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2007 Diesels: New Fuel, New Oil

New for 2007, all on-highway diesel engines must use Ultra-Low Sulfur Diesel (ULSD) fuel. That is not just for the Class 8 over-the-road semis. This federal mandate includes the diesel engine used in the Class 2 pickups and cargo vans and Class 3 step vans, and walk-in vans. This also includes snowplows, command buses, SWAT vans and tow trucks.

Even the Ford F-250 pickup with a diesel? Yes. The new federal emissions laws do not distinguish between light-duty and heavy-duty, nor do they allow exemptions for diesels in passenger cars or for law enforcement. Remember the huge changes when the nation went from leaded gasoline to unleaded gasoline? It is that kind of change for diesels.

The new diesels now have a catalytic converter-like after-treatment device (ATD), i.e., a catalyst and a filter, that needs occasional service. They require the use of ULSD fuel. They also require a new class of engine oil, CJ-4.

These changes impact virtually every police fleet manager. And, these changes affect every driver of a 2007 model year diesel...you have to be careful to use the right fuel because there are no nozzle diameter changes to prevent mistakes! Of course, the drivetrains cost more—from $2,000 to $7,000 more. And the ULSD fuel is more expensive and so is the CJ-4 engine oil.

The 2007 EPA emission regulations are aimed at reducing NOx emissions (acid rain) and particulates (soot). These regulations involve changes to the engines, changes to the fuel and changes to the engine oil. First, the new diesel fuel.


Sulfur is an emission enabler, i.e., it causes the kind of emissions that are harmful to the environment. Low sulfur fuel, with 500-ppm sulfur, is already in use across the country. That is the green label with yellow lettering and the code S500, i.e., Sulfur 500 ppm.

Ultra-Low Sulfur Diesel has 15-ppm sulfur, a 97% reduction. That is the green label with white lettering and the code S15, i.e., Sulfur 15 ppm. With limited refining capacity, most refiners plan to only make ULSD. This is required in all 2007 model diesels and can be used in all other model years of diesels. ULSD fuel entered the pipeline distribution system June 1 and will be widely available by Oct. 15. The use of ULSD is required by Jan. 1, 2007.

ULSD has given rise to a number of concerns, some valid and some not. The first concern, as with the transition away from leaded gasoline, is lubricity. Sulfur is a lubricant. Fuel with less sulfur may cause more fuel pump and injector wear.

More of a concern for over-the-road semis than police pickup trucks, the major fuel suppliers have committed to maintaining lubricity of low sulfur diesel with ultra-low sulfur fuel. This may mean a lubricity additive will be put in at the pipeline distribution terminals. It does not mean an after market additive is required. In fact, such aftermarket products are strongly discouraged.

Another concern is elastomer (O-ring) compatibility. ULSD fuel is compatible with current hoses, O-rings and other plastic and rubber parts.

The real challenges with ULSD fuel, however, are a potential loss in fuel economy, a potential reduction in horsepower and an increased cost of the fuel. ULSD has a higher cetane number than conventional diesel, meaning that ULSD fuel is easier to ignite. However, ULSD has a lower BTU, meaning that it has a lower energy content.

At this early point, the EPA is predicting a 1% loss in fuel economy, which, given the accuracy of other EPA mileage ratings, could be a 5% loss. The EPA is predicting a $0.05 per gallon increase in the ULSD fuel but no change in horsepower or torque.

Like the use of leaded gasoline damaging catalytic converters, the use of low sulfur diesel (instead of ULSD fuel) may damage the after-treatment devices. This will clog the filter faster, increase backpressure, reduce power, and also increase emissions. The use of the wrong diesel fuel is also a serious warranty issue.

Unlike the change to unleaded gasoline, the change to ULSD fuel does not involve a change in nozzle size to prevent the use of low sulfur fuel in ULSD vehicles. Unlike diesel fuel with a red or blue tint, ULSD fuel is water white, or clear. All vehicles that require the use of ULSD fuel have prominent labels calling for such.

Powertrain Changes

The diesel engines using ULSD fuel will have minor changes using technology introduced in 2002. These changes basically mean the use of a closed crankcase ventilation and double the amount of exhaust gas recirculation. More exhaust gas put back into the combustion chamber means more soot. And that calls for an after-treatment device, ATD.

The ATD replaces the muffler. The ATD is made up of two parts, the diesel oxidation catalyst and the diesel particulate filter. The filter is a ceramic honeycomb that traps unburned soot and non-combustible ash, i.e., particles. As exhaust gases pass through the ATD, it burns off most of the soot and filters out most of the ash. To get the terms correct, soot is combustible. It is partially burned diesel fuel. Ash is non-combustible. It comes from burning slight amounts of the engine oil.

The catalyst generates heat to burn off combustible soot collected in the filter. It uses three types of regeneration to do this. Passive regeneration takes place during normal driving activity when everything is flowing and up to normal operating temperatures.

Active regeneration occurs when the exhaust temperature is too low to trigger passive regeneration. The engine’s motor control module detects a build-up of backpressure as the carbon loads up the filter. It then injects a richer fuel mixture into the exhaust. This fuel burns in the catalyst, which forms the necessary heat to burn off the trapped carbon.

The third mode is the forced/stationary regeneration. While rare for over-the-road semis, this may be commonplace on stationary command buses and SWAT vans. The driver needs to manually activate this regeneration, which raises the engine RPM to the point where the exhaust gases are hot enough for regeneration.

While there is no flame involved in regeneration, the catalyst does produce higher exhaust temperature during this process. Externally, the after-treatment device runs as hot as a muffler, or about 500 deg F.

The catch is this diesel particulate filter needs occasional service to remove the ash from the filter. Plugged or dirty exhaust filters, of course, result in more backpressure and poor engine performance. Of course, special equipment, ranging from $8,000 to $50,000 is required to clean these filters. Federal law requires that these filters last at least 150,000 miles between cleaning. The ash removed from the filter is not considered a hazardous waste and may be disposed of in a conventional way, i.e., landfill. Engines that burn a lot of oil or engines that use the wrong oil may plug the filter faster. The correct engine oil simply MUST be used.

CJ-4 Motor Oil

Changes to the diesel engine drivetrain require changes to the engine oil. The latest API oil category is CJ-4, previously referred to as proposed category 10 (PC10). CJ-4 replaces CI-4 Plus engine oil. This new classification of diesel engine oil also meets the API class “SM” for gasoline engine oil. It is available in 10W-30 and 15W-40.

The CJ-4 engine oil is a critical part of the 2007 diesel powertrain for a number of reasons. The new engines run hotter as a result of increased use of exhaust gas recirculation. This 5- to 10-degree increase makes a huge difference in oil performance. The CJ-4 oil has greater resistance to thermal breakdown than CI-4 Plus oil.

More exhaust gas recirculation also means higher levels of soot. So, for the first time, limits are put on the amount of Sulfated Ash, Phosphorus and Sulfur (SAPS) contained in the oil. The result is low SAPS oil, which has been used in Europe for a number of years.

This CJ-4 class of oil has improved wear resistance, improved soot handling and improved piston ring deposit control compared to CI-4 Plus oil. It is better oil. Most of all, CJ-4 oil is compatible with the after-treatment device filter and catalyst. The older oils are not. The higher ash oils plug up the filter faster. The higher sulfur oils increase emissions.

The good news is that both the CJ-4 oil and the ULSD fuel are backwards compatible. Both can be used on older model year diesel engines. Bulk oil and bulk fuel tanks can be converted to the new products simply by using the old oil or fuel to less than a quarter full and refilling with the new oil or fuel. The fourth fill meets the standard for tank conversion.

The oil drain interval for CJ-4 oil, following the OEM recommendations, is the same. For fleets with extended oil drain intervals, an oil analysis like Shell Analyst™ should be performed. For more information on Ultra-Low Sulfur Diesel, after-treatment devices or CJ-4 (low SAPS) oil, contact Shell Oil officials via e-mail at info@shelltechtour.com, or visit their Web sites.

Published in Police Fleet Manager, Sep/Oct 2006

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