LPG Chimaera (Follow My Conversion)
Discussion
Hi,
I have not placed any comments so far, but I am a good friend of David and Chimaera owner, I know that David is a good mechanic, he knows his stuff and the Chimaera and do know that he would have fully researched all the info regarding his LPG conversation and believe that he had any doubt he would not have done it.
I also picked him up from where he is getting his conversion done (and go my Chimaera 500 on the dyno…) and can veto that the guys doing the work seem to know what they are doing when it comes to LPG conversion and are more that capable when it comes to fabricating (brackets and other bobbins David is having made by the guys…).
I am sure that (maybe after some fine tuning and hopefully straight from when he will pick the car up) the car will work really well and bring him the fuel economy his was looking for!
I am also pretty sure that a few other TVR owners will follow and do and LPG conversion (not me as I only did 4,000 miles during last year and with our baby arriving next months, I will do even less in the coming years, since the mrs, the baby and I cannot fit in the Chimaera, so not need in doing so…).
So I have to say well done David for taking the plunge with your project and well done for creating such a nice and detailed post about it on this forum… I am sure that when you will be going down the turbo route, again, you will do your research and my little finger tells me that the result will be good (and even though I am not following you down the gas route, I might go down the turbo route…)
The only thing Dave is doing wrong and you lot replying ;-) is talking in MPG. I believe those units (galloons for sure, miles I just about understand…) dates back from before computers where invented and therefore forums and should be left alone)… let’s talk like civilised people: in kilometres and litters, therefore consumptions should be expressed in xxx / 100 km (i.e, how many litters the car needs to cover 100 kms, just like manufacturers are starting to give us the consumption figures in magazines… and have been doing on the continent since people have been manufacturing cars…) ;-)
Frenchie
I have not placed any comments so far, but I am a good friend of David and Chimaera owner, I know that David is a good mechanic, he knows his stuff and the Chimaera and do know that he would have fully researched all the info regarding his LPG conversation and believe that he had any doubt he would not have done it.
I also picked him up from where he is getting his conversion done (and go my Chimaera 500 on the dyno…) and can veto that the guys doing the work seem to know what they are doing when it comes to LPG conversion and are more that capable when it comes to fabricating (brackets and other bobbins David is having made by the guys…).
I am sure that (maybe after some fine tuning and hopefully straight from when he will pick the car up) the car will work really well and bring him the fuel economy his was looking for!
I am also pretty sure that a few other TVR owners will follow and do and LPG conversion (not me as I only did 4,000 miles during last year and with our baby arriving next months, I will do even less in the coming years, since the mrs, the baby and I cannot fit in the Chimaera, so not need in doing so…).
So I have to say well done David for taking the plunge with your project and well done for creating such a nice and detailed post about it on this forum… I am sure that when you will be going down the turbo route, again, you will do your research and my little finger tells me that the result will be good (and even though I am not following you down the gas route, I might go down the turbo route…)
The only thing Dave is doing wrong and you lot replying ;-) is talking in MPG. I believe those units (galloons for sure, miles I just about understand…) dates back from before computers where invented and therefore forums and should be left alone)… let’s talk like civilised people: in kilometres and litters, therefore consumptions should be expressed in xxx / 100 km (i.e, how many litters the car needs to cover 100 kms, just like manufacturers are starting to give us the consumption figures in magazines… and have been doing on the continent since people have been manufacturing cars…) ;-)
Frenchie
Great comments from Frenchie there, thanks mate.
But you should know a gallon is bigger than a litre so it generates way more power
I have tested this theory in France Land on many occasions and my car consistently goes slower over there.
However, it's highly likely the amount of fine wine & cheese I consume while travelling France Land may have some effect on performance.
I believe this is why LPG is so readily available in France Land.
Although I have just discovered you need to fill your car backwards in France Land due to the stuff being called GPL (the correct LPG backwards).
Bonjour mon ami, your post was well cushty
But you should know a gallon is bigger than a litre so it generates way more power
I have tested this theory in France Land on many occasions and my car consistently goes slower over there.
However, it's highly likely the amount of fine wine & cheese I consume while travelling France Land may have some effect on performance.
I believe this is why LPG is so readily available in France Land.
Although I have just discovered you need to fill your car backwards in France Land due to the stuff being called GPL (the correct LPG backwards).
Bonjour mon ami, your post was well cushty
Ok Gas Sniffers lets get back to LPG.
What you guys may not know is when I started looking at all this last year I decided to place a post on the "LPG Discussion Forum".
The more technical amongst you who are interested in LPG (as I am), may want to have a read of the responses?
http://www.lpgforum.co.uk/viewtopic.php?f=30&t...
As with any forum environment there are individuals contributing with a wide range of skills & knowledge.
I encourage you to read the responses from the two respected professional LPG installers "Woody" & "Rossko".
Following my eventual decision to select the Canems Dual Fuel system, discussions began to centre around LPG fuel density corrections.
This was driven by the absence of a fuel temp input on the Canems system, all piggyback LPG systems utilise this signal which is taken at the reducer.
The main challenger being Rossko, who actually now seems to agree the LPG fuel density variables can be mapped out using the Canems software.
As Rossko says:
"I'm sure it'll be 'acceptable' as the physics work with you - under load (getting colder) you should overfuel"
My chosen installer Keith Woods "Woody" has always insisted, with the Canems system a fuel temp reference at the reducer is not required.
So lets understand exactly what's going on here.
Following the warm-up phase, during normal operating temperatures & engine load the fuel density will remain very constant as it follows engine coolant temperature.
Which in turn is governed by the thermostat, & assisted by the rad fans.
Other influencing factors are coolant capacity, coolant specific gravity, radiator surface area, air flow ect ect, which is why it's essential my cooling system is healthy & functioning correctly before I convert to LPG.
The only other factors affecting fuel density are:
As you can imagine with LPG that's returning to it's natural gaseous state from a compressed liquid, the higher the fuel demand the lower it's temperature will be, which in turn creates a higher fuel density & consequently a potential change in the AFR.
You could argue therefore the Canems DF should have a fuel delivery temperature input (which as we know it doesn't) to drive fuel density compensation.
On the face of it, it seems David at Canems may have missed a trick here, but did he?
Because the Canems DF is running a stand alone map not an emulation of the petrol map as with a piggyback, its very simple to shorten or lengthen the LPG injector duration fractionally to maintain your target AFR under load.
You would struggle to do this with a piggy back because the perimeters within the petrol map its emulating (& twisting for LPG) were never really designed to deal with such variances.
This why all piggybacks always take a fuel temp correction input from the reducer, it allows the piggyback to pull the petrol map about even further to compensate for changes in LPG fuel density.
But with the ability to directly map the Canems DF system, all the control you ever dreamt of is now directly back in the hands of the mapper
As such, when compared with a piggyback, it should still work perfectly with or without directly knowing the precise LPG fuel density at the reducer.
This is another reason for our use of EGT, close monitoring of Exhaust Gas Temperatures (in conjunction with AFR) ensures any dangerous lean conditions can be easily identified, and ultimately eliminated as part of the mapping process.
Finally, switch-over (petrol to LPG) is not automatic on the Canems, as it is with many LPG conversions.
The decision to select LPG during the petrol warm-up phase is made by me, not the ECU looking at fuel & or coolant temperatures, & actually I far prefer it like this, so yet another reason why I don't need a fuel temp sensor.
In my opinion the fuel density question remains an interesting one.
Like I've been saying all along, the devil is most definitely in the detail.
And the detail in this case is definitely the LPG mapping.
Boy, I do hope all this works out OK
What you guys may not know is when I started looking at all this last year I decided to place a post on the "LPG Discussion Forum".
The more technical amongst you who are interested in LPG (as I am), may want to have a read of the responses?
http://www.lpgforum.co.uk/viewtopic.php?f=30&t...
As with any forum environment there are individuals contributing with a wide range of skills & knowledge.
I encourage you to read the responses from the two respected professional LPG installers "Woody" & "Rossko".
Following my eventual decision to select the Canems Dual Fuel system, discussions began to centre around LPG fuel density corrections.
This was driven by the absence of a fuel temp input on the Canems system, all piggyback LPG systems utilise this signal which is taken at the reducer.
The main challenger being Rossko, who actually now seems to agree the LPG fuel density variables can be mapped out using the Canems software.
As Rossko says:
"I'm sure it'll be 'acceptable' as the physics work with you - under load (getting colder) you should overfuel"
My chosen installer Keith Woods "Woody" has always insisted, with the Canems system a fuel temp reference at the reducer is not required.
So lets understand exactly what's going on here.
Following the warm-up phase, during normal operating temperatures & engine load the fuel density will remain very constant as it follows engine coolant temperature.
Which in turn is governed by the thermostat, & assisted by the rad fans.
Other influencing factors are coolant capacity, coolant specific gravity, radiator surface area, air flow ect ect, which is why it's essential my cooling system is healthy & functioning correctly before I convert to LPG.
The only other factors affecting fuel density are:
- Fuel pressure (governed by the reducer)
- Engine load (fuel demand)
- Ambient engine bay temperature (while high in a TVR in practice this remains relatively consistent after warm-up)
As you can imagine with LPG that's returning to it's natural gaseous state from a compressed liquid, the higher the fuel demand the lower it's temperature will be, which in turn creates a higher fuel density & consequently a potential change in the AFR.
You could argue therefore the Canems DF should have a fuel delivery temperature input (which as we know it doesn't) to drive fuel density compensation.
On the face of it, it seems David at Canems may have missed a trick here, but did he?
Because the Canems DF is running a stand alone map not an emulation of the petrol map as with a piggyback, its very simple to shorten or lengthen the LPG injector duration fractionally to maintain your target AFR under load.
You would struggle to do this with a piggy back because the perimeters within the petrol map its emulating (& twisting for LPG) were never really designed to deal with such variances.
This why all piggybacks always take a fuel temp correction input from the reducer, it allows the piggyback to pull the petrol map about even further to compensate for changes in LPG fuel density.
But with the ability to directly map the Canems DF system, all the control you ever dreamt of is now directly back in the hands of the mapper
As such, when compared with a piggyback, it should still work perfectly with or without directly knowing the precise LPG fuel density at the reducer.
This is another reason for our use of EGT, close monitoring of Exhaust Gas Temperatures (in conjunction with AFR) ensures any dangerous lean conditions can be easily identified, and ultimately eliminated as part of the mapping process.
Finally, switch-over (petrol to LPG) is not automatic on the Canems, as it is with many LPG conversions.
The decision to select LPG during the petrol warm-up phase is made by me, not the ECU looking at fuel & or coolant temperatures, & actually I far prefer it like this, so yet another reason why I don't need a fuel temp sensor.
In my opinion the fuel density question remains an interesting one.
Like I've been saying all along, the devil is most definitely in the detail.
And the detail in this case is definitely the LPG mapping.
Boy, I do hope all this works out OK
Sardonicus said:
Dave you got to much time on your hands fella 
...... 
... keep the topic going though
The joys of a deeply dull desk bound job Simon ...... ... keep the topic going though I stopped crawling under cars every day years ago, cos its cold & filthy.
Now I'm desk bound, I'm warm & clean, but bored to death.
Sad indeed
Know anything about LPG fuel density mate?
ChimpOnGas said:
Sardonicus said:
Dave you got to much time on your hands fella ...... ... keep the topic going though
The joys of a deeply dull desk bound job Simon ...... ... keep the topic going though I stopped crawling under cars every day years ago, cos its cold & filthy.
Now I'm desk bound, I'm warm & clean, but bored to death.
Sad indeed
Know anything about LPG fuel density mate?
jr6yam said:
26MJ/L
Yup got that John.
Actually LPG has a typical specific calorific value of 46.1 MJ/kg compared with 43.5 MJ/kg for premium grade petrol.
Sounds encouraging right?
Well not exactly, LPG has an energy density per volume unit of 26 MJ/l (your figure), which is 20% lower than that of petrol.
Specific calorific value is very different to energy density.
However, the extremely high 110Ron octane level of LPG allows you (with a decent ignition system) to recover the potential performance loss, LPG also has a simpler carbon molecular chain.
Which means LPG is easier to burn & extract power from than petrol.
It's all down to those cheeky free radicals, don't you know
So with a mappable ignition system the end result is zero loss of power.
"The Lord Giveth & The Lord Taketh Away" leaving you with neither a gain or a loss.
But the reduction in calorific value will impact on fuel economy, your engine needs to eat more LPG Mars Bars than petrol Mars Bars to cover the same ground
I am working to a 15% loss in fuel economy when burning LPG over petrol, which is completely negated (& more so) given the 45% price deferential between the two fuels.
But I'm not referring to all this when I'm talking about LPG fuel density.
I'm looking at the effects of temperature on LPG fuel density.
Open the throttle especially under load, & a lot more gas is delivered, this reduces temperature which in turn changes fuel density, and ultimately will alter the air fuel ration unless compensation strategies are used.
Fortunately physics is on my side, all that will happen is the mixture will become colder & richer, which is exactly what you want.
However it could go too far, especially if coping strategies are not incorporated to mitigate the condition.
It's not really an issue TBH as it can easily be mapped out with the Canems system, but it should not be overlooked.
Told you I was bored
jr6yam said:
At what point does the LPG become gaseous?
Hi John, it doesn't take much to turn LPG to a liquid, just 160psi in fact.It compresses well too, taking up 274 times less space than it does as a gas.
When you release the pressurised liquid LPG to atmosphere it will boil, releasing vapour just like boiling water.
Except with LPG the boil happens at -42c
It's funny to think of something boiling at -42c, but that's exactly what's happening, it's the vapour released from the boil that the engine is consuming.
If you release loads of the stuff quickly, say when you accelerate hard up a hill, you get a bigger drop in temperature than you may want.
In these circumstances the density changes, therefore so does the mixture.
But we can map this out so it's no real issue, actually its an advantage, you get a nice cold richer mixture just when you need it most.
Another reason why LPG works so well with a turbo
QBee said:
SILICONEKID350HP said:
?................ and expansion vessels ! She has a free plumbing lesson every night .
heard you were expecting twins, Daz........! She has a free plumbing lesson every night . I was thinking more like a new twin new twin exhaust ..Edited by SILICONEKID350HP on Thursday 7th March 23:05
ChimpOnGas said:
jr6yam said:
At what point does the LPG become gaseous?
Hi John, it doesn't take much to turn LPG to a liquid, just 160psi in fact.It compresses well too, taking up 274 times less space than it does as a gas.
When you release the pressurised liquid LPG to atmosphere it will boil, releasing vapour just like boiling water.
Except with LPG the boil happens at -42c
It's funny to think of something boiling at -42c, but that's exactly what's happening, it's the vapour released from the boil that the engine is consuming.
If you release loads of the stuff quickly, say when you accelerate hard up a hill, you get a bigger drop in temperature than you may want.
In these circumstances the density changes, therefore so does the mixture.
But we can map this out so it's no real issue, actually its an advantage, you get a nice cold richer mixture just when you need it most.
Another reason why LPG works so well with a turbo
As I understand it the gas is supplied to the injectors at a fairly constant pressure? Gas will reach 90% of ambient Temperature very quickly, so the
distance from the vapouriser to the combustion chamber is important; along with flow and the thermal conductivity of the pipework.
In a hot engine bay there may not be as much Temperature drop as you may think
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