In an attempt to reduce emissions and enhance the performance of a lean - burn, spark
ignition engine, the effect of charge motion within the combustion chamber has been
examined. The two most prominent charge motions are those of intake generated swirl
and compression generated squish. A great deal of previous research work has focused
individually on these charge motions, but very little has been done with respect to a
detailed study of the combined effects of these phenomenon. The objective of this
research is to determine if an optimum combination of squish and swirl intensity exists, and if so what the effects on performace and emissions are.
The method by which this would be achieved was entirely experimental. The tests were
run using a Ricardo - Hydra Research engine fuelled by natural gas. It required the
design and construction of a swirl producing intake system followed by calibration on a
steady flow test bench by means of a paddle- wheel anemometer. This resulted in swirl
numbers in the range of 0 -1.6 at speeds in the range of 1000 - 2500 rpm. The variation
in squish intensity was achieved by the insertion of piston crowns with the desired squish intensity. The squish was radial in nature produced by a bowl-in-piston configuration
and a flat cylinder head. Squish ratios used were 0% , 30% , 50% and 70% which could
be achieved using a 10.2:1 compression ratio.
The testing was cycled through all possible squish and swirl combinations producing a set
of emissions and performance data. Initially tests were conducted at WOT, using SAE
correction factors for minor fluctuations in intake temperature and pressure. However a
second set of part load tests conducted at an intake manifold pressure of 95 kPa produced more meartingful results due to less variations in intake conditions. definite optimization of engine torque and emissions was determined at various squish
and swirl intensities and noted at all speed conditions. The effects were most prominent at
higher relative air - fuel ratio (RAFR) where improvements in performance were up to
5%. Over the range of RAFR 1.0 - 1.4 benefits were found to vary from 1% - 5% in
torque. The exhaust emissions results were less promising due to the increase in NO[sub x] as
torque increased, and only a slight THC reduction with increased swirl intensity was
noted.
Noticeable trends were the benefit of a higher squish ratio as the charge became leaner, as
well as when the speed was increased. Increased swirl intensity produced beneficial results
with the higher squish requiring a lower swirl intensity to reach the optimum combination.
A significant reduction in MBT timing was found as swirl no. was increased at all
operating conditions. This reduction in MBT timing persisted after performance
optimization had occurred indicating the beneficial effect of swirl on the initial burn time,
but less benefit is obtained from the main burn time.
The research project has brought to light a number of unexpected aspects of squish and
swirl interaction, and has consolidated trends which were expected from previous
research.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/3962 |
| Date | 11 1900 |
| Creators | Law, Michael |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
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