Are plug gaps with LPG/CNG narrower?

[CNG]

I'm a little confused re plug-gaps. I understand as a broad rule with all else equal we run narrow gaps with the gases over the same engine running petrol. I've experience of this with a late 90s Volvo. A coil-over-plug set-up, it'd be happy with 0.8mm gaps and petrol, whereas it'd eat coils and often misfire running 0.8mm gaps with gas. All was sweet at 0.7mm.

Fancy plugs didn't work any better. It got the cheapest Denso (£3-4 each) changed often.

My classic Land rover was fitted stock with an Old Skool 3Ω coil. 25 thou was well enough for liquid, yet a 1.2Ω (no ballast) coil 25 thou was required to run gas. No real surprise, yet 1.2Ω ran better with petrol too. A 3Ω coil was viable on petrol. Not so gas.

Are there broad rules, namely if the manual says 0.9mm for petrol, can we assume 0.8mm etc for the gases? I confess I don't have much experience of cars past 1999! It might be that the cars I run simply last, yet I just don't know what typical gaps are for *relatively* modern stuff. Throw in the gases and I've no clue. I've a VW EA287 engine here. VW don't specify a gap. Just the plug for petrol. It has a coil-pack (I assume 4 x coils in there) and HT leads. I shouldn't think I can run super wide gaps.

In the past I've bought the cheaper grades of either Denso or NGK plugs - and left the '£20 each' Iridium things well alone. My wisdom being 'Denso £10 a set eBay cheap-plugs-changed-often', have to be better than '£20 each' things left four times as long.

What will a VW EA287 engine want for gaps?

[LPGC]

My understanding of this...

It takes more heat to ignite LPG or CNG than it takes to ignite petrol but this isn't really relevant because any electric spark is easily hot enough to ignite any of them. However, it's more difficult to create an electric spark in an air/LPG or especially air/CNG mix than it is for an air/petrol mix.. For a given gap size you need more voltage to make a spark jump the gap in some gas mixtures than in other gas mixtures.

Going back around 20 years In the LPG conversion trade we used to sometimes have problems with weak ignition systems converting older (at the time) vehicles and a few make/model modern for the time vehicles but modern vehicles today tend to have more powerful ignition systems. Yes on some older vehicles we'd use a smaller plug gap for less chance of misfires. But we also found that in general some make/spec spark plugs seemed to give better results than others with cheap NGK single prong nickle plugs often being a good bet... much better than the expensive platinum upgrade plugs someone might have fitted at the time.

Obviously if the gap is too wide for the voltage in the air/fuel mix there won't be a spark so there will be a misfire but there's more to it than that, there's also the size of the spark (big gaps longer or bigger spark), where it is in the cylinder and whether there are any bits (of spark plug etc) shielding the spark from the gasses in the cylinder, all affecting not least flame propagation.

Other differences between petrol / LPG / CNG include the difference in flammability at different mixtures, stochiometric or slightly rich has the best chance of igniting but petrol will ignite at a wider range of mixtures than LPG which will ignite at a wider range of mixtures than CNG. Mixture also effects the propagation / burn speed.

The VW EA287 engine was made over a long period of time, we'd expect the ignition system to be improved over that period, so it might be that on an early one you'd need to fit something like the nickle single prog NGK plugs and maybe even need to close the gap a little while on later ones the standard (platinum?) plugs might be fine with standard gap.

It's good that modern ignition systems tend to be more powerful than older vehicle ignition systems because that's probably the main reason why long life platinum / iridium plugs can be used (and are usually standard fit) with them... and plugs on modern vehicles can be much more difficult and time consuming to change than on older vehicles, not something you'd want to do often so you want to fit long life plugs if you can. But if plugs are easy to change and the vehicle manufacturer lists a cheap nickle plug and an expensive platinum/iridium plug the cheap nickle plug might give less chance of misfires and work out no more expesive in the long run (can buy multiple sets of nickle plugs for the cost of iridium) so might as well fit cheap plugs and change them more often.

[CNG]

Thanks Simon. That makes it far clearer. In short you DON'T narrow gaps, least not on modern stuff because they run the coil-power anyway. The 'narrow-your-plug' mantra comes from an era when coil-power was low. Thus gap-narrowing was the workaround rather than as I saw it, what you do - because:

'gas innit'.

And you agree with my cheap-plugs-often doctrine. I think it's a 1993 design, swapping plugs on a VW EA287 is as easier than my Land rover!

Only yet again, I have a rare beast. I had a ex-factory 'Made for gas' proper, proper BiFuel Volvo. I understand it had ignition mapped for gas and a different cam profile. But it was really a 10.5:1 CR petrol-bias design. Middle-point.

This time I find myself with a BSX from 2011. By my standards this is bang-up to the moment.. This is your proper, proper CNG engine. It's a EA287 sub-variant with at least a 12.5 CR ( I think 13.5CR) and fewer concessions to the liquid stuff. It will run liquid but fuel economy is poor - it really is "Emergency Power' . The digital display actually flashes "Emergency Power' and makes this fact v.clear to you.

Only I'm confused here too. VW are not idiots. I understood you couldn't run petrol at 12.5CR. Clearly you won't know for fact, but how do you think they're achieving this? Is VW simply retarding ignition and insisting on Premium-grade at the pump, until it doesn't knock or is there more to it? My Volvo was left at a petrol freindly 10.5:1, certainly not at BSX levels. The BSX is 8-valve - fixed valve-timing. Very simple.

Reason I ask, I rarely run liquid in my classics - petrol is purely a Get-me-home-when-I-run-out option, can I just retard my ignition curve on petrol until it doesn't knock and take the performance/economy knock, this assumes... this is all VW are doing with the BSX?

[LPGC]

Is the factory converted Volvo LPG or CNG? If it's the Nikon Koltec type they have a gas distributor that has a stepper motor that has the stepper motor driver electronics built-in, they were always going wrong and difficult to obtain, different to all the other steppers used on other Nikon Koltec systems.

Not sure how the VW runs 12.5+:1 compression and still runs OK on petrol but there are various ways including premium fuel, retarded ignition, lean burn, Atkinson cycle, creating high swirl by only opening one inlet valve (partial cylinder de-activation), running high proportions of EGR, restricted throttle, etc.

If it's factory fitted with a petrol tank you shouldn't need to change anything to run on petrol because the manufacturer should already have set it up to be able to run on petrol at the flick of a switch? But it would be interesting to know what it does. Or do you mean you want to be able to run on petrol with one of your self-converted CNG only vehicles?

[Gilbertd]

You'll probably find that it has knock sensors so will automatically retard the ignition timing if it detects a knock. I have one car with twin turbos and needs at least 98 Octane fuel, if it is run on standard 95 Octane it is immediately obvious that the timing has been retarded the first time you put your foot down. Most modern cars run with the plug gaps at 1.1mm, over 40 thou. Running on gas it is advisable, but not always necessary, to close them down to nearer 20-25 thou but too small a gap can cause a misfire just the same as too big a gap can. Never liked Denso plugs though, I always use NGK. The NGK BPR6ES plugs that I use have a standard gap of 25 thou and are only £2 each, so £16 a set for me. I had a problem on one V8 Range Rover than would fire but just wouldn't catch and run properly. We ignored the plugs as it was obvious that they were new until we had exhausted all other eventualities. Bunged a set of used NKGs in it and it fired up immediately and ran perfectly.

[CNG]

But it would be interesting to know what it does. Or do you mean you want to be able to run on petrol with one of your self-converted CNG only vehicles?

The factory Volvo was Koltec CNG - I got myself a rich supply of stepper motors. It was definitely a petrol bias engine. Not so this VW.

Whatever this VW is doing, it is doing it. We have a heavily biased for gas, factory spec engine. VW have found a way to make it run. Hence the root of my Q is curiousity, It runs petrol as 'Emergency Power' I'm guessing and hoping I can transfer the lesson.

VW have clearly solved the problem to the point where their marketing department have petrol-use down as Emergency Power. My curiousity is piqued because my self-converted Land Rover suffers a massive power-hit when on gas - this as a concession to the occasional get-me-home moments where I too will swap to, ahem... 'Emergency Power'.

For my use, far better it run poorly for 1-2% of my miles and be optimised for gas. Because the reality is, my LR is 95% a gas power vehicle. Running a Leo and single-point OMVL reducer it starts on gas. Provided I'm not doing harm on petrol, if it stumbles a lot, and still gets me home, that's a win.

I'm wondering if I simply up the CR. retard the ignition and run things a bit rich (to cool things) and suck and see? I'm doing a engine rebuild now. Taking metal of the flat bits is easy and cheap enough. Putting metal back on if it doesn't work - not so.

Here's what I know:

The VW manual recommends premium fuel. You're cautioned to run basic fuel with a performance and economy hit. Gilbert you have to be right - there must be a knock-sensor to deal with this.

Most modern cars run with the plug gaps at 1.1mm, over 40 thou.

My problem is because it's one obscure engine, concrete info gets difficult. This engine is all over Ukraine & Russia. Internet info means I'm reading Russian in translation.

Plug seems to be NGK BKR6E at 0.8mm gap. But some say a NGK BKR6E-11 (1.1 gap - I think?)

BSX.png (109.17 KiB) Viewed 2957 times

I found it in finish. NGK say 0.8mm NGK BKR6E. Where in NGK nomenclature X is preset? Adjust to 0.8mm. Which is quite narrow?



With my wish to bias to gasification with my LR - In order to combat the daft retardation I'd use, am I right to run rich or would I aim to run weak.? I can see arguments for both approaches.

[Gilbertd]

The standard gap on an NGK 6962 BKR6E is 0.8mm which works out to an old school 25 thou. If you to get a BKR6E-11, it will have a different part number although it is the same plug but with a wider gap, everything else will be the same (thread length, diameter, hex size, heat range, etc).

Why would you want to retard the timing? You've already played with timing advance processors to increase the power, so advancing the timing and increasing the compression would be the way to go. I doubt you would be able to get much of an increase in compression just by skimming metal off, ideally you would need to use different pistons to get any meaningful increase.

[LPGC]

Some spark plug manufactures, if they list plug gap at all in the plug code, list it at the end of the code e.g. -11 would be a 1.1mm gap. If you had a choice of 1.1mm or 0.8mm gap then if you found the 1.1mm gap didn't cause misfires you should be able to run it with the 1.1mm gap without any disadvantage compared to a 0.8mm gap.

'Emergency Power' could point to the engine not running well on petrol or could point to the fact the petrol tank is so small.

Does the VW engine seem more powerful on CNG than on petrol (or vice/versa)?

You could maybe find out how the VW handles the different fuels by checking timing with an old-skool timing light (if you put it on a rolling road or if OBD live data gives timing info), and if it has a drive by wire throttle by checking manifold pressure at WOT. Normally we'd think the engine too old to have 'lean burn technology'. It is interesting that the power output for the BSX isn't listed in the table, normally we'd expect a 2.0 to be more powerful than a smaller engine in the same series, if it's less powerful perhaps it has a different head/cam.

Post crossed with Gilbert's.

I agree with Gilbert it's unlikely you'd be able to remove enough metal to make much difference to compression, when you start looking at engine combustion chambers it isn't like the piston in a lower compression engine doesn't come close to the head, it is more likely to still come close to the head but the head or piston have some sort of indent/dish. Increasing compression is also harder on the pistons, rods and crank... not sure how that would effect reliability of an old Land Rover 2.25 or 2.5 engine.

[CNG]

I'll play with the gaps and see how it goes. I bought the cheapest BKR6E (BKR6E-11 I think) at a £1 each, because I'll set the gap anyway.

I think I'm going to run-up the CR on my LR and to hell with it. It runs 9:1 now. I've got some flat-top pistons too. And there's a heap of metal to remove from the head. it's one 'VERY 'cooking-grade' engine. It definitely is not any interference engine!

The VW takes a mild power hit on CNG. I was wondering how my VW works at such a CR on petrol. I'll put my timing-light on the VW just for my curiousity.

Seems Ducati is doing 14:1 on petrol. (see 3:05)
https://www.youtube.com/watch?v=uA-kglFSq5I

How that's being done I think I will never know?! Mind, I had a 996 for a while, and they don't stay together long!

[LPGC]

I haven't seen the video yet but there are ways in which an engine can run a higher cr than we'd usually think viable, I mentioned some of them in a post above.

David Vizard used to tune Ford SOHC / Pinto engines to run high compression like 13:1, iIrc he said it was because the head ports were too large to flow adequately at lower rpm so they needed all the compression they could get to make power at low rpm, then at higher rpm the squish area in combustion chambers helped prevent detonation (which would still occur in the squish areas) spreading to be cylinder wide mixture detonation.. So in other words down to the shape of the combustion chambers, so not applicable to all engines.

[Pinger]

I'm wondering if I simply up the CR. retard the ignition and run things a bit rich (to cool things) and suck and see? I'm doing a engine rebuild now.

Rich to cool is a liquid fuel thing. It relies on drawing heat to evaporate the fuel.

[Pinger]

Seems Ducati is doing 14:1 on petrol. (see 3:05)
https://www.youtube.com/watch?v=uA-kglFSq5I

Haven't watched the video but that Ducati will be running a zillion rpm. At high engine speeds detonation is less of a problem as there is less time for detonation to occur. The bike race engines (with tiny cylinders) of the 1960s that ran to 18-20000 rpm ran on fuel with octane rating comparable to paraffin's.

[Pinger]

Re ignition systems, below is a copy and paste from another forum. The 'active dwell' it refers to is new to me but does indicate how far ignition systems have advanced from the days of points.

''I can believe primary resistance of less than 1 ohm on electronic ignition and I know of systems with 0.5 ohms.

Yes the primary current would be high and that's why points couldn't handle it and even if they could have handled it, the coil would overheat at low revs in very short order without active dwell control. The first electronic ignition did typically half the primary resistance and double the current but later versions with better dwell control went with much lower primary resistance. It was all about chasing near full coil saturation at high revs while limiting current and heating at lower revs and also about increasing spark energy.

Spark energy is proportional to the coil inductance times the primary current squared so more current has a big effect and more than offsets lower inductance. Lower primary resistance also lowers inductance and that allows the coil to charge much faster which would have been an objective particularly on six cylinder engines.

I still have points on my 79 BMW bike but it's wasteful of energy at low revs. In the diagram of coil current, the points open at A and close at B. Between B and C the coil is charging but beyond C the coil is fully saturated so the current to right of C does no useful work and is wasted as heat in the coil. Active dwell control in electronic ignitions solved all that by limiting dwell to what was actually needed at any particular revs and also limited current to a maximum value that may be less than the simple 12 volts divided by the primary resistance.''

[LPGC]

A lot of early 'electronic ignition' systems were add-ons to a standard points in distributor setup, some retained the points to switch transistors so the transistors switched the heavy current and points only had to switch a tiny current, others lke Lumenition replaced the points with an optical or inductive switch to switch transistors. But since coils make the spark when the power is disconnected rather than when connected a simple transistor points amplifier couldn't change dwell without affecting ignition timing... I think some of them did affect coil on time but they did it by pulsing the coil for a set period of time when the points opened, which would have the affect of retarding ignition timing unless the fitter/owner twisted the distributor to re-correct timing.

For 4 stroke coil on plug setups or 4 stroke single cylinder engines dwell angle could be nearly as long as 720degrees where-as for multi cylinder engines using a points distributor max possible dwell angle would be the 720 divided by number of cylinders... But as far as the coil(s) is concerned, as you implied it's not really about dwell angle it's about dwell (or on) time, there's no need to increase dwell time at lower rpm's but that's what old points setups did.

[CNG]

I'm not fool enough to think me and my box of spanners will do anything but make my VW worse by messing with its fuelling or ignition. My interest was in taking what VW does and applying its lessons to my own conversions.

In truth the power-hit a factory built CNG engine suffers vs. petrol-running is still pretty significant. And i suspect the BSX ; gas-biased as it is - has its petrol running compromised. Thus the grunt it could otherwise put out with petrol is less - all for CNG. Thus in conclusion, if this is as good as VW can do with their CNG vs petrol problem... they will have hobbled petrol running - and I very much doubt they're fools, what chance me?

Likely I'm not losing as much as I think.

Upping the CR in my LR will no doubt give a grunt increase, but now I've had more time to see the difference even VW can't reduce, maybe what I'm looking for is not within reach anyway. Certainly not if all i'm going to do is lop metal off a cylinder-head and retard / hobble the petrol running to do this. It won't be that simple anyway.

Conclusion - CNG.

Better I live with the power-drop. It's the nature of the beast. The price for going, er, cheaper.

VW Caddy Reducer.png (197.76 KiB) Viewed 2699 times

And even here cheap is relative. VW must make the world's priciest reducer. With a stepper motor and no rebuild kits Add another £200 for import charges You can buy a used one - but don't.

[LPGC]

Wonder what the stepper motor on the reducer does...(?). Perhaps if the OEM CNG setup on the VW failed, instead of replacing components you could fit your own closed loop CNG setup using more available and cheaper components. As you know, the VW mods that allow the engine to run a bit more efficiently on CNG will be due to changes to hard engine components affecting things like CR and valve timing, not mixture; The design should give the same benefits with an aftermarket CNG setup, both will the OEM and aftermarket aim to provide correct mixture. The potential main difference might be that an OEM setup might switch between different ignition advance curves if timing control is more advanced tham bobweights and vacuum like in a conventional oldskool distributor.

To get the most from the Landrover engine the timing curve might need to be different too, whether you modify the engine hard parts to increase cr etc or not. But the Landrover will only have a conventional oldskool distributor so if you modify its advance curve it could have negative effects when running on petrol.

[CNG]

I believe the stepper adjusts gas pressure. The Russian & Ukrainian forums put standard reducers and -if my understanding of ropey translations is correct - the effect is to starve fuel under load. Pressure sensor in gas-rail. The ECU flips to liquid at or near WOT. There's one loon that's put a Nevo on a BSX to run tri-fuel. Petrol / CNG + LPG. Three sets of tanks. Seems it can be done. Maybe he takes his LPG map via the CNG curve? I think LPG is cheaper or just easier to get in some parts of Russia??

None of that Joker/Wolf stuff, my LR has a dual-curve electronic dizzy. 123Ignition. There's three versions.... a numpty variant; a mobile phone (single curve) one ; mine with twin curves set by rolling road. Set such that a trigger wire - off the gas-solenoid - fires the gas curve. This muchly the way a Joker would.

https://123ignition.com/

The curves are VASTLY different. eg 6 degs = idle Petrol... 22 degs = idle CNG.

Not for everybody, seems to me you want a fair clue with what you're doing around BSX VW Ecofuels. I've got my head round it - I think. You'd better know why you want one. Ahem... including mine, all those I've seen have umpteen prior owners. That tells a story.

[LPGC]

Most likely the Nevo gets its Pinj input from the petrol ECU when that's running in petrol mode.

The 123igntion could maybe be improved by adding a knock sensor to log knocks and maybe automatically retard the ignition curve (or flag the point on the map for user review) where knock occurred.

For the tri-fuel setup it would be nice if the programmable ignition curve could have 3 settings, one for each fuel, and if it could learn (or you could copy/paste) the petrol curve to use as template for the LPG curve.

I've converted vehicles to run on tri fuel plenty times, either petrol, CNG and LPG or petrol, electric (hyrbrid) and LPG. Could even be done 4 fuels lol.

Wasn't CNG and LPG something you considered at one time, or was suggested to you for extra range in case you needed it over CNG range?

[CNG]

Most likely the Nevo gets its Pinj input from the petrol ECU when that's running in petrol mode.

Adding LPG to my BSX is not something I'll ever do only I have to ask, why would the Russians take-off the petrol, not the CNG? I'd think the CNG is already pretty close to what's required for LPG. Whereas it's be a greater leap to get from petrol to LPG.

Mind... because CNG takes up so much 'kin space,these Caddy are designed for the space from the off. Moving to all LPG on these must give galactic range. I get 320 on CNG. Assuming same tanks in LPG... 170Litres of LPG has to do 7-800 easy. There's heaps of vids showing this or a mix. Always Ruskies / Poles & Ukrainians. Later Caddy has a 1.4 lump. Not BSX. Here's two:

https://www.youtube.com/watch?v=ENZJgKYv6wA

https://www.youtube.com/watch?v=Tp9nERyBxE4

The 123igntion could maybe be improved by adding a knock sensor to log knocks and maybe automatically retard the ignition curve (or flag the point on the map for user review) where knock occurred.

That hadn't occurred to me. Fitting a knock-sensor must be possible. I'll search, I'm assuming someone sells an ECu that does this.

Wasn't CNG and LPG something you considered at one time, or was suggested to you for extra range in case you needed it over CNG range?

I looked at it. The LPG would knock the CNG range so much I'd start to need the LPG when i could be on CNG - it borders a circular logic.

[Gilbertd]

why would the Russians take-off the petrol, not the CNG? I'd think the CNG is already pretty close to what's required for LPG. Whereas it's be a greater leap to get from petrol to LPG.

Why? You are spending an awful lot of time to get a petrol engine to run CNG and even then it is way down on power, whereas to go from petrol to LPG requires virtually nothing. LPG is ridiculously cheap in Russia (currently 0.22 Euro per litre according to mylpg.eu) and not that much more expensive in Belarus. Admittedly, it might be in short supply at the moment but so would CNG. However, I wouldn't be happy with a CNG installation in Russia with the pressures involved. Admittedly it was 18 years ago when I drove to Belarus in my LPG Saab 900, but they insisted on filling LPG for you and wouldn't do it unless you were out of the car and the doors, bonnet and boot were all open so the leakage could dissipate. They expected there to be leakage..... Quite what precautions they would take with CNG I have no idea (although I don't recall seeing much CNG but LPG was everywhere)