Experimental Study On The Intake Port Fuel Dynamics For A Small SI Engine

Increasingly stringent regulations on motorcycle pollutant emissions have forced Chinese motorcycle manufacturers to adopt the Electronic Fuel Injection (EFI) System for motorcycles, following the same path the automotive industry has done. However, current motorcycle EFI system is much less advanced than its automotive equivalent, therefore, more fundamental studies are required to improve its performance and efficiency.The aim of this study is to experimentally determine the intake port fuel dynamics for a small motorcycle engine, based on the C. F. Aquino X-τmodel. The"fuel perturbation"method is used to identify the model parameters, X andτ. The"fuel perturbation"means introducing a step increase in the fuel injection pulse widths under engine steady state conditions to stimulate the fuel film dynamics, while keeping the engine speed and the throttle position constant. By curve-fitting the model-predicted air-fuel ratio trace and the UEGO sensor measured A/F trace using the least square routine, the model parameters X andτare determined. In order to cancel out the effects of the UEGO sensor response lag and the air-fuel ratio transport delays on the measured air-fuel ratio signals, experiments are designed to identify the time constants of the sensor and the time delays of the air-fuel ratio.Experiments are also carried out to find an engine temperature measurement point of the air-cooled motorcycle engine, which can be used as a proper reference indicating the influence of the temperature on the fuel film model parameters. This reference temperature serves the similar purpose as the engine coolant temperature as in water-cooled automotive engines. In common practice, cylinder head temperature or engine body temperature is used to indicate the thermal state of an air-cooled motorcycle engine, which usually donot indicate properly the actual value because these surface temperatures are strongly influenced by unsteady air-cooling conditions.Transient fuel compensation experiments based on the X-τmodel are conducted, using the parameters we have obtained. Air-fuel ratio excursions due to the fuel film effects are effectively reduced, and this result also suggests that the intake port fuel dynamics have been determined accurately.