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

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 were investigated using two direct injection spark ignition (DISI) engines with identical combustion chamber geometries and fuel injection systems. One of the engines had extensive optical access through a transparent piston crown and transparent cylinder liner, while the other all-metal engine enabled continuous running. Engine running was carried out at low and intermediate engine loads (~3 and ~6bar indicated mean effective pressure) and two engine speeds (2000 and 3500r/min). Specific fuel consumption was reduced by almost 6% without significant deterioration in gaseous exhaust pollutant emissions at the lowest engine speed of 2000rpm, lowest load of 2.7bar with the 2.1mm lift camshaft and only one inlet valve operating. The in-cylinder bulk flow and turbulence and the thermodynamic conditions during combustion were affected significantly by EIVC operation