Direct Injection for LPG in Cars - Why Not?

I think its already in use in Fords that

have the LPG only option

You have a wrong perception of the pressure inside a lpg cylinder- may be 1000psi- nescessary to liquify the gas- auto lpg uses liquid withdrawal, which must be reduced to something the motor can use, n ormally gaseous, though liquid withdrawal injection has been tried, but the problems were too great- lately, there are vapour injection systems, which seem to work- remember, household lpg uses vapour withdrawal, ie, the cylinder is upright!- whereas auto lays the cylinder down, & has to withdraw liquid!.

The LPG "cooker" may be primarily for cold weather. This past winter, my wife bought a small "camp stove" that uses cylinders of butane gas. She wanted to cook in the garage, so as not to smell up the house. The stove lit briefly, then the fire went out. She told me the store had sold her an emptyt gas cylinder. When I looked at the cylinder, the butane (b.p. 0.5 C) was a cold liquid, and not evaporating sufficiently to sustain a flame.

LPG in a naturally aspirated motor has been around for years. There was a company in California that did a lot of change overs, because of the difference in combustible medium (the lpg burns at a lower temp) the thermostat and camshft need to be replaced to facilitate the cooler running of the engine for optimal performance!!----------------> InVader (huggybare_44@yahoo.com)

Due to the high presure and the aerosol effect it will freeze up the metering and injection system. That why it needs warming up.

In theory it will work--IF the fuel injector will flow enough liquid. 2 main obstacles to overcome.

1) The LPG is not at a constant pressure. Gasoline fuel injection systems all utilize a recirculating pressure controlled feed loop. The fuel pump produces say 300 GPH at 60 psig, and the fuel pressure regulator spills excess back to the gasoline tank. Typical injector rail pressure is 40 psig (specific for each make). THis regulated pressure is adjusted as the intake manifold pressure changes to keep to differential pressure (injector feed to intake manifold) constant. You would have to re-plumb the fuel supply system to replicate this fuel presure regulating/recirculating loop for the LPG operation. It is essential to circulate the LPG to keep it from vaporizing in the fuel lines as it picks up engine heat (vapor-locking big time).

2) LPG has significantly lower BTU/gal (20% less) than gasoline. The fuel injectors and computer control system will have to be designed to accomodate this. Fuel flow for automotive fuel injection systems is controlled by adjusting the time the injector is open for each intake stroke. The 'on' pulse will have to be longer for the LPG, and proably beyond the 'allowable' adjustment range' of a 'gasoline calibrated' computer and oxygen sensor system. When the 'open' time adjustment exceeds about 10% of the 'expected value' stored in the engine control computer memory, the computer system is programmed to call this a 'fault' and the check engine light will come on.
When the 'on' time for an injector gets above 80%, actual fuel delivery tends to drop off.