Fuel School

Diesel and Middle Distillate Fuels 2011

Diesel fuel is defined as a mineral fuel oil for diesel engines and is part of the larger grouping known as middle distillates.

Middle distillates including kerosene, diesel, and heating oils are derived from crude oil using Atmospheric Distillation, Vacuum Distillation, Hydrotreating, Hydrocracking, Fluid Catalytic Cracking, and other methods.

This is important because within the consuming public there is a misunderstanding that diesel in particular is a homogenous product that has the same quality and characteristics everywhere. This is not the case; diesel fuels are refined from crude oils of different origins with different characteristics, different compositions, and different qualities. This refining takes place in refineries of different design and widely different capabilities, run by companies and people with vastly different competencies, that are trying to produce products to meet an ever changing customer, financial, and regulatory environment.

The result is the fuel you get can vary significantly from place to place and even from day to day in the same place.

Also now due to regulatory and environmental concerns the addition of biofuels to much of the diesel supply adds a whole new level of complexity because the base stocks and production characteristics and quality vary drastically. The addition of these biofuels has many implications and produces many problems for users of diesel and heating fuels.

This is important because the newest engines are being designed to run on laboratory grade diesel fuels that are close to perfect. The “perfect” fuel does not exist in the real world. They are also being evaluated for operability, reliability, performance, and emissions in near perfect conditions under ideal duty cycles. This produces engines that have excellent characteristics under ideal conditions, but that often perform less well under real world conditions.

Fuel Additives and Supplements are used in many processes in the drilling, production, crude transportation, refining, product transportation, storage, and ultimately use of fuels.

Without these Additives and Supplements there is no usable fuel.

For our purposes we will mainly be discussing post refining use of these products.

Fuel Additives and Supplements provide many necessary and beneficial characteristics including detergency to prevent the buildup of gums, varnishes, and carbon deposits in fuel tanks, fuel lines, pumps, filters, injectors, on and around valves, pistons, piston rings, exhaust gas recirculation (EGR’s) valves, computer sensors, turbochargers, diesel particulate filters (DPF’s),catalytic particulate traps (CPT’s), selective catalytic reduction (SCR) units, and other places; antioxidants to improve oxidative stability which slows or limits the reaction of oxygen in producing gums and otherwise breaking down fuels during production, transportation, and storage; thermal stability (typically called metal deactivators) to slow or limit the breakdown of fuels during high temperature storage and when recirculated during the operation of a diesel engine; corrosion inhibitors to limit or prevent the corrosive action of the fuel on soft metals, plastics, and rubber; biocides to kill and or prevent the growth of biological agents in fuels; cetane improvers to improve the compression ignition characteristics of the fuel when used in diesel engines; anti-icing agents to prevent the formation of ice crystals in fuels; cold flow improvers (anti-gels) to lower the temperatures at which one or more of the following takes place: cloud point (CP), cold filter plug point (CFPP), or pour point (PP); lubricity improvers to increase the lubricating ability of fuels used in diesel engines; fuel conductivity improvers or anti-static agents to prevent the buildup of static electrical charges in fuels (an explosion hazard) during transportation and loading and unloading; wax anti-settling agents to prevent waxes from falling out of solution during extended cold weather; water dispersion to remove water, limiting formation or gums, varnishes, carbon deposits, corrosion, and icing, atomization improver to improve fuel atomization by injectors and burner nozzles.

A Brief History of Diesel Fuels with EPA Mandated Changes

Petroleum derived diesel fuel was originally created through Atmospheric or Straight Run Distillation where crude oil is heated until vaporization takes place and then condensed into various components.

The EPA began regulating diesel fuels in 1993. Prior to this time diesel fuel, kerosene used in On-Highway, Off-Highway, Locomotive and Marine fuels plus Home Heating and Industrial Fuel Oil’s were unregulated by the EPA. Diesel fuels had sulfur contents of up to and sometimes exceeding 5000 ppm.

The initial regulations taking effect in 1993 were designed to reduce sulfur content in on-highway fuels to 500 ppm or less. At this time the original fuel with a sulfur content greater than 500 ppm was termed High Sulfur Diesel (HSD) and fuel with 500 ppm or less was termed Low Sulfur Diesel (LSD) fuel. In June of 2006 On-Highway Diesel fuel changed to Ultra-Low Sulfur Diesel (ULSD) with 15 ppm or less sulfur content.

In Europe they followed a similar path to reach what they now call no sulfur (10 ppm or less) fuel.

While HSD was banned from use in On-Highway vehicles in 1993, Non-Road (NR)(Off-Highway) and Locomotive and Marine (LM) or combined (NRLM) users were allowed to continue to use this fuel until June of 2007 when NR changed to LSD and then in June of 2010 when it changed to ULSD.

LM users were changed from HSD to LSD in June of 2007 and will change to ULSD in June of 2012.

Engines designed to run on HSD or LSD tend to suffer from lubricity problems when converted to ULSD. These problems include Buna and Nitrile O-Ring and Seals commonly used in those engines will dry out, shrink, and crack when sulfur content of the fuel is reduced. Also, the lower lubricity (lubricating ability) of ULSD causes rapid wear of pumps and injectors due to the lower quality metallurgical and hardness characteristics of these components in those engines.

The NR users are now seeing problems with existing equipment from the change to ULSD. It is expected that LM users will have significant problems with the change next year.

These problems tend to be more pronounced in construction, agricultural, prime power, standby power, locomotive, and marine equipment and engines that typically have a much longer service life and can be far more expensive to replace than is typically seen in On-Highway Trucks.

Europe:

In Europe similar regulations exist (they were several years ahead of North America in promulgating and implementing these rules) and although they have in the past produced fuels superior to those found in North America, they are having significant difficulties due to changes both regulatory and market driven.

In the market driven category the North Sea Oil Fields have now peaked in production and are being a long slow decline. One of the results is that crude is now being imported into several countries from other regions of the world. This imported crude is often of lower quality and is more difficult to refine in existing refineries.

Another issue is that North Sea field’s decline they tend to produce more of the lower quality crudes. The problem with both these North Sea and imported crudes is that most of the refineries in Europe were designed and built after World War II to operate on high quality (light sweet) crudes. These refineries are not as flexible as those in North America and they have trouble processing lower quality crude oils.

Also, in countries such as Germany that have little crude oil, they have developed coal gasification to produce synthetic diesel fuels from domestic coal supplies. While this fuel has some good characteristics, it is very problematic in the area of engine and fuel system deposits.

In the regulatory category there are several mandates in place requiring that given percentages of biodiesel be blended into all of the diesel fuel sold. In the UK it started at 5% and is now going to 7%. There are a number of issues with these fuels such as base stocks and production methods. In the North America most biofuel is produced from soybean oil, with small amount from used cooking oils. In the EU, Rapeseed oil was long considered the standard; however we are seeing more and more Palm Oil which is readily available from many sources at lower cost. However the fuel derived from this oil is very highly saturated and as a result hard to work with. It has very poor cold weather characteristics and combusts less well than other lighter oils.

As a result, the European OEM’s and consumers, who 5 years ago didn’t believe in additives for their fuels, are now becoming educated to the fact that they do need them.

OEM’s have designed and built fuel systems and engines for fuels of a very high quality. Also, as more and more cars are built using diesel engines the balance between diesel and gasoline is rapidly shifting to a diesel bias. Most of their refineries were built primarily to make gasoline and they are having difficulty switching to making more diesel.

As a result Europe is now and will continue to see more of the problems we have seen in North America for many years.

A typical refining process in 2011:

It is important to understand that refiners today are trying to obtain the highest yields of the most profitable products created during the refining process and do so while using the least expensive crudes that their refineries can process. The product streams (different products or product components) produced by a refinery can be adjusted or managed through the changes in the refining process and through the use of chemicals and catalysts to produce more or less of a given item. For example many refineries in the US are primarily interested in producing gasoline as it is usually the most profitable and highest volume product. In order to do this they may produce a diesel fuel with less desirable characteristics.

A refinery designed to produce high quality lubricants from crude with levels of paraffin wax may produce diesel with an unusually high wax content which in the summer is great (more wax equals more Btu’s), however in cold weather this fuel can be very difficult to use as it gells at a much higher temperature than normal fuel would.

In the US market most diesel and gasoline is called fungible which means it equivalent. Diesel and gasoline are produced to “Pipeline” spec so that fuel entering a pipeline as for example diesel #2 in any of the half dozen refineries in East Texas can be sold as Diesel #2 under any brand all the way up the East Coast of the US. The only thing that differentiates one brand from another is the additive package added during the loading of the truck that delivers it.

What this means is that refiners are trying to make the least expensive product possible that will still meet those very minimal fungible (pipeline) specs.

Now the other side of the coin, the diesel engine.

Diesel engines have evolved at an incredible pace over the last decade or so. We have seen them go from a large, heavy, noisy, smelly, black smoke belching engine used in trucks, construction equipment, railroads, large ships, and other heavy duty uses to an ultra-clean, efficient, quiet powerplant suitable for everything from the smallest automobile to the largest truck and even larger.

Regulatory and market driven forces have brought about these changes and although primarily positive in nature, there have certainly been some negative consequences such as far great cost of purchasing, operating, and maintaining these engines; the need for nearly complete computer control of the fuel and emissions systems, the addition of many expensive and somewhat delicate sensors to support the computers, the difficulty in training personnel to maintain and repair these complicated engines and their support systems.

Whereas twenty years ago a diesel engine was almost bullet-proof in that with relatively minor maintenance they could run on almost any fuel available. They could be expected to idle indefinitely then go to full power and stay there with no negative consequences. Engines with oil changes intervals as high as 50,000 miles (under proper monitored conditions). The fuel systems with fuel filters not much more sophisticated than a gym sock could handle very poor quality fuels with minimal problems. Exhaust systems consisted of some 3-5” pipe and a $100.00 muffler, no EGR valves, no DPF’s, CPT’s, or SCR’s.

This was a time where you could buy a brand new 350 horse engine in the crate for $12,000.00. How different things are today, when six fuel injectors can exceed that $12,000.00 amount. Today we have to deal with fuel system pump and injector tolerances of less than 2 microns (a human hair is 80 to 100 microns thick), we have systems to divert, cool, and re-inject exhaust gases into the intake air for emissions, the $100.00 muffler has been replaced by DPF’s, CPT’s, and SCR’s worth many thousands of dollars, and all of which require expensive and time consuming maintenance, we have computer controls that do amazing things, but which also cost thousands of dollars to buy and maintain.

One of the most interesting things to consider is that we are trying to operate these engines on fuels that are far poorer in quality than the Original Equipment Manufacturers (OEM’s) suggest or require.

For example; the Cetane rating of most fuel sold in the US is 40, the American Society for Testing of Materials (ASTM) minimum. However virtually every OEM owners/operators manual suggests or requires a Cetane rating of 45 or above; the ASTM minimum for diesel fuel lubricity is HFRR (High Frequency Reciprocating Rig) 520, whereas the Engine Manufacturers Association (EMA) and nearly every OEM owners/operators manual suggests 460 or better (lower number show greater lubricity); ASTM allowable water content is approximately four times greater than OEM specs. We know we have injection system components with less than 2 micron tolerances yet we still use fuel filters that only protect to 10 microns because the quality of the fuel is so poor they will plug rapidly when smaller media is used.

We know that these fuels are causing many problems in the field not seen in the lab. Some examples are particulate formation caused by poor or incomplete combustion of the fuel. These particulates form deposits on and around the fuel injectors, exhaust valves, piston rings, piston ring lands, piston crowns, EGR valves, EGR coolers, turbochargers, DPF’s, and CPT’s.

These deposits cause a wide range of problems including; poor performance, poor fuel economy, poor operability, higher emissions, EGR Valve plugging and performance issues, EGR Cooler plugging, active and manual CPT regeneration required far more often than desired, the need for removal and manual cleaning of CPT’s far more often than should be necessary, damage to turbochargers, coating or damage to engine and emissions sensors.

Stability, both Oxidative and Thermal is related to contents of the crude oil and the various refining processes used today. This less stabile fuel deteriorates or breaks down rapidly causing the formations of gums, varnishes, and carbon deposits which in turn can cause or exacerbate problems of incomplete combustion.

Cetane Rating is a measure of how quickly a fuel will auto-ignite under compression. In diesel engines sooner is generally better. The 40 rated we fuel we use makes cold starting much harder, creates clouds of white smoke until the engine warms, makes the engine very loud, and limits the performance characteristics of any engine it is used in.

Raising Cetane makes an engine easier to start (particularly in cold weather), allows it to warm up faster, makes it quieter, allows the engine timing to be advanced which makes the engine more efficient for better mileage, performance and lower emissions.

Detergent, contrary to popular belief there is no requirement for detergent in diesel fuels in North America. There is very poor detergency in North American fuels. This leads to many of the combustion quality issues we see.

There is no actual liquid water spec for fuel. It is generally agreed that there shouldn’t be any liquid water, but no real requirement. Permissible Dissolved Water level is unacceptably high resulting in gum formation, corrosion, and biological growth problems.

With the 2008 change to D975 the ASTM specification for diesel fuel that now allows up to 5% biodiesel to be added to #2 fuel without notification provided to the purchaser, there are new layers of complication being added to existing problems.

Biodiesel is very hygroscopic and is capable of holding as much as 1% dissolved water, approximately 10 times that of Ultra Low Sulfur Diesel (ULSD). This ability to hold water can and does lead to more aggressive gum formation, more corrosion problems, and greater problems with biological growth in fuels. Biodiesel also has less Btu’s per gallon and as it is based on a plant oil or animal fat, will turn rancid when stored for long periods. It produces higher levels of NOx when burned.

When biodiesel is blended with regular diesel it acts to destabilize the fuel and worsens its cold weather characteristics. The use of blended biodiesel becomes more problematic based on several factors including the base stock from which the biodiesel is made, the type and quality of the processes being used to produce the biofuel, the level of dissolved water, the Free Fatty Acids (FFA’s), the percentage of the biofuel blended with the petroleum diesel, the quality of the petroleum diesel being used, and the conditions and temperatures involved when the blending takes place.

Where all this leads is to the need for Supplemental or Remedial Additization in all diesel and heating fuels.

Under the current regulations and market conditions the quality of the fuels being produced and offered for commercial applications and to the general public does not meet the requirements or needs of the engines and emissions control systems being sold and used.

It is possible to Supplement or Remediate through Additization nearly all fuels to meet or exceed those requirements and needs.

It is cost effective for an end user whether commercial, industrial, railroad, marine, or the general public to Additize their fuels to Supplement or Remediate them to necessary levels.