|
LPG, CNG & LNG - General Info and Issues Share experiences and problems |
Information |
|
Anyone ever converted an XC90 V8?Views : 5527 Replies : 20Users Viewing This Thread : |
|
Thread Tools | Display Modes |
Mar 27th, 2017, 23:35 | #11 |
Premier Member
Last Online: Jan 15th, 2022 11:23
Join Date: Feb 2009
Location: Salisbury (ish)
|
My XC70 with the 3.2 IS6 engine runs equally well on gas as it does on petrol. One feature of the Prins VSI system is that if you floor the accelerator quickly, it switches back to petrol so you're probably never going to be able to get an accurate 0-60 time to see if there is any drop in performance.
|
Mar 28th, 2017, 20:40 | #12 | |
Trader Volvo in my veins
Last Online: Today 21:00
Join Date: Dec 2004
Location: Anglesey
|
Quote:
Thats a bit naff how your prins has been set. The 3.2 is not massively demanding and should not struggle on full load running on LPG |
|
The Following User Says Thank You to classicswede For This Useful Post: |
Mar 29th, 2017, 05:55 | #13 | |
Classic P80 1999 BiFuel
Last Online: Mar 6th, 2024 00:34
Join Date: Aug 2012
Location: 48mph Middle Lane M4
|
Quote:
On my NA car I do have a small drop-off, in peak power and torque, which I would expect, yet it's only noticeable if I press-on in a licence-losing style so frankly I'm not bothered. And 'Mr Jones' has a set-up (rightly or wrongly) to negate the perceived issue. How should it be set?
__________________
Bifuel V70 Classic 1999 [The Old Grumpy in the Corner, "When I was a lad... blah, bl**dy blah."] |
|
Mar 29th, 2017, 12:13 | #14 | |
Trader Volvo in my veins
Last Online: Today 21:00
Join Date: Dec 2004
Location: Anglesey
|
Quote:
The ECU retards the ignition on petrol with the boost. You do not loose any power with LPG due to the CR as this is the same for both petrol and LPG. Yes LPG could run a higher CR and make more power. LPG does have a lower calorific value so you need to use more than you do petrol to make the same power. The fuel then takes up a bit more space causing you to loose the 1% of power. Old mixer systems loose more but not major |
|
Mar 30th, 2017, 10:02 | #15 | |||
Classic P80 1999 BiFuel
Last Online: Mar 6th, 2024 00:34
Join Date: Aug 2012
Location: 48mph Middle Lane M4
|
Thanks classic, I bow to your greater knowledge here.
Sorry to sound dim on this, so LPG has lower calorific values than petrol for a given volume. This I understood. Apple for the teacher, help me here, I'm the sad anorak that would really like to grasp this, please, marks out of ten for the following... 1) Because we can't increase the capacity of the engine when running gas, for any given swept volume cycle of the engine, less energy is going in with LPG, so because we are forced into less energy going in, we must expect less energy out. 2) We could negate the effect of 1) by increasing the boost when running LPG by whatever proportion of energy we are short-measured. Hence if there's 5% less energy per stroke 'going in' running LPG, ideally we would up the boost by said 5% (solely on LPG, mind) and we're on a level with petrol. Because now, per cycle, we are putting the same energy in. 3) Does my point about some of the power loss is brought about due to the CR being fixed by petrol's lower CR requirement stand? In an ideal world you would up the CR when running LPG, only we can't? 4) You wrote Quote:
5) Quote:
6) Quote:
7) Am I getting my higher octane and further advance requirements remixed-up? a) LPG needs more advance because it has a slower flame-front? Hence is slower to ignite? Correct? b) LPG has a higher octane but it is of no advantage in a BiFuel conversion set-up because this property is hobbled. The engine can't be changed back and forth to suit each fuel? Which bits do I have right/wrong? In short if I have hte above about right, for there to be little or no power losses running LPG, what does a top-end install do to achieve this? Aside from more advance, or a altered advance curve, do they up the boost on gas for example?
__________________
Bifuel V70 Classic 1999 [The Old Grumpy in the Corner, "When I was a lad... blah, bl**dy blah."] Last edited by CNGBiFuel; Mar 30th, 2017 at 10:28. |
|||
Mar 30th, 2017, 22:56 | #16 |
Trader Volvo in my veins
Last Online: Today 21:00
Join Date: Dec 2004
Location: Anglesey
|
This fairly in depth but here goes
LPG has a calorific value of 46.1 MJ/kg and petrol is 45.8 MJ/kg so in weight has a higher value. However, its energy density per volume unit of 26 MJ/L is lower than that of petrol (about 0.5–0.58 kg/L, compared to 0.71–0.77 kg/L This means we need to put more LPG in than petrol to make the same power 1) no we are putting in practaly the same energy (what is lost is the tiny amount of air lost that is replaced with the extra fuel) 2) see above 3) As the CR is the same for petrol and LPG no power is lost. 4) It is possible with some ECU's to advance the timing or it can be done via seperate processors. The gain is so small on LPG it is rare to be done but is essential with CNG 5) The power loss with mixers systems comes from teh restriction on teh air intake introduced by the LPG mixer 6) LPG could make a fraction more power at WOT but we are only talking a small amount. Where a higher CR would really come into play would be at part throttle and would make the engine more efficient with the higher effective CR under part throttle. 7) a) LPG does not need more advance but can use it b) either way things will be slightly comprimised for one or the fuels. Either way the CR is striking a balance between part and full throttle. Timing advance for LPG is an option to get the most of what is there but the improvemnt is so small its bearly worth it. The advance that can be used is in mid range. With LPG the engine will work perfectly fine under all conditions as it has been set for running petrol. With CNG that is not the case, it needs a lot more advance to run correctly |
Apr 2nd, 2017, 23:12 | #17 |
Classic P80 1999 BiFuel
Last Online: Mar 6th, 2024 00:34
Join Date: Aug 2012
Location: 48mph Middle Lane M4
|
Thanks classic, so CR being below what LPG likes means, power does take a hit over what it would ideally be, but it's not the major factor. What is, is the lower density which compared to petrol this either depriving hte engine of fuel or air relative to petrol.
I had not realised CNG was so different to LPG in it's requirements. Thanks.
__________________
Bifuel V70 Classic 1999 [The Old Grumpy in the Corner, "When I was a lad... blah, bl**dy blah."] |
Apr 4th, 2017, 13:53 | #18 |
Trader Volvo in my veins
Last Online: Today 21:00
Join Date: Dec 2004
Location: Anglesey
|
CR is a complex thing as in most conditions regardless of fuel used drastically higher CR could be used as the cylinder is not being completly filled. It is WOT that limits how much CR can be used and is then traded off with timing.
CNG and LPG burn very differntly |
Apr 6th, 2017, 03:39 | #19 |
Classic P80 1999 BiFuel
Last Online: Mar 6th, 2024 00:34
Join Date: Aug 2012
Location: 48mph Middle Lane M4
|
I kinda grasp that CR is dependent on far more than fuel, combustion chamber shape and no least what the chamber can take with a full chrge of fuel and air. But it's been a long time since i read up on this stuff, I'm an electronics engineer, no motor tuner! I'm worried about hassling you but please a few more related Qs?
1) Am I correct is saying the reason LPG needs more advance than petrol, and CNG still more, is the slower flame-front. 2) Both are harder to ignite in the first anyway, correct? 3) But if this so, why am I told they run hotter, when I would expect cooler, or is it that once alight the flame is hotter? 4) In the ideal engine, one that only runs on one of the gases, removing any comprmises to run petrol, how would this 'ideal-engine' differ? 5) So a little bit of where I came in... no matter how much I thkweam and thweam, in three theoretical engines, Petrol; LPG; CNG, each optimised for its particular fuel, 'theoretically' we will never finish with the same power with the gas fuelled engines because no matter what else you do, the density of hte gases, means that per cycle the gas-engines will never able burn as much energy, simply because you've less room for the oxygen needed to burn it.
__________________
Bifuel V70 Classic 1999 [The Old Grumpy in the Corner, "When I was a lad... blah, bl**dy blah."] Last edited by CNGBiFuel; Apr 6th, 2017 at 04:14. |
Apr 10th, 2017, 22:28 | #20 | |
Trader Volvo in my veins
Last Online: Today 21:00
Join Date: Dec 2004
Location: Anglesey
|
Quote:
1) yes 2) yes 3) knowing the answer to 1 and 2 is the expert in the pub wrong? Well mostly yes he is wrong. The burn is not as hot. The engine will not run any hotter or cooler as the running temprature is controlled by the cooling system. Is the pub expert right in any way? Yes a little as LPG does not have any cooling effect or lubrication it is harder on the valves. 4) the engine would not differ much, possibly a slightly higher CR and a ignition map optimised for the fuel 5) The energy for a given volume is the limiting factor with vapour dosing. Direct liquid injection could possibly give more power than petrol but that would take some working out |
|
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests) | |
|
|