CNG / LPG - Timing Advance Processor
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  1. #1
    Fellow Frogger! Molerpa's Avatar
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    Default CNG / LPG - Timing Advance Processor

    I started the original post in spanish, to a few forums i use. But I'll try with my poor english, to make something understandable for you.

    Note: It is know that I work on CNG/LPG Research and Develompent, but please, don misunderstand this. I am just explaining a few things, I am not selling anything. This is part of the proud that I have for the company I work on.

    ************************************************** *****


    Based on the fact that LPG and CNG most of the times have lower flame speed than petrol, most of people used to increase timing to solve this, by turning the distributor, modifying the initial timing, which also alters all the timing. Obviously, on petrol, using this timing will make knocking, and if we don't care about it, we may have a broken piston... or worst.

    Besides that, we just modify the initial and HOPE to be the correct timing on all the RPM range... which most of the times is not. Normally an increase on low RPM is correct, added to less increase on high RPM.

    At first, the early TAP (timing advance processor) were just a "retarder" that you set on the distibutor the timing for CNG/LPG, and with the module, retard it when you're in petrol.

    Then, the newer types allowed you to set a fix degrees 6,9,12,15 over the timing you have (in this case, you leave the distributor where it goes (normal timing) and by operating dip-switches, you increase the timing.

    But, after that... the new era came!




    This is absolutely programmable.











    So far, you see the same than previous example... 6,9,12,15...
    but all these curves, can be edited, from 0 to 20 degrees, and on steps of 400 RPM. The firmware does interpolation between them. 1 deg, 100 RPM resolution.


    So, by using this (interface)



    and a laptop (or desktop computer, but is... a little heavy to transport)

    We do this...















    Yes. That is absolutely programmable. So, you can draw it with the mouse. Can set it on idle or not (the timing increase), etc.

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    Quote Originally Posted by luthier View Post
    It is simply impractical to expect a petrol motor to get through too much water. That's why God invented diesels.

  2. #2
    Fellow Frogger! Molerpa's Avatar
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    Icon8

    I had to make a document for the application of these devices, and why to use them, so... as I had to make it in both languages (we export a lot, more than 80% of the production), I'll put it here... So, you can also get bored with this...
    By the Term "CNG", or "NGV" is Compressed Natural Gas, or Natural Gas for Vehicles. In the case, read "LPG". Even when it is not the same combustible, the concept yes it is. You'll find "gasoline" instead of petrol.

    As the engine is a thermo-dynamic machine, designed to convert chemical energy into cinetic (mechanical) energy, the less dissipated on heat will be the more converted into cinetic energy, available on the flywheel. The cycle then, will be more efficient. When converting a car from gasoline to CNG, as the flame speed of Methane is slower than regular gasoline, using the timing devised for gasoline on CNG will decrease the efficiency of the engine. The resulting lack of power and torque, will not only be a disadvantage on performance. It will also affect the lifetime of the engine. The percentage of power loss is an index of what is going to be dissipated by heat on the inner parts of the engine, such as cylinder head, valves, piston head, etc. To avoid this, and to have an engine which lasts as long as possible, and with the smallest power loss, the installation and set-up of the proper Timing Advance Processor (TAP) is recommended.


    The timing on an engine is defined by the manufacturer, and it is to exploit to the maximum the combustion characteristics. By general rule, the timing is calculated to have the maximum pressure over the piston’s head between 1/5 and 2/5 on the descending stroke, after combustion.The amount of degrees that the mixture is ignited before the top dead center ( º BTDC) is because the flame speed is constant, and according to the RPM gain and time remaining to draw on the combustion on the piston head, is needed to increase the timing such as the RPM are increased. As explained before, this is for the original combustible, and as the CNG has slower flame speed, this has to be increased for CNG.





    Methane (main component of CNG) has an average of 30% lower flame speed than gasoline.
    To have the pressure peak at the same spot of the descending stroke, as it is on gasoline, the timing has to be increased (more degrees before TDC). This will bring beside the previously mentioned advantages, lower fuel consumption a better emissions level.


    On the Fig 1.2 it can be seen the power drop between CNG and Gasoline. The engine for this example is a Ford 1.3L 8V (Rocam) from a Ford Bantam (Courrier). Mixture is adjusted by ECU, and it is always perfect, but even so, the difference is important. Besides, the torque band starts even lower, when the load of the engine is maximum, at low RPM. This is a conversion without any Timming Advance processor.


    Hereunder a Dynotest will be found. Is a comparisson on the same engine, between gasoline, CNG with and without TAP, and CNG with TAP vs CNG without TAP. The same Ford 1.3L 8V Engine has been used.



    GASOLINE
    Torque: 116 Nm @2356
    Power: 56.1 Kw @5489RPM

    GAS
    Torque: 92 Nm @2175RPM
    Power: 44.3 Kw @5347RPM

    Using this absolute values (max power and torque) and doing some calculations, the power and torque drop can be revealed. 21.03% power drop, and 20.68% torque drop. However, the real important thing about all this, is not only the absolute value and power drop. As the main purpose of this engine is to move the car, and it is not a stationary engine, the torque and power curve will be analyzed now.




    On the Figure 1.4, the begining of the acceleration has been marked. Compared Gasoline and CNG, and beside the absolute drop (more than 20 %) a huge torque and power drop is shown at low RPM. As explained before, this is not a stationary engine. It will move the car beating the inertia many times a day. The 20% power drop even though is an important number, is not so important as in this case, almost 77% power drop at 1200 RPM (13 HP vs 3HP @1200 RPM) and near 70% torque drop (83Nm vs 25 @1500 RPM). Notice also that this engine will recover or “clean” not before the 2000 RPM. At lower RPM than that, is nearly impossible to drive it normally. Now, the same comparisson, but with a Timing Advance Processor Installed, and tuned.




    GASOLINA:
    Torque: 116 Nm @2356RPM
    Power: 56.1 Kw @5489RPM

    GAS:
    Torque: 102 Nm @2575RPM
    Power: 48.7 Kw @5338RPM


    Fig. 1.5: Dyno test Gasoline vs. CNG with the TAP tuned up for this car. Power loss: 13.20%. Torque drop: 12.06%
    The most important concept here, is not only the higher power available on CNG according to the previous dyno test. Related to what have been explained here before, the driveability of this set up will be much better than the previous one. At low RPM the torque and power available are similar to gasoline. Even if the max power and torque remained the same than the previous case (which is not, according to this comparisson), the results would be better. Now,CNG without TAP vs CNG with TAP



    GAS WITHOUT TAP
    Torque: 92 Nm @2175RPM
    Power: 44.3 Kw @5347RPM

    GAS WITH TAP
    Torque: 102 Nm @2575RPM
    Power: 48.7 Kw @5338RPM


    And the curve set for this vehicle was this one. Off course, by using the dyno, on several runs, to find out the best... And using the brake of the dyno also.



    Graphic and Numbers, speak by themselves...


    Quote Originally Posted by luthier View Post
    It is simply impractical to expect a petrol motor to get through too much water. That's why God invented diesels.

  3. #3
    Tadpole
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    Interesting to read of this unit you write of. I can see it would be of some use with an efi petrol engine not fitted with a knock sensor.

    Will this unit work side by side with a factory knock sensor timing retard?

    There is another website forum if you google propane forum raso enterprises - this site users would really take more interest in the unit I am sure

    I am curious as to where this unit is connected to the engine electricals, and if it is confined to single ignition coil systems or if it can work on coil pack sytems.

    Turbo applications catered for as well ?
    Last edited by frogbike; 26th April 2012 at 10:28 PM.

  4. #4
    Tadpole
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    hi

    i have a question about Peugeot 405 timing
    my car is 405 GLX my engine is xu7 with Sagem SL96 ECU
    so my problem is advance timing because my advance in 2500 RPM and uper is very high

    I checked with diagnostic scanner my Advance timing start applying @3000 RPM to 60 degrees !!! but idle is 8 to 12 this is ok but in 3000 to 6000 advance is 60 Between 40 and 60 plays, but most remain 60 degrees that causes knocking about 2.5k to 3.5k rpm

    Whats my engine-ECU-timing-sensors ... problem ?



    i think this value is very high for this engine speed so i want to you or anyone who knows what is the engine ignition table

    or is this that I said is true for this engine ?

    plz hlp me
    thank u so much
    Last edited by jodah; 20th February 2017 at 10:28 PM.

  5. #5
    Tadpole
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    up ...

  6. #6
    Tadpole
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    !!!!!!!!!!!!!!!!!!!!!!!!!!!

  7. #7
    Tadpole
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    i found my answer !

    SL96 naturally have more Advance vs other ECU's

    but for knocking i changed fuel air ratio from diag
    my fuel number was -8 so i raise it to 0 then knocking solved ....

  8. #8
    1000+ Posts PeterT's Avatar
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    LPG is dying a slow death in Australia. Shell no longer sell it.

    '92 205 Mi16
    '90 Mi16x4

  9. #9
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by PeterT View Post
    LPG is dying a slow death in Australia. Shell no longer sell it.

    Not according to the Shell website.

    Shell AutoGas | Shell Australia

    And in Victoria anyway, every Taxi and many commercial vehicles use LPG.

    And anecdotal evidence, gained from buying ULP , suggest nearly every fuel station sells LPG as well as ULP.

    AFAIK you can still purchase Holden and Ford liquid phase injection (LPI) vehicles off the showroom floor.

    So I'd suggest there is still quite a demand for LPG.

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