The 2007 model year diesel engines will feature fuel systems optimized for use with ULSD. The EPA is proud of this accomplishment: it is the first time that a fuel and engine have been harmonized to work together to reduce emissions and optimize performance. The key difference is that 2007 HDHR engines will utilize higher injection pressure and multi-injection capabilities, which allows further engine-out emission reductions.
PARTICULATE MATTER FILTERS
Diesel particulate matter filters are ceramic devices that collect particulate matter in the exhaust stream. The high temperature of the exhaust heats the ceramic structure and allows the particles inside to break down (oxidize) into less harmful compounds. They can be installed on new and used buses, but must be used in conjunction with ultralow sulfur diesel. The combination of PM filters and ULSD can reduce emissions of PM, HC and CO by 60 to 90 percent.
Beginning in 2007, PM filters will be standard issue on all diesel vehicles. However, PM filters are also available in a kit to retrofit older buses - though most work best on engines built after 1995. The cost of the kit can range from $5,000 to $10,000, but some buses may need the more expensive filters to compensate for lower exhaust temperatures.
EXHAUST GAS RECIRCULATION
Exhaust gas recirculation (EGR) systems reduce exhaust emissions that are not being cleaned by the other smog controls. Oxides of nitrogen (NOx) are produced when an engine gets too hot, but NOx formation can be reduced by recirculating some exhaust gases.
An EGR system recirculates exhaust into the intake stream. Exhaust gases have already combusted, so they do not burn again. Instead, they displace some of the normal intake and cool the combustion process by several hundred degrees and reduce NOx formation. These systems must precisely control the flow of recirculated exhaust: Too much flow will retard engine performance and cause a hesitation on acceleration. Too little flow will increase NOx and cause engine ping.
Manufacturers are predicting that the 2007 changes will not affect fuel economy. There are also no concerns about power. However, drivers may find a new chore - cleaning the ash from PM traps every 150,000 miles. Nonetheless, the arrival of the 2007 compliant buses will mark one very important departure: the belch of black smoke and fumes that used to characterize all diesel engines will be no more.
For 2010, more advanced NOx aftertreatment and Urea-SCR systems on transit buses will yield another 80 percent emission reduction over the 2007 technology (which already cut pollution in half). Urea-SCR systems are available in Europe and as a retrofit today, so while there are some concerns about how to keep the systems filled, the EPA is confi- dent those problems will be worked out by the time they are in vehicles. Right now, a Urea-SCR system needs to be re-filled every second to third fill-up, but industry is working on alternatives.
Because of the advances in vehicle technology catalyzed by the HDHR, passenger trucks and cars will also benefit, and themselves become more environmentally friendly.
Automakers also envision a cleaner, more efficient future for their vehicles. In the past year alone, several automakers such as Ford, DaimlerChrysler and GM have announced plans to bring new, clean diesel cars, pickup trucks and delivery vehicles to the market.
And industry is only part of the story. As technology innovations driven by the EPA's clean diesel program spreads to cars, since diesel engines tend to be more efficient than gas engines, our nation's energy security will be strengthened. This smart fuel use is part of President Bush's strategy for helping America jump off the treadmill of dependency on foreign sources of oil.
The 2007 Heavy Duty Highway Rule is only part of the story when it comes to the advances made by the EPA to make diesel engines cleaner. The SmartWay Program, a voluntary partnership between the freight industry and the EPA to promote fuel efficiency has recently added a new facet: SmartWay Grow & Go, which focuses on renewable fuels. One of the fuels it will promote, biodiesel, can be used by any diesel engine, regardless of the freight it is carrying.