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Abstract Knocking combustion for spark-ignition engine is related to auto-ignition of a portion of the unburned fuel-air mixture. In this investigation, the detailed chemical kinetic mechanism was engaged to numerically study the auto-ignition characteristics of hydrogen-enriched methane under engine-relevant conditions. Compared with the experimental data, the USC Mech 2.0 mechanism obtained the closest agreement, and it was adopted in the sensitivity analysis, the rate of production (ROP) analysis and the reaction pathway analysis. Results showed that at high temperature and high pressure, the ignition delay times (IDs) of CH4/H2 fuel blends reduce significantly (by two orders of magnitude at most) with rising hydrogen fraction, but the decline rate is not so obvious (within 37.3%) at low temperature. The sensitivity analysis indicated that at high temperature the reaction (R1) and reactions (R2, R3) promote each other while at low temperature only the reaction (R3) unilaterally facilitates the reaction (R12). The ROP analysis implied that the decrease of IDs of methane by hydrogen addition is realized through increasing the H, O, and OH radical production. Interestingly, the IDs for CH4/H2 fuel blends show different trends at different temperature, which decrease (by 47.5% at most) at low temperature but increase (by 132.7% at most) at high temperature as the equivalence ratio rises. The sensitivity analysis showed that the ignition kinetics for CH4/H2 fuel blends more depend on the CH4 concentration at low temperature but oxygen concentration at high temperature. This investigation not only supplements the fundamental combustion studies of CH4/H2 fuel blends in elevated pressures, but also reveals the influence mechanism of hydrogen addition and equivalence ratio on the IDs of CH4/H2 fuel blends at high pressure. More importantly, it may offer fundamental insights for the control of knocking combustion of spark-ignition (SI) engine.

Abstract Distributed energy system becomes increasingly popular due to high efficiency and low pollution emissions. When it operates following the electricity load, thermal energy storage system can be used to accommodate surplus cooling and heating and improve the energy efficiency. This study investigates the energy and economic performance of thermal storage systems for surplus cooling and heating in distributed energy system, considering the impacts of climates, building combinations and cooling/heating supply systems. Results show that the thermal storage system can improve the primary energy efficiency and is more useful when residential buildings adopt centralized heating and decentralized cooling systems. By varying climates and building combinations, the thermal storage system can improve the primary energy efficiency by 0.28%–3.69%. The economic performance is not promising with a long payback period. The main reason is that the overall utilization rate of the surplus energy is low (less than 45%), especially when the cooling/heating load is low continually during spring and autumn. Additionally, the effect of static and dynamic thermal storage model is analyzed. Results show that the static model would over-estimate the performance of the thermal storage system significantly and the dynamic model is recommended.

Abstract Liquid fuels are likely to remain the main energy source in long-range transportation and aviation for several decades. To reduce our dependence on fossil fuels, liquid biofuels can be blended to fossil fuels – or used purely. In this paper, coconut methyl ester, standard diesel fuel (EN590:2017), and their blends were investigated in 25 V/V% steps. A novel turbulent combustion chamber was developed to facilitate combustion in a large volume that leads to ultra-low emissions. The combustion power of the swirl burner was 13.3 kW, and the air-to-fuel equivalence ratio was 1.25. Two parameters, combustion air preheating temperature and atomizing air pressure were adjusted in the range of 150–350 °C and 0.3–0.9 bar, respectively. Both straight and lifted flames were observed. The closed, atmospheric combustion chamber resulted in CO emission below 10 ppm in the majority of the cases. NO emission varied between 60 and 183 ppm at straight flame cases and decreased below 20 ppm when the flame was lifted since the combustion occurred in a large volume. This operation mode fulfills the 2015/2193/EU directive for gas combustion by 25%, which is twice as strict as liquid fuel combustion regulations. The 90% NO emission reduction was also concluded when compared to a lean premixed prevaporized burner under similar conditions. This favorable operation mode was named as Mixture Temperature-Controlled (MTC) Combustion. The chemiluminescent emission of lifted flames was also low, however, the OH* emission of straight flames was clearly observable and followed the trends of NO emission. The MTC mode may lead to significantly decreased pollutant emission of steady-operating devices like boilers, furnaces, and both aviation and industrial gas turbines, meaning an outstanding contribution to more environmentally friendly technologies.

The effect of pilot injection timing and pilot injection mass on combustion and emission characteristics under medium exhaust gas recirculation (EGR (25%)) condition were experimentally investigated in high-speed diesel engine. Diesel fuel (B0), two blends of butanol and diesel fuel denoted as B20 (20% butanol and 80% diesel in volume), and B30 (30% butanol and 70% diesel in volume) were tested. The results show that, for all fuels, when advancing the pilot injection timing, the peak value of heat release rate decreases for pre-injection fuel, but increases slightly for the main-injection fuel. Moreover, the in-cylinder pressure peak value reduces with the rise of maximum pressure rise rate (MPRR), while NOx and soot emissions reduce. Increasing the pilot injection fuel mass, the peak value of heat release rate for pre-injected fuel increases, but for the main-injection, the peak descends, and the in-cylinder pressure peak value and NOx emissions increase, while soot emission decreases at first and then increases. Blending n-butanol in diesel improves soot emissions. When pilot injection is adopted, the increase of n-butanol ratio causes the MPRR increasing and the crank angle location for 50% cumulative heat release (CA50) advancing, as well as NOx and soot emissions decreasing. The simulation of the combustion of n-butanol–diesel fuel blends, which was based on the n-heptane–n-butanol–PAH–toluene mixing mechanism, demonstrated that the addition of n-butanol consumed OH free radicals was able to delay the ignition time.

The increasing environmental concerns and the significant growth of the waste to energy market calls for innovative and flexible technology that can effectively process and convert municipal solid waste into fuels and power at high efficiencies. To ensure the technical and economic feasibility of new technology, a sound understanding of the characteristics of the integrated energy system is essential. In this work, a comprehensive techno-economic analysis of a waste to power and heat plant based on integrated intermediate pyrolysis and CHP (Pyro-CHP) system was performed. The overall plant CHP efficiency was found to be nearly 60% defined as heat and power output compared to feedstock fuel input. By using an established economic evaluation model, the capital investment of a 5 tonne per hour plant was calculated to be £27.64 million and the Levelised Cost of Electricity was £0.063/kWh. This agrees the range of cost given by the UK government. To maximise project viability, technology developers should endeavour to seek ways to reduce the energy production cost. Particular attention should be given to the factors with the greatest influence on the profitability, such as feedstock cost (or gate fee for waste), maintaining plant availability, improving energy productivity and reducing capital cost.

Abstract Fuel properties play important roles both in the physical process of fuel air mixing and chemical process of combustion in the cylinder of diesel engines. There are many parameters to represent physical and chemical properties of a diesel fuel, which may affect combustion of diesel engine to different degrees. It is valuable to deeply understand the effects of fuel properties and the relations between some major properties as well. Therefore, the effects of diesel fuel properties on combustion and emissions have been experimentally investigated on a heavy-duty diesel engine in this study. In addition, the relationships among some major properties have been discussed. Twelve fuels with different fuel properties, which were produced by different refining processes from different refineries in China, were selected to ensure that the tested fuels have a wide representative. The results show that there is a strong correlation between fuel density and other fuel properties such as cetane number, aromatic hydrocarbon fraction, heat value, etc. Especially, the linear regression model between density and cetane number shows a certain reference significance. The cetane number of fuel with high density is low, which results in the delay of combustion and the rise of peak heat release rate at low load. There is no significant difference in brake thermal efficiency (BTE) for fuels with different fuel properties in the current study. However, the brake specific fuel consumption (BSFC) increases with the increase of fuel density because of the decrease in heat value. As the fuel density increases, the NOx emissions increase accordingly and the soot emissions roughly show an increasing trend as well. At low load, both CO and HC emissions obviously increase with the increase of fuel density. For example, at low load and low speed, CO and HC increase by 256%, 158% respectively as the fuel density increases from 800 kg/m3 to 920 kg/m3. Nonetheless, CO emissions remain a low level and show no obvious changes at medium and high loads, which is different from HC emissions that increase gradually especially for high speed conditions. The results of the European Steady-state Cycle (ESC) show that weighted BSFC and weighted emissions exhibit strong correlations with fuel density. When fuel density is bigger than a certain value (about 845 kg/m3), a rapid increasing trend is presented in the emissions of NOx, soot, CO and HC.

Abstract The different fuel injection time, fuel injection pressure, fuel types were investigated to achieve low temperature premixed combustion in four-cylinder light-duty diesel engine using a common rail injection system. The two blending proportions of black soldier fly biodiesel (BD) at 10% and 20% BD-diesel blends were compared with pure diesel fuel in the present study. The combustion, performance, and emission of black soldier fly biodiesel were explored and compared with the conventional diesel combustion. Experimental outcomes showed that under low load, early and late injection time can attain low temperature premixed combustion that resulted in prolonged ignition delay and increased heat release rate. It has been observed that equivalent fuel consumption rate of black soldier fly biodiesel was driven higher (245–260 g/kWh) by increasing fuel injection time and fuel injection pressure but lower than pure diesel fuel (255–270 g/kWh). Moreover, an oxide of nitrogen emission rises with early fuel injection time (100–1200 ppm) compared to late fuel injection time (200–300 ppm), whereas the pure diesel fuel has lower emission 900 ppm at early fuel injection time but the rate was similar at late fuel injection time (200 ppm), whereas the early and late fuel injection time can reduce the smoke emission 0.02 l/m than diesel fuel which has smoke emission 0.04 l/m and 0.08 early and late fuel injection time respectively. The low blending ratio 10% BD recorded the reduction in the oxide of nitrogen emission (50%) than 20% BD and similar effects was observed for equivalent fuel consumption. The heat release rate was found to be high in higher fuel injection pressure due to the increase in the proportion of premixed combustion. Furthermore, the oxide of nitrogen emission was increased with the rise of fuel injection pressure, but smoke emission reduced during the process.

Abstract A novel combined cooling and power (CCP) system integrating a supercritical carbon dioxide recompression Brayton cycle with an ejector transcritical carbon dioxide refrigeration cycle (E-TCRC) is proposed to realize the effective utilization of nuclear power. In the proposed system, a portion of CO2 exiting the pre-cooler is used to drive the E-TCRC for generating cooling and recovering partial waste heat of sCO2 turbine exhaust. The mathematical model and economic model of the proposed system are established under steady-state conditions. Besides, the exergy efficiency and total product unit cost of the system are selected as the main criteria to evaluate system performance. Parametric analysis is applied to study the effects of four key parameters on the system performance. The CCP system, conventional separated cooling and power (C-SCP) system and ejector separated cooling and power (E-SCP) system are optimized by single-objective and multi-objective optimization. Single-objective optimization reveals that the exergy efficiencies of the CCP system are up to 1.08%pt (percentage point), 0.80%pt and 0.47%pt higher than those of the C-SCP system at the corresponding evaporation temperatures (−20 °C, −10 °C and 0 °C). Besides, the CCP system performs better than the E-SCP system at lower turbine inlet pressures. The multi-objective optimization shows that when the evaporation temperature increases from −20 °C to 0 °C, the total product unit cost of the CCP system decreases from 10.087 $/GJ to 9.668 $/GJ, and exergy efficiency increases from 59.25% to 60.97%.