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Old 03-10-2021, 02:50 AM   #18 (permalink)
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I somehow omitted to click "Submit Reply" so typing again.

Originally Posted by cRiPpLe_rOoStEr View Post
They're supposed to be more fuel-efficient than a larger naturally-aspirated engine with port injection, but they're not as easy to service. No wonder in some countries Volkswagen only offers the 4-cyl naturally-aspirated 1.6L for models available elsewhere with the 1.0 and 1.4 TSI engines.
I must have been distracted, of course you're right, they are much more fuel efficient for city driving and low load conditions. I meant, they would inject more fuel under than a larger engine would under load. Consider a 1.4 TSI, producing roughly the same power of 150hp with a 2 liter NA. When under load and producing same power, the TSI would inject a little more fuel just to prevent preignition.

Originally Posted by cRiPpLe_rOoStEr View Post
It will depend on the expansion ratio of LPG while it vaporizes. So, even with a colder charge, it might not get so denser at all.

Could absorb the same amount of heat from the ambient air with a fewer amount of fuel, which would be good for fuel-economy without too much harm to performance.
Now I have to refer to my books from 15 years back in the university. The effect would mostly depend on heat of evaporation of LPG. I think stoichiometric ratio for LPG was around 16:1. This could lead us to an equation which we might solve for a known amount of air, making a lot of assumptions of course.

Originally Posted by cRiPpLe_rOoStEr View Post

When I refer to supplemental, it's what your car has. The injectors dedicated to operate with LPG are supplemental to the original fuel system fitted to the engine. And sure the trend toward direct injection may seem to not justify a switch from vapour-phase to liquid-phase on port-injection setups, but it's also worth to notice how pointless are some port-injection CNG adaptations on vehicles originally fitted with direct injection, which still require an amount of the original liquid fuel to be used in order to prevent damages to the stock injectors which are directly exposed to the flame spread.
I also meant that, but apparently omitted in my distraction. What is unknown (to me, and at the moment at least) is the extra injectors' ability to supply liquid fuel, in terms of both the amount of fuel they can supply and their reaction to a quickly evaporating fuel.

I don't know how they apply the liquid LPG injection with stock petrol injectors. It seems like a trial and error thing, which makes sense as all the liquid LPG aftermarket kits I know of are for specific models of cars.

If so, the way forward is:
- Find out if the extra injectors for LPG can use liquid LPG
- Set up the mechanism for adjusting fuel amount on the fly, and monitoring the AFR (invest in a wideband AFR sensor?)
- Start low, then find a ballpark figure for injector duty cycle under a generalized condition. Without knowing how much fuel our injectors can provide under a set pressure value, this could be the best we can do
- Continue optimizing. If I can, that is. Will require rpm, engine load, and possibly more parameters.
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