THE USE OF PERSONAL COMPUTER TO CONTROL THE AIR- FUEL RATIOS IN SI ENGINES FOR BEST PERFORMANCE

Abstract

Nowadays, controlling the air to fuel ratio in SI engines becomes an essential task. This is due to the environmental pollution problem and the depletion of petroleum resources. Running SI engines on the optimum air to file! ratio improves the fuel consumption and decreases harmful emissions in the exhaust as well.

The present work applies a self regulative concept by using an electronic-mechanical system to run the controlled SI engine on the optimum air to fuel ratio corresponding to the maximum thermal efficiency at certain load conditions. This is done in two different ways.

The first way is to create a look-up table of the optimum air to fuel ratios corresponding to load range from 10% to 90% of the full load. But due to engine aging , the performance decays and therefore, the look-up table values becomes old and does not represent the current performance of the engine. The second way is to select the optimum AIF ratio at the applied load while the engine is running. This is done by the on line computation of the engine thermal efficiency at a specified range of air-fuel ratio. Although the look-up table method has much less settling time but the table data should be updated from time to time.

Four sets of experiments were carried out. The first set focused on selection of the best parameters of the PID controller for good engine stability and a short settling time. The second set focused on the creation of a look up table for best economy air-fuel ratio values over a wide range of applied loads.