07-08-2012, 12:54 PM
EVALUATION OF INTAKE AIR SWIRL MOTION IN DI–DIESEL ENGINE USING COMPUTATIONAL FLUID DYNAMICS
EVALUATION OF IN TAKE AIR SWIRL PDF.pdf (Size: 3.3 MB / Downloads: 91)
ABSTRACT
In an Internal Combustion Engine the performance, efficiency and
emission formation depends on the formation of air-fuel mixture inside the
engine cylinder. In this study, the Computational Fluid Dynamics (CFD)
simulation to investigate the effect of Piston crown to the fluid flow field inside
the combustion chamber of a four-stroke direct injection automotive engines.
The analysis is focused on the study of the effect of the piston shape to the
fluid flow characteristics. The fluid flow dynamics plays an important role for
air-fuel mixture preparation to obtain the better engine combustion,
performance and efficiency in the appearance of swirl and tumble flows. These
two parameters represents the fluid flow behaviors occurred inside combustion
chamber which influences the air streams to the cylinder during intake stroke
and enhances greatly the mixing of air and fuel to give better mixing during
compression stoke.
INTRODUCTION
The in-cylinder flows of internal combustion engine have drawn much
attention to automotive researchers and scientist in the present times. It is due to
the fact that the flow structure generated by intake flows is related closely to the
design and performance. The production of high turbulence intensity is one of
the most important factors for stabilizing the ignition process and fast
propagation of flame, especially in the case of lean-burn combustion. In general,
two types of vortices are utilized in order to generate and preserve the
turbulence flows efficiently. The vortices are usually known as swrill and
tumble flows, which are organized rotations in horizontal and vertical plane of
engine cylinder, respectively. They contribute to the development of engine
performance by accelerating mixing of fuel and induced air. Hence it is
indispensable for development of an ICE with high compression ratio to realize
high turbulence intensity and lean burn combustion.
APPLICATIONS OF IC ENGINE
Internal combustion engines are most commonly used for mobile
propulsion in vehicles and portable machinery. In mobile equipment, internal
combustion is advantageous since it can provide high power-to-weight ratios
together with excellent fuel energy density. Generally using fossil fuel (mainly
petroleum), these engines have appeared in transport in almost all vehicles
(automobiles, trucks, motorcycles, boats, and in a wide variety of aircraft and
locomotives).
Where very high power-to-weight ratios are required, internal combustion
engines appear in the form of gas turbines. These applications include jet
aircraft, helicopters, large ships and electric generators.
LITERATURE SURVEY
The in-cylinder flows of Internal Combustion Engine (ICE) have drawn
much attention to the automotive researchers and scientist in the present times.
It is due to the fact that the flow structure generated by intake flows is related
closely to the design and performance of the ICEs. The production of high
turbulence intensity is one of the most important factors for stabilizing the
ignition process anc1 fast propagation of flame, especially in the case of leanburn
combustion. In general, two types of vortices are utilized in order to
generate and preserve the turbulence flows efficiently. These vortices are
usually know as swirl and tumble flows, which are organize rotations in the
horizontal and vertical plane of the engine cylinder, respectively. They
contribute to the improvement of engine performance by accelerating mixing of
fuel and induced air (Heywood, 1988). Hence, it is indispensable for the
development of an ICE with high compression ratio to realize high turbulence
intensity and lean burn combustion.
AIR MOTION
Diesel engines employs helical and/or directed ports in order to generate
a swirling motion in the cylinder during the compression stroke at around 330-
3400 ATDC. The swirling air is forced towards the piston-bowl as a result of the
squish motion generated above the piston crown. The competing action between
swirl and squish combined with the conservation of angular momentum of swirl
give rise to high swirl velocities inside the piston-bowl and high turbulence
levels near the bowl entry plane.
To analyze in cylinder air motion inside the cylinder., swirl and tumble
ratios for both on the sideways and nominal directions are calculated at each
time step or every crank angle degrees of engine cycle to identify the behavior
of fluid flow field characteristics among two different piston shapes.
The in-cylinder fluid motion in internal combustion engines is one of the
most important factors controlling the combustion process. It governs the fuelair
mixing and burning rates in diesel engines.The fluid flow prior to
combustion in internal combustion engines is generated during the induction
process and developed during the compression stroke. Therefore, a better
understanding of fluid motion during the induction process is critical for
developing engine designs with the most desirable operating and emission
characteristics.