John Collins

In-use NOx emissions from model year 2010 and 2011 heavy-duty diesel engines equipped with aftertreatment devices.

The California Air Resources Board (ARB) undertook this study to characterize the in-use emissions of model year (MY) 2010 or newer diesel engines. Emissions from four trucks: one equipped with an exhaust gas recirculation (EGR) and three equipped with EGR and a selective catalytic reduction (SCR) device were measured on two different routes with three different payloads using a portable emissions measurement system (PEMS) in the Sacramento area. Results indicated that brake-specific NOx emissions for the truck equipped only with an EGR were independent of the driving conditions. Results also showed that for typical highway driving conditions, the SCR technology is proving to be effective in controlling NOx emissions. However, under operations where the SCRs do not reach minimum operating temperature, like cold starts and some low load/slow speed driving conditions, NOx emissions are still elevated. The study indicated that strategies used to maintain exhaust temperature above a certain threshold, which are used in some of the newer SCRs, have the potential to control NOx emissions during certain low-load/slow speed driving conditions.

Measuring and Modeling Emissions from Extremely Low Emitting Vehicles

In recent years, automobile manufacturers have been producing gasoline-fueled vehicles that have very low tailpipe and evaporative emissions to meet stringent certification standards set by the U.S. Environmental Protection Agency and the California Air Resources Board. These extremely low-emitting vehicles are 98% to 99% cleaner than the catalyst-equipped vehicles produced in the mid-1980s. To understand better the emissions characteristics of these extremely low-emitting vehicles, as well as their potential impact on future air quality, researchers at the University of California, Riverside, have conducted a comprehensive study consisting of (a) an emissions measurement program, (b) the development of specific emissions models, and (c) the application of future emissions inventories to air quality models. Results have shown that in nearly all cases, these vehicles have emissions that are well below their stringent certification standards, and the vehicles continue to have low emissions as they age. On the basis of the measurement results, new modal emissions models have been created for both ultra-low-emission-certified vehicles and partial-zero-emission-certified vehicles. The model results compare well with actual measurements. With these models, it is possible to predict accurately future mobile source emissions inventories that will have an increasing number of these extremely low-emitting vehicles in the overall vehicle population. It is expected that the large penetration of these vehicles into the vehicle fleet will have a significant role in meeting ozone attainment levels in many regions.

In-Use NOx Emissions from Diesel and Liquefied Natural Gas Refuse Trucks Equipped with SCR and TWC, Respectively

The California Air Resources Board (ARB) and the City of Sacramento undertook this study to characterize the in-use emissions from model year (MY) 2010 or newer diesel, liquefied natural gas (LNG), and hydraulic hybrid diesel engines during real-world refuse truck operation. Emissions from five trucks, two diesels equipped with selective catalytic reduction (SCR), two LNGs equipped with three-way catalyst (TWC), and one hydraulic hybrid diesel equipped with SCR, were measured using a portable emissions measurement system (PEMS) in the Sacramento area. Results showed that the brake-specific NOx emissions for the LNG trucks equipped with the TWC catalyst were lowest of all the technologies tested. Results also showed that the brake specific NOx emissions from the conventional diesel engines were significantly higher despite the exhaust temperature being high enough for proper SCR function. Like diesel engines, the brake specific NOx emissions from the hydraulic hybrid diesel also exceeded certification although this can be explained on the basis of the temperature profile. Future studies are warranted to establish whether the below average SCR performance observed in this study is a systemic issue or is it a problem specifically observed during this work.

Real-world exhaust temperature profiles of on-road heavy-duty diesel vehicles equipped with selective catalytic reduction

On-road heavy-duty diesel vehicles are a major contributor of oxides of nitrogen (NOx) emissions. In the US, many heavy-duty diesel vehicles employ selective catalytic reduction (SCR) technology to meet the 2010 emission standard for NOx. Typically, SCR needs to be at least 200°C before a significant level of NOx reduction is achieved. However, this SCR temperature requirement may not be met under some real-world operating conditions, such as during cold starts, long idling, or low speed/low engine load driving activities. The frequency of vehicle operation with low SCR temperature varies partly by the vehicles vocational use. In this study, detailed vehicle and engine activity data were collected from 90 heavy-duty vehicles involved in a range of vocations, including line haul, drayage, construction, agricultural, food distribution, beverage distribution, refuse, public work, and utility repair. The data were used to create real-world SCR temperature and engine load profiles and identify the fraction of vehicle operating time that SCR may not be as effective for NOx control. It is found that the vehicles participated in this study operate with SCR temperature lower than 200°C for 11-70% of the time depending on their vocation type. This implies that real-world NOx control efficiency could deviate from the control efficiency observed during engine certification.

Real-World Exhaust Temperature and Engine Load Distributions of On-Road Heavy-Duty Diesel Vehicles in Various Vocations

Real-world vehicle and engine activity data were collected from 90 heavy-duty vehicles in California, United States, most of which have engine model year 2010 or newer and are equipped with selective catalytic reduction (SCR). The 90 vehicles represent 19 different groups defined by a combination of vocational use and geographic region. The data were collected using advanced data loggers that recorded vehicle speed, position (latitude and longitude), and more than 170 engine and aftertreatment parameters (including engine load and exhaust temperature) at the frequency of one Hz. This article presents plots of real-world exhaust temperature and engine load distributions for the 19 vehicle groups. In each plot, both frequency distribution and cumulative frequency distribution are shown. These distributions are generated using the aggregated data from all vehicle samples in each group.

Correction to Characterization of Particulate Matter Emissions from a Current Technology Natural Gas Engine

the figure showed a high mass fraction of lubrication oil derived elements and metals. Figure 4 of this erratum shows the corrected mass fraction of PM after the calculation error was addressed. The corrections of the error results in the conclusion that the mass fraction of lubrication oil derived elements and metals are less than 10% of total mass of PM. The comparison of distance-specific emissions of lubricationoil-derived elements from this study with previous SCRequipped diesel work presented by Hu et al. is discussed in Line 2, second column of page 8239 of the original manuscript. The original manuscript suggested that the distance-specific emissions of lubrication-oil-derived elements are an order of magnitude higher from TWC-equipped natural gas vehicles compared to DPF-SCR-equipped diesel over the UDDS driving cycle. As a result of the correction to the calculation, the results now conclude that the distance-specific emissions of lubrication-oil-derived elements from TWC-equipped natural gas engines are up to 2 times higher than the retrofit DPF-SCR equipped diesel engines. The overall conclusions of the study remain unchanged after the correction of the error. The original manuscript suggests the possibility of lubrication oil-derived elements from TWCequipped natural gas engines to contribute more toward particle number count in the 10 nm size range. The manuscript also suggests that renucleation of inorganic lubrication oil additives, passing through the combustion chamber of the engine to be the primary contributor to particle number count in this size range.