Abstract
A four-valve spark ignition engine combustion system has been tested with normal valve operation and with each inlet valve disabled in turn. A steady flow air rig has been used to establish the flow, barrel swirl and axial swirl characteristics. The combustion performance has been evaluated at five operating points, to determine the effect of the increased swirl with inlet valve disablement. The tests showed that the combustion was faster, with a lower level of cycle-by-cycle variation in combustion; the peak cylinder pressures also rose slightly and occurred closer to top dead centre (TDC). A computer model has been used to investigate the effect of faster burn on the trade-off between engine output, efficiency and nitrogen oxide emissions. It is concluded that a faster burn, with an ignition timing retarded to give the baseline output, should lead to a reduction in nitrogen oxide emissions. This is confirmed by a modelling exercise, which also indicated that using exhaust gas recirculation (EGR) should lead to reductions in both the nitrogen oxide emissions and the part load fuel consumption.
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