Mallikarjuna J M

In-cylinder air motion in an internal combustion (IC) engine has a strong influence on engine combustion, performance and exhaust emissions. In spark ignition engines, large-scale in-cylinder fluid flows like swirl and tumble generated during intake stroke will be later dissipated as turbulence during compression stroke before ignition which promotes flame kernel growth and propagation rate. These types of in-cylinder flows are more desirable in stratified and direct injection spark ignition engines. In IC engines, in-cylinder flows are mainly affected by shape of combustion chamber, intake manifold orientation, compression ratio, crank angle position and engine speed. This paper mainly deals with experimental analysis of in-cylinder tumble flows in a single-cylinder, four-stroke, two-valve engine under motoring conditions using standard and modified intake manifold orientations at an engine speed of 1000 rev/min., during intake and compression strokes using particle image velocimetry. In this study, the axes of the two intake manifolds considered are perpendicular to each other. The two-dimensional in-cylinder tumble flow measurements and analysis are carried out in the combustion space on a vertical plane passing through cylinder axis. Ensemble average velocity vectors are used to analyze tumble flow structures. The tumble ratio and average turbulent kinetic energy are evaluated and used to characterize tumble flows. From the results, it is observed that, at end of compression stroke, modified intake manifold orientation shows about 1.65 and 1.14 times higher tumble ratio and average turbulent kinetic energy respectively compared to standard intake manifold orientation. Present study will be useful in understanding effect of intake manifold orientation on nature of in-cylinder tumble flows under real engine conditions.

This paper deals with the investigations of the in-cylinder flow pattern around the intake valve of a single-cylinder internal combustion engine using Particle Image Velocimetry (PIV) at different intake air flow rates. The intake air flow rates are corresponding to the three engine speeds of 1000, 2000 and 3000 rev/min., at all the static intake valve opening conditions. In this study, in-cylinder flow structure is characterized by the tumble ratio and maximum turbulent kinetic energy of the flow fields. In addition, at two specified lines of the combustion chamber, the radial and axial velocity profiles have been plotted. From the results, it is found that the overall airflow direction at the exit of the intake valve does not change significantly with the air flow rate and intake valve opening conditions. The tumble ratio increases with increase in intake valve opening and not much affected by the change in the air flow rates. It is also found that, the variations of the velocity profiles at the two specified lines are smooth at full intake valve opening irrespective of the air flow rate. Also, their magnitudes increase with increase in the intake valve openings at all the air flow rates. The in-cylinder flow analysis carried out in this study may be useful for optimizing the intake valve opening of an internal combustion engine with respect to it's speed.

Future stringent emission norms are impelling researchers to look for new emission control techniques. Today, gasoline direct injection (GDI) engines are becoming more popular because of high potential to reduce exhaust emissions over a wide operating load range, unlike conventional port fuel injection (PFI) engines. Also, turbocharged GDI engines allow engine downsizing with a certain restriction on compression ratio (CR) due to knocking tendency, thereby limiting the fuel economy. However, use of exhaust gas recirculation (EGR) delays combustion and lowers the knocking tendency which will aid in improving the fuel economy. Therefore, this study is aimed to evaluate the effect of EGR rate on the performance and emission characteristics of a two-liter turbocharged four-stroke GDI engine by computational fluid dynamics (CFD) analysis. For the analysis, the CR of 9.3 and the engine speed of 1000 rev/min., are selected. The engine is operated at full-load conditions in the stoichiometric homogeneous mixture mode. The full cycle CFD simulations are carried out using the CONVERGE. The CFD results are validated by the available experimental data from the literature. The quantity of cooled EGR is varied from 0 to 15% to evaluate its effect on combustion, performance and emission characteristics of the engine. The results showed that the engine indicated mean effective pressure (IMEP) is increased by about 2% and the indicated thermal efficiency is increased by about 2.3% at 5% EGR rate as compared to that of no EGR. It is also found that heat release rate decreased with increase in EGR rate. The mean in-cylinder temperature decreased with increase in the EGR rate reducing NOx emissions.

Gasoline direct injection (GDI) engines are well known for their ability to operate at the stratified fuel-air mixture, and thereby they are highly efficient than port fuel injection (PFI) engines. However, the stratification of the in-cylinder mixture leads to higher nitrogen oxides (NOx) and soot emissions with lower hydrocarbon (HC) emissions. The PFI works under a homogeneous mixture, which leads to lower NOx and soot emissions with compensation of HC emissions. By combining the advantages of GDI and PFI modes, it is possible to achieve higher fuel efficiency with lower emissions. Therefore, in the present study, four different injection strategies, namely, pure GDI, gasoline-direct multiple-injection (GDMI), combined GDI with PFI (GDI-PFI), and pure PFI are investigated under various load conditions using computational fluid dynamics (CFD) analysis. The effect of these strategies on mixture formation, indicated mean effective pressure (IMEP), and emissions are evaluated. For the analysis, the equivalence ratio (ER) is varied from 0.5 to 0.9 under naturally aspirated conditions. From the results, it is found that in the GDI-PFI mode, at the split fraction of 0.6 and ER of 0.9, the NOx and soot emissions are at the minimum levels because of good partial stratification. The IMEP improved by about 10.6% and the HC emissions reduced by about 82.8% than that of the corresponding GDMI mode. However, the NOx and soot emissions increased by about 39.4% and 9.24%, respectively compared to that of the corresponding GDMI modes. Also, the average flame speed for the GDMI mode with the split fraction of 0.6 and ER of 0.9 is higher by about 3% than that of the GDI-PFI mode.

In-cylinder flow field structure in an internal combustion (I.C) engine has a major influence on the combustion, emission and performance characteristics. Fluid enters the combustion chamber of an I.C engine through the intake manifold with high velocity. Then the kinetic energy of the fluid resulting in turbulence causes rapid mixing of fuel and air, if the fuel is injected directly into the cylinder. With optimal turbulence, better mixing of fuel and air is possible which leads to effective combustion. A good knowledge of the flow field inside the cylinder of an I.C engine is very much essential for optimization of the design of the combustion chamber for better performance especially in modern I.C engines like gasoline direct injection (GDI), homogeneous charge compression ignition (HCCI) engines.The main objective of this work is to study the incylinder fluid flow field characteristics of a single-cylinder engine to see the effect of intake manifold inclination at equivalent rated engine speed using Particle Image Velocimetry (PIV) under various static intake valve lift conditions. To facilitate the PIV experiments, the metal cylinder of the engine was replaced by a transparent one. For every operating test condition, 50 image pairs were captured and processed using DAVIS software. From the results, it is seen that the in-cylinder flow structure is greatly influenced by the intake manifold inclinations irrespective of intake valve lift. Maximum Turbulent Kinetic Energy (TKE) was highest at full intake valve lift irrespective of the inclination. Also, the maximum TKE was the highest for 60° intake manifold inclination compared to other inclinations irrespective of the intake valve lift at equivalent rated engine speed. Finally, it is concluding that the analysis carried in this work is useful in predicting the flow and inturn optimizing combustion chamber of modern I.C engines.

This study focuses on effect of piston shape on in-cylinder flows in a conventional loop scavenged two-stroke engine using CFD. Three piston-shapes viz., flat, flat with center-bowl and flat with center-dome are analyzed along with a standard piston. The CFD solution has been obtained by using commercial CFD code STAR-CD. First, the CFD results are compared with those of experimental values obtained from particle image velocimetry (PIV). For comparison among various piston shapes, various parameters viz., velocity vector plots, tumble ratio (TR), turbulent kinetic energy (TKE) at various crank angles are used. Scavenging and trapping efficiencies are also calculated for each piston configuration. From the results, it is found that flat with center-bowl piston is the best in terms of in-cylinder flow characteristics. It gives higher TR and TKE with very little effect on efficiencies. © (2014) Trans Tech Publications, Switzerland.

In this paper, a computer simulation and experimental investigations on a single cylinder, four-stroke, spark ignited engine are carried out to optimize inlet valve closure timing and clearance volume for better part-load performance. The simulation procedure involves thermodynamic and global modeling techniques. Many sub-models have been used for predicting heat transfer, friction and gas exchange processes. Unburned hydrocarbons, carbon monoxide and nitric oxide emissions are also predicted. Experiments have been conducted on a single cylinder, air-cooled, four-stroke, spark-ignited engine. In this work, by varying inlet valve closure timing (IVCT) and clearance volume, geometric expansion ratio (GER) of engine alone is varied, while effective compression ratio (ECR) is kept constant, thereby GER/ECR ratio is altered. For modified engine, GER/ECR ratio is varied from 1.25 to 2. Experiments have been conducted for two effective compression ratios, viz., 7 and 8 at a speed of 1200 rpm. Performance and exhaust emission characteristics have been measured at different loads and GER/ECR ratios. The predicted performance and emission characteristics are compared with measured values and the agreement between the two is found to be good. It is observed that, for modified engine, considerable improvements have been found in the reduction of pumping losses (about 25.8 to 56%), increase in the brake thermal efficiency (about 13.6 to 25%), and reduction in unburned hydrocarbon emissions (about 18.5 to 58%). Finally, for modified engine, it is found that GER/ECR ratio of 1.5 gives the best performance compared to standard engine for both compression ratios.

The homogeneous charge compression ignition (HCCI) engines emit low levels of smoke and NOx emissions. However, control of ignition, which is mainly controlled by fuel composition, the equivalence ratio and the thermodynamic state of the mixture, is a problem. In this work, acetylene was as the fuel for operating a compression ignition engine in the HCCI mode at different outputs. The results of thermal efficiency and emissions have been compared with base diesel operation in the (compression ignition) CI mode. The relatively low self ignition temperature, wide flammability limits and gaseous nature were the reasons for selecting this fuel. Charge temperature was varied from 40 to 110°C. Thermal efficiencies were almost equal to that of CI engine operation at the correct intake charge temperature. NO levels never exceeded 20 ppm and smoke levels were always lower than 0.1 BSU. HC emissions were higher and were sensitive to charge temperature and output. However, investigations are required to further extend the operating range of acetylene HCCI operation. On the whole this work demonstrates that acetylene can be considered as a HCCI engine fuel.

The petroleum-based fuels are limited reserve fuels, with our present known reserves and the growing rate of consumption, it is feared that they are not going to last long. These finite resources of petroleum and highly concentrated in certain regions of the world has given rise to frequent disruptions and uncertainties in its supply and as well as price. This situation has created a problem to increase the prices of these oils. The growing dependence on oil has created great scarcities and hardships with serious economic imbalance. A part from the problem of fast vanishing reserves, Petroleum fueled vehicles discharge significant amount of pollutants. In view of these problems attempts must be made to develop the technology of alternate clean burning fuels. The alternative, which satisfies all these requirements, is bio-diesel. Bio-diesel is methyl or ethyl ester of fatty acid made from virgin or used vegetable oils (both edible and non-edible) and animal fat, by converting the triglyceride oils to methyl (or ethyl) esters with a process known as transesterification. Bio-fuels are important now and offer increase in potential for the future. This paper consists two phases. The phase one dealt with preparation of bio-diesel from Cotton Seed Oil (C.S.O), which is available at cheaper price, as it is byproduct from cotton industries. Its properties were determined experimentally and compared with the conventional diesel fuel. The second phase dealt with conduction of experiments on a single cylinder, 4-stroke, direct injection Diesel Engine without modifications at constant speed 1500 rpm for various loads using 100 % bio-diesel and conventional diesel fuel. It noticed that, the performance of the engine is not severely deviated by the substituted renewable biodiesel inaddition considerable decrease in smoke level. It is concluding that the biodiesel is superior fuel from the environmental and performance point of view, addition to this reducing the import of oil and consequentially improving energy security as a renewable alternate fuel. Copyright © 2006 by ASME.

This article aims to identify the best combination of intake port angle (IPA) and cylinder head pentroof angle (PA) of a gasoline direct injection (GDI) engine to achieve a simultaneous reduction in the fuel consumption and the exhaust emissions using computational fluid dynamics (CFD) and optimization techniques. The present study is carried out on a single-cylinder, four-stroke GDI engine. The design space is bound by the range of the IPA (35°, 80°) and the PA (5°, 20°). The initial data set consists of 80 design points, which are generated using the uniform Latin hypercube (ULH) algorithm. CFD simulations were carried out at all the points in the initial data set using CONVERGE at engine speed of 2,000 rev/min and the overall equivalence ratio of 0.7 ± 0.05. A prediction model based on the support vector machine algorithm is generated between the design inputs and the output parameters viz., indicated specific fuel consumption (ISFC), hydrocarbon (HC), nitric oxides (NOx), and soot. After sufficient validation of the prediction model, it is used for the optimization study. The optimization is carried out using the MOGA-II algorithm. The optimization study predicted that the IPA of 58° and the PA of 13.4° results best, in simultaneous reduction of the fuel consumption and the emissions. The results of the optimization study are further validated using the CFD analysis, which is carried out at the optimum design point. From the results, it is concluded that the optimization-driven design techniques could be effectively used to improve the engine performance and reduce the emissions simultaneously.