RevisionC-Developmentofconceptofcompressorforcommercialvehicle

The condition for minimum work is that the compression process should be isothermal.
The temperature after compression is:
T 2 = T 1 (p 2 /p 1 ) n-1/n
Delivery temperature increases with the pressure ratio.
η v = 1 − V c
V c
{( p 2
p 1
) 1/n − 1}
It can be seen that as the pressure ratio increases the volumetric efficiency decreases.
The reciprocating compressor is probably the best known and most widely used of all
compressors. It consists of a mechanical arrangement in which reciprocating motion is
transmitted to a piston, which is free to move in a cylinder. The displacing action of the piston,
together with the inlet valve or valves, causes a quantity of gas to enter the cylinder where it is in
turn compressed and discharged; Action of the discharge valve or valves prevents the backflow
of gas into the compressor from the discharge line during the next intake cycle. When the
compression takes place on one side of the piston only, the compressor is said to be a single
acting. The compressor is double acting when compression takes place on each side of the
piston. Configurations consist of a single cylinder or multiple cylinders on a frame. When a single
cylinder is used or when multiple cylinders on a common frame are connected in parallel, the
arrangement is referred to as a single-stage compressor. When multiple cylinders on a common
frame are connected in series, usually through a cooler, the arrangement is referred to as a
multistage compressor. Reciprocating compressor is classified into many categories with respect
to cylinder arrangement and drive methods. [5]
1.1.2.6 Oil free reciprocating compressor [5]
Oil free reciprocating compressors are broadly classified into two types. One is a trunk
piston type (Engine or Automotive piston type) and another is cross head type. The cross sections
of both compressors are shown below. The cross-head type compressor details are collected
from Bloch & Hoofer (1996). Fig. 1.10 Trunk piston compressor Fig. 1.11 Crosshead type piston
compressor.
Oil-free piston compressors have piston rings of PTFE or carbon; alternatively, the piston
and cylinder wall can be toothed as on labyrinth compressors. Larger machines are equipped
with a crosshead and seals on the gudgeon pins, ventilated intermediate piece to prevent oil from
being transferred from the crankcase and into the compression chamber. Lubricants less designs
have piston arrangements similar to lubricant-free versions, but do not have lubricant in the
crankcase. Generally, these machines have a grease pre-packed crankshaft and connecting rod
bearings.
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