Un-throttling a direct injection gasoline homogeneous mixture engine with variable valve actuation

Two direct injection spark ignition (DISI) engines with identical combustion chamber geometries and fuel injection systems were used to investigate fuel economy, exhaust emissions, the in-cylinder flow field, the fuel spray behaviour and combustion characteristics with early inlet valve closure (EIVC) strategies aimed at reducing parasitic induction work owing to throttling. One engine had extensive optical access through a transparent piston crown and transparent cylinder liner, while the other all-metal engine allowed continuous running. Engine running focused at low and intermediate engine loads (∼ 3 and ∼ 6 bar indicated mean effective pressure) and two engine speeds (2000 and 3500 r/min). The results show that the indicated specific fuel consumption (ISFC) could be reduced by almost 6 per cent without significant deterioration in gaseous exhaust pollutant emissions. The results also show that the in-cylinder bulk flow and turbulence and the thermodynamic conditions during combustion are affected significantly by EIVC operation.