Biodiesel Cold Soak Filterability - ASTM D6751 Annex A1

New ASTM Biodiesel Test Specification for Cold Weather Operability

The American Society for Testing of Materials has recently added a new test requirement to the D6751 Biodiesel Specification.

This new requirement is referred to as ASTM 6217 or as Annex A1 of ASTM D6751– Cold Soak Filterability.

Cold Soak Filtration Analysis is defined as: The time in seconds that it takes for cold soaked biodiesel to pass through two 0.8 micron filters and the amount of particulate matter expressed in milligrams per liter (mg/l) collected on the filter.

What does this mean? When biodiesel is stored in temperatures below 40°F for extended periods of time, certain components will precipitate (fall) out of solution and fall to the bottom of the storage tank. This precipitate will build in a thickening layer at or near the tank bottom. In general the colder the temperature and the longer the biodiesel stays at a given temperature, the more material will fall out.

This material can very quickly plug filters and shut down engines, usually at the worst time.

What is this material? It can have to do with the feedstock from which the biodiesel is created. Certain feedstocks, particularly Used Cooking Oils (UCO), Waste Vegetable Oil (WVO), and Animal Fats (Tallow) will produce high levels of precipitate. The material can also be due to incomplete removal of glycerin during the transestrification process.

This new test is a positive step in making biodiesel a more consistent user friendly product.

Diesel Doctor

Copyright 2009© - William Richards

Synthetic Oils - Are they Worth the Cost?

Synthetic Oils - Are they Worth the Cost?

Image courtesy of outboardmotoroilblog.com

Today we hear a lot of terms thrown around when discussing motor oils. Much of the time, they are being used incorrectly.

So let’s start with mineral oil, this is the oil most of us have used in one form or another since the internal combustion engine was created. Mineral oils are distilled from crude oil as part of the refining process.

There are three categories of mineral oils; Paraffinic, Naphthenic, and Aromatic. Mineral oil can be as simple as baby oil, or as complex as today’s heavy duty motor oils. The chemistry used to create multi-grade oils and pickup and hold contaminants in solution is extremely complex.

Synthetic – Synthetic Oils can be created from many different sources and can offer many helpful characteristics such as lower friction, better high temperature performance, better stability, better sheer stability, better cold start lubrication, reduced oxidation, improved protection against thermal breakdown, less tendency to form sludge, reduces evaporative loss, potentially extends drain intervals.

There are two main categories for synthetic oils the first is:

Polyalphaolefin (PAO) an American Petroleum Institute (API) Group IV Oil Base Oil

The second is:

Synthetic esters an API Group V Base Oils ((non-PAO) synthetics, including alkylated naphthalene’s, alkylated benzenes, diesters, polyolesters, polyglycols etc.)

There is also a category called Semi-Synthetics – a mixture of petroleum and up to 30% synthetic base oils. The name Semi-Synthetic is a misnomer, oils are either Synthetic or not. If they are a mixture then if you subscribe to the theory that a chain is only as strong as its weakest link applies and the mixture will only be as good as worst performing part of the mineral oil.

The primary reasons to change motor oil are because the oil gets dirty and or because the additive package in the oil gets used up. Dirty can mean physical dirt from the environment, soot from combustion, left over combustion products and a nearly endless list of contaminants.

The additive package provides friction reduction, neutralizes acids, holds contaminants in solution, prevents oxidation, prevents corrosion, and many other vital functions. The additives are consumed or used up over time and they need to be replenished or failure will result. The method most often used is to replace the oil. This method has the advantage of taking many or hopefully most of the contaminants out of the engine with it.

Synthetic Oils may or may not have super additive packages, but eventually the oil becomes dirty to the point that it needs to be filtered or replaced and the additive package replenished or again replaced. The problem is that synthetic oil becomes contaminated long before it is “worn out” and has to be replaced to prevent damage from the contaminants. This means that often you are unable to take full advantage of the superior chemistry and characteristics of synthetic oils.

When this happens the cost disadvantage of the synthetics outweigh its other advantages.

In situations of extreme cold, high heat, high loads, extended operation at high rpm, and other related situations synthetic oils offer many superior characteristics that may improve operability, increase engine life, provide better fuel economy, and potentially improve emissions.

However for the average grocery getter or most vehicles in normal operation the added cost of synthetic motor oil is probably not justified.

View all of the Fuel School articles at: www.lcbamarketing.com and click on Technical Articles

Please post your comments, thoughts, ideas, and suggestions.

Diesel Doctor

Copyright 2009© - William Richards

Natural Gas as a Transportation Fuel – A Cautionary Note

Natural Gas as a Transportation Fuel – A Cautionary Note

Natural Gas is currently being promoted as a domestic clean, safe, and cheaper alternative to petroleum fuels.


Some thoughts for your consideration.


Natural Gas as domestic source of energy. The US currently imports approximately 16% of its natural gas. Some comes to us by pipeline and some in the form of LNG via ship. Increasing the use of natural gas to replace petroleum fuels simply shifts our imports from one product to another.


Currently the US uses approximately 22% of our natural gas to create electricity. This is a poor use of a valuable resource for a need that has many other fuel sources available. If this was replaced by wind, solar, nuclear, and a future renewable bio-source (see previous article: The Richards Cycle) you could eliminate our imports.


Natural Gas as a clean motor fuel. Compressed Natural Gas (CNG) and Liquefied Natural Gas (LNG) both reduce certain emissions however they are not as clean as some would have us believe. If you look the whole basket of emissions that come out of the exhaust on an internal combustion engine, a 2010 Selective Catalytic Reduction (SCR) Diesel engine actually is less polluting than an equivalent CNG or LNG engine.


While I believe you can safely use CNG and LNG, it requires more training and much greater diligence on the part of drivers and operators vehicles and fueling stations. It is important to remember that it can take far longer to fuel LNG and particularly CNG fueled equipment. This long fueling cycle can lead to lack of attention and added expense in fueling equipment.


Natural Gas as cheaper alternative. Many people incorrectly try to compare a gallon of diesel to a gallon of LNG or a gallon of CNG. While the price per gallon of the LNG and CNG may appear to be cheaper, you need to consider the energy in the gallon. For example a gallon of diesel contains approximately 139,000 Btu’s of energy, while a gallon of LNG contains about 73,500 Btu’s, and CNG works to about 34,750. In short it takes about 4 times the space to store an equivalent amount of CNG as compared to diesel.


The other concerns with vehicles powered by CNG or LNG are that they are far more expensive to purchase, for example a school bus built to run on CNG can be $30,000.00 to $40,000.00 more than its diesel counterpart.



Also when you purchase a vehicle powered by CNG or LNG you locked into one supplier for all fuel system and some engine components for ever. There is virtually no secondary supplier compatibility. You limit the range and usefulness of the vehicle due to limited ability to refuel that vehicle away from its domicile. Lastly, you have to be concerned about the value of those vehicles when it comes time to trade or sell them. In many cases this limited resale market can make a used vehicle worthless.


There is an important and growing place for alternative fuel vehicles and equipment. It takes visionary leaders with long term commitment and very deep pockets to make a change to this type of equipment successful.

You can get more information on this and other fuel related subjects at: http://www.lcbamarketing.com and click on Fuel School Articles.

Please comment here and share your thoughts, ideas, and suggestions.


Diesel Doctor



Copyright 2009© - William Richards

Cetane Number – What it is and Why it’s so Important

Cetane Number – What it is and Why it’s so Important

Cooperative Fuel Research Engine (CFR)

Cetane is a measurement of a diesel fuel ignition and or combustion quality. This Cetane Number or CN is one of several components that determine the quality of diesel and biodiesel fuels. This number is used for light and middle distillate fuels. For heavy (residual) fuels Calculated Ignition Index (CII) and Calculated Carbon Aromaticity Index (CCAI) are used.

In some ways this measurement is similar to the Octane Ratings given to gasoline. In its simplest terms Cetane Number measures the delay between the start of fuel injection into the combustion chamber and the beginning of compression ignition (Auto-ignition).

In medium and high speed diesel engines (this all automotive and truck engines) fuel needs to have a CN between 38 and 55 to operate. In general the higher the CN number, the better for the engine and for emissions. However raising CN above 55 currently offers little if any benefit.

In the US the group setting the standards for CN is the American Society for Testing of Materials (ASTM) and currently the minimum is 40. While diesel engines will start and run with 40 CN fuel, they do not run as efficiently as they will at a higher number.

In Europe the European Union (EU) has systematically over several years raised the minimum from 38 to the current 51. This has allowed engine manufacturers to produce more efficient engines with lower emissions and better economy. Most fuel in the EU has a CN of 55 or even better.

Cetane Number is measured using a very expensive and arcane Cooperative Fuel Research (CFR) engine and a process that very complex.

You can also measure CN using an Ignition Quality Tester (IQT) which is somewhat less complex, but still quite costly.

There is a third measurement called Cetane Index (CI) that measures density and distillation range of the fuel and through a calculation provides a measurement. This method will calculate a reasonably accurate number for the refined diesel.

The problem is that today most diesel fuel uses additives to reach the desired Cetane Number and additives do not affect the density, thus the CI of a fuel containing additives is not accurate.

Some of you may have seen a device that looks like a battery fluid tester (a hydrometer). These devices are not capable of determining CN or CI with any accuracy.

You can raise CN by altering the refining process or through the use of Alkyl nitrates or di-tert-butyl peroxide additives. NOTE: Remember that additives do not raise CI.

Also, biodiesel, depending on the base oil from which it is derived has a natural Cetane Rating of 46 to as high as 60.

With the advent of Pilot or Multiple Pulse fuel injection, Cetane Number becomes more important than ever. The delay in auto-ignition (CN) affects the combustion timing, which has a significant effect on power output, fuel economy, and emissions.

Raising Cetane Number together with Improving Fuel Atomization is the fastest way to improve fuel economy and reduce emissions through the use of correctly formulated additives.

Please post your comments, ideas, and suggestions

More information at: http://www.lcbamarketing.com/ - Click on Fuel School Articles.

Diesel Doctor

Copyright 2009© - William Richards

Asphaltene's and Plugged Fuel Filters

Asphaltenes and Plugged Fuel Filters

Asphaltenes in diesel fuels are becoming a much larger problem since the introduction of Ultra-Low Sulfur Diesel (ULSD - S-15) fuels.

There are actually several problems that have come together to cause the filter plugging black slime we so often see today.

Asphaltenes are highly polarized long chain components in crude and the heavier refined oils. Under certain circumstances these compounds associate themselves to form complex colloidal structures.

In Low Sulfur Diesel (LSD – S-500), High Sulfur Diesel (HSD – S-5000) and heating and bunker fuels the higher aromatic content of the fuel tends to discourage the formation of the complex colloidal structures limiting the problem.

However the EPA mandated reduction in aromatic content in ULSD has allowed this problem to happen sooner, more often, and in cooler temperatures than had been seen previously.

Asphaltenes agglomerate into an oily sludge. This problem is made worse when water is added to mix.

Petroleum and bio-derived fuels all hold water suspended in them, ULSD unfortunately holds approximately twice as much as the LSD and HSD fuels we had seen prior to June of 2006. Biodiesel (B100) can hold ten (10) times as much water as LSD and HSD, so even small amounts of biodiesel blended with diesel fuels dramatically increases the amount of dissolved water present.

Blending of fuels refined from different crude stocks further exacerbates this problem. Also, warmer temperatures in storage or due to the recirculation of fuel by the engine fuel system speeds the process and thickens the sludge.

Fuel that looks perfect going into a clean tank can develop tiny asphaltene droplets in a matter of hours when recirculation temperatures exceed 140°F (note: some newer engine fuel temperature as it exits the head exceeds 210°F). These pin-prick sized droplets can plug a 10 micron fuel filter in 3ooo to 4000 miles or less 50 hours of operation.

Many people mistakenly see this as a biological (bacteria and fungi) problem, however in the majority of cases the accelerated biological growth is the result of near perfect growing conditions that allows this rapid growth after the filter plugging asphaltene material has blocked the filter(s).

Keeping the water out helps, but the real solution is a thermal stability additive, a oxidative stability additive, together with a water dispersant.

Please comment with your experiences, suggestions, and or questions.

Diesel Doctor

Copyright 2009©

Fuel Storage Tank Maintenance - Keep It Clean

Keep It Clean - Fuel Storage Tank Maintenance

Most owners and operators of fuel storage tanks do not understand that maintenance is required to safely and successfully operate fuel storage tanks.

We constantly hear that customers have tanks that have never been cleaned and worse yet, that they believe that they never need to check to see if they have any problems.

This is made even worse by the information that some fuel suppliers tell their customers; for example that it OK to have some water at the bottom of the tank.

Well here is some real world information for everyone on this subject.

Fuel Storage Tanks all require regular maintenance. They are designed with the pickup tube 3" to 6" from the tank bottom so that small amounts of water, sediment and other contaminants have a space they can settle out so that they will not be drawn into the vehicle or equipment tanks as fuel is pumped out. This water and sediment material will accumulate over time and will cause problems if not removed periodically.

Some will tell you that 1/2" or 1" or even 2" of water is alright, and they are flat out wrong. Every time fuel is transferred into that tank it stirs up all that material and it may take as long as a day for it to settle out again. In the meantime every tank you dispense fuel into gets some of this material.

If you have a steel tank that water is corroding your tank from the inside out and putting rust particles into your fuel. We often find above ground tanks only a few years old that have rusted from the inside to the point of leaking from water and sludge in the tank.

Many customers have electronic monitoring systems that provide constant readings showing fuel level, water level, and leak detection. Some of these customers will see 1/2" or a few gallons of water on these system and ignore it because they have been told it is not important.

One problem we see time and again is that the sensors on these monitoring systems fail and they don't tell you when they fail, they just go on showing the last reading forever. This goes on until they start pumping water into their equipment at which point someone checks the tank with a stick and water finding paste only find that they actually have several inches of water.

We have told all of our customers for many years that even though you have spent several thousand dollars for a state of the art monitoring system, you still need to have some one check every tank at least once a month with a stick and water finding paste.

And this rule should be written next to the monitor and maybe next to where you store the measuring stick: "The Only Acceptable Amount of Water in Any Fuel Storage Tank is ZERO (0)".

For those of your with in-ground steel tanks, these tanks have Sacrificial Anodes attached to them. These Anodes take the weak electrical current generated by the tank and pass it into the ground through them. This prevents the tank metal from corroding, however the Anode "Sacrifices" itself in this process. The Anode is used up over a period of time. When the Anode is "used up" the tank begins to corrode often very quickly. Tank owners should periodically check these Anodes and Replace them as necessary. In many states this is part of the required maintenance and testing procedures, however you should know this and check to be certain it has been properly done.

Caps, Sumps, and Vents should all be checked for integrity and to see that they are doing their intended job.

Fuel Storage is a vital link in getting clean fresh fuel safely and efficiently into vehicles and equipment. You have a big investment in the tank, its installation, and in the fuel in it. It only makes sense to properly maintain and protect this investment.

Today we have new challenges with Ultra-Low Sulfur Diesel (ULSD), Biodiesel, Gasohol, Conventional Gasoline, and Reformulated Gasoline containing any amount of Ethanol. These fuel products hold much higher levels of water and are much more corrosive than fuels we have traditionally dealt with. They require much higher levels of monitoring and maintenance to have a safe and trouble free delivery system.

We are happy to offer analysis and suggestions on how to operate and maintain your systems.

Please post your comments or questions here.

Diesel Doctor

Ultra-Low Sulfur Diesel Cold Weather Information

Ultra-Low Sulfur Diesel Fuel

Cold Weather Information

The Ultra-Low Sulfur Diesel (ULSD (S-15)) that we started to receive in mid 2006 has shown some dramatically different cold weather characteristics from the earlier High Sulfur (HSD (S-5000)) and Low Sulfur Fuels (LSD (S-500)).

These new characteristics including higher temperature gelling, wax dropout, icing, and difficulty in treating have in the first year and will continue into the foreseeable future to provide some significant challenges to distributors and end users during cold weather.

Due to these new characteristics users in areas of the US where they have not seen cold weather problems in the past, are now and will continue to see serious issues with gelling, wax dropout, and icing.

Here are the main issues known today:

Wax in diesel fuels – Paraffin wax is a natural and important part of diesel fuel. This wax provides several beneficial characteristics including high energy content (Btu’s), lubricity, stability, and viscosity. The negative characteristics mainly revolve around cold weather operation and include gelling and something new we refer to as wax dropout.

In HSD and LSD the wax characteristics were relatively well understood and consistent. For example the “Rule of Thumb” used for adding kerosene (#1 diesel, Jet A) to #2 fuel to lower Cold Filter Plug Point (CFPP) was that for every 10% kerosene added to #2 diesel you would lower CFPP by approximately 5°F. An example would be that a 50% blend would have improved CFPP by about 25°F.

However the new ULSD has had several important characteristics changed by the new refining processes. The catalytic cracking and hydrodesulfurization processes remove some of the wax, it alters the size and shape of the wax seed crystals in the fuel, lowers the aromatic content of the fuel, removes a significant amount of the Lubricity, and lowers the fuels ability to dissipate static electricity by as much as 100 times.

The result of this is that the ULSD fuel actually will gel at a higher temperature than the old LSD and HSD. This problem is made more difficult because we can no longer use regular kerosene (#1 diesel, Jet A) for cold weather blending. These fuels are considered High Sulfur and their use would cause the end fuel to have sulfur content higher than the allowable 15 ppm. So refiners have had to create an ULSD #1 specifically for winter blending purposes.

There are a number of problems with this new fuel. First, it is currently very expensive, ranging anywhere from $.30 to $1.00 more than regular kerosene, second it is not available in all areas, and third this new ULSD #1 is not as effective at lowering the Cloud Point (CP) and CFPP (gel point) of the fuel. For example; ULSD #2 when blended with 10% ULSD #1 will lower the CFPP by only 2°F or maybe 3°F. This means that a 50% blend would only improve CFPP by 10°F.

To make this problem even more difficult, many of the diesel fuel anti-gel additive products that have been on the market for last 5 to 30 years have little or no effect on ULSD. The change in fuel chemistry brought about by changes in the Catalytic Cracking processes and the addition of Hydrodesulfurization have rendered many of the most popular products nearly useless in ULSD.

There is a new cold weather problem that the industry has not adequately defined
as of today. We are calling this issue “Wax Dropout”. Wax Dropout occurs when diesel fuel is “cold saturated”. This where the fuel reaches a given temperature and stays at or below that temperature for a given period of time. This time period is usually between 48 and 72 hours or longer and the temperature can vary with different batches of fuel. This past winter we saw this problem at between 5°F and 10°F.

When the fuel gets to the Wax Dropout temperature, say for example 8°F and stays there for 48 to 72 hours, the wax will suddenly agglomerate and fall to the bottom of the container. This wax plugs filters and fuel lines until it is removed or until the fuel temperature is raised to a point where the fuel will reabsorb the wax.

Again there is a further complication, in that the “old” HSD and LSD wax would gradually start to reabsorb as the fuel temperature rose. With ULSD when wax dropout has occurred the wax does not begin to reabsorb until the fuel reaches fairly high temperatures, often above 40°F, 50°F or even higher. This can make the process of getting an engine with gelled fuel to run properly far more challenging than we have ever seen before.

In the fuel distribution and fleet operations businesses, we have relied on CFPP as
a measure of winter fuel quality for many years. CFPP is a fairly complicated test involving using a vacuum to draw a sample of fuel through a 45 um (micron) screen within a given period of time.

When the HSD and LSD were most prevalent and most fuel filters were 10 um there was a good correlation between CFPP and the temperature at which a standard fuel filter would plug. For example you could be relatively certain that a fuel testing for CFPP of -25°F would provide trouble free operation to -15°F to -20°F.

However the relationship is much different with ULSD. A ULSD fuel testing
-25°F CFPP might have filter plugging problems at between -5°F and -10°F. Also CFPP does not seem to be directly related to Wax Dropout. A fuel can test for
-15°F and still have Wax Dropout at 8°F.

Furthermore, OEM engine manufacturers have changed the media size of their fuel filters. Where 10 um has been almost an industry standard, we now see 7 um, 5 um, and even 2 um filters today. This throws the whole relationship between CFPP and winter operability out the window. For example fuel that is at the CP can have filter plugging problems with a 2 um fuel filter.

The industry has not yet agreed on or developed testing methods to measure cold weather operability with the new fuels and filters.

Until such time as the industry develops a test method for determining the relationship between CFPP, PP, Wax Dropout, and filter media size for ULSD, we suggest the following: For 10 um filters; Take the midpoint between PP and CFPP, for 7 um filters, take the midpoint between PP and CFPP, then take the midpoint between that number and the original CP, for 5 um and 2 um use the CP.

Water is more of a problem than ever before. Diesel and biodiesel fuels hold
water dissolved in them. The amount of water that ULSD is able to hold is greater than that of HSD or LSD. One of the characteristics of fuel is that its ability to hold water in solution diminishes as the temperature decreases. Fuel delivered at 70°F with 200 ppm of dissolved water will as the temperature drops begin to push that water out of the fuel into droplets. These droplets can be seen floating in the fuel and as temperatures reach and go below 32°F those droplets freeze becoming ice crystals.

As a result many of the cold weather problems where people believe they have fuel gelling problem are actually a fuel icing problem. If you have operability issues in temperatures above 0°F you should check to be sure that you aren’t dealing with ice.

Customers are regularly reporting situations where they have no water in storage tanks, no water in vehicle or equipment tanks, but they constantly have water in filters and separators. This is due to the dissolved water falling out of solution due to temperature changes.

Fuel and Water - They Don't Go Together

Fuel and Water

They don't mix and you shouldn't try to make them.

One of the more interesting characteristics that is shared by diesel, biodiesel, gasoline, and gasohol is that all these fuels are hygroscopic.

Hygroscopy is the ability of a substance to attract water molecules from the surrounding environment through either absorption or adsorption.

Some examples of this phenomenon are that Ultra-Low Sulfur Diesel (ULSD) will hold approximately 2/10 of 1% dissolved water. This may not sound like much, but if you do the numbers they show that 2/10 of 1% equals 2 gallons of water dissolved in 1000 gallons of fuel. If you work backwards, that would equal 1 gallon of water in 500 gallons of fuel, or 1 quart (32 ozs.), in 125 gallons, or 1 pint (16 ozs.), in 62.5 gallons, down to about 8 ozs. in a 30 gallon tank.

That much water can cause severe corrosion of fuel system components such as injectors, pumps, connectors, and even metal fuel tanks.

That level of water speeds the oxidation and chemical breakdown of the fuel.

That level of water is enough to encourage the growth of bacteria and fungi.

One of the most insidious characteristics of water dissolved in fuel is that the fuels ability to hold water is dependent on temperature. Simply put the warmer the fuel (up to a point) the more water it hold.

What often happens is that fuel stored for example at 60°F will absorb that 2/10% water then as the fuel in a vehicle gets colder more and more of that water is pushed out of the fuel becoming liquid water droplets.

These droplets can collect in filters and if the temperature drops below 32°F those droplets turn to ice crystals quickly plugging filters and causing other problems.

Fuel at 28°F can hold approximately 1/2 as much water as fuel at 60°F.

This means that you can have clear fuel with no liquid water at 60°F and if the temperature drops sufficiently, you can have large amounts of free water suddenly appear as the temperature drops.

To make matters worse biodiesel can pickup and hold 10 times as much water as ULSD. So adding 2% or 5% biodiesel to regular diesel can dramatically increase the level of dissolved water.

Gasoline containing Ethanol suffers the same problem.

A 10% Ethanol blend can hold 3.8 teaspoons of dissolved water at 60°F.

However if more water is added or if the temperature drops significantly this fuel suffers a problem called "Phase Separation".

In Phase Separation the dissolved (or liquid) water binds to the Ethanol and this Water/Ethanol mixture will drop out of the fuel.

This has a series of negative affects on the fuel quality and can have catastrophic effects on engines.

We will discuss more about this later.

We look forward to your comments and questions.

UREA use in 2009 and 2010 Diesel Vehicles

Urea Use in 2009 Light Duty and 2010 Medium and Heavy Duty Diesels

Hold on, here comes the next big change in diesel engines. Starting with the automotive market in 2009 and then with virtually all of the medium and heavy duty diesel vehicles in the 2010 model year, diesel engined vehicles will require an additional fluid to operate.

These vehicles will require an “aqueous urea solution” as defined by ISO 22241-1 using test methods described in ISO 22241-2:2006. This is a solution of 32.5% Urea in deionized water.

This Urea solution is used as part of a Selective Catalytic Reduction (SCR) system to reduce the NOx emissions of diesel fueled engines.

These systems require that a tank of the Urea solution be installed on the vehicle. The Urea is meter injected into the exhaust stream after the turbocharger where the exhaust heat will convert it to ammonia which is then used by a special type of catalytic converter to significantly reduce the formation of NOx. This system will function as long as there is Urea available.

This is a complicated system with maintenance requirements, cold weather operability issues (Urea freezes), and quality concerns.

There is a wide ranging debate on what type of driver information systems are to be required, what will happen if the system runs out of the Urea solution, and where Urea will be available.

Diesel Fuel Mileage Decrease in Winter

Why Diesel Fuel Economy Drops in the Winter

Diesel fuel, particularly in the northern tier states changes rather significantly from season to season. In the cold weather months generally starting in September or October refiners begin to alter the chemical composition of diesel fuels to improve cold weather operability characteristics to meet ASTM, Pipeline Operator, and Customer requirements and specifications.

Refiners talk about the components that come out of the refining process as “streams”. In a typical refinery today there can be over 180 “streams” coming from the refining of crude oil. The addition of lighter product streams are known by names such as “aromatic chemicals”, “naptha’s”,” kerosene’s” and others to #2 diesel (whether Ultra-Low Sulfur Diesel (S-15) or Low Sulfur Diesel (S-500)) will lower (improve) the Cloud Point (CP), Cold Filter Plug Point (CFPP) commonly referred to as the gel point, and Pour Point (PP) depending on how much of those components are added to the base fuel. Refiners have a lot of latitude in determining how much of and what components are used to make these improvements.

The issue from a fleet operators standpoint is that these changes lower energy (Btu) content of the fuel. It is normal for fuel economy to decrease from one to as much as five percent seasonally. This decrease can be further exacerbated by fuel racks and or distributors further cutting with kerosene to try and improve cold weather operability. The normal energy content of #2 ULSD ranges between 138,000 and 140,000 Btu’s, kerosene is much lower ranging between 130,000 and 135,000 Btu’s, whereas gasoline is about 124,000 Btu’s per gallon.

As you can see the more lighter components added to fuel, the lower the energy content. Note: ULSD has 1%-3% lower Btu content than the LSD. This is primarily due to reduction in wax content in ULSD.

So if you put all of this together in a time line, you can see that you begin using additive to improve cold weather performance at the same time the refiners are blending the fuel in a way that reduces Btu content which lowers your fuel economy, then in the spring you stop using additive at the same time the refiners are going to a “summer” blend which increases the Btu content and so your mileage goes up.

Other cold weather considerations are more idle time, slower transit speeds, more time in traffic, and even driving through snow all, of which can have a significant negative impact on fuel usage.

Cold Filter Plug Point versus Cloud Point

CFPP (Cold Filter Plug Point) vs. CP (Cloud Point)
Cold Weather Operability in Diesel Fuels including ULSD

Traditionally the two main considerations for diesel fuel have been Cloud Point (CP) and Cold Filter Plug Point (CFPP).

Let’s start by defining the terms:

Cloud Point (CP) ASTM D2500 – This test determines the point where wax becomes visible in a fuel sample. This wax first appears as a floating cloudiness in a transparent fuel.

Cold Filter Plug Point (CFPP) ASTM D6371 – This test is a more complicated procedure involving using a vacuum to draw a 20cc fuel sample through a 45 micron screen within a 60 seconds.

There is usually but not always a spread between CP and CFPP of 2°F to 8°F.

CP is a first indicator of cold weather operability temperatures for diesel fuels. It is a visible indication of paraffin wax in diesel fuels. Prior to the introduction of Ultra-Low Sulfur Diesel (ULSD, S-15) into the US market, the importance of CP was often discounted by many due to fact that diesel engines could generally successfully operate at temperatures many degrees below the CP.

Up until the introduction of ULSD many if not most operators used CFPP to provide a reference temperature for cold weather operability with diesel fuels. This is however a complicated and imperfect test. As mentioned above, CFPP uses a vacuum to draw a sample of the fuel through a 45 micron screen within a given time. The point at which the sample fails to go through the screen in 60 seconds is the CFPP.

The main issue is that up until recently most fuel filters used a 10 micron filtering media. The significant difference 10 microns and 45 microns caused a disparity between the test and real world operations. However many in the industry felt that this differential was consistent and that provided a reliable guide for cold weather operability.

For example if you had a CFPP of -30°F, you could feel reasonably confident that you could operate to -20°F.

However three new factors need to taken into account due to changes in fuels and engines.

1. The new ULSD fuel does not appear to provide the same consistent differential between CP and CFPP as we had come to expect with High-Sulfur Diesel (HSD, S-5000) and Low-Sulfur Diesel (LSD, S-500).

2. The new phenomenon of Wax Drop Out (WDO) where under periods of extended “Cold Soak” (48-72+ hours) the wax in the fuel suddenly drops out of the fuel can happen at temperatures that can be above the CP. This problem appears at this time to be independent of CP or CFPP.

3. As diesel engines have become more sophisticated there has been a rise in fuel injection pressures. In order to obtain these higher pressures OEM’s have had to manufacture pump and injector parts to ever closer tolerances. Today many injectors have tolerances in the 2 micron range. These tight tolerances and the very high cost of making and replacing these components have caused manufacturers to use fuel filters with smaller media to protect these components. Where in the past fuel filters typically were 10 microns, today we are seeing filters of 7, 5, and even 2 microns.

This makes the problems associated with ULSD even more difficult. Cloudy fuel that would easily pass through a 10 micron filter can often plug a 5 or 2 micron filter. This makes correcting the cold weather operability issues of ULSD like hitting a moving target. Today you need to adjust your fuel treatment to reflect the engines and filter arrangements in your fleet.

We are now suggesting a formula based on both CP and CFPP. Take the difference between CP and CFPP, divide by 1.5 and add to the CFPP to get a safe operability number.

Example: CP = 8°F, CFPP = 3°F

The difference between 8 and 3 = 5, 5 x .75 = 3.75, Take the CFPP of 3 and add the 3.75 to it equaling 6.75°F. You could expect to reliably operate that fuel in an engine with a 7 to 5 micron filter at 6-7°F.

For those operating 2 micron filters we suggest using the CP of the fuel.

For those still able to operate with 10+ micron filters, we are suggesting a number half way between CP and CFPP.

It is important to remember that the traditional method of using Kerosene or Jet A to “cut” or blend with HSD or LSD to lower the CFPP and Pour Point (PP) is not as effective or reliable as it was in the past when using the new ULSD #1 to cut or blend with ULSD #2.

Use of Diesel Fuel Additives - Year Round

Use of Diesel Fuel Additives
or
Additives's it’s not just for winter anymore

Once upon a time diesel engines were relatively simple pieces of big heavy, hard to break iron. You could put almost anything from kerosene to heating oil in them and they would run, maybe not well, but they would run.

Diesel fuel was considered a residual fuel, something left over from making the good stuff (gasoline). It was not supposed to be a good fuel; it was supposed to be a cheap fuel.

Even if this fairy tale was ever true (it actually was not), those days are long, long gone. Diesel engines today are as sophisticated as those of the worlds fastest Formula One race cars. These engines can have fuel system pressures of up to 35,000 psi and injector machining tolerances of 2 microns or less. Fuel filters that used filter down to 30 or 10 microns, now regularly filter down to 7, 5, and even 2 microns.

The new Ultra Low Sulfur Diesel (ULSD) that is now on the market is derived using various Catalytic Cracking refining processes that affect the quality of the fuel on many levels. The “new” ULSD has less oxidative stability, holds more suspended water, forms gums, varnishes, and carbon deposits more quickly, has less lubricity, gels at higher temperatures, is less thermally stable, is more corrosive, and in general is much more problematic.

In short the quality of the fuel has not kept up with the sophistication of the engines.

As a result you can no longer expect untreated fuel to meet the needs of your engines.

It is no longer good enough to treat your fuel just when it is cold outside. The needs for additional lubricity, higher Cetane, water dispersion, higher levels of oxidative and thermal stability, fuel injector cleaning, corrosion inhibition, fuel atomization require continuous year-round treating to protect your equipment and to maximize performance.

Winter Problems with Ultra-Low Sulfur Diesel (ULSD)

Winter Problems with Ultra-Low Sulfur Diesel (ULSD)

Which One of these Filters Would You Rather Have on Your Vehicle?

The above image is from February 5th 2007, the first real winter weather while using the “new” Ultra Low Sulfur Diesel (ULSD). After being told by refiners and many distributors that ULSD would be the “be all, end all” magic problem solver for all diesel engines, this is what really happened when it finally got cold and stayed cold for 48+ hours.

The red colored filter on the left is the result of a fuel distributor using so much anti-gel additive that it actually saturated the fuel to the point of completely plugging THOUSANDS of fuel filters over several days.

The filter on the right shows paraffin wax plugging it. This customer used ULSD #1 (ULSD Kerosene) to “cut” the ULSD #2 fuel. However the “new” ULSD #1 doesn’t work the same way as the “old” LSD Kerosene (see more below)

The new ULSD gels 4°F to 5°F sooner than the “old” Low Sulfur Diesel (LSD). The new ULSD is harder to treat for cold weather than the “old” LSD. Many additives that you have been using for years no longer work on the “new” ULSD. The “new” ULSD holds more dissolved water than the “old” LSD, causing ice formation as the temperature drops below freezing.

When treating with a cold flow improver (anti-gel), using the recommended treatment ratio provides a certain level of protection, using twice the recommended ratio may improve the gel point a little, however if you go beyond that level it will actually raise or worsen the gel-point. At treatment levels beyond 3-4 times the recommended ratio, you will begin to saturate the fuel and can actually plug a filter full of anti-gel additive. This is generally indicated by a reddish or pink colored wax-like substance covering the filter as much as ¼” thick. This wax-like substance will not readily melt at room temperature unlike paraffin wax that melts above 32°F.

In the past the general “Rule of Thumb” regarding using Kerosene (#1D) to “cut” #2 diesel was that for every 10% kerosene added to #2 diesel you would lower the Cold Filter Plug Point (CFPP) by approximately 5°F. So for example a 50%-50% blend of #2D and Kerosene would have lowered CFPP by approximately 25°F. The “new” ULSD #1 is far less aromatic and has much less solvency than did the old Kerosene. As a result the new ULSD #1 will only lower CFPP by 2°F-3°F. This means that a 50%-50% blend will only lower CFPP by 10°F to maybe 15°F.

If you have any comments or related incidents or problems, please post to this blog.

Doctor Diesel