The University Record, February 27, 1996
U report: 'Real-world' EPA regulations and high-quality emissions control systems are the secret to cleaner air
By Sally Pobojewski
News and Information Services
New EPA tailpipe emissions standards based on real-world data and high-quality emissions control system technology in new cars could cut the amount of smog-generating chemicals spewed into the atmosphere from automobile exhaust by as much as two-thirds, according to a U-M report.
"Automotive emissions of carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) are major factors in urban air pollution," says Marc Ross, professor of physics, who led the five-person research team. "Progress has been made to reduce these emissions over the past 25 years, but vehicle travel continues to in crease. Unless we make additional reductions in gram-per-mile emissions, much of this progress will disappear."
Results from the U-M emissions study were presented Feb. 26 in Detroit at the SAE International Congress & Exposition by Robert Goodwin, graduate student in physics, and Tom Wenzel from Lawrence Berkeley Laboratory. Additional members of the research team are Rick Watkins from the U-M and Michael Q. Wang of Argonne National Laboratory.
The researchers analyzed 1993 model car emissions data from several sources---including automotive manufacturers, the U.S. Environmental Protection Agency and the California Air Resources Boardto determine the source and quantity of auto emissions produced during different driving situations. They then projected the 1993 grams-per-mile emissions to estimate emissions for model years 2000 and 2010.
"There is a big difference between emission levels generated when cars were driven under real-world conditions and the official data produced during the controlled Federal Test Procedure (FTP) mandated by the EPA," Goodwin says. "Actual emissions of carbon monoxide and hydrocarbons from 1993 cars on the road today are about five times higher than the FTP tailpipe standard and actual N0x emissions are about twice the standard."
"Two factors---off-cycle driving and malfunctioning emissions control systems---were responsible for most of the additional pollutants," Ross adds.
Driving "off-cycle" means driving at higher engine power levels than those specified in the testing procedure manufacturers use to certify that new cars are in compliance with federal emissions standards, according to Ross. During this procedure, new cars with laboratory-aged catalysts run on a dynamometer, while the exhaust is collected in bags for analysis. The test requires a precise speed-time sequence. Cars never accelerate more than 3.3 mph and never reach speeds above 57 mph.
Today's drivers routinely accelerate faster and use higher power levels than those in the federal test procedure, which has not changed since the 1970s. To allow drivers to travel 65-plus miles per hour while pulling a trailer with the air-conditioner set on maximum, automotive manufacturers build in something called command enrichment.
"Extra fuel is introduced to cool the engine and catalyst during high-powered driving," Goodwin explains. "To do this, you have to override the emissions control system. Every time this happens, the rate of carbon monoxide emissions jumps by 1,000 times or more."
"Even though most people only drive from 1 percent to 5 percent of the time under command enrichment, it accounts for nearly half of all carbon monoxide emissions and 10 percent of all hydrocarbons," Ross says.
Because command enrichment is responsible for such a large portion of total auto emissions, the U-M report recommends the EPA adopt its proposed new regulations, which could require auto manufacturers to delay the onset of command enrichment slightly and cut back on the amount of extra fuel used.
The largest single pollutant source identified in the report was malfunctioning emissions control systems (ECS), often caused by damaged catalytic converters or failure of the oxygen sensor which controls the fuel-air ratio.
"Vehicles with malfunctioning ECS were responsible for almost half of the total emissions we analyzed," Wenzel says. "We found no evidence to support the common belief that these malfunctions are caused by owner or mechanic abuse. The incidence of ECS malfunctions in five-year-old cars varied from virtually zero to almost 30 percent, depending on the make and model of the vehicle. This supports our view that the problem originates with the manufacturer, not the owner or mechanic."
New remote sensing and on-board diagnostics technology will soon make it possible to identify ECS malfunctions as soon as they occur, according to Wenzel. "If these new technologies are used to identify malfunction-prone models and if manufacturers are encouraged to produce cars with consistently high-quality ECS, then substantial emissions reductions can be achieved by 2010."
The report was funded by the University, the Energy Foundation, Lawrence Berkeley Laboratory and Oak Ridge National Laboratory.