Etude de la combustion de gaz de synthèse issus d'un processus de ...

Chapter 5
From figure 5.15 is possible to conclude that the piston velocity is higher on the
compression stroke than on the expansion stroke for every case. The maximum
velocity on the compression stroke is around 15 m/s decreasing to around 14 m/s on
the expansion stroke. The piston speed of the movement is constantly changing in the
cylinder. Relatively great in the middle of the stroke, some nearby the dead centre
speed is relatively small and it is zero in the dead centre. On the compression stroke
the maximum velocity occurs around 110 ms and is not influenced by combustion
because ignition is made after that instant for the whole cases. On the expansion
stroke the maximum speed occurs at around 162 ms for ignition timing of 5.0 ms
BTDC, around 165 ms for 7.5 ms BTDC and 166 ms for 12.5 ms BTDC. An equivalent
rotation speed could be defined by the following expression:
Δ θ = 6NΔ t
(5.1)
tel-00623090, version 1 - 13 Sep 2011
Where θ is the crank angle in degrees, N the rotation speed and t the time. Taking into
account that each stroke represents 180 crank angle degrees, the mean equivalent
rotation speed for the compression stroke is 682 rpm. Considering the differences
verified on the piston displacement on the expansion stroke for the different fuels and
ignition timings, the mean equivalent rotation speed is also slightly changed.
Considering a criterion of 1.0 mm for the final piston position, we have an equivalent
rotation speed for the expansion stroke of 612 rpm for ignition timing of 5 ms BTDC
and 588 rpm for other ignitions timings for updraft syngas.
5.2.1.3 In-cylinder pressure repeatability
A set of three experiments was made for each syngas composition with various ignition
timings in order to verify its repetition. The pressure traces are shown in figure 5.16 for
updraft syngas after TDC synchronization.
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