Characterizing ammonia emission from light-duty gasoline vehicles under the influence of multiple factors and its correlation with conventional pollutants.

Ammonia (NH3), which is a precursor of secondary particulate matter (PM), can be produced through three-way catalyst (TWC) side reactions in light-duty gasoline vehicles (LDGVs), posing a threat to human health and air quality. To explore ammonia emission characteristics, 8 LDGVs and 1 hybrid electric light-duty vehicle (HEV) with various mileages traveled were analyzed with a chassis dynamometer system during regulation driving cycles. The emission factors of the adopted China VI in-use LDGVs were 7.04 ± 2.61 mg/km under cold-start conditions and 4.94 ± 1.69 mg/km under hot-start conditions. With increasing mileage traveled, the total ammonia emissions increased, and the difference between the cold/hot-start results decreased. The emissions of in-use LDGVs with bi-fuel engines were analyzed, and more ammonia was generated in the compressed natural gas (CNG) mode through the hydrocarbon (HC) reforming reaction. The relationship between the emissions of ammonia and conventional pollutants was established. During the initial cold-start phase, a delay in ammonia formation was observed, and the ammonia emissions conformed with the CO and HC emissions after exhaust heating. Vehicle specific power (VSP) analysis revealed that the interval of highest ammonia emissions corresponded to acceleration events at high speeds. For the HEV, the transition from motor to engine drive conditions contributed to ammonia emission occurrence because of the more pronounced cold-start events. The use of HEV technology could introduce additional uncertainties in controlling urban ammonia emissions. Detailed analysis of emission characteristics could provide data support for future research on ammonia emission standards and control strategies for LDGVs.

Particulate matter emissions from light-duty gasoline vehicles under different ambient temperatures: Physical properties and chemical compositions.

Fine particulate matter (PM2.5) from vehicle exhaust is typically emitted at breathing height and thus imposes severe adverse effects on human health and air quality. However, there is currently limited knowledge on the characteristics of PM2.5 in exhaust, specifically its chemical components, at different ambient temperatures. Particulate emissions from typical light-duty gasoline vehicles (LDGVs) were investigated on a chassis dynamometer according to the Worldwide Harmonized Light-Duty Test Cycle at ambient temperatures of 38 °C, 28 °C, 15 °C, 5 °C and - 7 °C. The results showed a significant increase in particulate mass (PM) and particle number (PN) emissions with decreasing ambient temperature, particularly during cold starts below 5 °C. The particle size distributions exhibited distinct bimodal patterns, with accumulation-mode (AM) particles (60-125 nm) dominating the gasoline direct injection (GDI) distribution and nucleation-mode (NM) particles (8-12 nm) dominating the port fuel injection (PFI) distribution. AM particles were more temperature-sensitive than NM particles. Lower temperatures produced higher emissions of elements, carbonaceous components, and large-ring polycyclic aromatic hydrocarbons, while water-soluble ions showed an opposite trend. The total toxic equivalent, primarily influenced by benzo[a]pyrene, was significantly higher at -7 °C. The penalty distribution of LDGV PM and PN, defined by comparing the emissions at the various temperatures to those at regulated temperatures (23-30 °C), exhibited notable temporal heterogeneity (winter > autumn > spring > summer) and spatial heterogeneity (northern China > southern China). These findings are essential for establishing more stringent vehicle emission standards and improving emission models in cold environments.

China 6 EGR gasoline vehicles without a GPF may struggle to meet the potential SPN10 limit.

Particles larger than 10 nm from engine exhaust are gaining global concerns. In light of this, to investigate how EGR affects gasoline vehicle SPN10 (solid particles larger than 10 nm) emissions, seven gasoline vehicles (hybrid or conventional) were studied experimentally. The results revealed that EGR vehicles risk failing the current limit (6 * 1011 #/km) more than those without EGR if the cut-off size was tightened from 23 nm to 10 nm. More specifically, during the WLTC test, EGR increased the SPN10 emission factors by 2 âˆ¼ 3 times depending on vehicle powertrains (conventional or hybrid). Notably, SPN10 emissions increased significantly when EGR was actively engaged but showed a decrease when the EGR rate remained constant. EGR and the enriched fuel-air mixture are the critical reasons for the increased SPN10.

Particle number emissions from fully warmed gasoline vehicles at various ambient temperatures.

Road vehicles have become the primary source of fine particles in many large cities. Vehicle hot-start PN emissions at various ambient temperatures were studied previously. Still, these studies used the same rolling resistance setting at different ambient temperatures and the tests at various ambient temperatures have similar PN emissions. Vehicles get larger resistance at cold ambient temperatures, so this experimental setting (same resistance at various ambient temperatures) is beyond the natural conditions. To evaluate how ambient temperatures affect the PN emissions from fully warmed vehicles, two vehicles were tested at four ambient temperatures: -10 °C, 0 °C, 23 °C, and 40 °C. Vehicle resistance variations under different ambient temperatures were taken into consideration. The observed results proved that PN emission would significantly deteriorate under cold conditions even when the vehicles are thoroughly warmed. The PN emission factor at -10 °C could be six times higher than at 23 °C. The deteriorated PN emission is caused by enhanced fuel enrichment and GPF regeneration, and larger vehicle resistance under cold ambient temperatures is the underlying reason for the increased PN emission. For the first time, this study proved that PN emission from fully warmed vehicles would significantly deteriorate when the ambient temperature decreases. The results could be used for emission models, inventory, and regulations.

Effects of a start-stop system for gasoline direct injection vehicles on fuel consumption and particulate emissions in hot and cold environments.

Engine start-stop (S&S) technology has been substantially incorporated into modern vehicles to save fuel during idling in congested urban areas because fuel economy regulations have become more stringent. However, the potential for increasing particle emissions after engine restarts, especially in cold environments, is of great concern. To investigate the effects of S&S systems on fuel consumption and tailpipe emissions, a chassis dynamometer was employed to measure the fuel consumption, particulate matter (PM), solid particle number (PN), particle number size distribution and black carbon (BC) for a typical gasoline direct injection vehicle when the S&S was on (S&S-on) and when the S&S was off (S&S-off) according to the worldwide harmonized light-duty test cycle in both hot (28 °C) and cold (5 °C) environments. S&S operation resulted in 3.1-4.3% fuel-savings at 28 °C but had a tendency to increase particulate emissions, especially of BC (21.8-31.8%) and PM (19.2-32.8%). Although PN emissions with S&S-on over the entire cycle were slightly lower than those with S&S-off, more particles were emitted during the engine restart moments. In a cold environment, the fuel-savings advantage of the S&S system was weakened, and the negative impacts on the particle emissions during the restart moment worsened. The S&S system resulted in higher abundances of accumulation mode particles, especially under cold ambient conditions. The relationship between the PN reduction rates and idling segments was determining to be exponential. Our results indicate that the S&S system, which may increase particle emissions during restarts, does save fuel, and that a comprehensive evaluation of the system in cold environments is needed to determine the serviceability of new engine technologies and after-treatments.

Primary organic gas emissions from gasoline vehicles in China: Factors, composition and trends.

Continuous tightening emission standards (ESs) facilitate the reduction of organic gas emissions from gasoline vehicles. Correspondingly, it is essential to update the emissions and chemical speciation of total organic gases (TOGs), including volatile organic compounds (VOCs), intermediate volatility organic compounds (IVOCs), CH4, and unidentified non-methane hydrocarbons (NMHCs) for assessing the formation of ozone and secondary organic aerosol (SOA). In this study, TOG and speciation emissions from 12 in-use light-duty gasoline vehicle (LDGV) exhausts, covering the ESs from China II to China V, were investigated on a chassis dynamometer under the Worldwide Harmonized Light-duty Test Cycle (WLTC) in China. The results showed that the most effectively controlled subgroup in TOG emissions from LDGVs was VOCs, followed by the unidentified NMHCs and IVOCs. The mass fraction of VOCs in TOGs also reduced from 61 ± 9% to 46 ± 18% while the IVOCs gently increased from 2 ± 0.4% to 8 ± 4% along with the more stringent ESs. For the VOC subsets, the removal efficiency of oxygenated VOCs (OVOCs) was lower than those of other VOC subsets in the ESs from China IV to V, suggesting the importance of OVOC emission controls for relatively new LDGVs. The IVOC emissions were mainly subject to the ESs, then driving cycles and fuel use. The formation potentials of ozone and SOA from LDGVs decreased separately 96% and 90% along with the restricted ESs from China II-III to China IV. The major contributor of SOA formation transformed from aromatics in the VOC subsets for China II-III vehicles to IVOCs for China IV/V vehicles, highlighting that IVOC emissions from LDGVs are also needed more attentions to control in future.

Tailpipe emissions from gasoline direct injection (GDI) and port fuel injection (PFI) vehicles at both low and high ambient temperatures.

Vehicle emissions are greatly influenced by various factors that are related to engine technology and driving conditions. Only the fuel injection method and ambient temperature are investigated in this research. Regulated gaseous and particulate matter (PM) emissions from two advanced gasoline-fueled vehicles, one with direct fuel injection (GDI) and the other with port fuel injection (PFI), are tested with conventional gasoline and ethanol-blended gasoline (E10) at both -7 °C and 30 °C. The total particle number (PN) concentrations and size distributions are monitored with an Electrical Low Pressure Impactor (ELPI(+)). The solid PN concentrations are measured with a condensation particle counter (CPC) after removing volatile matters through the particle measurement program (PMP) system. The results indicate that decreasing the ambient temperature from 30 °C to -7 °C significantly increases the fuel consumption and all measured emissions except for NOx. The GDI vehicle exhibits lower fuel consumption than the PFI vehicle but emits more total hydrocarbons (THC), PM mass and solid PN emissions at 30 °C. The adaptability of GDI technology appears to be better than that of PFI technology at low ambient temperature. For example, the CO, THC and PM mass emission factors of the PFI vehicle are higher than those of the GDI vehicle and the solid PN emission factors are comparable in the cold-start tests at -7 °C. Specifically, during start-up the particulate matter emissions of the PFI are much higher than the GDI. In most cases, the geometric mean diameter (GMD) of the accumulation mode particles is 58-86 nm for both vehicles, and the GMD of the nucleation mode particles is 10-20 nm. The results suggest that the gaseous and particulate emissions from the PFI vehicle should not be neglected compared to those from the GDI vehicle especially in a cold environment.