Fuel Economy of Plug-In Hybrid Electric and Hybrid Electric Vehicles: Effects of Vehicle Weight, Hybridization Ratio and Ambient Temperature

Hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs) are evolving rapidly since the introduction of Toyota Prius into the market in 1997. As the world needs more fuel-efficient vehicles to mitigate climate change, the role of HEVs and PHEVs are becoming ever more important. While fuel economies of HEVs and PHEVs are superior to those of internal combustion engine (ICE) powered vehicles, they are partially powered by batteries and therefore they resemble characteristics of battery electric vehicles (BEVs) such as dependence of fuel economy on ambient temperatures. It is also important to understand how different extent of hybridization (a.k.a., hybridization ratio) affects fuel economy under various driving conditions. In addition, it is of interest to understand how HEVs and PHEVs compare with BEVs at a similar vehicle weight. This study investigated the relationship between vehicle mass and vehicle performance parameters, mainly fuel economy and driving range of PHEVs focused on 2018 and 2019 model years using the test data available from fuel economy website of the US Environmental Protection Agency (EPA). Previous studies relied on modeling to understand mass impact on fuel economy for HEV as there were not enough number of HEVs in the market to draw a trendline at the time. The study also investigated the effect of ambient temperature for HEVs and PHEVs and kinetic energy recovery of the regenerative braking using the vehicle testing data for model year 2013 and 2015 from Idaho National Lab (INL). The current study assesses current state-of-art for PHEVs. It also provides analysis of experimental results for validation of vehicle dynamic and other models for PHEVs and HEVs

Temperature effects on methanogenesis and sulfidogenesis during anaerobic digestion of sulfur-rich macroalgal biomass in sequencing batch reactors

Methanogenesis and sulfidogenesis, the major microbial reduction reactions occurring in the anaerobic digestion (AD) process, compete for common substrates. Therefore, the balance between methanogenic and sulfidogenic activities is important for efficient biogas production. In this study, changes in methanogenic and sulfidogenic performances in response to changes in organic loading rate (OLR) were examined in two digesters treating sulfur-rich macroalgal waste under mesophilic and thermophilic conditions, respectively. Both methanogenesis and sulfidogenesis were largely suppressed under thermophilic relative to mesophilic conditions, regardless of OLR. However, the suppressive effect was even more significant for sulfidogenesis, which may suggest an option for H2S control. The reactor microbial communities developed totally differently according to reactor temperature, with the abundance of both methanogens and sulfate-reducing bacteria being significantly higher under mesophilic conditions. In both reactors, sulfidogenic activity increased with increasing OLR. The findings of this study help to understand how temperature affects sulfidogenesis and methanogenesis during AD

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Department of Urban and Environmental Engineering (Environmental Science and Engineering)Anaerobic digestion (AD) is widely applied in the treatment of various organic wastes or wastewaters, and biogas (mainly CH4 and CO2) produced from AD is considered a promising renewable energy source. Producing methane rich biogas from waste biomass through AD is considered a viable option for sustainable energy supplies. Macroalgae, particularly harmful and/or inedible types, have recently emerged as an attractive feedstock for biogas production. Macroalgal biomass is rich in easily biodegradable organics and contains little lignin, which is advantageous for efficient bioconversion. Most previous studies on the AD of macroalgal biomass have tested edible seaweed species with high agricultural value, reducing the economic feasibility of using macroalgae as a feedstock for biogas production. Ulva is a macroalgal genus noted for causing harmful green tides worldwide. Green tides have significant environmental and economic consequences related to the accumulation and decay of bloomed algal biomass. Given that macroalgal blooms have become more frequent and severe with global warming, biomethanation of Ulva biomass is considered environmentally and economically appealing. However, there are practical limitations for using Ulva biomass as a sole feedstock; these limitations are primarily related to its high nitrogen and sulfur contents relative to carbon content. A low C:N ratio can result in an accumulation of free ammonia, which severely inhibits methanogenesis. Particularly, the high sulfur content of Ulva biomass can cause an excessive production of hydrogen sulfide (H2S) through dissimilatory sulfate reduction by sulfate reducing bacteria (SRBs) during AD. H2S is toxic to methanogens and other microorganisms involved in AD, and additionally, SRBs compete directly with methanogens for common substrates (i.e., H2 and acetate). The rigid macroalgal structures and seasonal variation in production are also characteristics of Ulva biomass that limit its use as a biomethanation feedstock. In this doctoral thesis, the AD of sulfur rich Ulva biomass was investigated to achieve stable and robust methanogenic performance, with particular emphases on methanogenesis and sulfidogenesis. In Study 1, the mono digestion of Ulva biomass was investigated with various reactor configurations of batch, repeated batch, continuous stirred tank reactor, and sequencing batch reactor. The results of these experiments demonstrated that Ulva had a high potential as feedstock for biogas production through AD in terms of organic removal and methane productivity. However, H2S production at high levels negatively affected methanogenesis, particularly during long term continuous operation. It was therefore suggested that sulfide control is important for stable Ulva AD ii in continuous mode. In Study 2, co--digestion of Ulva biomass with cheese whey was investigated as an approach to reduce sulfide production and to mitigate the limitations of Ulva as a sole substrate (e.g., low C/N ratio and seasonality). The co--digestion experiments were performed in continuous reactors with the substrate mixing ratio implemented in various manners: one with gradual increase and the other with gradual decrease in the Ulva fraction in the substrate mixture. The co--digestion with cheese whey resulted in an enhancement of methanogenic performance with reduced sulfidogenesis compared to the mono--digestion of Ulva biomass. The optimal mixing ratio between Ulva biomass and cheese whey for co--digestion was determined based on the methane recovery and treatment capacity. However, a considerable amount of H2S was still produced in the co--digestion reactors, suggesting the need for further research on effective sulfide control. In Study 3, promoting direct interspecies electron transfer (DIET) between electro--syntrophic partners involved in AD was attempted to further enhance the biomethanation of Ulva biomass with cheese whey in a mixture (at the optimal mixing ratio determined in Study 2). Recent studies have reported that electrically conductive material, such as magnetite (Fe3O4), serve as electrical conduit and stimulate DIET between electroactive exoelectrogenic fatty acid oxidizers and electrotrophic methanogens, thereby accelerating methanogenesis. This suggests that it may be possible, by adding conductive material, to increase electron flow to methanogenesis rather than to sulfate reduction using DIET. To examine such a possibility, the performances of the continuous co--digestion reactors with or without magnetite addition were comparatively analyzed. Interestingly, by adding magnetite, nearly complete removal of H2S was achieved in situ, whereas no significant effect was observed on methane production. It was experimentally proven that H2S was removed by the microbial oxidation to elemental sulfur (S0). Based on the microbial community analysis results and thermodynamic calculations, the newly found fate of sulfur under anaerobic conditions is proposed to be driven by a novel electro--syntrophic association between anaerobic sulfide--oxidizing bacteria and electrotrophic methanogenesis. This finding suggests the new possibility for in situ sulfide control and S0 recovery in continuous AD of sulfur--rich biomass. In conclusion, this PhD study examined the biomethanation of sulfur--rich Ulva biomass and suggests different approaches for enhancing methanogenic performance and process stability in continuous systems. Furthermore, a novel strategy for in situ H2S control by magnetite--promoted DIET is proposed. The stimulation of anaerobic sulfide oxidation to S0 via DIET in the presence of magnetite (or other conductive materials) is a remarkable observation that has not been reported. iii The findings of this study has introduced a novel dimension in anaerobic sulfur metabolism and the possibility of in situ H2S control by promoting DIET in sulfur-rich methanogenic environments.clos

Biomethanation of Harmful Macroalgal Biomass in Leach-Bed Reactor Coupled to Anaerobic Filter: Effect of Water Regime and Filter Media

Ulva is a marine macroalgal genus which causes serious green tides in coastal areas worldwide. This study investigated anaerobic digestion as a way to manage Ulva waste in a leach-bed reactor coupled to an anaerobic filter (LBR-AF). Two LBR-AF systems with different filter media, blast furnace slag grains for R1, and polyvinyl chloride rings for R2, were run at increasing water replacement rates (WRRs). Both achieved efficient volatile solids reduction (68.4-87.1%) and methane yield (148-309 mL/g VS fed) at all WRRs, with the optimal WRR for maximum methane production being 100 mL/d. R1 maintained more stable methanation performance than R2, possibly due to the different surface properties (i.e., biomass retention capacity) of the filter media. Such an effect was also noted in the different behaviors of the LBR and AF between R1 and R2. The molecular analysis results revealed that the development of the microbial community structure in the reactors was primarily determined by the fermentation type, i.e., dry (LBR) or wet (AF)

Complex refractive index, single scattering albedo, and mass absorption coefficient of secondary organic aerosols generated from oxidation of biogenic and anthropogenic precursors

Refractive index and optical properties of biogenic and anthropogenic secondary organic aerosol (SOA) particles were investigated. Aerosol precursors, namely longifolene, α-pinene, 1-methylnaphthalene, phenol, and toluene were oxidized in a Teflon chamber to produce SOA particles under different initial hydrocarbon concentrations and hydroxyl radical sources, reflecting exposures to different levels of nitrogen oxides (NOx). The real and imaginary components (n and k, respectively) of the refractive index at 375 nm and 632 nm were determined by Mie theory calculations through an iterative process, using the χ2 function to evaluate the fitness of the predicted optical parameters with the measured scattering, absorption, and extinction coefficients from a Photoacoustic Extinctiometer and Cavity Attenuated Phase Shift Spectrometer. Single scattering albedo (SSA) and bulk mass absorption coefficient (MAC) at 375 nm were calculated. SSA values of SOA particles from biogenic precursors (longifolene and α-pinene) were ∼0.98–0.99 (∼6.3% uncertainty), reflecting purely scattering aerosols regardless of the NOx regime. However, SOA particles from aromatic precursors were more absorbing and displayed NOx-dependent SSA values. For 1-methylnaphthalene SOA particles, SSA values of 0.92–0.95 and ∼0.75–0.90 (∼6.1% uncertainty) were observed under intermediate- and high-NOx conditions, respectively, reflecting the absorbing effects of SOA particles and NOx chemistry for this aromatic system. In mixtures of longifolene and phenol or longifolene and toluene SOA under intermediate- and high-NOx conditions, k values of the aromatic-related component of the SOA mixture were higher than that of 1-methylnaphthalene SOA particles. With the increase in OH exposure, kphenol decreased from 0.10 to 0.02 and 0.22 to 0.05 for intermediate- and high-NOx conditions, respectively. A simple relative radiative forcing calculation for urban environments at λ = 375 nm suggests the influence of absorbing SOA particles on relative radiative forcing at this wavelength is most significant for aerosol sizes greater than 0.4 µm. Copyright © 2019 American Association for Aerosol Research</p