pulse jet engine

1. pulse jet engine
 A pulsejet engine is a type of jet engine in which combustion occurs
in Pulses.
 Air is compressed and combusted intermittently instead of continuously.
 They have better power to weight ratio than other engines.
 Pulsejet engines are a lightweight form of jet propulsion, but usually have
a poor compression ratio, and hence give a low specific impulse.
Types:
Valved
valve less

2. valve-less pulsejet
In these, the exhaust mechanism is controlled by
its geometry itself.
Following are the steps followed:
1.Initial air + fuel=ignition
2.Increase in pressure , exhaust-1.
3.After exhaust-1,pressure decrease which draws
more air in form of returning flame and more air +
fuel + compression
4.Ignition of compressed air-fuel mixture.
5.Power strokes starts from here, exhaust-2 with
more power than exhaust-1.
Due to the geometry of valve-less engine , the
exhaust happens on both intake and exhaust sides
but more propulsion would be in longer tube i.e.,
exhaust pipe.

3. Valved pulse jet
Valved pulsejet engines use a mechanical valve
to control the flow of expanding exhaust,
forcing the hot gas to go out of the back of the
engine through the tailpipe only, and allow
fresh air and more fuel to enter through
the intake.
Steps involved:
First part of the cycle: air flows through the
intake (1), and is mixed with fuel (2).
Second part: the valve (3) is closed and the
ignited fuel-air mix (4) propels the craft.

4. Lenoir cycle:
• The Lenoir cycle is an idealized thermodynamic
cycle often used to model a pulse-jet engine.
• Comprises of 3 cycles:
▫ Heat added at constant volume.
▫ Adiabatic Expansion.
▫ Exhaust of the hot gasses at a constant
pressure.
• Thrust can be directly calibrated on the basis that
the cycle is completed over two working strokes.

5. Efficiency of Lenoir cycle
 1-2:isochoric heat addition
 2-3:isentropic expansion
 3-1:isobaric heat rejection

6. comparing Lenoir cycle and Otto cycle
 The absence of any
compression process in the
design leads to lower thermal
efficiency than the more well
known Otto cycle and Diesel
cycle.
 And also the power obtained in
the combustion phase is
effectively used for exhaust
which in case of other cycles
the compression process uses
some power obtained from the
combustion phase eventually
increasing the work input.
 But overall thermal efficiency is
less in Lenoir cycle compared to
other cycles as the heat addition
is done in the absence of high
pressure(without compression