Recent changes in diesel engine technology have resulted in a much more complex diesel fuel and engine world than ever before. And that has brought with it a host of concerns. Fire apparatus are not exempt from these concerns.
One of those concerns is fuel injector deposits, including a new type of deposit, internal diesel injector deposits (IDID), which more likely to cause poor engine performance.
The diesel fuel slate has changed significantly in the last five to seven years. Ultra-low sulfur diesel (ULSD), introduced in 2006, now represents approximately 79 percent of all diesel fuel supplied in the United States.
ULSD fuel has different solubility behaviors than higher-sulfur fuels of the past. That means potential deposit-causing impurities in the fuel are less soluble in ULSD fuels; they are more likely to come out of the fuel and deposit on critical engine parts.
Biodiesel is now a significant part of the fuel landscape as the Renewable Fuel Standard mandated a minimum use of 1 billion gallons in 2012, and that amount grew in 2013 and beyond. Even good-quality biodiesel brings more complexity and the potential for additional deposit-causing materials to be present in the final fuel blend.
Engine manufacturers are bringing more sophisticated engine technology to the marketplace, that's partly in response to more stringent diesel exhaust emissions requirements. The newer common rail diesel engines (CRDE) inject fuel at very high pressures (30,000 psi and higher in some cases).
This high-pressure fuel injection provides a finely atomized spray for optimized combustion, as long as the engine's fuel injectors are operating properly as designed.
Vehicle operators, fuel marketers and engine manufacturers are increasingly seeing deposits forming on the internal parts of fuel injectors. If left untreated, these deposits can lead to power loss, reduced fuel economy and in extreme cases, increased downtime and higher maintenance costs due to premature replacement of stuck injectors.
These new deposits are primarily caused by certain common corrosion inhibitors used in the fuel reacting with trace amounts of sodium, causing salts that are less soluble in ULSD fuels than in the higher sulfur fuels of the past.
Why diesel fuel additives are needed
ASTM D-975 Diesel Fuel Specification is a very broad specification document, and as such all diesel fuels from different producers are not the same. The quality and chemical makeup of diesel fuels from different producers vary significantly due to a variety of crude oil sources.
This is even more important with the influx of various tar sand, shale oil and other heavier crude oils being refined into diesel fuels.
ASTM D-975 does not require the petroleum refiner to add any diesel fuel additives. Since the specification is very broad, the petroleum refineries need only to tweak their production cut points and perhaps add a small amount of specific chemicals to allow nearly all refinery diesel fuels produced to fit within the specification.
Those common rail diesel engines require the use of extra diesel fuel IDID detergents, stabilizers, corrosion inhibitors, deposit modifiers and lubricity agents in order to protect fine engine tolerances and ensure the integrity of the engine's performance.
Most diesel fuel producers and marketers add little, if any, of these chemistries to the diesel fuels they sell. The task of upgrading or improving the diesel fuel for better performance is left to the fuel purchaser and consumer.
Diesel fuels in cold temperatures
Winter diesel blend fuels are a combination of No.2 diesel fuel blended with ultra-low sulfur kerosene. Commonly used in the United States, this blend yields significantly less power production and substantially reduced fuel economy, which costs the diesel fuel user more money.
It also contains a lower BTU content, which costs much more compared with No.2 diesel fuel properly treated with the right winterization additives.
For a 30 percent diesel/kerosene blend, that additional cost can be roughly 15 to 20 cents more per gallon during the wintertime. Typically, that blended diesel fuel will deliver only about a 10 degree F drop in the cold filter plugging point, that is, the winter operability temperature reduction.
When diesel fuel surpasses this point, the wax crystals that result clog the fuel filter and starve the engine of fuel, preventing it from starting. The correct cold-flow improver fuel additives can achieve a better result for a cost of pennies on the gallon.
There is considerable agreement among additive manufacturers about the need for deposit-control additives (detergents) in all diesel fuels. This is especially true when considering the new common rail fuel injector (CRFI) engines being manufactured.
Fire departments should not expect that these additives will ever be used and added by the petroleum refineries — especially at the required high IDID dosage rates for CRFI engines — or any intermediate fuel terminal operators.
That's because the major pipeline operators controlling fuel distributions throughout North America are very concerned with carryover contamination to jet fuel deliveries. Hence, they do not allow diesel fuels with such chemistries to be put in their pipelines, a position unlikely to change anytime soon.
The unspoken word is that diesel fuel additives with the proper level of detergent most likely have to be added very close to the point of sale, if not at the point of fuel consumption. This task will need to be taken on by the end user — the fire department.
Better diesel engine performance
ASTM D-975 only requires a minimum 40 cetane engine number. Cetane engine number, or CN, indicates the combustion speed of diesel fuel. It is an inverse of the similar octane rating for gasoline.
Increasing the diesel fuel's CN, by adding a cetane improver additive, can enable the engine to achieve better combustion efficiency of the diesel fuel and increased brake horsepower.
But, the petroleum refineries generally add only enough cetane improver additive to ensure their finished diesel fuels meet the minimum requirement of 40 CN. And, they do not generally add it to raise the CN anywhere near 50 and above.
So, the task of enhancing the diesel fuel's CN is left to the buyer and end-user.
There is some disagreement on this point with at least one fuel additive manufacturer saying that there's no additional engine performance benefit once the CN rating exceeds 52. If that's true, then why is the current European Union CN specification for diesel fuel slated to jump from 51 (EN 590:2009) to a minimum of 55?
Most diesel fuel in the United States is manufactured and delivered to the market with typical CN of between 43 and 46. How are the European diesel engines requiring a CN greater than 50 being imported into the U.S. markets expected to operate properly?
Particularly for those fire departments that operate European-manufactured fire apparatus, cetane improver additive will need to be added to diesel fuels; using the additive could improve the performance of diesel engines manufactured in the U.S.
Several diesel engine manufacturers have voiced a strong desire to see the American CN standard increased from the current minimum 40 to a minimum 50. However, the reluctance by U.S. petroleum refiners to increase the cost of their fungible diesel fuel products means that using a CN improver additive falls to the diesel engine fleet owners.
There are many good diesel fuel additives on the market, but no additive can do everything. Know what you want and need.
For many years, business teachers have taught their students that they can have the best quality and the best service for the best price. The kicker is that they can expect to have two out of the three, but not all three, at the same time.
The same is true of diesel fuel additives and really any fuel additive. You can have something that does a lot of things, does them very well or effectively, does them at a very low treatment ratio, and does them for low cost. You can have some of these, but typically not all of these together.