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We have developed a new wall wetting model to predict the transient Air/Fuel ratio excursion in a port fuel injected (PFI) engine due to changes in air or fuel flow. The quasi-dimensional model accounts for fuel films both in the port as well as in the cylinder of a PFI engine and includes the effects of back-flow on the port fuel films to redistribute and vaporize the fuel. A multi-component fuel model is included in the simulation; it gives realistic fuel behavior and allows the effects of different fuel distillation curves to be studied. The multi-component fuel model calculates the changing composition of the fuel puddles in the port and cylinder during the cycle. The inclusion of an in-cylinder fuel film allows the model to be used for cold start conditions down to 290 K. The model uses the Reynold's analogy to calculate the fuel vaporization process and uses a boundary layer calculation to solve for the liquid film flow.

An investigation of transient A/F characteristics was conducted using a 1.6 liter engine equipped with a Sequential Electronic Fuel Injection (SEFI) system. The engine was tested on a dynamometer facility capable of providing environmental temperatures as low as 10°F. A test procedure was developed to determine the effects of steady state A/F, engine speed, size of throttle ramp, injection timing, and hardware changes, on the transient A/F characteristics while the engine warmed up. It was found that, under cold operating conditions, the A/F excursions for the SEFI system were similar to those previously measured for a Central Fuel Injection (CFI) system on the same engine. It was also found that the sensitivity of the A/F excursions to variations in the test parameters, while quite dramatic at reduced temperatures, decreased as the engine warmed up.

An engine dynamometer test facility-capable of controlling temperatures from 0°F to 150°F was used to investigate A/F control characteristics of a 1.6 liter engine with single point fuel injection. Two types of tests were run. In the first, the effect of induction system temperature on manifold wall wetting and transient A/F control was determined. In the second, a cold start procedure was developed to determine the effect of engine temperature on the percent of fuel which burns by observing exhaust A/F during steady state operation while the engine warms up. It was found that transient A/F control problems due to manifold wall wetting are much greater than steady state problems associated with incomplete fuel burning.

The effect of local heating on transient A/F excursions is investigated experimentally on the 5 Liter, Central Fuel Injected engine. Data are presented which show the effect of heating the throttle plates and plenum floor respectively on transient A/F excursions, and these data are interpreted in relation to a dynamic wall-wetting model. The benefits of local heating for reduction of A/F transients during warm up are also discussed.

The two year design-development program for the sonic carburetor is reviewed. Use of the sonic nozzle as an air flow meter, and the design criteria to achieve low unchoke points is discussed. The relation between sonic flow and improved fuel atomization and A/F ratio distribution to the engine is also discussed. Unchoke data and A/F distribution data are presented, and the tradeoffs between low unchoke points and good A/F distribution are explained. Conclusions are drawn relative to the overall benefits of the sonic carburetor.