Abstract
A heavy-duty naturally aspirated diesel engine was converted into a turbocharged, aftercooled, CNG engine. A lean combustion system was adopted for economy and durability. An electronic engine control system was developed to make the operational characteristics of the CNG engine almost the same as the base diesel engine and to maintain as low levels of exhaust emissions as possible. This paper deals with several features implemented in the electronic control system, such as controls for air-fuel ratio, ignition timing, idle speed, overrun protection and exhaust brake, as well as self diagnostic and fail-safe functions.