This paper describes the optimization of the piston bowl geometry and the operating conditions of a dual-fuel engine based on a compression ignition engine using gasoline port fuel injection and diesel direct injection. KIVA-3V code coupled with a CHEMKIN chemistry solver was used for simulation and a micro-genetic algorithm was used as the optimization algorithm. The micro-genetic algorithm has a smaller population than a conventional genetic algorithm. And in the optimization, the proposed algorithm has six populations for each generation, sixteen variables composed of seven geometry variables and nine operating condition variables. As a result of optimization, a 9% improvement in the gross indicated specific fuel consumption and a simultaneous decrease of the overall NOx and soot emissions were achieved. Also, the amounts of carbon monoxide and unburned hydrocarbons were decreased. The baseline case has a re-entrant shape, while the optimized case has a shallow shape and a narrower spray angle. Furthermore, under operating conditions, the gasoline/total fuel ratio was increased to 90% (similar to a gasoline HCCI (Homogenous charge compression ignition) engine), the EGR (Exhaust gas recirculation) rate was increased to 40% for dilution, and both the boost pressure and initial temperature were decreased. (C) 2017 Elsevier Ltd. All rights reserved.