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The fuel effects on throttle transients in PFI spark ignition engines were assessed through experiments with simultaneous step change of the throttle position from part load to WOT and increment of the injected fuel amount. The test matrix consisted of various gasoline/methanol blends from pure gasoline to pure methanol, coolant temperatures at 40C (for cold engine condition) and 80C (for warm engine), and different levels of fuel enrichment at the WOT condition. The x-τ model was used to interpret the engine GIMEP response in the transient. Using the model, a procedure was developed to calculate the parameters of the transient from the data. These parameters were systematically regressed against the fuel distillation points, the increment in injected fuel mass in the transient, and the enthalpy required to evaporate the fuel increment as the explanatory variables.

The fuel injection process in the port of a firing 4-valve SI engine at part load and 25°C head temperature was observed by a high speed video camera. Fuel was injected when the valve was closed. The reverse blow-down flow when the intake valve opens has been identified as an important factor in the mixture preparation process because it not only alters the thermal environment of the intake port, but also strip-atomizes the liquid film at the vicinity of the intake valve and carries the droplets away from the engine. In a series of “fuel-on” experiments, the fuel injected in the current cycle was observed to influence the fuel delivery to the engine in the subsequent cycles.