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Abstract The present study experimentally quantified the pyrolysis behaviors of waste tea (WT) as a function of four heating rates using thermogravimetric-Fourier transform infrared spectrometry and pyrolysis-gas chromatography-mass spectrometry analyses. The maximum weight loss of WT (66.79%) occurred at the main stage of devolatilization between 187.0 and 536.5 °C. The average activation energy estimates of three sub-stages of devolatilization were slightly higher (161.81, 193.19 and 224.99 kJ/mol, respectively) by the Flynn-Wall-Ozawa than Kissinger-Akahira-Sunose method. Kinetic reaction mechanisms predicted using the master-plots were f (α) = (3/2)(1 − α)2/3[1 − (1 − α)1/3]−1, f (α) = (1 − α)2, and f (α) = (1 − α)2.5 for the three sub-stages, respectively. The prominent volatiles of the WT pyrolysis were CO2 > C O > phenol > CH4 > C O > NH3 > H2O > CO. A total of 33 organic compounds were identified including alkene, acid, benzene, furan, ketone, phenol, nitride, alcohol, aldehyde, alkyl, and ester. This study provides a theoretical and practical guideline to meeting the engineering challenges of introducing WT residues in the bioenergy sector.

Abstract Catalytic fast co-pyrolysis (co-CFP) of bamboo sawdust and waste tire over HZSM-5 and MgO was conducted using a tandem pyrolysis and upgrading system which consists of a bubbling fluidized bed and a fixed bed reactor. HZSM-5 mixed and sequential with MgO modes were studied to explore the additive effect for the promotion of aromatic hydrocarbons. Experimental results indicated that co-CFP of bamboo sawdust with waste tire over pure HZSM-5 increased the yields of pyrolysis oil and char, while the gas yield decreased with the increasing of waste tire percentage in the feedstock blends. The product distribution of pyrolysis oil obtained from co-CFP of bamboo sawdust and waste tire over pure HZSM-5 was dominated by aromatic hydrocarbons, and the relative concentration increased from 26.71 to 71.50% as the waste tire percentage elevated from 0 to 60 wt%. Co-CFP of bamboo sawdust and waste tire using HZSM-5 mixed with MgO mode produced a higher yield of pyrolysis oil than the sequential mode when HZSM-5/MgO mass ratio was raised from 1:4 to 1:1. However, the sequential mode was proved to be more effective in the promotion of aromatic hydrocarbons than the mixed mode at a higher HZSM-5 proportion. A positive additive effect for alkylbenzenes was found when the sequential mode was used at varying HZSM-5/MgO mass ratios. Regarding the olefins, C10 olefins were main products, and limonene selectivity increased at first and then decreased with the highest selectivity of 38.87% occurring at HZSM-5/MgO of 2:3 in the mixed mode case. The additive effect of HZSM-5 and MgO indicated that both the mixed and sequential modes inhibited the formation of polycyclic aromatic hydrocarbons with the most significant additive effect obtained at HZSM-5/MgO mass ratio of 1:1 using the mixed mode.

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.

Abstract A novel dual functional heat pump and power generation integration system (DFHPPGIS) using a scroll machine as compressor and expander is proposed in this paper. It can be operated in both reverse Carnot cycle (RCC) heat pump mode and organic Rankine cycle (ORC) power generation mode. Compared with single system, this system can improve the utilization efficiency of geothermal water and generate more economic benefits. Three kinds of ORC and RCC working fluids are compared to select refrigerant R245fa as the most suitable fluid for the system. Then the model of DFHPPGIS is built to analyze its energy, exergy and economic performance as the variation of geothermal water inlet temperature. Results of theoretical calculation show that there is a conflict between total cost and payback period of the system. The system with lower total cost shows high payback period and vice versa. Thus, a multi-objective optimization for the system is conducted to determine the optimal geothermal water inlet temperature based on the ideal point decision making method. Exergy loss of the system under the optimal condition is analyzed to reveal which component has the largest exergy loss. The results indicate that in this proposed system, if the total cost based optimized design is chosen, payback period is 136.4% higher than its minimum value. If the method of payback period based optimized design is selected, total cost is 15.3% higher than its minimum value. The system has a heat capacity of 250.19 kW and a power output of 17.83 kW at the optimal geothermal water inlet temperature of 80℃ as well as the total cost and payback period of the system are 37.31 k$ and 4.87 years. In addition, the scroll machine has the largest exergy loss in both RCC and ORC mode, which is the component that needs to be mostly optimized in the further development.

Abstract The experiment and simulation investigation of vehicle energy management (VEM) were carried out on a passenger car equipped with a turbocharged gasoline engine. The research results show that the vehicle takes on the characteristic of overcharge under urban conditions to guarantee the power by sacrificing economy. Exhaust energy after catalytic converter and the greater circulation heat transfer loss that account for more than one-third of total energy under New European Driving Cycle (NEDC) are wasted without being used, which indicates that the tested vehicle has great potential for recovering the waste heat. To solve these problems, the VEM model coupled multiple physical fields was developed and calibrated. Original turbocharger was reformed to hybrid turbocharger with the aid of simulation model, and its optimal control strategy based on equivalent consumption minimization strategy (ECMS) was designed. The one-dimensional numerical engine model was introduced into algorithms, which opens new windows for the development of VEM optimization strategies. After the transformation of hybrid turbocharger, the overcharge phenomenon under urban driving cycle has been eliminated. The main contribution to fuel saving comes from the reduction of pumping loss and alternator power consumption. The energy saving rate of hybrid turbocharger in different driving cycles ranges from 1% to 5%, which is mainly affected by the deterioration degree of overcharge on the economy of original machine and the characteristics of regeneration conditions in different driving cycles.

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.