Cleaning Up Diesel Pollution - Union of Concerned Scientists

Cleaning Up Diesel Pollution l 21LUBRICATING OILSWhat are they? Oils used to lubricate heavydiesel engines can generate particulate emissionsin two ways. First, the metallic portion of the oil,which cannot be burned, produces ash. Second,oil that evaporates in the crankcase and diffusesinto the combustion chamber produces soot(DieselNet, 1998). Replacing metal additives withnonmetallic compounds should thus reduce theamount of ash generated, and using synthetic oils,which can be formulated to evaporate only withina narrow, high-temperature range, may alsoreduce particulate matter.Current use and outlook: Lubricating oils arenot currently regulated by the EPA. Filling thisregulatory gap could prove a sound strategy forreducing particulate emissions, particularly fromolder vehicles that do not have to meet morestringent emissions standards.CLEANING UP NEW ENGINESA number of technologies for cleaning up newheavy diesel equipment are currently available orunder development. New systems combining exhaustgas recirculation, advanced turbochargers,and advanced fuel injection are already being usedin today’s highway vehicles, while technologiesto reduce nitrogen oxides, such as nitrogen oxideadsorbers and selective catalytic reduction, arein the development phase.Engine modificationsEXHAUST GAS RECIRCULATIONWhat is it? Exhaust gas recirculation (EGR)returns a portion of the engine’s exhaust to thecombustion chamber. In the process, nitrogenoxide emissions are reduced because inert gasesdisplace some of the oxygen that would otherwiseenter the engine. Cooling the exhaust gas before itenters the combustion chamber can reduce emissionseven further. However, EGR may increaseparticulates and engine wear while lowering fueleconomy (DieselNet, 2000). Sulfur in the dieselfuel also poses a corrosive threat to the system.Current use and outlook: EGR has been a keystrategy for manufacturers attempting to complywith the EPA’s stricter nitrogen oxide standardsfor highway trucks and buses (which most manufacturershad to meet by October 2002). CooledEGR will also be a likely necessity for manufacturersof heavy diesel equipment between 100and 750 hp in order to meet Tier 3 standardsstarting in 2005.ADVANCED TURBOCHARGERSWhat are they? Turbochargers are compressorsused in many types of diesel engines to increaseair pressure. Utilizing the engine’s exhaustgas and a turbine, turbochargers increase enginepower by increasing the amount of air inductedinto the engine. Unfortunately, in rapid accelerationor stop-and-go conditions, diesel engines areoften fuel-rich (too much fuel and not enoughair), resulting in unburned emissions of hydrocarbons,carbon monoxide, particulates, and smoke.In turbocharged engines, this fuel-rich period,called turbolag, also wastes fuel and lowers fueleconomy. Advanced turbochargers (e.g., variableSpecial Requirementsof Smaller EnginesEngines rated below 75 hp will require adjustmentsin the form of electronic controls, turbochargers,or advanced fuel injection systems in order to employadvanced emission controls for nitrogen oxides andparticulate matter. Nitrogen oxide adsorber catalysts,for example, require engines to modulate between leanand rich operation. Packaging these systems to ensurethat functionality is not compromised will also requirespecial engineering.