LPG injection

[robert dingli]

Mike writes,
> 
> I was looking at a SAE book on the Natural Gas Vehicle Challenge and
> several of the entries used Bosch injectors which I'm guessing are standard
> pintle type injectors used in gasoline vehicles. I took a quick glance
> at the paper from some Nebraska university and it talked about having
> two levels of pressure regulation the final one supplying the injectors at
> 100psi (as I remember). It also seemed that they used two injectors per
> cylinder to get enough flow. This lead me to wonder what are the reasons
> for wanting to inject liquid propane instead of propane vapor. From the
> various threads on the subject I gather that there might be some problem
> getting the liquid to a vapor at low temperatures. I'd guess that it takes
> less injection time to inject a given mass of fuel as a liquid. Wouldn't
> you need some pressure regulator in either case? I suppose the density of 
> propane vapor would vary considerably with the temperature but as long as
> it followed the ideal gas law it should be easy to compensate for.

Based on some of our work with port injected CNG and propane,

The benefits of injecting as a liquid as I see them are:
- inlet charge cooling
- simple multi port control
- no gas carburettor restrictions

The technical problems to be adressed:
- any vapourisation within the lines or injector will adversly effect flow
  The LPG would need to be pumped to a pressure higher than the vapour
  pressure in the tank to avoid vapourisation due to higher temps/ lower
  pressure along the lines
- injector lubrication
- injector degradation due to internal cavitation
- inlet charge over cooling

Injection as a gas is possible using specialised injectors, but doesn't
offer the benefit of intercooling the air stream.  Using the vapouriser to
cool an air-con system rather than using a compressor would utilise some
of the cooling affect.  This could be a suitable alternative for some
applications.

Robert

-- 
    Robert Dingli   r.dingli at ee.mu.oz.au
Power and Control Systems    (+613) 9344 7966
Thermodynamics Research Labs (+613) 9344 7712
     University of Melbourne, AUSTRALIA 
**  he who dies with the most toys, wins  **