1. DIESEL CYCLE
MET 401
POWER PLANT ENGINEERING
DR. TAIB ISKANDAR MOHAMAD

2. Diesel power plant
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 Typically up to 50 MW
 Used as
 Supplement
 Peak load
 Portable – emergency
Advantages
Quick start
Compact size
Disadvantages
high maintenance cost
fuel

3. AN OVERVIEW OF RECIPROCATING ENGINES
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4. AN OVERVIEW OF RECIPROCATING ENGINES
Compression ratio
Mean effective
pressure
• Spark-ignition (SI) engines
• Compression-ignition (CI) engines
Nomenclature for reciprocating engines.
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5. OTTO CYCLE: THE IDEAL CYCLE FOR
SPARK-IGNITION ENGINES
Actual and ideal cycles in spark-ignition engines and their P-v diagrams.
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6. The two-stroke engines are
Four-stroke cycle
generally less efficient than
1 cycle = 4 stroke = 2 revolution their four-stroke counterparts
Two-stroke cycle but they are relatively simple
1 cycle = 2 stroke = 1 revolution and inexpensive, and they
have high power-to-weight
and power-to-volume ratios.
T-s
diagram
of the
ideal Otto Schematic of a two-stroke
cycle. reciprocating engine.
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7. In SI engines,
the
compression
ratio is limited
by
autoignition
or engine
knock.
The thermal efficiency of the Otto Thermal efficiency of the ideal
cycle increases with the specific Otto cycle as a function of
heat ratio k of the working fluid. compression ratio (k = 1.4).
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8. DIESEL CYCLE: THE IDEAL CYCLE
FOR COMPRESSION-IGNITION ENGINES
In diesel engines, only air is compressed during the
compression stroke, eliminating the possibility of
autoignition (engine knock). Therefore, diesel engines
can be designed to operate at much higher compression
ratios than SI engines, typically between 12 and 24.
• 1-2 isentropic
compression
• 2-3 constant-
pressure heat
addition
• 3-4 isentropic
expansion
• 4-1 constant-
volume heat
rejection.
In diesel engines, the spark plug is replaced
by a fuel injector, and only air is compressed
during the compression process.
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9. Cutoff
ratio
for the same compression ratio
Thermal
efficiency of
the ideal Diesel
cycle as a
function of
compression
and cutoff
ratios (k=1.4).
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10. Example
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An ideal Diesel cycle with air as the working fluid has a
compression ratio of 18 and a cutoff ratio of 2. At the beginning of
the compression process, the working fluid is at 100 kPa, 27°C,
and 2000 cm3. Utilizing the cold-air standard assumptions,
determine
(a) the temperature and pressure of air at the end of each process
(b) the net work output and the thermal efficiency
(c) the mean effective pressure.

11. QUESTIONS
Dual cycle: A more realistic Diesel engines operate at
ideal cycle model for modern, higher air-fuel ratios than
high-speed compression ignition gasoline engines. Why?
engine. Despite higher power to
weight ratios, two-stroke
engines are not used in
automobiles. Why?
The stationary diesel
engines are among the
most efficient power
producing devices (about
50%). Why?
What is a turbocharger?
Why are they mostly used
in diesel engines
compared to gasoline
P-v diagram of an ideal dual cycle. engines.
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