نشریه سوخت و احتراق
سال دهم شماره 2 (پیاپی 20، پاییز 1396)

Biodiesel and some nano-catalysts are an important additive to diesel fuel and can improve the engine performance and reduce emissions. In this study, biodiesel was added to pure diesel with ratios of 5 and 10 percent. Then, the carbon nanotubes were mixed as additive with these blends with concentrations of 30, 60, and 90 ppm to evaluate the performance, emissions, and vibration levels in a diesel engine. An ANN model, based on standard back-propagation learning algorithm for the engine, was developed. Multi-layer perception network (MLP) was used. The input or independent parameters were fuel blend, engine speed, fuel density, fuel viscosity, LHV, intake manifold pressure, fuel consumption, exhaust gas temperature, oxygen contained in exhaust gases, oil temperature, relative humidity and ambient air pressure. The target parameters were performance, emissions and RMS and Kurtosis of engine vibrations. The results showed that the specific fuel consumption and CO and UHC emissions decreased, while NOx emission increased. Also, the ANN model showed the training algorithm of back-propagation with 20-20 neurons in hidden layers (logsig-logsig) is able to predict different parameters with good performance and accuracy. The corresponding R-values for training, validation and testing were 0.9999, 0.9985 and 0.9994, respectively.

Biodiesel, due to its environmental benefits and similar properties with diesel, is considered as a fossil fuel alternative. Rapeseed oil is used to produce biodiesel in presence of K2CO3/Al2O3. For catalyst preparation K2CO3 was loaded on the Al2O3 as support using impregnation. Taguchi’s experimental setup was used in a completely randomized design with two replications for transesterification reaction and investigating the effects of reaction time, temperature and catalyst concentration on biodiesel production efficiency and to optimize the number of experiments. Also, molar ratio of 15 to 1 (alcohol:oil), catalyst concentrations of 0.5, 1, 1.5, 2, 3 and 5 wt.%, reaction temperatures of 55, 65 and 75 °C, reaction times of 0.5, 1, 1.5, 2, 2.5 and 3 hr. and stirring rate of 600 rpm was used for transesterification reaction. Highest biodiesel yield (99%) was obtained by transesterification process at 65 °C using 2 wt. % of K2CO3/Al2O3 for 2 hr. Comparing these results to other researcher’s results shows that the loading ratio of K2CO3 compared to KNO3 and Ca(NO3)2 can increase the biodiesel production efficiency in alumina-based catalysts. Analysis of variance analysis with regard to catalyst, reaction time and temperature variables indicates that temperature changes have no significant effect on the efficiency of methyl ester production, but the effects of time and catalyst concentration on the reaction rate is quite significant.

Homogeneous charge compression ignition (HCCI) is an advantageous combustion concept for internal combustion engines in terms of efficiency and pollutant emissions. However, the limited operating range of this combustion concept suppressed its successful utilization. One applicable method to use this combustion concept in engines is to combine it with other similar combustion strategies, such as diesel and partially premixed combustion (PPC), while each combustion concept come into work during its optimum operating range. In this study, the transition from partially premixed combustion (PPC) to homogeneous charge compression ignition (HCCI) combustion is determined based on investigating the performance and emission characteristics obtained from experimental data. The determination is based on the fact that in the direct-injection (DI) HCCI combustion, the stratification generated from the fuel injection is not an influencing factor. The results reveal that in the case of very early fuel injection timing (when the whole injection is completed before 60 crank angle degrees to top dead center) the HCCI combustion regime is obtained.

In this investigation, HZSM-5 zeolite with AlCl3 as aluminum source were synthesized by hydrothermal method and modified with cobalt. HZSM-5 and Co/HZSM-5 zeolites were used to investigate the product distribution in LPG fuel cracking. The prepared HZSM-5 and Co/HZSM-5 catalysts were characterized by XRD, FTIR, SEM, BET, XRF, NH3-TPD and Al MAS NMR analyses. The results of NH3-TPD showed that the acidity of Co/HZSM-5 zeolite was lower than HZSM-5. Aluminum distribution in the framework of HZSM-5 was determined by chemical analysis of XRF and reflectance UV-Visible analysis. The results indicated that the proportion of close Al atoms and single Al atoms in the zeolite framework was found to be 28.6% and 71.4%, respectively. The obtained olefin yield for Co/HZSM-5 (48.1%) was higher than HZSM-5 (45.4%) in catalytic cracking of LPG fuel. The yield of C5 heavy products, the formed coke and deactivation rate for Co/HZSM-5 catalyst were lower than unmodified HZSM-5.

In current research, the simultaneous effects of pilot fuel quantity and pilot injection timing on air-fuel mixing process, engine performance and the amount of pollutant emissions have been investigated in a High Speed Direct Injection (HSDI) turbo-charged diesel engine. For this purpose, a modified parameter called “Homogeneity Factor (HF)” has been applied as a new measure for analyzing the air-fuel mixing process. The simulated results has been firstly compared with the experimental data and a very good agreement has been achieved for simulating the in-cylinder pressure, the heat release rate and the amount of pollutant emissions. The results show that the pilot fuel quantity is more effective on air-fuel mixing quality than pilot injection timing. By advancing the start of pilot injection timing, the maximum amount of Homogeneity Factor (HF) during pilot injection, is achieved at an earlier time. As a result, for earlier SOP timing, a sufficient mixing is available to achieve a more homogeneous at the time of ignition.

In this article, steam injection into oxidizer and hydrogen injection into fuel are studied in order to reduce carbon monoxide production with CO2 injection into oxidizer in oxy-fuel combustion. For this purpose, one dimensional simulations with a counter flow diffusion flame solver and three dimensional simulations with openFoam software were performed. In the one dimensional simulations, the effects the injections on carbon monoxide emission index are investigated. The results indicate that injecting steam into the oxidizer decreases carbon monoxide emission index, while injecting hydrogen into the fuel acts in reverse. In the three dimensional study, due to very high computational costs, only the effect of steam injection into oxidizer is investigated as a suitable solution for reducing carbon monoxide emissions. The results obtained in thesesimulations show that steam injection in the oxidizer reduces of carbon monoxide production in the reactionzone and also the emissions from the furnace outlet.

The change in the Fermi level at the catalyst surface affects the catalytic activity. One way to change this level is to use an external electric field in the heterogeneous catalytic process. In this research, HZSM-5 was loaded with iron oxide and inserted in an external electric field with the proper strength for analyzing catalytic activity. This research is the first report presented for the synergistic effect of zeolite and external electric field to produce olefin, which has a higher activity than conventional methods. In a high voltage electric field, the energy band deviates, and the deviation of energy band increased the activity. The experimental design of the CCD was done using Design-Expert 7.3 software so that the relationship between the four process variables, namely: temperature, electrical current, the distance between the two electrodes, and the amount of metal load, are obtained. The square model was significant for response variables. The results indicate that the maximum yield (50.42%) can be resulted at 662.5 ° C, the intensity of the electric current input 3.67 mA, the distance between the two electrodes of 8 mm and the loading of the metal 6.7 3 wt.%.