The document discusses several internal combustion engine cycles including the dual cycle, Otto cycle, diesel cycle, Miller cycle, two-stroke cycles, Stirling cycle, and Lenoir cycle. The dual cycle injects fuel earlier in the compression stroke compared to early diesel engines, allowing some combustion at constant volume. The Miller cycle has a longer expansion stroke than compression stroke, improving efficiency. Two-stroke cycles have advantages of simplicity but higher emissions. The Stirling cycle uses external combustion and can achieve theoretical maximum efficiency. The Lenoir cycle was the first successful internal combustion engine, igniting fuel without compression.

1. 7. Dual Cycle
 Instead of injecting the fuel late in the compression stroke
near TDC, as was done in early engines, modern CI
engines start to inject the fuel much earlier in the
cycle, somewhere around 20° bTDC.
 The first fuel then ignites late in the compression stroke,
and some of the combustion occurs almost at constant
volume at TDC, much like the Otto cycle. This cycle is
called Dual cycle or limited-Pressure cycle.

2.  Thermodynamic analysis of Dual cycle

3.  (ηt)actual = 0.85 (η)Diesel
 (ηt)actual = 0.85 (η)Dual

4. 8. Comparison of Otto, Diesel and Dual
Cycles.
 The thermal efficiency of each cycle can be written:
 ηt = 1 - (qout / qin)
 The area under the process lines on T-s coordinates is
equal to the heat transfer.
 If all the cycles operate on the same compression ratio:
 So, (ηt)Otto > (η)Dual > (η)Diesel

5.  A more realistic way to compare these three cycles would
be to have the same peak pressure which is an actual
design limitation in engines.
 So, (ηt)Diesel > (η)Dual > (η)Otto

6. 8. Miller Cycles.
 The Miller cycle, named after R. H.
Miller (1890-1967), has an
expansion ratio greater than the
compression ratio.
 A Miller cycle engine uses unique
valve timing to obtain the same
desired results.
 The amount of air ingested into
each cylinder is controlled by
closing the intake valve at the
proper time, long before BDC
(point 7).

7.  The resulting cycle is 6-7-1-7-2-3-4-5-6.
 The net indicated work is the area within loop 7-2-3-4-5-7.
 The compression ratio is:
rc = V7/V2
and the larger expansion ratio is:
re = V4/V2 = V4/V3
 The shorter compression stroke which absorbs work,
combined with the longer expansion stroke which produces
work, results in a greater net indicated work per cycle.
 The Miller cycle engine has essentially no pump work
(ideally none). This results in higher thermal efficiency.
 Another variation of this cycle can be obtained if the
intake air is unthrottled and the intake valve is closed
after BDC.
 This results in cycle 6-7-5-7-2-3-4-5-6.

8.  For either variation of the cycle to work efficiently, it is
extremely important to be able to close the intake valve
at the precise correct moment in the cycle (point 7).
 This control was not possible until variable valve timing
was perfected and introduced.
 Automobiles with Miller cycle engines were first marketed in
the latter half of the 1990s.
 A typical value of the compression ratio is about 8:1, with
an expansion ratio of about 10:1.
 To produce more power, Miller cycle engines are usually
supercharged or turbocharged with peak intake
manifold pressures of 150-200 kPa.

9. 10. Comparison of Miller Cycle and
Otto Cycle.
 It is important that the temperature at the beginning of
combustion for either cycle be low enough so that self-
ignition and knock do not become problems.
 Lower exhaust temperature means less energy is lost in
the exhaust, with more of it used as work output in the
longer expansion stroke.

10. 11. Two-Stroke Cycles.
 The very smallest engines (chain saws) and the largest
engines (marine engines) almost always operate on two-
stroke cycle.
 No modern automobiles is now made in high volume with
a 2-st cycle because of emissions laws of the various
countries.
 Thermodynamic analysis of 2-st SIE cycle

11.  Scavenging is a process in which the air pushes out most
of the remaining exhaust residual from the previous cycle
through the open exhaust port into the exhaust system.

12.  Thermodynamic analysis of 2-st CIE cycle

13. 12. Stirling Cycle.
 While it is not a true internal combustion engine, the concept
of the Stirling engine uses a free-floating, double-acting
piston with a gas chamber on both ends of the cylinder.
 Combustion does not occur within the cylinder, but the
working gas is heated with an external combustion process.

14.  (ηt )Stirling = 1 - (Tlow / Thigh)
 This is the same thermal efficiency as a Carnot cycle
and is the theoretical maximum possible.
 Although a real engine cannot operate reversibly, a well-
designed Stirling engine can have a very high thermal
efficiency.
 Problems with Stirling engines include sealing, warm-up
time needed, and high cost.
 Other possible applications include refrigeration,
stationary power, and heating of buildings.

15. 13. Lenoir Cycle.

16.  The first half of the first stroke was intake, with air-fuel
entering the cylinder at atmospheric pressure (process 1-2).
 At about halfway through the first stroke, the intake valve
was closed and the air-fuel mixture was ignited without
any compression.
 Combustion raised the temperature and pressure in the
cylinder almost at constant volume in the slow-moving
engine (process 2-3).
 The second half of the first stroke then became the power or
expansion process 3-4.
 Near BDC, the exhaust valve opened and blowdown
occurred (4-5).
 This was followed by the exhaust stroke 5-1, completing the
two-stroke cycle.
 There was essentially no clearance volume.

17.  Thermodynamic analysis of Lenoir cycle