The call for greenhouse gas emission reduction as the result of global warming has been the main cause of the more rigorous emission legislation in the road transportation sector. In response to such requirements, car makers opt for the ‘down-sizing’ trend for engine displacement with the aim to increase brake thermal efficiency by increasing engine load (mean effective pressure). However, this leads to higher potential of engine knocking and elevated NOx emissions. This study investigates the effects of combustion phasing induced by water injection via the intake manifold of a naturally aspirated GDI engine at MBT ignition timing fuelled with E20. Water up to 30% of fuel mass is portinjected during high engine load and maximum NOx reduction of up to 82% could be achieved as the result of lower RoHR caused by vaporisation of water. Water injection prolonged the ignition delay and combustion duration (CA1090) without deterioration of combustion stability (%COV of IMEP). The optimisation of ignition timing based on MBT can improve CO emission compared to EGR systems. The proposed study demonstrates the possibility to achieve low nitrogen emissions without the need of precious metal-based catalysts.