Measurements of in-cylinder mixture strength and fuel accumulation in the inlet port of a gasoline - injected engine during very rapid throttle openings

Abstract

The mixture strength in a cylinder of a port-injected gasoline engine was monitored continuously during very rapid throttle openings. The data on mixture strength were combined with other engine data collected in order to obtain for each successive engine cycle: the air—fuel ratio within the cylinder and the change in the fuel mass accumulating on the inlet port of the cylinder being monitored. The four-cylinder spark-ignition engine used had a displacement of 1.6 litre, four valves per cylinder and multipoint sequential fuel injection controlled by an electronic management system programmed for three - way catalyst operation. All tests were conducted with the engine coolant at the temperature of 90°C and at a constant engine speed of 2000 r/min. The engine transient involved very rapid throttle openings which were completed within about 15 ms. Small and large throttle openings were investigated along with the effect of altering the type and condition of the fuel injectors. The engine response to the fast throttle opening comprised a sharp rise in the air—fuel ratio (maximum gravimetric air—fuel ratio of around 25:1) which lasted for only a single cycle, followed by a drop in the air-fuel ratio (minimum air—fuel ratio of about 10:1) and, subsequently, a gradual rise towards a stoichiometric air—fuel ratio within about 10 engine cycles.