U.S. fleets are starting to use 15-parts-per-million (ppm) ultra-low sulfur diesel (ULSD) fuel. This past summer, ULSD was in the pipeline; in September, it was available for delivery; on October 15, the diesel fuel was available for retail sales. Some 80 percent of diesel fuel available by Oct 15, 2007 will be ULSD, and 20 percent will be 500-ppm low sulfur diesel (LSD) with a target date of December 2010 for 100-percent ULSD availability. Off-road equipment will still use 5,000 ppm where available.
Afleet management concern is the cleaning characteristics of ULSD in removing deposits in fuel-tank infrastructure, the supplier delivery trucks, storage tanks, and fleet vehicle fuel tanks. These concerns are being met with increased-efficiency fuel filters on the infrastructure fuel pumps and on fleet vehicles.
Another concern is fuel filter change-out frequency cycles during the initial surge of early filter contamination and the subsequent relaxed change-out cycle as contamination is eliminated.
Still another concern is the new fuel’s reduced lubricity and current vehicle fuel system-ULSD compatibility. For decades, the transit industry has used #1 diesel, jet fuel, and kerosene with two- and four-stroke diesel engines to limit smoke emissions in urban environments and has not noticed premature injector and diesel fuel pump deterioration and/or failures. Differences are not expected,
but aftermarket suppliers will address this challenge in the rebuilding process.
Fuel Temperatures Present Concerns
Diesel fuel sold at temperatures above 60 degrees presents additional concern, since at that temperature, fuel economy statistics are impacted. Sixty degrees is the national standard for dispensing diesel fuel. When fuel at higher temperatures is introduced into a vehicle fuel tank, the physical quantity of the diesel fuel shrinks, affecting that vehicle’s mpg.
Most diesel fuel systems return fuel pumped through a vehicle with an ambient engine temperature of about 180 degrees to the vehicle fuel tank, again impacting fuel expansion, which is averaged with ambient fuel tank size and quantity, further influencing the expansion and conversion of the fuel quantity, affecting mpg readings.
Fuel pumped into the vehicle from above-ground tanks at temperatures higher than the vehicle fuel tank inventory temperature results in fuel quantity contraction and an increased cost per
gallon. That cost increase,multiplied by 5,000 gallons per vehicle per year, is a minor expense compared to 20,000 gallons per vehicle per year. Volume exacerbates the loss in mpg value.
2007 Inaugurates Engine System Changes to Meet Regulations
2007 will introduce diesel particulate filters (DPF), which will require cleaning by compressed air and/or fluids to wash out captured particles. Cleaning tools will cost $500-$5,000. DPFs will have a calculated location in the exhaust system to maintain and adequate +/- 900 degrees F. When mounted equipment is installed on the chassis, the DPF location cannot be altered since it would impact the DPF residual temperature and thus impair its performance, requiring
replacement due to clogged conditions.
Enter the diesel oxidation catalyst (DOC), located between the engine exhaust manifold and the DPF, for post-2007 system use called a selective catalytic reduction (SCR) process.
The DOC component is designed to have a catalyst, either diesel fuel or an ammonia product (urea), in a waterbased liquid solution sprayed into it to raise the exhaust temperature to 1,200 degrees F to burn and/or clean out the DPF. This process, known as aftertreatment or regeneration, lasts 20 minutes and requires continuously running the engine to clean the system. A dashboard light indicates the process is in operation.
To avoid burning the nearby ground, roadway, grass, and/or groundcover during the after-treatment cycle, a horizontal diffuser is installed at the end of the exhaust system to diffuse the exhaust
stream.
The exhaust gas recirculation (EGR) process is designed to cool
combustion chamber temperatures to reduce nitrogen-oxide emissions
(NOx). This system has existed since 2002, but has been ramped up to reduce the NOx level to meet the morestringent 2007 standards.
To keep increased exhaust gases in the cylinder, the exhaust valve is open longer and/or the single or multiple turbocharger pushes more of the exhaust through the air-to-air coolers into the intake process. While some manufacturers take the exhaust gases before the DPF, others take it after the DPF because the exhaust gas is cleaner
and cooler. Manufacturers choose single, double, or variable vane turbochargers to do this efficiently.
Fuel pressure has increased with each system design upgrade to efficiently increase fuel in the combustion process with a more-diffused injection spray into the cylinders.
These system changes increase engine compartment temperatures, so a
larger and more efficient cooling system has been designed and installed to keep temperatures under control for on-road vehicles.
Tier System Regulates Off-Road Vehicles
Off-road vehicles — yellow iron — have a similar program called a tier
system. Tier I, Tier II, and Tier III systems are for equipment with various horsepower engines. Lower horsepower units started in the mid 1990s with Tier I. The system has evolved to Tier III at the present time with the manufacture of higher horsepower engines.
Chart 1 indicates Environmental Protection Agency (EPA) expectations with Tier I to Tier III requirements. Tier IV standards for 2010 will be published in the near future.
