Kent C. Johnson

Real-world operation conditions and on-road emissions of Beijing diesel buses measured by using portable emission measurement system and electric low-pressure impactor.

On-road measurement is an effective method to investigate real-world emissions generated from vehicles and estimate the difference between engine certification cycles and real-world operating conditions. This study presents the results of on-road measurements collected from urban buses which propelled by diesel engine in Beijing city. Two widely used Euro III emission level buses and two Euro IV emission level buses were chosen to perform on-road emission measurements using portable emission measurement system (PEMS) for gaseous pollutant and Electric Low Pressure Impactor (ELPI) for particulate matter (PM) number emissions. The results indicate that considerable discrepancies of engine operating conditions between real-world driving cycles and engine certification cycles have been observed. Under real-world operating conditions, carbon monoxide (CO) and hydrocarbon (HC) emissions can easily meet their respective regulations limits, while brake specification nitrogen oxide (bsNO(x)) emissions present a significant deviation from its corresponding limit. Compared with standard limits, the real-world bsNO(x) emission of the two Euro III emission level buses approximately increased by 60% and 120% respectively, and bsNO(x) of two Euro IV buses nearly twice standard limits because Selective Catalytic Reduction (SCR) system not active under low exhaust temperature. Particle mass were estimated via particle size distribution with the assumption that particle density and diameter is liner. The results demonstrate that nanometer size particulate matter make significant contribution to total particle number but play a minor role to total particle mass. It is suggested that specific certified cycle should be developed to regulate bus engines emissions on the test bench or use PEMS to control the bus emissions under real-world operating conditions.

Evaluation of the European PMP Methodologies during On-Road and Chassis Dynamometer Testing for DPF Equipped Heavy-Duty Diesel Vehicles

This study evaluated the UN-ECE Particle Measurement Programme (PMP) protocol for the measurement of solid particle number emissions under laboratory and on-road conditions for two passive diesel particle filters (DPF)–equipped medium and heavy-heavy duty diesel vehicles. The PMP number emissions were lower than the European light-duty certification value (9.6 × 1011 #/mi) for all standardized cycles, but exceeded this value during some higher load on-road driving conditions. Particle number measurements were generally less variable than those of the PM mass for the on-road testing, but had comparable or greater variability than PM mass for the laboratory measurements due to outliers. These outliers appear to be real events that are not apparent with integrated filter methods. The particle number measurements for the low cut point CPCs (3–7 nm) below the PMP system were approximately an order of magnitude higher than those for the PMP-compliant CPC (23 nm), indicating the presence of a large fraction of solid sub-23 nm particles. Although such particles are defined as solid by the PMP method, their actual state is unknown. Nucleation particles with a large sulfate contribution formed under a variety of conditions when the exhaust temperature near the DPF exceeded a “critical” temperature, typically >300°C.

Nature of Sub-23-nm Particles Downstream of the European Particle Measurement Programme (PMP)-Compliant System: A Real-Time Data Perspective

This study provides an evaluation of the nature of sub-23-nm particles downstream of the European Particulate Measurement Programme (PMP) methodology, with prescribed cycles and on-road flow-of-traffic driving conditions. Particle number concentrations and size distributions were measured using two PMP measurement systems running simultaneously. For this analysis, the focus is on the real-time results from multiple instruments. The results revealed that a significant fraction of particles downstream of both PMP systems for all tested cycles were below 11 nm. The fraction of sub-11-nm particles observed downstream of the PMP system decreased when the overall dilution ratio of one PMP system was increased from 300 to 1500, suggesting those sub-11-nm particles were formed through re-nucleation of semivolatile precursors. When the evaporation tube temperature was increased from 300°C to 500°C, no difference in particle number concentrations was observed, suggesting that incomplete evaporation of semivolatile particles did not contribute to those sub-11-nm particles. Particle emissions were about one order of magnitude higher during flow-of-traffic driving along a highway with a steep grade than during the prescribed driving cycles. During the same flow-of-traffic condition, a sudden jump in PMP operationally defined solid particle concentration was observed, while the accumulation mode particle concentrations in the constant volume sampling (CVS) tunnel measured by an engine exhaust particle sizer (EEPS) only showed a slight increase. This discrepancy was attributed to the extensive growth of the re-nucleated particles downstream of the PMP systems. Copyright 2012 American Association for Aerosol Research

Comparison of Vehicle Exhaust Particle Size Distributions Measured by SMPS and EEPS During Steady-State Conditions

Fast-sizing spectrometers, such as the TSI Engine Exhaust Particle Sizer (EEPS), have been widely used to measure transient particle size distributions of vehicle exhaust. Recently, size distributions measured during different test cycles have begun to be used for calculating suspended particulate mass; however, several recent evaluations have shown some deficiencies in this approach and discrepancies relative to the gravimetric reference method. The EEPS converts electrical charge carried by particles into size distributions based on mobility classification and a specific calibration, and TSI recently released a matrix optimized for vehicle emissions as described by Wang et al. (Submitteda). This study evaluates the performance of the new matrix (soot matrix) relative to the original matrix (default matrix) and reference size distributions measured by a scanning mobility particle sizer (SMPS). Steady-state particle size distributions were generated from the following five sources to evaluate exhaust particulates with various morphologies estimated by mass-mobility scaling exponent: (1) A diesel generator operating on ultralow sulfur diesel, (2) a diesel generator operating on biodiesel, (3) a gasoline direct-injection vehicle operating at two speeds, (4) a conventional port-fuel injection gasoline vehicle, and (4) a light-duty diesel (LDD) vehicle equipped with a diesel particulate filter. Generally, the new soot matrix achieved much better agreement with the SMPS reference for particles smaller than 30 nm and larger than 100 nm, and also broadened the accumulation mode distribution that was previously too narrow using the default matrix. However, EEPS distributions still did not agree with SMPS reference measurements when challenged by a strong nucleation mode during high-load operation of the LDD vehicle. This work quantifies the range of accuracy that can be expected when measuring particle size distribution, number concentration, and integrated particle mass of vehicle emissions when using the new static calibration derived based on the properties of classical diesel soot. Copyright 2015 American Association for Aerosol Research

Using a new inversion matrix for a fast-sizing spectrometer and a photo-acoustic instrument to determine suspended particulate mass over a transient cycle for light-duty vehicles

ABSTRACT Integrated particle size distribution (IPSD) is a promising alternative method for estimating particulate matter (PM) emissions at low levels. However, a recent light-duty vehicle (LDV) emissions study showed that particle mass estimated using IPSD (MIPSD) with the TSI Engine Exhaust Particle Sizer (EEPS) Default Matrix was 56–75% lower than mass derived using the reference gravimetric method (MGrav) over the Federal Test Procedure (FTP). In this study, MIPSD calculated with a new inversion matrix, the Soot Matrix, is compared with MGrav and also photoacoustic soot mass (MSoot), to evaluate potential improvement of the IPSD method for estimating PM mass emissions from LDVs. In addition, an aerodynamic particle sizer (APS) was used to estimate mass emission rates attributed to larger particles (0.54–2.5 µm in aerodynamic diameter) that are not measured by the EEPS. Based on testing of 10 light-duty vehicles over the FTP cycle, the Soot Matrix significantly improved agreement between MIPSD and MGrav by increasing slopes of MIPSD/MGrav from 0.45–0.57 to 0.76–1.01 for gasoline direct injected (GDI) vehicles; however, for port-fuel injection (PFI) gasoline vehicles, a significant discrepancy still existed between MIPSD and MGrav, with MIPSD accounting for 34 ± 37% of MGrav. For all vehicles, strong correlations between MIPSD and MSoot were obtained, indicating the IPSD method is capable of capturing mass of soot particles. The discrepancy between the MIPSD and MGrav for PFI vehicles, which have relatively low PM emissions (0.22 to 1.83 mg/mile), could be partially due to limited size range of the EEPS by not capturing larger particles (0.54–2.5 µm) that accounts for ∼0.08 mg/mile of PM emission, uncertainties of particle effective density, and/or gas-phase adsorption onto filters that is not detected by in situ aerosol instrumentation. Copyright

Uncertainty in Gravimetric Analysis Required for LEV III Light-Duty Vehicle PM Emission Measurements

Author(s): Swanson, Jacob; Pham, Liem; Xue, Jian; Durbin, Tom; Russell, Robert; Miller, Wayne; Kittelson, David; Jung, Heejung; Johnson, Kent

Gasoline Particulate Filters as an Effective Tool to Reduce Particulate and Polycyclic Aromatic Hydrocarbon Emissions from Gasoline Direct Injection (GDI) Vehicles: A Case Study with Two GDI Vehicles

We assessed the gaseous, particulate, and genotoxic pollutants from two current technology gasoline direct injection vehicles when tested in their original configuration and with a catalyzed gasoline particulate filter (GPF). Testing was conducted over the LA92 and US06 Supplemental Federal Test Procedure (US06) driving cycles on typical California E10 fuel. The use of a GPF did not show any fuel economy and carbon dioxide (CO2) emission penalties, while the emissions of total hydrocarbons (THC), carbon monoxide (CO), and nitrogen oxides (NOx) were generally reduced. Our results showed dramatic reductions in particulate matter (PM) mass, black carbon, and total and solid particle number emissions with the use of GPFs for both vehicles over the LA92 and US06 cycles. Particle size distributions were primarily bimodal in nature, with accumulation mode particles dominating the distribution profile and their concentrations being higher during the cold-start period of the cycle. Polycyclic aromatic hydrocarbons (PAHs) and nitrated PAHs were quantified in both the vapor and particle phases of the PM, with the GPF-equipped vehicles practically eliminating most of these species in the exhaust. For the stock vehicles, 2-3 ring compounds and heavier 5-6 ring compounds were observed in the PM, whereas the vapor phase was dominated mostly by 2-3 ring aromatic compounds.

Assessment of the emissions from the use of California Air Resources Board qualified diesel fuels in comparison with Federal diesel fuels

The California Air Resources Board (CARB) has regulated the properties of diesel fuel sold in California since 1988 to lower emissions of particulate matter (PM) and oxides of nitrogen (NOx). Although many studies have shown that reduced levels of aromatics and higher cetane numbers can improve emissions, the actual impact of CARB fuels on in-use diesel emissions has not yet been extensively studied, especially as diesel engine and aftertreatment technology has evolved over the years. This study evaluates the differences between California and Federal diesel fuels with heavy-duty engine and chassis dynamometer tests. The engine dynamometer results showed that NOx emissions for the Federal fuels ranged from 4.7% to 9.5% higher than the CARB diesel. These NOx reductions are similar to the estimates being used in the latest regulations. The chassis dynamometer test results did not show as consistent trends for NOx as those seen for the engine dynamometer testing. For the chassis dynamometer testing, four out of ten vehicles showed consistent reductions in NOx, with emissions for the Federal fuels ranging from 3.3% to 9.9% higher than the CARB diesel, while the other six vehicles did not show consistent fuel impacts. On an absolute level, the NOx benefit for CARB diesel shows a decline with continuing advances in engine technology. The results showed that CARB diesel did not show strong benefits for PM. The results also showed that the introduction of aftertreatment systems for PM and NOx will, over time, largely eliminate any potential benefits that might be obtained through the use of CARB diesel, although NOx benefits will persist through to 2020.

Characterizing emission rates of regulated pollutants from model year 2012 + heavy-duty diesel vehicles equipped with DPF and SCR systems

The regulated emissions of five 2012 and newer, low-mileage, heavy-duty Class 8 diesel trucks equipped with diesel particulate filters (DPFs) and selective catalytic reduction (SCR) systems were evaluated over test cycles representing urban, highway, and stop-and-go driving on a chassis dynamometer. NOx emissions over the Urban Dynamometer Driving Schedule (UDDS) ranged from 0.495 to 1.363g/mi (0.136 to 0.387g/bhp-hr) for four of the normal emitting trucks. For those trucks, NOx emissions were lowest over the cruise (0.068 to 0.471g/mi) and high-speed cruise (0.067 to 0.249g/mi) cycles, and highest for the creep cycle (2.131 to 9.468g/mi). A fifth truck showed an anomaly in that it had never regenerated throughout its relatively short operating lifetime due to its unusual, unladed service history. This truck exhibited NOx emissions of 3.519g/mi initially over the UDDS, with UDDS NOx emissions decreasing to 0.39g/mi after a series of parked regenerations. PM, THC, and CO emissions were found to be very low for most of the testing conditions, due to the presence of the DPF/SCR aftertreatment system, and were comparable to background levels in some cases.

A comparison of a mini-PEMS and a 1065 compliant PEMS for on-road gaseous and particulate emissions from a light duty diesel truck

The primary goal of this study was to compare emissions measurements between a 1065 compliant PEMS, and the NTK Compact Emissions Meter (NCEM) capable of measuring NOx, PM, and solid PN. Both units were equipped on a light-duty diesel truck and tested over local, highway, and downtown driving routes. The results indicate that the NOx measurements for the NCEM were within approximately ±10% of those the 1065 compliant PEMS, which suggests that the NCEM could be used as a screening tool for NOx emissions. The NCEM showed larger differences for PM emissions on an absolute level, but this was at PM levels well below the 1 mg/mi level. The NCEM differences ranged from -2% to +26% if the comparisons are based on a percentage of the 1.0 mg/mi standard. Larger differences were also seen for PN emissions, with the NCEM measuring higher PN emissions, which can primarily be attributed to a zero current offset that we observed for the NCEM, which has been subsequently improved in the latest generation of the NCEM system. The comparisons between the 1065 compliant PEMS and the NCEM suggest that there could be applications for the NCEM or other mini-PEMS for applications such as identification of potential issues by regulatory agencies, manufacturer evaluation and validation of emissions under in-use conditions, and potential use in inspection and maintenance (I/M) programs, especially for heavy-duty vehicles.