What engine is best for CNG, mechanical or electronic?
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Thread: What engine is best for CNG, mechanical or electronic?

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    Default What engine is best for CNG, mechanical or electronic?

    I've been reading a lot on adding CNG to your diesel. Fascinating stuff! There are some great threads out there including this one on CNGchat.com
    http://www.cngchat.com/forum/showthread.php?t=26&page=1

    Anyway, I've been trying to figure out what engine would be best for CNG, an electronic one or a mechanical. I guess CNG blending can more than double your gas mileage by basically putting CNG in place of it. It's flash point is higher than gasoline (somewhere around 1200' I think). So it basically detonates with the diesel fuel injection. Not only do you get something like 100 hp and better efficiency but good milage too. The tank is cumbersome but if you had a large pickup for example I think you're OK.

    According to that thread (towards the end) there are something like 4 or 5 manufacturers making both EPA and "off-road" certified kits for CNG into diesels. It's definitely something I would be into especially if I were commuting...

    The way they work is its based on vaccum. CNG is pulled in according to draw from the turbo (or intake for NA engines) before the turbo. At idle it runs on diesel only and then accordingly added depending on how much vacuum you have happening. You can then adjust from 25 to 50/60% safely (I've been reading as much as 80%) and somehow it knocks down your fuel consumption as well...

    So that would be the idea, I'd want to get screamin diesel mileage with a smaller CNG tank like a "12 gallon" or so which would mostly be used for commuting to and from work. The CNG directly offsets whatever the diesel consumption would be so a 25% blend would reduce the diesel use by 25% (so a 16 would get 21/22 or so MPG) and your CNG use would be 12 gallons @ 16 mpg total consumption / divided by 4 (or x .25). If that makes sense. But the kicker is it adds horsepower and I've been hearing all sorts of numbers.. And finally, how do you control your diesel fueling? Pretty funny and pretty simple. It's as far as just letting off the throttle.

    One thing I've noticed is both electronic and mechanical diesels have "boost readers" that either go directly into the injection pump, or to an electronic sensor that then provides input to the computer.

    It is pretty interesting uh?
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    Default my .02 cents

    i have seen a mack engine with a propane setup but never heard or seen it run, it was in a shop, and i wasn't that interested at the time.

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    ive seen cng powered cummins and it appears that they have a spark plug in each cylinder as well? seemed odd. they where in city buses.
    Scott in CA
    1970 bronco 4bt, compound hx30 and hx40, F&R D60's, 47RH, 38'shttp://www.4btswaps.com/forum/showth...t=bronco+build

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    Those are ones that run only on CNG so they require a spark plug. In this case it uses a minimal amount of diesel fuel to ignite the CNG depending on your ratio... I had a good talk with Marc Deluca yesterday who is making kits for CNGs to diesels. He also has a suburban with a 4BT (also running CNG) and is a member of this site it turns out...

    http://www.delucafuelproducts.com/

    Still definitely peaking my interest
    1991 Toyota Pickup, Mercedes 300D OM617 diesel
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    My 'burb w/4BT is getting 70 mpg on #2 using cng. It does somewhere around 20 mpg on cng. I don't know for sure because I fill right off our gas well and don't have a meter. I am using too much cng to make alot of power because of detonation. If I back way off on the gas, I can make more power. I am running a prototype microcontroller in my Duramax that can very accurately control fuel delivery and has detonation and egt control. It is achieving over 400 mpg on #2 on the highway, therefore it is running on almost all gas. I won't be able to do that with the 4BT because of the engine being under much more load and no intercooler.
    '04.5 Silverado CCLB Duramax Allison w/cng injection
    '95 C2500 Suburban 4BT w/cng injection, 4L80E
    '05 Jeep Liberty diesel w/cng injection
    '91 V30 CCLB 454 4L80E lp gas
    '72 Impala 350 lp gas

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    The CNG won't just be detonating on diesel injection, it'll be detonating just due to the heat of compression.
    It does have a higher autoignition temp than propane (580C vs 480C), but given that I can detonate propane in my diesel at cold idle, I'd still expect CNG to detonate.

    I can't understand why you'd want to run an engine on detonation. Trading MPG for engine damage just doesn't make sense.

    Some autoignition temps here.
    http://www.engineeringtoolbox.com/fu...res-d_171.html
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    The point is to avoid detonation. My microcontroller has a detonation sensor that limits the gas to avoid it, as well as egt sensing to limit gas also. It will maximize the amount of gas used while avoiding detonation and high egts.
    '04.5 Silverado CCLB Duramax Allison w/cng injection
    '95 C2500 Suburban 4BT w/cng injection, 4L80E
    '05 Jeep Liberty diesel w/cng injection
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    Quote Originally Posted by marcdeluca View Post
    The point is to avoid detonation. My microcontroller has a detonation sensor that limits the gas to avoid it, as well as egt sensing to limit gas also. It will maximize the amount of gas used while avoiding detonation and high egts.
    I'm curious as how you're going to avoid detonation?
    My experiments show the detonation is always there, only the volume changes with the amount injected.

    I have audible violent detonation with lpg at 0.4% of the intake air volume at cold idle.
    CNG has a higher autoignition point, but not high enough to be outside normal operational temps.
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    The detonation sensor listens to the sound level of the engine. I set a threshold that is slightly above the noise level at full throttle on #2 only. I have run heavy lp and cng for 127K miles, much of that running at least three to one gas to diesel.
    '04.5 Silverado CCLB Duramax Allison w/cng injection
    '95 C2500 Suburban 4BT w/cng injection, 4L80E
    '05 Jeep Liberty diesel w/cng injection
    '91 V30 CCLB 454 4L80E lp gas
    '72 Impala 350 lp gas

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    Quote Originally Posted by marcdeluca View Post
    The detonation sensor listens to the sound level of the engine. I set a threshold that is slightly above the noise level at full throttle on #2 only. I have run heavy lp and cng for 127K miles, much of that running at least three to one gas to diesel.
    The sound level of a diesel at full throttle would mask a herd of elephants.
    If you're already running that much LP gas, then you're already detonating and your sensor isn't picking it up or the rapid increase in cylinder pressure that accompanies it.

    Take a look at this:
    http://www.offroadexpress.co.nz/video/lpg-idling-diesel
    Last edited by Dougal; 09-04-2009 at 06:57 PM.
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    Detonation only occurs when the gas/air mixture is rich enough to ignite under compression. Natural gas has a very narrow range of flammability. Too rich or too lean and it won't ignite by spark. The key is to keep the mixture lean enough to not detonate. It is easy to tell when detonation starts, even on a loud engine. I can show the output of the knock sensor on an oscilloscope and compare diesel only operation to supplemented operation. At light load, I use 1uL of diesel per injection at highway speed on my Dmax. The engine is as quiet as a gasoline engine, and the o'scope shows less noise than running diesel only. When towing, the knock sensor limits the gas and more diesel is added to get the required power.
    '04.5 Silverado CCLB Duramax Allison w/cng injection
    '95 C2500 Suburban 4BT w/cng injection, 4L80E
    '05 Jeep Liberty diesel w/cng injection
    '91 V30 CCLB 454 4L80E lp gas
    '72 Impala 350 lp gas

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    Quote Originally Posted by marcdeluca View Post
    Detonation only occurs when the gas/air mixture is rich enough to ignite under compression. Natural gas has a very narrow range of flammability. Too rich or too lean and it won't ignite by spark. The key is to keep the mixture lean enough to not detonate. It is easy to tell when detonation starts, even on a loud engine. I can show the output of the knock sensor on an oscilloscope and compare diesel only operation to supplemented operation. At light load, I use 1uL of diesel per injection at highway speed on my Dmax. The engine is as quiet as a gasoline engine, and the o'scope shows less noise than running diesel only. When towing, the knock sensor limits the gas and more diesel is added to get the required power.
    The "too lean to detonate" theory is for external ignition source (i.e. spark).
    It doesn't apply to auto-ignition from heating as occurs in a diesel engine.

    Did you see the video? That's 0.4% LPG, the lower flammability limit is 2%.
    Yes that's right, it's detonating violently at 1/5th of the concentration that is commonly believed to be safe.

    What % fumigation rates are you running?
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    Haven't had a chance to watch it yet.
    Unless I have to tow, my Dmax runs 95% cng. I is getting around 15mpg GGE on gas while getting 300 mpg on diesel.
    My understanding is that it doesn't auto-ignite under compression unless it is within the flammability range, but will ignite when the diesel fuel is injected. Remember that ng has a much higher octane rating than lp, so you can run much higher percentages.
    I have sold at least 50 systems for starionary engines, up to 1100 hp. Many of these run 70% NG. I have sold a few hundred for pickups and semi trucks. It does work.
    Last edited by marcdeluca; 09-05-2009 at 05:48 AM.
    '04.5 Silverado CCLB Duramax Allison w/cng injection
    '95 C2500 Suburban 4BT w/cng injection, 4L80E
    '05 Jeep Liberty diesel w/cng injection
    '91 V30 CCLB 454 4L80E lp gas
    '72 Impala 350 lp gas

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    Quote Originally Posted by marcdeluca View Post
    My understanding is that it doesn't auto-ignite under compression unless it is within the flammability range, but will ignite when the diesel fuel is injected. Remember that ng has a much higher octane rating than lp, so you can run much higher percentages.
    That's the rub, there is no safe percentage as shown by the video.
    I have detonation at 1/5th of the lower flammabily limit.

    Commercial LPG engines run far reduced compression ratios to avoid detonation, commercial CNG engines can run a little more compression, but still not anywhere near 18:1.
    Check the specs on the cummins-westport gas engines.


    Quote Originally Posted by marcdeluca View Post
    I have sold at least 50 systems for starionary engines, up to 1100 hp. Many of these run 70% NG. I have sold a few hundred for pickups and semi trucks. It does work.
    There's no dispute that it adds power and depending on the gas price it can save fuel costs.
    But detonation is an extremely bad thing to subject your engine to.
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    I watched the video. That engine isn't detonating, it is misfiring. When the lp starts going in, the engine speed increases. This causes the governor to start pulling back on the fuel. It pulls back so far that it shuts off diesel completely. When this happens, there is nothing to ignite the gas, and the engine begins to stall. This reduces the rpms. The governor then adds fuel to maintain idle, and it starts to run again. It speeds up, the governor pulls back, and the process begins again. There is no reason to add gas at idle, this is when a diesel is using very little fuel anyway. Only add gas once the engine is under load. My fully mechanical system only starts adding gas once the turbo starts making boost, then it keeps adding more gas as boost climbs. My electronic prototype gives more control over the fuel delivery, but neither system adds any gas at idle or deceleration.
    '04.5 Silverado CCLB Duramax Allison w/cng injection
    '95 C2500 Suburban 4BT w/cng injection, 4L80E
    '05 Jeep Liberty diesel w/cng injection
    '91 V30 CCLB 454 4L80E lp gas
    '72 Impala 350 lp gas

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    Quote Originally Posted by marcdeluca View Post
    I watched the video. That engine isn't detonating, it is misfiring. When the lp starts going in, the engine speed increases. This causes the governor to start pulling back on the fuel. It pulls back so far that it shuts off diesel completely. When this happens, there is nothing to ignite the gas, and the engine begins to stall. This reduces the rpms. The governor then adds fuel to maintain idle, and it starts to run again. It speeds up, the governor pulls back, and the process begins again. There is no reason to add gas at idle, this is when a diesel is using very little fuel anyway. Only add gas once the engine is under load. My fully mechanical system only starts adding gas once the turbo starts making boost, then it keeps adding more gas as boost climbs. My electronic prototype gives more control over the fuel delivery, but neither system adds any gas at idle or deceleration.
    There is a large amount of noise and shaking which doesn't show up due to the frame rate of the camera and the position of the camera microphone.

    It's not misfiring, misfiring due to defuel doesn't making loud banging noises.
    If it were defuelled due to increased speed, then then decrease in fuel would be exactly the same across each cylinder, resulting in smooth running. Definitely not the case here.
    Further, the gas in this is as well mixed as possible, going through first an air filter (laminiser), then a spinning turbo (turbulent mixer). So any variation in air/lpg mix from cylinder to cylinder is minimised.

    In addition, there is no hunting in speed, which would be necessary to fit with your defuelling argument. The speed would have to increase beyond idle, then drop back to idle before fuelling was reapplied. The governers in my fuel pump are large mechanical flyweights, they do not act that fast.

    The autoignition point of lpg is lower than the compression temperatures in a diesel engine. This is the elephant in the room that all the vendors try to ignore.
    Last edited by Dougal; 09-05-2009 at 08:18 PM.
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    One of the engines running my system runs a blower 24/7. It used to use 150 gal of diesel a week. It now uses 30 gal a week. 80% natural gas. It has been running almost a year on gas. It would seem to me that if it is detonating it would have broken by now. Many other engines in sawmills are running 9 hrs a day making 250 hp at 70% gas and not blowing up. I recommend that you don't touch fumigation with a 10 foot pole since you are convinced that it murders every engine that it touches. Done property, it works well. Done wrong, it will ruin an engine. This is all I have to say on the subject.
    '04.5 Silverado CCLB Duramax Allison w/cng injection
    '95 C2500 Suburban 4BT w/cng injection, 4L80E
    '05 Jeep Liberty diesel w/cng injection
    '91 V30 CCLB 454 4L80E lp gas
    '72 Impala 350 lp gas

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    for cng engines i prefer a mechanical system, specially if it's a dedicated cng one...

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    Quote Originally Posted by marcdeluca View Post
    There is no reason to add gas at idle, this is when a diesel is using very little fuel anyway. Only add gas once the engine is under load. My fully mechanical system only starts adding gas once the turbo starts making boost, then it keeps adding more gas as boost climbs. My electronic prototype gives more control over the fuel delivery, but neither system adds any gas at idle or deceleration.
    I'm going to convert my 6BT to dual-fuel as soon retailer has tested their conversion kit. It's so new product here in Finland that nobody has any real world experience with it. Neither isn't much info available. I was told that there would be a valve on a fuel line, that's used to restrict fuel flow so that engine barely idles. But is the CNG mixer mounted before the turbo like it was said earlier on this thread?

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    I registered to this site because I was looking info about marrying Allison behind Cummins, and info in general about Ally, but now that I found that here's knowledge about CNG powered diesels, too, this is even better place

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    Hi Heikki! There used to be a motor cycle champion named Heikki.

    Here it is: http://www.heikkimikkola.be/site_mik.../biografie.htm
    Last edited by DieselSchlepper; 05-07-2012 at 06:34 PM.
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    Probably Cummins-WEstport engines are what you want.
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    Quote Originally Posted by DieselSchlepper View Post
    Probably Cummins-WEstport engines are what you want.
    actually it seems like he would rather want to use both diesel and natural gas at the same engine... only diesel at idle and a lower amount of diesel to generate the spark to operate with gas at higher engine speeds... i've already seen some workarounds with similar setups using a carburettor attached to the intake manifold to inject the gas and the diesel injection pump with a retractable lock to allow either a lower diesel flow to use as a "liquid spark plug" or the regular amounts of diesel when natural gas is not available...

    then, an all-mechanical engine still seems to be the most suitable option to mess with gas blends
    http://formspring.me/kamikazeondrugz

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    Quote Originally Posted by cRiPpLe_rOoStEr View Post
    actually it seems like he would rather want to use both diesel and natural gas at the same engine... only diesel at idle and a lower amount of diesel to generate the spark to operate with gas at higher engine speeds... i've already seen some workarounds with similar setups using a carburettor attached to the intake manifold to inject the gas and the diesel injection pump with a retractable lock to allow either a lower diesel flow to use as a "liquid spark plug" or the regular amounts of diesel when natural gas is not available...

    then, an all-mechanical engine still seems to be the most suitable option to mess with gas blends
    Yep, you're right! Dedicated CNG-engine is not feasible option because lack of refill stations in here. There's only one station close to my work, and actually that's the only station in whole city. Not to mention the short operation range with reasonable tank size. I could stuff the whole undercarriage full on different size tanks, but it would be very, very expensive.

    But with dual-fuel I don't have to worry about refilling CNG, if I run out of it, I just drive with diesel. I'm waiting to hear some mileage numbers from retailer, but I estimated that I have fill the 120 litre tank twice/week to be able to drive on dual-fuel mode constantly.

    Mechanically injected diesel is cheapest to convert, but CR-engine would have much better adjustability. Before I knew any better about mech. dual-fuels, I thought about using Mega Squirt to have multipoint CNG-injection, but on that just the injection system costs more than the whole mixer system.

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    Quote Originally Posted by Heikki View Post
    Mechanically injected diesel is cheapest to convert, but CR-engine would have much better adjustability. Before I knew any better about mech. dual-fuels, I thought about using Mega Squirt to have multipoint CNG-injection, but on that just the injection system costs more than the whole mixer system.
    some more accurate adjustments are obviously not a bad thing at all, but the all-mechanical ends up with a higher cost-effectiveness... also, since the engine is already turbocharged it suffers less power variations than a non-turbocharged (no wonder some non-turbo diesel engines have an altitude compensator pin to run leaner on higher lands)...
    http://formspring.me/kamikazeondrugz

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    Aside from the other issues, an electronic diesel engine will not cope well with another fuel source. Even if you can electronically control the delivery of your second fuel, getting the different systems to work with each other will be a problem.
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    Quote Originally Posted by Dougal View Post
    Aside from the other issues, an electronic diesel engine will not cope well with another fuel source. Even if you can electronically control the delivery of your second fuel, getting the different systems to work with each other will be a problem.
    it's not impossible at all and have already been done, but cost-effectiveness is not so high
    http://formspring.me/kamikazeondrugz

    http://cripplerooster.blogspot.com/ - if you can't read in portuguese (or even spanish that is closely simillar) use the google translate

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    Thanks for resurrecting this thread from the past. I love the banter and am re-interested in duel fuel because of it. I would like to know if anybody /manufacture makes anything for the 4bt. And... is it cost effective?

    Thanks for any input.

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    I actually found some of my own answers (with some help from Marc Deluca) and Internet Searching. Too cool You can find a conversion package for pretty much all vehicles. Surprisingly, on a diesel it plumbs in before the turbo and is operated with vacuum. (others are plumbed in after the diesel and are controlled by boost pressure) The caution on the 4bt is you must maintain 30% diesel to a running engine when adding CNG. Regular gas engines can run on gasoline or CNG exclusively with a switch on the dash board. What impressed me was the price of CNG. I saw a lot of stations asking $2.00 per gallon (equivalent) or so. In Corpus Christi they were asking 78.5 cents per gallon (equivalent). So I went to the pump and found out it was owned and operated by the city. The representative I spoke with stated that many pumps are privately owned and they are looking to pay the investment off quickly. He stated that the price tells you that. He mentioned that many of the city's vehicles run on CNG. For those looking for a conversion, there are two new companies in Corpus Christi doing conversions for regular folks like me as well. We talked about filling stations at home. They are expensive to put in ( about 5K) but the pay back is quicker than expected. The city employee explained that they sell gas at 1000 cubic feet for (approx) $2.00. This is equivalent to 8 gallons of gas. He stated that this equates to .25 cents per gallon. Then you have to add the hidden costs like the electricity to run the fill station (CNG gas pump) and saving for gas pump compressor maintenance when it reaches 10k hours.

    Other tid - bits. It seems they use electronic kits to shut the gasoline injectors down and run off CNG at the intake hose. Some are programmed that once they run out of CNG they switch automatically back to gas.

    PRO

    No carbon deposits - Oil lasts longer
    Extend life of the engine.
    Clean burning
    Fuel is abundant in the USA.
    Reduction of oil dependency from foreign nations.
    Cheaper fuel
    Greater engine HP

    Cons:
    Fuel not available everywhere
    CNG Tank Size May limit vehicle storage.
    Tank Costs - I have seen 300 for a 2 gal tank to 1700.00 for a 13.5 gal tank. and the Tanks are HEAVY.

    Basically I have learned enough in the past three days to want to keep inquiring.
    Last edited by FATMAN; 05-30-2012 at 07:05 PM. Reason: sentence structure - Grammar
    Got the 4BT, Collecting Parts, Dreaming of the Day.

  31. #30
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    Hey I built my kit my self and there is nothing to it and the parts are pretty easy to get. I also got anywhere from 5-10 mpg better fuel milage.

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