Combustion stress in compression-ignition engines.
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Date
1989
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Abstract
South Africa produces alternative fuels from a number of different
sources. The properties of a fuel are known to affect the nature
of combustion in compression-ignition engines significantly, and
have occasionally resulted in engine failures. Combustion analyses
have been conducted on a wide range of fuels and combustion has
been thoroughly quantified. However, the role played by the
different combustion variables in failures was not known. The
result was that it was not possible to predict the implications of
variations in the nature of combustion. There was thus a need to
investigate the relative role of combustion variables in the
failure of engines.
The mechanisms of combustion and engine failure were studied. All
the variables required to determine combustion and engine
durability were measured simultaneously. This research required
the development of a complete engine research facility as well as
specialized transducers. Fast response surface thermocouples were
designed and constructed in order to monitor transient surface
temperatures. Heat transfer rates were then calculated with the
aid of Fourier analysis. Dynamic stresses were monitored by
strain-gauges applied to the engine.
A special high speed data
acquisition system was developed. An existing heat release model
was modified and used to calculate combustion rates. A
comprehensive finite element model was developed to calculate
piston temperatures and stresses. The role of each combustion
variable in stress and durability was investigated by statistical
analysis.
The results successfully identified the causes of combustion
related engine failures. The primary cause of engine failure was found to be thermal loading. The principal cause of any variation
in thermal loading and thus engine durability was maximum cylinder
pressure. The life of the engine was proved to be determined
almost entirely by peak cylinder pressure. The role of the rate
of pressure rise was proved to be insignificant.
All the implications of variations in the nature of combustion can
now be determined accurately. It will thus be possible to optimise
engine modifications and fuel properties before validation by
durability testing.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1989.
Keywords
Diesel motor--Combustion., Diesel motor--Alternate fuels., Theses--Agricultural engineering.