采用米氏和激光诱导荧光成像研究汽车燃料喷嘴产生的丙烷/液化石油气（LPG）喷雾结构与燃料和环境压力的关系

When a gasoline engine is converted to propane (LPG, Autogas) there is usually a reduction in power. This loss can be
mitigated by careful design of the injection system such that the heat required for evaporation of the LPG is drawn from
the intake air and not the intake walls. The air is cooled and densified, resulting in an increase in volumetric efficiency.
To do this effectively requires the injector spray pattern to be known. There are many studies on the structure of
gasoline sprays, but few of LPG sprays.
In this work we have imaged LPG sprays from a gasoline direct injection (GDI) injector, a port fuel injector, and from long
and short pipes usually used to connect a remote LPG metering valve to the injection point in the manifold. Both Mie
and LIF imaging have been used. For the LIF, acetone is added to the LPG. Images were taken in an optically accessed
pressure chamber at pressures from atmospheric to 20 bar and with fuel line pressures from 10 to 80 bar.
The imaging of the pipe-coupled injection system shows that (1) there is significant but not complete evaporation in the
pipe, the amount of evaporation depending on the length and diameter of the pipe, and (2) during its travel down the
pipe the injected pulse of fuel spreads out so that the duration of the LPG pulse at the manifold end is, for 300mm pipes,
five times the original duration at the injector, and even greater for 600mm pipes such that fuel is always emerging from
the pipe. When fuel evaporated in the pipe the latent heat required is taken from the pipe wall and not from the induced
air, where it might usefully cool and densify the air, boosting engine torque. The fuel emerges from the pipe in a narrow
jet. This may be less conducive to good mixing than the broad spray which emerges from the close coupled system
(which has the injection valve mounted directly on the manifold.
The structure of the sprays and the amount of evaporation that occurs before the fuel enters the manifold explains the
observed differences in engine torque and in-cylinder mixture temperature observed with the different systems.
The spray structure of the direct injector is similar with gasoline and LPG. The spray structure is more sensitive to
changes in fuel or chamber pressure than to the type of fuel. The droplet size may vary with fuel type, resulting in a
different spray structure when exposed to the strong in-cylinder air motion of a direct injection engine.