Propane enrichment for diesels 5

[sportster]

I recently read about an after-market kit for electronic injection turbo-diesel automobiles which injected propane into the intake manifold. This proportedly improved emmissions (gaseous and particulate), power, torque, and fuel-economy. The system ran on a maximum 15% propane (15% of caloric imput I presume). Economy must have been computed as % ultimate efficencey of the combined fuels(?). The kit seemed to rely on the electronic diesel-fuel management system to lean out the charge to achieve appropriate exhaust O2 levels. Unfortunately, I've forgotten the name of the company and have had no success searching the internet...

I am interested in finding independant studies or documentation of this type of "dual-fuel" system and verifying its benefits. Does anyone know of application of this system?

 

[franzh]

Be warned that there are many "snake oil salesmen" on the market and the net! I have participated in a great deal of research with dual fuel fumigation, both natural gas and propane and have seen my share.

Propane has an octane level and fuel sensitivity levels that prohibits it from being used in CI engines with a static compression ratio much over 16.5 to 1.

Very small amounts (minor fraction) of propane can provide GREAT amounts of power, and is the reason for the great prolification of these kits being marketed today.

I have seen some inside notes from one of these kit makers, and the way they calculated the percentage of use is that they use 1 gallon propane per 6.5 gallons of diesel (HUH?).

Also, as of this posting, the EPA has not recognised the minor fraction fumigation as an alternative fuel, and no propane fumigation systems have EPA approval.

Several kit makers advertise a 30% gain in power with a 30% gain in fuel economy because the propane acts as a catalyst, increasing the efficiency of combustion, burning 90% of the diesel!

Something is missing, like my first class in Thermo 101.

The concept is a great idea, but the marketing folks are driving the engineers. Propane in the diesel engine is not new, and a little bit is fine, but with almost all things, if a little bit is good, a lot is better. One transmission manufacturer has declined warranty on some beta systems because of the power and torque load increases.


Regards.

 

[franzh]

One additional comment, many of these kit manufacturers offer "drive adjustable power levels" which is a direct violation of the EPA anti-tampering law. My last statement about a little bit being good and a lot being better is targeted at the driver selecting the level of usable power by a simple switch or cable-pull.

Somehow, when a driver becomes used to a particular vehicles performance criteria, they desire more. Liken this to a beginning hot-rodder; first the big tires, then the carburetor, then the manifold, cam, headers, transmission, suspension, etc.

Once the driver becomes accustomed to the lower levels of fumigation, they feel they want more power and increase the amount of propane. A driver adjustable system is probably the worst thing to happen here, since a little power is fine, but a lot of power can be damaging.

Regards.

 

[sportster]

Thanks, franzh, for your response, and sorry that it has taken me so long to respond. I hope this reply gets to you, as I have some more questions. "Minor fraction fumigation" is a Phase i will now have to search on the net, but I still haven't found academic research about this subject, only "snake-oil", as you've said.

I am interested in quantified information about the moderate power boost and improved emmissions that could be available from minor fraction fumigation with LPG of CI deisel engines, as well as the possible minor benefit that cleaner operation might have on engine wear. I would like to know what levels of fumigation produce corresponding power output, and at what point this dual mixture begins to damage a "stock" engine. I am particularly interested in the potential emmissions improvement. Is this improvement in NOX and SO emissions and/or particulates? What and to what extent?

If these are indeed advantages of minor fraction fumigation, I'm suprised that they seem to be ignored by the EPA. If no propane systems are approved by the EPA, does this mean that these after-market kits are not street-legal?

If you can point me in teh direction of some existing, reputatable research, I would greatly appreciate it. And again, thanks for the response.

 

[JayMaechtlen]

how is the propane metered?
when is it used- part power or full power conditions, or both?

since c-i engines always take a "full breath", the only time most of the air will get used (for burning fuel) is at full power. I don't know how much excess air is available at full power conditions in a typical c-i engine.
(more importantly, in "your" c-i engine.)

A c-i engine with turbo could be harder to evaluate- add more heat, the turbo will pump more air- limitations being the turbo performance, etc...

add propane to use some of the excess air, get more power, maybe help burn any of the (liquid)fuel that otherwise sneaks out unburned or partially burned (soot).

now- will the propane politely wait till the proper time, and not ignite/detonate early?
will it burn well/completely under part-power conditions?
will it steal some of the air that was needed to burn the liquid fuel, leading to more unburned/partially burned liquid fuel?

and, if you keep adding more fuel, will the turbo keep winding up, and overspeed/overload/frag your motor?

cheers
jay

 

[JayMaechtlen]

there's a thread about air-fuel rations in the Automotive Powertrain forum, looks like good info.
It appears the the "excess air" available varies wildly from one engine design to another...

 

[franzh]

Yes, to most of the above. CI engines are always "full breath" engines, which means that the same air mass is ingested for each stroke of the engine, regardless of the load setting (non-turbo). The air volume increases with increased engine rpm (total volume per second), which can be used to meter the fuel. Most of the currently available systems use a venturi with a weak signal to start the flow of fuel at some arbitrary point in its mid to upper load range. Some of the marketed systems flow a fixed amount of fuel at boost which is not proportional to engine load or rpm. Propane is not desired at low speeds. There are a very few electronic injected systems currently in R&D, but show some promise.

The EPA states that a minor fraction fuel is less than 50% of the primary fuel. Since it is difficult to get propane to operate in a CI engine at ratios above 15 to 20%, it is a minor fraction fuel. The higher the static compression ratio of the engine, the lower the fraction of propane. The higher the turbo boost, the lower the fraction. Also remember that propane has a critical compression ratio somewhere around 12:1, at which it may begin its combustion process by compression generated heat, usually quite a bit before the diesel injection process.

One reason the EPA has not addressed these applications is that most of them are not initialized during the normal FTP-75 driving cycle, or if they are, it is only for a finite period. Also, there is not established testing protocol since the engine is a dual fuel application (bi-fuel?).

Although the diesel engine only uses the amount of air needed to oxidize the fuel during the combustion process, (the excess air comment) when propane is metered in, the balance of the air is mixed with propane vapor, which also burns, but with the balance of the air. Propane burns quicker and has a higher pressure spike than diesel. You now have two distinctly different combustion processes taking place inside the combustion chamber, and a phenomenon called “colliding flame fronts”.

And lastly, the use of propane in a diesel engine can produce copious amounts of power, but also cause catastrophic engine damage. OEM dealerships are now instructing their diesel technicians to look for signs of a recently removed fumigation system, and if they are found, an engine warranty is voided, often along with the transmission warranty! Also, there is no significant amount of cost-per-mile savings when using a fumigated fuel, for reference: diesel has 150,000 btu’s per gallon, propane 91,500. Its hard to justify the savings at 15% substitution.

By the way, I am a very staunch advocate for alternative fuels, propane in specific, but want it used responsibly. I conduct research and training in gaseous fuels.

Best regards;

 

[mikey62]

i have been using andfitting fumigation type systems to ci engines for 18 months and have reports by qut marking greenhouse gas decreases and fuel savings quantified at 8 cents per klm with no damage to engines i would love to here from you on this subject michaeleve@bigpond.com.au cheers mike

 

[franzh]

Mike:
In the US with most diesel engines (used by medium duty service in the 5.9 to 7.4 L region), the marketers of the dual fuel systems claim a 25% increase in power with the same percentage reduction in fuel usage. Maybe with the diesel, but the LPG use increases. I have done the dyno work, seen the engines, read the emissions, and drawn my own conclusions. Locally, LPG fuel is about 15 cents higher per gallon than Diesel, at about 60% the energy value.

Diesel-LPG has its place, as a competent, quality installed system, without driver overrides, and minor fraction values, somewhere in the 10-12% range.

Very modern diesel engines with drive-by-wire and electronic injection, and aggressive computer controls, are hard to trick by dumping in another fuel.

Your comment about reducing greenhouse gasses is partially correct, the CO2 does drop, but the HC's, CO, and NOx increase.

Regards;

Franz

 

[GregLocock]

Hi Franz, mikey's writing from O, where LPG is around 40% of the price of diesel, so the economic argument is a lot more compelling.

I'm a bit puzzled why the CO2 should drop, unless the CO rises in direct proportion.

Is the actual combustion efficiency improved by this LPG injection?



Cheers

Greg Locock

 

[franzh]

Ahhh! The wonderful land of Ozzz. That explains everything (grin {;=)

The last Diesel I tested emissions on showed about a 4% decrease in CO2 when about 5% lpg vapor was fed into the engine at 10% load (estimated to be a low load cruise). When the air balance is altered with a gaseous fuel (and displaced too), the CO2 ratio changes too. The lpg ignition point (CCR), pressure rise and drop, and flame travel speed are totally different than diesel. These colliding flame fronts cause very unusual exhaust readings that often skew an amateurs rational’s, and reasoning’s. Here in the US, NOx is the big bugger, and dumping fuel in raises the combustion temperature way past the Nox generation point.

The EPA has not authorized any emission testing protocols yet, mostly because any of the kits marketed here do not even energize at the levels offered on the FTP-75 or the new US-06, and I think on the Euro medium duty standard either. Since the kits do not energize, the readings are no different than the OEM certified, thus meeting the EPA’s mandate that any system installed do not “effectively increase emissions over the baseline engine”.

ARRRGGHH!
Diesels do not operate at the nice tight Stoich window that gasoline/petrol engines do, so any emission calculations based on chemistry are pretty well a guessing game.

Help any?

Still haven’t figured why the cruise liner had the “thump” at cruise yet, but I think it may have to do with two screws in synchopation. This ought to get the thread readers guessing!

Franz

 

[ivymike]

well I'm familiar with "screws" from watching Das Boot, and "syncopation" from HS band class...

Are you suggesting that there was some sort of "beat" phenomena going on? And btw, where the heck did this topic come from?

 

[franzh]

Mr. Locock has an alter ego, a world authority on large ships.

Franz

 

[GregLocock]

Woah thar, Mr Franz. I'm an interested amateur in the world of ships,whereas, for my sins, I'm a fully paid up noise and vibration engineer in the automotive field.


Cheers

Greg Locock

 

[franzh]

Regardless, I find your knowledge on large ships extensive, and after all, if not for peer review, what other form of status is there?

(Now for my pat on the back!)
Franz

 

[evelrod]

He doesn't do a half bad job on car stuff either. He even does those funney little solar cars, too. ---And, he likes Minis, which puts him at the top of MY list.
Plus, the rest of the members, myself included, have placed him on top as 'el numero uno' by voting for his posts in the automotive forums.
Try not to let this all go to your head, mate, but I do post this with sincerity.


Rod

 

[phasers]

Thanks for the thread on propane. Very informative.

I have a Ford DIT diesel and I see some of the owners chatting about it on other sites. I don't see any need to add something like this. The added cost of fuel, the additional components, appears to be more trouble then it would be worth. Seems to me the best way to up power in a diesel would be to add an intercooler change to a smaller turbine housing to compensate for pressure drop and watch for excessive EGTs.


phasers

 

[sportster]

Thanks for continuing to feed me info on this Propane/diesel thang...interesting beat/synchpation crypto-ditty too. Guess you guys know each other....

It sounds like moderate fumigation (5-12%) offers some increased power and a linear increase in engine wear (is there a decreased production of particulates that might benifit engine wear? Straight propane engines don't pollute their oil).

Sounds like NOX production might be increased by Propane, but how significantly at low propane %? It seems to me that if you have carbon in your fuel you are going to get the corresponding amount of CO2 -- in fact, I would guess that the best way to exhaust Carbon would be at Maximum CO2 levels, else you get CO or soot, which is a big pollution factor in diesels; which brings me to third:

Emissions:
Their are two emissions issues with diesels: greenhouse/acid rain and human health.
I don't know what the CO2/CO/NOX/sulfur emissions for modern diesels are and what the U.S. and European requirements are for these (Reader: Please steer me to web-site, lay-digestible info on these topics). How do the emission of diesels compare to those of gasoline engines, underload, and after 100K miles? Its my impression that diesels are better on gaseous emissons and bad on particulates. I believe that damage to the humans lungs is less of a "sin" than damage to the larger ecosystem. Aren't particulates unburned carbon?

As far as why:
being able to use 10% of an alternative fuel gives one a different fuel-market to exploit, as noted about. Minor enrichment takes little modification and is there to take or leave. Propane is still not a fuel that it would be easy to drive accross country on; This dual-fuel option would promote and exploit the expansion of the automotive propane fuel-delivery infrastruction without being wedded to it. On-board propane could be used to great advantage in other ways on certain types of vehicles: Heaters, generators, refrigeration. Imagine that you had a small propane engine in your engine bay that could drive the engine mounted compressor and generator through clutch engagement or a couple of opposed freewheels (hell! If you wanted you could simply detach these place them elsewhere in your vehicle to solve other auto design issues.) small propane engines start, run and maintain more easily than liquid fuel models, and produce only H20 and CO2. Think of it as extended battery maintence and backup. You could also take the load of these parasitic devices in times when you wanted full HP to the drivetrain. Thirdly, as a further refinement of systems like VW's (euro-only!) Eco-diesel concept, you could shut the diesel down at idle and run you A/C and creep in bumper-to -bumper traffic in the propane engine alone. You could also use it as an alternate starter, a handy thing on a hard-cranking diesel. Am I sounding like a crank? Talk to me....

 

[evelrod]

A 'trolling motor' for a VW ? Hmmmmmmmmmm.


Rod

 

[franzh]

Sportster:
Great comments. The single biggest problem with a vehicle operating on two fuels is training the driver to fill with both, or either. For years, large manufacturers have discovered that starting an engine on a gaseous fuel is easier on the engine, less polluting, faster catalyst warm up, longer lasting engine since no liquid fuel wash down, etc. The problem was training the driver to find and fill two fuel systems, and the transition period when the gaseous fuel stopped, and the liquid fuel began.

Visualize this, the engine starts on propane and runs for about 1 minute. Total fuel consumed about ½ pint. But during this period, the driver would back out of a driveway and begin to accelerate on a city street, just about the time the engine switches fuel. How to make the transition smooth without bucking or backfiring is the problem. The advantage is that the engine is starting on a dry fuel, no cylinder washdown, good fuel distribution, a rich enough mixture to preheat the cat. The HC’s and CO are handled by the rapidly heating cat and since there is minimal particulate production with a rich gaseous fuel mixture, there is almost no contamination of the oil.

Also, running two fuels brings into play the engine management system, how do you optimize two different and separate fuel systems? OEM’s have had a difficult enough time with one, much less two.

Your comments on the diesel emissions are well placed. Consider this: Diesel engines are unthrottled and inherently produce more NOx because of excess air. The addition of propane decreases the air BUT increases the combustion temperature and pressure, resulting in increased NOx and HC’s, but at slightly decreased PM (more fuel, less diesel, higher temps, equal power at a lower throttle setting.)

There is a well-established propane distribution network in the US, and in most of the world too. Take all the other alternative fuels vehicles worldwide, then quadruple the amount, and propane vehicles are still more than that too! It IS possible to drive coast to coast on a pure propane vehicle, I have done so, with a little planning. Remember the Olds diesel produced in the late 1970’s? In the owners glovebox was a diesel distribution outlet guide showing car friendly diesel outlets. The same is possible with propane.

Final parting thought, remember that diesel fuel has a higher caloric value by weight than propane. It takes 1.6 times the amount of propane to produce the same power as diesel.

Regards;
Franz