Longtime stalker, now hoping to have some time!

[cRiPpLe_rOoStEr]

Originally Posted by octinum

I'd prefer some boot between the rear bumper and the child seat at the back.

No wonder some models available only as a hatchback in Western Europe often had a sedan bodystyle for markets such as Turkey.

Never driven a deux chevaux myself.

Neither did I.

Small turbo engines rely on very rich mixtures under high load conditions to prevent preignition.

Direct injection became so prevalent on newer generation of turbocharged engines because it doesn't require such a very rich air-fuel ratio. Downside is an increase to NOx emissions, and even some particulate matter buildup which used to be previously seen as more troublesome to Diesel engines than to spark-ignited ones.

LPG as vapor also replaces some of the air in the intake charge. So less oxygen to burn an already low energy content fuel.

What I'm thinking is to use the cooling effect of LPG as it vaporizes in the intake manifold. This should also be a simpler system without the need for the evaporator.

Either going through the evaporator or being allowed to vaporize naturally at the intake manifold, an amount of the charge air would always be replaced at a port-injection engine operating with LPG. With the cooling effect, there is a lower NOx emission, even though the AFR could still be leaner than with a vapour-phase injection.

As you said, some manufacturers just use the original gasoline injectors for two purposes, so a common, cheap injector from a gasoline car should work.

I have only found mentions to the usage of stock injectors for direct-injection engines. Port-injection ones may still require supplemental injectors only for the LPG, just like the 5th-generation CNG conversion setups.

[octinum]

Originally Posted by cRiPpLe_rOoStEr

Direct injection became so prevalent on newer generation of turbocharged engines because it doesn't require such a very rich air-fuel ratio. Downside is an increase to NOx emissions, and even some particulate matter buildup which used to be previously seen as more troublesome to Diesel engines than to spark-ignited ones.

Right, missed that point. Though that's limited as well, I remember reading that small VW engines with both turbochargers and direct injection consume more than larger NA engines with similar output. However, this comment might be for an older generation TFSI.

Alfa Romeo JTS engines suffered from some soot buildup; long time users say equally maintained Twin Sparks (port injected) "keep" their performance longer than JTS because of this.

Originally Posted by cRiPpLe_rOoStEr

Either going through the evaporator or being allowed to vaporize naturally at the intake manifold, an amount of the charge air would always be replaced at a port-injection engine operating with LPG. With the cooling effect, there is a lower NOx emission, even though the AFR could still be leaner than with a vapour-phase injection.

You're on spot again. But fuel vaporized in the intake manifold would also help a denser charge, lowering charge temperature. The injectors could provide more fuel per cycle as well; as the vaporization would happen _after_ injection. I believe it would be beneficial in any case; better than vapor injection at least.

Originally Posted by cRiPpLe_rOoStEr

I have only found mentions to the usage of stock injectors for direct-injection engines. Port-injection ones may still require supplemental injectors only for the LPG, just like the 5th-generation CNG conversion setups.

I haven't found any references to supplemental injectors too. I have a feeling that the manufacturers never bothered with port injected ones when the trend is toward direct injection, and the extra cost for liquid injection tech would be harder to justify for an already mature market of port injected vapor phase kits.

This is not a problem for me though. I already want to be able to switch to "stock" when required, so I'm not touching the gasoline hardware. I want to play with the sequential LPG kit on my car. If anything goes wrong (short of a fire that is ), I want to switch to the virgin fueling system from the factory, at least until I'm safely home.

[octinum]

OK now, thanks to the very welcome provocation from @cRiPpLe_rOoStEr, I think I now have enough posts accumulated for me to post links.

So let me tell you about my car, which (AFAIK) was never imported to the countries that I presume most of you live. It's a 1997 Xantia X1 (pre-facelift) VSX, hatchback. The same body shape as the following, but in dark blue:

https://www.citroenorigins.co.uk/en/cars/xantia

Not as aerodynamic as its bigger brother XM, but with a very aerodynamically dirty underbelly, I believe it has potential.

The highlight of this car is its suspension. There were 3 types of suspensions on Xantias, one was the regular hydropneumatic suspension, second was Hydractive II (my car), and third was the Activa, which still is the top car on the famous Moose Test.

Hydropneumatic Citroens have steel spheres filled with nitrogen. They don't have steel springs and conventional dampers. Both springing and damping occur in the spheres, nitrogen gas acting as the spring and holes in the sphere "neck" acting as damper elements. The green thing is an example:
https://en.wikipedia.org/wiki/Hydrop...bol_Xantia.jpg

Hydropneumatic Xantias have 5 or 6 spheres, depending on version. 4 of these spheres are responsible for ride, assigned to each wheel.

My Hydractive II Xantia has 8 spheres (yeah, I know, my car has balls. 8 of them ). In Hydractive II system, there are 3 spheres responsible for ride on each axle. On "normal" mode, the car is suspended on 6 spheres, 3 front and 3 rear. Spheres on each axle are interconnected hydraulically.

An ECU tracks various sensors, such as speed, steering wheel angle, steering wheel angle change rate, brake pressure etc. When a sudden change in direction, or a high speed curve is detected, the middle spheres are disconnected from the system. This also cuts the connection between right and left wheels. So each wheel is now suspended by its own sphere.

The spheres for each wheel, also called "corner spheres" are stiffer than those on regular hydropneumatics (in other words, normal soft ride is provided by the middle spheres and the hydraulic interconnections). This decreases body roll. I believe maximum roll angle is around 2.5 degrees in this mode.

So, does this help with fuel economy? It does when traveling downhill, or when you want a little more rapid progress. I had this mountain pass in the city I lived before; I would just let the car go downhill, my foot off the accelerator. Most other cars, including modern and upmarket ones, would brake on every curve. I, on the other hand, would get to keep momentum.

This also goes when you're in a hurry. Again, where most "hot" drivers would accelerate until the curve and brake hard, I would just hold an average speed, with minimal if any braking on curves, and still keep up with them.

The power loss for the hydraulic pump is negligible.

Suspension is height adjustable, though only one out of four positions is intended for normal driving. The lowest and the highest positions are maintenance modes, and the high mode is only for driving over obstacles slowly.

But the "normal" driving position can be lowered or raised by tinkering with the height correctors on each axle. This no doubt would compromise comfort, but I don't think it would risk any damage to the car when done sensibly.

[cRiPpLe_rOoStEr]

Originally Posted by octinum

I remember reading that small VW engines with both turbochargers and direct injection consume more than larger NA engines with similar output. However, this comment might be for an older generation TFSI.

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.

Alfa Romeo JTS engines suffered from some soot buildup; long time users say equally maintained Twin Sparks (port injected) "keep" their performance longer than JTS because of this.

Oily vapors from the crankcase vent would stick to the manifold and then trap some soot from the EGR in an engine with direct injection. With port-injection on the other hand, not only the fuel vaporizes and burns cleaner, but the oily vapors dillute more effectively with the air/fuel mixture than it would happen with charge air only.

fuel vaporized in the intake manifold would also help a denser charge, lowering charge temperature

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.

The injectors could provide more fuel per cycle as well; as the vaporization would happen _after_ injection. I believe it would be beneficial in any case; better than vapor injection at least.

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.

I haven't found any references to supplemental injectors too. I have a feeling that the manufacturers never bothered with port injected ones when the trend is toward direct injection, and the extra cost for liquid injection tech would be harder to justify for an already mature market of port injected vapor phase kits.

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.

[freebeard]

I'm just stumbling into the conversation, but can't the injectors be direct, in the port or in the throttle body?

IIRC some race cars had the injectors above a throttle body for each cylinder, with almost no intake runners. [citation needed]

[cRiPpLe_rOoStEr]

Originally Posted by freebeard

I'm just stumbling into the conversation, but can't the injectors be direct, in the port or in the throttle body?

Unless it resorted to individual throttle bodies, which BTW might be as much of a PITA as multiple carburettors to deal with, it's not worth to use throttle-body injection with LPG in that car. On a sidenote, when GM started certifying CNG conversions in Brazil, it already resorted to port injection for the gaseous fuel system even though the stock fuel injection was a TBI.

[octinum]

Originally Posted by freebeard

I'm just stumbling into the conversation, but can't the injectors be direct, in the port or in the throttle body?

IIRC some race cars had the injectors above a throttle body for each cylinder, with almost no intake runners. [citation needed]

For multi-point injection like this particular car, intake runners are the preferred location. The LPG injectors are mounted on holes, drilled on the runners before the petrol injectors (i.e. closer to the plenum), as close as possible to them to minimize injection timing issues. The LPG controller ECU uses the vehicle's ECU injector signals as a template.

Single point injection ones used to use throttle body I think.

[octinum]

I somehow omitted to click "Submit Reply" so typing again.

Originally Posted by cRiPpLe_rOoStEr

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

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

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.

[cRiPpLe_rOoStEr]

Originally Posted by octinum

When under load and producing same power, the TSI would inject a little more fuel just to prevent preignition.

It might be more related to NOx mitigation, at the expense of the particulate matter emissions which now require them to resort to a particulate filter just like Diesels have been done for a while. Direct injection already mitigates preignition quite effectively even with a leaner AFR and higher compression ratio.

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.

Sure it will depend on the extra injectors being designed specifically for LPG.

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.

Notice the liquid-phase injection through the stock injectors only applies to engines fitted with direct injection.

[cRiPpLe_rOoStEr]

Check this: https://gazeo.com/automotive/technol...icle,9297.html