main combustion, 10-90% heat-release, was quite fast for all load control strategies, indicating high turbulence. This could not be seen in the early combustion, however.An increase in fuel conversion efficiency could be achieved with up to 9%. The emissions of NOx were reduced by 4-5 g/kWh with LIVC for loads between 4-8 bar IMEPnet.