Abstract:This study gives an overview of available literature on flow patterns such as swirl, tumble and squish in internal combustion engines and their impacts of turbulence enhancement, combustion efficiency and emission reduction. Characteristics of in-cylinder flows are summarized. Different design approaches to generate these flows such as directed ports, helical ports, valve shrouding and masking, modifying piston surface, flow blockages and vanes are described. How turbulence produced by swirl, tumble and squish… Show more
“…Squish level is determined by the gap between the piston and the head. According to Taylor, the diameter of the gap having a value of less than 0.005 is very important in terms of improvement [20]. The upper surface view of the piston for two different combustion chambers is presented in Fig.…”
This study includes numerical analysis of diesel engine with different bowl geometry. 3D CFD analyzes of the engine with asymmetrical piston geometry were performed in Ansys Forte software. In the study, a single-cylinder, four-stroke and direct injection diesel engine was used. It has been tested where the maximum torque is obtained as the operating condition at 2000 rpm. According to the results obtained from the analyzes, the new combustion chamber system (NCCS) geometry provided a 40.3% reduction in soot emissions while NO emissions increased slightly with the 8-cavity bowl geometry created in the combustion chamber compared to the standard combustion chamber system (SCCS). Increasing air velocity and turbulent kinetic energy (TKE) values in the combustion chamber affected the evaporation levels of the fuels. As a result, the improved mixture formation caused a decrease in incomplete combustion products (CO, HC and soot). The NCCS geometry according to SCCS type, an increase of approximately 4.2% occurred in the calculated squish rates. It has been observed that the increase in the bowl surface area causes the combustion and thus the temperature to spread over a larger area on the piston.
“…Squish level is determined by the gap between the piston and the head. According to Taylor, the diameter of the gap having a value of less than 0.005 is very important in terms of improvement [20]. The upper surface view of the piston for two different combustion chambers is presented in Fig.…”
This study includes numerical analysis of diesel engine with different bowl geometry. 3D CFD analyzes of the engine with asymmetrical piston geometry were performed in Ansys Forte software. In the study, a single-cylinder, four-stroke and direct injection diesel engine was used. It has been tested where the maximum torque is obtained as the operating condition at 2000 rpm. According to the results obtained from the analyzes, the new combustion chamber system (NCCS) geometry provided a 40.3% reduction in soot emissions while NO emissions increased slightly with the 8-cavity bowl geometry created in the combustion chamber compared to the standard combustion chamber system (SCCS). Increasing air velocity and turbulent kinetic energy (TKE) values in the combustion chamber affected the evaporation levels of the fuels. As a result, the improved mixture formation caused a decrease in incomplete combustion products (CO, HC and soot). The NCCS geometry according to SCCS type, an increase of approximately 4.2% occurred in the calculated squish rates. It has been observed that the increase in the bowl surface area causes the combustion and thus the temperature to spread over a larger area on the piston.
“…oxidizer and fuel which lead to combustion instability. Swirling, which is an organized set of flow pattern of the mixture of air and fuel rotating inside the combustion chamber of a combustor 20) . It is required in order to enhance the combustion process by forming a secondary recirculation zone 21) .…”
As the population of the world is growing rapidly, the demand for energy that is clean and efficient is increasing. Combustion is one of the major ways of energy conversion that produces very high amount of pollutant emission, as such the research arena has been taken over by coming up with combustion processes that are cleaner and efficient by the combustion engineers. Flameless combustion is one of the new techniques discovered by researchers to suppress NOx emission due to the low temperature inside the combustion zone that is well below the dissociation temperature of Nitrogen. Homogenous or proper mixing is another major factor that enhances combustion efficiency. An asymmetric swirling combustor is a unique shaped combustor that was developed by researchers in order to enhance better mixing inside the combustion zone without the need for an external swirler. The review investigated several parameters such as temperature uniformity, fuel flexibility and level of pollutant emission as discussed by researchers and it was found that the asymmetric swirling combustor is very efficient with temperature uniformity of about 0.9, thermal efficiency of 53% and very low NOx and CO of about 2ppm and 24ppm according to researchers. It was recommended that the combustor should be investigated under different flow configurations i.e. forward and reverse flow in order to know the optimum direction of flow for the asymmetric swirling combustor.
“…Lower flame propagation speed exposes the flame's propagation to interact with turbulence and the in-cylinder macro movements, like swirl and tumble. 47,48 The higher displacement of the centroid for the flame-covered area indicates the stronger influence of swirl and tumble for the case of flames with low propagation speed; the higher Heywood circularity factor indicates the distortion in the flame front by the turbulence. Therefore, the movement and distortions can lead to instabilities to the flame propagation, like non-homogeneous propagation or, as observed in Figure 6, differences in the flame border wrinkling.…”
Thermal processes and power generation systems may employ producer gas generated through gasification as an alternative to replace natural gas with lower carbon footprint. However, pure producer gas in engines is associated with a significant power derating that can be mitigated by blending it with other biofuels. This work evaluated the effects of methane and producer gas blends on the performance of a SI engine. The additions of methane were 10%, 25% and 50% on a molar basis. The results demonstrated that adding 25% methane to producer gas is enough to sustain the combustion reaction with good stability and a power derating of 10.8%. The addition of 50% methane to producer gas attains efficiency and combustion characteristics remarkably similar to pure natural gas with a power de-rating of 5.4%. Emissions indicated that carbon monoxide (CO) has decreased with the addition of methane to producer gas from 85 to 3.43 g/kWh, while nitrogen oxides ([Formula: see text]) emissions have increased from 0 to 8.85 g/kWh. In the case of unburned hydrocarbons (UHC), emissions did not considerably change before adding 25% methane to producer gas and stayed constant at approximately 10 g/kWh. Engines designed to run on natural-gas could use this mixture without significant modifications to the combustion chamber while decreasing NOx emissions.
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