Small engine control by fuzzy logic

Small spark-ignition gasoline-fuelled internal-combustion engines can be found all over the world performing in various roles including power generation, agricultural applications and motive power for small boats. To attain low cost, these engines are typically air-cooled, use simple carburettors to regulate the fuel supply, and employ magneto ignition systems. Electronic control, of the sort found in automotive engines, has seldom proved cost-effective for use with small engines. However, the future trend towards engines that have low levels of polluting exhaust emissions will make electronic control necessary, even for small engines. This paper describes a fuzzy control system applied to a small engine to achieve regulation of the fuel injection system. The system determines the amount of fuel required by a fuzzy algorithm that uses the engine speed and manifold air pressure as input values. The parameters of this fuzzy control paradigm were a collection of rules and fuzzy-set membership functions. These were intuitively comprehensible by the operator. This facilitated the calibration process, leading to quick and convenient tuning. Experimental results show that a considerable improvement in fuel regulation was achieved compared to the original carburettor-based engine configuration. In addition measurements of HC and CO emissions show a corresponding reduction.