Internal combustion engine based cogeneration and trigeneration plants are capable of producing several energy types from a single fuel input simultaneously. An increase in the number of cogeneration and trigeneration plants especially in social and industrial facilities day by day has strengthened the role of these plants in the study of energy efficiency and distributed generation. In addition to those, realization of license exemption for facilities want to produce electricity just for their energy demands by ensuring the condition of 80% total efficiency, low carbon emission of systems contain gas engines, rapid operation for synchronization and shortness of payback periods make cogeneration and trigeneration plants popular in recent years.