An investigation of cyclic variability in a single-cylinder spark ignition engine fuelled by natural gas was carried out. The effects of combustion chamber shape and compression ratio were examined intensively. Four different combustion chambers were tested and compression ratio was varied in the range of 8.5:1 to 15:1. For each test condition, the in-cylinder pressure data were recorded at each degree of crank angle rotation for a total of two hundred consecutive engine cycles. These pressure-time histories were used for the detailed study of combustion characteristics. The generalized plot of maximum pressure and location at which maximum pressure occurs was demonstrated as an effective means of diagnosing the cyclic variability. It was shown that compression ratio had negligible effect on cyclic variability, but combustion chamber shape had a strong influence. The indicated mean effective pressure proved to be a good index for measuring cyclic variability for a wide range of operating conditions. However, for specific cases in which the variation of indicated mean effective pressure shows poor sensitivity, maximum pressure and maximum rate of pressure rise are useful measures. For high compression ratio engines, a compact combustion chamber arranged around the spark plug has been shown to be superior for reducing cyclic variability. In addition, a study of a model for the small-scale structure of turbulence using the data from these experiments showed good agreement with those from the literature. Alternative assumptions for estimating turbulence length scale were tested and a preferred method is recommended. The study showed that the fast burning combustion chamber is the solution to reduce cyclic variation. However, cyclic variations of maximum pressure and its location in the fast burning condition still exist and continued research to reduce these cyclic variations should concentrate on the variation of characteristics of flame kernel creation and growth from cycle to cycle.
| Identifer | oai:union.ndltd.org:ADTP/275068 |
| Date | January 1990 |
| Creators | Chanchaona, Somchai |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated., http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm, Copyright: The author |
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