Experimental and Numerical Study of Swirling ... - Solid Mechanics
Experimental and Numerical Study of Swirling ... - Solid Mechanics Experimental and Numerical Study of Swirling ... - Solid Mechanics
Experi imental and Numerical N Stud dy of Swirling g Flow in Scaveenging Processs for 2-Stroke Marin ne Diesel Engin nes Fig gure 1.5: Intak ke Port arrangem ment for Uniflow U Scavengi ing Syste em. (Heywood J. B., 1988 8). Figure 1.6: Cyl linder liner with scavenging ports. (ww ww.brighthub.com m). Chapter 1 the cyli inder radius (F Figure 1.5 & 1.6). The scavvenging ports, depending oon differen nt engine designs, are at ann angle with tthe cylinder raadius to impaart tangent tial velocities producing a swirling airr column. Thhe resulting iin cylinder confined sw wirling flow rremoves the eexhaust gases from cylindeer, provide es fresh air charge for the nnext cycle andd introduces swwirl to enhance mixing of injected fu uel and its connsequent combbustion. Moreeover, it also hhas a coolin ng effect on th he cylinder linner and exhaust valve. In caase of a non-axxis symmet tric swirl, an uneven tempperature distrribution at thhe walls can bbe resulted d. Thus inves stigation of inn-cylinder connfined swirlinng flow is a keey step for rward in optim mization of scaavenging process and develoopment of moore efficient uniflow scav venging processs. Air enttering the cylindeer through Scavenging ports. Experim mental results available in sccientific literatture, focused oon studying thhe uniflow w scavenging process p in largee low speed mmarine diesel eengines, are veery few com mpared to sca avenging in otther (smaller and high speed ) two strokke 8 Introduction
Experimental and Numerical Study of Swirling Flow in Scavenging Process for 2-Stroke Marine Diesel Engines Chapter 1 diesel engines. Nishimoto et al. (1984) obtained the shape of the front surface of the scavenging air using thermocouple in a uniflow model engine. The model engine used hot air for scavenging the cylinder filled with air at room temperature. It was observed that with the increase in the engine rpm (rotations per minute) and port angle, the scavenging air front surface profile changes from jet like to a wake like profile analogous to vortex breakdown in an axial flow vortex chamber. A method was also proposed to obtain a flat profile front surface at an arbitrary Reynolds number for maximum scavenging efficiency. Laser Doppler Velocimetry (LDV) experiment was conducted on a model test engine by Dedeoglu (1988). The measurements involved using a single liquid and cylinder liner with different intake port configurations. Result show that the in-cylinder flow consists of a rotational flow in the cylinder axis region and a potential flow in the near wall region. Nakagawa et al. (1990) used 2-component LDV measurements on a model of large, low speed engine with large bore acrylic cylinder and using air. The tangential/ swirl velocity profile for piston at TDC is found to be governed by the scavenging port angle. Larger port angles resulted in a larger axial velocity drop in the central region of the cylinder thus occasionally resulting in a reverse flow. Litke (1999) studied the influence of the scavenging port angles on the scavenging efficiency by using liquids on a 1:4 scaled engine model instead of gases. It was observed that the highest scavenging efficiency is obtained with an inlet scavenging port angle of 20°. The results also indicated a better performance of using scavenging ports with combination of different angles compared to the ports with uniform angle. 1.6 Scope of thesis Large physical size and high in-cylinder pressure for LSE makes experimental investigations in the engine very expensive to conduct and difficult to get optical access. The scavenging process is transient and complex in nature thus making statistics difficult. In terms of variation in geometry of the flow domain, piston is in continuous motion during the scavenging process thus changing the cylinder length and also the effective shape of air intake ports. Such complex inlet flow conditions make it difficult to distinguish between inlet effects and swirling flow effects. Regarding the flow physics, mixing and stratification of exhaust gases with fresh air charge occurs while in-cylinder mass flow rate changes between opening and closing of the scavenging ports. This simultaneous variation in flow domain and flow physics consequently affects the in-cylinder swirl characteristics and the type of the vortex generated by the swirl. Considering the complex nature of the real engine scavenging process, a detailed understanding of the incylinder scavenging process requires isolation and consequent study of each flow phenomenon in a simplified form. The complex physics can then be better analyzed by gradually adding different flow effects. 9 Introduction
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<strong>Experimental</strong> <strong>and</strong> <strong>Numerical</strong> <strong>Study</strong> <strong>of</strong> <strong>Swirling</strong> Flow in Scavenging Process for 2-Stroke<br />
Marine Diesel Engines<br />
Chapter 1<br />
diesel engines. Nishimoto et al. (1984) obtained the shape <strong>of</strong> the front surface<br />
<strong>of</strong> the scavenging air using thermocouple in a uniflow model engine. The<br />
model engine used hot air for scavenging the cylinder filled with air at room<br />
temperature. It was observed that with the increase in the engine rpm<br />
(rotations per minute) <strong>and</strong> port angle, the scavenging air front surface pr<strong>of</strong>ile<br />
changes from jet like to a wake like pr<strong>of</strong>ile analogous to vortex breakdown in<br />
an axial flow vortex chamber. A method was also proposed to obtain a flat<br />
pr<strong>of</strong>ile front surface at an arbitrary Reynolds number for maximum<br />
scavenging efficiency. Laser Doppler Velocimetry (LDV) experiment was<br />
conducted on a model test engine by Dedeoglu (1988). The measurements<br />
involved using a single liquid <strong>and</strong> cylinder liner with different intake port<br />
configurations. Result show that the in-cylinder flow consists <strong>of</strong> a rotational<br />
flow in the cylinder axis region <strong>and</strong> a potential flow in the near wall region.<br />
Nakagawa et al. (1990) used 2-component LDV measurements on a model <strong>of</strong><br />
large, low speed engine with large bore acrylic cylinder <strong>and</strong> using air. The<br />
tangential/ swirl velocity pr<strong>of</strong>ile for piston at TDC is found to be governed<br />
by the scavenging port angle. Larger port angles resulted in a larger axial<br />
velocity drop in the central region <strong>of</strong> the cylinder thus occasionally resulting<br />
in a reverse flow. Litke (1999) studied the influence <strong>of</strong> the scavenging port<br />
angles on the scavenging efficiency by using liquids on a 1:4 scaled engine<br />
model instead <strong>of</strong> gases. It was observed that the highest scavenging efficiency<br />
is obtained with an inlet scavenging port angle <strong>of</strong> 20°. The results also<br />
indicated a better performance <strong>of</strong> using scavenging ports with combination<br />
<strong>of</strong> different angles compared to the ports with uniform angle.<br />
1.6 Scope <strong>of</strong> thesis<br />
Large physical size <strong>and</strong> high in-cylinder pressure for LSE makes experimental<br />
investigations in the engine very expensive to conduct <strong>and</strong> difficult to get<br />
optical access. The scavenging process is transient <strong>and</strong> complex in nature<br />
thus making statistics difficult. In terms <strong>of</strong> variation in geometry <strong>of</strong> the flow<br />
domain, piston is in continuous motion during the scavenging process thus<br />
changing the cylinder length <strong>and</strong> also the effective shape <strong>of</strong> air intake ports.<br />
Such complex inlet flow conditions make it difficult to distinguish between<br />
inlet effects <strong>and</strong> swirling flow effects. Regarding the flow physics, mixing <strong>and</strong><br />
stratification <strong>of</strong> exhaust gases with fresh air charge occurs while in-cylinder<br />
mass flow rate changes between opening <strong>and</strong> closing <strong>of</strong> the scavenging ports.<br />
This simultaneous variation in flow domain <strong>and</strong> flow physics consequently<br />
affects the in-cylinder swirl characteristics <strong>and</strong> the type <strong>of</strong> the vortex<br />
generated by the swirl.<br />
Considering the complex nature <strong>of</strong> the real engine scavenging process, a<br />
detailed underst<strong>and</strong>ing <strong>of</strong> the incylinder scavenging process requires<br />
isolation <strong>and</strong> consequent study <strong>of</strong> each flow phenomenon in a simplified<br />
form. The complex physics can then be better analyzed by gradually adding<br />
different flow effects.<br />
9<br />
Introduction
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