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Combustion chambers and processes
Published in M.J. Nunney, Light and Heavy Vehicle Technology, 2007
In petrol engines this is promoted by arranging for the piston crown to be brought into very close proximity with a limited portion of the combustion chamber roof. By this means a squish area is formed, which again is a term that was first applied by H.R. Ricardo. The effect of this squish area is such that, as the piston approaches the end of its compression stroke, the air and fuel charge trapped in the diminishing space is forcibly ejected across the combustion chamber. In so doing it enters the enlarged and, in some cases, streamlined portion of the chamber, which imparts a turbulent motion to the charge (Figure 3.19a).
Basic Processes of Internal Combustion Engines
Published in K.A. Subramanian, Biofueled Reciprocating Internal Combustion Engines, 2017
Squish is defined as the radial inward motion of air into the bowl of a piston at almost the end of a compression stroke (a few degrees crank angle before TDC) (Figure 5.11). The squish velocity for different types of bowl profiles is given by Equations 5.66 and 5.67 (Heywood, 1988).
Performance and combustion characteristics of a retrofitted CNG engine under various piston-top shapes and compression ratios
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Anh Tuan Le, Dang Quoc Tran, Thanh Tam Tran, Anh Tuan Hoang, Van Viet Pham
When the cylinder head or piston-top surface is not flat but is shaped such as bowl-in-piston combustion chamber, this piston-generated axial flow, during compression stroke and expansion stroke, produces radial or transverse flows due to variances in the axial gap between the cylinder head and piston-top surfaces across the cylinder cross-section, these flows are called squish. In short, squish is the transverse or radial mixture motion that happens toward the end of the compression stroke and the beginning part of the expansion stroke, when a portion of the piston-top and cylinder head approach (or separate from) each other closely. Figure 3 indicates how mixture is thereby moved into the open region of the combustion chamber at the end of compression process. The amount of squish is strongly affected by the proportion of the squish area and the cylinder cross-section area.
Influence of modified pent roof combustion cavity on diesel engine performance and emission characteristics
Published in International Journal of Ambient Energy, 2019
L. Karikalan, M. Chandrasekaran, S. Ramasubramanian, P. Vivek
The CI engine combustion is generally influenced by the turbulence of air, which is normally created by the combustion chamber design. Each and every combustion chamber design creates its own pattern of turbulence to offer proper mingling of air and fuel in a little time to reduce the ignition lag. Air swirl provided the combustion chamber produces high comparative velocity amongst fuel drops and air. When the fuel is introduced into the burning cavity, the spray cone is disturbed owing to the air motion and turbulence. The onset of burning will source an additional turbulence that could be steered by the contour of the burning cavity. Swirl is generally utilized in diesel engines to encourage speedier mixing amongst the air and the injected fuel. Swirl is also utilized to hustle the burning process and in two-stroke engines. Squish is the term specified to the radially inner or crosswise motion that arises towards the completion of the compression when a portion of piston surface and cylinder head approaches closely each other (Harshavardhan and Mallikarjuna; Xiaomao et al. 2015).
Experimental investigation of piston bowl geometry effects on performance and emissions characteristics of diesel engine at variable injection pressure and timings
Published in International Journal of Ambient Energy, 2018
Vedharaj et al. (2015) Optimised the combustion bowl geometry for fuel – kapok methyl ester having blends in different proportions like 25%, 50%, 75% and 100%. trapezoidal combustion chamber (TRCC)- and toroidal combustion chamber (TCC)-type piston bowl geometries were chosen and results were compared to the conventional design of hemispherical type combustion chamber (HCC). Results showed that TCC-type piston possesses high performance and low emissions rate than TRCC and HCC at all blends. Likewise Li et al. (2010) showed the effects of same type of geometries at low and medium loads using computational modelling (CFD). It is found that the small and narrow entry to combustion chamber could generate a better squish, especially at high engine speed, hence enhancing the mixing of air and fuel. In a comprehensive simulation study carried by Taghavifar, Khalilarya, and Jafarmadar (2014) on 1.8 L diesel engine, flame modelling was done to analyse in detail the combustion chemistry and reaction rate.