Comparison of emissions in heavy-duty diesel trucks

Dr. Neil Canter, Contributing Editor | TLT Tech Beat August 2012

New study tested five trucks over a three-year period using a portable emissions measurement system.

KEY CONCEPTS
• Emissions generated by five trucks from model years 1999, 2005, 2007, 2009 and 2010 were studied through the use of a portable emissions measurement system.
• Most of the trucks studied were driven with both ultralow sulfur diesel and 20% biodiesel.
• Emission controls added to ensure compliance with EPA’s increasingly strict regulations are working as particulate matter and NO_x dropped by 90% when comparing the 1999 and 2010 model year trucks.

VEHICLE EMISSION REMAIN A MAJOR CONCERN as the lubricant industry is playing an important role in developing engine oils to minimize this problem as much as possible. One relatively new factor that needs to be dealt with is the growing use of biofuels.

In a previous TLT article, automobile emissions were monitored in five U.S. cities over a 10-year period (1). Infrared and ultraviolet light techniques were used to monitor the levels of carbon monoxide, carbon dioxide, hydrocarbons and NO. The study found that emissions in these cities declined over the decade in which they were monitored. One interesting aspect was that emissions from older vehicles remained relatively stable.

The EPA has placed more stringent regulations on the emissions of diesel vehicles, particularly for particulate matter and NO_x. For the former, EPA established a standard of 0.1 g/bhp-hr (brake horse power per hour) between 1998 and 2006. This figure has been reduced to 0.01 g/bhp-hr since 2007.

In the case of NO_x, the initial requirement was 4.0 g/bhp-hr between 1998 and 2003. This figure dropped to 0.2 g/bhp-hr, which was phased in between 2007 and 2010.

The change in today’s standards suggests that emissions for heavy-duty diesel trucks have declined compared to the mid-1990s. Dr. Chris Frey, professor of civil, construction and environmental engineering at North Carolina State University in Raleigh, N.C., says, “Some questions have been raised about whether there is need to do a study to confirm that emissions from heavy-duty trucks have in fact declined. We found that past studies on trucks were highly variable.”

This factor led Frey to develop a more effective and economical way to measure truck emissions. Such an approach provides a better way to assess how the changes in emissions regulations have impacted the level of emissions generated by trucks.

PORTABLE EMISSION MEASUREMENT SYSTEM
Frey, in collaboration with Gurdas Sandhu, a graduate student, has measured the emissions generated by five trucks over a three-year period. The trucks were from model years 1999, 2005, 2007, 2009 and 2010. Frey says, “We did the study in collaboration with the North Carolina Department of Transportation (NCDOT) which selected the trucks. One area that the NCDOT was particularly interested in was the effect that the use of biofuel had on emissions because they were an early adopter of biofuel.”

For this reason, emissions measurements were taken on the five trucks driven with 20% biodiesel. Three of the five trucks were also operated with ultralow sulfur diesel. A portable emissions measurement system (PEMS) was attached to the truck engine to measure hydrocarbon, carbon monoxide and carbon dioxide using a light scattering technique. Engine revolutions per minute, intake air temperature and manifold absolute pressure were measured by using an engine sensor array.

Each of the trucks operated for NCDOT on five specific routes within the state of North Carolina. All of the trucks operated out of the NCDOT depot in Raleigh. The PEMS is warmed up for 45 minutes prior to the truck leaving the depot. The researchers followed the truck and made periodic checks of the PEMS.

Figure 1 shows how the PEMS is installed on a truck. In doing the study, Frey indicated that a good deal of attention was paid to ensuring the data was accurate and reliable. He says, “We followed the trucks in a separate vehicle and verified that the PEMS was working when a truck would stop to make a delivery. Quality checks were made on the information obtained and data was excluded, if we were not sure about its reliability. Each PEMS was also calibrated before each file measurement, and the data collected was benchmarked against other sources.”


Figure 1. A portable emissions measurement system was attached to the truck engine, as shown, to determine emissions generated by five trucks from model years 1999, 2005, 2007, 2009 and 2010. (Courtesy of North Carolina State University)

The most significant conclusion from this study was that the emissions controls added to ensure compliance with EPA’s increasingly strict regulations are working. He says, “In comparing data from the 1999 model year truck versus 2010, we found both particulate matter and NO_x had dropped by 90%.”

In assessing the impact of biodiesel, Frey found mixed results. He said, “Carbon monoxide emissions were lower with biodiesel because it is oxygenated as compared to standard petroleum derived fuel. Particulate matter varied from one truck to another. Hydrocarbon levels were below the detection limits in all cases and a slight reduction in NO_x levels was seen in some cases.”

In a future study, Frey plans to evaluate emissions coming from locomotives using biodiesel. He adds, “We also plan to study the railroad lubricant and determine its impact on engine emissions.”

A second project will look at the real-world emissions generated by refuse trucks, which go through very frequent stopping. Frey says, “We will look at a range of model years and truck types, including front and rear loaders.”

Additional information on this study can be found in a recent publication (2) or by contacting Frey at frey@ncsu.edu.

REFERENCES
1. Canter, N. (2008), “Determining On-Road Emissions,” TLT, 64 (5), pp. 10-11.
2. Sandhu, G. and Frey, H. (2012), “Real-World Measurement and Evaluation of Heavy-Duty Truck Duty cycles, Fuels and Emission Control Technologies,” Presented at the 91st Annual Meeting of the Transportation Research Board, TRB 12-4674, click here.

Neil Canter heads his own consulting company, Chemical Solutions, in Willow Grove, Pa. Ideas for Tech Beat items can be sent to him at neilcanter@comcast.net.