What is the heat of combustion for a H2:O2 4.1:1 mixture in BTUs/ Nm3 or MJ/Nm3
Also for 2:1 and 3:1 and 5:1 mixture ratios.

In the case of fuel-rich mixtures like those in the question, the heat of combustion for the mixture should be calculated on the basis of the oxygen content of the mixture. The heat of combustion per mole oxygen is twice the heat of combustion per mole hydrogen, i.e., it is 286*2 kJ per mole O2. You should be able to do the calculations based on this reply.