The objective of this project is to understand the role of real engine circumstances on auto-ignition in ultra-lean dual-fuel gas mixtures. The research is carried out using both experimental and computational studies. The experimental studies conducted at Aalto University utilizes an optical research engine and laser diagnostics facilities. Large Eddy Simulation is used to complement the experimental studies. Detailed reaction kinetics calculations used to to gain a deeper insight into the role of inhomogenities in mixture preparation and of mixing on the auto-ignition process.