Stoichiometric fuel

Can someone explain to me how it is possible that HHO decrease the fuel consumption?
I read that the stoichiometric ratio of diesel or gasoline changes from 14.6:1 to 20:1. But looking to the definition of the stoichio it is a fixed value depending on the molecular weight for a 100% burning. This can never be changed. Burning efficiency for diesel is +/- 50% for gasoline +/- 30%. The amount of HHO is +/- 0.1% of the air intake or <1% of the fuel injected. What causes the 30% saving on fuel? As the air/fuel ratio cannot be changed? What happens during combustion?

Why can not the air fuel ratio be changed? Only someone with very sophisticated equipment will be able to determine what is happening in the combustion chamber. That is were some of what gives us gains happens. There is lot of theory but little real tests to confirm the theories. The bottom line is if there is gains you should be satisfied. If there is no gains then something is wrong and that could be a number of things. There is no doubt that if everything is right there is gains. The amount can be debated and is over stated in a lot of cases. Some claim the gains are only because the air fuel ratio is changed to a leaner mixture. Maybe, but there should be excess heat if this is the case and there is not when done right.