Ajay Kumar Yadav

Influence of low-temperature combustion and dimethyl ether-diesel blends on performance, combustion, and emission characteristics of common rail diesel engine: a CFD study

Due to presence of more oxygen, absence of carbon-carbon (C-C) bond in chemical structure, and high cetane number of dimethyl ether (DME), pollution from DME operated engine is less compared to diesel engine. Hence, the DME can be a promising alternative fuel for diesel engine. The present study emphasizes the effect of various exhaust gas recirculation (EGR) rates (0–20%) and DME/Diesel blends (0–20%) on combustion characteristics and exhaust emissions of common rail direct injection (CRDI) engine using three-dimensional computational fluid dynamics (CFD) simulation. Extended coherent flame model-3 zone (ECFM-3Z) is implemented to carry out combustion analysis, and k-ξ-f model is employed for turbulence modeling. Results show that in-cylinder pressure marginally decreases with employing EGR compared to without EGR case. As EGR rate increases, nitrogen oxide (NO) formation decreases, whereas soot increases marginally. Due to better combustion characteristics of DME, indicated thermal efficiency (ITE) increases with the increases in DME/diesel blend ratio. Adverse effect of EGR on efficiency for blends is less compared to neat diesel, because the anoxygenated region created due to EGR is compensated by extra oxygen present in DME. The trade-off among NO, soot, carbon monoxide (CO) formation, and efficiency is studied by normalizing the parameters. Optimum operating condition is found at 10% EGR rate and 20% DME/diesel blend. The maximum indicated thermal efficiency was observed for DME/diesel ratio of 20% in the present range of study. Obtained results are validated with published experimental data and found good agreement.

CFD Simulation of a Common Rail Diesel Engine with Biobutanol-Diesel Blends for Various Injection Timings

Turmoil in petroleum market and stringent environment guidelines, accelerated the research in the field of alternative fuels for Internal Combustion engines. Biofuel is gaining venerable importance as it is renewable and substitute to the fossil fuels. This study investigates the potential of butanol fueling in a diesel engine. In this computational fluid dynamics (CFD) simulation, the effect of injection timing and butanol-blends on the exhaust emission and combustion characteristics of common rail direct injection (CRDI) engine is studied. The simulation is carried out for wide range of injection timings from 0° to 30° BTDC, and butanol-diesel blends from, 10, 20, and 30% at very high injection pressure (~90 MPa). Three dimensional computational code is implemented to solve conservation equations based on finite volume method. SIMPLE (semi-implicit method for pressure-linked equations) algorithm is used to obtain velocity and pressure at each computational cell. The flow within the combustion chamber is simulated using the k-ξ-f turbulence model. Extended coherent flame model-3 zone (ECFM3Z) is employed to carry out combustion analysis. In-cylinder fuel injection is studied using blob injection which assumes orifice diameter as fuel droplet diameter. As the percentage of the butanol blend increases, NO, CO increases and soot formation decrease as compare to neat diesel. Optimum injection timing obtained for maximum indicated thermal efficiency for 10–30% blend is 27° BTDC, whereas, for neat diesel it is 24° BTDC. Obtained results are validated with available literature data and found good agreement.

Effect of exhaust gas recirculation rate on performance, emission and combustion characteristics of a common-rail diesel engine fuelled with n-butanol–diesel blends

ABSTRACT Increasing fears of fossil fuel attenuation and tough emission protocols compel the research community to explore alternative renewable fuels for diesel engines. Butanol is desirable among renewable fuels due to its properties favorable to diesel engines. This study focused on the suitability of exhaust gas recirculation (EGR) and optimum injection timing on the performance, combustion and exhaust emission characteristics of common-rail direct-injection (CRDI) engine fueled with n-butanol-blended diesel using experimental and computational fluid dynamics (CFD) simulation. Various EGR rates and injection timings are considered for different butanol–diesel blends (0, 10, 20 and 30%). Obtained simulation results are validated with experimental data and found to be in good agreement. For all EGR rates and blends, nitrogen oxide (NO) emission is reduced drastically, whereas carbon monoxide (CO) and soot emissions are decreased moderately, with increase in n-butanol–diesel blends. The CO and soot emissions increase with EGR rate due to oxygen deficiency as well. Brake thermal efficiency is reduced by approximately 1% for neat diesel (Bu0) with increase in EGR rates. Soot emission for Bu30 (15 ° Before top dead centre (BTDC) is decreased by 23, 25, 24 and 26% for 0, 10, 20 and 30% EGR rates, respectively, compared to Bu0 (12° BTDC).

Optimum Operating Conditions for Subcritical/Supercritical Fluid-Based Natural Circulation Loops

Natural circulation loop (NCL) is simple and reliable due to absence of moving components and is preferred in applications where safety is of foremost concern such as nuclear power plants, high pressure thermal power plants, etc. In the present study, optimum operating conditions based on maximum heat transfer rate in NCLs have been obtained for subcritical as well as supercritical fluids. In recent years there is a growing interest in the use of carbon dioxide as loop fluid in NCLs for a variety of heat transfer applications due to its excellent thermophysical environmentally benign properties. In the present study, three dimensional CFD analysis of a carbon dioxide based NCL with isothermal source and sink has been carried out. Results show that heat transfer rate is much higher in the case of supercritical phase (if operated near pseudocritical region) than subcritical phase. In the subcritical option, higher heat transfer rate is obtained in case of liquid operated near saturation condition. Correlations for optimum operating condition are obtained for supercritical a CO2 based NCL in terms of reduced temperature and reduced pressure so that they can be employed for a wide variety of fluids operating in supercritical region. Correlations are also validated with different loop fluids. These results are expected to help design superior optimal NCLs for critical applications.

Effect of Tilt Angle on Subcritical/Supercritical Carbon Dioxide-Based Natural Circulation Loop With Isothermal Source and Sink

In recent years, a growing popularity of carbon dioxide (CO2) as a secondary fluid has been witnessed in both forced as well as in natural circulation loops (NCLs). This may be attributed to the favorable thermophysical properties of CO2 in addition to the environmental benignity of the fluid. However, an extensive literature review shows that studies on CO2-based NCLs are very limited. Also, most of the studies on NCLs do not consider the three-dimensional variation of the field variables. In the present work, three-dimensional computational fluid dynamics (CFD) models of a NCL with isothermal source and sink have been developed to study the effect of tilt angle in different planes. Studies have been carried out employing subcritical (liquid and vapor) as well as supercritical phase of CO2 as loop fluid at different operating pressures and temperatures. Results are obtained for a range of tilt angles of the loop, and a significant effect is observed on heat transfer, mass flow rate, and stability of the loop. It was also found that changing the orientation of the loop could be an elegant and effective solution to the flow instability problem of NCLs.

Effect of bioethanol–diesel blends, exhaust gas recirculation rate and injection timing on performance, emission and combustion characteristics of a common rail diesel engine

ABSTRACT This investigation is focused on the effect of exhaust gas recirculation (EGR) and injection timing on the performance, combustion and exhaust emission characteristics of common rail direct injection (CRDI) engine fueled with bioethanol-blended diesel using computational fluid dynamics (CFD) simulation. Simulation is carried out for various EGR rates (0, 10, 20 and 30%), two different injection timings, and two different bioethanol–diesel blends (10 and 20%) at injection pressure. The equivalence ratio is kept constant in all the cases of bioethanol–diesel blends. The results indicate that the mean CO formation and ignition delay increase, whereas mean NO formation and in-cylinder temperature decrease, with increase in the EGR rate. Further, with an increase in percentage of the bioethanol blends, CO and soot formation decrease as compared to neat diesel. A significant increase in in-cylinder pressure (15%) is found at 14° before top dead centre (BTDC) compared to 9° BTDC, which leads to an increase in indicated thermal efficiency of 4% for neat diesel at 30% EGR. In the present study, maximum indicated thermal efficiency is obtained in the case of 10 and 20% bioethanol–diesel blend, and remains constant for all EGR rates considered in the study. Obtained results are validated with the available literature data and indicate good agreement.