Air-Fuel Ratio Control in a Multi-Fuel Internal Combustion Engine

An apparatus for controlling air-fuel ratio in an internal combustion engine consuming more than one fuel type comprising:

• (a) a direct fuel injector introducing a first fuel into a combustion chamber of said internal combustion engine;
• (b) a second fuel injector introducing a second fuel into said combustion chamber;
• (c) an electronic control programmed to:
• (i) determine a target air-fuel ratio as a function of engine operating conditions;
• (ii) determine an actual air-fuel ratio from said engine operating conditions;
• (iii) determine a first fuel quantity of said first fuel to introduce through said direct fuel injector as a function of said engine operating conditions;
• (iv) determine a second fuel quantity of said second fuel such that said actual air-fuel ratio equals said target air-fuel ratio to within a predetermined range of tolerance when said first fuel quantity and said second fuel quantity are introduced into said combustion chamber, said second fuel quantity determined as a function of said engine operating conditions, said target air-fuel ratio, said actual air-fuel ratio and said first fuel quantity;
• and
• (v) actuate said direct fuel injector to introduce said first fuel quantity and said second fuel injector to introduce said second fuel quantity into said combustion chamber.