Megasquirt Support Forum (MSEXTRA)

Hi
There are now Injectors available for injecting LPG directly into the inlet manifold
The performance gains are significant - http://www.lpgli.com/lpg.html

I am wondering if anyone else has dabbled with these systems

Questions that come to my mind

What would be the injector timing be? - would it have to be advanced relative to petrol to allow for the evaporation of the LPG from liquid to Vapor...
Because the Liquid expands many many time is volume - would the injector timing to so small as to be impractical for a MS3.

Thoughts


Gary

There are quite a few alternative truths on the website, primarily because they assume that the LPG system they are comapring against is a mixer system (not a sequential system) and because they assume this will be a piggy-back installation based around an already running petrol engine.

They also state that the same (type of) injectors are used for liquid LPG as for petrol. If that is the case, then any standard software ought to be able to control them. (LPG is more corrosive than petrol, so the seals used need to be "inert".) The LPG may also typically be under VERY high pressure, e.g. 8bar, as that is the typical pressure in the tank. CNG injectors are already available and have been for some time, so this is not a new devlopment.

"Injector timing" is a defined term and is when the injector fires. I believe you meant to ask about injector pulsewidth duration.

No one on this forum has expressed any opinion about injector timing for ordinary LPG even and I don't know how that may want to be varied
if the liquid is yet to vaporise.

MS3 ought to easily be able to control such a setup.

kind regards
Marek

in the us there is a company with a fleet of delivery trucks that have been runninglpg port injection on gm's 7.4,8.1 and 6.0 vortec since 2003. it runs the oe computer and emission certified.

We have worked on several alternative fuel projects using port injected LPG and CNG. However, the systems we worked with used vapor phase injectors. I haven't worked with ones that tried to inject the fuel as a liquid. I would expect these to have larger puddling effects (more acceleration and warmup enrichment) compared to gasoline, but that is only a guess.

Once liquid LPG comes out of the injector there's nothing that prevents it from staying in that state; it vaporises almost immediatly.
There's no puddling possible unless you're able to hold it under high pressure, or keep it cold enough to prevent vaporising which is -42°C/-44°F.

The rate of expansion from liquid to vapour changes largely by the liquid's temperature.
To be able to control the exact amount of liquid LPG so it provides the precise amount of vapour one needs to monitor fuel temps greatly and adjust accordingly.

With the evaporasion of LPG, a lot of heat is drawn from the surrounding areas which means a colder intake charge enters the engine, which is a benefit almost all engines would like.

BigBlockMopar wrote:Once liquid LPG comes out of the injector there's nothing that prevents it from staying in that state; it vaporises almost immediatly.
There's no puddling possible unless you're able to hold it under high pressure, or keep it cold enough to prevent vaporising which is -42°C/-44°F.

The rate of expansion from liquid to vapour changes largely by the liquid's temperature.
To be able to control the exact amount of liquid LPG so it provides the precise amount of vapour one needs to monitor fuel temps greatly and adjust accordingly.

With the evaporasion of LPG, a lot of heat is drawn from the surrounding areas which means a colder intake charge enters the engine, which is a benefit almost all engines would like.

Does it require a really small PW when injecting liquid LPG ?

I don't see a big problem with injecting liquid LPG.
I have a Tahoe with a 5.3 vortec, and Landi Renzo Omegas LPG injection system, controlled by OEM ECU. This is with a vapuoriser, and has a max powerloss of 2-3%. I don't notice any powerloss.
But they have a system for direct injected engines, that I think uses the OEM injectors and liquid LPG.
If keeping the LPG liquid I don't think it wil be a problem with low pw, if using proper liquid injectors. Stoich AFR for LPG is real close to gas/petrol, and LPG weight about 15% less than gas/petrol.
And yes, of course it's important to keep track of temperature and pressure in the LPG.
I have no problem beliving a liquid LPG injection may gain a real power increase compared to gas/petrol, considering the low power loss with port injected vapourised LPG.
Especialy with a boosted engine, with benefits of both high octane and a cooler charge because of the liquid LPG.
Sounds like a thing I would like to try in the future

OEM gasoline injectors can't stand the (possible) pressures present in a Propane fuel system. They can burst open.
Specially made LPI injectors should be used.

Yves wrote:Does it require a really small PW when injecting liquid LPG ?

Or a relatively smaller injector size.

In addition to my previous reply;
The LPG fuel temperature also varies pressure inside the injector, adding another variable to the mix. Besides that liquid LPG injector also needs a fuel pump in the propanetank that (tries to) keep a steady pressure/flow from the tank to the engine bay.
The propane's fueltank temperature can also change during a trip, altering the fuelpressure again as well.

I have no direct experience with liquid LPG injection, but there's a Dutch company overhere called 'Prins' that mainly uses Keihin injectors and has quite some experience in this field;
http://www.prinsautogas.com/en/products ... ystem.html

Thanks everyone for your interesting replies

I have a bit of LPG experience - mainly LPG Carby
I have a very hot Ford Small Block (351 cleveland) which runs 2 OHG Carbys on a custom made 8V flat plane manifold

The main problem with LPG (in my experience) on performance motors has been the flow limitations of turning the Liquid into a bulky gas then feed enough of this gas into a 5.8 liter motor spinning at 6000 plus

Which is why I am running 2 converters, feeding 2 OHG 1100 cfm carbs, through 2, holley 750 square bore throttle bases. Along with a huge duration and lift cam. On LPG, this motor takes off at 1200 to 1300 Rpm and revs out until the valves bounce approaching 7800

Up until now I have not been very interested in electronic control of the vapor systems - because of the limitations described above.

BUT the idea of injecting frozen LPG into the manifold - is very intriguing to me - in my mind it sounds like Supercharging and Intercooling without the drawbacks.

There is a lot of interest out there on this issue because all the LPG installers I have spoken to only have piggyback kits available to them
Which does not help if you are dealing with an 1964 Ford F100 with a 460 big block on board.

But Mega-Squirting is what we do - So - "How hard Could It Be" - Jeremy Clarkson

Any clues appreciated...

The Netherlands, as mentioned above, has some companies supplying lpg injection systems and there are even seperate parts available.
Like stated above, it has it's specifical demands and it seems that variations in the system due to temperature and pressure may vary a lot, causing issues with consistent fueling;

Outside of that lpg has an advantag in it's high octane rating, letting you employ a higher compression and/or more ignition timing, which both enhance power output. However the engine becomes an lpg unit only.

I have been running a 5litre v12 on LPG for several years now, fully sequentially using MS3/3X, so it isn't hard. It's setup for dual fuel butI rarely use petrol as there seems to be no point in burning money. Performance wise they appear to be no different to each other.

As others have pointed out, the main worry is the high fuel pressure lines direct to the engine. All LPG gas systems will have the high pressure hard lines terminate at the reducer whith a flexible low pressure line to the injectors.

Keihin do make CNG/LPG gas injectors which are probably not suitable on account of the volume flowed.

Given the volume ratio of liquid:gas, I'd expect the injectors for liquid to have to be sized smaller to accommodate that so there may not be very many types available on the market that have suitably low flow rates. As a comparison, a Keihin orange spot injector, if you run petrol through it, will flow about 15-20 times the fuel that a 180cc/min injector will depending on pulsewidth.

kind regards
Marek

For reference, my Vauxhall Monaro with factory LS1 had an LPG kit fitted by a previous owner. It has a secondary ECU and injects gaseous LPG sequentially into the manifold with one reducer in the engine bay.

James

I will be installing a similar system in my '73 Dodge Dart. It currently has an IMPCO vaporiser with IMPCO 425 propane carb on the intake.
This will be replaced with a single stage vaporiser and port-injectors.

I will at first mostlikely keep both fuel systems operational during the build and let Megasquirt switch between fuelsystems based on engine coolant temperature.
Start with IMPCO carb and switch over to vapour injection after a couple of minutes.

Vapour injection installed as a single fuel system is supposed to be tricky when outside temps are low/freezing.
Depending on engine-demand, frozen (LPG) particles could pass through the injectors and play havoc with mixture-control when they expand 270 times in the intake manifold.
Fuel lines should have some amount of heat in them to prevent this.

I think there are a few misconceptions here regarding liquid/gaseous lpg.
The only reason it stays in a liquid state is that it is under very high pressure. As soon as that is released, it vaporises instantly.

The piggyback type of lpg systems retrofitted to cars always start on petrol because generally speaking, they are designed to be fitted to any car and thus have to cater for cars with small engines and coolant volumes.

When the lpg vaporises it uses the heat in its environment to do this and there is a temperature drop as a result. For a small car, with a correspondingly low volume of coolant, if starting from a cold start, it is possible that the lpg reducer will want to remove more heat from the circulating coolant than can be replenished by the water pump and reheated by the car's engine within the first few minutes of starting. This tends to want to freeze up the reducer. The other factor here is that these installations often tee the vaporiser through the heater pipes, which are only 5/8" diameter, so only a fraction of the car's coolant is sampled.

From a theoretical point of view, the lpg system will perform predictably when the coolant being extracted by the reducer is sustainably being replaced by engine heated water.

For example, my car has 20 litres of coolant and 100% of that goes through thre reducers. It never has a problem starting from cold.

At constant motorway speeds, the engine temperature settles at 79'c, i.e. the thermostats keep the radiator blocked off as all of the water borne engine heat is recycled by the reducers.

The "safe" operating window for the bolt on piggyback lpg systems thus are usually set to start on petrol, but switch over to gas as soon as a certain rpm is reached and the coolant is above 30-40'c, but a well designed stand alone system doesn't need to mimic that if operating circumstances are different.

kind regards
Marek