Outer Limits 4x4 Board

Posted: **Mon Jun 01, 2009 9:48 am**

Just wondering if anyone else is having an issue getting any power and fuel economy benefits from their N/A diesel fitted with D-Gas .

I have had 5 different systems including the latest Version2 TPI system installed over the last 11 1/2 months with only a minimal 3.5% power increase and a rise in running costs of 16%.

Hard to stomach when the sales blurb quotes 16% on a tired old engine with 430000 on the clock and fuelsavings of up to 30% with a minimum saving of 15% or your money back.

Well believe me, the money back guarantee is non existent. This D-Gas experience has been the worst automotive purchase i have made in over 33 years of motoring.

I must congratulate the mechanic who has been exceptional in his efforts, since the initial gas installation was butchered by the installer recommended by The Sydney salesman of this product.

If anyone would like to see pictures and fuel results I have obtained using D-Gas's own fuel calculator please PM me and I will gladly show you why I am pissed off with the results. I was going to try and get my money back through VCAT but will instead show all 4wd ers i meet how the system performs so they can make their own mind up

Posted: **Mon Jun 01, 2009 11:22 am**

There is a lot of misunderstanding about diesel LPG systems. You can tune them for increased economy or an increase in power, and can even set them up for both, depending very heavily on driving style.

I'm interested to see your dyno results and hear how it has been tuned. the bottom line on N/A engines is, however, that the LPG displaces some of the air that would otherwise be drawn into the cylinder on the induction stroke. The net result of this is that there is less oxygen available for combustion, less nitrogen available for expansion. the potential benefit available is that the LPG burns (for want of a better term) more easily than the diesel, and the combustion of the LPG can assist the combustion of diesel fuel droplets that might otherwise have been too big/cold to combust. in a N/A IDI diesel, good tune and good injector condition will have much the same result.

if you are not seeing any fuel economy increase (or power for that matter), I humbly suggest that perhaps the ratio of LPG to diesel has not been set up correctly, that there is too much diesel in the mix, and possibly too much LPG too.

I know you're waaaaaaaaaay past trying to fix it however there are others on the board who have had similar systems installed and have better (albeit marginal) results on the same engine, maybe they have more helpful advice.

I'm sorry to hear of your experience and am disappointed that Dgas won't give you a refund.

cheers
DD

Posted: **Mon Jun 01, 2009 3:18 pm**

So it's not possible to get more power from a NA engine which is already running near thermal limits.

Who'd have guessed?

If you can post up any dyno charts or fuel consumption records here, then please do. There is way too much hype and misinformation regarding these systems.

It will help others if you post up details of your setup too. Your username suggests a toyota 1HZ, but it's good to know for sure.

Posted: **Mon Jun 01, 2009 3:24 pm**

Believe me , we have tried many many jet combinations through the 5 gas systems and the best result was a 3.5% power increase using 38% gas, put a smaller jet in and the power increase lessens.

I too am disappointed about not getting a refund, I was told to take it up with the initial installer, but the installers don't guarantee the results D-Gas does and the Sydney salesman has just wiped his hands of me. He is not to be trusted.

Setup is 1HZ, Uni Filter, Extractors and 2 1/2" exhaust.

It's also fitted with D-Gas's latest version 2 timed pulse injection system

Posted: **Mon Jun 01, 2009 4:40 pm**

I am currently going through the same thing with TUNIT and a module that I had fitted to my Mazda 6 Turbo Diesel. Somehow they couldn't understand why I was pissed off at 5% increase for $1500 when they advertise 20%. Still fighting it at the moment. I am currently getting Tune number 3 loaded up. Mond you I still have to pay for the dyno runs to prove that it isn't working.

Cheers
Paul

Posted: **Mon Jun 01, 2009 10:10 pm**

nelpd96 wrote:I am currently going through the same thing with TUNIT and a module that I had fitted to my Mazda 6 Turbo Diesel. Somehow they couldn't understand why I was pissed off at 5% increase for $1500 when they advertise 20%. Still fighting it at the moment. I am currently getting Tune number 3 loaded up. Mond you I still have to pay for the dyno runs to prove that it isn't working.

Cheers
Paul

Yeah been there as well, the onus is always on the buyer to prove it's not working. But hopefully by letting others know of their non existent warranty and smoke and mirrors GUARANTEES it will save some others from being shafted and cost them a few sales as well.

Posted: **Mon Jun 01, 2009 11:31 pm**

I had dgas on my defender

It was the best thing i ever did! increase in power was massive and fuel economy improved!

In wa we got an extra money back so the cost was minimal

Does it depend on the car or motor perhaps, as the seller said the defender motor 1998, was not that efficient and allowed for a lot of diesel not to burnt, black smoke coming out the exhaust, with dgas no problem and resulted in more power!

My thought anyhow!

Posted: **Tue Jun 02, 2009 6:15 am**

jedo wrote:Does it depend on the car or motor perhaps, as the seller said the defender motor 1998, was not that efficient and allowed for a lot of diesel not to burnt, black smoke coming out the exhaust, with dgas no problem and resulted in more power!

The seller is full of it.

The landrover TDI's are very efficient diesels, if you have black smoke then you have a tuning issue or an air delivery problem. It has nothing to do with the design of the engine.

What was your before and after fuel economy?

Posted: **Tue Jun 02, 2009 7:22 am**

i have seen some patrols running d-gas and they blew just as much black smoke as they always do plus u can get 20% more power out of a diesel just by tuning it different .have u tried the department of fair trading to see what they say

Posted: **Tue Jun 02, 2009 12:01 pm**

defmec wrote:have u tried the department of fair trading to see what they say

I was going to suggest something like this - given how much time/money has already been thrown at it, i would say that finding some legal advice on this issue ould be #1 priority for me.

Posted: **Tue Jun 02, 2009 12:19 pm**

in response to kiwibacan, i used to get between 600-700km w/o dgas with it went up just over 900km, i was happy with that, but i had mine with more performance.

Shame about others experiences i would have gladly recommended it but not will show more caution

Posted: **Tue Jun 02, 2009 12:58 pm**

jedo wrote:in response to kiwibacan, i used to get between 600-700km w/o dgas with it went up just over 900km, i was happy with that, but i had mine with more performance.

Shame about others experiences i would have gladly recommended it but not will show more caution

How many litres for that distance?
If it's based off an 80 litre fill, then your economy isn't any better than what most get on straight diesel.
How many litres of gas does it use on average?

Posted: **Tue Jun 02, 2009 10:19 pm**

After reading posts like this one I can see why people become very negative. I think too many installers have jumped on the bandwagon to make a quick buck with-out a full understanding of how to set up a system properly - giving the diesel gas industry a bad name.

Kiwi Bacon, you have been very negative ever since you fed un-metered and large volumes of gas down an intake at idle to prove that pre-combustion occurred using gas on a direct injection diesel.

FACT - lpg in most turboed diesels does work - although some of the claims are rediculous.

FACT - most naturally aspirated diesels doen't get enough oxygen as it is - with-out losing some intake volume to LPG. Most NA diesels do not benefit enough from LPG to warrant the cost - although I have done a few that have worked quite well - mainly trucks.

I use a number of processor controlled systems and tune them with the appropriate programs, an air fuel ratio meter, and a pyro. On some of our systems where Customers are after maximum power, I utilise the services of a well known Brisbane diesel specialist and a dyno to get the diesel tuned correctly before turning the gas on and tuning the gas on the dyno.

We have helped install a system on a Toll longhaul Kenworth with C15 Cat motor and it is achieving an 18% improvement in fuel economy - their cheapest running longhaul truck on the eastern seaboard. It does work!!

I take the installations seriously and I knock back more requests than I accept for diesel gas conversions.

I am a Diesel Fitter by trade, and a LPG Installer, have an associate diploma in Mech Eng, am a member of the IAME and LPG Australia. On behalf of the serious and dedicated Diesel Gas installers out there - it is not the concept or the systems (that I work with) that are at fault - but the installers with-out enough training or knowledge - and those that will install a system for anyone that enquires about it - regardless of the outcome.

Do your research if looking at Diesel Gas. OL members - feel free to PM me with questions if you like - regardless of where you live. I may not respond immediately but I will help where I can.

Peter K.

Posted: **Wed Jun 03, 2009 1:20 am**

I bought a turbocharger info book and it has a bit on diesel and propane injection

The basics of a diesel is that at idle, it'll be running around a 60+:1 air/fuel ratio when under load this might drop down to 20:1 air/fuel ratios, running lower air/fuel ratios may/will produce smoke so diesel's that are tuned up correctly and have plenty of air shouldn't be making any smoke.

So here a brief run down of what it says about diesel/gas:

Gas injection can make a lot of power IF there is a LOT of surplus air, if there' NO surplus air then there'll be no benefit at all.

propane can be good as the auto-ignition temp is 1004F vs 851F methanol 495F, petrol and 410F diesel, so when injected really sparsely into the air stream meaning less than 10% of the air/fuel ratio (no diesel) propane will only ignite after the diesel has ignited so the idea is basically have the propane be a scavenger of air.

some disadvantages to propane injection are.

Propane has a much lower heat yield per gallon used compared to diesel, which ends up about 70% to diesel and 75% to petrol by the gallon.

High EGTs

Some companies will claim better performance because they are basing it around burn rates and btus of the propane because it's meant to scavenge any left over air.

Other people disagree on the reality of this as standard diesels would be producing high amounts of hydrocarbons which isn't the case.

Though it does say you can make a LOT! of power from propane injection but you need the air surplus as well.

So you could tweak the waste gate or change the compressor wheel to a smaller size and thus get boost up thus more air and then inject some propane and go from there, but unlike NOS propane has to be metered out all the time ONLY with high or WOT gas pedal so that the amount of air/fuel ratio is correct for lean flammability limits.

So maybe the problem how ever...

Troopy93 wrote:3.5% power increase using 38% gas, put a smaller jet in and the power increase lessens.

Maybe your injecting too much gas and just straving the whole engine as diesel's really need air as their fuel and the diesel is only used to turn air into power.

no air = no power thus go no where.

Posted: **Wed Jun 03, 2009 6:03 am**

bowtie landie wrote: Kiwi Bacon, you have been very negative ever since you fed un-metered and large volumes of gas down an intake at idle to prove that pre-combustion occurred using gas on a direct injection diesel.

Do you expect me to be enthusiastic about an engine suffering detonation with a fumigation rate measured at 0.4% lpg?

What mix do your systems run at?

You appear to be a vendor, you should state that clearly in these discussions to avoid confusion.
LPG fumigation certainly adds power if air is available. There's no dispute there. But the way it adds power is not good for the engine.
I'll believe the claims of efficiency gains when I see BSHC proven on a dyno.

Posted: **Wed Jun 03, 2009 6:08 am**

zagan wrote:propane can be good as the auto-ignition temp is 1004F vs 851F methanol 495F, petrol and 410F diesel, so when injected really sparsely into the air stream meaning less than 10% of the air/fuel ratio (no diesel) propane will only ignite after the diesel has ignited so the idea is basically have the propane be a scavenger of air.

This "internet fact" that lpg won't ignite under a certain % mix (often quoted around 2%, not 10%) is not true for internal combustion. I have a video of my engine detonating audibly and shaking badly when fed a mix at 0.4% concentration.
This is 1/5th of the dose that according to many will never preignite.

The source of this "internet fact" apprears to be people looking up the "lower flammability limits" which apply for external ignition (i.e. trying to light a cold gas mix with a hot flame).
Spontaneous combustion caused by internal heating doesn't appear to have a lower limit of flammability, hence different rates of LPG fumigation only affect how audible the detonation is.

A lot of people react quite strongly to this point, mainly those making money off these systems.

Posted: **Wed Jun 03, 2009 12:41 pm**

KiwiBacon wrote:
bowtie landie wrote: Kiwi Bacon, you have been very negative ever since you fed un-metered and large volumes of gas down an intake at idle to prove that pre-combustion occurred using gas on a direct injection diesel.
Do you expect me to be enthusiastic about an engine suffering detonation with a fumigation rate measured at 0.4% lpg?

What mix do your systems run at?

You appear to be a vendor, you should state that clearly in these discussions to avoid confusion.
LPG fumigation certainly adds power if air is available. There's no dispute there. But the way it adds power is not good for the engine.
I'll believe the claims of efficiency gains when I see BSHC proven on a dyno.

KB - Peter is a landie owner and from my (few) dealings with him seems like a decent bloke.

Btw, we have an engine dyno here at work (uni). I could arrange for an independant test to be done at cost if anyone is interested.

Posted: **Wed Jun 03, 2009 5:40 pm**

kiwibacon, didnt you base that on airflow not fuel flow?
there is an ideal percantage as a comparison to the amount of diesel, not to the amount of air for internal combustion engines.

i have D-GAS on mine, very happy with it, but mine is turbod, and have been happier with it since i changed my rear housing on the turbo to a 63 from an 82, so it spools much quicker, and the midrange torque is just fun.

im sure i could make the same power from diesel, but i had the gas stuff laying around, so only had to buy the underbonnet kit so it was cheap for me to do, and $/km when i drive sensibly is better than i ever got, NA or turbo'd on straight gas.

i can also use more fuel than i used to now as i have turned up the diesel and run gas, but on highway driving, i can use well under 10L/100 of diesel, and about 28% more gas.

bowtie landie, what do your processor controlled units run off on a dinosaur motor like a td42?
i want mine to be based on RPM, boost and throttle position to keep an ideal amount of gas at all times, whereas my older dgas system is boost referenced only, cant complain about how it works, but its a bit basic and im sure it could be improved...

Posted: **Wed Jun 03, 2009 7:00 pm**

love ke70 wrote:kiwibacon, didnt you base that on airflow not fuel flow?
there is an ideal percantage as a comparison to the amount of diesel, not to the amount of air for internal combustion engines.

Yes, based on air flow.

Anyone who tells you they meter gas based on fuel flow is telling porkies. There is not one fumigation kit on the market which regulates gas based on diesel flow.
The throttle position on a diesel has no set relationship with the fuel quantity being injected. Doesn't matter whether it's mechanical or efi controlled.

What do you consider the "ideal amount of gas" and what are you basing this ideal on?

Posted: **Wed Jun 03, 2009 7:42 pm**

i dont know the ideal, no one will tell you, they just say aim for this percentage LPG over a tankfull of diesel, so yes it comes down to matching the right amount of LPG to the amount of fuel.
i can bridge the hobbs switch on mine at idle, so it injects gas, and it will raise the idle to about 1200, but it does not pre-ignite.

ideal amount of LPG in my un-informed opinion is simply enough to make the power you want, without causing undue cylinder pressures through pre-ignition. then factor in economy etc and find the happy medium.

Posted: **Wed Jun 03, 2009 8:22 pm**

KiwiBacon wrote:[
The throttle position on a diesel has no set relationship with the fuel quantity being injected.

if the throttle position does not control injection volume, what does, exactly?

mechanical or electronic, injection volume is controlled primarily by throttle position and rpm. secondary inputs include manifold/boost pressure, air temperature, coolant temperature - but no matter how many inputs there are, there is a set relationship between throttle position and injection volume. the map or algorithm (be it mechanical and analogue or digital and electronic) has as many dimensions as there are inputs, but for a given rpm (and boost, air temp, etc), a given throttle position will always supply a defined fuel delivery volume.

my 2c on the "economy" debate; adding LPG (even with correct tuning and winding back the diesel) will always increase the litres/100km consumption where the "before" is diesel litres/100km, and the "after" is (diesel litres + LPG litres)/100km, however the $ per 100km can and should go down - you will need maybe 130%v/v LPG of the diesel you take out of the equation, but that LPG costs only 40%v/v compared with diesel fuel. so does adding LPG make the vehicle more "economical"? FUEL economical, no. $/distance economical, yes it should. It should also increase the range of the vehicle so long as the diesel fuel capacity is not reduced to accommodate the LPG capacity.

on the question of detonation, I have fiddled with home brew setups and did not observe the severe detonation you describe; I never had one set up long enough to experiment with consumption/economy, I did it only to see if the increased power claims were valid - and my observations (on a 1HZ) indicated that I could not get a discernible "seat of the pants" power/torque increase, over a wide range of diesel and LPG mixes. I also tried it for giggles on my 1HD-FT and it "works" in that there is power to be had from LPG however the same power is available just as easily by fiddling the diesel fueling alone, and with lower EGTs.

I think we agree that anyone installing a diesel LPG fumigation system alone with the hope of a significant power increase is going to be disappointed - but it is arguable that there is a legitimate market for these systems for the purposes of reduced $/km running costs and increased range. On the subject of accelerated engine wear, I have no evidence, but LPG can be hell on petrol engines, especially when poorly tuned, and any reduction in diesel fuel with its lubricating properties (albeit reduced with low sulphur fuels) in the mix, accompanied by the hotter burning LPG, may well increase upper cylinder wear.

we have an ex Cummins bloke at work, I'll try and remember to ask him what he knows about LPG systems at the bigger end of the road engine market - I understand a lot of council/garbage trucks use (or used to use) these kinds of setups?

an interesting topic anyway.

DD

Posted: **Wed Jun 03, 2009 8:23 pm**

love ke70 wrote:i dont know the ideal, no one will tell you, they just say aim for this percentage ...

because nobody knows?

Posted: **Wed Jun 03, 2009 9:06 pm**

dumbdunce wrote:
KiwiBacon wrote:[
The throttle position on a diesel has no set relationship with the fuel quantity being injected.

if the throttle position does not control injection volume, what does, exactly?

mechanical or electronic, injection volume is controlled primarily by throttle position and rpm.

I think that was Dougal's point. TP AND rpm. If you are chugging up a hill in a diesel and you put your foot flat to the floor, fuel does not increase unless RPM does.

So a diesel+LPG type system would have to measure both simultaneously to meter gas with fuel injected.

Posted: **Wed Jun 03, 2009 9:34 pm**

All my fuel results from the first system to the latest.

The Average fuel use over 80,000km was 14.88l/100km this included all low range 4wd work beach work etc.

The 12.91l/100km is what the vehicle got on a diesel only trip on the freeway.All the diesel/gas figures are based on freeway KM only.

Date Distance Diesel Litres Diesel Price Diesel K/L Diesel L/100K LPG Litres LPG Price LPG K/L LPG L/100K Total K/L Total L/100K Total % Fuel Eff
27/8/03-7/7/08 79981km 14.88l/100km average
08 Jul 2008 111 12.49 $1.689 8.91 11.22 5.40 $0.689 20.61 4.85 6.22 16.07 -19.72%
14 Jul 2008 484 59.51 $1.689 8.14 12.29 17.89 $0.679 27.07 3.69 6.26 15.98 -19.26%
17 Jul 2008 320 42.87 $1.699 7.46 13.40 9.50 $0.689 33.68 2.97 6.11 16.37 -21.16%
27 Jul 2008 619 69.47 $1.699 8.91 11.23 25.50 $0.689 24.27 4.12 6.52 15.35 -15.93%
13 Aug 2008 580 75.04 $1.709 7.73 12.94 22.01 $0.659 26.36 3.79 5.98 16.73 -22.87%
25 Aug 2008 572 74.50 $1.689 7.68 13.02 19.16 $0.679 29.85 3.35 6.11 16.37 -21.20%
17 Oct 2008 503 68.45 $1.599 7.35 13.60 18.18 $0.709 27.69 3.61 5.81 17.21 -25.02%
31 Oct 2008 600 77.23 $1.549 7.76 12.88 20.60 $0.709 29.11 3.44 6.13 16.32 -20.92%
18 Dec 2008 546 79.95 $1.339 6.83 14.63 21.52 $0.479 25.39 3.94 5.38 18.57 -30.52%
Version 2 TPI
23 Feb 2009 559 66.25 $1.229 8.44 11.85 15.33 $0.599 36.46 2.74 6.85 14.59 -11.58%
24 Feb 2009 262 33.44 $1.229 7.83 12.76 7.66 $0.599 34.20 2.92 6.37 15.69 -17.75%
10 Mar 2009 576 71.51 $1.209 8.05 12.41 16.69 $0.599 34.51 2.90 6.53 15.31 -15.73%
04 Apr 2009 591 75.23 $1.197 7.86 12.72 18.03 $0.577 32.80 3.05 6.34 15.77 -18.19%
08 Apr 2009 607 77.26 $1.229 7.86 12.72 16.98 $0.599 35.77 2.80 6.45 15.52 -16.84%
22 Apr 2009 257 33.17 $1.219 7.75 12.91 DIESEL ONLY
03 Jun 2009 395 53.49 $1.119 7.38 13.54 11.74 $0.579 33.65 2.97 6.06 16.51 -21.86%

Posted: **Thu Jun 04, 2009 5:46 am**

dumbdunce wrote:
KiwiBacon wrote:[
The throttle position on a diesel has no set relationship with the fuel quantity being injected.

if the throttle position does not control injection volume, what does, exactly?

Have you ever been inside the governor of a fuel injection pump? They're a seriously impressive piece of engineering.
The maximum volume which can be injected per stroke isn't constant across the rev range, whether it's a mechanical profiled cam plate or a lookup table buried in the firmware, the maximum injection volume is modified to fit the following:

The engines VE curve.
The desired torque rise.
Limits of smooth operation.
Thermal limits.
Smoke limits.
RPM limits (fuel cut at set rpm)
Boost pressure (sometimes a seperate device).
Coolant temperature.
Altitude (sometimes a seperate device).

Under full fuelling at the calibrated maximum torque (provided all other inputs allow) you'll get maximum fuel. The same pedal position elsewhere in the rev range with the same inputs could easily give 25% less fuel through the VE curve alone.
When boost, altitude, coolant temp change you can be below half that fuel dose.
I'm talking about fuel dose per stroke, this is independent of rpm but the factors which set limits are heavily rpm dependent.

So no, a given throttle position will not always supply a defined fuel delivery volume.
The x litres of gas to y litres of diesel as an average over a tank means nothing to the actual gas/air or gas/diesel ratios in operation. If it was a stationary generator or pump running at set speed and load it would mean something.

I do agree with the rest of your post though.

The "diesel engine reference book" (worth owning) has a whole chapter devoted to dual fuelling diesels.
In the table of gases used it has propane and butane (LPG is a mix of the two).
The comments on each are:
Propane - Poor detonation characteristics compared to methane.
Butane - Poor detonation characteristics.

They also mention that the preignition causes excessive rates of pressure rise, high temperature and increased heat transfer often leading to engine damage.

Posted: **Thu Jun 04, 2009 6:47 am**

KiwiBacon wrote:
The "diesel engine reference book" (worth owning) has a whole chapter devoted to dual fuelling diesels.
In the table of gases used it has propane and butane (LPG is a mix of the two).
The comments on each are:
Propane - Poor detonation characteristics compared to methane.
Butane - Poor detonation characteristics.

They also mention that the preignition causes excessive rates of pressure rise, high temperature and increased heat transfer often leading to engine damage.

Thanks for that Dougal. Looks good - might have to get a copy...

Editorial Reviews
Product Description
The Diesel Engine Reference Book, Second Edition, is a comprehensive work covering the design and application of diesel engines of all sizes. The first edition was published in 1984 and since that time the diesel engine has made significant advances in application areas from passenger cars and light trucks through to large marine vessels. The Diesel Engine Reference Book systematically covers all aspects of diesel engineering, from thermodynamics theory and modelling to condition monitoring of engines in service. It ranges through subjects of long-term use and application to engine designers, developers and users of the most ubiquitous mechanical power source in the world. The latest edition leaves few of the original chapters untouched. The technical changes of the past 20 years have been enormous and this is reflected in the book. The essentials however, remain the same and the clarity of the original remains. Contributors to this well-respected work include some of the most prominent and experienced engineers from the UK, Europe and the USA. Most types of diesel engines from most applications are represented, from the smallest air-cooled engines, through passenger car and trucks, to marine engines. The approach to the subject is essentially practical, and even in the most complex technological language remains straightforward, with mathematics used only where necessary and then in a clear fashion. The approach to the topics varies to suit the needs of different readers. Some areas are covered in both an overview and also in some detail. Many drawings, graphs and photographs illustrate the 30 chapters and a large easy to use index provides convenient access to any information the readers requires.
Product Details

* Hardcover: 682 pages
* Publisher: Butterworth-Heinemann; 2 edition (May 1999)
* Language: English
* ISBN-10: 0750621761
* ISBN-13: 978-0750621762

Posted: **Thu Jun 04, 2009 6:57 am**

ISUZUROVER wrote: Thanks for that Dougal. Looks good - might have to get a copy...
Editorial Reviews
Product Description
The Diesel Engine Reference Book, Second Edition, is a comprehensive work covering the design and application of diesel engines of all sizes. The first edition was published in 1984 and since that time the diesel engine has made significant advances in application areas from passenger cars and light trucks through to large marine vessels. The Diesel Engine Reference Book systematically covers all aspects of diesel engineering, from thermodynamics theory and modelling to condition monitoring of engines in service. It ranges through subjects of long-term use and application to engine designers, developers and users of the most ubiquitous mechanical power source in the world. The latest edition leaves few of the original chapters untouched. The technical changes of the past 20 years have been enormous and this is reflected in the book. The essentials however, remain the same and the clarity of the original remains. Contributors to this well-respected work include some of the most prominent and experienced engineers from the UK, Europe and the USA. Most types of diesel engines from most applications are represented, from the smallest air-cooled engines, through passenger car and trucks, to marine engines. The approach to the subject is essentially practical, and even in the most complex technological language remains straightforward, with mathematics used only where necessary and then in a clear fashion. The approach to the topics varies to suit the needs of different readers. Some areas are covered in both an overview and also in some detail. Many drawings, graphs and photographs illustrate the 30 chapters and a large easy to use index provides convenient access to any information the readers requires.
Product Details

* Hardcover: 682 pages
* Publisher: Butterworth-Heinemann; 2 edition (May 1999)
* Language: English
* ISBN-10: 0750621761
* ISBN-13: 978-0750621762

My copy was published for SAE International by The Bath Press in the UK, the price was quite good compared to other sources.
ISBN 0-7680-0403-9

Posted: **Thu Jun 04, 2009 8:52 am**

KiwiBacon wrote:

if the throttle position does not control injection volume, what does, exactly?

Have you ever been inside the governor of a fuel injection pump? They're a seriously impressive piece of engineering.[/quote]

more than a few times. they are quite simple in principle. in the simplest case (eg a VE pump on a toyota 2L (or early 1HZ for that matter) or an inline port helix metering pump on a Nissan SD33, the ONLY inputs that control metering are RPM and pedal position - there is a force balance between the throttle input and the governor input that determines collar (VE) or rack (port helix) position. for a given rpm, a given pedal position will determine a preset injection volume.

The maximum volume which can be injected per stroke isn't constant across the rev range, whether it's a mechanical profiled cam plate or a lookup table buried in the firmware

again in the simple cases above, full pedal (and sometimes much less than) will result in full fuel delivery until rpm approaches governed speed and fuel cut.

the maximum injection volume is modified to fit the following:

The engines VE curve.
The desired torque rise.
Limits of smooth operation.
Thermal limits.
Smoke limits.
RPM limits (fuel cut at set rpm)
Boost pressure (sometimes a seperate device).
Coolant temperature.
Altitude (sometimes a seperate device).

yes, the maximum fuel is set to accommodate some of those parameters, by plunger stroke/cam plate/helix profile, and the max fuel screw setting. that maximum fuel setting will be available across much of the rpm range for a full throttle setting. real time modification of that maximum fueling by other inputs (aneroids/boost compensators/temperature sensors) may increase or decrease the maximum available volume (up to the hard set maximum defined by full travel of the collar or rack). in a VE pump, max fuel is theoretically available at stall since the governor input drops to zero, maximum stroke is available to the plunger - neatly resulting in a full fuel pulse for startup.

Under full fuelling at the calibrated maximum torque (provided all other inputs allow) you'll get maximum fuel. The same pedal position elsewhere in the rev range with the same inputs could easily give 25% less fuel through the VE curve alone.
When boost, altitude, coolant temp change you can be below half that fuel dose.
I'm talking about fuel dose per stroke, this is independent of rpm but the factors which set limits are heavily rpm dependent.

yes

So no, a given throttle position will not always supply a defined fuel delivery volume.

I disagree. At a stated RPM, temperature, boost etc, a given throttle position will give a defined fuel delivery. if the engine is held at a constant RPM, temperature, manifold pressure, the pedal alone defines fueling.

The x litres of gas to y litres of diesel as an average over a tank means nothing to the actual gas/air or gas/diesel ratios in operation. If it was a stationary generator or pump running at set speed and load it would mean something.

definitely. I think we're saying the same thing, and that the point is that pedal position ALONE is not a reliable (or even slightly useful) input parameter for the metering of LPG into a diesel engine.

I do agree with the rest of your post though.

The "diesel engine reference book" (worth owning) has a whole chapter devoted to dual fuelling diesels.
In the table of gases used it has propane and butane (LPG is a mix of the two).
The comments on each are:
Propane - Poor detonation characteristics compared to methane.
Butane - Poor detonation characteristics.

They also mention that the preignition causes excessive rates of pressure rise, high temperature and increased heat transfer often leading to engine damage.

"poor", "excessive" and "increased" are interesting but hardly quantitative - it would be interesting to see some actual figures. For a system in such wide use there must surely be some published research with some numbers attached.

The question of appropriate metering is significant - especially on hydromechanically injected engines where it is virtually impossible to extract real time fuel metering data from the engine/control system. having never played with a commercial system I had assumed they used an evaporator and mixer similar to spark ignition LPG systems however the discussion here seems to indicate not, and that pedal position is used as the only input for gas flow?

I need to go and appropriately meter some discipline to my children. full rack

Posted: **Thu Jun 04, 2009 9:26 am**

dumbdunce wrote: more than a few times. they are quite simple in principle. in the simplest case (eg a VE pump on a toyota 2L (or early 1HZ for that matter) or an inline port helix metering pump on a Nissan SD33, the ONLY inputs that control metering are RPM and pedal position - there is a force balance between the throttle input and the governor input that determines collar (VE) or rack (port helix) position. for a given rpm, a given pedal position will determine a preset injection volume.

I've only been inside inline governors, in those the maximum fuel volume continually varies with rpm as the governor rotates a control plate.
VE pumps must have a similar setup or they'd have to chose between blowing black smoke at high and low rpm or taking a big hit on available torque.

Take out all of the extra fluff (altitude, temperature, boost etc) and you still have a VE curve which is nowhere near flat. If the fuel curve can't follow that then you're giving away a lot of performance and creating a lot of emission problems.

dumbdunce wrote: definitely. I think we're saying the same thing, and that the point is that pedal position ALONE is not a reliable (or even slightly useful) input parameter for the metering of LPG into a diesel engine.

Yep.

dumbdunce wrote: For a system in such wide use there must surely be some published research with some numbers attached.

You'd think so wouldn't you? The DERB does mention a research paper I'll have a search for later.
But the typical uses of a fumigated diesels seem to be running on landfill type gases which are less susceptible to preignition/knock/detonation than the propane/lpg systems in great demand in aussie (due to a very low lpg price) which appear to have no easy to find supporting research.

The commercial systems appear to range from simple on/off gas flows to actively metered depending on boost, pedal position and egt. I haven't found a mention of air flow monitoring.
However, I haven't heard of any system having a knock sensor and this remains the primary concern.

Posted: **Thu Jun 04, 2009 2:32 pm**

dumbdunce wrote: For a system in such wide use there must surely be some published research with some numbers attached.

Hmm, looks like there are a few relevant papers:

Effect of engine parameters and type of gaseous fuel on the performance of dual-fuel gas diesel engines-A critical review
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Author(s): Sahoo BB (Sahoo, B. B.)2, Sahoo N (Sahoo, N.)1, Saha UK (Saha, U. K.)1
Source: RENEWABLE & SUSTAINABLE ENERGY REVIEWS Volume: 13 Issue: 6-7 Pages: 1151-1184 Published: AUG-SEP 2009
Times Cited: 0 References: 45 Citation MapCitation Map
Abstract: Petroleum resources are finite and, therefore, search for their alternative non-petroleum fuels for internal combustion engines is continuing all over the world. Moreover gases emitted by petroleum fuel driven vehicles have an adverse effect on the environment and human health. There is universal acceptance of the need to reduce such emissions. Towards this, scientists have proposed various solutions for diesel engines, one of which is the use of gaseous fuels as a supplement for liquid diesel fuel. These engines, which use conventional diesel fuel and gaseous fuel, are referred to as 'dual-fuel engines'. Natural gas and bio-derived gas appear more attractive alternative fuels for dual-fuel engines in view of their friendly environmental nature. In the gas-fumigated dual-fuel engine, the primary fuel is mixed outside the cylinder before it is inducted into the cylinder. A pilot quantity of liquid fuel is injected towards the end of the compression stroke to initiate combustion. When considering a gaseous fuel for use in existing diesel engines, a number of issues which include, the effects of engine operating and design parameters, and type of gaseous fuel, on the performance of the dual-fuel engines, are important. This paper reviews the research on above issues carried out by various scientists in different diesel engines. This paper touches upon performance, combustion and emission characteristics of dual-fuel engines which use natural gas, biogas, producer gas, methane, liquefied petroleum gas, propane, etc. as gaseous fuel. It reveals that 'dual-fuel concept' is a promising technique for controlling both NO, and soot emissions even on existing diesel engine. But, HC, CO emissions and 'bsfc' are higher for part load gas diesel engine operations. Thermal efficiency of dual-fuel engines improve either with increased engine speed, or with advanced injection timings, or with increased amount of pilot fuel. The ignition characteristics of the gaseous fuels need more research for a long-term use in a dual-fuel engine. It is found that, the selection of engine operating and design parameters play a vital role in minimizing the performance divergences between an existing diesel engine and a 'gas diesel engine'. (C) 2008 Elsevier Ltd. All rights reserved.
Document Type: Review
Language: English
Author Keywords: Combustion; Carbon dioxide; Dual-fuel; Efficiency; Emissions; Gaseous fuel
KeyWords Plus: NATURAL-GAS; EMISSION CHARACTERISTICS; COMBUSTION PROCESSES; PRODUCER GAS; PILOT FUEL; LIMITS
Reprint Address: Saha, UK (reprint author), Indian Inst Technol, Dept Mech Engn, Gauhati 781039, India
Addresses:
1. Indian Inst Technol, Dept Mech Engn, Gauhati 781039, India
2. Indian Inst Technol, Ctr Energy, Gauhati 781039, India

Effect of variation in LPG composition on emissions and performance in a dual fuel diesel engine
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Author(s): Saleh HE (Saleh, H. E.)
Source: FUEL Volume: 87 Issue: 13-14 Pages: 3031-3039 Published: OCT 2008
Times Cited: 0 References: 26 Citation MapCitation Map
Abstract: This paper investigates the effect of variation in LPG composition on emissions and performance characteristics in a dual fuel engine run on diesel fuel and five gaseous fuel of LPG with different composition. To quantify the best LPG composition for dual fuel operation especially in order to improve the exhaust emissions quality while maintaining high thermal efficiency comparable to a conventional diesel engine, a two-cylinder, naturally aspirated, four-stroke, DI diesel engine converted to run as pilot-injected dual fuel engine. The tests and data collection were performed under various conditions of load at constant engine speed. From the results, it is observed that the exhaust emissions and fuel conversion efficiency of the dual fuel engine are found to be affected when different LPG composition is used as higher butane content lead to lower NO, levels while higher propane content reduces CO levels. Fuel #3 (70% propane, 30% butane) with mass fraction 40% substitution of the diesel fuel was the best LPG composition in the dual fuel operation except that at part loads. Also, tests were made for fuel #3-diesel blend in the dual fuel operation at part loads to improve the engine performances and exhaust emissions by using the Exhaust Gas Recirculation (EGR) method. (c) 2008 Elsevier Ltd. All rights reserved.
Document Type: Article
Language: English
Author Keywords: dual fuel engine; LPG; emissions; performance; exhaust gas recirculation
KeyWords Plus: NATURAL-GAS; COMBUSTION
Reprint Address: Saleh, HE (reprint author), Helwan Univ, Fac Engn, Dept Power Mech Engn, POB 11718, Cairo, Egypt
Addresses:
1. Helwan Univ, Fac Engn, Dept Power Mech Engn, Cairo, Egypt

Combustion and emission characteristics of a diesel engine fuelled with diesel-propane blends
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Author(s): Ma ZH (Ma, Zhihao)1, Huang ZH (Huang, Zuohua)1, Chongxiao LX (Li, Chongxiao)1, Wang XB (Wang, Xinbin)1, Miao HY (Miao, Haiyan)1
Source: FUEL Volume: 87 Issue: 8-9 Pages: 1711-1717 Published: JUL 2008
Times Cited: 1 References: 14 Citation MapCitation Map
Abstract: In this paper, the combustion and emission characteristics of a direct injection diesel engine operating on diesel-propane blends were investigated. The results showed that under the same operating condition, the effective thermal efficiency increased with the increase of propane proportion in the blends. Ignition delay and combustion durations of diesel-propane blends were decreased with the increase of propane proportion in the blends. Maximum cylinder pressure, maximum rate of pressure rise, maximum rate of heat release and maximum mean combustion temperature of the diesel-propane blends increased with the increase of propane proportion in the blends. Simultaneous reduction in exhaust CO, HC and smoke emissions could be realized when operating on the diesel-propane blends. Exhaust NO, emission gave an increasing trend when operating on the diesel-propane blends. (C) 2007 Elsevier Ltd. All rights reserved.
Document Type: Article
Language: English
Author Keywords: diesel; propane; combustion; emissions; engine
KeyWords Plus: FLASH ATOMIZATION; GAS
Reprint Address: Huang, ZH (reprint author), Xian Jiaotong Univ, Sch Energy & Power Engn, State Key Lab Multiphase Flow Power Engn, Xian 710049, Peoples R China
Addresses:
1. Xian Jiaotong Univ, Sch Energy & Power Engn, State Key Lab Multiphase Flow Power Engn, Xian 710049, Peoples R China

An experimental study of the dual-fuel performance of a small compression ignition diesel engine operating with three gaseous fuels
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Author(s): Stewart J (Stewart, J.), Clarke A (Clarke, A.), Chen R (Chen, R.)
Source: PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART D-JOURNAL OF AUTOMOBILE ENGINEERING Volume: 221 Issue: D8 Pages: 943-956 Published: AUG 2007
Times Cited: 0 References: 27 Citation MapCitation Map
Abstract: A dual-fuel engine is a compression ignition (CI) engine where the primary gaseous fuel source is premixed with air as it enters the combustion chamber. This homogenous mixture is ignited by a small quantity of diesel, the 'pilot', that is injected towards the end of the compression stroke. In the present study, a direct-injection CI engine, was fuelled with three different gaseous fuels: methane, propane, and butane. The engine performance at various gaseous concentrations was recorded at 1500 r/min and quarter, half, and three-quarters relative to full a load of 18.7 kW In order to investigate the combustion performance, a novel three-zone heat release rate analysis was applied to the data. The resulting heat release rate data are used to aid understanding of the performance characteristics of the engine in dual-fuel mode.

Data are presented for the heat release rates, effects of engine load and speed, brake specific energy consumption of the engine, and combustion phasing of the three different primary gaseous fuels.

Methane permitted the maximum energy substitution, relative to diesel, and yielded the most significant reductions in CO2. However, propane also had significant reductions in CO2 but had an increased diffusional. combustion stage which may lend itself to the modern high-speed direct-injection engine.
Document Type: Article
Language: English
Author Keywords: dual-fuel; alternative gaseous fuels; three-zone heat release analysis; combustion phasing; carbon dioxide (CO2) reductions
KeyWords Plus: GAS; COMBUSTION
Reprint Address: Clarke, A (reprint author), Univ Loughborough, Wolfson Sch Med & Mfg Engn, Loughborough LE11 3TU, Leics England
Addresses:
1. Univ Loughborough, Wolfson Sch Med & Mfg Engn, Loughborough LE11 3TU, Leics England
2. Univ Loughborough, Dept Aeronaut & Automot Engn, Loughborough, Leics England

Effects of fuel injection timing on combustion and emission characteristics of a diesel engine fueled with diesel-propane blends
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Author(s): Ma ZH (Ma, Zhihao), Huang ZH (Huang, Zuohua), Li CX (Li, Chongxiao), Wang XB (Wang, Xinbin), Miao HY (Miao, Haiyan)
Source: ENERGY & FUELS Volume: 21 Issue: 3 Pages: 1504-1510 Published: MAY-JUN 2007
Times Cited: 1 References: 12 Citation MapCitation Map
Abstract: In this paper, the effects of fuel injection timing on fuel consumption, combustion, and emission characteristics fueled with diesel and diesel-propane blends in a single-cylinder diesel engine were investigated. The results showed that the effects of fuel injection timing on the performance of the engine exhibited the similar trends for both the diesel fuel and the diesel-propane blends. At the same engine speed and brake mean effective pressure, the specific fuel consumption decreases when operating on the diesel-propane blends comparing with that on the diesel fuel. The peak cylinder pressure, the maximum heat release rate, the proportion of the premixed heat release, the maximum cylinder mean gas temperature, the duration of cylinder mean gas temperature over 1500 K, and NOx emission decrease while retarding the fuel injection timing. The total combustion duration, the emissions of CO, HC, and smoke increase while retarding the fuel injection timing. For the same engine speed, the engine load and the fuel injection timing, the cylinder peak pressure, the maximum heat release rate, the proportion of the premixed heat release, the maximum cylinder mean gas temperature, and NOx emission increase while increasing the propane proportion in the fuel blends. The total combustion duration, the CO, HC, and smoke concentrations decrease while increasing the propane proportion in the fuel blends.
Document Type: Article
Language: English
Reprint Address: Huang, ZH (reprint author), Xian Jiaotong Univ, State Key Lab Multiphase Flow Power Engn, Xian 710049, Peoples R China
Addresses:
1. Xian Jiaotong Univ, State Key Lab Multiphase Flow Power Engn, Xian 710049, Peoples R China
2. Henan Univ Sci & Technol, Coll Vehicle & Mot Power Engn, Luoyang 471003, Peoples R China

A study on the characteristics of combustion with butane and propane in a retrofitted diesel engine
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Author(s): Choi GH, Bae SC, Bin Han S, Chung YJ
Source: PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART D-JOURNAL OF AUTOMOBILE ENGINEERING Volume: 218 Issue: D8 Pages: 915-920 Published: AUG 2004
Times Cited: 1 References: 17 Citation MapCitation Map
Abstract: The purpose of this study was to investigate the characteristics of combustion and exhaust-gas temperature of a liquefied petroleum gas (LPG) engine when using butane and propane as fuel. A conventional diesel engine was modified into a LPG engine that utilized an LPG fuel system instead of a diesel fuel injection pump. The study was performed with different compositions of butane and propane, such as 100 per cent butane, 100 per cent propane, 50 per cent butane-50 per cent propane, 70 per cent butane-30 per cent propane, and 30 per cent butane-70 per cent propane. The major conclusions of this work are as follows: MBT spark ignition timing was similar with different butane/propane fuel blends, except at the 100 per cent butane, 1200 r/min condition; engine torque and power were not influenced by varying butane/propane fuel blends; and exhaust gas temperature was increased at higher engine speeds, and it was decreased by a maximum of 15degreesC with different butane/propane fuel blends.
Document Type: Article
Language: English
Author Keywords: butane; compression ratio; engine speed; exhaust-gas temperature; liquefied petroleum gas; propane; retrofitted engine
Reprint Address: Choi, GH (reprint author), Keimyung Univ, Dept Mech & Automot Engn, 1000 Shindang Dong, Taegu 704701, South Korea
Addresses:
1. Keimyung Univ, Dept Mech & Automot Engn, Taegu 704701, South Korea
2. Induk Inst Technol, Seoul, South Korea
3. Daegu Mirae Coll, Taegu, South Korea

Exhaust emissions from an indirect injection dual-fuel engine
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Author(s): Abd Alla GH, Badr OA, Soliman HA, Abd Rabbo MF
Source: PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART D-JOURNAL OF AUTOMOBILE ENGINEERING Volume: 214 Issue: D3 Pages: 333-340 Published: 2000
Times Cited: 0 References: 14 Citation MapCitation Map
Abstract: Diesel engines operating on gaseous fuels are commonly known as dual-fuel engines. In the present work, a single-cylinder, compression ignition, indirect injection research (Ricardo E6) engine has been installed at United Arab Emirates University for investigation of the exhaust emisssions when the engine is operating as a dual-fuel engine. The influence of changes in major operating and design parameters, such as the concentration of gaseous fuel in the cylinder charge, pilot fuel quantity, injection timing and intake temperature, on the production of exhaust emissions was investigated. Diesel fuel was used as the pilot fuel, while methane or propane was used as the main fuel which was inducted in the intake manifold and mixed with the intake air. The experimental investigations showed that the poor emissions at light loads can be improved significantly by increasing the concentration of gaseous fuel (total equivalence ratio), employing a large pilot fuel quantity, advancing the injection timing of the pilot fuel and increasing the intake temperature. It is demonstrated that, in general, any measure that tends to increase the size of the combustion regions within the overly lean cylinder charge will reduce markedly the concentrations of unburned hydrocarbons and carbon monoxide in the exhaust gases.
Document Type: Article
Language: English
Author Keywords: exhaust emissions; dual-fuel engine; pilot fuel; gaseous fuel; injection timing; intake temperature; combustion characteristics; NOx emissions
Reprint Address: Abd Alla, GH (reprint author), Al Ain Tech Sch, POB 17835, Al Ain, U Arab Emirates
Addresses:
1. Zagazig Univ, Shoubra Fac Engn, Dept Mech Engn, Cairo, Egypt

AUTOIGNITION OF LOW-HEATING VALUE GASES IN A DIRECT-INJECTED DIESEL-ENGINE
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Author(s): ROMERO CE, MORRIS G, MCMILLIAN MH
Source: COMBUSTION SCIENCE AND TECHNOLOGY Volume: 96 Issue: 4-6 Pages: 369-385 Published: 1994
Times Cited: 2 References: 22 Citation MapCitation Map
Abstract: The autoignition of gaseous mixtures representative of coal derived low-heating value fuels in a direct-injected diesel engine was theoretically investigated over a pressure and temperature ranges of IO to 50 atm and 800 to 1000 K respectively. A computer model was validated with experimental data from an engine operated on direct injected synthetic coal gas. The computed results demonstrated the importance of the characteristic time associated with the chemical kinetics when compared to the fluid mixing. High gas temperatures resulting from high compression ratios, high boost, high inlet air temperatures or other ignition aids are needed to ignite these gases in a compression-ignition engine in a timely manner. The predicted sensitivity of the autoignition delay time to changes in the engine operating conditions was significant for temperature but almost negligible for pressures up to and slightly in excess of 30 atm.
Document Type: Article
Language: English
Author Keywords: LOW-BTU-GAS; DIESEL ENGINE; KINETICS MODELING
KeyWords Plus: OXIDATION; PROPENE; PROPANE; JET
Reprint Address: ROMERO, CE (reprint author), W VIRGINIA UNIV, DEPT MECH ENGN, MORGANTOWN, WV 26505 USA
Addresses:
1. US DOE, MORGANTOWN ENERGY TECHNOL CTR, MORGANTOWN, WV 26507 USA

Three-Dimensional Computational Fluid Simulation of Diesel and Dual Fuel Engine Combustion
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Author(s): Liu CK (Liu, Chengke)1, Karim GA (Karim, G. A.)1
Source: JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME Volume: 131 Issue: 1 Article Number: 012804 Published: JAN 2009
Times Cited: 0 References: 14 Citation MapCitation Map
Abstract: A 3D computational fluid dynamics model with a reduced detailed chemical kinetics of the combustion of diesel and methane fuels is developed while considering turbulence during combustion to simulate the mixture flow, formation, and combustion processes within diesel and diesel/methane dual fuel engines having swirl chambers. The combustion characteristics of the pilot injection into a small prechamber are also investigated. Modeled results were validated by a group of corresponding experimental data. The spatial and temporal distributions of the mixture temperature, pressure, and velocity under conditions with and without liquid fuel injection and combustion are compared. The effects of engine speed, injection timing, and the addition of carbon dioxide oil the combustion process of dual fuel engines are investigated. It is found that in the absence of any fuel injection and combustion, the swirl center is initially formed at the bottom-left of the swirl chamber, and then moved up with continued compression in the top-right direction toward the highest point. The swirling motion within the swirl and main combustion chambers promotes the evaporation of the liquid pilot and the combustion processes of diesel and dual fuel engines. It was observed that all earlier autoignition call be obtained through injecting the pilot fuel into the small prechamber compared with the corresponding swirl chamber operation. It is to be shown that reduced engine emissions and improved thermal efficiency can be achieved by a two-stage homogenous charge compression ignition combustion. [DOI: 10.1115/1.2981175]
Document Type: Article
Language: English
Author Keywords: dual fuel engine; swirl chamber; small prechamber; autoignition
Reprint Address: Liu, CK (reprint author), Univ Calgary, Dept Mech & Mfg Engn, 2500 Univ Dr, NW Calgary, AB T2N 1N4 Canada
Addresses:
1. Univ Calgary, Dept Mech & Mfg Engn, NW Calgary, AB T2N 1N4 Canada

Outer Limits 4x4 Board

D-Gas giving no benefits, anyone else having issues??

D-Gas giving no benefits, anyone else having issues??