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The performance of a pintle-type gasoline injector has been studied. Observations performed on test-rigs and running engines suggest that under conditions of low manifold pressure a ‘pencil-jet’ formation may replace the well atomized spray normally produced by the injector. Importantly, this phenomenon was not observed when using substitute fuels such as n-heptane. It is concluded that both the mechanical design of the injector and the combination of the liquid properties density, viscosity and surface tension influence the ability of a given injector to produce a well atomized spray at low manifold pressures. The paper discusses measures to prevent pencil-jet formation.

Droplet size measurements were performed on the spray from a pintle-type gasoline injector. These quantified the influence of the fuel properties, relative fuel/air velocity and manifold air density upon the droplet sizes. Dimensional analysis and knowledge of the atomization process was used to derive equations predicting mean droplet diameters. Constants and exponents used in these equations were evaluated by correlation with the measured data. The equations were used to predict the individual or combined influence of the above variables. It is concluded that the influence of variations in properties between production gasolines on atomization is likely to be small.