An Integrated System for Energy-efficient Exhaust Aftertreatment for Heavy-duty Vehicles

New regulations by the California Air Resources Board (CARB) demand a stringent 0.02 g/hp-hr tailpipe NOx limit by the year 2027, requiring Selective Catalytic Reduction (SCR) catalysts to provide high NOx conversions even at low (below 200°C) exhaust temperatures. This work describes utilizing an Electrically Heated Mixer System (EHM system) upstream of a Light-Off Selective Catalytic Reduction (LO-SCR) catalyst followed by a conventional aftertreatment (AT) system containing DOC, DPF, and SCR, enabling high NOx conversions meeting CARB’s NOx emission target. The AT catalysts were hydrothermally aged to Full Useful Life. Conventional unheated Diesel Exhaust Fluid (DEF) was injected upstream of both the LO-SCR and primary downstream SCR. The EHM system allowed for DEF to be injected as low as 130°C upstream of the LO-SCR, whereas, in previous studies, unheated DEF was injected at 180°C or dosed at 130°C with heated DEF. The combination of unheated DEF, EHM system, LO-SCR, and downstream SCR enabled the needed increase in NOx efficiency in low exhaust temperatures, which was observed in drive cycles such as in cold-FTP, LLC, and World Harmonized Transient Cycle (WHTC). There were several-fold reductions in tailpipe NOx using this configuration compared to its baseline: 3.3-fold reduction in FTP, 22-fold in Low Load Cycle (LLC), 38-fold in Beverage Cycle, 8-fold in “Stay Hot” Cycle, and 10-fold in WHTC. Finally, it is shown that the EHM system can heat the exhaust gas, such as during a cold start, without needing additional heating hardware integrated into the system. These results were observed without performing changes in the engine base calibration.

Environmental problems have become a major issue for diesel engine development. Although emission aftertreatment systems such as DPFs (diesel particulate filters), LNTs (lean NOx traps) and SCR (selective catalytic reduction) have been used in diesel vehicles, the manufacturing cost increase caused by this equipment can be hard to be control. Thus, it is better for engine emissions to be reduced by improving the combustion system. A dual-fuel combustion concept is a recommended method to improve a combustion system and effectively reduce emissions. Low reactivity fuel including gasoline and natural gas, which was supplied to the intake port by the FPI (port fuel injector), improved the premixed air-fuel mixture conditions before ignition. Additionally, a small amount of high reactivity fuel, in this case diesel, was injected into the cylinder directly as an ignition source. This dual-fuel combustion promises lower levels of NOx (nitrogen oxide) and PM (particulate matter) emissions due to the elimination of local rich regions in the cylinder. However, it is challenging to control the dual-fuel combustion because the combustion stability and efficiency deteriorate due to the lack of ignition source and reactivity. Thus, it is important to establish an appropriate dual-fuel operating strategy to achieve stable, high efficiency and low emission operation. As a result of this research, a detailed operating method of dual-fuel PCI (premixed compression ignition) was introduced in detail at a low speed and low load condition by using a single cylinder diesel engine. Engine operating parameters including the gasoline ratio, a diesel injection strategy consisting of multiple injectors and timing, the EGR (exhaust gas recirculation) rate and the intake pressure were controlled to satisfy the low ISNOx (indicated specific NOx) and PM emissions levels (0.21 g/kWh and 0.1 FSN, 0.040 g/kWh, respectively) as per the EURO-6 regulation without any after-treatment systems. The results emphasized that a well-constructed dual-fuel PCI operating strategy showed low NOx and PM emissions and high GIE (gross indicated fuel conversion efficiency) with excellent combustion stability.

<p indent="0mm">Diesel vehicle exhaust aftertreatment technology is a cornerstone in the ongoing effort to meet increasingly stringent emission regulations and achieve green, low-carbon transportation. The enforcement of the China VI standards has significantly reduced pollutant emissions, showcasing the effectiveness of current aftertreatment technologies. However, despite these advancements, considerable challenges remain in further enhancing the efficiency and managing the costs associated with these technologies. The need for continuous improvement is driven by the evolving regulatory landscape and the global push for sustainability. New materials and technological advances have emerged in recent years, offering fresh strategies for resolving these persistent challenges. This analysis aims to provide a thorough overview of the most recent developments in key catalysts used in the exhaust aftertreatment systems of diesel vehicles. This review delves into the innovative application of advanced catalytic materials within core systems, including diesel oxidation catalysts (DOCs), diesel particulate filters (DPFs), selective catalytic reduction (SCR) catalysts, and ammonia slip catalysts (ASC). These systems all play a critical role in the overall performance of diesel exhaust aftertreatment, and their optimization is essential to meet increasingly stringent emission standards. This review evaluates the possibility of several catalytic materials in practical, real-world applications by carefully examining the structural design, active component properties, and underlying mechanisms by which these materials enhance exhaust gas purification reactions. The review highlights the importance of the synergistic interaction between the four conventional aftertreatment technologies. For instance, DOCs produce carbon monoxide (CO) and nitrogen dioxide (NO₂) through the oxidation of hydrocarbons, which is crucial for enhancing the reaction efficiency of both DPFs and SCR systems. However, DPFs are highly effective in capturing soot and reducing the energy consumption typically associated with regeneration processes through passive regeneration. The SCR system works closely with ASC to efficiently reduce nitrogen oxides (NO<italic>x</italic>) while preventing ammonia slip, a common issue in aftertreatment systems. The complex interactions between these units must be considered throughout the design and optimization of the entire exhaust treatment system to achieve optimal treatment performance and comply with strict emission requirements. Advancements in catalyst development have led to more efficient, cost-effective, and sustainable materials. However, further research is warranted to enhance the scientific understanding of these systems, especially using advanced characterization techniques. <italic>In-situ</italic> technologies offer high precision in observing dynamic changes at active sites. The energetic pathways of elementary processes at active sites can be determined by leveraging the powerful data processing capabilities of machine learning in conjunction with molecular dynamics simulations and Density Functional Theory (DFT) calculations. This method will also uncover new descriptors of structure-activity relationships, guiding the design of catalysts with superior low-temperature activity, durability, selectivity, and regeneration efficiency. Future plans call for tighter regulations on pollutants, including N₂O and NH₃, due to the expected introduction of Euro 7 standards and China VII emission requirements. These regulations will drive further innovation in exhaust treatment technologies. Future research should focus on developing multi-pollutant control technologies. For example, multifunctional catalysts capable of reducing NO<italic>x</italic>, decomposing N₂O, and oxidizing NH₃ could be vital in meeting China VII standards. To sum up, this review offers a comprehensive analysis of the state of diesel vehicle exhaust aftertreatment technology today, highlighting the vital role that key materials will play in fostering future innovation. It underscores the importance of ongoing research and development efforts to meet evolving regulatory demands, enhance system performance, and ensure the sustainability of diesel exhaust management systems.

Rising fuel costs and efforts for reducing greenhouse gases have led researchers to propose optimized models of combustion which have high efficiency and low emissions. Reactivity controlled compression ignition (RCCI) engines are attractive due to their high efficiency and low NOx and soot emissions over a wide range of operating conditions. In this study, methane and n-heptane are used as low and high reactive fuels, respectively, to create suitable fuel stratification within the cylinder. Modeling is carried out by AVL FIRE coupled with a chemical kinetics solver to investigate the effects of fuel ratio, initial temperature and equivalence ratio on the combustion performance and emission characteristics. Methane/n-heptane ratios are varied according to the energy ratio of each fuel while total input energy and total equivalence ratios are fixed. By increasing methane energy ratio from 65% to 85% in the constant intake temperature and pressure, the mixture Octane number increases, which would lead to an increase in ignition delay up to 5 crank angles. As a result, IMEP would be enhanced and also NOx emission decreases because of lower combustion temperature. By increasing intake temperature, the maximum in-cylinder pressure, heat release rate and NOx emission would increase significantly while soot emission decreases, and also ringing intensity increases up to 10%. On the other hand, increasing intake temperature reduces volumetric efficiency; as a result, IMEP is reduced by 11%. Also by increasing equivalence ratio from 0.35 to 0.55 in a constant energy ratio, noticeable growth in the maximum amount of pressure and temperature could be achieved; consequently, NOx emission would increase significantly, IMEP increases by 43%, and ISFC decreases by 30%. The results indicate that these parameters have significant effects on the heavy-duty RCCI engine performance and emissions.

Resum. La regulaci mundial d'emissions contaminants en el sector de l'automoci est sent cada vegada ms estricta. La implantaci de nous procediments est pressionant la indstria cap a la cerca de noves tecnologies que complisquen els objectius de reducci d'emissions contaminants. En el mig termini s'espera que les proves d'emissions a baixa temperatura ambient siguen obligatries en el procs d'homologaci. La combusti a baixes temperatures influeix de forma important en la velocitat de la reacci comportant un augment de les emissions i finalment a l'apagat de flama. Sota aquestes condicions, es produeix un augment de les emissions d'hidrocarburs (HC) i monxid de carboni (CO) aix com un augment del consum de combustible. A ms, en condicions de baixa temperatura ambiente les emissions d'xids de nitrogen (NOx) poden augmentar a causa de la desactivaci dels sistemes de recirculaci de gasos d'escapament. En la present tesi, s'ha analitzat l'efecte de la baixa temperatura ambiente en un motor disel HSDI. Els assajos van ser realitzats en cicles de conducci NEDC i WLTC. La influncia directa de les baixes temperatures en les emissions es va analitzar per mitj de la mesura bruta de contaminants, aiges a dalt dels sistemes de postractament. El funcionament dels sistemes de postractament tamb va ser avaluat a baixes temperatures mitjanant l'eficincia de la oxidaci cataltica de HC i CO. Els resultats d'aquest estudi van mostrar una deterioraci general de les emissions i del rendiment efectiu a baixes temperatures. L'efecte de les baixes temperatures variava depenent de les condicions de crrega. El cicle NEDC es consolida com el pitjor escenari de conducci, per a la realitzaci de proves a baixa temperatura, amb un increment del 270% en HC, 250% en NOx, 125% en CO i 20% en consum especfic. El major grau de crrega juntament amb el carcter ms transitori del cicle WLTC van mostrar un efecte menor de les baixes temperatures ambient amb un augment del 150% en HC i 250% en NOx. A diferncia del cicle NEDC, les emissions de CO es van reduir en un 20% i no es va detectar un augment del consum de combustible. A ms de l'augment de la formaci de contaminants, l'anlisi del catalitzador d' oxidaci va mostrar una reducci de l'eficincia en tots dos cicles de conducci NEDC i WLTC. El present treball t per objectiu analitzar i comparar dos sistemes de gesti trmica per a la millora del funcionament dels MCIA a baixes temperatures. El primer sistema estava basat en la gesti del flux de refrigerant per a evitar subrefredament en condicions de funcionament en fred. D'una banda, es van proposar estratgies de baix i nul flux en el circuit de refrigerant motor. D'altra banda, es van realitzar assajos amb 0 flux en el circuit de refrigerant del WCAC per a evitar el subrefredament de l'aire d'admissi durant punts de baixa crrega en condicions de funcionament en fred. L'altre sistema incloa la recuperaci d'energia trmica de l'escapament (EGHR). El refrigerant del WCAC es va emprar com flut de recuperaci connectantse amb un bescanviador d'escapament per a l'absorci d'energia trmica residual. L'energia recuperada era lliurada en el WCAC a l'aire per a accelerar l'augment de la temperatura d'admissi. La primera part dels resultats de la gesti trmica estan centrats en l'anlisi individual dels diferents sistemes de gesti. En les conclusions es comparen tots els sistemes proposats explicant les diferncies entre ells. Mitjanant l's del EGHR les emissions de HC van ser redudes, durant els punts de baixa crrega, en comparaci de la resta d'estratgies trmiques plantejades. L'anlisi energtic del EGHR es va centrar en l'eficincia i en l'estudi de la recuperaci per canvi de fase. El paper que l'entalpia de canvi de fase juga en la recuperaci de calor residual va ser estudiat per mitj del mesurament de concentraci de vapor d'aigua en el gas d'escapament en l'entrada i eixida del bescanviador del EGHR. La condensaci del vapor d'aigua de l'escapamanet va representar el 25% de tota l'energia recuperada.

&lt;div&gt;The stringent emission regulations for Internal Combustion Engines (ICEs) spawned a great amount of research in the field of innovative combustion approaches characterized by high efficiency and low emissions. Previous research demonstrate that such promising techniques, named Low-Temperature Combustion (LTC), combine the benefits of Compression Ignition (CI) engines, such as high compression ratio and unthrottled lean mixture, with low engine-out emissions using a properly premixed air-fuel mixture. Due to longer ignition delay and high volatility compared to diesel, gasoline-like fuels show good potential for the generation of a highly premixed charge, which is needed to reach LTC characteristics. In this scenario, gasoline Partially Premixed Combustion (PPC), characterized by the high-pressure direct injection of gasoline, showed good potential for the simultaneous reduction of pollutants and emissions in CI engines. However, previous research on gasoline CI highlight that a key factor for the optimization of both efficiency and pollutants is the proper management of Exhaust Gas Recirculation (EGR). This work presents the experimental investigation performed running a light-duty CI engine, operated with gasoline PPC, and varying the mass of recirculated gases trapped in the combustion chamber. To guarantee the stability of gasoline autoignition in all the tested conditions, a specific experimental layout has been developed to accurately quantify the amount of trapped residual gases due to the internal and external EGR. The obtained results clearly highlight the impact of EGR on the combustion process and emissions, demonstrating that optimization of charge dilution with EGR is fundamental to guarantee the optimal compromise between efficiency and emissions over the whole operating range.&lt;/div&gt;

Expansion of stable operational range in MILD hydrogen combustion based on catalytic techniques

Integrated process for synthetic natural gas production from coal and coke-oven gas with high energy efficiency and low emission

The thermodynamic characteristics of high efficiency, internal-combustion engines

Natural gas-fired combined cycle plants are nowadays one of the most efficient and environmentally friendly energy complexes. High energy efficiency and low specific emissions are achieved primarily due to the high average integral temperature of heat supply in the Brayton–Rankine cycle. In this case, the main sources of energy losses are heat losses in the condenser of the steam turbine plant and heat losses with the exhaust gases of the waste heat boiler. This work is related to the analysis of the thermodynamic and economic effects in the transition from binary to trinary cycles, in which, in addition to the gas and steam–water cycles, there is an additional cycle with a low-boiling coolant. A method for the feasibility study of a waste heat recovery unit for trinary plants is proposed. The schematic and design solutions described will ensure the increased energy and economic performance of combined cycle power plants. Based on the results of the thermodynamic optimization of the structure and parameters of thermal schemes, it was found that the use of the organic Rankine cycle with R236ea freon for the utilization of the low-grade heat of a trinary plant’s exhaust gases operating from a GTE-160 gas turbine makes it possible to achieve a net electrical efficiency of 51.3%, which is a 0.4% higher efficiency for a double-circuit combined cycle gas turbine plant and a 2.1% higher efficiency for a single-circuit cycle with similar initial parameters. On the basis of the conducted feasibility study, the parameters and characteristics of the heat exchangers of the regenerative system of the waste heat recovery unit are substantiated. The use of plain fin-and-tube heat exchangers in the regenerative system of the utilization cycle is the most promising solution. It was found that the level of allowable pressure loss in the regenerator of 10 kPa and the degree of regeneration of 80% allow for maximum economic efficiency of the waste heat recovery unit.

CO 2 reduction potential of future coal gasification based power generation technologies

Electric vehicles (EVs) hold promise for attaining sustainable development objectives and mitigating the effects of global climate change due to their substantial benefits, such as high energy efficiency and low carbon emissions. Research on purchase intentions and behaviors may accelerate the adoption of EVs. Considering that the number of studies on EVs increases in tandem with the size of the market and that mutual interaction supports this two-way growth, conducting studies on consumer behavior in this area in countries where the electric vehicle market is developing, such as Turkey, will provide valuable insights for both the industry and the government. In this study, published articles on the consumer behavior of current and potential purchasers of electric vehicles were analyzed on the axis of Turkey, and the trend of academic studies in the literature was systematized from a holistic standpoint. Co-citation, co-keyword, geographical, and thematic analysis were applied to articles about EV consumer behaviors published between 2004 and 2022 in journals indexed by WoS, Scopus, TR Index, and DergiPark. The results of this study can inform numerous inter-disciplinary studies and researchers on the consumer behavior of electric vehicles. The bibliometric analysis of academic studies on electric vehicle consumers not only closes the market’s knowledge gap and accelerates the adoption process by increasing consumer awareness, but also provides industry representatives and policymakers with insights for the expansion of the EV market.

It is important to deal with energy saving in buildings of one city level, and plan the energy system from one building to one city level. We strongly suggest conducting urban building energy planning (UBEP) in the urban planning field in China. There are two main characteristics of an urban building energy system. First, the terminal building energy demand is dynamically timely. Second, the energy demand, energy sources supply, energy equipments, and networks of heating, cooling, gas, and electricity, are distributed in an urban space. It is meaningful to conduct an innovative urban energy planning with space distribution and time dynamic simulation. Therefore, an UBEP simulation tool, developed by our research group, is introduced. Finally, a case of energy planning in Beijing City in 2010 for heating and air conditioning system is dynamically simulated and analyzed. To meet the same building energy demand in Beijing, such as heating, air conditioning, gas, and electricity, different energy equipments, such as boiler, combined heating and power, combined cooling, heating, and power system, and heat pump based on different energy sources, such as coal, gas, and electricity, should be planned alternatively. Also, an optimum urban energy system with high energy efficiency and low environmental emission can be achieved. This simulation tool contains most models of heating and cooling energy systems in China. We can validate the models with statistical data from previous or present simulation, and the simulation results in future planning can serve as guidance for the construction of municipal energy infrastructure. We can conclude that simulation in time dimension shows the characteristics of dynamic load in each nodes of the energy flow. The objective is to present the comparison of different scenarios and optimize the planning schemes.

Gas separation using polymeric membranes is generally believed to be poorly suited for CO2 capture from gas turbine based power plants, because the high air-to-fuel ratios produce large amounts of exhaust gas containing strongly diluted CO2. The driving force for selective permeation is obtained by compressing the entire exhaust stream, resulting in a significant energy penalty. Additional energy is required for permeate compression, which is impaired by the other gases emitted with CO2. In spite of these difficulties, the present study is concerned with membrane systems, which the authors believe warrant further investigation. The attention was focused on natural gas combined cycles (NGCC), so as to have a starting point with high energy efficiency and low baseline emissions. To reduce the exhaust gases and to concentrate the CO2, the NGCC is fitted with a flue gas recirculation system, which has proven to leave plant performance substantially unaffected. The energy requirements for exhaust gas compression are reduced by introducing a heat exchanger between the compressed and residual exhaust gas and recovering heat from the latter. The membrane separator has been modeled using conservative data reported in the literature. Various configurations, such as multiple compression-expansion and multistage membrane units, are considered. Permeate compression is also modeled, so as to highlight the influence of permeate purity on this process. The results show a rather moderate performance penalty. A specific emission of 100 g CO2/kWh corresponds to 48 percent efficiency. Admittedly a CO2 separator for a power plant would be larger than any other membrane system designed for other purposes. However, the system appears technically feasible and would offer valuable benefits in terms of emissions.

Full course evolution characteristics of DPF active regeneration under different inlet HC concentrations