A smart way to control A/F mixture ratio in small utility engines is needed to meet future emission standards and to improve fuel economy. Dell'Orto proposes a novel carburation technology, that join an effective way to vary A/F mixture with a closed-loop electronic control strategy. The electronic carburetor is able to control A/F mixture ratio in the lean combustion range, improving both emission and fuel economy.
The mixture formation control is achieved by meaning of a solenoid valve on a main air bleed circuit. An electronic controller is used to drive the solenoid valve, according to the engine operating conditions.
The test engine used is a four stroke, air cooled, single cylinder OHV engine with CDI ignition and mechanical speed governor. The control strategy is based on engine speed monitoring. The system normally forces the mixture on the lean side. An incipient lean misfire event is detected by cycle periods processing. When cycle by cycle deviation threshold is detected, then electronic controller forces the mixture to go back to the rich side, for the better combustion. Then, the system returns again to control the mixture in the lean range. By adjusting the control parameters, a lean and stable running is achieved. Results on SAE J1088 six mode test cycle shows a strong reduction in fuel consumption as well as in the HCs and CO emissions.
The system detects directly the lean bondary condition, and thus it's self adaptive to the various operating conditons such as altitude, wears, filter clogging, carbon deposits, tolerances, climatic conditions, fuels and so on. After start and transient behaviour are also improved, since the system control A/F mixture according to the engine requirements.
This new development is designed to simply replace the standard carburetors. No additional sensors are required. Electric power requirements for control unit and solenoid valve supply are very low. Furthermore, the final product concept is shown, reducing the system to one component by integrating the electronic controller.