75 Development of an Electronically Controlled Carburetion System to Reduce the Exhaust Emissions of Small IC Engines for Handheld Power Tools

In order to meet the new stringent emission limits for small handheld power tools technologies like methods to improve the scavenging process and after treatment devices are deployed. Additionally, professional machines such as chain saws add particular requirements to avoid mechanical failures. By precise control of the carburetion it is possible to yield the necessary reduction of the emission level yet to maintain the performance of the engine.

Thus, the development of an Electronically Controlled Carburetion System to reduce the exhaust emissions of small IC engines for handheld power tools was initiated at the WHZ, Germany. Key requirements of such a system are: low cost, high reliability, low electrical power consumption, high accuracy in metering the fuel demand of the engine. First results are promising. A correlation between exhaust gas temperature and the fuel demand of the engine was confirmed for both, wide open throttle and part load operation. A strategy to calibrate the temperature-fuel consumption relation for individual engines or varying ambient conditions was developed. The delivery ratio between fuel demand vs. fuel supply is better than 1.5% over the range of operation.

Based on this principle it is possible to design a simple economical electronically controlled carburetion system with low electrical power consumption which is essential for the application in handheld tools.