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Abstract The Department of Energy “Co-Optimization of Fuels and Engines” initiative aims to simultaneously develop novel high-performance fuels with advanced engine designs to reduce petroleum consumption. To achieve commercialization, advanced engines running on alternative fuels still must meet emissions regulations. Warm three-way catalysts (TWC) are very effective at meeting the stringent emissions regulations on pollutants such as nitrogen oxides (NOx), non-methane organic gases (NMOG) and carbon monoxide (CO) from gasoline-fueled spark-ignition (SI) engines operating under stoichiometric conditions; thus, most SI engine emissions occur during cold-start, when the TWC has not yet achieved light-off. In the current study, the light-off behavior of novel high-performance fuel candidates has been investigated on a hydrothermally-aged commercial TWC using a synthetic engine-exhaust flow reactor system according to industry guidelines. Over 30 potential fuel components were examined in this study, including alkanes, alkenes, alcohols, ketones, esters, aromatic ethers, and non-oxygenated aromatic hydrocarbons. Short-chain acyclic oxygenates, including alcohols, ketones, and esters, tended to light off at relatively low temperatures, while alkenes, aromatics, and cyclic oxygenates tended to light off at relatively high temperatures. The light-off behavior of alkanes and alkenes depended strongly on their size and structure. In terms of the influence on CO light-off on the TWC, the fuels fell into two distinct categories: (i) non-inhibiting species including C2-C3 alcohols, alkanes, acyclic ketones, and esters; and (ii) inhibiting species including alkenes, aromatic hydrocarbons, cyclic oxygenates, and C4 alcohols.

Abstract Radiant heating and cooling systems have significant energy-saving potential and are gaining popularity in commercial buildings. The main aim of the experimental study reported here was to characterize the behavior of radiant cooling systems in a typical office environment, including the effect of ceiling fans on stratification, the variation in comfort conditions from perimeter to core, control on operative temperature vs. air temperature and the effect of carpet on cooling capacity. The goal was to limit both the first cost and the perceived risk associated with such systems. Two types of radiant systems, the radiant ceiling panel (RCP) system and the radiant slab (RS) system, were investigated. The experiments were carried out in one of the test cells that constitute the FLEXLAB test facility at the Lawrence Berkeley National Laboratory in March and April 2016. In total, ten test cases (five for RCP and five for RS) were performed, covering a range of operational conditions. In cooling mode, the air temperature stratification is relatively small in the RCP, with a maximum value of 1.6 K. The observed stratification effect was significantly greater in the RS, twice as much as that in the RCP. The maximum increase in dry bulb temperature in the perimeter zone due to solar radiation was 1.2 K for RCP and 0.9 K for RS – too small to have a significant impact on thermal comfort. The use of ceiling fans was able to reduce any excess stratification and provide better indoor comfort, if required. The use of thin carpet requires a 1 K lower supply chilled water temperature to compensate for the added thermal resistance, somewhat reducing the opportunities for water-side free cooling and increasing the risk of condensation. In both systems, the difference between the room operative temperature and the room air temperature is small when the cooling loads are met by the radiant systems. This makes it possible to use the air temperature to control the radiant systems in lieu of the operative temperature, reducing both first cost and maintenance costs.

Abstract A promising and shortly emerging energy supply chain network based on residential-scale microgeneration through micro combined heat and power systems is proposed, modeled and optimized in this work. Interchange of electrical energy can take place among the members of this domestic microgrid, which is connected to the main electrical grid for potential power interchange with it. A mathematical programming framework is developed for the operational planning of such energy supply chain networks. The minimization of total costs (including microgeneration system’s startup and operating costs as well as electricity production revenue, sales, and purchases), under full heat demand satisfaction, constitutes the objective function in this study. Additionally, an alternative microgrid structure that allows the heat interchange within subgroups of the overall microgrid is proposed, and the initial mathematical programming formulation is extended to deal with this new aspect. An illustrative example is presented in order to highlight the particular significance of selecting a proper optimization goal that thoroughly takes into account the major operational, technical and economic driven factors of the problem in question. Also, a number of real-world size case studies are used to illustrate the efficiency, applicability and the potential benefits of the microgeneration energy supply chain networks suggested in this study. Finally, some concluding remarks are drawn and potential future research directions are identified.

Abstract Reactivity Controlled Compression Ignition (RCCI) engines hold promise for decreasing NOx and particulate emissions. RCCI engines use direct injection (DI) to introduce a high reactivity fuel into the cylinder while a lower reactivity fuel is port fuel injected (PFI). A large reactivity difference between high reactive (diesel) and low reactive (natural gas) fuels provides a strong control variable for phasing and shaping combustion heat release in RCCI engines. Two diesel fuels, a High Reactive Diesel (HRD) fuel with a cetane number (CN) of 85 and a U.S. Ultra-Low Sulfur Diesel (ULSD) fuel with a cetane number of 49 were selected for this study. The effects of these two diesel fuels with methane as the low reactivity premixed fuel were compared in RCCI combustion mode and in Conventional Diesel Combustion (CDC) mode. The hypothesis is that using a HRD fuel in RCCI applications, with a double injection strategy, increases the reactivity of the mixture in the squish region, promoting combustion and consequently reducing unburned hydrocarbons and carbon monoxide. These emissions are generally difficult to control in RCCI combustion at high Blend Ratio (BR). In addition, a larger reactivity difference between the two fuels in RCCI applications, extends the combustion duration and reduces the Maximum Pressure Rise Rate (MPRR) and in-cylinder peak pressure. The reduction in MPRR in RCCI combustion mode makes it possible to operate the engine at higher engine loads without exceeding the MPRR mechanical constraint. The experiments were performed on a 1.9L inline 4 cylinder turbocharged compression ignition (CI) engine modified for dual fuel operation at an engine speed of 1500 RPM and 8 bar IMEP. A full factorial Design of Experiment (DOE) test program and analysis was conducted with four input variables including the diesel fuel reactivity, BR, Exhaust Gas Recirculation (EGR) and Direct Injection (DI) strategy and at two levels of interest. This analysis was used to quantify the impact of the independent input variables on engine out emissions, performance, and MPRR mechanical constraint. Following the DOE testing and analysis the optimum injection strategy to maximize the Brake Thermal Efficiency (BTE) was found for both fuels by sweeping the main Start of Injection timing (SOImain). The results of the DOE analysis showed that the cetane number is the most significant factor that effects HC and CO emissions. The experimental results showed that HRD fuel provides a 2% improvement in brake-thermal efficiency, a 14 g/kW.hr reduction in HC emissions, and 0.5% lower Coefficient of Variation (COV) of Indicated Mean Effective Pressure (IMEP) compared to the baseline diesel-NG RCCI combustion.

Abstract A new concept was developed for feed layer formation control and to obtain continuous pellet production when pelletizing torrefied biomass. The materials pelletized were softwood forest residues and a hardwood species which both had been torrefied at 308 °C for 9 min. The torrefied wood chips were milled over a screen size of 6 mm and the torrefied feedstock moisture content was adjusted to about 9% before pelletizing. Two types of pelletizers were used; one with a stationary ring die and one with a rotating ring die. With a traditional, non-cooled die configuration, the die temperature increased to 75–78 °C. During temperature increment, pellet production deteriorated and finally ceased at approximately 80 °C. This phenomenon was caused by a breakdown of the feed-layer formation between the free rolling rollers and the die. However, continuous production could be sustained when the die was cooled. A new tool was developed based on nozzle injection of water directly onto the feed layer. By this course of action pellet production was sustained at temperatures well above 80 °C. This proof-of-concept for a new tool to control sub-process interactions in ring die pelletizing also includes use of low initial moisture content to utilize the flowability of torrefied particulates and, thus, avoid problems connected to feeding, conveying and silo discharging which frequently occurs at higher feedstock moisture contents.

Abstract Desalination powered by renewable energy sources is an attractive solution to address the worldwide water-shortage problem without contributing significant to greenhouse gas emissions. A promising system for renewable energy desalination is the utilization of low-temperature direct contact membrane distillation (DCMD) driven by a thermal solar energy system, such as a salt-gradient solar pond (SGSP). This investigation presents the first experimental study of fresh water production in a coupled DCMD/SGSP system. The objectives of this work are to determine the experimental fresh water production rates and the energetic requirements of the different components of the system. From the laboratory results, it was found that the coupled DCMD/SGSP system treats approximately six times the water flow treated by a similar system that consisted of an air–gap membrane distillation unit driven by an SGSP. In terms of the energetic requirements, approximately 70% of the heat extracted from the SGSP was utilized to drive thermal desalination and the rest was lost in different locations of the system. In the membrane module, only half of the useful heat was actually used to transport water across the membrane and the remainder was lost by conduction in the membrane. It was also found that by reducing heat losses throughout the system would yield higher water fluxes, pointing out the need to improve the efficiency throughout the DCMD/SGSP coupled system. Therefore, further investigation of membrane properties, insulation of the system, or optimal design of the solar pond must be addressed in the future.

Abstract Predicting the distribution and resource of gas hydrates and understanding gas hydrate forming mechanisms are critical for assessing natural gas hydrate exploration potential, as well as exploiting hydrates. This study aims to provide a portable solution for evaluating resource of natural gas hydrate and quantifying contribution of methane sources via numerical simulations constrained by site-specific data. To numerically describe the complex process of biogenic methane production, an integrated simulation package, TOUGH + Hydrate + React (TOUGH + HR), was developed by coupling reactive transport, biodegradation and deposition of organic matter with behavior of hydrate-bearing system. Based on observed data from site SH2 in the South China Sea, a growing one-dimensional column model was constructed, and simulated via the developed TOUGH + HR tool. The results showed that when considering biogenic methane was the only source for hydrate, simulated maximum saturation of hydrate reached ~ 0.19, which is much lower than the observed value (~0.46), suggesting that the in-situ biogenic methane is not enough to form the high-saturation hydrate. When the upward flux of methane (considered as thermogenic methane) increased to 1.00 × 10−11 k g · m - 2 · s - 1 , both simulated saturation and distribution of hydrates matched the observed data well, including the profile of remained total organic carbon (TOC), the location of interface between dissolved methane and sulfate (SMI), and the derived chlorinity. Simulation results suggest that the ratio of biogenic methane to thermogenic methane forming hydrates was about 1:3. Predicted amount of methane hydrate using the column model was 3258.33 kg, very close to the estimated based on field observation (3112.82 kg).

Abstract While the use of energy efficient absorption heat pumps has been typically limited to the high capacity commercial and industrial applications, the use of a semi-open absorption heat pump for water heating has been demonstrated to be an energy efficient alternative for residential scale applications. A semi-open absorption system uses ambient water vapor as the refrigerant in the absorber where its heat of phase change is transferred to the process water, cooling the solution in the absorber. The solution is pumped to the desorber, where by adding heat, the water vapor is released from the solution and condensed in the condenser. The heat of phase change of water vapor is transferred to process water again in the condenser. This cycle when implemented with a membrane-based absorber in a plate and frame form of heat exchanger using ionic liquids can overcome the challenges related to the system architecture of conventional absorption heat pumps like the lower efficiency at small scale, crystallization/corrosion issues with the desiccants and the high cost of hermetically sealed components. The cycle COP for such a system was previously demonstrated by Chugh et al. for high humidity conditions. In this experimental study, design improvements were made that expand the system’s applicability to more practical and standardized test conditions. With these improvements, the performance of the system was evaluated. The results presented in this study demonstrate the improved system’s viability as a heat pump water heater conforming to standard water heater test conditions. Performance was measured at a cycle thermal COP of 1.2 with a hot water delivery water temperature of 56 °C and ambient air at 19 °C and 49% RH.

Abstract Although experimental studies have shown that Ga3Ni5 is a promising catalyst for carbon dioxide (CO2) hydrogenation to methanol (CH3OH), the roles that cluster size and support play in the reaction are not clear. This research was set to study the quantitative and qualitative impacts of the size and support of Ga-Ni clusters on CO2 hydrogenation to CH3OH at electronic and molecular levels by using density functional theory (DFT). Ga3Ni5, Ga6Ni10, Ga12Ni20, Ga15Ni25, and Ga24Ni40 nanoclusters, and γ-Al2O3- and SiO2- supported Ga6Ni10 were chosen as the study objects. Results show that adsorption energies of intermediates are highly related to intermediates’ characteristics and clusters’ active sites. Moreover, cluster size has no linear relation with the adsorption strengths of intermediates, while it has significant impact on the activation barrier of the rate-limiting step of hydrogenation process. Ga6Ni10 cluster has the lowest activation barrier of 1.04 eV due to the d-band center location and the exposed active sites of clusters. Compared with unsupported Ga6Ni10 clusters, Ga6Ni10/SiO2 and Ga6Ni10/γ-Al2O3 increase the adsorption energies of the intermediates and the activation barriers of the rate-limiting steps due to the lower electron transfer ability of Ga6Ni10 on SiO2 and γ-Al2O3 supports. Therefore, a support that can increase the electron transfer abilities of catalysts are preferable. The findings will be very beneficial for preparing new Ga-Ni catalysts for CO2 hydrogenation to CH3OH.